WO2014181869A1 - 光変調器ドライバ回路および光送信器 - Google Patents
光変調器ドライバ回路および光送信器 Download PDFInfo
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- WO2014181869A1 WO2014181869A1 PCT/JP2014/062480 JP2014062480W WO2014181869A1 WO 2014181869 A1 WO2014181869 A1 WO 2014181869A1 JP 2014062480 W JP2014062480 W JP 2014062480W WO 2014181869 A1 WO2014181869 A1 WO 2014181869A1
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Definitions
- the present invention relates to an optical modulator driver circuit capable of switching between a low power / limit operation mode and a linear operation mode according to an operation mode of an optical transmission system, and an optical transmitter using the optical modulator driver circuit. .
- FIG. 40 shows a configuration example of a general optical transmitter for 100 Gb / s transmission.
- a transmission block for one polarization in polarization multiplexing is shown.
- the optical transmitter of FIG. 40 includes a DSP (Digital Signal Processor) unit 100 that performs digital signal processing of transmission data Data, and multiplexers (MUX: Multiplexer) 101-I, 101 that multiplex symbols output from the DSP unit 100.
- DSP Digital Signal Processor
- MUX Multiplexer
- optical modulator driver circuits 102-I and 102-Q for amplifying signals output from the MUXs 101-I and 101-Q, a laser diode (LD) 103, and continuous light from the LD 103
- an optical I / Q modulator 104 that modulates and outputs the output signals from the optical modulator driver circuits 102-I and 102-Q.
- 41A shows the output signal of the MUX 101-I
- FIG. 41B shows the output signal of the optical modulator driver circuit 102-I
- FIG. 41C shows the optical output signal of the optical I / Q modulator 104 on a plane.
- the DSP unit 100 includes an FEC encoding unit 1000 that performs FEC (Forward Error Correction) encoding on transmission data Data, and a symbol mapping unit that executes symbol mapping according to a modulation format on a signal after FEC encoding 1001.
- FEC Forward Error Correction
- the electrical signal for driving the optical I / Q modulator 104 is a binary signal. Therefore, the optical modulator driver circuits 102-I and 102-Q are required to have a limit operation (operation to limit and amplify a small signal or a large signal to a desired amplitude value) in order to improve the eye opening of the modulator drive waveform. It is done.
- the optical modulator driver circuits 102-I and 102-Q used in the 100 Gb / s optical transmission system are not required to have high linearity (characteristic for linearly amplifying the input signal). I can say that.
- FIG. 42 shows a configuration example of an optical transmitter to which transmission end signal processing can be applied and which can also support higher-order modulation formats such as QAM.
- FIG. 42 also shows a transmission block for one polarization in the polarization multiplexing.
- the optical transmitter in FIG. 42 includes a DSP unit 200 that performs digital signal processing of transmission data Data, MUXs 201-I and 201-Q that multiplex symbols output from the DSP unit 200, and MUXs 201-I and 201-Q.
- DA converters (DAC: Ddigital-to-Analog Converter) 202-I and 202-Q that convert data output from the analog signals and optical modulator driver circuits that amplify signals output from the DACs 202-I and 202-Q 203-I, 203-Q, LD 204, and optical I / Q modulator 205 that modulates the continuous light from LD 204 with the output signal of optical modulator driver circuit 203-I, 203-Q and outputs the modulated light.
- Yes. 43A shows the output signal of the DAC 202-I
- FIG. 43B shows the output signal of the optical modulator driver circuit 203-I
- FIG. 43C shows the optical output signal of the optical I / Q modulator 205 on a plane.
- FIG. 43A shows the output signal of the DAC 202-I
- FIG. 43B shows the output signal of the optical modulator driver circuit 203-I
- FIG. 43C shows the optical output signal of the optical I / Q modulator 205
- the DSP unit 200 includes: A pre-equalization unit 2002 that performs pre-equalization processing of chromatic dispersion and nonlinear response of an optical modulator on a signal, and spectrum shaping for suppressing crosstalk between channels at the time of wavelength division multiplexing (WDM) transmission A signal spectrum shaping unit 2003 that performs (Nyquist filter) processing on a signal and a transmission FE equalization unit 2004 that performs transmission FE (Forward Equalizer) equalization on the signal for an optical modulator are necessary.
- a pre-equalization unit 2002 that performs pre-equalization processing of chromatic dispersion and nonlinear response of an optical modulator on a signal, and spectrum shaping for suppressing crosstalk between channels at the time of wavelength division multiplexing (WDM) transmission
- WDM wavelength division multiplexing
- a signal spectrum shaping unit 2003 that performs (Nyquist filter) processing on a signal
- a transmission FE equalization unit 2004 that performs transmission FE (Forward Equalizer) equalization on the signal for
- the electric signal for driving the optical I / Q modulator 104 is a binary signal “0” or “1” as described above.
- the electrical signal for driving the optical I / Q modulator 205 is simple. It is not a “0” or “1” signal, but a signal containing information in the amplitude axis direction.
- the electric signal for driving the optical I / Q modulator 205 is a quaternary signal as shown in FIG. 43B.
- the optical modulator driver circuit has a linear response, that is, an input signal. Is required to be linearly amplified.
- the optical transmitter as shown in FIG. 42 can also cover a conventional system that handles binary signals.
- FIGS. 44A and 44B are diagram showing the input / output characteristics of the limit driver circuit
- FIG. 44B is a diagram showing the input / output characteristics of the linear driver circuit.
- the horizontal axis represents the amplitude (or input power) of the input signal Vin
- the vertical axis represents the amplitude (or output power) of the output signal Vout of the driver circuit.
- the circuit can be designed by setting the maximum amplitude Aoutmax of the signal that can be output by the driver circuit as the desired output amplitude Aout (Aoutmax ⁇ Aout), and thus the power efficiency is very good. Further, when handling a binary signal, the limit operation of the driver circuit is preferable from the viewpoint of improving the eye opening of the optical modulator driving waveform.
- the linear driver circuit since it is necessary to widen the linear operation range, the maximum amplitude Aoutmax of the signal that can be output by the driver circuit itself is sufficiently large, and the desired output amplitude Aout with respect to the assumed input amplitude Ain. Must be designed so that the linearity can be obtained linearly (design with a large back-off). Since the power consumption of a general driver circuit increases in proportion to the maximum output amplitude of the circuit, the power consumption increases in a linear driver circuit.
- the present invention has been made to solve the above-described problems, and an optical modulator driver capable of switching between a low power / limit operation mode and a linear operation mode in accordance with a modulation format to be applied, equalization processing, or the like.
- An optical transmitter using a circuit and an optical modulator driver circuit is provided.
- An optical modulator driver circuit includes an amplifier that amplifies an input signal and outputs a signal for driving the optical modulator, and a current amount adjustment circuit that can adjust a current amount of the amplifier according to a desired operation mode. It is characterized by providing.
- the optical transmitter of the present invention includes a signal processing unit that performs signal processing of transmission data in accordance with the operation mode of the optical transmission system, and a DA converter that converts a digital signal processed by the signal processing unit into an analog signal.
- An optical modulator driver circuit for amplifying a signal output from the DA converter, an optical modulator for modulating continuous light input from a light source with an output signal of the optical modulator driver circuit, and the optical transmission Control signal generating means for generating a first control signal for controlling an operation mode of the optical modulator driver circuit based on information relating to an operation mode of the system.
- the operation mode of the optical transmission system to which the optical modulator driver circuit of the present invention is applied (modulation format and presence / absence of transmission end signal processing). Accordingly, the linear operation mode and the limit operation mode can be appropriately switched and used, and the power consumption can be greatly reduced in the limit operation mode.
- the gain of the amplifying unit itself can be reduced to zero by setting the current amount of the amplifying unit to zero, it is also possible to enter a shutdown (no signal output) mode.
- the linear operation mode and the limit operation mode of the optical modulator driver circuit can be appropriately switched and used according to the operation mode of the optical transmission system. It becomes possible to reduce electric power.
- the optical modulator driver circuit is in an optimum state for the operation form of the optical transmission system. Can be set.
- FIG. 1 is a diagram showing an outline of an optical modulator driver circuit according to a first embodiment of the present invention.
- FIG. 2 is a diagram showing input / output characteristics of the optical modulator driver circuit according to the first embodiment of the present invention.
- FIG. 3 is a circuit diagram showing the configuration of the optical modulator driver circuit according to the first embodiment of the present invention.
- FIG. 4 is a circuit diagram showing another configuration of the optical modulator driver circuit according to the first embodiment of the present invention.
- FIG. 5 is a diagram showing input / output characteristics of the optical modulator driver circuit of FIG.
- FIG. 6 is a diagram showing input / output characteristics of the optical modulator driver circuit of FIG.
- FIG. 7 is a block diagram showing the configuration of the optical modulator driver circuit according to the second embodiment of the present invention.
- FIG. 1 is a diagram showing an outline of an optical modulator driver circuit according to a first embodiment of the present invention.
- FIG. 2 is a diagram showing input / output characteristics of the optical modulator driver circuit according to
- FIG. 8 is a diagram showing input / output characteristics of the optical modulator driver circuit of FIG.
- FIG. 9 is a block diagram showing another configuration of the optical modulator driver circuit according to the second embodiment of the present invention.
- FIG. 10 is a diagram showing input / output characteristics of the optical modulator driver circuit of FIG.
- FIG. 11 is a diagram showing input / output characteristics of the linear gain variable circuit according to the second embodiment of the present invention.
- FIG. 12 is a circuit diagram showing a configuration of the optical I / Q modulator.
- FIG. 13 is a diagram showing input / output characteristics of the MZ modulator used in the optical I / Q modulator of FIG.
- FIG. 14 is a diagram for explaining a conventional method for compensating the nonlinearity of the MZ modulator.
- FIG. 10 is a diagram showing input / output characteristics of the optical modulator driver circuit of FIG.
- FIG. 11 is a diagram showing input / output characteristics of the linear gain variable circuit according to the second embodiment of the present invention.
- FIG. 15 is a circuit diagram showing a configuration of a current source of the optical modulator driver circuit of FIG.
- FIG. 16 is a diagram for explaining a method of controlling the current source of FIG.
- FIG. 17 is a circuit diagram showing a configuration of a current source of the optical modulator driver circuit of FIG.
- FIG. 18 is a diagram illustrating a method for controlling the current source of FIG.
- FIG. 19 is a circuit diagram showing a configuration of an optical modulator driver circuit according to the fourth embodiment of the present invention.
- FIG. 20 is a circuit diagram showing another configuration of the optical modulator driver circuit according to the fourth example of the present invention.
- FIG. 21 is a circuit diagram showing a configuration of an optical modulator driver circuit according to the fifth embodiment of the present invention.
- FIG. 22 is a circuit diagram showing another configuration of the optical modulator driver circuit according to the fifth example of the present invention.
- FIG. 23 is a circuit diagram showing a configuration of an optical modulator driver circuit according to the sixth embodiment of the present invention.
- FIG. 24 is a circuit diagram showing another configuration of the optical modulator driver circuit according to the sixth embodiment of the present invention.
- FIG. 25 is a circuit diagram showing a configuration of an optical modulator driver circuit according to the seventh embodiment of the present invention.
- FIG. 26 is a circuit diagram showing a configuration of a conventional Gilbert cell type variable gain circuit.
- FIG. 27 is a circuit diagram showing a configuration of a conventional Mayer-type gain variable circuit.
- FIG. 28 is a circuit diagram showing the configuration of the linear gain variable circuit according to the eighth embodiment of the present invention.
- FIG. 29 is a circuit diagram showing another configuration of the linear gain variable circuit according to the eighth embodiment of the present invention.
- FIG. 30 is a circuit diagram showing a configuration of an optical modulator driver circuit according to the ninth embodiment of the present invention.
- FIG. 31 is a circuit diagram showing another configuration of the optical modulator driver circuit according to the ninth embodiment of the present invention.
- FIG. 32 is a circuit diagram showing another configuration of the optical modulator driver circuit according to the ninth embodiment of the present invention.
- FIG. 33 is a circuit diagram showing another configuration of the optical modulator driver circuit according to the ninth embodiment of the present invention.
- FIG. 34 is a block diagram showing the configuration of the optical transmitter according to the tenth embodiment of the present invention.
- FIG. 35 is a diagram for explaining the linearity control method of the optical modulator driver circuit according to the tenth embodiment of the present invention.
- FIG. 36 is a diagram for explaining another method of controlling the linearity of the optical modulator driver circuit in the tenth embodiment of the present invention.
- FIG. 37 is a block diagram showing the configuration of the optical transmitter according to the eleventh embodiment of the present invention.
- FIG. 38 is a diagram for explaining the linearity control method of the optical modulator driver circuit according to the eleventh embodiment of the present invention.
- FIG. 39 is a diagram for explaining another method of controlling the linearity of the optical modulator driver circuit in the eleventh embodiment of the present invention.
- FIG. 40 is a block diagram illustrating a configuration example of a conventional optical transmitter.
- FIG. 41A is a diagram showing an output signal of the multiplexer of FIG. 41B is a diagram showing an output signal of the optical modulator driver circuit of FIG.
- FIG. 41C is a diagram in which the optical output signal of the optical I / Q modulator of FIG. 40 is constellated and displayed on a plane.
- FIG. 42 is a block diagram showing a configuration example of another conventional optical transmitter.
- 43A is a diagram showing an output signal of the DA converter of FIG. 43B is a diagram showing an output signal of the optical modulator driver circuit of FIG.
- FIG. 43C is a diagram in which the optical output signal of the optical I / Q modulator of FIG. 42 is constellated and displayed on a plane.
- FIG. 44A is a diagram showing input / output characteristics of a limit driver circuit.
- FIG. 44B is a diagram showing input / output characteristics of the linear driver circuit.
- FIG. 1 is a diagram showing an outline of an optical modulator driver circuit according to this embodiment
- FIG. 2 is a diagram showing input / output characteristics of the optical modulator driver circuit according to this embodiment.
- the horizontal axis represents the amplitude (or input power) of the input signal Vin
- the vertical axis represents the amplitude (or output power) of the output signal Vout of the optical modulator driver circuit.
- the definition of the horizontal axis and the vertical axis is the same for the subsequent input / output characteristics.
- the optical modulator driver circuit 1 of the present embodiment has an operation mode switching control terminal 4 in addition to an input terminal 2 and an output terminal 3, and is limited by the operation state (modulation format and presence / absence of transmission end signal processing).
- the operation mode and the linear operation mode can be switched.
- the signal CTL input to the operation mode switching control terminal 4 is linked to the operation mode of the optical transmission system to which the optical modulator driver circuit 1 is applied.
- a control signal from the DSP may be used, or manual setting / adjustment may be performed.
- the optical modulator driver circuit 1 detects the operation mode of the system to which the driver circuit 1 is applied based on a signal received from the outside, and outputs the signal CTL input to the operation mode switching control terminal 4 by the driver circuit itself. It may be automatically generated.
- a certain desired output amplitude Aout can be obtained with respect to a certain input amplitude Ain in both the limit operation mode and the linear operation mode. It is preferable.
- a circuit configuration method for realizing the optical modulator driver circuit 1 of this embodiment will be described below. Switching between the low power / limit operation mode and the linear operation mode can be realized by adjusting the current amount of the optical modulator driver circuit 1, and can be realized by the circuit configurations shown in FIGS.
- the circuits shown in FIGS. 3 and 4 are both circuits that function as differential amplifiers. However, in the case of FIG. 3, it is necessary to use a plurality (two or more) of current sources capable of ON / OFF control of the tail current. In the case of FIG. 4, an arbitrary number (one or more) of variable current sources capable of controlling the tail current is used.
- the optical modulator driver circuit 1 shown in FIG. 3 includes a transistor Q10 having a base connected to the positive phase input terminal 2P, a collector connected to the negative phase output terminal 3N, a base connected to the negative phase input terminal 2N, and a collector Transistor Q11 connected to positive-phase output terminal 3P, one end connected to power supply voltage VCC, the other end connected to collector resistor R10 connected to the collector of transistor Q10, one end connected to power supply voltage VCC, and the other end Collector resistor R11 connected to the collector of transistor Q11, emitter resistor R12 having one end connected to the emitter of transistor Q10, emitter resistor R13 having one end connected to the emitter of transistor Q11, and emitter resistors R12 and R13 having one end connected to the emitter of transistor Q11 And the other end is connected to the power supply voltage VEE (VCC> VEE).
- VinP is a positive phase input signal
- VinN is a negative phase input signal
- VoutP is a positive phase output signal
- VoutN is a negative phase output signal.
- a plurality of parallel current sources IS10 capable of turning on and off the tail current of the differential amplifier 50 are used, and the amount of current flowing through the differential amplifier 50 is controlled to control the optical modulator driver circuit 1. Realize mode switching. When linear operation of the optical modulator driver circuit 1 is required, all current sources IS10 are turned on by the control signal CTL input to the operation mode switching control terminal 4 to maximize the tail current amount. Operation in mode is possible. When the limit operation of the optical modulator driver circuit 1 is required, at least one of the plurality of current sources IS10 is turned on and the rest are turned off by the control signal CTL input to the operation mode switching control terminal 4. Operation in the limit operation mode is possible by reducing the amount of current.
- FIG. 5 is a diagram showing input / output characteristics of the optical modulator driver circuit 1 of FIG.
- the amount of tail current of the differential amplifier 50 can be reduced in the limit operation mode compared to the linear operation mode. It will be possible. Further, by individually selecting the current source IS10 to be turned off, the input / output characteristics from the linear operation mode to the limit operation mode can be arbitrarily selected, and therefore the input / output characteristics of the optical modulator driver circuit 1 are linear. And fine adjustment of power and power consumption are also possible.
- the base is connected to the positive phase input terminal 2P
- the collector is connected to the negative phase output terminal 3N
- the base is connected to the negative phase input terminal 2N
- the collector is The transistor Q21 connected to the positive phase output terminal 3P, one end connected to the power supply voltage VCC, the other end connected to the collector of the transistor Q20, one end connected to the power supply voltage VCC, and the other end
- Collector resistor R21 connected to the collector of transistor Q21, emitter resistor R22 having one end connected to the emitter of transistor Q20, emitter resistor R23 having one end connected to the emitter of transistor Q21, and emitter resistors R22 and R23 having one end connected to the emitter of transistor Q21 Is connected to the other end, the other end is connected to the power supply voltage VEE, and an operation mode switching control terminal.
- variable current sources IS20 Metropolitan capable of controlling the tail current in response to the signal CTL is input to.
- the transistors Q20 and Q21 and the resistors R20 to R23 constitute a differential amplifier 52, and the variable current source IS20 constitutes a current amount adjusting circuit 53.
- the optical modulator driver circuit 1 in FIG. 4 is similar in concept to that in FIG. 3, but the control method is different.
- a variable current source IS20 capable of controlling the tail current of the differential amplifier 52 is used, and the mode switching of the optical modulator driver circuit 1 is realized by controlling the amount of current flowing through the differential amplifier 52. To do.
- FIG. 6 is a diagram showing input / output characteristics of the optical modulator driver circuit 1 of FIG.
- the current amount is set large (to the maximum value) by the control signal CTL input to the operation mode switching control terminal 4. Operation in the operation mode is possible.
- the limit operation of the optical modulator driver circuit 1 it is possible to operate in the limit operation mode by reducing the amount of current by the control signal CTL input to the operation mode switching control terminal 4. If this control method is adopted, it is possible to finely adjust the linearity and power consumption by analog (continuous) control, not by stepwise control as in the circuit of FIG. Since the amount of current that can be passed through one variable current source IS20 is limited, the number of variable current sources IS20 may be determined according to the required current amount, and the variable current sources IS20 may be connected in parallel.
- bipolar transistors are used as the transistors Q10, Q11, Q20, and Q21.
- the transistors are not limited to bipolar transistors, and FET-based transistors such as CMOS may be used.
- FET-based transistors such as CMOS may be used.
- the base may be replaced with the gate
- the collector may be replaced with the drain
- the emitter may be replaced with the source.
- the optical modulator driver circuit 1 of this embodiment also has a variable gain function.
- the maximum gain is obtained in the linear operation mode, and the gain is reduced in the limit operation mode. Therefore, an output amplitude level difference depending on the operation mode occurs with respect to a certain input amplitude Ain assumed as described above.
- the output amplitude from the DAC on the DSP side that is, the input amplitude to the optical modulator driver circuit
- the circuit of the first embodiment can be used as an optical modulator driver circuit without any problem.
- a predetermined desired output amplitude with respect to a certain input amplitude Ain in both the linear operation mode and the limit operation mode. Aout is preferably obtained.
- a circuit configuration is proposed in which a certain desired output amplitude Aout can be obtained with respect to a certain input amplitude Ain assumed in both the linear operation mode and the limit operation mode.
- the circuits of FIGS. 3 and 4 are used as output circuits, and a linear gain variable circuit is added to the previous stage to form a driver circuit having a two-stage configuration.
- FIG. 7 is a block diagram showing the configuration of the optical modulator driver circuit 1 of this embodiment
- FIG. 8 is a diagram showing the input / output characteristics of the optical modulator driver circuit 1 of FIG.
- the optical modulator driver circuit 1 of the present embodiment uses the circuit of FIG. 3 or FIG. 4 as the output circuit 11, and a linear gain variable circuit 10 whose output terminal is connected to the input terminal of the output circuit 11 in the preceding stage. It is added.
- the linear gain variable circuit 10 is a circuit whose gain can be adjusted according to the gain control signal GCTL input to the gain control terminal 5.
- the gain is decreased in the linear operation mode, and the gain is increased in the limit operation mode.
- a circuit capable of obtaining the output amplitude Aout can be realized. Applying the circuit of FIG. 3 or FIG. 4 as the output circuit 11 having the largest power consumption must be ensured for a fixed load system (50 ⁇ in the assumed application) is the limit operation mode. It is most effective in reducing power consumption during the hour.
- FIG. 9 is a block diagram showing another configuration of the optical modulator driver circuit 1 of the present embodiment
- FIG. 10 is a diagram showing input / output characteristics of the optical modulator driver circuit 1 of FIG.
- the optical modulator driver circuit 1 of FIG. 9 uses the circuit of FIG. 3 or FIG. 4 as the input circuit 12, and a linear gain variable circuit 13 whose input terminal is connected to the output terminal of the input circuit 12 is added to the subsequent stage. It is a thing. Thereby, a mode switching function similar to the configuration of FIG. 7 can be realized.
- linear gain variable circuits 10 and 13 shown in FIGS. 7 and 9 a circuit having a linear gain variable characteristic as shown in FIG. 11 is assumed as a single unit. By adding such linear gain variable circuits 10 and 13, it is possible to perform variable gain and amplitude adjustment in a wide range in each of the linear operation mode and the limit operation mode. It is also possible to optimize the drive amplitude of the device.
- a control signal from the DSP may be used, or it may be manually set and adjusted.
- the optical modulator driver circuit 1 detects an operation mode of a system to which the driver circuit 1 is applied based on a signal received from the outside, and automatically generates a signal GCTL to be input to the gain control terminal 5 by the driver circuit itself. You may do it.
- the optical I / Q modulators 104 and 205 as shown in FIGS. 40 and 42 which are driven by the optical modulator driver circuit 1, include an MZ (Mach-Zehnder) modulator 300 as shown in FIG. Consists of The MZ modulator 300 has a nonlinear input / output characteristic, and the characteristic is generally a sine (sine wave) curve as shown in FIG.
- MZ Machine-Zehnder
- the DSP pre-equalization unit does not compensate for the non-linearity of the MZ modulator 300
- the optical modulator driver circuit 1 of this embodiment shown in FIGS. 7 and 9 is used, as described above, variable gain and amplitude adjustment are possible in each of the linear operation mode and the limit operation mode. It is possible to compensate for the nonlinearity of the MZ modulator.
- FIG. 15 is a circuit diagram showing a configuration of the current source IS10 of the optical modulator driver circuit 1 shown in FIG. 3, and FIG. 16 is a diagram for explaining a control method of the current source IS10.
- n is an integer of 2 or more
- current sources IS10 connected in parallel has a base connected to the operation mode switching control terminal 4 and a collector connected to the other ends of the emitter resistors R12 and R13 in FIG.
- Current source transistor Q12 (Q12-1 to Q12-n), and resistor R14 (R14-1 to R14-n) having one end connected to the emitter of the current source transistor Q12 and the other end connected to the power supply voltage VEE It consists of.
- the current source transistor Q12 is controlled by the control signal V CS (CTL in FIG. 3) input to the operation mode switching control terminal 4 to switch the current amount of the current source IS10, and the optical modulator The operation mode switching of the driver circuit 1 is realized.
- the control signal V CS is a binary signal for turning on / off the current source transistor Q12 as shown in FIG.
- a voltage V CS — OFF V CS — OFF ⁇ VEE
- Each current source transistor Q12 may individually receive control signals V CS. That may be prepared control signal V CS to the number of the current source transistor Q12. When all the current source transistors Q12 are turned on, the optical modulator driver circuit 1 in FIG. 3 operates in the linear operation mode. Further, when at least one of the plurality of current source transistors Q12 is turned on and the rest are turned off, the optical modulator driver circuit 1 of FIG. 3 operates in the limit operation mode. Each current source transistor Q12 may be controlled by the same control signal V CS .
- FIG. 17 is a circuit diagram showing a configuration of the current source IS20 of the optical modulator driver circuit 1 shown in FIG. 4, and FIG. 18 is a diagram for explaining a control method of the current source IS20.
- the current source IS20 has a base connected to the operation mode switching control terminal 4, a collector connected to the other end of the emitter resistors R22 and R23 of FIG. 4, and one end connected to the emitter of the current source transistor Q22.
- the resistor R24 is connected to the other end and connected to the power supply voltage VEE.
- the configuration of the current source itself is the same as that shown in FIG. 15, but the control method is different. Since the current source IS20 in FIG. 17 is used as a variable current source, the continuous control signal V CS (CTL in FIG. 4) is not a binary control signal as shown in FIG. used. Thus, by using the continuous control signal V CS , the input / output characteristics of the optical modulator driver circuit 1 in FIG. 4 can be continuously changed from the linear operation mode to the limit operation mode.
- FIG. 17 shows a configuration example in which the current source transistor Q22 has one configuration, but a plurality of the configurations in FIG. 17 are connected in parallel, and each current source transistor Q22 is controlled by a common control signal V CS or a different control signal V CS . You may do it. 15 and 17, the control signal V CS may be directly applied to the current source transistors Q12 and Q22 from the outside, or a voltage conversion circuit (voltage level shift circuit) according to the interface with the control side. Etc.) or the like.
- V CS voltage conversion circuit
- FIG. 15 and 17 show examples in which bipolar transistors are used as the current source transistors Q12 and Q22.
- FET type transistors may be used.
- the base When using an FET transistor, the base may be replaced with the gate, the collector replaced with the drain, and the emitter replaced with the source.
- the optical modulator driver circuit is a one-stage or two-stage circuit, but an amplifier circuit that linearly responds according to the required gain may be added as appropriate. Further, when the optical modulator driver circuit has a multistage configuration, it may be integrated on one chip or may be configured on a multichip.
- FIG. 19 is a circuit diagram showing a configuration of the optical modulator driver circuit 1 according to the present embodiment.
- 19 is a transistor in which the base is connected to the bias terminal 6, the collector is connected to the negative phase output terminal 3N, and the emitter is connected to the collector of the transistor Q10 in the circuit shown in FIG. Q13 and a transistor Q14 having a base connected to the bias terminal 6, a collector connected to the positive phase output terminal 3P, and an emitter connected to the collector of the transistor Q11 are added.
- Transistors Q10, Q11, Q13, Q14 and resistors R10-R13 form a differential amplifier 54. A predetermined bias voltage is applied to the bias terminal 6.
- FIG. 20 is a circuit diagram showing another configuration of the optical modulator driver circuit 1 of the present embodiment.
- the optical modulator driver circuit 1 of FIG. 20 is a transistor in which the base is connected to the bias terminal 6, the collector is connected to the negative phase output terminal 3N, and the emitter is connected to the collector of the transistor Q20 in the circuit shown in FIG. Q23 and a transistor Q24 having a base connected to the bias terminal 6, a collector connected to the positive phase output terminal 3P, and an emitter connected to the collector of the transistor Q21 are added.
- Transistors Q20, Q21, Q23, Q24 and resistors R20-R23 form a differential amplifier 55.
- the cascode transistors Q13, Q14, Q23, and Q24 are added as in this embodiment, the mirror effect can be reduced, and the impedance of the optical modulator driver circuit viewed from the collector side can be increased. It is possible to improve the band and reflection characteristics.
- FIG. 21 is a circuit diagram showing a configuration of the optical modulator driver circuit 1 according to the present embodiment. The same reference numerals are given to the same configurations as those in FIG.
- the optical modulator driver circuit 1 of FIG. 21 includes a differential amplifier 56 including transistors Q10 and Q11 and resistors R12 and R13, a current amount adjusting circuit 51 including a current source IS10, and an input terminal connected to the positive phase input terminal 2P.
- the output transmission line 21N connected to the output terminal 3N, one end connected to the output end of the input transmission line 20P, the other end connected to the power supply voltage VCC, and one end connected to the output end of the input transmission line 20N
- the resistor R16 is connected, the other end is connected to the power supply voltage VCC, one end is connected to the input end of the output transmission line 21P, the other end is connected to the power supply voltage VCC, and the other end is output. Is connected to the input end of the line 21N, the other end is composed of connected resistors R18 Metropolitan to the supply voltage VCC.
- Each differential amplifier 56 in FIG. 21 is disposed along the input transmission lines 20P and 20N and the output transmission lines 21P and 21N, the base of the transistor Q10 is connected to the input transmission line 20P, and the base of the transistor Q11 is the input transmission line.
- the collector of the transistor Q10 is connected to the output transmission line 21N, and the collector of the transistor Q11 is connected to the output transmission line 21P.
- FIG. 22 is a circuit diagram showing another configuration of the optical modulator driver circuit 1 of the present embodiment, and the same components as those in FIG. 4 are denoted by the same reference numerals.
- the optical modulator driver circuit 1 in FIG. 22 includes a differential amplifier 57 including transistors Q20 and Q21 and resistors R22 and R23, a current amount adjusting circuit 53 including a current source IS20, input transmission lines 20P and 20N, and an output.
- Transmission lines 21P, 21N one end connected to the output end of the input transmission line 20P, the other end connected to the power supply voltage VCC, one end connected to the output end of the input transmission line 20N, the other end
- the resistor R26 connected to the power supply voltage VCC, one end is connected to the input end of the output transmission line 21P, the other end is connected to the resistor R27 connected to the power supply voltage VCC, and one end is connected to the input end of the output transmission line 21N.
- the other end of the resistor R28 is connected to the power supply voltage VCC.
- the base of the transistor Q20 is connected to the input transmission line 20P
- the base of the transistor Q21 is the input transmission line.
- the collector of the transistor Q20 is connected to the output transmission line 21N
- the collector of the transistor Q21 is connected to the output transmission line 21P.
- the differential amplifiers 56 and 57 in FIGS. 21 and 22 may have a cascode configuration as described in the fourth embodiment.
- FIG. 23 is a circuit diagram showing a configuration of the optical modulator driver circuit 1 according to the present embodiment. The same reference numerals are given to the same configurations as those in FIGS.
- the optical modulator driver circuit 1 of FIG. 23 is obtained by adding an emitter follower circuit to the input portion of each differential amplifier 56 in the optical modulator driver circuit shown in FIG.
- the emitter follower circuit on the positive phase side has a base connected to the input transmission line 20P, a collector connected to the power supply voltage VCC, an emitter connected to the base of the transistor Q10, and one end of the transistor Q15.
- the current source IS11 is connected to the emitter and the other end is connected to the power supply voltage VEE.
- the emitter-follower circuit on the opposite phase side in FIG. 23 has a base connected to the input transmission line 20N, a collector connected to the power supply voltage VCC, an emitter connected to the base of the transistor Q11, and one end of the transistor Q16.
- the current source IS12 is connected to the emitter and the other end is connected to the power supply voltage VEE.
- FIG. 24 is a circuit diagram showing another configuration of the optical modulator driver circuit 1 of the present embodiment.
- the same reference numerals are given to the same configurations as those in FIGS.
- the optical modulator driver circuit 1 of FIG. 24 is obtained by adding an emitter follower circuit to the input portion of each differential amplifier 57 in the optical modulator driver circuit shown in FIG.
- the emitter follower circuit on the positive phase side in FIG. 24 has a base connected to the input transmission line 20P, a collector connected to the power supply voltage VCC, an emitter connected to the base of the transistor Q20, and one end of the transistor Q25.
- the current source IS21 is connected to the emitter and the other end is connected to the power supply voltage VEE.
- the emitter follower circuit on the opposite phase side in FIG. 24 has a base connected to the input transmission line 20N, a collector connected to the power supply voltage VCC, an emitter connected to the base of the transistor Q21, and one end of the transistor Q26.
- a current source IS22 is connected to the emitter and the other end is connected to the power supply voltage VEE.
- the input impedance can be increased and the matching of the input part can be improved.
- the input bias point of each stage can be optimized.
- the operations of the differential amplifiers 56 and 57 in FIGS. 23 and 24 are the same as those of the differential amplifiers 50 and 52 described in the first embodiment.
- the differential amplifiers 56 and 57 shown in FIGS. 23 and 24 may have a cascode configuration as described in the fourth embodiment.
- FIG. 25 is a circuit diagram showing a configuration of the optical modulator driver circuit 1 according to the present embodiment.
- the optical modulator driver circuit 1 of FIG. 25 has an input transmission line 30 whose input end is connected to the input terminal 2, an output transmission line 31 whose output end is connected to the output terminal 3, and one end of the input transmission line 30.
- a resistor R31 connected to the output end, the other end connected to the power supply voltage VDD, a resistor R32 connected to the input end of the output transmission line 31 and the other end connected to the power supply voltage VDD, and an input signal Vin
- the input signal bias control circuit 32 applies a DC bias to the input transmission line 30 and the amplifier 58 disposed along the output transmission line 31.
- Each amplifier 58 in FIG. 25 includes a transistor Q30 having a gate connected to the input transmission line 30, a gate connected to the bias terminal 6, a drain connected to the output transmission line 31, and a source connected to the drain of the transistor Q30.
- the transistor Q31 and a resistor R30 having one end connected to the source of the transistor Q30 and the other end connected to the power supply voltage VSS (VDD> VSS). A predetermined bias voltage is applied to the bias terminal 6.
- an input signal bias control circuit 32 serving as a current amount adjustment circuit is provided, and the DC bias level of the input signal Vin is set according to the control signal CTL input to the operation mode switching control terminal 4.
- the amount of current flowing through the amplifier 58 can be adjusted. That is, in the linear operation mode, the DC bias level of the input signal Vin is increased to increase the current amount to increase the linearity of the response. In the limit operation mode, the DC bias level of the input signal Vin is decreased to reduce the current amount. It is possible to save power.
- FIG. 25 shows a circuit example using FETs as the transistors Q30 and Q31.
- the transistors are not limited to FETs as in the previous embodiments, and bipolar transistors may be used.
- the gate may be replaced with the base
- the drain may be replaced with the collector
- the source may be replaced with the emitter.
- a circuit having a cascode configuration is shown, but the circuit may be configured by deleting the cascode transistor Q31 at the top of each amplifier 58.
- the base is connected to the gain control terminals 5P and 5N, and the gain constituting the upper differential pair (gain adjustment unit) that performs gain adjustment according to the gain control signals GCT and GCC.
- the collector of the amplifying transistor Q44 is connected to the emitters of the gain adjusting transistors Q40 and Q41, and the collector of the amplifying transistor Q45 is connected to the emitters of the gain adjusting transistors Q42 and Q43. Then, the positive phase output signal VoutP is output from the collectors (normal phase output terminal 8P) of the transistors Q41 and Q43, and the negative phase output signal VoutN is output from the collectors (negative phase output terminal 8N) of the transistors Q40 and Q42.
- the base is connected to the gain control terminals 5P and 5N, and the gain adjustment that constitutes the upper differential pair (gain adjustment unit) that performs gain adjustment according to the gain control signals GCT and GCC.
- Transistors Q50, Q51, and gain adjustment transistors Q52 which have bases connected to gain control terminals 5N, 5P and constitute an upper differential pair (gain adjustment unit) that performs gain adjustment according to gain control signals GCC, GCT, Q53, transistor Q54 whose base and collector are connected to power supply voltage VCC, emitter connected to the collector of transistor Q50, transistor whose base and collector are connected to power supply voltage VCC, and transistor whose emitter is connected to the collector of transistor Q53 Q55 and the bottom difference where the base is connected to the positive phase input terminal 7P and the negative phase input terminal 7N Amplifying transistors Q56 and Q57 constituting a pair (amplifying unit), a constant current source IS50 having one end connected to the emitters of the amplifying transistors Q56 and
- the collector of the amplifying transistor Q56 is connected to the emitters of the gain adjusting transistors Q50 and Q51, and the collector of the amplifying transistor Q57 is connected to the emitters of the gain adjusting transistors Q52 and Q53. Then, the positive phase output signal VoutP is output from the collector (positive phase output terminal 8P) of the transistor Q51, and the negative phase output signal VoutN is output from the collector (negative phase output terminal 8N) of the transistor Q52.
- the transistors Q40 to Q43 and Q50 to Q53 have a gain adjustment function, but the sensitivity of gain adjustment can be controlled by inserting an emitter resistor R E — U into the transistors Q40 to Q43 and Q50 to Q53.
- FIG. 28 is a circuit diagram showing the configuration of the linear gain variable circuits 10 and 13 of this embodiment.
- the linear gain variable circuits 10 and 13 of FIG. 28 are different from the gain variable circuit of FIG. 26 in that a resistor R42 inserted between the emitter of the gain adjusting transistor Q40 and the collector of the amplifying transistor Q44, and a gain adjusting circuit.
- a resistor R47 inserted between the current source IS40 and the current source IS40 is added. It is.
- the gain adjusting transistors Q40 to Q43 constitute a gain adjusting unit
- the amplifying transistors Q44 and Q45 constitute an amplifying unit.
- the resistance values of the resistors R42 to R45 are R E — U
- the resistance values of the resistors R46 and R47 are R E — L.
- FIG. 29 is a circuit diagram showing another configuration of the linear gain variable circuits 10 and 13 of the present embodiment. 29 is different from the gain variable circuit of FIG. 27 in that a resistor R52 inserted between the emitter of the gain adjusting transistor Q50 and the collector of the amplifying transistor Q56, and a gain adjusting circuit.
- a resistor R57 inserted between the current source IS50 and the current source IS50 is added. It is.
- the gain adjusting transistors Q50 to Q53 constitute a gain adjusting unit
- the amplifying transistors Q56 and Q57 constitute an amplifying unit.
- the resistance values of the resistors R52 to R55 are R E — U
- the resistance values of the resistors R56 and R57 are R E — L.
- the conventional variable gain circuit the emitter resistors R42 ⁇ R45 of the resistance R E _ U, R52 ⁇ R55 and emitter resistance of the resistance value R E _ L R46, R47, R56, R57 and
- the linear gain variable circuits 10 and 13 excellent in linear operation can be realized.
- FIG. 30 is a circuit diagram showing a configuration of the optical modulator driver circuit 1 of the present embodiment, and the same reference numerals are given to the same configurations as those in FIGS.
- the optical modulator driver circuit 1 in FIG. 30 uses the current source IS10 described in FIG. 3 instead of the current source IS40 in FIG.
- FIG. 31 is a circuit diagram showing another configuration of the optical modulator driver circuit 1 of the present embodiment, and the same reference numerals are given to the same configurations as those in FIGS.
- the optical modulator driver circuit 1 in FIG. 31 uses the current source IS10 described in FIG. 3 instead of the current source IS50 in FIG.
- FIG. 32 is a circuit diagram showing a configuration of the optical modulator driver circuit 1 of the present embodiment, and the same reference numerals are given to the same configurations as those in FIGS.
- the optical modulator driver circuit 1 in FIG. 32 uses the current source IS20 described in FIG. 4 instead of the current source IS40 in FIG.
- FIG. 33 is a circuit diagram showing another configuration of the optical modulator driver circuit 1 of the present embodiment, and the same reference numerals are given to the same configurations as those in FIGS.
- the optical modulator driver circuit 1 of FIG. 33 uses the current source IS20 described in FIG. 4 instead of the current source IS50 of FIG.
- Reference numerals 59 and 60 in FIGS. 30 to 33 denote linear gain variable circuits.
- the linear gain variable circuits 59 and 60 correspond to the linear gain variable circuits 10 and 13 excluding the current sources IS40 and IS50.
- the configurations that are cascade-connected in the second embodiment are integrated into one. It becomes possible.
- FIG. 34 is a block diagram showing the configuration of the optical transmitter according to the present embodiment.
- the same components as those in FIG. 42 are denoted by the same reference numerals.
- the optical transmitter of this embodiment includes a DSP 200 (signal processing means) that performs digital signal processing of transmission data Data according to the operation mode of the optical transmission system, and MUXs 201-I and 201 that multiplex symbols output from the DSP 200.
- DACs 202-I and 202-Q for converting data output from MUX 201-I and 201-Q into analog signals
- optical modulator drivers for amplifying signals output from DACs 202-I and 202-Q Circuits 203-I and 203-Q, an LD 204 serving as a light source, and an optical I / Q modulator 205 that modulates and outputs continuous light from the LD 204 with output signals of the optical modulator driver circuits 203-I and 203-Q.
- a control signal generating unit 206 that generates.
- the DSP 200 includes an FEC encoding unit 2000 that performs FEC encoding on transmission data Data, a symbol mapping unit 2001 that performs symbol mapping according to a modulation format on a signal after FEC encoding, A pre-equalization unit 2002 that performs pre-equalization processing of the nonlinear response of the modulator on the signal, and a signal that performs spectrum shaping (Nyquist filter) processing on the signal to suppress inter-channel crosstalk during WDM transmission A spectrum shaping unit 2003, a transmission FE equalization unit 2004 that performs transmission FE equalization for an optical modulator on a signal, and the like are provided.
- the modulation format can be changed according to an external command, and the functions of the pre-equalization unit 2002 and the signal spectrum shaping unit 2003 can be turned ON / OFF.
- information INF relating to the operation mode (modulation format, transmission end signal processing, etc.) of the optical transmission system is output (extracted) from the DSP 200, and the control signal generator 206 performs arithmetic processing on the information INF, and the calculation result Is used as a control signal CTL to control the balance between the linearity of the input / output characteristics of the optical modulator driver circuits 203-I and 203-Q and the power consumption, and the gain of the optical modulator driver circuits 203-I and 203-Q.
- the linearity of the input / output characteristics of the optical modulator driver circuits 203-I and 203-Q is unnecessary, and QAM handles electrical signals with amplitude modulation. If so, linearity is required.
- the pre-equalization function when the pre-equalization function is OFF, the linearity of the input / output characteristics of the optical modulator driver circuits 203-I and 203-Q is not necessary, and when the pre-equalization function is ON, the linearity Sexuality is required.
- the signal spectrum shaping Neyquist filter
- the signal spectrum shaping function When the signal spectrum shaping function is OFF, the linearity of the input / output characteristics of the optical modulator driver circuits 203-I and 203-Q is unnecessary, and the signal spectrum shaping function When is ON, linearity is required. As a whole system, it is necessary to determine whether or not the linearity of the input / output characteristics of the optical modulator driver circuits 203-I and 203-Q is necessary according to the plurality of items.
- the optical modulator driver circuits 203-I and 203-Q Is required to operate in a linear operation mode. Further, when the linearity of the input / output characteristics of the optical modulator driver circuits 203-I and 203-Q is required for any one of the functions shown in Table 1, the optical modulator driver circuit 203-I , 203-Q may be operated in a linear operation mode.
- the linearity of the input / output characteristics of the optical modulator driver circuits 203-I and 203-Q is necessary for one function shown in Table 1, and the linearity is unnecessary for another function.
- the optical modulator driver circuits 203-I and 203-Q only need to operate linearly to some extent.
- using the optical modulator driver circuits 203-I and 203-Q in an intermediate mode between the complete linear operation mode and the limit operation mode is optimal from the balance of linearity and power consumption. there is a possibility.
- the following control method can be considered for linearity control of the input / output characteristics of the optical modulator driver circuits 203-I and 203-Q.
- FIG. 35 is a diagram for explaining the linearity control method of this embodiment.
- the arithmetic processing performed by the control signal generation unit 206 is logical sum (OR) processing.
- “1” is output from the symbol mapping unit 2001 of the DSP 200
- “0” is output from the symbol mapping unit 2001.
- the pre-equalization function is ON, “1” is output from the pre-equalization unit 2002 of the DSP 200, and when the pre-equalization function is OFF, “0” is output from the pre-equalization unit 2002.
- the pre-equalization function is ON, “1” is output from the pre-equalization unit 2002 of the DSP 200, and when the pre-equalization function is OFF, “0” is output from the pre-equalization unit 2002.
- the control signal generation unit 206 When the information output from the symbol mapping unit 2001, the pre-equalization unit 2002, and the signal spectrum shaping unit 2003 is ORed by the control signal generation unit 206, at least one information is “1”, that is, the optical modulator driver circuit 203 ⁇ .
- the control signal CTL becomes “1” when at least one function that requires linearity of the input / output characteristics of I and 203-Q is operating.
- the optical modulator driver circuits 203-I and 203-Q operate in the linear operation mode.
- all the information output from the symbol mapping unit 2001, the pre-equalization unit 2002, and the signal spectrum shaping unit 2003 is “0”, that is, the linearity of the input / output characteristics of the optical modulator driver circuits 203-I and 203-Q.
- the optical modulator driver circuits 203-I and 203-Q operate in the limit operation mode. As described above, in the example of FIG. 35, switching between the complete linear operation mode and the limit operation mode is executed.
- (A) modulation format, (B) pre-equalization, and (C) spectrum shaping are targeted for information extraction, but linearity with respect to optical modulator driver circuits 203-I and 203-Q. If there is another function or operation mode related to the request, information may be added without being limited to (A) to (C).
- FIG. 36 is a diagram for explaining another linearity control method of this embodiment.
- the arithmetic processing performed by the control signal generation unit 206 is weighted addition processing.
- the operation modes of the optical modulator driver circuits 203-I and 203-Q not only two modes of a complete linear operation mode and a limit operation mode but also an intermediate operation mode is assumed.
- “1” is output from the symbol mapping unit 2001 of the DSP 200 in the case of the QAM format
- “0” is output from the symbol mapping unit 2001 in the case of the QPSK format.
- Information “1” or “0” output from the symbol mapping unit 2001 is output from INFa
- information “1” or “0” output from the pre-equalization unit 2002 is output from INFb
- the weight coefficients a, b, and c corresponding to the functions of (A) modulation format, (B) pre-equalization, and (C) spectrum shaping are linear with respect to the optical modulator driver circuits 203-I and 203-Q. Increase the value of the function with higher demand.
- optical modulator driver circuits 203-I and 203-Q can be adjusted. If linearity is acceptable to some extent, the optical modulator driver circuits 203-I and 203-Q are adjusted by adjusting the optical modulator driver circuits 203-I and 203-Q so that linearity corresponding to the linearity is obtained. It becomes possible to suppress the power consumption of Q.
- (A) modulation format, (B) pre-equalization, and (C) spectrum shaping are targeted for information extraction, but linearity requirements for optical modulator driver circuits 203-I and 203-Q are required. If there is another function or operation mode related to, information is not limited to (A) to (C).
- optical transmission distance In the case of an optical transmitter capable of finely adjusting the linearity of the input / output characteristics of the optical modulator driver circuits 203-I and 203-Q as in the example of FIG. 36, information on the optical transmission distance is also added as a linearity requirement item. Can be considered. That is, if the optical transmission distance is long, it is necessary to improve the transmission signal quality.
- the linearity of the input / output characteristics of the optical modulator driver circuits 203-I and 203-Q is set high, and if the optical transmission distance is short, Since it is considered that a certain degree of non-linearity in the optical modulator driver circuits 203-I and 203-Q is allowed, the linearity is reduced and the power consumption of the optical modulator driver circuits 203-I and 203-Q is suppressed.
- VinP is a positive phase input signal inputted to the positive phase input terminal 2P of the optical modulator driver circuit 203-I
- VinN is a negative phase input terminal 2N of the optical modulator driver circuit 203-I
- VoutP is a positive phase output signal output from the positive phase output terminal 3P of the optical modulator driver circuit 203-I to the optical I / Q modulator 205
- VoutN is an optical modulator driver circuit 203.
- Vin is an input signal input to the input terminal 2 of the optical modulator driver circuit 203-I
- Vout is output from the output terminal 3 of the optical modulator driver circuit 203-I to the optical I / Q modulator 205.
- Output signal is an input signal input to the input terminal 2 of the optical modulator driver circuit 203-I
- Vout is output from the output terminal 3 of the optical modulator driver circuit 203-I to the optical I
- the tail current amounts of the differential amplifiers 50, 54, and 56 are set in the limit operation mode. Since it can be reduced compared to the linear operation mode, the power consumption can be reduced accordingly.
- variable current source IS20 that can control the tail current of the differential amplifiers 52, 55, and 57 is used, and the current flowing through the differential amplifiers 52, 55, and 57 is The mode switching of the optical modulator driver circuit 203-I is realized by controlling the amount.
- variable current sources IS20 Since the amount of current that can flow through one variable current source IS20 is limited, the number of variable current sources IS20 may be determined according to the required amount of current, and the variable current sources IS20 may be connected in parallel. 25 can be applied to both the linearity control method described in FIG. 35 and the linearity control method described in FIG.
- the configuration and control method of the current source IS20 of the optical modulator driver circuit 203-I using the configurations of FIGS. 4, 20, 22, and 24 are as described in FIGS.
- the configuration of the current source itself is the same as that shown in FIG. 15, but the control method is different.
- a continuous control signal CTL is used as shown in FIG.
- the input / output characteristics of the optical modulator driver circuit 203-I in FIG. 4 can be continuously changed from the linear operation mode to the limit operation mode.
- 3, 4, 15, 17, and 19 to 25 show examples in which bipolar transistors are used as the transistors Q10 to Q14, Q20 to Q24, Q30, and Q31.
- the transistor is not limited, and a FET-based transistor may be used.
- the base may be replaced with the gate
- the collector may be replaced with the drain
- the emitter may be replaced with the source.
- 3, 4, and 19 to 25 the configuration of the I (in-phase) channel optical modulator driver circuit 203 -I is described, but the Q (quadrature) channel optical modulator driver circuit 203 is described.
- the configuration of -Q is the same.
- the control signal generation unit 206 may be realized using a circuit, or may be realized using a computer operating with software.
- a computer includes a CPU (Central Processing Unit) and a storage device.
- the CPU executes the processing of the control signal generation unit 206 described in the present embodiment and the following embodiments according to the program stored in the storage device.
- the linear operation mode and the limit operation mode of the optical modulator driver circuits 203-I and 203-Q can be appropriately switched and used according to the operation mode of the optical transmission system. It is possible to reduce power consumption in the limit operation mode. In addition to the use in the two modes of the linear operation mode and the limit operation mode, it is possible to use in an intermediate operation mode between them, and the optical modulator driver circuit is in an optimum state for the operation form of the optical transmission system. 203-I and 203-Q can be set.
- FIG. 37 is a block diagram showing the configuration of the optical transmitter according to the present embodiment.
- the same components as those in FIG. 34 are denoted by the same reference numerals.
- the optical transmitter of the present embodiment adds an FPGA (Field-Programmable Gate Array) 207 serving as signal processing control means to the optical transmitter of the tenth embodiment, and executes control of the operation mode of the DSP 200 using the FPGA 207. In this way, the information INF regarding the operation mode is obtained from the FPGA 207.
- FPGA Field-Programmable Gate Array
- FIG. 38 is a diagram for explaining the linearity control method of this embodiment.
- information INF relating to the operation mode (modulation format, transmission end signal processing, etc.) of the optical transmission system is acquired from the FPGA 207.
- the FPGA 207 outputs “1” as the information INFa related to the modulation format in the case of the QAM format, and outputs “0” as the information INFa in the case of the QPSK format.
- the FPGA 207 outputs “1” as information INFb related to the pre-equalization function when the pre-equalization function is ON, and outputs “0” as information INFb when the pre-equalization function is OFF.
- the FPGA 207 outputs “1” as the information INFc related to the signal spectrum shaping function when the signal spectrum shaping (Nyquist filter) function is ON, and outputs “0” as the information INFc when the signal spectrum shaping function is OFF.
- the arithmetic processing performed by the control signal generation unit 206 in FIG. 38 is the OR processing described in the example in FIG. In the case of the example in FIG. 38, the configuration described in FIGS. 3, 15, 19, 21, 23, and 25 may be used as the optical modulator driver circuits 203-I and 203-Q.
- FIG. 39 is a diagram for explaining another linearity control method of this embodiment.
- the operation of the FPGA 207 is as described above.
- the arithmetic processing performed by the control signal generation unit 206 in FIG. 39 is the weighted addition processing described in the example in FIG.
- the configuration described in FIGS. 4, 17, 20, 22, 24, and 25 may be used as the optical modulator driver circuits 203-I and 203-Q.
- the same effect as that of the tenth embodiment can be obtained.
- the gain adjustment function is closely related to the input / output characteristics of the optical I / Q modulator 205 of the optical transmitter.
- the optical I / Q modulator 205 includes an MZ (Mach-Zehnder) modulator 300 as shown in FIG.
- the MZ modulator 300 generally exhibits a nonlinear input / output characteristic of a sine (sine wave) curve as shown in FIG. Therefore, when the optical I / Q modulator 205 is driven with a driving amplitude that provides the maximum transmittance, distortion occurs.
- the optical I / Q modulator is driven with a binary signal as in the conventional 100 Gb / s optical transmission system, the distortion does not become a problem.
- the electrical signal for driving the optical I / Q modulator 205 is simple. This is not a “0” or “1” signal, but a signal containing information in the direction of the amplitude axis, so that distortion of the optical I / Q modulator 205 becomes a problem.
- the input / output characteristics of the MZ modulator 300 can be generalized as a sine curve. It is considered that it is relatively easy to give the conversion unit 2002 a characteristic (arc sine curve characteristic) opposite to the input / output characteristic of the MZ modulator 300.
- pre-equalization unit 2002 of the DSP 200 With characteristics opposite to the input / output characteristics of the MZ modulator 300, pre-equalization can be performed so that the modulated optical signal is linear.
- the amplifier driver circuits 203-I and 203-Q only need to output to the optical I / Q modulator 205 a drive signal having an amplitude that provides the maximum transmittance regardless of the operation mode.
- the pre-equalization unit 2002 of the DSP 200 is not provided with a function that gives characteristics opposite to the input / output characteristics of the MZ modulator 300, or if this function is OFF, the maximum transmittance can be obtained.
- the optical I / Q modulator 205 is driven with an amplitude drive signal, the modulated optical signal is distorted due to the nonlinear characteristics of the MZ modulator 300 in the optical I / Q modulator 205.
- gain control is performed in order to realize control using a relatively linear drive region of the MZ modulator 300, that is, control for reducing the output amplitude of the optical modulator driver circuits 203-I and 203-Q.
- the signal GCTL is supplied to the optical modulator driver circuits 203-I and 203-Q.
- Such a gain control signal GCTL can be generated by using the control signal CTL described so far.
- the optical I / Q modulator 205 operates in the linear operation region in the linear operation mode (the value of the control signal CTL is “1”).
- the gain control signal GCTL for reducing the output amplitude of the optical modulator driver circuits 203-I and 203-Q may be output.
- the control signal generation unit 206 also increases the gain control signal GCTL that increases the output amplitude of the optical modulator driver circuits 203-I and 203-Q to the maximum in the limit operation mode (the value of the control signal CTL is “0”). Should be output.
- Vin is an input signal input to the input terminal 2 of the optical modulator driver circuit 203 -I
- Vout is input from the output terminal 3 of the optical modulator driver circuit 203 -I to the optical I / Q modulator 205. This is an output signal to be output.
- any one of the circuits in FIGS. 3, 4, and 19 to 25 may be used as the output circuit 11, and the linear gain variable circuit 10 may be connected to the preceding stage of the output circuit 11.
- any of the circuits of FIGS. 3, 4, and 19 to 25 may be used as the input circuit 12, and the linear gain variable circuit 13 may be connected to the subsequent stage of the input circuit 12.
- the configuration of the I-channel optical modulator driver circuit 203-I is described, but the configuration of the Q-channel optical modulator driver circuit 203-Q is the same.
- the configuration of the linear gain variable sections 10 and 13 is as shown in FIGS.
- the gain control signals GCT and GCC in FIGS. 28 and 29 correspond to the gain control signal GCTL in FIGS.
- VinP is a positive phase input signal inputted to the positive phase input terminal 2P of the optical modulator driver circuit 203-I
- VinN is inputted to the negative phase input terminal 2N of the optical modulator driver circuit 203-I
- the negative phase input signal VoutP is a positive phase output signal output from the positive phase output terminal 3P of the optical modulator driver circuit 203-I to the optical I / Q modulator 205
- VoutN is the optical modulator driver circuit 203-I. This is a negative phase output signal output from the negative phase output terminal 3N to the optical I / Q modulator 205.
- the configurations that are cascade-connected in FIGS. 7 and 9 can be integrated into one.
- the configuration of the I-channel optical modulator driver circuit 203-I is described, but the configuration of the Q-channel optical modulator driver circuit 203-Q is the same.
- the present invention can be applied to an optical modulator driver circuit.
- SYMBOLS 1 Optical modulator driver circuit, 2, 2P, 2N, 7P, 7N ... Input terminal, 3, 3P, 3N, 8P, 8N ... Output terminal, 4 ... Operation mode switching control terminal, 5, 5P, 5N ... Gain Control terminal, 6 ... bias terminal, 10, 13, 59, 60 ... linear gain variable circuit, 11 ... output circuit, 12 ... input circuit, 20P, 20N, 30 ... input transmission line, 21P, 21N, 31 ... output transmission line 32, input signal bias control circuit, 50, 52, 54-58 ... differential amplifier, 51, 53 ...
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Abstract
Description
以下、本発明の実施例について図面を参照して説明する。図1は本実施例に係る光変調器ドライバ回路の概要を示す図、図2は本実施例に係る光変調器ドライバ回路の入出力特性を示す図である。図2の横軸は入力信号Vinの振幅(あるいは入力パワー)、縦軸は光変調器ドライバ回路の出力信号Voutの振幅(あるいは出力パワー)である。以降の入出力特性についても横軸、縦軸の定義は同様とする。
第1実施例では、線形動作モード時に利得最大となり、リミット動作モード時に利得が小さくなる振舞いとなる。それゆえ、先に述べたように想定されるある入力振幅Ainに対し、動作モードによる出力振幅レベル差が生じる。システム上、このような振舞いが許容される場合、例えば運用状態(変調フォーマットや送信端信号処理の有無)に応じてDSP側でDACからの出力振幅つまりは光変調器ドライバ回路への入力振幅を任意に調整できる場合であれば、第1実施例の回路をそのまま光変調器ドライバ回路として使用して問題ない。しかしながら、運用の簡便化を考えると、光変調器ドライバ回路においては、線形動作モードとリミット動作モードのどちらの動作モードにおいても、想定されるある入力振幅Ainに対し、ある決まった所望の出力振幅Aoutが得られることが好ましい。
次に、第1実施例の光変調器ドライバ回路1における電流源の具体的構成および制御方法について説明する。図15は図3に示した光変調器ドライバ回路1の電流源IS10の構成を示す回路図、図16は電流源IS10の制御方法を説明する図である。並列に接続されたn(nは2以上の整数)個の電流源IS10は、それぞれベースが動作モード切替用制御端子4に接続され、コレクタが図3のエミッタ抵抗R12,R13の他端に接続された電流源トランジスタQ12(Q12-1~Q12-n)と、一端が電流源トランジスタQ12のエミッタに接続され、他端が電源電圧VEEに接続された抵抗R14(R14-1~R14-n)とから構成される。
また、図15、図17の構成において、制御信号VCSは外部から電流源トランジスタQ12,Q22に直接印加してもよいし、制御側とのインタフェースに応じて電圧変換回路(電圧のレベルシフト回路等)などを介して印加してもよい。
第1実施例では、光変調器ドライバ回路を単純な増幅器として記載したが、帯域改善や反射低減の目的からカスコード構成としてもよい。図19は本実施例に係る光変調器ドライバ回路1の構成を示す回路図である。図19の光変調器ドライバ回路1は、図3に示した回路において、ベースがバイアス端子6に接続され、コレクタが逆相出力端子3Nに接続され、エミッタがトランジスタQ10のコレクタに接続されたトランジスタQ13と、ベースがバイアス端子6に接続され、コレクタが正相出力端子3Pに接続され、エミッタがトランジスタQ11のコレクタに接続されたトランジスタQ14とを追加したものである。トランジスタQ10,Q11,Q13,Q14と抵抗R10~R13とは差動増幅器54を構成している。バイアス端子6には所定のバイアス電圧が印加される。
第1実施例および第4実施例で示した回路については、集中定数回路として構成してもよいし、分布定数構成回路として構成してもよい。図21は本実施例に係る光変調器ドライバ回路1の構成を示す回路図であり、図3と同様の構成には同一の符号を付してある。図21の光変調器ドライバ回路1は、トランジスタQ10,Q11と抵抗R12,R13とからなる差動増幅器56と、電流源IS10からなる電流量調整回路51と、入力端が正相入力端子2Pに接続された入力伝送線路20Pと、入力端が逆相入力端子2Nに接続された入力伝送線路20Nと、出力端が正相出力端子3Pに接続された出力伝送線路21Pと、出力端が逆相出力端子3Nに接続された出力伝送線路21Nと、一端が入力伝送線路20Pの出力端に接続され、他端が電源電圧VCCに接続された抵抗R15と、一端が入力伝送線路20Nの出力端に接続され、他端が電源電圧VCCに接続された抵抗R16と、一端が出力伝送線路21Pの入力端に接続され、他端が電源電圧VCCに接続された抵抗R17と、一端が出力伝送線路21Nの入力端に接続され、他端が電源電圧VCCに接続された抵抗R18とから構成される。
図23は本実施例に係る光変調器ドライバ回路1の構成を示す回路図であり、図3、図21と同様の構成には同一の符号を付してある。図23の光変調器ドライバ回路1は、図21に示した光変調器ドライバ回路において、各差動増幅器56の入力部にエミッタフォロワ回路を付加したものである。
図23の逆相側のエミッタフォロワ回路は、ベースが入力伝送線路20Nに接続され、コレクタが電源電圧VCCに接続され、エミッタがトランジスタQ11のベースに接続されたトランジスタQ16と、一端がトランジスタQ16のエミッタに接続され、他端が電源電圧VEEに接続された電流源IS12とから構成される。
図24の逆相側のエミッタフォロワ回路は、ベースが入力伝送線路20Nに接続され、コレクタが電源電圧VCCに接続され、エミッタがトランジスタQ21のベースに接続されたトランジスタQ26と、一端がトランジスタQ26のエミッタに接続され、他端が電源電圧VEEに接続された電流源IS22とから構成される。
図23、図24の各差動増幅器56,57の動作は第1実施例で説明した差動増幅器50,52と同様である。なお、図23、図24の各差動増幅器56,57を第4実施例で説明したようにカスコード構成としてもよい。
第5実施例、第6実施例では、差動構成を例にしているが、差動構成に限るものでなく、単相の分布構成回路でも同様の電流量制御で同様の効果が得られる。図25は本実施例に係る光変調器ドライバ回路1の構成を示す回路図である。図25の光変調器ドライバ回路1は、入力端が入力端子2に接続された入力伝送線路30と、出力端が出力端子3に接続された出力伝送線路31と、一端が入力伝送線路30の出力端に接続され、他端が電源電圧VDDに接続された抵抗R31と、一端が出力伝送線路31の入力端に接続され、他端が電源電圧VDDに接続された抵抗R32と、入力信号VinにDCバイアスを与える入力信号バイアス制御回路32と、入力伝送線路30および出力伝送線路31に沿って配置された増幅器58とから構成される。
次に、第2実施例の線形利得可変回路10,13の具体的な構成法について説明する。一般的な利得可変回路としては、図26に示すようなギルバートセル型の利得可変回路や図27に示すようなメイヤー型の利得可変回路が知られている。
第2実施例では、線形利得可変回路10と出力回路11とを縦続接続するか、あるいは入力回路12と線形利得可変回路13とを縦続接続しているが、第8実施例の構成に第1実施例の電流源を適用することで、第1実施例の構成と第8実施例の構成を1つにまとめることが可能である。図30は本実施例の光変調器ドライバ回路1の構成を示す回路図であり、図3、図28と同様の構成には同一の符号を付してある。図30の光変調器ドライバ回路1は、図28の電流源IS40の代わりに、図3で説明した電流源IS10を用いたものである。
次に、光変調器ドライバ回路の線形性制御および利得制御を実行する手法について述べる。図34は本実施例に係る光送信器の構成を示すブロック図であり、図42と同一の構成には同一の符号を付してある。本実施例の光送信器は、光伝送システムの運用形態に応じて送信データDataのデジタル信号処理を行うDSP200(信号処理手段)と、DSP200から出力されたシンボルを多重化するMUX201-I,201-Qと、MUX201-I,201-Qから出力されたデータをアナログ信号に変換するDAC202-I,202-Qと、DAC202-I,202-Qから出力された信号を増幅する光変調器ドライバ回路203-I,203-Qと、光源となるLD204と、LD204からの連続光を光変調器ドライバ回路203-I,203-Qの出力信号により変調して出力する光I/Q変調器205と、光伝送システムの運用形態に関する情報INFに応じて光変調器ドライバ回路203-I,203-Qへの制御信号CTLを生成する制御信号生成部206とを備えている。
CTL=INFa×a+INFb×b+INFc×c ・・・(1)
なお、図25の構成については図35で説明した線形性制御方法、図36で説明した線形性制御方法のいずれにも適用することができる。
また、図3、図4、図19~図25では、I(同相)チャネルの光変調器ドライバ回路203-Iの構成について説明しているが、Q(直交)チャネルの光変調器ドライバ回路203-Qの構成も同様である。
次に、本発明の第11実施例について説明する。図37は本実施例に係る光送信器の構成を示すブロック図であり、図34と同一の構成には同一の符号を付してある。本実施例の光送信器は、第10実施例の光送信器に信号処理制御手段となるFPGA(Field-Programmable Gate Array)207を追加し、DSP200の運用形態の制御をFPGA207を用いて実行するようにし、運用形態に関する情報INFをFPGA207から取得するようにしたものである。その他の構成は第10実施例で説明したとおりである。
第10実施例、第11実施例では、光変調器ドライバ回路の入出力特性の線形性と消費電力とのバランスのみを制御するようにしていたが、さらに光変調器ドライバ回路の利得を制御するようにしてもよい。
以下、光変調器ドライバ回路の利得制御の考え方とその手法について説明する。利得の調整機能については、光送信器の光I/Q変調器205の入出力特性と深く関係する。光I/Q変調器205は、図12に示したようにMZ(Mach-Zehnder)変調器300から構成される。
Claims (13)
- 入力信号を増幅して光変調器駆動用の信号を出力する増幅器と、
所望の動作モードに応じて前記増幅器の電流量を調整可能な電流量調整回路とを備えることを特徴とする光変調器ドライバ回路。 - 請求項1記載の光変調器ドライバ回路において、
前記電流量調整回路は、前記増幅器を構成するトランジスタと接続され、所望の動作モードに応じて前記トランジスタを流れる電流の量を調整することを特徴とする光変調器ドライバ回路。 - 請求項1記載の光変調器ドライバ回路において、
前記電流量調整回路は、所望の動作モードに応じて前記増幅器の電流量を調整することにより、前記増幅器の入出力特性を変化させ所望の入力信号に対する増幅応答の線形性を制御することを特徴とする光変調器ドライバ回路。 - 請求項1記載の光変調器ドライバ回路において、
前記電流量調整回路は、所望の動作モードを示す2値の第1の制御信号に応じて個別にON/OFF可能な2個以上の電流源、または所望の動作モードおよび所望の特性を示す連続的な第1の制御信号に応じて連続的に電流量を制御可能な1個以上の可変電流源からなることを特徴とする光変調器ドライバ回路。 - 請求項1記載の光変調器ドライバ回路において、
前記電流量調整回路は、前記増幅器に入力される入力信号のDCバイアスレベルを所望の動作モードに応じて調整可能な入力信号バイアス制御回路からなることを特徴とする光変調器ドライバ回路。 - 請求項1記載の光変調器ドライバ回路において、
さらに、前記増幅器の前段または後段に線形利得可変回路を備えることを特徴とする光変調器ドライバ回路。 - 請求項6記載の光変調器ドライバ回路において、
前記線形利得可変回路は、
入力信号が入力される増幅用トランジスタを含む増幅部と、
前記増幅用トランジスタとカスコード接続された利得調整用トランジスタを含み、第2の制御信号に応じて前記増幅用トランジスタの出力信号の振幅を調整する利得調整部と、
前記増幅部および利得調整部に定電流を供給する定電流源と、
前記増幅用トランジスタのエミッタと前記定電流源との間に挿入された第1のエミッタ抵抗と、
前記利得調整用トランジスタのエミッタと前記増幅用トランジスタのコレクタとの間に挿入された第2のエミッタ抵抗とからなることを特徴とする光変調器ドライバ回路。 - 請求項1記載の光変調器ドライバ回路において、
前記増幅器の代わりに線形利得可変回路を備え、
前記線形利得可変回路は、
入力信号が入力される増幅用トランジスタを含む増幅部と、
前記増幅用トランジスタとカスコード接続された利得調整用トランジスタを含み、第2の制御信号に応じて前記増幅用トランジスタの出力信号の振幅を調整する利得調整部と、
前記増幅用トランジスタのエミッタと前記電流量調整回路との間に挿入された第1のエミッタ抵抗と、
前記利得調整用トランジスタのエミッタと前記増幅用トランジスタのコレクタとの間に挿入された第2のエミッタ抵抗とからなり、
前記電流量調整回路は、
所望の動作モードを示す2値の制御信号に応じて個別にON/OFF可能な2個以上の電流源、または所望の動作モードおよび所望の特性を示す連続的な制御信号に応じて連続的に電流量を制御可能な1個以上の可変電流源からなることを特徴とする光変調器ドライバ回路。 - 請求項1記載の光変調器ドライバ回路において、
さらに、入力端が光変調器ドライバ回路の入力端子に接続され、出力端が電源電圧に接続された入力伝送線路と、
入力端が電源電圧に接続され、出力端が光変調器ドライバ回路の出力端子に接続された出力伝送線路とを備え、
前記増幅器と前記電流量調整回路とは、それぞれ前記入力伝送線路および出力伝送線路に沿って複数個配置され、
各増幅器の入力端子が前記入力伝送線路に接続され、各増幅器の出力端子が前記出力伝送線路に接続されることを特徴とする光変調器ドライバ回路。 - 光伝送システムの運用形態に応じて送信データの信号処理を行う信号処理手段と、
この信号処理手段で処理されたデジタル信号をアナログ信号に変換するDAコンバータと、
このDAコンバータから出力された信号を増幅する、請求項1乃至9のいずれか1項に記載の光変調器ドライバ回路と、
光源から入力された連続光を前記光変調器ドライバ回路の出力信号により変調して出力する光変調器と、
前記光伝送システムの運用形態に関する情報に基づいて前記光変調器ドライバ回路の動作モードを制御する第1の制御信号を生成する制御信号生成手段とを備えることを特徴とする光送信器。 - 請求項10記載の光送信器において、
前記制御信号生成手段は、前記信号処理手段から前記光伝送システムの運用形態に関する情報を取得することを特徴とする光送信器。 - 請求項10記載の光送信器において、
さらに、前記光伝送システムの運用形態に応じて前記信号処理手段の運用形態を制御する信号処理制御手段を備え、
前記制御信号生成手段は、前記信号処理制御手段から前記光伝送システムの運用形態に関する情報を取得することを特徴とする光送信器。 - 請求項10記載の光送信器において、
前記制御信号生成手段は、さらに前記第1の制御信号に基づいて、前記光変調器ドライバ回路の利得を制御する第2の制御信号を生成することを特徴とする光送信器。
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US14/889,127 US10243664B2 (en) | 2013-05-09 | 2014-05-09 | Optical modulator driver circuit and optical transmitter |
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