WO2012078169A1 - Balanced light detector and related method - Google Patents
Balanced light detector and related method Download PDFInfo
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- WO2012078169A1 WO2012078169A1 PCT/US2010/059866 US2010059866W WO2012078169A1 WO 2012078169 A1 WO2012078169 A1 WO 2012078169A1 US 2010059866 W US2010059866 W US 2010059866W WO 2012078169 A1 WO2012078169 A1 WO 2012078169A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/66—Non-coherent receivers, e.g. using direct detection
- H04B10/69—Electrical arrangements in the receiver
- H04B10/693—Arrangements for optimizing the preamplifier in the receiver
- H04B10/6931—Automatic gain control of the preamplifier
Definitions
- This disclosure relates generally to optical systems, and in particular, to a balanced light detector and related method.
- Photo or light detectors are ubiquitously employed in many optical processing applications. These detectors are typically used to convert received light energy into electrical signals. The generated electrical signals are then typically processed in accordance with the relevant optical applications.
- Balanced light detectors employ two photo detecting diodes for reducing common mode noise.
- Common mode noise is one that similarly affects two or more signals, such as interference or internally- generated noise.
- a balanced light detector usually employs a pair of photodiodes adapted to generate respective currents from received lights, a pair of transimpedance amplifiers adapted to convert the currents into respective voltages, and a differential device adapted to generate an output as a function of the difference in the voltages from the amplifiers. By subtracting these voltages, cancellation of common mode noise occurs, thereby reducing noise at the output of a balance light detector. Additionally, feedback may also be employed in order to improve the common noise rejection.
- balanced light detectors employ transimpedance amplifiers that are direct current (DC)-coupled. These types of transimpedance amplifiers have a frequency response that extends down to substantially DC. Accordingly, these amplifiers amplify the DC component at the respective outputs of the photodiodes, and provide the amplified DC voltages to the differential device for common mode noise cancellation. For some applications involving relatively high frequencies, however, DC-coupled transimpedance amplifiers may not be suitable or require more complex electronics in order for them to properly work. Accordingly, only alternating current (AC)-coupled transimpedance amplifiers may be available.
- AC alternating current
- the balance light detector comprises a first photodiode adapted to generate a first current based on a first received light; a first transimpedance amplifier adapted to generate a first AC voltage based the first current; a second photodiode adapted to generate a second current based on a second received light, a second transimpedance amplifier adapted to generate a second AC voltage based the first current, a control module adapted to control a gain of the first transimpedance amplifier based on a gain-adjusted difference between rectified first and second AC voltages; and a differential device adapted to generate an output signal based on a difference between the first and second AC voltages.
- the control module may be configured to control the gain of the first transimpedance amplifier in order to improve the rejection of common mode noise present in the received light.
- FIG. 1 illustrates a block diagram of an exemplary optical system in accordance with an aspect of the disclosure.
- FIG. 2 A illustrates a block diagram of an exemplary balanced light detector in accordance with another aspect of the disclosure.
- FIG. 2B illustrates a block diagram of an exemplary control logic module in accordance with another aspect of the disclosure.
- FIG. 3A illustrates a block diagram of another exemplary balanced light detector in accordance with another aspect of the disclosure.
- FIG. 3B illustrates a block diagram of another exemplary control logic module in accordance with another aspect of the disclosure.
- FIG. 1 illustrates a block diagram of an exemplary optical system 100 in accordance with an aspect of the disclosure.
- This diagram illustrates a typical application or use of a balanced light detector. It shall be understood that a balanced light detector may be used in many other distinct manners. Additionally, this diagram is simplified for explanation purposes, but such optical system may include additional components.
- the optical system 100 comprises a light source module 102, a sampling optics module 104, an optics processing module 106, and a balanced light detector 108.
- the light source module 102 emits light energy with a defined wavelength or wavelength range, such as in the infrared, visible and/or ultraviolet ranges.
- the sampling optics module 104 couples a portion of the light energy from the light source module 102 to generate a sampled light EB, and directs the remaining portion to the optics processing module 106.
- the optics processing module 106 processes the transmitted light from the sampling optics module 104 based on the defined process to generate an output light E A .
- Both the output light EA and the sampled light EB are received by the balanced light detector 108, which generates an output voltage Vo based on these two inputs.
- the balanced light detector 108 converts the light energy EA and EB into the output voltage Vo in a manner so as to reject or reduce common mode noise. More specifically, in the balanced light detector 108, photodiodes convert the respective light energy EA and EB into currents IA and IB. A pair of transimpedance amplifiers convert the currents IA and IB into respective voltages VSENSE-A and VSENSE-B.
- a control logic module develops a control signal VCNTL for the gain of one of the transimpedance amplifiers based on the voltages VSENSE-A and VSENSE-B.
- a differential device generates the output voltage Vo based on a difference between the voltages VSENSE-A and VSENSE-B.
- FIG. 2 A illustrates a block diagram of an exemplary balanced light detector 200 in accordance with another aspect of the disclosure.
- the balanced light detector 200 may be an exemplary detailed implementation of the detector 108, previously discussed.
- the balanced light detector 200 comprises first and second photodiodes 202 and 212, a variable-gain transimpedance amplifier 204, a fixed-gain transimpedance amplifier 214, a control logic module 220, a differential device 230 (e.g., a voltage summer or subtracter), and a buffer 240.
- a differential device 230 e.g., a voltage summer or subtracter
- the first photodiode 202 is adapted to receive light energy EA and convert it into a current IA.
- the variable-gain transimpedance amplifier 204 is adapted to convert the current IA into a voltage VSENSE-A based on a variable gain GA that is controlled by control signal VCNTL generated by the control logic module 220.
- the second photodiode 212 is adapted to receive light energy EB and convert it into a current IB.
- the fixed-gain transimpedance amplifier 204 is adapted to convert the current IB into a voltage VSENSE-B based on a substantially fixed gain GB.
- the control logic module 220 generates the control voltage VCNTL for controlling the gain GA of the transimpedance amplifier 204 based on the voltages VSENSE-A and VSENSE-B.
- the differential device 230 generates a differential voltage that is based on a difference between the voltages VSENSE-A and VsENSE-B. This differential voltage is passed through the buffer 240 to generate an output voltage Vo of the balanced light detector 200. Common mode noise present in the voltages VSENSE-A and VSENSE-B is cancelled by the differential device 230, thereby substantially reducing common mode noise in the output voltage Vo.
- the control logic module 220 helps to improve the common mode noise rejection by adjusting the gain GA of the transimpedance amplifier 204. As discussed in more detail below, the control logic module 220 generates the gain control voltage VCNTL based on a difference between the voltages VSENSE-A and VSENSE-B. However, the transimpedance amplifiers 204 and 214 may only be AC- coupled, and not DC-coupled, and thus the voltages VSENSE-A and VSENSE-B are AC voltages.
- control logic module 220 rectifies the voltages VSENSE-A and VSENSE-B to generate corresponding DC voltages VDC-A and VDC-B, then generates the control voltage VCNTL based on a difference between the DC voltages and a negative gain -Gc applied to the difference.
- the negative gain - Gc is configured to reduce common mode noise at the output voltage Vo of the detector 220 by forcing the DC voltages VDC-A and VDC-B to be substantially the same due to the feedback operation.
- FIG. 2B illustrates a block diagram of an exemplary control logic module 220 in accordance with another aspect of the disclosure.
- the control logic module 220 may be a detailed exemplary implementation of the control logic module of FIG. 2A.
- the control logic module 220 comprises a rectifier module A 222, a rectifier module B 224, a differential device 226 (e.g., a voltage summer or subtractor), and an amplifier 228.
- the rectifier module A 222 is adapted to rectify the voltage VSENSE-A to generate a DC voltage VDC-A.
- the rectifier module B 224 is adapted to rectify the voltage VSENSE-B to generate a DC voltage VDC-B.
- the differential device 226 generates a voltage based on a difference between the voltages VDC-A and VDC-B.
- the amplifier 228 then amplifies the differential voltage in accordance with a negative gain -Gc to generate the gain control voltage VCNTL.
- the negative gain -Gc may be adjusted to substantially minimized the common mode noise at the output voltage Vo of the detector 200.
- the optimum negative gain -Gc may be determined empirically and/or by calculations.
- FIG. 3A illustrates a block diagram of an exemplary balanced light detector 300 in accordance with another aspect of the disclosure.
- the balanced light detector 300 may be another exemplary detailed implementation of the detector 108, previously discussed.
- the balanced light detector 300 comprises first and second photodiodes 302 and 304, variable-gain transimpedance amplifiers 310 and 320, a control logic module 330, a differential device 350 (e.g., a voltage summer or subtractor), and a buffer 360.
- a differential device 350 e.g., a voltage summer or subtractor
- the transimpedance amplifier 310 may be characterized by having a high pass filter (HPF) component 312 to indicate that it is only an AC-coupled amplifier, and not DC-coupled.
- HPF high pass filter
- the transimpedance amplifier 310 is also characterized by having a gain component 314.
- the gain component 314 has a gain GA that varies substantially exponential with a gain control voltage VCNTL as indicated by the exponential component 316.
- the transimpedance amplifier 320 is similarly characterized, including an HPF component 322, a gain component 324 with a gain GB, and a control voltage-to-gain exponential component 326.
- the first photodiode 302 is adapted to receive light energy EA and convert it into a current IA.
- the transimpedance amplifier 204 is adapted to convert the current IA into an AC voltage VSENSE-A based on a variable gain GA that is controlled by signal VCNTL generated by the control logic module 330.
- the second photodiode 212 is adapted to receive light energy EB and convert it into a current IB.
- the transimpedance amplifier 204 is adapted to convert the current IB into an AC voltage VSENSE-B based on a gain GB that is fixed by a substantially constant voltage VFIXED.
- the control logic module 330 generates a voltage VCNTL for controlling the gain GA of the transimpedance amplifier 310 based on the voltages VSENSE-A and VSENSE-B.
- the differential device 350 generates a voltage that is based on a difference between the voltages VSENSE-A and VSENSE-B. This voltage is passed through the buffer 360 to generate an output voltage Vo of the balanced light detector 200.
- the differential device 350 generating an output voltage Vo that is a function of the difference between voltages VSENSE-A and VsENSE-B, common mode noise at the output voltage Vo is substantially cancelled.
- the control logic module 330 helps to improve the common mode noise rejection by adjusting the gain GA of the transimpedance amplifier 310. As discussed in more detail below, the control logic module 330 generates the gain control voltage VCNTL based on a difference between the voltages VSENSE-A and VsENSE-B. Since, as previously discussed, the transimpedance amplifiers 310 and 320 may only be AC-coupled, and not DC-coupled, the voltages VSENSE-A and VsENSE-B are then AC voltages.
- control logic module 330 low pass filters, rectifies, and generates the logarithms of the voltages VSENSE-A and VsENSE-B to generate corresponding DC voltages VDC-A and VDC-B.
- the control logic module 330 also generates a voltage based on a difference between the DC voltages VDC-A and VDC-B and then applies a negative gain -Gc to the differential voltage to generate the gain control voltage VCNTL.
- the negative gain -Gc is configured to reduce common mode noise at the output voltage Vo of the detector 300.
- FIG. 3B illustrates a block diagram of another exemplary control logic module 330 in accordance with another aspect of the disclosure.
- the control logic module 330 may be a detailed exemplary implementation of the control logic module of FIG. 3A.
- the control logic module 330 comprises first and second low pass filters (LPF) 332 and 338, a rectifier module A 334, another rectifier module B 340, a LOG module A 336, another LOG module 342, a differential device 344 (e.g., a voltage summer or subtractor), and an amplifier 346.
- LPF low pass filters
- the LPF 332 is adapted to filter the voltage VSENSE-A to ensure that the feedback loop is substantially stable
- the rectifier module A 334 is adapted to rectify the filtered voltage VSENSE-A
- the log module A 336 is adapted to take the logarithm of the rectified voltage to generate a DC voltage VDC-A.
- the LPF 338 is adapted to filter the voltage VSENSE-B to ensure that the feedback loop is substantially stable
- the rectifier module B 340 is adapted to rectify the filtered voltage VSENSE-B
- the log module B 342 is adapted to take the logarithm of the rectified voltage to generate a DC voltage VDC-B.
- the logarithm of the two voltages are taken to cancel out the effects of the exponential control voltage-to-gain response of the transimpedance amplifier 310, so as to make the gain response more linear with the control voltage VCNTL.
- the differential device 344 generates a voltage based on a difference between the voltages VDC-A and VDC-B.
- the amplifier 346 then amplifies the differential voltage in accordance with a negative gain -Gc to generate the gain control voltage VCNTL.
- the negative gain -Gc may be adjusted to substantially minimized the common mode noise in the output voltage Vo of the detector 300.
- the optimum negative gain -GC may be determined empirically, by calculations, and/or by other techniques.
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Abstract
This disclosure relates to a balanced light detector and related method The balance light detector includes a first photodiode adapted to generate a first current based on a first received light, a first transimpedance amplifier adapted to generate a first AC voltage based the first current, a second photodiode adapted to generate a second current based on a second received light, a second transimpedance amplifier adapted to generate a second AC voltage based the first current, a control module adapted to control a gain of the first transimpedance amplifier based on a gam-adjusted difference between rectified first and second AC voltages, and a differential device adapted to generate an output signal based on a difference between the first and second AC voltages The control module may be configured to control the gain of the first transimpedance amplifier in order to improve the rejection of common mode noise
Description
PATENT COOPERATION TREATY (PCT) PATENT APPLICATION
FOR
BALANCED LIGHT DETECTOR AND RELATED METHOD
Inventor:
OVIDIO H. ANTON
Prepared by:
George L. Fountain
FOUNTAIN LAW GROUP, INC.
18201 Von Karman Ave., Suite 960
Irvine, CA 92612
Tel: (949) 769-6991
(Fax): (949) 769-6995
BALANCED LIGHT DETECTOR AND RELATED METHOD
FIELD
[0001] This disclosure relates generally to optical systems, and in particular, to a balanced light detector and related method.
BACKGROUND
[0002] Photo or light detectors are ubiquitously employed in many optical processing applications. These detectors are typically used to convert received light energy into electrical signals. The generated electrical signals are then typically processed in accordance with the relevant optical applications.
[0003] The conversion of optical signals into electrical signals typically does not occur in a noiseless manner. Noise from distinct sources, such as signal interference, diode noise, thermal noise, and others, finds its way into the produced electrical signals. This is one of the reasons that single-ended light detectors are not desirable since they do not generally have an effective mechanism to noise.
[0004] Balanced light detectors, on the other hand, employ two photo detecting diodes for reducing common mode noise. Common mode noise is one that similarly affects two or more signals, such as interference or internally- generated noise. A balanced light detector usually employs a pair of photodiodes adapted to generate respective currents from received lights, a pair of transimpedance amplifiers adapted to convert the currents into respective voltages, and a differential device adapted to generate an output as a function of the difference in the voltages from the amplifiers. By subtracting these voltages, cancellation of common mode noise occurs, thereby reducing noise at the output of a balance light detector. Additionally, feedback may also be employed in order to improve the common noise rejection.
[0005] Often, balanced light detectors employ transimpedance amplifiers that are direct current (DC)-coupled. These types of transimpedance amplifiers have a frequency response that extends down to substantially DC. Accordingly,
these amplifiers amplify the DC component at the respective outputs of the photodiodes, and provide the amplified DC voltages to the differential device for common mode noise cancellation. For some applications involving relatively high frequencies, however, DC-coupled transimpedance amplifiers may not be suitable or require more complex electronics in order for them to properly work. Accordingly, only alternating current (AC)-coupled transimpedance amplifiers may be available.
[ 0006 ] Thus, there is a need for a balanced light detector and related method that employs AC-coupled transimpedance amplifiers to effectively perform common mode noise rejection.
SUMMARY
[ 0007 ] An aspect of the disclosure relates to a balanced light detector and related method. The balance light detector comprises a first photodiode adapted to generate a first current based on a first received light; a first transimpedance amplifier adapted to generate a first AC voltage based the first current; a second photodiode adapted to generate a second current based on a second received light, a second transimpedance amplifier adapted to generate a second AC voltage based the first current, a control module adapted to control a gain of the first transimpedance amplifier based on a gain-adjusted difference between rectified first and second AC voltages; and a differential device adapted to generate an output signal based on a difference between the first and second AC voltages. The control module may be configured to control the gain of the first transimpedance amplifier in order to improve the rejection of common mode noise present in the received light.
[ 0008 ] Other aspects, advantages and novel features of the disclosure will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 illustrates a block diagram of an exemplary optical system in accordance with an aspect of the disclosure.
[0010] FIG. 2 A illustrates a block diagram of an exemplary balanced light detector in accordance with another aspect of the disclosure.
[0011] FIG. 2B illustrates a block diagram of an exemplary control logic module in accordance with another aspect of the disclosure.
[0012] FIG. 3A illustrates a block diagram of another exemplary balanced light detector in accordance with another aspect of the disclosure.
[0013] FIG. 3B illustrates a block diagram of another exemplary control logic module in accordance with another aspect of the disclosure.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0014] FIG. 1 illustrates a block diagram of an exemplary optical system 100 in accordance with an aspect of the disclosure. This diagram illustrates a typical application or use of a balanced light detector. It shall be understood that a balanced light detector may be used in many other distinct manners. Additionally, this diagram is simplified for explanation purposes, but such optical system may include additional components.
[0015] The optical system 100 comprises a light source module 102, a sampling optics module 104, an optics processing module 106, and a balanced light detector 108. The light source module 102 emits light energy with a defined wavelength or wavelength range, such as in the infrared, visible and/or ultraviolet ranges. The sampling optics module 104 couples a portion of the light energy from the light source module 102 to generate a sampled light EB, and directs the remaining portion to the optics processing module 106. The optics processing module 106, in turn, processes the transmitted light from the sampling optics module 104 based on the defined process to generate an output light EA.
[0016] Both the output light EA and the sampled light EB are received by the balanced light detector 108, which generates an output voltage Vo based on these two inputs. As discussed in more detail below, the balanced light detector 108 converts the light energy EA and EB into the output voltage Vo in a manner so as to reject or reduce common mode noise. More specifically, in the balanced light detector 108, photodiodes convert the respective light energy EA and EB into currents IA and IB. A pair of transimpedance amplifiers convert the currents IA and IB into respective voltages VSENSE-A and VSENSE-B. SO as to improve the common mode noise rejection, a control logic module develops a control signal VCNTL for the gain of one of the transimpedance amplifiers based on the voltages VSENSE-A and VSENSE-B. A differential device generates the output voltage Vo based on a difference between the voltages VSENSE-A and VSENSE-B.
[0017] FIG. 2 A illustrates a block diagram of an exemplary balanced light detector 200 in accordance with another aspect of the disclosure. The balanced light detector 200 may be an exemplary detailed implementation of the detector 108, previously discussed. The balanced light detector 200 comprises first and second photodiodes 202 and 212, a variable-gain transimpedance amplifier 204, a fixed-gain transimpedance amplifier 214, a control logic module 220, a differential device 230 (e.g., a voltage summer or subtracter), and a buffer 240.
[0018] The first photodiode 202 is adapted to receive light energy EA and convert it into a current IA. The variable-gain transimpedance amplifier 204 is adapted to convert the current IA into a voltage VSENSE-A based on a variable gain GA that is controlled by control signal VCNTL generated by the control logic module 220. Similarly, the second photodiode 212 is adapted to receive light energy EB and convert it into a current IB. The fixed-gain transimpedance amplifier 204 is adapted to convert the current IB into a voltage VSENSE-B based on a substantially fixed gain GB.
[0019] The control logic module 220 generates the control voltage VCNTL for controlling the gain GA of the transimpedance amplifier 204 based on the voltages VSENSE-A and VSENSE-B. The differential device 230 generates a differential voltage that is based on a difference between the voltages VSENSE-A
and VsENSE-B. This differential voltage is passed through the buffer 240 to generate an output voltage Vo of the balanced light detector 200. Common mode noise present in the voltages VSENSE-A and VSENSE-B is cancelled by the differential device 230, thereby substantially reducing common mode noise in the output voltage Vo.
[0020] The control logic module 220 helps to improve the common mode noise rejection by adjusting the gain GA of the transimpedance amplifier 204. As discussed in more detail below, the control logic module 220 generates the gain control voltage VCNTL based on a difference between the voltages VSENSE-A and VSENSE-B. However, the transimpedance amplifiers 204 and 214 may only be AC- coupled, and not DC-coupled, and thus the voltages VSENSE-A and VSENSE-B are AC voltages. Accordingly, the control logic module 220 rectifies the voltages VSENSE-A and VSENSE-B to generate corresponding DC voltages VDC-A and VDC-B, then generates the control voltage VCNTL based on a difference between the DC voltages and a negative gain -Gc applied to the difference. The negative gain - Gc is configured to reduce common mode noise at the output voltage Vo of the detector 220 by forcing the DC voltages VDC-A and VDC-B to be substantially the same due to the feedback operation.
[0021] FIG. 2B illustrates a block diagram of an exemplary control logic module 220 in accordance with another aspect of the disclosure. The control logic module 220 may be a detailed exemplary implementation of the control logic module of FIG. 2A. The control logic module 220 comprises a rectifier module A 222, a rectifier module B 224, a differential device 226 (e.g., a voltage summer or subtractor), and an amplifier 228.
[0022] The rectifier module A 222 is adapted to rectify the voltage VSENSE-A to generate a DC voltage VDC-A. Similarly, the rectifier module B 224 is adapted to rectify the voltage VSENSE-B to generate a DC voltage VDC-B. The differential device 226 generates a voltage based on a difference between the voltages VDC-A and VDC-B. The amplifier 228 then amplifies the differential voltage in accordance with a negative gain -Gc to generate the gain control voltage VCNTL. The negative gain -Gc may be adjusted to substantially minimized the common
mode noise at the output voltage Vo of the detector 200. The optimum negative gain -Gc may be determined empirically and/or by calculations.
[ 0023 ] FIG. 3A illustrates a block diagram of an exemplary balanced light detector 300 in accordance with another aspect of the disclosure. The balanced light detector 300 may be another exemplary detailed implementation of the detector 108, previously discussed. The balanced light detector 300 comprises first and second photodiodes 302 and 304, variable-gain transimpedance amplifiers 310 and 320, a control logic module 330, a differential device 350 (e.g., a voltage summer or subtractor), and a buffer 360.
[ 0024 ] The transimpedance amplifier 310 may be characterized by having a high pass filter (HPF) component 312 to indicate that it is only an AC-coupled amplifier, and not DC-coupled. The transimpedance amplifier 310 is also characterized by having a gain component 314. The gain component 314 has a gain GA that varies substantially exponential with a gain control voltage VCNTL as indicated by the exponential component 316. The transimpedance amplifier 320 is similarly characterized, including an HPF component 322, a gain component 324 with a gain GB, and a control voltage-to-gain exponential component 326.
[ 0025 ] The first photodiode 302 is adapted to receive light energy EA and convert it into a current IA. The transimpedance amplifier 204 is adapted to convert the current IA into an AC voltage VSENSE-A based on a variable gain GA that is controlled by signal VCNTL generated by the control logic module 330. Similarly, the second photodiode 212 is adapted to receive light energy EB and convert it into a current IB. The transimpedance amplifier 204 is adapted to convert the current IB into an AC voltage VSENSE-B based on a gain GB that is fixed by a substantially constant voltage VFIXED.
[ 0026 ] The control logic module 330 generates a voltage VCNTL for controlling the gain GA of the transimpedance amplifier 310 based on the voltages VSENSE-A and VSENSE-B. The differential device 350 generates a voltage that is based on a difference between the voltages VSENSE-A and VSENSE-B. This voltage is passed through the buffer 360 to generate an output voltage Vo of the
balanced light detector 200. By the differential device 350 generating an output voltage Vo that is a function of the difference between voltages VSENSE-A and VsENSE-B, common mode noise at the output voltage Vo is substantially cancelled.
[ 0027 ] The control logic module 330 helps to improve the common mode noise rejection by adjusting the gain GA of the transimpedance amplifier 310. As discussed in more detail below, the control logic module 330 generates the gain control voltage VCNTL based on a difference between the voltages VSENSE-A and VsENSE-B. Since, as previously discussed, the transimpedance amplifiers 310 and 320 may only be AC-coupled, and not DC-coupled, the voltages VSENSE-A and VsENSE-B are then AC voltages. Accordingly, the control logic module 330 low pass filters, rectifies, and generates the logarithms of the voltages VSENSE-A and VsENSE-B to generate corresponding DC voltages VDC-A and VDC-B. The control logic module 330 also generates a voltage based on a difference between the DC voltages VDC-A and VDC-B and then applies a negative gain -Gc to the differential voltage to generate the gain control voltage VCNTL. The negative gain -Gc is configured to reduce common mode noise at the output voltage Vo of the detector 300.
[ 0028 ] FIG. 3B illustrates a block diagram of another exemplary control logic module 330 in accordance with another aspect of the disclosure. The control logic module 330 may be a detailed exemplary implementation of the control logic module of FIG. 3A. The control logic module 330 comprises first and second low pass filters (LPF) 332 and 338, a rectifier module A 334, another rectifier module B 340, a LOG module A 336, another LOG module 342, a differential device 344 (e.g., a voltage summer or subtractor), and an amplifier 346.
[ 0029 ] The LPF 332 is adapted to filter the voltage VSENSE-A to ensure that the feedback loop is substantially stable, the rectifier module A 334 is adapted to rectify the filtered voltage VSENSE-A, and the log module A 336 is adapted to take the logarithm of the rectified voltage to generate a DC voltage VDC-A. Similarly, the LPF 338 is adapted to filter the voltage VSENSE-B to ensure that the feedback loop is substantially stable, the rectifier module B 340 is adapted to rectify the
filtered voltage VSENSE-B, and, the log module B 342 is adapted to take the logarithm of the rectified voltage to generate a DC voltage VDC-B. The logarithm of the two voltages are taken to cancel out the effects of the exponential control voltage-to-gain response of the transimpedance amplifier 310, so as to make the gain response more linear with the control voltage VCNTL.
[ 0030 ] The differential device 344 generates a voltage based on a difference between the voltages VDC-A and VDC-B. The amplifier 346 then amplifies the differential voltage in accordance with a negative gain -Gc to generate the gain control voltage VCNTL. The negative gain -Gc may be adjusted to substantially minimized the common mode noise in the output voltage Vo of the detector 300. The optimum negative gain -GC may be determined empirically, by calculations, and/or by other techniques.
[ 0031 ] While the invention has been described in connection with various embodiments, it will be understood that the invention is capable of further modifications. This application is intended to cover any variations, uses or adaptation of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as come within the known and customary practice within the art to which the invention pertains.
Claims
1. A balanced light detector, comprising:
a first photodiode adapted to generate a first current based on a first received light;
a first amplifier adapted to generate a first voltage based on the first current and a first gain;
a second photodiode adapted to generate a second current based on a second received light;
a second amplifier adapted to generate a second voltage based on the second current and a second gain;
a control module adapted to separately receive the first and second voltages, and generate a gain control signal for adjusting the first gain of the first amplifier based on the first and second voltages; and
a first differential device adapted to generate an output voltage based on the first and second voltages.
2. The balanced light detector of claim 1, wherein the control module comprises:
a first rectifier module adapted to rectify the first voltage;
a second rectifier module adapted to rectify the second voltage;
a second differential device adapted to generate a differential signal based on a difference between the first and second voltages; and
a third amplifier adapted to apply a third gain to the differential signal to generate the gain control signal.
3. The balanced light detector of claim 2, wherein the third gain is a negative gain.
4. The balanced light detector of claim 1, wherein the control module comprises:
a first rectifier module adapted to rectify the first voltage; a first logarithm device adapted to generate a first intermediate voltage based on a logarithm of the rectified first voltage;
a second rectifier module adapted to rectify the second voltage;
a second logarithm device adapted to generate a second intermediate voltage based on a logarithm of the rectified second voltage;
a second differential device adapted to generate a differential signal based on a difference between the first and second intermediate voltages; and
a third amplifier adapted to apply a third gain to the differential signal to generate the gain control signal.
5. The balanced light detector of claim 4, wherein the first gain is configured to vary substantially exponential with the gain control signal.
6. The balanced light detector of claim 1, wherein the control module comprises:
a first low pass filter adapted to filter the first voltage;
a first rectifier module adapted to rectify the filtered first voltage;
a first logarithm device adapted to generate a first intermediate voltage based on a logarithm of the filtered and rectified first voltage;
a second low pass filter adapted to filter the second voltage;
a second rectifier module adapted to rectify the filtered second voltage; a second logarithm device adapted to generate a second intermediate voltage based on a logarithm of the filtered and rectified second voltage;
a second differential device adapted to generate a differential signal based on a difference between the first and second intermediate voltages; and
a third amplifier adapted to apply a third gain to the differential signal to generate the gain control signal.
7. The balanced light detector of claim 1, wherein the first amplifier comprises a transimpedance amplifier.
8. The balanced light detector of claim 7, wherein the transimpedance amplifier comprises: a high pass filter component; and
a gain component adapted to vary the first gain in a nonlinear manner with respect to the gain control signal.
9. The balanced light detector of claim 1, wherein the second gain of the second amplifier is substantially fixed.
10. The balanced light detector of claim 1, wherein the second amplifier comprises a transimpedance amplifier.
11. The balanced light detector of claim 1, wherein the first and second amplifiers are only AC-coupled.
12. The balanced light detector of claim 1, wherein the first differential device comprises a voltage summer or subtracter.
13. The balanced light detector of claim 1, further comprising a buffer adapted to reproduce the output voltage from the first differential device.
14. A method of generating an output signal based on first and second received lights, comprising:
generating a first AC voltage based on the first received light;
rectifying the first AC voltage to generate a first DC voltage;
generating a second AC voltage based on the second received light;
rectifying the second AC voltage to generate a second DC voltage;
controlling the generation of the first AC voltage based on the first and second DC voltages; and
generating the output signal based on the first and second AC voltages.
15. The method of claim 14, wherein controlling the generation of the first AC voltage comprises adjusting a gain associated with the generation of the first AC voltage based on the first and second DC voltages.
16. The method of claim 14, wherein controlling the generation of the first AC voltage is based on a difference between the first and second DC voltages.
17. The method of claim 16, wherein controlling the generation of the first AC voltage is based on a control signal being a function of the difference between the first and second DC voltages and a gain.
18. The method of claim 17, wherein the gain is negative.
19. An apparatus for generating an output signal based on first and second received lights, comprising:
a first circuit adapted to generate a first AC voltage based on the first received light;
a first rectifier adapted to rectify the first AC voltage to generate a first DC voltage;
a second circuit adapted to generate a second AC voltage based on the second received light;
a second rectifier adapted to rectifying the second AC voltage to generate a second DC voltage;
a control module adapted to a control signal for controlling a gain of the first circuit based on the first and second DC voltages; and
a third circuit adapted to generate the output signal based on the first and second AC voltages.
20. The apparatus of claim 19, wherein the control module is adapted to vary the gain of the first circuit to reduce common mode noise in the output signal.
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PCT/US2010/059866 WO2012078169A1 (en) | 2010-12-10 | 2010-12-10 | Balanced light detector and related method |
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PCT/US2010/059866 WO2012078169A1 (en) | 2010-12-10 | 2010-12-10 | Balanced light detector and related method |
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