CN111835290A

CN111835290A - Power amplification system suitable for Bluetooth device and related power amplification method

Info

Publication number: CN111835290A
Application number: CN201910305462.7A
Authority: CN
Inventors: 邓平援
Original assignee: Realtek Semiconductor Corp
Current assignee: Realtek Semiconductor Corp
Priority date: 2019-04-16
Filing date: 2019-04-16
Publication date: 2020-10-27
Anticipated expiration: 2039-04-16
Also published as: CN111835290B

Abstract

The power amplification system comprises a voltage-controlled oscillator, a frequency divider, a mixer and a summing amplifier. The voltage-controlled oscillator is used for providing input signals with the frequency being a non-integral multiple of a preset frequency; the frequency divider is coupled to the voltage-controlled oscillator and used for receiving the input signal and dividing the frequency of the input signal to respectively generate an in-phase signal and a quadrature signal corresponding to the input signal; the frequency mixer is respectively coupled with the voltage-controlled oscillator and the frequency eliminator and is used for mixing the input signal transmitted by the voltage-controlled oscillator and the in-phase signal transmitted by the frequency eliminator to output a mixed signal; the summing amplifier is coupled to the mixer and the frequency divider respectively for integrating the mixed signal and the quadrature signal to generate an output signal with a predetermined frequency.

Description

Power amplification system suitable for Bluetooth device and related power amplification method

Technical Field

The present invention relates to power amplifier applications, and more particularly, to power regulation for Bluetooth (Bluetooth) transmission.

Background

For a conventional direct-up transmitter (direct-up transmitter), if the frequency of a Voltage Controlled Oscillator (VCO) is selected to be at the same frequency as an even harmonic (even harmonic) of a Power Amplifier (PA), the frequency of the VCO may be affected by the frequency of the PA, which is also called a power amplifier pulling effect (PA-pulling), so that the Error Vector Magnitude (EVM) is degraded, and thus the communication quality is degraded. For example, in a 2.4GHz Bluetooth transmitter, the power amplifier pulling effect is generated when the VCO signal is at 2.4GHz or a multiple thereof (e.g., 4.8GHz, 9.6 GHz).

There are several prior arts that have been set forth to solve the above problems, and in order to have a more specific concept, the following will be made to generally describe these related arts:

referring to FIG. 1, FIG. 1 is a schematic diagram of a conventional Bluetooth transmitter, which is referred to as "H.Darabi, et al", "A Dual-Mode 802.11b/Bluetooth Radio in 0.35um CMOS", "IEEEJ.Solid State Circuits, pp.698-706. Mar.2005". In the bluetooth Local Oscillator (LO) generation architecture shown in fig. 1, to avoid causing power amplifier pulling effects on the VCO, the VCO frequency is selected to be 2/3 of the LO frequency (2.4GHz), i.e., 1.6 GHz; wherein the Mixer (Mixer) adopts a double sideband Mixer (DSB) architecture. The disadvantages of this approach are: in addition to the 2.4GHz signal at the output of the mixer, there is an additional non-ideal spur (spur) at 800MHz, which results in a large influence on the power amplification characteristics.

Referring to fig. 2, fig. 2 is a schematic diagram of a fractional frequency multiplier of the prior art (see "a. bias" a 2.7-6.1GHz CMOS Local Oscillator Based on frequency multiplication by 3/2, "2011 norcphip"), wherein when the VCO is intentionally selected to be 2/3 times 2.4G to avoid the pulling effect of the power amplifier, the output of the mixer needs to be further reduced by 3/2 times to obtain a 2.4G signal. In order to achieve the purpose, the document first divides the frequency of the VCO by two through a frequency divider, and then creates the effect of multiplying by three through a frequency multiplying manner, and finally obtains the output frequency of the VCO multiplied by 1.5 times. However, the odd-numbered multiplying scheme is required, and the odd-numbered multiplying scheme is not only very complicated in design but also increases a lot of cost, so that the direct multiple reduction at the output terminal is not ideal.

US20110140746a1 discloses a Single Side Band (SSB) Mixer architecture as a Mixer (Mixer), which can additionally suppress non-ideal spurs, but has the disadvantage that both inputs of the Mixer require In-phase/Quadrature (I/Q) signals.

Referring to fig. 3, US7894778 discloses a Multiband (Multiband) LO generator, which can adjust the frequency to 1.5 times or 1.25 times, thereby reducing the tuning range of the VCO. However, the disadvantage of the above approach is that the ideal spur will be closer to the desired output frequency with the degree of the decimal.

In addition, US patent No. US9548774 discloses an N-path filter architecture for generating a band reject (band reject) frequency response through the N-path filter, and the output end uses a Double Side Band (DSB) mixer to filter out the non-ideal spurs, but the drawback is that it needs to generate the clock required for N-path filtering, if N is 4, it needs to generate a clock with 25% duty cycle (duty cycle), and if the filtering effect is good, the order must be increased. The disadvantage of the above method is that the order expansion is not easy, and the higher the order, the smaller the duty cycle (duty cycle) of the operation, and therefore the more power consumption.

In addition, U.S. Pat. nos. US7515931 and US8121214 propose to filter out the undesired spurs by using a Band-pass filter (BPF), which is relatively simple but has the disadvantage of occupying a large area, which is undoubtedly an increase in cost.

In view of the above, many of the prior art techniques fail to improve the power amplifier pulling effect without side effects, and there is a need for a novel method and related circuit to improve the above-mentioned problems.

Disclosure of Invention

The present invention is directed to a power amplification system and related method for bluetooth devices, which can solve the bottleneck of the prior art without side effects.

At least one embodiment of the present invention provides a power amplification system for a bluetooth device, the power amplification system is configured to generate an output with a predetermined frequency, and the power amplification system includes a voltage-controlled oscillator, a frequency divider, a mixer, and a summing amplifier. The voltage-controlled oscillator is used for providing an input signal with a frequency which is a non-integral multiple of the preset frequency; the frequency divider is coupled to the voltage-controlled oscillator and configured to receive the input signal and divide the frequency of the input signal to generate an in-phase (in-phase) signal and a quadrature (quadrature) signal corresponding to the input signal, respectively; the frequency mixer is respectively coupled with the voltage-controlled oscillator and the frequency eliminator and is used for mixing the input signal transmitted by the voltage-controlled oscillator and the in-phase signal transmitted by the frequency eliminator to output a mixed signal; and the summing amplifier is respectively coupled with the frequency mixer and the frequency divider and is used for integrating the mixed signal and the orthogonal signal to generate a first output signal with the frequency multiplication of the preset frequency.

At least one embodiment of the present invention provides a power amplifying method for a bluetooth device, the power amplifying system generating an output with a predetermined frequency, the power amplifying method comprising: providing an input signal with a frequency which is a non-integral multiple of the predetermined frequency; dividing the frequency of the input signal to generate an in-phase signal and an orthogonal signal corresponding to the input signal; mixing the input signal from the voltage-controlled oscillator and the in-phase signal from the frequency divider to output a mixed signal; and integrating the mixed signal and the quadrature signal to generate a first output signal having a frequency multiplied by the predetermined frequency.

In summary, the present invention generates the inverse spur signal to eliminate the spur by way of forward feedback (Feed forward), which not only does not require I/Q phase in the mixer, but also does not require high order filtering or inductor at the output end, so as to eliminate the non-ideal spur of the mixer. In other words, the present invention can achieve the desired PA effect at a lower cost, eliminating the non-ideal spurs.

Drawings

Fig. 1 to 3 are filters designed for harmonic interference in the prior art.

Fig. 4 is a schematic diagram of a power amplification system suitable for a bluetooth device according to an embodiment of the present invention.

Fig. 5 is a schematic diagram of an amplitude phase controller of the power amplification system of fig. 4 according to an embodiment of the invention.

Fig. 6 is a schematic diagram of the summing amplifier of fig. 4 according to an embodiment of the invention.

Fig. 7 is a schematic diagram of the power amplification system shown in fig. 4 applied to 2.4GHz bluetooth transmission.

Fig. 8 is a flowchart of a power amplification method for a bluetooth device according to an embodiment of the present invention.

Description of the symbols:

400 power amplification system

410 voltage controlled oscillator

420 frequency divider

430 frequency mixer

440 summing amplifier

450 amplitude phase controller

460 in-phase/quadrature generator

S1 input signal

S2 in-phase signal

S3 quadrature signal

S4 adjusted quadrature signal

S5 mixed signal

S6, S7, S8 output signals

PI _1, PI _2 in-phase path

PQ _1, PQ _2 orthogonal paths

R1, R2 resistance

802 to 810 steps

Detailed Description

Certain terms are used throughout the description and following claims to refer to particular components. As one of ordinary skill in the art will appreciate, hardware manufacturers may refer to a component by different names. In the present specification and the claims that follow, elements are distinguished not by differences in name but by differences in function. In the following description and in the claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to. Also, the term "coupled" is used herein to encompass any direct or indirect electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.

As can be seen from the introduction to the prior art, these techniques also pay a heavy price in design and cost while addressing the power amplifier pulling effect. The invention provides a simple design, which mainly uses forward feedback (fed forward) technique to make reverse spur signal to eliminate non-ideal spur, not only the mixer does not need I/Q phase (i.e. does not need to divide the received signal into in-phase (in-phase) signal and quadrature (quadrature) signal), but also the output end does not need to set high-order filter to perform high-order filtering or set inductor, so as to eliminate the non-ideal spur of the mixer. Unlike the so-called feedback (feed back) technique, the feed forward technique employed by the present invention can be broadly understood as: the interference is predicted and handled before it affects the system.

Referring to fig. 4, fig. 4 is a schematic diagram of a power amplification system 400 for a bluetooth device according to an embodiment of the present invention, to solve the above-mentioned problems of the prior art, the VCO frequency is first set at a non-integer (non-integer) frequency of the PA harmonic, and the VCO frequency and the divided-by-2 frequency of the VCO are sent to a Mixer (Mixer) to generate a required local oscillation frequency (LO frequency). The power amplification system 400 is configured to generate an output with a predetermined frequency (LO), wherein the predetermined frequency may be, for example, twice the local oscillator frequency (2LO), but the invention is not limited thereto. The power amplification system 400 may include a Voltage Controlled Oscillator (VCO) 410, a frequency divider 420, a mixer 430, an adder 440, an amplitude and phase controller 450, and an In-phase/Quadrature (I/Q) generator 460. The vco 410 is configured to provide an input signal with a frequency that is a non-integer multiple of the predetermined frequency (i.e., a signal that is not an integer multiple of LO), and in the present embodiment, the vco 410 provides the input signal S1 with a frequency of 4/3 LO.

The frequency divider 420 is coupled to the vco 410, and is configured to receive the input signal with a frequency of 4/3LO from the vco 410 and divide the frequency of the input signal S1 to generate an in-phase (in-phase) signal S2 and a quadrature (quadrature) signal S3 corresponding to the input signal S1, respectively. The frequency divider 420 may be a divide-by-2 circuit (labeled "/2" in the figure), and the in-phase signal S2 and the quadrature signal S3 are 90 degrees out of phase, but the invention is not limited thereto, and the frequency divider 420 may be replaced by a divide-by-4 circuit, for example.

The mixer 430 is coupled to the vco 410 and the divider 420, respectively, for mixing the input signal S1 (with a frequency of 4/3LO) from the vco 410 and the in-phase signal S2 (with a frequency of 2/3LO) from the divider 420 to output a mixed signal S5, wherein the mixed signal S5 has a frequency of 2LO and has non-ideal spurs (labeled "(2 LO), (2/3 LO)" in the figure) at a frequency 2/3LO, which is a phenomenon that is difficult to avoid. The mixer 430 may be implemented by a double side band mixer (DSB), but the invention is not limited thereto, and the DSB is well known in the art and will not be described in detail herein.

The amplitude and phase controller 450 is coupled between the adder amplifier 440 and the divider 420, and is configured to receive the quadrature signal S3 from the divider 420 and accordingly generate an adjusted quadrature signal S4 (denoted as "- (2/3 LO)") with a frequency of 2/3LO, wherein the quadrature signal S3 is 90 degrees out of phase with the in-phase signal S2, and the adjusted quadrature signal S4 can generate an anti-phase spur signal with the same frequency and opposite phase (180 degrees out of phase) through proper adjustment of the amplitude and phase controller 450, so as to cancel the spur component in the mixed signal S5. In addition to the 90 degree phase delay provided by the quadrature signal S3, the path between the amplitude phase controller 450 and the summing amplifier 440 provides a certain degree of phase delay (e.g., 45 degree phase delay), and the final phase delay of the adjusted quadrature signal S4 can be achieved by properly adjusting the amplitude phase controller 450 (e.g., 45 degree phase delay).

Fig. 5 is a schematic diagram of the amplitude and phase controller 450 of the power amplification system 400 of fig. 4 according to an embodiment of the invention. As shown in fig. 5, which is a basic structure of the amplitude and phase controller of the present invention, the gain of the differential amplifier is controlled by the N-bit signal, so as to achieve the effect of adjusting the signal amplitude; in addition, the M-bit signal is used to control the low-pass filter capacitor output by the differential amplifier, so as to achieve the effect of adjusting the signal phase. Generally, the amplitude-phase controller 450 can be implemented with a first order low pass filter, and if the parasitic capacitance generated by the circuit is not enough to generate the required delay, a higher order low pass filter, such as a second order low pass filter, can be used.

The adder amplifier 440 is coupled to the mixer 430 and the amplitude-phase controller 450, and is configured to add the mixed signal S5 and the processed quadrature signal S4 to generate a frequency-multiplied (2LO) output signal S6 with a predetermined frequency. The summing amplifier 440 can be implemented by the architecture of fig. 6, and fig. 6 is a schematic diagram of the summing amplifier 440 of fig. 4 according to an embodiment of the invention, wherein the summing amplifier 440 is implemented by a dual-input differential amplifier, and the undesired spurs output by the mixer 430 are added to and cancelled by the inverted waveform (i.e., the processed quadrature signal S4 with a 180-degree difference), so as to achieve the effects of suppressing the undesired spurs and amplifying the desired signal. As shown in fig. 6, the load of the summing amplifier 440 can be saved in overall area by using the resistors R1 and R2, but the resistors in fig. 6 can be replaced by inductors in order to further enhance the effect of suppressing the spurs.

The in-phase/quadrature signal generator 460 is coupled to the output terminal of the summing amplifier 440, and is configured to process the output signal (2LO) of the summing amplifier 440 to generate at least one output signal having the predetermined frequency (LO). Output signals S7 and S8 having predetermined frequencies (LO) are obtained from the outputs of the in-phase path PI _2 and the quadrature path PQ _2, respectively. Since the purpose of the i/q signal generator 460 is only to reduce the frequency of the output signal of the summing amplifier 440 by 1, the i/q signal generator 460 may be omitted in some cases.

For a better understanding of the present invention, the following description will be given by using a comparative practical example. Referring to fig. 7, fig. 7 is a schematic diagram illustrating the power amplification system 400 shown in fig. 4 being applied to 2.4GHz bluetooth transmission. As mentioned above, if the VCO signal is a frequency multiplication of 2.4G (e.g. 2.4GHz, 4.8GHz, 9.6GHz), the pulling effect (pulling) problem of the power amplifier is encountered, so in fig. 7, when the target local oscillator signal (LO) is 2.4GHz, the VCO 410 provides 3.2GHz input to avoid the problem, but the invention is not limited thereto. The mixer 430 then receives the 3.2GHz signal from the VCO 410 and the 1.6GHz signal divided by 2 from the in-phase path PI _1, and mixes the two signals. After mixing, the mixer generates 4.8GHz and 1.6GHz signals (i.e., non-ideal spurs that must be attenuated or filtered before generating the LO signal). On the other hand, the amplitude and phase controller 450 generates an inverse phase 1.6GHz spike signal with the same amplitude and 180 degrees phase delay according to the divided-by-2 1.6GHz signal from the quadrature path PQ _ 1. Since the phase delayed by 90 degrees can be directly obtained by using the frequency divider 420 circuit of divide-by-2, the phase adjustment range of the amplitude phase controller 450 can be reduced, thereby reducing the phase adjustment order. Finally, after the addition by the adder 440, the non-ideal spurs are cancelled, so that a clean 4.8GHz signal is obtained, and after 460 processing, the required 2.4GHz output is obtained.

Fig. 8 is a flowchart of a power amplification method for a bluetooth device according to an embodiment of the present invention. Please note that, if substantially the same result is obtained, the steps are not necessarily performed according to the order shown in FIG. 8. The method illustrated in fig. 8 may be employed by the power amplification system 400 of fig. 4 and may be briefly summarized as follows:

step 802: providing an input signal with a frequency which is a non-integral multiple of a predetermined frequency;

step 804: dividing the frequency of the input signal to generate an in-phase signal and an orthogonal signal corresponding to the input signal;

step 806: mixing the input signal from the voltage-controlled oscillator and the in-phase signal from the frequency eliminator to output a mixed signal;

step 808: integrating the mixed signal and the quadrature signal to generate an output signal having the predetermined frequency;

step 810: and (6) ending.

Since the details of each step in fig. 8 should be easily understood by those skilled in the art after reading the above paragraphs, further description will be omitted here for the sake of brevity.

In summary, the present invention generates the backward spur signal by the forward feedback to eliminate the spur, so as to effectively solve the problem encountered in the prior art, for example, eliminate the spur in the output signal without increasing a large amount of cost (without using a high-order filter or a band-pass filter). Furthermore, although the content of the description mainly emphasizes that the present invention is applicable to a bluetooth system, the present invention is not limited thereto. For example, under the same/similar concept, the power amplification system and the power amplification method of the invention can also be applied to a Wireless Fidelity (WiFi) architecture, such as the WiFi2.4g/5G architecture, which can effectively improve the power amplifier pulling effect therein, thereby improving the communication quality of WiFi.

The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.

Claims

1. A power amplification system for a bluetooth device, the power amplification system for generating an output at a predetermined frequency, the power amplification system comprising:

a Voltage Controlled Oscillator (VCO) for providing an input signal having a frequency that is a non-integer multiple of the predetermined frequency;

a frequency divider, coupled to the vco, for receiving the input signal and dividing the frequency of the input signal to generate an in-phase (in-phase) signal and a quadrature (quadrature) signal corresponding to the input signal, respectively;

a frequency mixer, coupled to the voltage-controlled oscillator and the frequency divider, for mixing the input signal from the voltage-controlled oscillator and the in-phase signal from the frequency divider to output a mixed signal; and

and the addition amplifier is respectively coupled with the frequency mixer and the frequency divider and used for integrating the mixed signal and the orthogonal signal to generate a first output signal with the frequency multiplication of the preset frequency.

2. The power amplification system of claim 1, further comprising:

an In-phase/Quadrature (I/Q) generator coupled to the output of the summing amplifier for processing the first output signal to generate at least one second output signal having the predetermined frequency.

3. The power amplifier system of claim 1 wherein the frequency divider circuit is a divide-by-2 circuit and the in-phase signal and the quadrature signal are 90 degrees out of phase.

4. The power amplification system of claim 1 further comprising an amplitude phase controller coupled between the summing amplifier and the frequency divider for receiving the quadrature signal and generating an adjusted quadrature signal accordingly.

5. The power amplification system of claim 4, wherein the amplitude phase controller comprises:

an amplitude control unit for adjusting the amplitude of the quadrature signal according to the signal amplification factor of the mixer; and

a phase control unit for adjusting the phase of the quadrature signal.

6. The power amplification system of claim 5, wherein the phase control unit adjusts the phase of the quadrature signal according to the phase of the quadrature signal and a path delay between the summing amplifier and the amplitude phase controller to generate the adjusted quadrature signal.

7. The power amplification system of claim 4 wherein the adjusted quadrature signal is an inverted spur signal to cancel the spur signal generated by the mixer.

8. The power amplification system of claim 1, wherein the voltage controlled oscillator provides an input signal having a frequency of 4/3 times the predetermined frequency.

9. The power amplification system of claim 1, wherein the mixer is a Double Sideband (DSB) mixer.

10. A power amplification method for a bluetooth device, the power amplification system for generating an output at a predetermined frequency, the power amplification method comprising:

providing an input signal with a frequency which is a non-integral multiple of the predetermined frequency;

dividing the frequency of the input signal to generate an in-phase (in-phase) signal and a quadrature (quadrature) signal corresponding to the input signal;

mixing the input signal from the voltage-controlled oscillator and the in-phase signal from the frequency divider to output a mixed signal; and

the mixed signal and the quadrature signal are integrated to generate a first output signal having a frequency multiplied by the predetermined frequency.