CN111835290B - Power amplification system suitable for Bluetooth device and related power amplification method - Google Patents

Abstract

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-integer multiple of a preset frequency; the frequency divider is coupled to the voltage-controlled oscillator and used for receiving the input signal and frequency-dividing the input signal so as to respectively generate an in-phase signal and a quadrature signal corresponding to the input signal; the mixer is coupled to the voltage-controlled oscillator and the frequency divider respectively, and is used for mixing the input signal transmitted by the voltage-controlled oscillator and the in-phase signal transmitted by the frequency divider 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 and related power amplification method suitable for bluetooth device

Technical Field

The present invention relates to the application of a power amplifier, and in particular to power adjustment for Bluetooth transmission.

Background technique

For traditional direct-up transmitters, if the frequency of the voltage controlled oscillator (VCO) is selected to be the same frequency as the even harmonic of the power amplifier (PA), the VCO frequency may be affected by the frequency of the PA, also known as the PA-pulling effect, which deteriorates the error vector magnitude (EVM) and thus the communication quality. Taking a 2.4GHz Bluetooth transmitter as an example, when the VCO signal is 2.4GHz or its multiples (such as 4.8GHz, 9.6GHz), the PA-pulling effect will occur.

At present, there are some previous technologies that have been used to solve the above problems. In order to have a more specific concept, the following will give a general introduction to these related technologies:

Please refer to FIG. 1 , which is a schematic diagram of a Bluetooth transmitter of the prior art. For more details, please refer to “H. Darabi, et al., “A Dual-Mode 802.11b/Bluetooth Radio in 0.35um CMOS,” IEEE J. Solid State Circuits, pp. 698-706. Mar. 2005”. In the Bluetooth local oscillator (LO) generation architecture shown in FIG. 1 , in order to avoid causing a power amplifier pulling effect on the VCO, the VCO frequency is selected at 2/3 of the LO frequency (2.4GHz), that is, 1.6GHz; wherein the mixer (Mixer) adopts a double sideband mixer (DSB) architecture. The disadvantage of this approach is that in addition to the 2.4GHz signal at the output end of this mixer, there will be an additional non-ideal spur at 800MHz, resulting in a significant impact on the power amplifier characteristics.

Please refer to FIG. 2, which is a schematic diagram of a fractional frequency multiplier of the prior art (for details, please refer to “A. Bevilacqua “A 2.7-6.1GHz CMOS Local Oscillator Based on Frequency Multiplication by 3/2,” 2011 NORCHIP”). When the VCO is deliberately selected to be 2/3 times of 2.4G to avoid the pulling effect of the power amplifier, the output of the mixer needs to be restored by 3/2 times to obtain a 2.4G signal. In order to achieve this goal, this document first divides the frequency of the VCO by two through a frequency divider, and then creates a three-fold effect through frequency multiplication, and finally obtains an output frequency of 1.5 times the VCO frequency. However, the above method must use an odd-numbered frequency multiplication structure, and the odd-numbered frequency multiplication structure is not only very complex in design, but also increases a lot of cost. Therefore, this method of directly restoring the frequency by multiples at the output end is not ideal.

US Publication No. US20110140746A1 discloses a technology of using a single sideband (SSB) mixer architecture as a mixer. Although this technology can additionally suppress non-ideal spikes, the disadvantage is that both input ends of the mixer require in-phase/quadrature (I/Q) signals.

Next, referring to FIG. 3, US Pat. No. US7894778 discloses a multiband LO generator that can adjust the frequency to 1.5 times or 1.25 times, thereby reducing the frequency modulation range of the VCO. However, the disadvantage of the above approach is that the non-ideal spikes will become closer to the desired output frequency as the decimalization degree increases.

In addition, US Patent No. US9548774 discloses an N-path filter architecture, which is used to generate a band reject frequency response through an N-path filter, and a double sideband (DSB) mixer is used at the output to filter out non-ideal spikes. However, the disadvantage is that it is necessary to generate a clock required for N-path filtering. If N=4, a clock with a duty cycle of 25% is required. If a good filtering effect is to be achieved, the order must be increased. The disadvantage of the above method is that it is not easy to expand the order, and the higher the order, the smaller the duty cycle, and therefore the more power consumption.

In addition, US Pat. Nos. 7,515,931 and 8,121,214 propose using a band-pass filter (BPF) to filter out non-ideal spikes. Although the band-pass filter is relatively simple, it has the disadvantage of occupying a large area, which is undoubtedly an increase in cost.

In summary, many prior arts are unable to improve the problem of the pulling effect of a power amplifier without causing side effects, and therefore a novel method and related circuit are needed to improve the above problem.

Summary of the invention

The object of the present invention is to provide a power amplification system and related method suitable for a Bluetooth device, so as to solve the bottleneck faced by the prior art without causing side effects.

At least one embodiment of the present invention provides a power amplification system suitable for a Bluetooth device, the power amplification system is used to generate an output of a predetermined frequency, and the power amplification system includes a voltage-controlled oscillator, a frequency divider, a mixer, and an adding amplifier. The voltage-controlled oscillator is used to provide an input signal with a frequency that is a non-integer multiple of the predetermined frequency; the frequency divider is coupled to the voltage-controlled oscillator, and is used to receive the input signal and divide the input signal to generate an in-phase signal and a quadrature signal corresponding to the input signal; the mixer is coupled to the voltage-controlled oscillator and the frequency divider, and is used to mix the input signal transmitted from the voltage-controlled oscillator and the in-phase signal transmitted from the frequency divider to output a mixed signal; and the adding amplifier is coupled to the mixer and the frequency divider, and is used to integrate the mixed signal and the quadrature signal to generate a first output signal having a multiple of the predetermined frequency.

At least one embodiment of the present invention provides a power amplification method suitable for a Bluetooth device. The power amplification system is used to generate an output of a predetermined frequency. The power amplification method includes: providing an input signal with a frequency that is a non-integer multiple of the predetermined frequency; dividing the input signal to generate an in-phase signal and a quadrature signal corresponding to the input signal respectively; mixing the input signal transmitted from the voltage-controlled oscillator and the in-phase signal transmitted from the divider to output a mixed signal; and integrating the mixed signal and the quadrature signal to generate a first output signal having a multiple of the predetermined frequency.

In summary, the present invention mainly generates a reverse spike signal through a forward feedback method to eliminate the spike. This method not only does not require an I/Q phase for the mixer, but also does not require a high-order filter or an inductor at the output end, thereby eliminating the non-ideal spike of the mixer. In other words, the present invention can achieve the desired PA effect at a lower cost and eliminate the non-ideal spike.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 to FIG. 3 show filters designed for harmonic interference in the prior art.

FIG. 4 is a schematic diagram of a power amplification system applicable to a Bluetooth device according to an embodiment of the present invention.

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

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

FIG. 7 is a schematic diagram of applying the power amplification system shown in FIG. 4 to 2.4 GHz Bluetooth transmission.

FIG. 8 is a flow chart of a power amplification method applicable to a Bluetooth device according to an embodiment of the present invention.

Symbol Description:

400 Power Amplification System

410 Voltage Controlled Oscillator

420 Frequency Divider

430 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 signal

PI_1, PI_2 in-phase path

PQ_1, PQ_2 orthogonal paths

R1, R2 resistors

Steps 802-810

Detailed ways

Certain words are used in the specification and subsequent patent applications to refer to specific components. Those with ordinary knowledge in the field should understand that hardware manufacturers may use different terms to refer to the same component. This specification and subsequent patent applications do not use differences in names as a way to distinguish components, but use differences in the functions of the components as the criteria for distinction. The word "including" mentioned throughout the specification and subsequent claims is an open-ended term and should be interpreted as "including but not limited to". In addition, the word "coupled" here includes any direct and indirect electrical connection means. Therefore, if the text describes a first device coupled to a second device, it means that the first device can be directly electrically connected to the second device, or indirectly electrically connected to the second device through other devices or connection means.

From the introduction of the previous technologies, it can be seen that these technologies, while solving the pulling effect of the power amplifier, also pay a heavy price in design and cost. The present invention proposes a simple design, which mainly uses the forward feedback technique to create a reverse spike signal to eliminate the non-ideal spike. Not only does the mixer not require I/Q phase (that is, there is no need to divide the received signal into in-phase signal and quadrature signal), the output end does not need to set a high-order filter to perform high-order filtering or set an inductor, so as to eliminate the non-ideal spike of the mixer. Different from the so-called feedback technology, the feedforward technology used in the present invention can be roughly understood as: predicting and responding to interference before it affects the system.

Please refer to FIG. 4, which is a schematic diagram of a power amplifier system 400 for a Bluetooth device according to an embodiment of the present invention. In order to solve the problems of the prior art, the present invention sets the VCO frequency at a PA harmonic non-integer frequency at first, and sends the VCO frequency and the VCO frequency divided by 2 to a mixer to generate the required local oscillation frequency (LO frequency). The power amplifier system 400 is used to generate an output of a predetermined frequency (LO), wherein the predetermined frequency may be, for example, twice the local oscillator frequency (2LO), but the present invention is not limited thereto. The power amplifier system 400 may include a voltage controlled oscillator (VCO) 410, a frequency divider 420, a mixer 430, an adding amplifier 440, an amplitude phase controller 450, and an in-phase/quadrature (I/Q) generator 460. The voltage controlled oscillator 410 is used to provide an input signal whose frequency is a non-integer multiple of the predetermined frequency (ie, a signal that is not an integer multiple of LO). In this embodiment, the voltage controlled oscillator 410 provides an input signal S1 whose frequency is 4/3 LO.

The frequency divider 420 is coupled to the voltage controlled oscillator 410, and is used to receive an input signal with a frequency of 4/3LO transmitted from the voltage controlled oscillator 410, and divides the input signal S1 to generate an in-phase signal S2 and a quadrature signal S3 corresponding to the input signal S1. The frequency divider circuit 420 can be a divide-by-2 circuit (marked as "/2" in the figure), and the phases of the in-phase signal S2 and the quadrature signal S3 are 90 degrees apart, but the present invention is not limited thereto. For example, the frequency divider circuit 420 can be replaced by a divide-by-4 circuit.

The mixer 430 is coupled to the voltage controlled oscillator 410 and the frequency divider 420, respectively, to mix the input signal S1 (frequency is 4/3LO) from the voltage controlled oscillator 410 and the in-phase signal S2 (frequency is 2/3LO) from the frequency divider 420, so as to output a mixed signal S5, wherein the mixed signal S5 has a frequency of 2LO and has a non-ideal spike at the frequency 2/3LO (labeled as "(2LO), (2/3LO)" in the figure), which is a phenomenon that is difficult to avoid. The mixer 430 can be implemented by a double sideband mixer (DSB) mixer, but the present invention is not limited thereto, and the double sideband mixer is a well-known structure in the art, and the details are not repeated.

The amplitude phase controller 450 is coupled between the adding amplifier 440 and the frequency divider 420, and is used for receiving the orthogonal signal S3 transmitted from the frequency divider 420, and generating an adjusted orthogonal signal S4 (labeled as "-(2/3LO)") with a frequency of 2/3LO, wherein the orthogonal signal S3 is 90 degrees out of phase with the in-phase signal S2, and through proper adjustment of the amplitude phase controller 450, the adjusted orthogonal signal S4 can generate an anti-phase spike signal with the same frequency and opposite phase (180 degrees difference) to offset the spike component in the mixed signal S5. In addition to the 90-degree phase delay provided by the orthogonal signal S3, the path between the amplitude phase controller 450 and the summing amplifier 440 provides a certain degree of phase delay (e.g., a 45-degree phase delay). By properly adjusting the amplitude phase controller 450 (e.g., generating a 45-degree phase delay), the final phase delay of the adjusted orthogonal signal S4 can reach 180 degrees.

FIG5 is a schematic diagram of an amplitude phase controller 450 of the power amplifier system 400 of FIG4 according to an embodiment of the present invention. As shown in FIG5, the basic architecture of the amplitude and phase controller of the present invention is shown. By controlling the gain of the differential amplifier through an N-bit signal, the effect of adjusting the signal amplitude can be achieved. In addition, by controlling the low-pass filter capacitor output by the differential amplifier through an M-bit signal, the effect of adjusting the signal phase can be achieved. Generally speaking, the amplitude phase controller 450 can be implemented by a first-order low-pass filter. If the parasitic capacitance generated by the circuit is not enough to produce the required delay, a higher-order low-pass filter, such as a second-order low-pass filter, can be used.

The adding amplifier 440 is coupled to the mixer 430 and the amplitude phase controller 450 respectively, and is used to add the mixed signal S5 and the processed quadrature signal S4 to generate a double frequency (2LO) output signal S6 with a predetermined frequency. The adding amplifier 440 can be implemented by the structure of FIG. 6, which is a schematic diagram of the adding amplifier 440 of FIG. 4 according to an embodiment of the present invention. The adding amplifier 440 is implemented by a dual-input differential amplifier. The non-ideal spikes output by the mixer 430 are offset by adding the non-ideal spikes and the inverted waveform (i.e., the processed quadrature signal S4 with a phase difference of 180 degrees), so as to suppress the non-ideal spikes and amplify the desired signal. As shown in FIG. 6, the use of resistors R1 and R2 as the load of the adding amplifier 440 can save the overall area. However, if the effect of suppressing spikes is to be further improved, the resistors in FIG. 6 can be replaced by inductors.

The in-phase/quadrature signal generator 460 is coupled to the output terminal of the summing amplifier 440, and is used 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 the predetermined frequency (LO) can be obtained from the outputs of the in-phase path PI_2 and the quadrature path PQ_2, respectively. Since the purpose of the in-phase/quadrature signal generator 460 is only to reduce the frequency of the output signal of the summing amplifier 440 by 1 times, the in-phase/quadrature signal generator 460 can be omitted in some cases.

In order to have a better understanding of the present invention, a more practical example will be applied to illustrate the following. Please refer to FIG. 7, which is a schematic diagram of applying the power amplifier system 400 shown in FIG. 4 to 2.4 GHz Bluetooth transmission. As mentioned earlier, if the VCO signal is a multiple of 2.4 GHz (e.g., 2.4 GHz, 4.8 GHz, 9.6 GHz), the power amplifier pulling effect (PA pulling) problem will be faced. Therefore, in FIG. 7, when the target local oscillation signal (LO) is 2.4 GHz, the voltage controlled oscillator 410 provides a 3.2 GHz input to avoid the above problem, but the present invention is not limited to this. The mixer 430 then receives the 3.2 GHz signal from the voltage controlled oscillator 410 and the 1.6 GHz signal after being divided by 2 from the in-phase path PI_1, and mixes the two. After mixing, the mixer generates 4.8 GHz and 1.6 GHz signals (i.e., non-ideal spikes, which must be attenuated or filtered before generating the LO signal). On the other hand, the amplitude phase controller 450 generates an anti-phase 1.6GHz spike signal with the same amplitude and a phase delay of 180 degrees according to the 1.6GHz signal after division by 2 transmitted from the orthogonal path PQ_1. Since the divider 420 circuit using the divider by 2 can directly obtain a phase delayed by 90 degrees, the phase adjustment range of the amplitude phase controller 450 can be reduced, thereby reducing the order of phase adjustment. Finally, after addition by the adder 440, since the non-ideal spike has been offset, a clean 4.8GHz signal can be obtained, and after processing by 460, the required 2.4GHz output can be obtained.

FIG8 is a flow chart of a power amplification method for a Bluetooth device according to an embodiment of the present invention. Please note that the steps do not necessarily have to be executed in the order shown in FIG8 if substantially the same result can be obtained. The method shown in FIG8 can be adopted by the power amplification system 400 of FIG4 and can be simply summarized as follows:

Step 802: Provide an input signal having a frequency that is a non-integer multiple of a predetermined frequency;

Step 804: Divide the input signal to generate an in-phase signal and a quadrature signal corresponding to the input signal respectively;

Step 806: Mix the input signal from the voltage controlled oscillator and the in-phase signal from the frequency divider to output a mixed signal;

Step 808: Integrate the mixed signal and the quadrature signal to generate an output signal having the predetermined frequency;

Step 810: End.

Since those skilled in the art can easily understand the details of each step in FIG. 8 after reading the above paragraphs, further description will be omitted here for the sake of brevity.

In summary, the present invention generates a reverse spike signal through forward feedback to eliminate spikes, which can effectively solve the problems faced by the prior art. For example, it can eliminate spikes in the output signal without increasing a lot of costs (without using high-order filters or bandpass filters). In addition, although the content of the specification mainly emphasizes that the present invention is applicable to Bluetooth systems, the present invention is not limited to this. For example, under the same/similar concept, the power amplification system and power amplification method of the present invention can also be applied to Wireless Fidelity (WiFi) architectures, such as WiFi2.4G/5G architectures, 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. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims (10)

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 (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 voltage-controlled oscillator for receiving the input signal and dividing the input signal to generate an in-phase signal and a quadrature signal, respectively;

the mixer is coupled to the voltage-controlled oscillator and the frequency divider respectively and used for mixing the input signal transmitted by the voltage-controlled oscillator and the in-phase signal transmitted by the frequency divider so as to output a mixed signal; and

and the summing amplifier is coupled to the mixer and the frequency divider respectively and used for integrating the mixed signal and the quadrature 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 a second output signal having the predetermined frequency.

3. The power amplifying system according to claim 1, wherein the frequency divider is a divide-by-2 circuit and the in-phase signal is 90 degrees out of phase with the quadrature signal.

4. The power amplifying system according to 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, 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 for canceling the spur signal generated by the mixer.

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

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

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

providing an input signal with a frequency that is a non-integer multiple of the predetermined frequency by a voltage-controlled oscillator;

frequency-dividing the input signal by a frequency divider to generate an in-phase signal and an quadrature signal corresponding to the input signal, respectively;

the input signal transmitted by the voltage-controlled oscillator and the in-phase signal transmitted by the frequency divider are mixed by a mixer so as to output a mixed signal; and

the mixed signal and the quadrature signal are integrated by an adder amplifier to generate a first output signal having a multiple of the predetermined frequency.