A closed-loop feedback amplification circuit based on waveform predistortion and a working method thereof

Abstract

The application discloses a closed-loop feedback amplification circuit based on waveform predistortion, comprising: a predistortion waveform fitter, connected with a signal input port and an output sampling circuit respectively; a digital-to-analog converter, receiving a fitted digital waveform signal of the predistortion waveform fitter; a class-D power amplifier, receiving an analog signal of the digital-to-analog converter and a closed-loop feedback signal of a closed-loop feedback circuit respectively; and an adaptive filter, receiving an amplified signal of the class-D power amplifier. The application adopts a class-D power amplification circuit based on hardware closed-loop feedback of waveform predistortion technology, and has the advantages of high output stability, small distortion, high output efficiency, high output bandwidth, small phase delay, small volume, light weight, high reliability and the like. Meanwhile, an adaptive filter module and method are adopted for output, suitable filters are selected according to different output parameters, and the output efficiency of the power amplifier is improved, so that the application can be used for a standard power source in the field of electric power measurement.

Description

Technical Field

[0001] This invention relates to the field of power amplifier technology, and in particular to a closed-loop feedback amplifier circuit based on waveform predistortion and its operating method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Currently, current power amplifier solutions in the field of power measurement are mainly divided into two categories: one is a linear power amplifier solution using readily available integrated power amplifiers and discrete components; the other is an SPWM switching power amplifier solution using MOSFETs for switching chopping. Linear integrated power amplifier solutions generally use existing integrated power amplifiers from ADI or TI, commonly used as high-power audio power amplifiers. The problem with direct audio power amplifiers is that while the bandwidth is large enough, there is a few percent attenuation at higher frequencies. This is not a problem for audio power amplifiers, but for standard source power amplifiers used in power measurement, the accuracy requirement is generally within 0.1%, which is difficult to meet. Furthermore, their phase delay is relatively large, making it difficult to control phase accuracy when used as a standard source power amplifier for power measurement. Additionally, their efficiency is low, generally around 25%, which is problematic under light loads. The first method offers two advantages: lower output efficiency and the use of SPWM switching amplifiers. While SPWM switching amplifiers offer higher efficiency (around 70%), the output frequency is limited by the SPWM carrier frequency. Currently, carrier frequencies are typically in the tens of kHz range. To ensure the distortion of the filtered output signal, the frequency of the signal within the carrier must be at least an order of magnitude lower than the carrier frequency. Bandwidth is limited by the carrier frequency and is also affected by the switching speed, the subsequent LC filter circuit, and loop stability. Currently, the typical output signal is a pure 50Hz sine wave or a power frequency superimposed with harmonics. The harmonic frequency is generally less than 22nd, with a content rate of less than 20%, making it difficult to output wide-range, high-order, high-content harmonics. Furthermore, switching amplifiers cannot completely filter out the carrier, resulting in poor distortion and output stability. Additionally, the high harmonic frequency also affects the harmonic output due to the carrier's influence.

[0004] Therefore, there are problems with current power amplifiers used in standard power sources in the field of power measurement. Linear power amplifiers have high output stability and low distortion, but low efficiency. Switching power amplifiers have high output efficiency, but low output stability and high distortion. Therefore, there is an urgent need to find a power amplifier device and method that can combine the advantages of linear power amplifiers and switching power amplifiers. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a closed-loop feedback amplifier circuit based on waveform predistortion and its operating method, which can select appropriate filters for different output frequencies to improve the power amplifier output efficiency.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a closed-loop feedback amplifier circuit based on waveform predistortion, comprising:

[0008] A predistortion waveform fitter is connected to the signal input port and the output sampling circuit, respectively.

[0009] A digital-to-analog converter that receives the fitted digital waveform signal from a predistortion waveform fitter;

[0010] The Class D power amplifier receives the analog signal from the digital-to-analog converter and the closed-loop feedback signal from the closed-loop feedback circuit, respectively.

[0011] An adaptive filter receives the amplified signal from a Class D power amplifier.

[0012] Furthermore, the predistortion waveform fitter generates a fitted digital waveform signal for correcting the output distortion of the power amplifier by sampling the output signal and the input signal.

[0013] Furthermore, the predistortion waveform fitter outputs the fitted digital waveform signal to the digital-to-analog converter via the SPI interface. The digital-to-analog converter generates an analog signal, which, together with the closed-loop feedback signal, is output to the Class D power amplifier.

[0014] Furthermore, the closed-loop feedback circuit is connected to the power amplifier output, and the closed-loop feedback circuit feeds the power amplifier output back to the input of the Class D power amplifier.

[0015] Furthermore, the output sampling circuit is connected to the power amplifier output, and the output sampling circuit samples the power amplifier output.

[0016] Furthermore, the predistorted waveform fitter includes a multiplexed A / D converter and a dual-core DSP.

[0017] Furthermore, the dual-core DSP includes a sampling data processing and analysis unit. The dual-core DSP reads the sampling value data of the multi-channel AD converter through the SPI interface and calculates the amplitude, frequency, and phase electrical parameters of the input signal and the output sampling signal through the sampling value data.

[0018] Furthermore, the closed feedback circuit samples the current value output by the power amplifier through a high-precision current transformer and a precision sampling resistor.

[0019] Furthermore, the adaptive filter is used to filter out the high-frequency carrier signal emitted by the Class D amplifier.

[0020] Secondly, the present invention provides a method for operating a closed-loop feedback amplifier circuit based on waveform predistortion, comprising:

[0021] A fast feedback channel for the power amplifier output is achieved through a closed-loop feedback circuit, thus completing the power amplification output.

[0022] The power amplifier output value and input signal value are sampled by the output sampling circuit, and the power amplifier output value is adjusted by the predistortion waveform fitting algorithm to achieve high-precision adjustment of the power amplifier output waveform.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] This invention employs a Class D power amplifier circuit with hardware closed-loop feedback based on waveform predistortion technology. It has advantages such as high output stability, low distortion, high output efficiency, high output bandwidth, low phase delay, small size, light weight, and high reliability. At the same time, the output adopts an adaptive filter module and method to select appropriate filters for different output parameters, thereby improving the power amplifier output efficiency. It can be used as a standard power source in the field of power measurement.

[0025] Additional advantages will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0027] Figure 1 This is a schematic diagram of the power amplifier provided in Embodiment 1;

[0028] Figure 2 This is a diagram of the predistortion waveform fitter provided in Embodiment 1;

[0029] Figure 3 This is the dual-core DSP diagram provided in Embodiment 1;

[0030] Figure 4 This is a diagram of the digital-to-analog converter provided in Embodiment 1;

[0031] Figure 5 This is the schematic diagram of the Class D power amplifier provided in Embodiment 1;

[0032] Figure 6 This is the closed-loop feedback circuit diagram provided in Embodiment 1;

[0033] Figure 7 This is the output sampling circuit diagram provided in Embodiment 1;

[0034] Figure 8 This is the adaptive filter diagram provided in Embodiment 1. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0036] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0037] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0038] In this invention, terms such as "fixed connection," "connected," and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on this invention.

[0039] Example 1

[0040] In a first aspect, the present invention provides a closed-loop feedback amplifier circuit based on waveform predistortion, comprising:

[0041] A predistortion waveform fitter is connected to the signal input port and the output sampling circuit, respectively.

[0042] A digital-to-analog converter that receives the fitted digital waveform signal from a predistortion waveform fitter;

[0043] The Class D power amplifier receives the analog signal from the digital-to-analog converter and the closed-loop feedback signal from the closed-loop feedback circuit, respectively.

[0044] An adaptive filter receives the amplified signal from a Class D power amplifier.

[0045] Specifically,

[0046] Figure 1This is a block diagram of the overall system of a power amplifier. The power amplifier mainly consists of a signal input port, a predistortion waveform fitter, a DA converter, a Class D power amplifier, an output sampling circuit, a closed-loop feedback circuit, an adaptive filter, and a power amplifier output port. The predistortion waveform fitter is connected to the signal input port and samples the input signal. It is also connected to the output sampling signal and samples the power amplifier output signal. By sampling the output and input signals, the predistortion waveform fitter generates a fitted digital waveform signal to correct the output distortion of the power amplifier, which is then used by the subsequent digital-to-analog converter (DAC). The predistortion waveform fitter is connected to the DAC and outputs the fitted digital waveform signal to the DAC via an SPI interface. The DAC generates an analog signal, which, along with the closed-loop feedback signal, is output to the Class D power amplifier. The system comprises the following components: a digital-to-analog converter (DAC) connected to a Class D power amplifier; a closed-loop feedback signal connected to the Class D power amplifier; the analog signal output from the DAC and the closed-loop feedback signal together control the output of the Class D power amplifier; an adaptive filter connected to the Class D power amplifier; the Class D power amplifier requires a stage-following LC filter to filter out high-frequency carrier signals; the value of the LC filter needs to be determined based on the carrier frequency and signal frequency; since the power amplifier has a wide bandwidth, the LC filter needs to be selected with appropriate values ​​according to different bandwidths; an adaptive filter connected to the power amplifier output port; the filtered signal output through the power amplifier output port; a closed-loop feedback circuit connected to the power amplifier output; and an output sampling circuit connected to the power amplifier output, sampling the power amplifier output.

[0047] The following are Figure 1 The units within will be described in detail:

[0048] S1 Predistortion Waveform Fitter

[0049] The output sampling is connected to a multi-channel AD converter, and the signal input is also connected to a multi-channel AD converter. The multi-channel AD converter samples the input signal and the output signal of the power amplifier. The multi-channel AD converter is connected to a dual-core DSP. The dual-core DSP reads the sampled data from the multi-channel AD converter via an SPI interface. One CPU of the dual-core DSP processes the sampled data, while the other core CPU runs a predistortion waveform fitting algorithm. By analyzing the sampled data of the input signal and the power amplifier's output signal, a fitted digital waveform signal is generated. The dual-core DSP is also connected to the predistortion waveform fitting algorithm, which runs within the dual-core DSP. One core CPU of the dual-core DSP processes the sampled data, while the other core CPU runs the predistortion waveform fitting algorithm. By analyzing the sampled data of the input signal and the power amplifier's output signal, a fitted digital waveform signal is generated. The predistortion waveform fitting algorithm is connected to the fitted digital waveform signal, and the fitted digital waveform signal is output to the digital-to-analog converter via an SPORT interface.

[0050] 1.1 Multi-channel AD converter

[0051] The multi-channel AD converter uses ADI's AD7608 and has 8 synchronous sampling inputs, which can simultaneously sample the input signal and the output signal of the power amplifier.

[0052] 1.2 Dual-core DSP

[0053] The multi-channel AD converter is connected to the sampling data analysis and processing unit, which runs within one core of the dual-core DSP. It reads the sampled values ​​from the multi-channel AD converter via the SPI interface and analyzes and calculates the amplitude, frequency, phase, and other electrical parameters of the input signal and the output sampling circuit signal. The predistortion waveform fitting algorithm is connected to the fitted digital waveform signal. The predistortion waveform fitting algorithm runs within the other core of the DSP. Using the sampled data and analyzed electrical parameters, it calculates and fits the digital sampled values ​​of the input and output signals to form a digital waveform signal. This fitted digital waveform signal is converted to an analog signal by a digital-to-analog converter (DAC) and used in conjunction with the closed-loop feedback circuit signal to control the Class D power amplifier. The fitted digital waveform signal is then connected to the DAC, converted to an analog signal, and used together with the closed-loop feedback circuit signal to drive the Class D power amplifier.

[0054] The dual-core DSP uses ADI's BF609, which has two cores and a maximum clock speed of 480MHz. It also has 128M of DDR synchronous memory and 32M of asynchronous Flash memory. One core runs the sampling data processing and analysis, while the other core runs the predistortion waveform fitting algorithm to fit the digital waveform signal and performs calculations synchronously, providing the device with powerful signal processing capabilities and reducing phase delay errors caused by CPU operations.

[0055] The sampling data processing and analysis unit uses a dual-core DSP to read the sampled data from the multi-channel AD converter via the SPI interface, and calculates the amplitude, frequency, phase and other electrical parameters of the input and output sampled signals based on the sampled data.

[0056] The predistortion waveform fitting algorithm first establishes a digital predistortion model. This invention uses a polynomial model, as follows:

[0057]

[0058] Where a k b k Polynomial coefficients

[0059] Among them, a k b k Let K be the coefficients of the polynomial model, K be the order of the model, x(t) be the polynomial of the input signal, and z(t) be the polynomial of the feedback signal. Since the order K and the polynomial model coefficients a... k b k The order of the model and the coefficients of the polynomial model significantly affect its accuracy, making the selection of appropriate model order and coefficients crucial. Practical applications involve comparing different K and a... k b k The optimal model order and polynomial coefficients are determined by the normalized mean square error (NMSE) between the model output and the actual output under certain conditions, thus determining the final mathematical expression of the power amplifier digital predistortion model.

[0060] The digital waveform signal is fitted within a dual-core DSP. By sampling and analyzing the input and output sampled signals, a predistortion waveform fitting algorithm is used to generate the final fitted digital waveform signal. This signal is then converted into an analog signal via a digital-to-analog converter. Together with the closed-loop feedback signal, the analog signal is fed back to control the Class D power amplifier, thereby controlling the power amplifier output.

[0061] S2 Digital-to-Analog Converter

[0062] The invention uses ADI's true 18-bit voltage-type DAC, model AD5781, which employs a multi-functional three-wire serial interface, capable of operating at a clock rate of up to 35MHz, and compatible with standard SPI and QSPI. TMMICROWIRE TM It is compatible with DSP interfaces and has a built-in power-on reset circuit to ensure that the DAC outputs to 0V after power-on and maintains a known output impedance state until a valid write operation is performed on the device. It has output clamping characteristics, which can place the output in a defined load state, providing a flexible control method for power amplifiers. The typical output voltage noise value is 1.1uV, providing excellent signal output quality. The integral nonlinearity is 0.5LSB, which means that its amplitude adjustment linearity can reach 0.5 / (2^18)=1.9ppm, which can perform high-precision adjustment of power amplifier output.

[0063] The voltage signal output of the AD5781DAC is followed by the operational amplifier AD8676, and then fed back to control the Class D power amplifier together with the closed-loop feedback signal to control the power amplifier output.

[0064] S3.D Class Power Amplifier

[0065] This invention uses TI's Class D amplifier TPA3251, with a bandwidth of up to 100kHz. For power amplifiers used in the power industry, only a few kHz is needed. The typical THD+N is 0.005%, while standard sources in the power industry generally require less than 1%. The output efficiency is as high as 90%, while the efficiency of a typical linear power amplifier is about 25%, and the efficiency of a typical SPWM switching power amplifier is about 75%. It also has comprehensive protection functions, including undervoltage, overvoltage, clipping, and short-circuit protection, ensuring the reliability of the entire power amplifier.

[0066] like Figure 5 As shown in the schematic diagram, the power amplifier input signal of the Class D power amplifier comes from the predistortion waveform fitter and the sum of the closed-loop feedback signal; it is connected to an external power supply, including DVDD, AVDD, PVDD, and the power supply itself; Vout+ and Vout- are the power amplifier output signals, which need to be filtered by an adaptive filter.

[0067] S4. Closed-loop feedback circuit

[0068] This invention uses high-precision platinum resistance thermometers and high-precision current transformers as closed-loop feedback sampling devices. Their typical temperature drift is 1ppm and annual drift is less than 50ppm, ensuring the high precision of the power amplifier. Its bandwidth is more than several hundred kHz, ensuring the high bandwidth of the power amplifier and enabling high-precision output of each harmonic.

[0069] The closed-loop feedback circuit is connected to the power amplifier output and samples the current value output by the power amplifier through a high-precision current transformer and a precision sampling resistor. The closed-loop feedback circuit is also connected to a Class D power amplifier and samples the current value of the Class D power amplifier. Through I / V conversion using a high-precision current transformer and a precision sampling resistor, the current value is amplified and output by the Class D power amplifier along with the analog signal output by the digital-to-analog converter.

[0070] S5 output sampling circuit

[0071] The output sampling circuit is connected to the power amplifier output and samples the current value output by the power amplifier through a high-precision current transformer and a precision sampling resistor. The output sampling circuit is also connected to the predistortion waveform fitter. The output sampling circuit samples the current value output by the power amplifier and outputs it to the multiplexer in the predistortion waveform fitter through I / V conversion using a high-precision current transformer and a precision sampling resistor to complete the analog-to-digital conversion measurement.

[0072] The output sampling circuit of this invention uses high-precision platinum resistance thermometers and high-precision current transformers as sampling devices. Its typical temperature drift is 1ppm and annual drift is less than 50ppm, ensuring high precision of the sampling feedback signal. Its bandwidth is over several hundred kHz, ensuring high bandwidth of sampling. The output signal is transmitted to the predistortion waveform fitter with high fidelity. By comparing it with the input signal and combining it with the predistortion waveform fitting algorithm, a fitted digital waveform signal is generated. The analog signal and closed-loop feedback signal are generated by the digital-to-analog converter and sent to the Class D power amplifier. Finally, the output distortion of the power amplifier is corrected, solving the problem of output distortion of Class D power amplifiers.

[0073] S6 Adaptive Filter

[0074] The adaptive filter is connected to a Class D power amplifier. The output of the Class D amplifier is a mixed signal of the carrier signal and the actual amplified signal. A filter needs to be added after the Class D power amplifier to filter out the carrier signal and retain the effective amplified signal. The adaptive filter is also connected to a predistortion waveform fitter. The predistortion waveform fitter calculates and analyzes the actual value of the power amplifier output, controls the corresponding switching switch, selects filters with different parameters, reduces the distortion of the power amplifier output, and improves the power amplifier output efficiency. Finally, the adaptive filter is connected to the power amplifier output. The output of the Class D power amplifier is filtered by the adaptive filter before being output.

[0075] The output of a Class D power amplifier chip is actually a mixed signal output of carrier and signal. Therefore, a filter is needed after the amplifier output stage to remove the carrier signal and select the useful amplified signal. Since this power amplifier has a wide output frequency range, multiple filters are used at the output to achieve high efficiency. The output signal of the power amplifier is sent to a predistortion waveform fitter through an output sampling circuit. The predistortion waveform fitter samples and calculates the frequency, amplitude, phase and other parameters of the output waveform. Based on the calculated parameters of the power amplifier output waveform, an appropriate output filter is selected to reduce the distortion of the power amplifier output and improve the output efficiency of the power amplifier.

[0076] Example 2.

[0077] Secondly, the present invention provides a method for operating a closed-loop feedback amplifier circuit based on waveform predistortion, comprising:

[0078] A fast feedback channel for the power amplifier output is achieved through a closed-loop feedback circuit, thus completing the power amplification output.

[0079] The power amplifier output value and input signal value are sampled by the output sampling circuit, and the power amplifier output value is adjusted by the predistortion waveform fitting algorithm to achieve high-precision adjustment of the power amplifier output waveform.

[0080] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A closed-loop feedback amplifier circuit based on waveform predistortion, characterized in that, include: A predistortion waveform fitter is connected to the signal input port and the output sampling circuit, respectively. The predistortion waveform fitter includes a multi-channel AD converter and a dual-core DSP. The dual-core DSP includes a sampling data processing and analysis unit. The dual-core DSP reads the sampling value data of the multi-channel AD converter through the SPI interface and calculates the amplitude, frequency, and phase electrical parameters of the input signal and the output sampling signal through the sampling value data. A digital-to-analog converter that receives the fitted digital waveform signal from a predistortion waveform fitter; The Class D power amplifier receives analog signals from the digital-to-analog converter and closed-loop feedback signals from the closed-loop feedback circuit, respectively; the closed-loop feedback circuit samples the current value output by the power amplifier through a high-precision current transformer and a precision sampling resistor. An adaptive filter receives the amplified signal from a Class D power amplifier and selects a suitable output filter based on the calculated parameters of the power amplifier's output waveform.

2. The closed-loop feedback amplifier circuit based on waveform predistortion as described in claim 1, characterized in that, The predistortion waveform fitter generates a fitted digital waveform signal for correcting the output distortion of the power amplifier by sampling the output signal and the input signal.

3. The closed-loop feedback amplifier circuit based on waveform predistortion as described in claim 2, characterized in that, The predistortion waveform fitter outputs the fitted digital waveform signal to the digital-to-analog converter via the SPI interface. The digital-to-analog converter generates an analog signal, which, together with the closed-loop feedback signal, is output to the Class D power amplifier.

4. The closed-loop feedback amplifier circuit based on waveform predistortion as described in claim 3, characterized in that, The closed-loop feedback circuit is connected to the power amplifier output, and the closed-loop feedback circuit feeds the power amplifier output back to the input of the Class D power amplifier.

5. A closed-loop feedback amplifier circuit based on waveform predistortion as described in claim 4, characterized in that, The output sampling circuit is connected to the power amplifier output, and the output sampling circuit samples the power amplifier output.

6. The closed-loop feedback amplifier circuit based on waveform predistortion as described in claim 1, characterized in that, The adaptive filter is used to filter out the high-frequency carrier signal emitted by the Class D amplifier.

7. A method for operating a closed-loop feedback amplifier circuit based on waveform predistortion, characterized in that, include: A fast feedback channel for the power amplifier output is achieved through a closed-loop feedback circuit, thus completing the power amplification output; the closed feedback circuit samples the current value of the power amplifier output through a high-precision current transformer and a precision sampling resistor. The power amplifier output value and input signal value are sampled by the output sampling circuit, and the power amplifier output value is adjusted by the predistortion waveform fitting algorithm to achieve high-precision adjustment of the power amplifier output waveform. The predistortion waveform fitter includes a multi-channel AD converter and a dual-core DSP. The dual-core DSP includes a sampling data processing and analysis unit. The dual-core DSP reads the sampling value data of the multi-channel AD converter through the SPI interface, calculates the amplitude, frequency, and phase electrical parameters of the input signal and the output sampling signal through the sampling value data, and selects an appropriate output filter based on the calculated parameters of the power amplifier output waveform.

8. The method for operating a closed-loop feedback amplifier circuit based on waveform predistortion as described in claim 7, characterized in that, The predistortion waveform fitter generates a fitted digital waveform signal for correcting the output distortion of the power amplifier by sampling the output signal and the input signal.

9. The method for operating a closed-loop feedback amplifier circuit based on waveform predistortion as described in claim 7, characterized in that, The predistortion waveform fitter outputs the fitted digital waveform signal to the digital-to-analog converter via the SPI interface. The digital-to-analog converter generates an analog signal, which, together with the closed-loop feedback signal, is output to the Class D power amplifier.

10. The method for operating a closed-loop feedback amplifier circuit based on waveform predistortion as described in claim 7, characterized in that, The closed-loop feedback circuit is connected to the power amplifier output, and the closed-loop feedback circuit feeds the power amplifier output back to the input of the Class D power amplifier.

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