A digital aided harmonic elimination method and a multiple frequency filterless transmitter

Abstract

The application provides a digital auxiliary harmonic elimination method and a multiple frequency filterless transmitter, which are used to solve the technical problems of the existing harmonic elimination method, such as the decrease of DC to RF conversion efficiency, the difficulty in meeting the harmonic suppression requirement, the large occupation space of the switch filter group, the high cost, the high energy consumption and the inability to suppress the spectrum leakage close to the signal band. The harmonic elimination method is as follows: injecting each analog signal with the same energy and opposite phase to the multiple harmonic signals output by the power amplifier on the output path of the power amplifier, so as to offset each harmonic signal output by the power amplifier; specifically, coupling the generated multiple harmonic signals, inserting zero values and performing FFT transformation to extract each harmonic signal; shifting the phase of each harmonic signal by 180 degrees, and then performing frequency conversion and energy adjustment to obtain each analog signal with the same energy and opposite phase to the multiple harmonic signals output by the power amplifier.

Description

Technical Field

[0001] This invention relates to multi-frequency radio frequency transmitters, and more particularly to a digitally assisted harmonic cancellation method and a multi-frequency filterless transmitter. Background Technology

[0002] With the rapid development of wireless standards, there is a need for a radio platform that can transparently support all existing standards. Because these standards differ in their spectrum and modulation schemes, multi-standard, multi-mode Software Defined Radio (SDR) is employed. SDR RF transmitters need to operate across a wide radio spectrum to achieve backward compatibility and handle both existing and upcoming wireless standards. Furthermore, they need to provide compatibility with older generations of wireless communications, leading to the development of multi-frequency RF transmitters.

[0003] However, multi-frequency RF transmitters face a critical challenge: handling harmonic and intermodulation interference generated by the nonlinear power amplifier (PA) within the operating band. Digital pre-distortion (DPD) is a common linearization scheme that captures and models the nonlinear behavior of the PA, generating an inverse model to predistort the signal and compensate for intermodulation interference. However, DPD cannot completely eliminate harmonic components. Currently, power back-off and filtering methods are commonly used to eliminate harmonics. The principle of power back-off is to suppress harmonics generated by the nonlinear power amplifier by operating the PA far below its saturation point within the linear region. However, this leads to a decrease in DC-to-RF conversion efficiency, wasting energy and requiring expensive and bulky cooling mechanisms to ensure reliability. Furthermore, in the case of multi-frequency operations, harmonics are amplified within the operating range, and power back-off alone may not be sufficient to meet the harmonic suppression requirements. The specific principle of the filtering elimination method is as follows: Radio frequency filters are used to suppress harmonics. Specifically, a switching filter bank is placed at the output of the power amplifier (PA), and a suitable operating frequency is configured according to the input signal frequency. If the input signal frequency is ω0, the switching filter bank creates a passband at the center frequency ω0, while harmonic signals 2ω0, 3ω0…mω0 cannot pass through the filter's stopband, thus achieving harmonic elimination. This method requires switching the switching filter bank to select the operating frequency band and simultaneously suppress harmonics. However, as the number of harmonics increases, the structure of the switching filter bank becomes complex and bulky, not only occupying a large space and incurring high costs, but also increasing power consumption. Furthermore, the filtering elimination method also suffers from the problem of being unable to suppress spectral leakage near the signal band. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problems of decreased DC-to-RF conversion efficiency and potential failure to meet harmonic suppression requirements in existing power back-off methods for eliminating harmonic components, as well as the technical problems of large footprint, high cost, high energy consumption, and inability to suppress spectral leakage near the signal band in filtering elimination methods. The invention provides a digital-assisted harmonic elimination method and a multi-frequency filterless transmitter.

[0005] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0006] A digitally assisted harmonic cancellation method, characterized by the following steps:

[0007] 1. The original input signal is pre-distorted. The pre-distorted signal is then converted from digital to analog and then up-converted before entering the power amplifier for power amplification.

[0008] 2. Inject analog signals of opposite phase and same energy to the multiple harmonic signals currently output by the power amplifier into the output path of the power amplifier to cancel out the multiple harmonic signals currently output by the power amplifier.

[0009] The analog signals, which are out of phase and have the same energy as the multiple harmonic signals currently output by the power amplifier, are obtained through the following method:

[0010] a) Couple the power amplifier to generate multiple harmonic signals, and perform down-conversion and analog-to-digital conversion on the coupled multiple harmonic signals;

[0011] b) Insert zero values ​​into the time domain of the multiple harmonic signals processed in step a, and then perform FFT transformation on the multiple harmonic signals after zero insertion to obtain the frequency domain characteristics of each harmonic signal. Extract each harmonic signal in sequence according to the frequency domain characteristics of each harmonic signal.

[0012] c) The extracted harmonic signals are phase-shifted by 180 degrees to obtain signals with opposite phase to each harmonic signal;

[0013] d) The signal that is out of phase with each harmonic signal is converted to the analog domain, and then frequency conversion and energy adjustment are performed to obtain analog signals that are out of phase with each harmonic signal currently output by the power amplifier and have the same energy.

[0014] This invention also provides a multi-frequency filterless transmitter that eliminates harmonics using the above-mentioned digitally assisted harmonic cancellation method, comprising a power amplifier, a digital-to-analog converter, an up-conversion unit, and a predistorter. The input terminal of the predistorter is used to receive the original input signal and perform predistortion processing on it to obtain a predistorted signal. The digital-to-analog converter and the up-conversion unit are used to sequentially perform digital-to-analog conversion and up-conversion processing on the predistorted signal output from the predistorter before sending it to the power amplifier for power amplification. Its features are:

[0015] It also includes a harmonic cancellation unit and a power combiner;

[0016] The harmonic cancellation unit includes a coupler, a downconversion unit, an analog-to-digital conversion unit, a harmonic signal processing module, a digital-to-analog converter, a frequency conversion module, and an error amplifier connected in the input-output order.

[0017] The first input terminal of the power combiner is connected to the output terminal of the power amplifier; the input terminal of the coupler is connected to the output terminal of the power combiner and is used to couple the multiple harmonic signals generated by the power amplifier and combined by the power combiner.

[0018] The downconversion unit and the analog-to-digital conversion unit are used to perform downconversion and analog-to-digital conversion processing on the coupled multiple harmonic signals in sequence.

[0019] The harmonic signal processing module is used to insert zero values ​​in the time domain of the multiple harmonic signals after down-conversion and analog-to-digital conversion, and then perform FFT transformation on the zero-placed multiple harmonic signals to extract each harmonic signal. Then, the extracted harmonic signals are phase-shifted by 180 degrees to obtain signals with opposite phase to the extracted harmonic signals, i.e., the anti-phase signals of each harmonic signal.

[0020] The digital-to-analog converter is used to convert the inverse phase signals of each harmonic signal into the analog domain;

[0021] The frequency conversion module is used to multiply the frequency of the anti-phase signal of each harmonic signal converted to the analog domain by multiple harmonic harmonic frequencies ω0 to obtain the target frequency of the anti-phase signal of each harmonic signal, and then add the target frequencies of the anti-phase signals of each harmonic signal to obtain the synthesized anti-phase analog signal of each harmonic signal.

[0022] The error amplifier is used to adjust the energy of the inverse analog signals of the synthesized harmonic signals to obtain analog signals with opposite phase and the same energy as the harmonic signals of the power amplifier.

[0023] The second input terminal of the power combiner is connected to the output terminal of the error amplifier, and is used to cancel the harmonic signals output by the power amplifier by analog signals that are opposite in phase and have the same energy as the harmonic signals of the power amplifier.

[0024] The second output terminal of the coupler is connected to an external transmitting device and is used to transmit the signal output by the power combiner after power combining.

[0025] The advantages of this invention compared to the prior art are as follows:

[0026] 1. The present invention provides a digitally assisted harmonic cancellation method that directly couples multiple harmonic signals generated by a power amplifier and injects their reverse signals into the output path of the power amplifier, thereby canceling out the multiple harmonics generated by the power amplifier and achieving precise harmonic suppression. Compared with traditional harmonic cancellation methods, this digitally controlled harmonic cancellation technology can avoid setting up a switching filter bank at the output of the power amplifier while accurately suppressing harmonics and achieving linearized output, simplifying the transmitter structure and greatly reducing the cost and power consumption of the transmitter.

[0027] 2. The present invention provides a multi-frequency filterless transmitter, which effectively eliminates intermodulation interference through a predistorter. At the same time, by setting a harmonic cancellation unit to couple multiple harmonic signals of the power amplifier and generating analog signals with opposite phase to the multiple harmonic signals, the signals are injected into the output path of the power amplifier through a power combiner, so that they cancel out the harmonic signals currently output by the power amplifier. This reduces the nonlinear distortion of the power amplifier, optimizes the system, achieves the purpose of linearizing and amplifying the original signal, effectively improves the quality and effect of the transmitted signal, and greatly reduces energy consumption. Attached Figure Description

[0028] Figure 1 This is a schematic diagram illustrating the principle of using zero-insertion and FFT transform to perform spectrum analysis and obtain information on each harmonic in step 2 of an embodiment of the digitally assisted harmonic elimination method of the present invention.

[0029] Figure 2 The present invention provides a schematic diagram of a multi-frequency harmonic filterless transmitter.

[0030] The specific labeling in the attached diagram is as follows:

[0031] 1-Predistorter; 2-Power amplifier; 3-Digital-to-analog converter; 4-Upconverter; 5-Power combiner; 6-Coupled; 7-Downconverter; 8-Analog-to-digital converter; 9-Harmonic signal processing module; 10-Digital-to-analog converter; 11-Frequency conversion module; 12-Error amplifier. Detailed Implementation

[0032] To make the advantages and features of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] A digitally assisted harmonic cancellation method specifically includes the following steps:

[0034] 1) Elimination of intermodulation distortion

[0035] To eliminate intermodulation distortion, this invention employs existing digital predistortion techniques, specifically by placing an indirect learning structure (DPD) model at the front end of the power amplifier to achieve linearization in the baseband unit. Specifically, the original input signal undergoes predistortion processing using the DPD model. The predistorted signal is then sequentially converted from digital to analog and up-converted before entering the power amplifier for power amplification.

[0036] 2) Elimination of harmonic distortion

[0037] Due to the nonlinear behavior of the power amplifier, the original input signal (the original baseband signal to be transmitted) will generate multiple harmonic interferences after passing through the power amplifier. Therefore, this invention injects analog signals with opposite phase and the same energy as the multiple harmonic signals currently output by the power amplifier into the output path of the power amplifier to cancel the multiple harmonic signals currently output by the power amplifier.

[0038] Specifically, the analog signals that are out of phase and have the same energy as the multiple harmonic signals currently output by the power amplifier are obtained through the following method:

[0039] a) Couple the multiple harmonic signals generated by the power amplifier, and then perform down-conversion and analog-to-digital conversion on the coupled multiple harmonic signals in sequence.

[0040] b) Because the multiple harmonic components of the coupling are mixed and cannot be distinguished, harmonic processing is required. For example... Figure 1 As shown, zero values ​​are inserted into the time domain of the multiple harmonic signals after down-conversion and analog-to-digital conversion. Then, FFT transformation is performed on the zero-placed multiple harmonic signals to obtain the frequency domain characteristics of each harmonic signal. The frequency domain characteristics of each harmonic signal are analyzed, and each harmonic signal is extracted in turn.

[0041] As can be seen from the properties of the FFT transform, after zero-interpolation of a signal in the time domain, the signal spectrum obtained by the FFT transform will undergo a corresponding compression change. Specifically, the number of zero-interpolation values ​​is determined by the number of sequence points to be processed. If the sequence to be processed is interpolated by a factor of m, the sequence spectrum is compressed to 1 / m of its original value. Let the fundamental frequency (i.e., the main link signal transmission frequency) be ω0, then the frequency of the mth harmonic is mω0. By interpolating it by a factor of m, the mth harmonic can be shifted to the position of the fundamental frequency, thereby extracting the required harmonics. This method using the FFT transform can obtain the information of each harmonic without increasing additional resources.

[0042] c) The extracted harmonic signals are phase-shifted by 180 degrees to obtain signals with opposite phase to each harmonic signal.

[0043] d】Since the signals that are opposite in phase to each harmonic signal after the above processing are close to zero frequency and are no longer real harmonic signals, the spectrum of the signals that are opposite in phase to each harmonic signal is first converted to the analog domain, and then frequency conversion and energy adjustment are performed to obtain analog signals that are opposite in phase to each harmonic signal and have the same energy as the current output harmonic signal of the power amplifier.

[0044] The present invention provides a digitally assisted harmonic cancellation method that directly couples the multiple harmonic signals generated by the power amplifier and injects their reverse signals into the output path of the power amplifier, so that they cancel out the multiple harmonics generated by the power amplifier and thus achieve linearization. Compared with traditional harmonic cancellation methods, this method simplifies the transmitter structure, avoids setting up a variable filter bank at the output of the power amplifier, and greatly reduces the cost and power consumption of the transmitter.

[0045] This invention also provides a filterless transmitter that eliminates harmonics using the above-described digitally assisted harmonic cancellation method, such as... Figure 2 As shown, it includes a power amplifier 2, a digital-to-analog converter 3, an up-conversion unit 4, a predistorter 1, a harmonic cancellation unit, and a power combiner 5.

[0046] The input terminal of predistorter 1 is used to receive the original input signal. In this embodiment, the original input signal is two mutually orthogonal I0 and Q0 digital signals. After predistorting the two mutually orthogonal I0 and Q0 digital signals, predistorter 1 obtains two mutually orthogonal predistorted signals.

[0047] The predistorter 1, digital-to-analog converter 3, upconverter 4, and power amplifier 2 are connected in the order of input and output. The two mutually orthogonal predistortion signals output by the predistorter 1 are converted into two mutually orthogonal analog signals by the digital-to-analog converter 3. Then, these two mutually orthogonal analog signals are sent to the upconverter 4 for processing, that is, multiplied with a local oscillator with a phase difference of 90° for mixing operation, and then linearized in the high-frequency domain. The upconverted signals are synthesized by an adder and then input into the power amplifier 2 for power amplification.

[0048] The harmonic cancellation unit includes a coupler 6, a downconversion unit 7, an analog-to-digital conversion unit 8, a harmonic signal processing module 9, a digital-to-analog converter 10, a frequency conversion module 11, and an error amplifier 12, which are connected in sequence according to the input and output order.

[0049] The first input terminal of the power combiner 5 is connected to the output terminal of the power amplifier 2; the input terminal of the coupler 6 is connected to the output terminal of the power combiner 5 and is used to couple the multiple harmonic signals generated by the power amplifier 2 and combined by the power combiner 5.

[0050] The downconversion unit 7 and the analog-to-digital converter 8 are used to sequentially downconvert and convert the coupled multiple harmonic signals. Specifically, a frequency converter or digital mixer is used to shift the frequency of the coupled multiple harmonic signals downward, and then the signals are converted into digital signals by the analog-to-digital converter 8. Finally, the signals are synthesized by an adder and input into the harmonic signal processing module 9.

[0051] The harmonic signal processing module 9 is used to perform zero-plugging processing on the time domain of the input signal, and then perform FFT transformation on the multiple harmonic signals after zero-plugging to extract each harmonic signal. Then, the extracted harmonic signals are phase-shifted by 180 degrees to obtain signals with opposite phase to the extracted harmonic signals, i.e., the anti-phase signals of each harmonic signal.

[0052] The digital-to-analog converter 10 is used to convert the inverse phase signals of each harmonic signal to the analog domain. The frequency conversion module 11 is used to multiply the frequency of the inverse phase signal of each harmonic signal converted to the analog domain by the fundamental frequency ω0 to obtain the target frequency of the inverse phase signal of each harmonic signal, and then add the target frequencies of the inverse phase signals of each harmonic signal through an adder to obtain the synthesized inverse phase analog signal of each harmonic signal.

[0053] Error amplifier 12 is used to adjust the energy of the inverse analog signal of each harmonic signal synthesized to obtain analog signals with opposite phase and the same energy as each harmonic signal of power amplifier 2.

[0054] The second input terminal of the power combiner 5 is connected to the output terminal of the error amplifier 12, and is used to cancel the harmonic signals output by the power amplifier 2 by analog signals that are opposite in phase and have the same energy as the harmonic signals of the power amplifier 2.

[0055] The second output terminal of the coupler 6 is connected to an external transmitting device and is used to transmit the signal output after power combining by the power combiner 5.

[0056] The multi-frequency filterless transmitter provided by this invention effectively eliminates intermodulation interference through the predistorter 1. At the same time, by setting up a harmonic cancellation unit to couple multiple harmonic signals of the power amplifier and generating analog signals with opposite phases of the multiple harmonic signals, these signals are then injected into the output path of the power amplifier through the power combiner 5, so that they cancel out the harmonic signals currently output by the power amplifier. This reduces the nonlinear distortion of the power amplifier, achieves the purpose of linearizing and amplifying the original signal, and effectively improves the quality and effect of the transmitted signal.

[0057] The above description is only used to illustrate the technical solutions of the present invention, and is not intended to limit them. For those skilled in the art, modifications can be made to the specific technical solutions described in the above embodiments, or equivalent substitutions can be made to some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions protected by the present invention.

Claims

1. A digitally assisted harmonic cancellation method, characterized in that, Includes the following steps:

1. The original input signal is pre-distorted. The pre-distorted signal is then converted from digital to analog and then up-converted before entering the power amplifier for power amplification.

2. Inject analog signals of opposite phase and same energy to the multiple harmonic signals currently output by the power amplifier into the output path of the power amplifier to cancel out the multiple harmonic signals currently output by the power amplifier. The analog signals, which are out of phase and have the same energy as the multiple harmonic signals currently output by the power amplifier, are obtained through the following method: a) Couple the power amplifier to generate multiple harmonic signals, and perform down-conversion and analog-to-digital conversion on the coupled multiple harmonic signals; b) Insert zero values ​​into the time domain of the multiple harmonic signals processed in step a, and then perform FFT transformation on the multiple harmonic signals after zero insertion to obtain the frequency domain characteristics of each harmonic signal. Extract each harmonic signal in sequence according to the frequency domain characteristics of each harmonic signal. c) The extracted harmonic signals are phase-shifted by 180 degrees to obtain signals with opposite phase to each harmonic signal; d) The signal that is out of phase with each harmonic signal is converted to the analog domain, and then frequency conversion and energy adjustment are performed to obtain analog signals that are out of phase with each harmonic signal currently output by the power amplifier and have the same energy.

2. A multi-frequency filterless transmitter that uses the digital-assisted harmonic cancellation method of claim 1 to eliminate harmonics, comprising a power amplifier (2), a digital-to-analog converter (3), an up-conversion unit (4), and a predistorter (1), wherein the input terminal of the predistorter (1) is used to receive the original input signal and perform predistortion processing on it to obtain a predistorted signal; the digital-to-analog converter (3) and the up-conversion unit (4) are used to sequentially perform digital-to-analog conversion and up-conversion processing on the predistorted signal output by the predistorter (1) before sending it to the power amplifier (2) for power amplification; characterized in that: It also includes a harmonic cancellation unit and a power combiner (5); The harmonic cancellation unit includes a coupler (6), a down-conversion unit (7), an analog-to-digital conversion unit (8), a harmonic signal processing module (9), a digital-to-analog converter (10), a frequency conversion module (11), and an error amplifier (12) connected in sequence according to the input and output order. The first input terminal of the power combiner (5) is connected to the output terminal of the power amplifier (2); the input terminal of the coupler (6) is connected to the output terminal of the power combiner (5) and is used to couple the multiple harmonic signals generated by the power amplifier (2) and combined by the power combiner (5). The downconversion unit (7) and the analog-to-digital conversion unit (8) are used to perform downconversion and analog-to-digital conversion processing on the coupled multiple harmonic signals in sequence. The harmonic signal processing module (9) is used to insert zero values ​​in the time domain of the multiple harmonic signals processed by down-conversion and analog-to-digital conversion, and then perform FFT transformation on the multiple harmonic signals after zero insertion to extract each harmonic signal. Then, the extracted harmonic signals are phase-shifted by 180 degrees to obtain signals with the opposite phase to the extracted harmonic signals, i.e., the anti-phase signals of each harmonic signal. The digital-to-analog converter (10) is used to convert the inverse phase signals of each harmonic signal into the analog domain; The frequency conversion module (11) is used to multiply the frequency of the anti-phase signal of each harmonic signal converted to the analog domain by multiple harmonic multiples of the fundamental frequency ω0 to obtain the target frequency of the anti-phase signal of each harmonic signal, and then add the target frequencies of the anti-phase signals of each harmonic signal to obtain the synthesized anti-phase analog signal of each harmonic signal. The error amplifier (12) is used to adjust the energy of the inverse analog signal of the synthesized harmonic signal to obtain the analog signal with the opposite phase and the same energy as the harmonic signal of the power amplifier (2). The second input terminal of the power combiner (5) is connected to the output terminal of the error amplifier (12) and is used to cancel the harmonic signals output by the power amplifier (2) by analog signals that are opposite in phase and have the same energy as the harmonic signals of the power amplifier (2). The second output terminal of the coupler (6) is connected to an external transmitting device for transmitting the signal output after power combining by the power combiner (5).

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