Digital pre-distortion circuit and method for generating pre-distorted signal

Abstract

The invention relates to a digital pre-distortion circuit and a method for generating a pre-distorted signal. The digital pre-distortion circuit comprises a non-storage nonlinear operation circuit, a mutual adjustment type filter circuit and a signal combination circuit. The non-storage non-linear operation circuit performs non-storage and non-linear operation on the transmission signal to generate a first signal. The first signal includes a signal component corresponding to the transmission signal and a signal component of an intermodulation signal generated by the radio frequency power amplifier in response to the transmission signal without a storage effect. The intermodulation filter circuit filters the first signal to generate a second signal. The second signal simulates an intermodulation signal generated by the radio frequency power amplifier in response to the transmission signal under the storage effect. The signal combining circuit is used for combining the transmission signal and the second signal to generate a pre-distortion signal.

Description

Technical Field

[0001] The invention relates to predistortion processing of transmission signals, and in particular to a digital predistortion circuit and a method for generating a predistortion signal. Background Art

[0002] Today's wireless transmission devices typically have RF power amplifiers, and the RF power amplifiers are used to amplify the transmission signal in order to offset the energy loss during the transmission process. However, the RF power amplifier is a nonlinear element. Especially when the transmission signal has a high peak-to-average power ratio, the transmission signal will produce severe in-band signal distortion after being processed by the RF power amplifier, thereby reducing the signal quality. At the same time, it will also cause out-of-band energy leakage and interfere with adjacent channels.

[0003] Therefore, a novel signal processing method and architecture are needed to effectively reduce the signal distortion generated after the transmission signal is processed by the RF power amplifier. Summary of the invention

[0004] The object of the present invention is to provide a digital predistortion circuit and a method for generating a predistortion signal to reduce the interference of an intermodulation distortion signal in a signal output by a wireless communication transmission device to an adjacent channel.

[0005] According to one embodiment of the present invention, a digital predistortion circuit includes a non-storage nonlinear operation circuit, an intermodulation filter circuit and a signal combining circuit. The non-storage nonlinear operation circuit is used to perform a non-storage and nonlinear operation on a transmission signal to generate a first signal. The non-storage and nonlinear operation is a nonlinear operation of a radio frequency power amplifier configured in a wireless communication transmission device without a storage effect. The first signal is an output analog signal of the radio frequency power amplifier without a storage effect, and the first signal includes a signal component corresponding to the transmission signal and a signal component corresponding to an intermodulation signal of the transmission signal. The intermodulation filter circuit is coupled to the non-storage nonlinear operation circuit to filter the first signal to generate a second signal. The second signal simulates an intermodulation signal generated by the radio frequency power amplifier in response to the transmission signal with a storage effect. The signal combining circuit is used to combine the transmission signal and the second signal to generate a predistortion signal.

[0006] According to one embodiment of the present invention, a method for generating a predistortion signal includes: performing a non-storage and non-linear operation on a transmission signal to generate a first signal, wherein the non-storage and non-linear operation simulates a non-linear operation of a radio frequency power amplifier configured in a wireless communication transmission device without a storage effect, the first signal is an output analog signal of the radio frequency power amplifier without a storage effect, and the first signal includes a signal component corresponding to the transmission signal and a signal component corresponding to an intermodulation signal of the transmission signal; filtering the first signal to generate a second signal, wherein the second signal simulates an intermodulation signal generated by the radio frequency power amplifier in response to the transmission signal with a storage effect; and combining the transmission signal and the second signal to generate a predistortion signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a schematic diagram showing a wireless communication transmission device according to an embodiment of the present invention.

[0008] Figure 2 is an example of a spectrum plot showing the output signal of an RF power amplifier.

[0009] Figure 3A This is an example of a spectrum produced after a non-memory nonlinear power amplification operation of an RF power amplifier.

[0010] Figure 3B This is an example of the spectrum produced after the nonlinear power amplification operation with storage through the RF power amplifier.

[0011] Figure 4 is a flow chart showing an exemplary method for generating a predistortion signal according to an embodiment of the present invention.

[0012] Figure 5 is a block diagram showing an example of a digital pre-distortion circuit according to an embodiment of the present invention.

[0013] Figure 6 is a block diagram showing an example of a coefficient generating circuit according to an embodiment of the present invention.

[0014] Explanation of symbols

[0015] 10: Wireless communication transmission device

[0016] 50: Digital signal processing circuit

[0017] 51, 54: Digital to Analog Converter

[0018] 52, 55: Low pass filter

[0019] 53, 56: Upconverter

[0020] 57: Local Oscillator

[0021] 58: Signal Synthesizer

[0022] 59: RF Power Amplifier

[0023] 60: Antenna

[0024] 61: Normalized operation circuit

[0025] 62: Interpolation and extrapolation operation circuit

[0026] 63: Value adjustment circuit

[0027] 64: Inverse Discrete Fourier Transform Operation Circuit

[0028] 100, 500: Digital pre-distortion circuit

[0029] 510: Non-storage Non-Linear Operation Circuit

[0030] 520: Mutually Adjusted Filter Circuit

[0031] 530: Signal combining circuit

[0032] 600: Coefficient generation circuit

[0033] A, B, C, D: Node

[0034] IM:Intermodulation signal

[0035] IM3-1, IM3-2: Third-order intermodulation signals

[0036] IM5-1, IM5-2: Fifth-order intermodulation signal

[0037] IMD3_Meas: Intermodulation distortion signal data at multiple frequency points

[0038] In_Sig: Input signal

[0039] PS: Predistortion signal

[0040] Shaped_IM: Shaped intermodulation signal

[0041] TS:Transmission Signal DETAILED DESCRIPTION

[0042] Figure 1 is a schematic diagram showing a wireless communication transmission device 10 (eg, a Wi-Fi system) according to an embodiment of the present invention. Figure 1As shown, the wireless communication transmission device 10 may include a digital signal processing (DSP) circuit 50, digital to analog converters 51 and 54 (in Figure 1 denoted as "D / A" for simplicity), low pass filters 52 and 55 (in Figure 1 The wireless communication device 10 includes a digital signal processing circuit 50, which includes a digital signal processing circuit 50 and a digital signal processing circuit 51. The digital signal processing circuit 50 includes a digital signal processing circuit 51 and a digital signal processing circuit 52. The digital signal processing circuit 50 includes a digital signal processing circuit 52 and a digital signal processing circuit 53. Figure 1 The digital signal processing circuit 50 is a circuit that receives an in-phase signal and transmits an in-phase signal and a quadrature signal (e.g., a signal with a 90-degree phase shift) to a signal synthesizer 58 through two channels, such as an in-phase signal channel (referred to as I channel) and a quadrature signal channel (referred to as Q channel). Finally, the synthesized signal is amplified by an RF power amplifier 59 and output to an antenna 60 for transmission. In detail, the signal output by the digital signal processing circuit 50 is a digital baseband / intermediate frequency signal, which is then converted from digital to analog by digital-to-analog converters 51 and 54 to generate analog baseband / intermediate frequency signals. Finally, the analog baseband / intermediate frequency signals on the respective channels are upconverted by upconverters 53 and 56 according to the local oscillation signal output by the local oscillator 57 to generate analog RF signals.

[0043] In order to offset the nonlinear distortion generated by the RF power amplifier 59, the digital signal processing circuit 50 may have a related digital pre-distortion (DPD) operation to perform corresponding pre-distortion processing on the digital input signal based on the nonlinear behavior of the RF power amplifier 59, so that the operation of the digital pre-distortion processing and the nonlinear distortion of the RF power amplifier offset each other, thereby obtaining an output signal with good linearity.

[0044] In detail, in this embodiment, the wireless communication transmission device 10 may further include a digital pre-distortion circuit 100, wherein the digital pre-distortion circuit 100 may be disposed in the digital signal processing circuit 50, but the present invention is not limited thereto. The digital pre-distortion circuit 100 may provide a corresponding inverse function according to the estimation result of the nonlinear distortion of the RF power amplifier 59 to perform digital pre-distortion processing to offset the nonlinear distortion generated by the RF power amplifier, thereby obtaining an output signal with good linearity.

[0045] Assume that the input and output relationship of the RF power amplifier is expressed as PA out =a1PA in +a3PA in3 +a5PA in 5 +…, where PA in is the input signal of the RF power amplifier, PA out is the output signal of the RF power amplifier, the cubic term a3PA in 3 The third-order intermodulation signal generated in response to the input signal, the fifth power term a5PA in 5 The fifth-order intermodulation signal is generated in response to the input signal, and by analogy, it can be understood that the third-order intermodulation signal, the fifth-order intermodulation signal, etc. are all intermodulation signals generated by the nonlinear behavior of the signal RF power amplifier, and the difference between the intermodulation signal and the first-order signal can be called intermodulation distortion (IMD for short).

[0046] Figure 2 is an example of a spectrum plot showing the output signal of an RF power amplifier, illustrating the intermodulation distortion caused by the nonlinear behavior of the RF power amplifier. Figure 2 It can be seen that in the spectrum corresponding to the output signal of the RF power amplifier, in addition to the frequency components corresponding to the input signal In_Sig, it also includes the frequency components corresponding to the third-order intermodulation signals IM3-1 and IM3-2, and the frequency components corresponding to the fifth-order intermodulation signals IM5-1 and IM5-2.

[0047] If the input signal of the RF power amplifier is a dual-frequency sine wave signal, for example, the input dual-frequency signal is PA in =A1cos(ω1t)+A2cos(ω2t), then the output signal of the RF power amplifier can be expressed as follows:

[0048] PA out =(a1A1+3 / 4a3A1 3 +3 / 2a3A1A2 2 )cos(ω1t)+(a1A2+3 / 4a3A2 3 +3 / 2a3A2A1 2 )c

[0049] os(ω2t)+3 / 4A1 2 A2a3cos(2ω1t-ω2)t+3 / 4A1A2 2 a3cos(2ω2t-ω1)t+…(omitted below)

[0050] The part corresponding to the signal cos(2ω1t-ω2)t and cos(2ω2t-ω1)t is the third-order intermodulation signal component. Since the frequency of the third-order intermodulation signal is close to the frequency of the original input signal, it is easy to have a serious impact on the quality of the amplifier output signal. Therefore, in one embodiment of the present invention, the digital pre-distortion circuit 100 can simulate the third-order intermodulation signal generated by the nonlinear behavior of the RF power amplifier according to the input signal, and generate a pre-distortion signal accordingly. However, it should be noted that the present invention is not limited to only using the digital pre-distortion circuit 100 to simulate the third-order intermodulation signal, and the digital pre-distortion circuit 100 can also be used to simulate other orders of intermodulation signals according to the required signal quality. Since the concepts of using the digital pre-distortion circuit 100 to simulate third-order, fifth-order, etc. intermodulation signals are similar, the following paragraphs will use the third-order intermodulation signal as an example for simplicity.

[0051] In addition, it should be noted that Figure 2 This is a simplified spectrum example, in which the frequency components corresponding to the third-order intermodulation signals IM3-1 and IM3-2 and the frequency components corresponding to the fifth-order intermodulation signals IM5-1 and IM5-2 are shown outside the signal band (or transmission band) of the input signal. However, in actual operation, the third-order, fifth-order, etc. intermodulation signals may contain some frequency components that fall within the transmission band of the input signal. Generally speaking, the frequency components that fall within the transmission band of the input signal (for example, Figure 2 The signal within the frequency range of the input signal In_Sig shown in the figure is called an in-band signal, and the signal outside the transmission band of the input signal is called an out-of-band signal. As mentioned above, in-band signal distortion will reduce signal quality, and out-of-band intermodulation distortion will cause out-of-band energy leakage and interfere with adjacent channels. In particular, the IEEE standard usually specifies the transmission spectrum mask (Transmit Spectrum Mask) corresponding to each transmission band. Therefore, in order to comply with the transmission spectrum mask specified by the IEEE, the digital predistortion circuit 100 must perform corresponding predistortion processing on the out-of-band intermodulation signal to eliminate out-of-band leakage and meet the specifications of the transmission spectrum mask.

[0052] In addition to nonlinear behavior, the operation of RF power amplifiers may also be subject to memory effects. Memory effects are caused by time variations in the amplifier's transfer characteristics and can be defined as changes in the amplitude and phase components of the current distortion due to previous input signals.

[0053] Figure 3A This is an example of the spectrum produced after the memoryless nonlinear power amplification operation of the RF power amplifier. Figure 3B This is an example of the spectrum generated after the nonlinear power amplification operation with storage of the RF power amplifier. Assuming that the input dual-frequency signal frequencies are ω1 and ω2, the energy of the third-order intermodulation signal generated after the nonlinear operation without storage will be symmetrical in the spectrum, while after the nonlinear operation with storage, the energy of the third-order intermodulation signal generated will be asymmetrical in the spectrum.

[0054] Since the storage effect is an effect that cannot be ignored during the actual operation of the RF power amplifier, in the embodiment of the present invention, the digital pre-distortion circuit 100 can also flexibly take the storage effect of the RF power amplifier into consideration, so that the simulated intermodulation signal can more effectively offset the nonlinear distortion generated by the RF power amplifier.

[0055] In an embodiment of the present invention, a predistortion signal is generated in a two-stage manner, wherein the first stage simulates the nonlinear operation of the RF power amplifier without a storage effect (e.g., nonlinear power amplification operation), and the second stage reshapes the intermodulation signal component in the simulation result into the intermodulation distortion with a storage effect. Compared with the prior art, the two-stage method for generating a predistortion signal can effectively simplify the circuit design of the digital predistortion circuit and the computational complexity required by the digital predistortion circuit, and can also flexibly reshape the intermodulation distortion according to the transmission spectrum mask specification required to be met by the wireless communication transmission device product, thereby optimizing the signal quality of the frequency band to be processed, and enabling the digital predistortion circuit and the corresponding predistortion signal generation method to be widely used in various wireless communication systems.

[0056] Figure 4 is a flow chart showing an exemplary method for generating a predistortion signal according to an embodiment of the present invention, comprising the following steps:

[0057] Step S402: Perform a non-storage and non-linear operation on a transmission signal to generate a first signal. Here, the transmission signal is an input signal of the digital predistortion circuit and is also a signal to be transmitted by the wireless communication transmission device. Therefore, the transmission signal will eventually pass through a radio frequency power amplifier (e.g., Figure 1 The signal is transmitted after being processed by the RF power amplifier 59 shown in the figure. In addition, the non-storage and non-linear operation simulates the non-linear operation of the RF power amplifier without the storage effect.

[0058] Step S404: Filter the first signal to generate a second signal. In an embodiment of the present invention, the second signal simulates an intermodulation signal generated by the RF power amplifier in response to the transmission signal under the memory effect, and the second signal is an intermodulation signal shaped according to the communication quality requirements (for example, the transmission spectrum mask specification to be met).

[0059] Step S406: Combine the transmission signal and the second signal to generate a predistortion signal.

[0060] In an embodiment of the present invention, the predistortion signal may be provided to other signal processing devices in the wireless communication transmission device, such as but not limited to Figure 1 The digital-to-analog converters 51 and 54, low-pass filters 52 and 55, upconverters 53 and 56, signal synthesizer 58, and RF power amplifier 59 are shown coupled after the digital signal processing circuit 50. Since the predistortion signal is a signal obtained by corresponding predistortion processing of the transmission signal to offset the nonlinear distortion of the RF power amplifier, the output signal of the RF power amplifier with good linearity can be obtained at the antenna 60 end.

[0061] Figure 5 2 is a block diagram showing an example of a digital pre-distortion circuit according to an embodiment of the present invention. The digital pre-distortion circuit 500 may include a non-storage non-linear operation circuit 510, an inter-adjustment filter circuit 520, and a signal combining circuit 530. The non-storage non-linear operation circuit 510 and the inter-adjustment filter circuit 520 are used to implement the first stage and the second stage signal processing respectively.

[0062] According to one embodiment of the present invention, the non-storage non-linear operation circuit 510 is used to perform a non-storage and non-linear operation on the transmission signal to generate a first signal. As described above, the transmission signal TS of the non-storage non-linear operation circuit 510 is a signal to be transmitted through a wireless communication transmission device, and the non-storage and non-linear operation simulates the non-linear operation of a radio frequency power amplifier configured in the wireless communication transmission device without a storage effect. For example, the non-storage non-linear operation circuit 510 is used to simulate the operation of the radio frequency power amplifier, but the input signal and the output signal power of the non-storage non-linear operation circuit 510 are made the same, thereby simulating the non-linear operation of the radio frequency power amplifier without a storage effect. In addition, in one embodiment of the present invention, the first signal is an output analog signal of the radio frequency power amplifier without a storage effect, and the first signal includes a signal component corresponding to the transmission signal and a signal component corresponding to an intermodulation signal of the transmission signal.

[0063] Figure 5Spectrum examples of signals obtained by the digital predistortion circuit 500 at each node are also shown in the figure to assist in explaining the signal processing flow in the digital predistortion circuit 500. The signal spectra corresponding to the nodes A and B are shown on the left and right sides of the non-storage non-linear operation circuit 510, respectively, wherein the signal spectrum shown near the node A is a spectrum example of the transmission signal TS, and the signal spectrum shown near the node B is a spectrum example of the first signal output by the non-storage non-linear operation circuit 510. In one embodiment of the present invention, the first signal includes a signal component of the transmission signal TS and a signal component of the intermodulation signal IM corresponding to the transmission signal TS, so in Figure 5 In addition, in one embodiment of the present invention, the intermodulation signal IM corresponding to the transmission signal TS may be a third-order intermodulation (IM3) signal (and / or higher-order intermodulation signals) generated in response to the transmission signal TS, but the present invention is not limited thereto.

[0064] According to an embodiment of the present invention, the non-storage non-linear operation circuit 510 can use basic logic operation elements to implement a mathematical model to perform non-storage and non-linear operation on the transmission signal, wherein the mathematical model can simulate or describe the input and output relationship of the RF power amplifier, and the mathematical model simulates or describes the non-linear operation of the RF power amplifier without storage effect. Therefore, the obtained first signal does not include a signal component corresponding to a previous transmission signal.

[0065] For example, a corresponding mathematical model is obtained by inputting a plurality of test signals with different frequencies into the RF power amplifier and observing the corresponding output signals. It should be noted that if a mathematical model is used to simulate the nonlinear operation of the RF power amplifier under the storage effect, the mathematical model will be a very complex model, for example, involving a huge matrix operation. In the embodiment of the present invention, since the non-storage non-linear operation circuit 510 performs non-storage and non-linear operation on the transmission signal, the non-storage non-linear operation circuit 510 does not need to perform complex operations, thereby effectively simplifying the circuit design and complexity of the non-storage non-linear operation circuit 510.

[0066] The first signal generated by the non-storage nonlinear operation circuit 510 is provided to the intermodulation filter circuit 520 for filtering to generate a second signal. The signal spectrum corresponding to the node C is shown on the right side of the intermodulation filter circuit 520. The signal obtained at the node C is the shaped intermodulation signal Shaped_IM (i.e., the second signal). Figure 5 3 different examples of integer results are shown in Figure 5 (in the figure, they are marked as (i), (ii) and (iii) respectively for distinction).

[0067] According to an embodiment of the present invention, the intermodulation filter circuit 520 can simulate or describe the operation of the RF power amplifier under the storage effect, so the second signal is also a simulation signal, which is used to simulate the intermodulation signal generated by the RF power amplifier in response to the transmission signal under the storage effect. For example, compared with the signal spectrum example of node B, the energy of the intermodulation signal in the signal spectrum example of node C will change with the frequency change.

[0068] In one embodiment of the present invention, the second signal (i.e., the shaped intermodulation signal Shaped_IM) is an out-of-band intermodulation signal including a plurality of frequency components outside a transmission band of the transmission signal TS. In other words, in one embodiment of the present invention, the second signal can be used to simulate an out-of-band intermodulation signal or an out-of-band intermodulation distortion generated in response to the transmission signal. In addition, in one embodiment of the present invention, the second signal does not include a signal component corresponding to the transmission signal TS. Figure 5 In the spectrum examples (i), (ii) and (iii) of the shaped intermodulation signal Shaped_IM shown in FIG. 1 , the frequency components corresponding to the transmission signal TS are not included, or the second signal does not include frequency components within a transmission band of the transmission signal. For example, in the spectrum of the shaped intermodulation signal Shaped_IM, the energy or amplitude within the transmission band of the transmission signal is 0.

[0069] As described above, in the digital predistortion circuit proposed in the present invention, the intermodulation distortion can be flexibly shaped according to the transmission spectrum mask specification that the wireless communication transmission device product needs to comply with. Therefore, the frequency response corresponding to the intermodulation filter circuit 520 can be flexibly designed according to the required transmission spectrum mask specification. For example, assuming that the local oscillation signal of the transmission signal TS is close to the right channel of the transmission band of the transmission signal, the right-side out-of-band intermodulation signal generated by the RF power amplifier at this time may become an out-of-band leakage signal, and it is easy to violate the out-of-band leakage regulations formulated by various countries. Therefore, as shown in the spectrum example (i) of the shaped intermodulation signal Shaped_IM, the intermodulation filter circuit 520 shapes the right-side intermodulation signal of the transmission band of the transmission signal, so that the shaped intermodulation signal Shaped_IM can simulate the intermodulation signal generated by the RF power amplifier in response to the transmission signal under the storage effect, and the spectrum example (i) of the shaped intermodulation signal Shaped_IM only contains the frequency components of the intermodulation signal on the right side of the transmission band. Similarly, the spectrum example (ii) of the shaped intermodulation signal Shaped_IM may only include the frequency components of the intermodulation signal on the left side of the transmission band, while the spectrum example (iii) of the shaped intermodulation signal Shaped_IM may include the frequency components of the intermodulation signal on both sides of the transmission band.

[0070] Finally, the signal combining circuit 530 combines the transmission signal with the second signal (ie, the shaped intermodulation signal Shaped_IM) to generate a predistortion signal. Figure 5 , wherein the spectrum examples of the predistortion signal PS generated according to three different shaped intermodulation signals are respectively shown on the right side (node ​​D) of the signal combining circuit 530 (corresponding to the signal spectrum examples (i), (ii) and (iii) shown at node C). In the embodiment of the present invention, the signal combining circuit 530 may subtract the second signal from the transmission signal (or add the inverted second signal) to generate the predistortion signal, thereby eliminating the out-of-band interference component that will eventually leak out of the transmission band in the output signal of the RF power amplifier.

[0071] It should be noted that Figure 5 The signal spectra shown in FIG. 1 are only some examples of various implementation results, so Figure 5 The signal spectrum examples shown in the figure are not intended to limit the scope of the present invention.

[0072] According to an embodiment of the present invention, the intermodulation filter circuit 520 may perform a convolution operation on the first signal according to a plurality of time domain coefficients to generate a second signal. In addition, in an embodiment of the present invention, the time domain coefficients may be generated by performing an inverse Fourier transform on a plurality of normalized frequency point data. The plurality of normalized frequency point data are generated based on the amplitudes and phases of a plurality of intermodulation signals (or intermodulation distortion signals) corresponding to a plurality of test signals with different frequencies at a plurality of frequency points.

[0073] Figure 6 6 is a block diagram showing an example of a coefficient generation circuit 600 according to an embodiment of the present invention. In the embodiment of the present invention, the coefficient generation circuit 600 is used to establish time domain coefficients used by the inter-adjustment filter circuit 520. The coefficient generation circuit 600 may include a normalization operation circuit 61, an interpolation and extrapolation operation circuit 62, a value adjustment circuit 63 and an inverse discrete Fourier transform (IDFT) operation circuit 64 (in Figure 6 It is labeled as “IDFT operation circuit” for simplicity).

[0074] First, a plurality of test signals with different frequencies can be set as input signals of the RF power amplifier, and the test signals can be sequentially input into the RF power amplifier to sequentially obtain a plurality of intermodulation signals (which are also equivalent to intermodulation distortion signals) corresponding to the plurality of test signals, and the amplitudes and phases of the plurality of intermodulation signals or intermodulation distortion signals at a plurality of frequency points can be obtained (for example, by measuring or analyzing the frequency spectra corresponding to the plurality of intermodulation signals or intermodulation distortion signals) as the measurement data of the intermodulation signals (or intermodulation distortion signals) at a plurality of frequency points (in Figure 6 In the figure, it is marked as “IMD3_Meas”, and each measurement data therein may include the amplitude component and the phase component of the intermodulation distortion respectively).

[0075] Next, the normalization operation circuit 61 performs a normalization operation on the measured data. For example, the normalization operation circuit 61 can take the measured data corresponding to one of the multiple frequency points as the reference data, and divide the values ​​corresponding to the remaining measured data by the values ​​corresponding to the reference data to obtain multiple normalized frequency point data.

[0076] Next, the interpolation and extrapolation circuit 62 performs interpolation and / or extrapolation operations based on the multiple normalized frequency point data to generate the frequency point data required for performing the inverse discrete Fourier transform. Since the frequency set by the test signal may not be equal to the frequency corresponding to the frequency taps required for the subsequent inverse discrete Fourier transform, in the embodiment of the present invention, the required frequency point data can be generated by interpolation and / or extrapolation operations based on known data (i.e., the multiple normalized frequency point data previously obtained).

[0077] Next, the value adjustment circuit 63 adjusts the data of the frequency points required for performing the inverse discrete Fourier transform accordingly as required. For example, in one embodiment of the present invention, the second signal is used to simulate the out-of-band intermodulation distortion generated in response to the transmission signal, so the value adjustment circuit 63 can set the data content of the frequency points falling within the transmission band of the transmission signal to 0. In addition, the value adjustment circuit 63 can also adjust the data content of one or more frequency points according to the required transmission spectrum mask specification, for example, setting the data content of the frequency points that do not need to be pre-distorted to 0, and retaining the data content of the frequency points that need to be pre-distorted.

[0078] Finally, the IDFT operation circuit 64 performs inverse Fourier transformation on the multiple normalized frequency point data adjusted by the value adjustment circuit 63 to generate multiple time domain coefficients. The time domain coefficients can be provided to the mutual adjustment filter circuit 520 as the time domain coefficients of the filter circuit.

[0079] According to one embodiment of the present invention, the mathematical model implemented by the non-storage nonlinear operation circuit 510 and the time domain coefficients of the mutually adjustable filter circuit 520 can be dynamically adjusted according to communication requirements. For example, when switching channels or when the required transmission spectrum mask specification changes, the mathematical model and the time domain coefficients are re-estimated using a test signal, thereby enabling the digital pre-distortion circuit 100 / 500 to be widely used in various wireless communication systems.

[0080] In addition, as described above, in the embodiment of the present invention, a predistortion signal is generated in a two-stage manner, including using the non-storage nonlinear operation circuit 510 and the mutual adjustment filter circuit 520 to respectively implement the first stage and the second stage of signal processing. Since the non-storage nonlinear operation circuit 510 performs non-storage and nonlinear operation on the transmission signal, the non-storage nonlinear operation circuit 510 does not need to perform complex operations, thereby effectively simplifying the circuit design and complexity of the non-storage nonlinear operation circuit 510. In addition, since the time domain coefficients of the mutual adjustment filter circuit 520 can be dynamically adjusted according to actual communication requirements, the application range of the digital predistortion circuit 100 / 500 can be increased and the signal quality of the frequency band to be processed can be optimized.

[0081] The above descriptions are only preferred embodiments of the present invention. All equivalent changes and modifications made according to the claims of the present invention should fall within the scope of the present invention.

Claims

1. A digital predistortion circuit, comprising: A non-storage non-linear operation circuit, used for performing a non-storage and non-linear operation on a transmission signal to generate a first signal, wherein the non-storage and non-linear operation simulates a non-linear operation of a radio frequency power amplifier configured in a wireless communication transmission device without a storage effect, the first signal is an output analog signal of the radio frequency power amplifier without a storage effect, and the first signal includes a signal component corresponding to the transmission signal and a signal component corresponding to an intermodulation signal of the transmission signal; an intermodulation filter circuit, coupled to the non-storage nonlinear operation circuit, for filtering the first signal to generate a second signal, wherein the second signal simulates an intermodulation signal generated by the RF power amplifier in response to the transmission signal with a storage effect; and A signal combining circuit is used for combining the transmission signal and the second signal to generate a predistortion signal. 2 . The digital predistortion circuit of claim 1 , wherein the inter-adjustment filter circuit performs a convolution operation on the first signal according to a plurality of time domain coefficients to generate the second signal. 3 . The digital predistortion circuit of claim 1 , wherein the second signal is an out-of-band intermodulation signal including a plurality of frequency components outside a transmission band of the transmission signal. 4 . The digital predistortion circuit of claim 1 , wherein the second signal does not include a frequency component within a transmission frequency band of the transmission signal. 5 . The digital predistortion circuit of claim 1 , wherein the first signal does not include a signal component corresponding to a previously transmitted signal.

6. The digital predistortion circuit of claim 2 , wherein the plurality of time domain coefficients are generated by performing inverse Fourier transform on a plurality of normalized frequency point data, and the plurality of normalized frequency point data are generated based on amplitudes and phases of a plurality of intermodulation signals corresponding to a plurality of test signals with different frequencies at a plurality of frequency points. 7 . The digital pre-distortion circuit as claimed in claim 1 , wherein the intermodulation signal corresponding to the transmission signal is a third-order intermodulation signal generated in response to the transmission signal.

8. A method for generating a predistortion signal, comprising: Performing a non-storage and non-linear operation on a transmission signal to generate a first signal, wherein the non-storage and non-linear operation simulates a non-linear operation of a radio frequency power amplifier configured in a wireless communication transmission device without a storage effect, the first signal is an output analog signal of the radio frequency power amplifier without a storage effect, and the first signal includes a signal component corresponding to the transmission signal and a signal component corresponding to an intermodulation signal of the transmission signal; filtering the first signal to generate a second signal, wherein the second signal simulates an intermodulation signal generated by the RF power amplifier in response to the transmission signal with a memory effect; and The transmission signal is combined with the second signal to generate a predistortion signal.

9. The method of claim 8, further comprising: A convolution operation is performed on the first signal according to a plurality of time domain coefficients to generate the second signal. 10 . The method of claim 8 , wherein the second signal is an out-of-band intermodulation signal including a plurality of frequency components outside a transmission band of the transmission signal.

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