Communication system and output power linearization method thereof

Abstract

The present disclosure relates to a communication system and an output power linearization method thereof. A communication system includes a power amplifier, a receiving filter, an analog-to-digital converter, an output analog circuit and a predistortion circuit. The power amplifier is used to amplify a radio frequency input signal to generate a radio frequency output signal, and the radio frequency input signal is generated based on a baseband signal. The receiving filter is used to receive a feedback signal generated based on the radio frequency output signal and output a filtered feedback signal. The bandwidth of the filtered feedback signal is at least 3 to 5 times the bandwidth of the radio frequency input signal. The analog-to-digital converter is used to convert the filtered feedback signal into a digital input signal. The output analog circuit is used to generate a reference signal that simulates the radio frequency output signal based on the digital input signal and the baseband signal. The predistortion circuit is used to establish a predistortion model based on the reference signal.

Description

Technical Field

[0001] The present disclosure relates to a communication system, and more particularly to a communication system capable of simulating the characteristics of its power amplifier to linearize the output power. Background Art

[0002] Since the power amplifier in the communication system is a nonlinear element, the bandwidth of the RF signal will be greatly expanded after amplification, which will reduce the output quality of the communication system and may violate telecommunications regulations. Technologies such as digital predistortion and power back-off are often used to improve the linearity of the power amplifier. Traditional digital predistortion technology usually sets an analog filter on the feedback path to reduce the bandwidth of the feedback signal, thereby reducing the bandwidth and resolution requirements of the analog-to-digital converter in the subsequent circuit. However, this approach will reduce the amount of information available when establishing the predistortion model, and thus fail to obtain the correct compensation parameters. Summary of the invention

[0003] The present disclosure document provides a communication system, which includes a power amplifier, a receiving filter, an analog-to-digital converter, an output analog circuit and a pre-distortion circuit. The power amplifier is used to amplify an RF input signal to generate an RF output signal, and the RF input signal is generated based on a baseband signal. The receiving filter is used to filter a feedback signal generated based on the RF output signal and output the filtered feedback signal. The bandwidth of the filtered feedback signal is at least 3 to 5 times the bandwidth of the RF input signal. The analog-to-digital converter is used to convert the filtered feedback signal into a digital input signal. The output analog circuit is used to generate a reference signal that simulates the RF output signal based on the digital input signal and the baseband signal. The pre-distortion circuit is used to establish a pre-distortion model based on the reference signal.

[0004] The present disclosure document provides a communication system, which includes a power amplifier, a receiving filter, an analog-to-digital converter and a digital logic circuit. The power amplifier is used to amplify a radio frequency input signal to generate a radio frequency output signal, and the radio frequency input signal is generated according to a baseband signal. The receiving filter is used to filter a feedback signal generated according to the radio frequency output signal, and output the filtered feedback signal. The bandwidth of the filtered feedback signal is at least 3 to 5 times the bandwidth of the radio frequency input signal. The analog-to-digital converter is used to convert the filtered feedback signal into a digital input signal. The digital logic circuit is used to simulate the input and output characteristics of the power amplifier according to the digital input signal and the baseband signal to generate a simulation result, and is used to establish a pre-distortion model according to the simulation result.

[0005] The present disclosure provides an output power linearization method, which includes the following process: using a power amplifier of a communication system to amplify a radio frequency input signal to generate a radio frequency output signal, wherein the radio frequency input signal is generated according to a baseband signal; generating a feedback signal according to the radio frequency output signal, and filtering the feedback signal to generate a filtered feedback signal, and the bandwidth of the filtered feedback signal is at least 3 to 5 times the bandwidth of the radio frequency input signal; performing analog-to-digital conversion on the filtered feedback signal to convert the filtered feedback signal into a digital input signal; generating a reference signal that simulates the radio frequency output signal according to the digital input signal and the baseband signal; and establishing a predistortion model according to the reference signal.

[0006] The communication system and output power linearization method described above can utilize complete information about the RF output signal to establish a correct pre-distortion model. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 FIG. 1 is a simplified functional block diagram of a communication system according to an embodiment of the present disclosure.

[0008] Figure 2A FIG. 4 is a schematic diagram of a frequency spectrum of a feedback signal after filtering by a filter at a receiving end in an embodiment.

[0009] Figure 2B FIG. 4 is a schematic diagram of a spectrum of a digital input signal in an embodiment.

[0010] Figure 2C FIG. 4 is a schematic diagram of a frequency spectrum of a digital input signal filtered by a first digital filter in an embodiment.

[0011] Figure 3 FIG. 1 is a simplified functional block diagram of a communication system according to an embodiment of the present disclosure.

[0012] Figure 4 FIG. 1 is a simplified functional block diagram of a communication system according to an embodiment of the present disclosure.

[0013] Figure 5 FIG. 4 is a flow chart of an output power linearization method according to an embodiment of the present disclosure.

[0014] Figure 6 For further explanation Figure 5 Detailed flow chart of process S508. DETAILED DESCRIPTION

[0015] The following will illustrate the embodiments of the present disclosure with reference to the related drawings. In the drawings, the same reference numerals represent the same or similar elements or method flows.

[0016] Figure 11 is a simplified functional block diagram of a communication system 100 according to an embodiment of the present disclosure. The communication system 100 includes a predistortion circuit 102, a digital-to-analog converter 104, an output filter 106, a power amplifier 108, a coupler 110, an attenuator 112, a local oscillator 114, a receiving filter 116, an analog-to-digital converter 118, an output analog circuit 120, a mixer MXa, and a mixer MXb. The predistortion circuit 102 is used to perform predistortion processing on a baseband signal 10 and transmit the predistorted baseband signal 10 to the digital-to-analog converter 104. The input and output ends of the digital-to-analog converter 104 are respectively coupled to the predistortion circuit 102 and the output filter 106, and the output filter 106 is used to filter the baseband signal 10 in an analog form. The local oscillator 114 and the mixer MXa are used to modulate the baseband signal 10 output by the output filter 106 to generate a radio frequency input signal 20. Then, the power amplifier 108 amplifies the RF input signal 20 to generate a RF output signal 30. The communication system 100 can utilize Figure 1 The feedback path shown is used to adaptively adjust the pre-distortion model in the pre-distortion circuit 102 , wherein the pre-distortion model is used to improve the linearity of the power amplifier 108 .

[0017] In detail, the coupler 110 and the attenuator 112 are used together to feedback the RF output signal 30. In practice, the coupler 110 can be implemented by a metal wire parallel to the transmission line between the power amplifier 108 and the subsequent load. The local oscillator 114 and the mixer MXb demodulate the signal output by the attenuator 112 to generate the feedback signal 40. The receiving end filter 116 is used to filter out the noise generated by the attenuator 112 and the mixer MXb, and transmit the filtered feedback signal 40 to the analog-to-digital converter 118.

[0018] Figure 2A FIG. 4 is a schematic diagram of the frequency spectrum of the feedback signal 40 after being filtered by the receiving filter 116 in an embodiment. Figure 1 and Figure 2A In the process of establishing the predistortion model of the predistortion circuit 102, the bandwidth of the RF output signal 30 may be extended to at least 3 to 5 times the bandwidth of the RF input signal 20. On the other hand, the noise generated by the attenuator 112 and the mixer MXb will be higher than the highest frequency of the multiple frequency components of the RF output signal 30. Therefore, the feedback signal 40 received by the receiving filter 116 will not only have the component corresponding to the RF output signal 30, but also have the noise generated by the attenuator 112 and the mixer MXb in a higher frequency band. Figure 2AAs shown, the receiving filter 116 filters out at least a portion of the noise generated by the attenuator 112 and the mixer MXb, and retains the component corresponding to the RF output signal 30 in the filtered feedback signal 40 .

[0019] In other words, the bandwidth of the filtered feedback signal 40 can also be at least 3 to 5 times the bandwidth of the RF input signal 20. Since the receiving filter 116 retains most of the frequency components of the feedback signal 40 corresponding to the RF output signal 30, the output analog circuit 120 and the pre-distortion circuit 102 can obtain sufficient information for calculation in the operation described below to establish a correct pre-distortion model.

[0020] Please refer to Figure 1 , the analog-to-digital converter 118 converts the filtered feedback signal 40 into a digital input signal 50, and the output analog circuit 120 generates a reference signal 60 for simulating the RF output signal 30 according to the digital input signal 50 and the baseband signal 10 output by the predistortion circuit 102. In this way, the predistortion circuit 102 can obtain relevant information about the input and output characteristics of the power amplifier 108 from the reference signal 60, and then establish an appropriate predistortion model to improve the linearity of the power amplifier 108.

[0021] Figure 2B FIG. 5 is a schematic diagram of a spectrum of a digital input signal 50 in an embodiment. Figure 2B As shown, due to the noise shaping effect of the ADC 118, the quantization noise may be concentrated in the high frequency region of the digital input signal 50. In some embodiments, the ADC 118 may be implemented as a continuous-time Sigma-Delta ADC with high input bandwidth and high resolution.

[0022] The output analog circuit 120 includes a model parameter determination circuit 122, a first digital filter 124, a second digital filter 126, and a power amplifier analog circuit 128. The first digital filter 124 is coupled to the analog-to-digital converter 118 to filter out high-frequency quantization noise in the digital input signal 50. In this way, the output analog circuit 120 and the pre-distortion circuit 102 will not misjudge the waveform and spectrum of the RF output signal 30, and thus will not establish an erroneous pre-distortion model.

[0023] Figure 2CFIG. 1 is a schematic diagram of a spectrum of a digital input signal 50 after filtering by the first digital filter 124 in an embodiment. The first digital filter 124 transmits the filtered digital input signal 50 to the model parameter determination circuit 122. In addition, the second digital filter 126 is coupled between the power amplifier analog circuit 128 and the model parameter determination circuit 122, and is used to filter a reference signal 60, and transmit the filtered reference signal 60 to the model parameter determination circuit 122. The reference signal 60 is generated by the power amplifier analog circuit 128 according to the baseband signal 10 output by the predistortion circuit 102.

[0024] In some embodiments, the first digital filter 124 and the second digital filter 126 have the same configuration. For example, the first digital filter 124 and the second digital filter 126 have the same cutoff frequency, so that the filtered digital input signal 50 and the filtered reference signal 60 have the same or similar bandwidth.

[0025] The model parameter determination circuit 122 is used to provide an adjustment signal 70 to the power amplifier simulation circuit 128 according to the baseband signal 10, the filtered digital input signal 50 and the filtered reference signal 60. The model parameter determination circuit 122 determines the difference between the filtered digital input signal 50 and the filtered reference signal 60, and determines one or more parameters included in the adjustment signal 70 according to the comparison result. The power amplifier simulation circuit 128 adjusts its built-in power amplifier model according to the one or more parameters included in the adjustment signal 70, so that the reference signal 60 is close to the RF output signal 30. In other words, the adjustment signal 70 is used to make the reference signal 60 close to the RF output signal 30.

[0026] In some embodiments, the model parameter determination circuit 122 performs a least squares operation to generate the adjustment signal 70 .

[0027] In other embodiments, in order to make the power amplifier model built in the power amplifier simulation circuit 128 present the characteristics of the power amplifier 108 as faithfully as possible, the model parameter determination circuit 122 dynamically (multiple times) changes the adjustment signal 70. When the model parameter determination circuit 122 dynamically changes the adjustment signal 70, the filtered reference signal 60 dynamically approaches the filtered digital input signal 50, that is, the reference signal 60 dynamically approaches the RF output signal 30.

[0028] Figure 3FIG. 1 is a simplified functional block diagram of a communication system 300 according to an embodiment of the present disclosure. The communication system 300 is similar to the communication system 100 of FIG. 1 , except that the output analog circuit 320 of the communication system 300 does not need to include the aforementioned second digital filter 126. The model parameter determination circuit 122 of the output analog circuit 320 can calculate one or more parameters required by the power amplifier analog circuit 128 according to the difference between the baseband signal 10 output by the predistortion circuit 102 and the filtered digital input signal 50.

[0029] In one embodiment, the model parameter determination circuit 122 of the communication system 300 only needs to perform a least squares operation once to obtain one or more parameters required by the power amplifier simulation circuit 128 .

[0030] As can be seen from the above, the communication system 300 can not only further reduce the circuit area, but also speed up the establishment of the pre-distortion model. The remaining connection methods, components, implementation methods and advantages of the aforementioned communication system 100 are all applicable to the communication system 300, and are not repeated here for the sake of brevity.

[0031] Figure 4 FIG. 4 is a simplified functional block diagram of a communication system 400 according to an embodiment of the present disclosure. In this embodiment, a digital logic circuit 401 is used to implement Figure 1 The digital logic circuit 401 simulates the input and output characteristics of the power amplifier 108 according to the digital input signal 50 and the baseband signal 10 to generate a simulation result, and then adaptively adjusts the predistortion model stored therein according to the simulation result, wherein the predistortion model is used to improve the linearity of the power amplifier 108.

[0032] The digital logic circuit 401 includes a control circuit 410 and a memory 420. The control circuit 410 can read and execute the model parameter determination module 422, the first digital filter module 424, the second digital filter module 426 and the power amplifier simulation module 428 implemented by program codes stored in the memory 420 to respectively implement Figure 1 The functions of the model parameter determination circuit 122, the first digital filter 124, the second digital filter 126 and the power amplifier analog circuit 128 are not repeated here for the sake of brevity.

[0033] In this embodiment, the aforementioned reference signal 60, adjustment signal 70, filtered digital input signal 50, and filtered reference signal 60 can each be implemented using one or more digital data stored in the memory 420. For example, the control circuit 410 can execute the first digital filter module 424 to calculate a complex exponential function corresponding to the filtered digital input signal 50, and store the complex exponential function at one or more addresses in the memory, and so on.

[0034] In some embodiments, the second digital filter module 426 does not need to be stored in the memory 420. At this time, the control circuit 410 can read and execute the model parameter determination module 422, the first digital filter module 424 and the power amplifier simulation module 428 stored in the memory 420 to respectively implement Figure 3 The functions of the model parameter determination circuit 122, the first digital filter 124 and the power amplifier analog circuit 128 are not repeated here for the sake of brevity.

[0035] Figure 5 FIG. 5 is a flow chart of an output power linearization method 500 according to an embodiment of the present disclosure. The output power linearization method 500 includes the following processes S502 to S510.

[0036] Process S502 : Amplify the RF input signal 20 using the power amplifier 108 of the communication system (eg, the communication system 100 , 300 or 400 mentioned above) to generate the RF output signal 30 . The RF input signal 20 is generated according to the baseband signal 10 .

[0037] Process S504: Generate a feedback signal 40 according to the RF output signal 30. Then, filter the feedback signal 40 to generate a filtered feedback signal 40. The bandwidth of the filtered feedback signal 40 may be at least 3 to 5 times the bandwidth of the RF input signal 20. For example, Figure 1 The receiving filter 116 filters out at least part of the noise generated by the attenuator 112 and the mixer MXb to generate the filtered feedback signal 40 , and the frequency of the noise generated by the attenuator 112 and the mixer MXb can be higher than the highest frequency of the multiple frequency components of the RF output signal 30 .

[0038] Process S506: Utilize the analog-to-digital converter (eg, Figure 1 The analog-to-digital converter 118 performs analog-to-digital conversion processing on the filtered feedback signal 40 to convert the filtered feedback signal 40 into a digital input signal 50.

[0039] Process S508 : Generate a reference signal 60 that simulates the RF output signal 30 according to the digital input signal 50 and the baseband signal 10 .

[0040] Process S510 : establishing a predistortion model according to the reference signal 60 , wherein the predistortion model is used to perform predistortion processing on the baseband signal 10 .

[0041] Figure 6 Detailed flowchart for further explaining process S508. Process S508 may include the following processes S602 to S608.

[0042] Process S602: Generate a reference signal 60 according to the baseband signal 10. For example, using Figure 1 The power amplifier analog circuit 128 generates a reference signal 60 according to the baseband signal 10 output by the predistortion circuit 102 .

[0043] Process S604 : Filter the digital input signal 50 to generate a filtered digital input signal 50 .

[0044] Process S606 : Filter the reference signal 60 to generate a filtered reference signal 60 .

[0045] Process S608: Provide an adjustment signal 70 according to the baseband signal 10, the filtered digital input signal 50 and the filtered reference signal 60. The adjustment signal 70 is used to modify the reference signal 60 so that the reference signal 60 is close to the RF output signal 30. For example, the adjustment signal 70 may include Figure 1 The power amplifier simulation circuit 128 adjusts one or more parameters required by its built-in power amplifier model.

[0046] In the process S608 of some embodiments, the baseband signal 10 and the filtered digital input signal 50 may be used to generate the adjustment signal 70 without using the filtered reference signal 60 .

[0047] Certain words are used in the specification and the scope of the patent application to refer to specific components. However, those with ordinary knowledge in the relevant technical field should understand that the same component may be referred to by different terms. The specification and the scope of the patent application do not use the difference in name as a way to distinguish components, but use the difference in function of the components as the basis for distinction. The "include" mentioned in the specification and the scope of the patent application is an open-ended term, so it should be interpreted as "include but not limited to". In addition, "coupling" here includes any direct and indirect connection means. Therefore, if the text describes a first element coupled to a second element, it means that the first element can be directly connected to the second element through electrical connection or signal connection methods such as wireless transmission, optical transmission, etc., or indirectly electrically or signal connected to the second element through other elements or connection means.

[0048] In addition, unless otherwise specified in the specification, any singular term also includes the plural term.

[0049] The above are only preferred embodiments of the present disclosure. All equivalent changes and modifications made according to the claims of the present disclosure should fall within the scope of the present disclosure.

[0050]

Explanation of symbols

[0051] 100,300,400: Communication system

[0052] 102: Pre-distortion circuit

[0053] 104: Digital to Analog Converter

[0054] 106: Output filter

[0055] 108: Power Amplifier

[0056] 110: Coupler

[0057] 112: Attenuator

[0058] 114: Local Oscillator

[0059] 116: Receiver filter

[0060] 118:Analog-to-digital converter

[0061] 120,320: Output analog circuit

[0062] 122: Model parameters determine circuit

[0063] 124: First digital filter

[0064] 126: Second digital filter

[0065] 128: Power amplifier simulation circuit

[0066] 10: Baseband signal

[0067] 20: RF input signal

[0068] 30: RF output signal

[0069] 40: Feedback signal

[0070] 50: Digital input signal

[0071] 60: Reference signal

[0072] 70: Adjust signal

[0073] MXa,MXb:Mixer

[0074] 401: Digital Logic Circuits

[0075] 410: Control circuit

[0076] 420: Memory

[0077] 422: Model parameters determine the module

[0078] 424: First digital filter module

[0079] 426: Second digital filter module

[0080] 428: Power amplifier simulation module

[0081] 500: Output Power Linearization Method

[0082] S502~S510,S602~S608: Process

Claims

1. A communication system comprising: a power amplifier for amplifying a radio frequency input signal to generate a radio frequency output signal, wherein the radio frequency input signal is generated according to a baseband signal; a receiving filter for filtering a feedback signal generated according to the RF output signal and outputting the filtered feedback signal, wherein the bandwidth of the filtered feedback signal is at least 3 to 5 times the bandwidth of the RF input signal; an analog-to-digital converter, used for converting the filtered feedback signal into a digital input signal; an output analog circuit for generating a reference signal simulating the RF output signal according to the digital input signal and the baseband signal; and a pre-distortion circuit for establishing a pre-distortion model according to the reference signal, in, The output analog circuit includes: a power amplifier analog circuit, used for providing the reference signal according to the baseband signal; a first digital filter, for filtering the digital input signal to provide a filtered digital input signal; a second digital filter, configured to filter the reference signal to provide a filtered reference signal; as well as A model parameter determination circuit is used to provide an adjustment signal to the power amplifier analog circuit according to the baseband signal, the filtered digital input signal and the filtered reference signal, wherein the adjustment signal is used to make the reference signal approach the RF output signal.

2. The communication system according to claim 1, wherein: When the model parameter determining circuit dynamically changes the adjustment signal, the reference signal after filtering dynamically approaches the digital input signal after filtering.

3. The communication system according to claim 1, wherein: When the model parameter determination circuit dynamically changes the adjustment signal, the reference signal dynamically approaches the RF output signal.

4. The communication system according to claim 1 further comprises an attenuator coupled to the receiving filter and a mixer coupled between the receiving filter and the attenuator, wherein the receiving filter is used to filter out at least a portion of the noise generated by the attenuator and the mixer to generate the filtered feedback signal, and the frequency of the at least a portion of the noise generated by the attenuator and the mixer is higher than the highest frequency of the multiple frequency components of the RF output signal.

5. A communication system comprising: a power amplifier for amplifying a radio frequency input signal to generate a radio frequency output signal, wherein the radio frequency input signal is generated according to a baseband signal; a receiving filter for filtering a feedback signal generated according to the RF output signal and outputting the filtered feedback signal, wherein the bandwidth of the filtered feedback signal is at least 3 to 5 times the bandwidth of the RF input signal; an analog-to-digital converter, used for converting the filtered feedback signal into a digital input signal; as well as a digital logic circuit for simulating the input-output characteristics of the power amplifier according to the digital input signal and the baseband signal to generate a simulation result, and for establishing a predistortion model according to the simulation result, The digital logic circuit includes a memory, in which the following modules implemented by program codes are stored: a power amplifier simulation module, used for providing a reference signal simulating the RF output signal according to the baseband signal; a first digital filter module, used for filtering the digital input signal to provide a filtered digital input signal; a second digital filter module, configured to filter the reference signal to provide a filtered reference signal; and A model parameter determination module is used for providing an adjustment signal to the power amplifier simulation module according to the baseband signal, the filtered digital input signal and the filtered reference signal, wherein the adjustment signal is used for making the reference signal approach the RF output signal.

6. An output power linearization method, applicable to a communication system, and the output power linearization method comprises: A power amplifier of the communication system is used to amplify a radio frequency input signal to generate a radio frequency output signal, wherein the radio frequency input signal is generated according to a baseband signal; generating a feedback signal according to the RF output signal, and filtering the feedback signal to generate the filtered feedback signal, wherein the bandwidth of the filtered feedback signal is at least 3 to 5 times the bandwidth of the RF input signal; Using an analog-to-digital converter of the communication system to perform an analog-to-digital conversion process on the filtered feedback signal to convert the filtered feedback signal into a digital input signal; generating a reference signal simulating the RF output signal according to the digital input signal and the baseband signal; and A pre-distortion model is established based on the reference signal. in, The process of generating the reference signal that simulates the RF output signal includes: generating the reference signal according to the baseband signal; Performing filtering on the digital input signal to generate a filtered digital input signal; as well as An adjustment signal is provided according to the baseband signal and the filtered digital input signal, wherein the adjustment signal is used to correct the reference signal so that the reference signal is close to the RF output signal.

7. The output power linearization method according to claim 6, wherein: The process of generating the feedback signal according to the RF output signal includes: At least a portion of noise generated by an attenuator and a mixer of the communication system is filtered out to generate the filtered feedback signal, wherein the frequency of the at least a portion of the noise generated by the attenuator and the mixer is higher than the highest frequency of the multiple frequency components of the RF output signal.

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