JP5228521B2 - Distortion compensation circuit, transmission apparatus, communication system, and distortion compensation method - Google Patents

Description

  The present invention relates to a distortion compensation circuit, a transmission apparatus, a communication system, and a distortion compensation method, and more particularly to a distortion compensation circuit, a transmission apparatus, a communication system, and a distortion compensation method for a power amplifier that amplifies a digital orthogonal baseband transmission signal.

  In recent years, in a digital mobile communication system, a predistortion method has been proposed as a typical distortion compensation technique for suppressing adjacent channel leakage power due to nonlinear distortion of power amplification means (see, for example, Patent Document 1).

  FIG. 6 is a configuration diagram of an example of a transmission apparatus including the predistortion type distortion compensation circuit described in Patent Document 1.

  Referring to FIG. 1, transmission apparatus 100 includes transmission data generation unit 1, distortion compensation calculation unit 2 to which transmission data generated by transmission data generation unit 1 is input, and distortion compensation calculation unit 2. And digital / analog (D / A) converters 3-1 and 3-2 to which transmission data is inputted.

  Further, the transmission apparatus 100 includes a quadrature modulator 4 to which transmission data converted from digital to analog by digital / analog (D / A) converters 3-1 and 3-2 is input, a reference signal generation unit 5, and the like. And a power amplifying unit 6 to which transmission data orthogonally modulated by the orthogonal modulator 4 is input.

  Furthermore, the transmission apparatus 100 includes a directional coupler 7 that feeds back a part of transmission data that has been power amplified by the power amplification unit 6, a quadrature demodulator 8 that receives a feedback signal from the directional coupler 7, It includes analog / digital (A / D) converters 9-1 and 9-2 to which feedback signals demodulated by the quadrature demodulator 8 are input.

  Further, the transmission device 100 converts from analog to digital by an amplitude calculation unit 10 to which transmission data generated by the transmission data generation unit 1 is input, and analog / digital (A / D) converters 9-1 and 9-2. And an error calculation and compensation data generation unit 11 to which the transmission data, the data calculated by the amplitude calculation unit 10 and the transmission data generated by the transmission data generation unit 1 are input.

  The reference signal generated by the reference signal generation unit 5 is input to the quadrature modulator 4 and the quadrature demodulator 8, and the compensation data generated by the error calculation and compensation data generation unit 11 is input to the distortion compensation calculation unit 2. The

  Next, the operation of the transmission device 100 will be described. The digital orthogonal baseband signal generated by the transmission data generation unit 1 is input to the distortion compensation calculation unit 2.

  The distortion compensation calculation unit 2 performs distortion compensation by complex multiplication of the digital orthogonal baseband signal based on the distortion calculation data generated by the error calculation and compensation data generation unit 11.

  The D / A converters 3-1 and 3-2 convert the distortion-compensated digital quadrature baseband signal into an analog quadrature baseband signal.

  The quadrature modulator 4 performs quadrature modulation of the analog quadrature baseband signal using the reference signal from the reference signal generator 5.

  The power amplifying unit 6 amplifies the power of the quadrature-modulated analog quadrature baseband signal.

  Part of the output of the power amplifier 6 is fed back to the quadrature demodulator 8 by the directional coupler 7.

  The quadrature demodulator 8 demodulates the analog quadrature baseband signal using the reference signal from the reference signal generator 5.

  A / D converters 9-1 and 9-2 convert the demodulated analog quadrature baseband signals into digital quadrature baseband signals.

  The error calculation and compensation data generation unit 11 compares the digital orthogonal baseband signal with the digital orthogonal baseband signal from the transmission data generation unit 1 and generates distortion compensation data using the amplitude value from the amplitude calculation unit 10 as an address. To do. Then, the error calculation and compensation data generation unit 11 outputs the distortion compensation data to the distortion compensation calculation unit 2 using the amplitude value as an address.

  Note that a configuration employing a digital system for quadrature modulation and quadrature demodulation and a configuration using a frequency converter instead of direct modulation have been studied. Also, a configuration has been proposed in which distortion compensation calculation is performed using the squared power value of the amplitude value by the amplitude calculation unit 10 as an address instead of using the amplitude value by the amplitude calculation unit 10 as an address.

  However, a distortion generation mechanism in an amplifier is represented not only by AM (amplitude modulation) / AM characteristics and AM / PM (phase modulation) characteristics with respect to instantaneous input amplitude (or power) but also by a memory effect. There exists a “characteristic whose current nonlinear characteristic is affected by a past state”.

  FIG. 7 is a graph showing an example of the AM / AM characteristic with respect to the input amplitude of the related high-power amplifier. This figure is data obtained by plotting the data sampled in time series against the input amplitude without being aware of the past state of the input amplitude. Referring to the figure, there are a plurality of data for the same amplitude value.

  FIG. 8 is a diagram showing a waveform obtained by tracing time changes for some points of the AM / AM characteristic sample data shown in FIG. Referring to FIG. 8, it can be seen that even when the input amplitude is the same, the data draws different trajectories depending on the time change (past state).

  FIG. 9 is a diagram showing AM / AM characteristics obtained by sampling only the points where the input amplitude has increased as a time change for the AM / AM characteristic sample data shown in FIG. 7, and FIG. 10 shows the input amplitude decreasing as the time change. It is a figure which shows the AM / AM characteristic which sampled only the done point. The curve in FIG. 10 is obtained by approximating each sample data with a polynomial.

  Since the compensation table data in the distortion compensation circuit is generated from the discrete sample data by an arithmetic process that minimizes the error, the compensation table data is almost like the inverse characteristic of this polynomial curve. Here, it can be seen that the AM / AM characteristic observed in the input amplitude rising point sample is different from the AM / AM characteristic observed in the input amplitude falling point sample.

  Similarly, FIG. 11 is a diagram showing an example of the AM / PM characteristic of the high output amplifier with respect to the input amplitude. In particular, it is data obtained by plotting data sampled in time series with respect to the input amplitude without being aware of the past state of the input amplitude. There are a plurality of data for the same input amplitude value.

  FIG. 12 is a diagram showing a waveform obtained by tracing time changes for some points of the AM / PM characteristic sample data shown in FIG. It can be seen that even for the same input amplitude, different trajectories are shown due to time changes (past states).

  FIG. 13 is a diagram showing AM / PM characteristics obtained by sampling only the points where the input amplitude is increased as a time change for the AM / PM characteristic sample data shown in FIG. 11, and FIG. It is a figure which shows the AM / PM characteristic which sampled only the done point.

  The curve in FIG. 14 is obtained by approximating each sample data with a polynomial. Since the compensation table data in the distortion compensation circuit is generated from the discrete sample data by an arithmetic process that minimizes the error, the compensation table data is almost like the inverse characteristic of this polynomial curve.

  Here, it can be seen that the AM / PM characteristic observed in the input amplitude rising point sample is different from the AM / PM characteristic observed in the input amplitude falling point sample.

  The distortion generation mechanism in the amplifier includes not only the AM / AM characteristic and AM / PM characteristic with respect to the instantaneous input amplitude (or power) but also the characteristic that the current nonlinear characteristic is influenced by the past state, represented by the memory effect. Exists.

  For this reason, in a configuration including a distortion compensation table that is referred to using only the instantaneous input amplitude (or power) as an address, nonlinear distortion generated by the memory effect cannot be compensated, so that a sufficient distortion compensation effect cannot be obtained. There was a problem.

  On the other hand, a non-linear compensation circuit that compensates for the memory effect using a FIR (finite impulse response) filter is described in Patent Document 2, and in order to obtain the same effect as the FIR filter, compensation coefficients stored in a plurality of compensation tables are set. Patent Document 3 discloses a distortion compensation circuit that combines signals with different delays.

  In addition, there is provided a distortion compensation device that generates an unbalanced IM (inter-modulation) characteristic so that an amplitude component and a phase component are different when the power is the same when the power is increasing and when the power is decreasing. It is described in Patent Document 4.

  Further, Patent Document 5 discloses a distortion compensation apparatus that reads out a distortion compensation coefficient corresponding to the power or amplitude of the current and past transmission signals from the memory and updates the distortion compensation coefficient based on the output signal of the transmission power amplifier. .

JP 2003-168931 A JP 2005-033632 A JP 2004-320598 A Re-special table 2004-095689 RE-spec table 2001-008320

  However, the inventions described in Patent Documents 2 to 5 have a problem that an algorithm for deriving a compensation coefficient is complicated, and accordingly, a convergence time of distortion compensation becomes long.

  Therefore, an object of the present invention is to use an existing distortion compensation table (a distortion compensation table referred to using only the instantaneous input amplitude (or power) as an address) and improve the distortion compensation effect with the existing algorithm as it is. A distortion compensation circuit, a transmission apparatus, a communication system, and a distortion compensation method are provided.

In order to solve the above problems, a distortion compensation circuit according to the present invention includes first and second error calculation units for calculating distortion compensation data of the amplifier based on an input signal and a feedback signal of the amplifier, and the first and second error calculation units. The first and second compensation tables in which the calculation results in the two error calculation unit are written, and the error for calculating the distortion compensation data depending on whether the amplitude of the input signal has increased or decreased compared to the previous input. A first switch for switching the calculation unit; a second switch for switching a compensation table and a read address for reading the distortion compensation data depending on whether the amplitude of the input signal has increased or decreased compared to the previous input ; An amplitude determination unit that determines whether the amplitude of the input signal has increased or decreased from the previous input and notifies the first switcher of the result, and whether the amplitude of the input signal has increased from the previous input Descent An amplitude comparison unit that determines whether or not the second switch is informed, an amplitude calculation unit that sets a read address of the first and second compensation tables based on the amplitude of an input signal, and the first and second A distortion compensation calculation unit that reads the distortion compensation data from the compensation table and compensates the distortion of the amplifier based on the distortion compensation data, and the distortion compensation is performed when the amplitude of the input signal is higher than that at the previous input. When the data is calculated by the first error calculation unit and falls, the second error calculation unit calculates the data, and when the amplitude of the input signal is higher than that at the previous input, the distortion compensation data is changed to the first error calculation unit. It is read from the compensation table, and when it descends, it is read from the second compensation table .

  According to another aspect of the present invention, there is provided a transmission apparatus including the above distortion compensation circuit.

  A communication system according to the present invention includes the above-described transmission device.

In addition, the distortion compensation method according to the present invention provides the first or second error calculation unit that calculates the error calculation data of the amplifier depending on whether the amplitude of the input signal has increased or decreased compared to the previous input. The first step of switching to the second step, the second step of writing the calculation result by the error calculation unit into the first or second compensation table corresponding to the error calculation unit, and the amplitude of the input signal increased from the previous input A compensation table for reading out the distortion compensation data and a third step of switching the readout address to the first or second compensation table according to whether it has fallen, and the amplitude of the input signal has risen or fallen compared to the previous input. A fourth step of determining whether the amplitude of the input signal has increased or decreased from the previous input, and determining the result of the third step. A fifth step of notifying the first, a sixth step of setting read addresses of the first and second compensation tables based on the amplitude of the input signal, and reading the distortion compensation data from the first and second compensation tables, A seventh step of compensating for distortion of the amplifier based on distortion compensation data, and the distortion compensation data is computed by the first error computing unit when the amplitude of the input signal is higher than that at the previous input, and is lowered The distortion compensation data is read from the first compensation table when the second error calculation unit calculates the amplitude of the input signal and the amplitude of the input signal is higher than that at the previous input, and when the amplitude decreases, the second It is read from the compensation table .

  According to the present invention, it is possible to improve the distortion compensation effect using an existing distortion compensation table (a distortion compensation table referred to using only the instantaneous input amplitude (or power) as an address) and using the existing algorithm. .

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  First, the operating principle of the present invention will be described prior to describing the embodiment of the present invention.

  FIG. 1 is a basic configuration diagram of an example of a distortion compensation circuit according to the present invention. Referring to the figure, a distortion compensation circuit 50 according to the present invention includes a first error calculation unit 51 that calculates distortion compensation data of an amplifier based on an input signal and a feedback signal of the amplifier (power amplifier 6 in FIG. 6), and And a second error calculation unit 52.

  Further, the distortion compensation circuit 50 includes a first compensation table 53 and a second compensation table 54 in which the calculation results in the first error calculation unit 51 and the second error calculation unit 52 are written, respectively, and the amplitude of the input signal is the previous input. And a first switch 55 that switches an error calculation unit that calculates the distortion compensation data according to whether the time has risen or fallen.

  Further, the distortion compensation circuit 50 includes a compensation table for reading distortion compensation data and a second switch 56 for switching a read address according to whether the amplitude of the input signal has increased or decreased compared to the previous input. Is done.

  That is, as an example, when the amplitude of the input signal is higher than that at the previous input, the error calculator is switched to the first error calculator 51 by the first switch 55, and distortion compensation is performed by the first error calculator 51. Data is calculated and the calculation result is written in the first compensation table 53.

  On the other hand, when the amplitude of the input signal is lower than the previous input, the error calculator is switched to the second error calculator 52 by the first switch 55, and distortion compensation data is calculated by the second error calculator 52. Then, the calculation result is written in the second compensation table 54.

  In addition, regarding the reading of the compensation data from the first compensation table 53 and the second compensation table 54, when the amplitude of the input signal is higher than that at the previous input, the compensation table is switched to the first compensation table 53, Compensation data is read from the 1 compensation table 53.

  On the other hand, when the amplitude of the input signal is lower than that at the previous input, the compensation table is switched to the second compensation table 54, and compensation data is read from the second compensation table 54.

  Next, the basic operation of an example of the distortion compensation circuit according to the present invention will be described. FIG. 2 is a flowchart showing the basic operation of an example of the distortion compensation circuit according to the present invention.

  Referring to the figure, the first switch 55 switches the error calculation unit that calculates distortion compensation data to the error calculation unit 51 or 52 according to the increase or decrease of the amplitude of the input signal (step S1).

  Next, the error calculator 51 or 52 that has calculated the distortion compensation data writes the calculation result in the corresponding compensation table 53 or 54 (step S2).

  Next, the second switch 56 switches the compensation table for reading the distortion compensation data to the compensation table 53 or 54 according to the increase or decrease of the amplitude of the input signal (step S3).

  That is, in the present invention, distortion compensation data is written into separate compensation tables when the amplitude of the input signal rises and falls, and distortion compensation data is read from the separate compensation table when the amplitude of the input signal rises and falls. Although the read configuration is included, the data write and read algorithms are the same as those in the existing distortion compensation table.

  Therefore, according to the present invention, it is possible to improve the distortion compensation effect using the existing distortion compensation table (the distortion compensation table referred to only with the instantaneous input amplitude (or power) as an address) and using the existing algorithm as it is. It becomes.

  Next, a first embodiment of the present invention will be described. FIG. 3 is a configuration diagram of the first embodiment of the distortion compensation circuit according to the present invention. In the figure, the same components as those of the related distortion compensation circuit (see FIG. 5) are denoted by the same reference numerals, and the description thereof is omitted.

  Referring to FIG. 3, a distortion compensation circuit 20 according to the present invention includes a distortion compensation calculation unit 2 that calculates distortion compensation of a power amplifier (see power amplifier 6 in FIG. 6), and an amplitude calculation unit that calculates the amplitude of an input signal. 10 and an error calculation and compensation data generation unit 21 that generates error calculation and compensation data based on the input signal and the calculation result of the amplitude calculation unit 10.

  The error calculation and compensation data generation unit 21 corresponds to the error calculation and compensation data generation unit 11 of the related art (FIG. 6).

  The error calculation and compensation data generation unit 21 includes a polar coordinate conversion unit 12-1 that performs polar conversion of the input signals I and Q, and feedback signals I ′ from A / Ds 9-1 and 9-2 (see FIG. 6) (not shown). , Q ′, a polar coordinate conversion unit 12-2 that performs a polar coordinate conversion, and an amplitude determination unit 15 that determines the amplitude information R output from the polar coordinate conversion unit 12-1.

  Further, the error calculation and compensation data generation unit 21 switches a switch 16-1 that switches an error calculation unit (described later) that is an output destination of data from the polar coordinate conversion unit 12-1 according to a determination result in the amplitude determination unit 15. 16-2, and switches 16-3 and 16-4 for switching an error calculation unit (described later) as an output destination of information from the polar coordinate conversion unit 12-2 according to the determination result in the amplitude determination unit 15. Consists of.

  Further, the error calculation and compensation data generation unit 21 inputs the information from the polar coordinate conversion units 12-1 and 12-2 via any one of the switches 16-1 to 16-4 and performs an error calculation. -1 and 13-2, and compensation tables 14-1 and 14-2 in which calculation results in the error calculation units 13-1 and 13-2 are written, respectively.

  Further, the error calculation and compensation data generation unit 21 compares the current input amplitude value Rn from the amplitude calculation unit 10 with the previous input amplitude value Rn−1, and a delay that delays the amplitude information by one sample. The circuit 17 is configured to include a switch 16 that switches the reference addresses (amplitude addresses) of the compensation tables 14-1 and 14-2 based on the comparison result in the amplitude comparison unit 18.

  Further, the error calculation and compensation data generating unit 21 compares the selector 19-1 for switching between the compensation tables 14-1 and 14-2 for reading the amplitude data based on the comparison result in the amplitude comparing unit 18, and the comparison in the amplitude comparing unit 18. And a selector 19-2 for switching between compensation tables 14-1 and 14-2 for reading out phase data based on the result.

  Further, the error calculation and compensation data generation unit 21 includes switches 16 and 16-1 to 16-4, selectors 19-1 and 19-2, error calculation units 13-1 and 13-2, and compensation tables 14-1 and 14. -2 and a program storage unit 32 in which a program shown in the flowchart of FIG. 2 is stored.

  The amplitude value R calculated by the amplitude calculator 10 is a reference address for referring to the compensation tables 14-1 and 14-2.

  Next, the operation of the first embodiment will be described.

  First, processing for generating and updating distortion compensation data will be described. The input I and Q signals and the feedback I ′ and Q ′ signals are converted into amplitude information (input R and feedback R ′) and phase information (input θ and feedback θ ′) by the polar coordinate conversion units 12-1 and 12-2, respectively. Convert.

  Based on the information, an error calculation is performed between the input amplitude R and the feedback amplitude R ′, and the input phase θ and the feedback phase θ ′, and the result is reflected in the compensation tables 14-1 and 14-2.

  At this time, the amplitude determination unit 15 determines an increase or decrease in the input signal amplitude of the input amplitude R.

  As a determination method, from the time-series data of the sampled input amplitude, it is determined that the time change (ΔR) is an increase when the time change (ΔR) is positive, and a decrease when the change is negative. In this case, the sample data is distributed to the error calculator 13-2 by the switches 16-1 and 16-2.

  When there is no change in amplitude over time (ΔR = 0), it is assumed that the switches 16-1 and 16-2 are not changed from the previous state.

  The calculation results of the error calculation unit 13-1 based on the input amplitude rise point sample and the error calculation unit 13-2 based on the input amplitude drop point sample are reflected in the compensation table 14-1 and the compensation table 14-2, respectively.

  Here, although the compensation table has two surfaces, the error calculation for each and the update processing for the table may be the same as the algorithm of the related distortion compensation circuit.

  Next, the distortion compensation data reference and output processing will be described. In the related distortion compensation circuit, the compensation table is referred to using the instantaneous input amplitude as an address.

  However, in the present invention, the delay circuit 17 includes the compensation table 14-1 based on the input amplitude rising point sample and the compensation table 14-2 based on the input amplitude falling point sample, and delays the amplitude information from the amplitude calculating unit 10 by one sample. The comparator 18 compares the instantaneous input amplitude Rn with the input amplitude Rn-1 one sample before, thereby determining whether the input signal amplitude is rising or falling.

  When Rn> Rn−1, it is determined to be rising, and when Rn <Rn−1, it is determined to be decreasing, and the switch 16 uses the input amplitude rising point sample compensation table 14-1 and the input amplitude falling point sample compensation table 14−. 2 is switched, and the compensation data is switched by selectors 19-1 and 19-2. When there is no time change in amplitude (Rn = Rn−1), it is assumed that the switch 16, the selector 19-1, and the selector 19-2 are not changed from the previous state.

  As described above, according to the first embodiment of the present invention, by providing the compensation table by the input amplitude rising point sample and the compensation table by the input amplitude falling point sample, the error calculation for each table, and the table The update process remains the same as the algorithm of the related distortion compensation circuit, and the memory effect affected by the past amplitude state can be compensated.

  Next, a second embodiment of the present invention will be described. FIG. 4 is a configuration diagram of the second embodiment of the present invention. The second embodiment relates to a transmission device. Referring to the figure, the transmitter 40 according to the present invention includes a distortion compensation circuit 20 (see FIG. 3).

  Further, the configuration of the transmission device 40 other than the distortion compensation circuit 20 is the same as the configuration in which the error calculation and compensation data generation unit 11, the distortion compensation calculation unit 2, and the amplitude calculation unit 10 are excluded from the related device of FIG. Since the configuration and operation of the distortion compensation circuit 20 have already been described, description thereof is omitted here.

  As described above, according to the second embodiment of the present invention, since the transmission device 40 includes the distortion compensation calculation unit 20, the memory effect affected by the past amplitude state is the same as in the first embodiment. Can be compensated.

  Next, a third embodiment of the present invention will be described. FIG. 5 is a block diagram of the third embodiment of the present invention. The third embodiment relates to a communication system. Referring to the figure, a communication system 60 according to the present invention includes a transmission device 40 and one or a plurality of terminal devices 41-1 to 41-n (n is a positive integer) that communicate with the transmission device 40. It is comprised including.

  The transmission device 40 is the transmission device shown in the second embodiment (see FIG. 4). The transmission device 40 is a transmission device provided in a base station as an example, and includes a distortion compensation circuit that compensates for distortion generated in a power amplifier of a transmission system.

  On the other hand, the terminal devices 41-1 to 41-n are portable terminals as an example, and communicate with the transmission device 40 wirelessly.

  As described above, according to the third embodiment of the present invention, since the communication system 60 includes the transmission device 40, the memory effect affected by the past amplitude state is compensated as in the second embodiment. It becomes possible to do.

  Note that the present invention can also be applied to a communication system in which the transmission device 40 and the terminal devices 41-1 to 41-n perform wired communication.

  Next, a fourth embodiment of the present invention will be described. The fourth embodiment relates to a distortion compensation method program. Referring to FIG. 3, the error calculation and compensation data generation unit 21 according to the present invention includes a control unit 31 and a program storage unit 32.

  As described above, the control unit 31 includes the switches 16 and 16-1 to 16-4, the selectors 19-1 and 19-2, the error calculation units 13-1 and 13-2, and the compensation tables 14-1 and 14-2. Control. The program storage unit 32 stores a program shown in the flowchart of FIG.

  The control unit 31 of the error calculation and compensation data generation unit 21 reads a distortion compensation method program from the program storage unit 32, and switches 16 and 16-1 to 16-4 and selectors 19-1 and 19-2 according to the program. The error calculators 13-1 and 13-2 and the compensation tables 14-1 and 14-2 are controlled. Since the control content has already been described, the description thereof is omitted here.

  As described above, according to the fourth embodiment of the present invention, by providing the compensation table by the input amplitude rising point sample and the compensation table by the input amplitude falling point sample, the error calculation for each table, and the table The update process remains the same as the algorithm of the related distortion compensation circuit, and a program capable of compensating for the memory effect affected by the past amplitude state is obtained.

  As another embodiment, the table reference address for updating the distortion compensation table and outputting the compensation data may be a power value that is a square of the amplitude value instead of the amplitude value.

  In addition, as a condition for switching the processing for the compensation table, the above embodiment has shown an example in which the state one sample before due to the delay is used to determine whether the amplitude in the time change of the input signal amplitude has increased or decreased. A configuration in which the number of samples is changed according to characteristics is also possible.

It is a basic composition figure of an example of a distortion compensation circuit concerning the present invention. 3 is a flowchart showing a basic operation of an example of a distortion compensation circuit according to the present invention. 1 is a configuration diagram of a first embodiment of a distortion compensation circuit according to the present invention. FIG. It is a block diagram of 2nd Embodiment of this invention. It is a block diagram of 3rd Embodiment of this invention. 10 is a configuration diagram of an example of a transmission device including a predistortion type distortion compensation circuit described in Patent Document 1. FIG. It is a figure which shows the graph of an example of AM / AM characteristic with respect to the input amplitude of a related high output amplifier. It is a figure which shows the waveform which traced the time change about the one part point of AM / AM characteristic sample data shown in FIG. It is a figure which shows the AM / AM characteristic which sampled only the point which the input amplitude raised as a time change about the AM / AM characteristic sample data shown in FIG. It is a figure which shows the AM / AM characteristic which sampled only the point where the input amplitude fell as a time change. It is a figure which shows an example of the AM / PM characteristic of the high output amplifier with respect to input amplitude. It is a figure which shows the waveform which traced the time change about the one part point of AM / PM characteristic sample data shown in FIG. It is a figure which shows the AM / PM characteristic which sampled only the point which the input amplitude raised as a time change about the AM / PM characteristic sample data shown in FIG. It is a figure which shows the AM / PM characteristic which sampled only the point where the input amplitude fell as a time change.

Explanation of symbols

2 Distortion Compensation Operation Unit 10 Amplitude Calculation Unit 12 Polar Coordinate Conversion Unit 13 Error Calculation Unit 14 Compensation Table 15 Amplitude Determination Unit 16 Switch 17 Delay Circuit 18 Amplitude Comparison Unit 19 Selector 20 Distortion Compensation Circuit 21 Error Calculation and Compensation Data Generation Unit 31 Control Unit 32 program storage unit 40 transmission device 41 terminal device 50 distortion compensation circuit 51 first error calculation unit 52 second error calculation unit 53 first compensation table 54 second compensation table 55 first switch 56 second switch 60 communication system

Claims (4)

First and second error calculators for calculating distortion compensation data of the amplifier based on an input signal and a feedback signal of the amplifier;
First and second compensation tables in which calculation results in the first and second error calculation units are written, respectively;
A first switch that switches an error calculation unit that calculates the distortion compensation data according to whether the amplitude of the input signal has increased or decreased compared to the previous input;
A compensation table that reads out the distortion compensation data and a second switch that switches a readout address according to whether the amplitude of the input signal has increased or decreased compared to the previous input ;
An amplitude determination unit that determines whether the amplitude of the input signal has increased or decreased from the previous input and notifies the first switch of the result;
An amplitude comparison unit that determines whether the amplitude of the input signal has increased or decreased from the previous input and notifies the second switch of the result;
An amplitude calculator configured to set read addresses of the first and second compensation tables based on the amplitude of the input signal;
A distortion compensation calculation unit that reads out the distortion compensation data from the first and second compensation tables and compensates for distortion of the amplifier based on the distortion compensation data;
When the amplitude of the input signal increases from the previous input, the distortion compensation data is calculated by the first error calculation unit, and when it decreases, the distortion calculation data is calculated by the second error calculation unit,
The distortion compensation data is read from the first compensation table when the amplitude of the input signal is higher than that at the previous input, and is read from the second compensation table when it is lowered. circuit. A transmitter comprising the distortion compensation circuit according to claim 1. A communication system including the transmission device according to claim 2. A first step of switching the error calculation unit for calculating distortion compensation data of the amplifier to the first or second error calculation unit according to whether the amplitude of the input signal has increased or decreased compared to the previous input;
A second step of writing a calculation result by the error calculation unit into a first or second compensation table corresponding to the error calculation unit;
A third step of switching the compensation table for reading out the distortion compensation data and the readout address to the first or second compensation table according to whether the amplitude of the input signal has increased or decreased compared to the previous input;
A fourth step of determining whether the amplitude of the input signal has increased or decreased compared to the previous input and notifying the result to the first step;
A fifth step of determining whether the amplitude of the input signal has increased or decreased from the previous input and notifying the result to the third step;
A sixth step of setting read addresses of the first and second compensation tables based on the amplitude of the input signal;
Reading the distortion compensation data from the first and second compensation tables, and compensating the distortion of the amplifier based on the distortion compensation data,
When the amplitude of the input signal increases from the previous input, the distortion compensation data is calculated by the first error calculation unit, and when it decreases, the distortion calculation data is calculated by the second error calculation unit,
The distortion compensation data is read from the first compensation table when the amplitude of the input signal is higher than that at the previous input, and is read from the second compensation table when it is lowered. Method.

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