JPH08256020A - Linear compensation circuit - Google Patents

Abstract

PURPOSE: To reduce the memory capacity of initial data by memorizing only the specified sample value of the initial value of distortion correction data and preparing the other data while interpolating them. CONSTITUTION: An initial value memory 19 does not store distortion correction amounts corresponding to all modulated signal levels but stores only required sample data. Concerning data between sample data, they are estimated/ interpolated while using data for several samples. Therefore, when they are estimated/interpolated, the sample data intervals are decided so as not to damage compensation characteristics. When a power source is turned on, a microprocessor 17 inputs the distortion correction amount sample data from the initial value memory 19 and calculates data excepting for the omitted sample data according to an estimation/interpolation algorithm while using the sample data for several samples. The calculated data and initial value for correction are written through a data selector 16 into a RAM 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a linear compensation circuit for compensating the non-linearity of an amplifier.

[0002]

2. Description of the Related Art An example of conventional technology will be described with reference to FIG. The transmission data sequence input from the input terminal is input to the waveform generation ROM (Read Only Memory) 1. Band-limited complex baseband signal waveform data is written in advance in the waveform generation ROM 1, and the complex baseband signal corresponding to the input transmission data string is read out.
The output of the waveform generation ROM 1 is transferred to the RAM by the adder 2.
The compensation data is added to the compensation data stored in the (Random Access Memory) 14, and the compensation data is given in advance so that the output level of the amplifier 5 becomes linear with respect to the input level of the transmission data string. The content of the compensation data in the RAM 14 is
As a result of adding the compensation data and the output signal from the waveform generation ROM 1, complex signal waveform data having characteristics opposite to the input / output characteristics of the amplifier 5 is written so that the nonlinear distortion of the amplifier 5 is canceled. .

Next, the output signal of the adder 2 is input to a DA converter / LPF (Low Pass Filter) 3, converted from a digital signal to an analog signal, and unnecessary components are removed by the LPF, followed by quadrature modulation. Given to vessel 4. The quadrature modulator 4 quadrature-modulates the output signal of the oscillator 8 with the input baseband signal and supplies it to the amplifier 5. Here, in order to adaptively change the value of the RAM 14, a part of the output signal of the amplifier 5 is detected via the directional coupler 7 and demodulated by the quadrature demodulator 9 using the output of the oscillator 8. . The demodulated signal is the LP of the LPF / AD modulator 10.
After being band-limited by F, it is converted into a complex baseband signal by an AD converter. Further, the output signal of the waveform generation ROM 1 is delayed by the delay device 15 to obtain a transmission baseband signal with a matched timing, and the demodulated signal is subtracted from the transmission baseband signal with a matched timing by the subtracter 11. The output signal of the subtractor 11 is multiplied by the required coefficient K (0 <K ≦ 1) by the multiplier 12
Multiply by. Further, the output signal of the multiplier 12 is added to the output signal of the RAM 14 by the adder 13.

According to the above operation, when the demodulation baseband signal is larger than the modulation baseband output signal of the waveform generation ROM 1, the compensation data in the RAM 14 is rewritten so as to be larger, and vice versa. If the demodulation baseband signal is smaller than the modulation baseband output signal of the waveform generation ROM 1, the content of the compensation data in the RAM 14 is rewritten so as to be smaller. In this way, even if the characteristic of the amplifier 5 changes, it is controlled so as to follow adaptively. However, when the power is turned on,
Since the value of the RAM 14 is not sufficiently converged, the nonlinear characteristic of the amplifier cannot be accurately compensated. Therefore, when the power is turned on, the amplifier compensation initial value is read from the initial value ROM 19 via the data selector 16 and the RAM 14 is read.
Please write in and allow sufficient compensation. When the power is turned on, after writing the initial value to the RAM 14, the data selector 16 supplies the output signal from the waveform generation ROM 1 to the RAM 14.

[0005]

However, in the above-mentioned prior art, for all modulated baseband signals,
Since the initial data for compensating the amplifier must be stored, the amount of data to be stored is very large.
An object of the present invention is to eliminate this drawback and provide a linear compensation circuit with a reduced initial data memory capacity.

[0006]

In order to achieve the above object, the present invention focuses on that the non-linear distortion of a power amplifier is a gradual distortion component and its distortion correction data is also a gradual characteristic. However, only a specific sample value of the distortion correction data initial value is stored in memory, and other data is created by interpolation.

[0007]

As a result, it is not necessary to store the amplifier compensation initial data for all the baseband signals output from the waveform generation ROM 1, but only the minimum sample data required for interpolation. Since it is enough, it is possible to significantly reduce the memory amount.

[0008]

Embodiments of the present invention will be described with reference to FIGS. 1 and 3. The operation of predistortion is the same as the conventional example. FIG. 3 is a diagram showing the relationship between the output signal of the waveform generation ROM 1 and the distortion correction value. The initial value memory 19 shown in FIG. 1 does not store the distortion correction amount for all modulation signal levels as shown in FIG. 3, but stores only required sample data (data indicated by ●). I will let you. For the data between the sample data (data with circles), use sample data of several samples,
Estimate / interpolate. Therefore, the sample data interval is an interval that does not impair the compensation characteristics when the estimation / interpolation is performed. When the power is turned on, the microprocessor 17 inputs the distortion correction amount sample data from the initial value memory 19,
Data other than the missing sample data is calculated by an estimation / interpolation algorithm using sample data of several samples. The compensation initial value composed of the data thus calculated and the sample data is written in the RAM 14 via the data selector 16. After writing the initial value to the RAM 14 when the power is turned on, the data selector 16 outputs the output signal from the waveform generation ROM 1 to the RAM 14.
Supply to.

[0009]

As described above, according to the present invention, the amount of initial data for amplifier compensation to be stored can be greatly reduced, and the memory capacity can be reduced. Regarding the memory capacity of the initial value memory, if the sample data interval is N (N is a natural number of 2 or more), the capacity is only 1 / N, and a significant reduction in memory capacity can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a conventional technique.

FIG. 3 is a diagram showing a relationship between a waveform generation ROM output and a distortion correction value.

[Explanation of symbols]

1 ... Waveform generation ROM 2 ... Adder 3 ... D / A / LPF 4 ... Quadrature modulator 5 ... Amplifier 6 ... Antenna 7 ... Directional coupler 8 ... Oscillator 9 ... Quadrature demodulator 10 ... L
PF / A / D 11 ... Subtractor 12 ... Multiplier 13 ... Adder 14 ... R
AM 15 ... Delay device 16 ... Data selector 17 ... Microprocessor 19 ... Initial value ROM

Claims (1)

[Claims] 1. Computation for calculating the compensation data given an addition means for adding compensation data to an input signal, an amplification means for amplifying the signal after the addition, and an output signal of the amplification means and the input signal. A linear compensating circuit comprising: means for storing a predetermined number of sample data in advance; and means for interpolating and estimating the sample data to calculate initial compensation data. circuit.