JP3041995B2 - Non-linear compensation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonlinear compensation circuit,
In particular, the present invention relates to a non-linear compensation circuit using a digital circuit as a compensation distortion generating circuit in a pre-distortion type compensation circuit for compensating input / output nonlinear characteristics of a high-frequency band high power amplifier.

[0002]

2. Description of the Related Art A conventional nonlinear compensation circuit is constituted by an analog circuit, and a transistor amplifier, a diode circuit or the like is used as a distortion generating circuit. For example, as shown in FIG. 2 (see Japanese Patent Publication No. 58-16802),
Branch device 22, two high-frequency amplifiers 23 and 24, synthesizer 2
5.

That is, the input from the input terminal 21 is transmitted to the branching device 2
The signal is supplied to a high-frequency amplifier 23 for generating distortion via the signal line 2 and the output is applied to a combiner 25 to form a first path. The other output branched by the splitter 22 is similarly supplied to the synthesizer 25 via the high-frequency amplifier 24 to form a second path, and the output of the synthesizer 25 is taken out from the output terminal 26. In addition, 2
7, 28 are terminators.

In this configuration, two high-frequency amplifiers 2
Transmission characteristics such as amplitude, delay, frequency characteristics, gain, and input / output characteristics of 3 and 24 are almost the same, and only operation levels are different. That is, the amplifier 23 operates in the non-linear range, and the amplifier 24 operates in the linear range. Further, by combining these outputs in a substantially antiphase relationship, a non-linear characteristic in which the increase in the output power is larger than the increase in the input power can be obtained.

[0005]

The above-mentioned conventional nonlinear compensation circuit uses an analog circuit such as a transistor amplifier, a diode, or a limiter circuit as a distortion generating circuit, and almost adjusts the input / output characteristics of the distortion generating circuit. It is impossible to do. As a result, the input / output characteristics of the nonlinear compensation circuit have a disadvantage that they are not always ideal for compensating for the nonlinearity of a high-output amplifier, such as the occurrence of third-order cross modulation and higher-order cross modulation due to nonlinearity. is there.

An object of the present invention is to provide a nonlinear compensation circuit which can improve input / output characteristics and can suitably compensate for nonlinearity, and is realized by a digital circuit.

[0007]

A non-linear compensation circuit according to the present invention comprises a first frequency converter for converting the frequency of an input analog signal, and a local oscillator for exciting a local oscillation signal to the first frequency converter. An analog-to-digital converter for converting an analog signal of the first frequency converter to a digital signal; and a plurality of non-linear characteristics assumed in advance by inputting each of the digital signals bifurcated from the analog-to-digital converter. ROMs that convert numerical values to memory values
Two digital-to-analog converters for respectively converting the outputs of these ROMs to analog signals, a filter cascade-connected to each of the digital-to-analog converters, and a filter provided by the local oscillation signal. Second frequency converters for converting the output of the converter to the frequency of the original analog signal, a synthesizing circuit for synthesizing the outputs of these second frequency converters, and one of the second frequency converters A phase shifter inserted between one of them and the input of the combining circuit.

[0008]

According to the structure of the present invention, a signal of an arbitrary frequency is converted into a frequency that can be digitally processed, then divided into two, converted into required signals, and then converted into the original frequency. By changing the phase of one signal and synthesizing both signals, any AM-AM, AM-P
M transfer characteristics can be realized.

[0009]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of one embodiment of the present invention. FIG.
The embodiment has an input terminal 1, a frequency converter 2, a local oscillator 3, a power distributor 4, and an A / D converter 5. Also, the output of the A / D converter 5 is branched into two, and each branch path has a ROM 6, 7, a D / A converter 8,
9, the band-pass filters 10 and 11 and the local oscillation signal of the local oscillator 3 are distributed to the frequency converters 12 and 13 via the power distributor 4 and frequency-converted. The frequency-converted signals of the two branch paths are connected to an output terminal 16 via a synthesizing circuit 15. A 90-degree phase shifter 14 is connected between the frequency converter 12 and the synthesizing circuit 15 on one branch path.
The ROMs 6 and 7 store digital values of various non-linear characteristics set in advance, and may be configured by an arithmetic circuit. Further, the bandpass filters 10 and 11 may be low-pass filters. According to this configuration, the RF input signal input from the input terminal 1 is converted into a frequency that can be digitally processed by the frequency converter and digitized by the A / D converter 5. The digitized signal is split into two and input independently to the ROM operation circuits 6 and 7, where the input digital value is preset in the ROM in accordance with the input / output characteristics of the compensated high-output amplifier. Is converted to a logical value of the non-linear characteristic in accordance with the table or program. The converted digital values are again converted into analog signals by the D / A converters 8 and 9 and the filters 10 and 11 and then converted by the frequency converters 13 and 14 to the same frequency as the input RF signal. The output of the frequency converter 12 in one branch is passed through a 90-degree phase shifter 15, the vector is synthesized by a synthesis circuit 16 with a phase difference of 90 degrees from the other branch, and output from an output terminal 17.

Here, the A / D converter, ROM, D /
In one non-linear circuit composed of an A-converter, an arbitrary AM-AM
Although it can have non-linear characteristics, in this configuration AM-
It is difficult to have PM nonlinear characteristics at the same time. However, here, the nonlinear characteristic required for the nonlinear compensation circuit is decomposed into two orthogonal components, and R
Since an AM-AM nonlinear circuit read from the OM is provided and one of the phases is shifted by 90 ° and combined, desired desired AM-AM nonlinear characteristics and AM-PM nonlinear characteristics can be obtained comprehensively. Becomes

The 90-degree phase shifter 14 and the synthesizing circuit 15
Can obtain the same function by replacing it with a 90-degree hybrid. Also, the phase shifter does not necessarily need to be at 90 degrees, and the phase difference between the two waves may be n × 180 ° (n = 0, plus or minus 1, plus or minus 2,...).

[0012]

As described above, according to the present invention, in order to obtain a nonlinear signal by two branched digital signals,
It has two A / D converters, a ROM, a D / A converter, and a filter, and combines both signals by shifting the phase of the signal of one of the circuits. AM-AM and AM-PM transfer characteristics having the following form can be realized. That is, the non-linear characteristic of the high-output amplifier can be compensated, and there is an effect that the third-order cross modulation and the high-order cross modulation generated by the non-linearity can be minimized.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional nonlinear compensation circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input terminal 2, 12, 13 Frequency converter 3 Local oscillator 4 Power divider 5 A / D converter 6, 7 ROM 8, 9 D / A converter 10, 11 Bandpass filter 14 90 degree phase shifter 15 Synthesis circuit 16 output terminal

Claims (1)

(57) [Claims] 1. A first frequency converter for converting the frequency of an input analog signal, a local oscillator for exciting a local oscillation signal to the first frequency converter, and an analog signal of the first frequency converter An analog-to-digital converter that converts the digital signal into a digital signal, and inputs each digital signal bifurcated from the analog-to-digital converter and performs numerical conversion to a plurality of memory values having a non-linear characteristic assumed in advance.
ROMs, two digital-to-analog converters for respectively converting the outputs of these ROMs to analog signals, filters respectively cascaded to these digital-to-analog converters, and the local oscillation signal. Two second frequency converters for converting the output of the filter to the frequency of the original analog signal, a synthesizing circuit for synthesizing the outputs of the second frequency converters, and the second frequency converter And a phase shifter inserted between any one of the above and the input of the synthesis circuit.