JP2006304229A - Nonlinear conversion circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonlinear conversion circuit which outputs a processed signal in which an input signal to a nonlinear amplifying circuit is processed so that out-of-band noise generated outside a band of a desired signal of an output signal of the nonlinear amplifying circuit is suppressed. <P>SOLUTION: A nonlinear conversion circuit 1a is provided with an amplitude adjusting circuit composed of an amplitude detection circuit 4 detecting an instantaneous value of an amplitude of an input signal, an amplitude level nonlinear conversion circuit 6a, a nonlinear function setting circuit 8a, a delay circuit 10a, an adjusting circuit 12, and a bandwidth restriction circuit 14a. The larger the gain compression is in the input/output characteristic of a nonlinear amplifying circuit to the instantaneous value of the amplitude of the input signal detected by the amplitude detection circuit 4, the larger the amplitude adjusting circuit the input signal is attenuated, and the amplitude adjusting circuit outputs the generated processed signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a nonlinear conversion circuit that outputs a processed signal obtained by processing an input signal to a nonlinear amplifier circuit so as to suppress out-of-band noise generated in an output signal of the nonlinear amplifier circuit.

  In a radio base station used in a mobile communication system such as a mobile phone or a PHS (Personal Handy phone System), the signal is amplified by an amplifier circuit in order to reach a mobile station at a remote location. In general, an input / output characteristic of an amplifier circuit is nonlinear. For this reason, even when the input signal (power) is increased, the amplifier circuit distorts the output signal (power) without increasing as much as the input signal due to gain compression.

  Therefore, the input signal to the amplifier circuit needs to consider the nonlinearity of the input / output characteristics of the amplifier circuit as described above. For example, a code division multiple access (CDMA) signal is a code-multiplexed signal, and therefore, when the phase component of the code of each signal matches, the amplitude sharply increases. Amplitude fluctuations become severe. When such a signal with a large fluctuation in amplitude is input to the amplifier circuit, the amplitude of the signal instantaneously reaches the saturation region of the amplifier circuit, and the output signal from the amplifier circuit is greatly distorted. Such distortion of the output signal becomes noise (hereinafter referred to as “out-of-band noise”) outside the desired signal band (hereinafter referred to as “out-of-band noise”) and interferes with adjacent channels and adjacent communication systems. End up.

  In general, in the case of a signal (input signal) before amplification, a distortion component outside the band can be suppressed to a low level by a band limiting filter (for example, a FIR (Finite Impulse Response) filter). However, since the amplified signal (output signal) has a high transmission power level, a band limiting filter cannot be used, and distortion components leak outside the output signal band (adjacent channel or adjacent communication system). (The power leaked to the adjacent channel is referred to as “Adjacent Channel Leakage Power (ACLP)”).

  Further, a predistortion type distortion compensation amplifier circuit is known as means for reducing distortion caused by nonlinearity of an amplifier circuit by processing a signal before amplification (Patent Documents 1 and 2). The predistortion type distortion compensation amplifier circuit is predistorted by predistorting the input signal so as to cancel the distortion component generated in the output signal due to the nonlinearity of the amplifier circuit. An amplifier circuit that outputs a signal.

Japanese Patent Laid-Open No. 11-154880 JP 2002-374129 A

  However, the predistortion type distortion compensation amplifier circuit shapes the waveform of the input signal so as to cancel the higher order mode component of the output signal, and the amplitude of the input signal as described above instantaneously falls in the saturation region of the amplifier circuit. It is not assumed that it will be reached, and the out-of-band noise associated therewith is not compensated. As another means, there is a limiter circuit that limits the amplitude above a certain value. However, since the limiter circuit includes a higher-order mode component in the waveform of the input signal, it increases the out-of-band noise generated outside the desired signal band.

  The present invention has been made to solve the above problems, and outputs a processed signal obtained by processing an input signal to the nonlinear amplifier circuit so as to suppress out-of-band noise generated in the output signal of the nonlinear amplifier circuit. An object is to realize a nonlinear conversion circuit.

  The present invention is a nonlinear conversion circuit that outputs a processed signal obtained by processing an input signal to a nonlinear amplifier circuit so as to suppress out-of-band noise generated outside a desired signal band of the output signal of the nonlinear amplifier circuit. The amplitude detection circuit that detects the instantaneous value of the amplitude of the input signal and the gain compression in the input / output characteristics of the nonlinear amplifier circuit with respect to the detected instantaneous value of the amplitude of the input signal, the greater the gain compression, the more the input signal is attenuated. And an amplitude adjustment circuit that outputs a processed signal.

  The amplitude adjusting circuit is preset with a nonlinear function for generating a correction signal having a larger amplitude as the gain compression in the input / output characteristics of the nonlinear amplifier circuit with respect to the detected instantaneous value of the amplitude of the input signal is larger. A correction signal generation circuit that outputs a correction signal generated based on a function; and a processing circuit that subtracts the correction signal from the input signal and outputs a processed signal generated thereby. desirable.

  The amplitude adjustment circuit includes a peak detection circuit that detects a timing at which the amplitude of the input signal instantaneously peaks, and gain compression in the input / output characteristics of the nonlinear amplifier circuit with respect to the instantaneous value of the detected amplitude of the input signal. The larger the value, the more the nonlinear function for generating an impulse signal with a larger amplitude is set in advance, the impulse signal generation circuit for outputting the impulse signal generated based on the nonlinear function, and the band limitation of the impulse signal in the desired signal band It is desirable that a band limiting circuit for outputting a correction signal generated thereby and a processing circuit for subtracting the correction signal from the input signal and outputting a processed signal generated thereby.

  ADVANTAGE OF THE INVENTION According to this invention, the nonlinear conversion circuit which outputs the processed signal which processed the input signal to a nonlinear amplifier circuit so that the out-of-band noise which generate | occur | produces in the output signal of a nonlinear amplifier circuit is suppressed is realizable.

Hereinafter, the nonlinear conversion circuits according to the first to third embodiments will be described in detail with reference to the drawings. FIG. 1 shows a configuration of a nonlinear conversion circuit 1 according to the present embodiment and a nonlinear amplification circuit 2 in which out-of-band noise generated in the output signal is suppressed by the processed signal output from the nonlinear conversion circuit 1. FIG. Note that a CDMA signal is input to the nonlinear conversion circuit 1 as an input signal. Further, although a modulation circuit and a frequency conversion circuit are inserted between the nonlinear conversion circuit 1 and the nonlinear amplification circuit 2, description thereof is omitted here. The nonlinear conversion circuit 1 shown in FIG. 1 outputs a processed signal obtained by processing an input signal to the nonlinear amplifier circuit 2 so as to suppress out-of-band noise generated outside the desired signal band of the output signal of the nonlinear amplifier circuit 2.
“First Embodiment”

  Hereinafter, the nonlinear conversion circuit according to the first embodiment will be described in detail. FIG. 2 is a diagram illustrating the configuration of the nonlinear conversion circuit according to the first embodiment. FIG. 3 is a diagram illustrating a state of signal processing in the nonlinear conversion circuit according to the first embodiment. In FIG. 2, a nonlinear conversion circuit 1a includes an amplitude detection circuit 4, an amplitude level nonlinear conversion circuit 6a, a nonlinear function setting circuit 8a, a delay circuit 10a, an adjustment circuit 12, and a band limiting circuit 14a that constitute the amplitude adjustment circuit. I have.

  In FIG. 1, a CDMA input signal is input to the nonlinear conversion circuit 1a. The input signal is shown in FIG. As described above, since the input signal of the CDMA system is a code-multiplexed signal, when the phase component of the code of each signal matches, the amplitude sharply increases and the amplitude fluctuates. For this reason, the amplitude of the input signal input to the nonlinear conversion circuit 1a varies as shown in FIG. The input signal input to the nonlinear conversion circuit 1a is branched and input to the amplitude detection circuit 4 and the delay circuit 10a.

  The amplitude detection circuit 4 oversamples the inputted input signal and detects an instantaneous value of the amplitude of the input signal. Note that the sampling frequency is desirably set to at least twice the chip rate of the spreading code for spreading the input signal. The instantaneous value of the amplitude of the input signal detected by the amplitude detection circuit 4 is input to the amplitude level nonlinear conversion circuit 6a.

  The amplitude level nonlinear conversion circuit 6a generates a correction coefficient for correcting the amplitude of the input signal based on the instantaneous value of the amplitude of the input signal and the nonlinear function set in the nonlinear function setting circuit 8a described later. When the amplitude of the input signal is adjusted by the generated correction coefficient, the nonlinear function increases the gain compression in the input / output characteristics of the nonlinear amplifier circuit 2 with respect to the instantaneous value of the amplitude of the input signal. It is set to greatly attenuate. The input / output characteristics of the nonlinear amplifier circuit 2 are shown in FIG. By inputting the processed signal generated by such a nonlinear function to the nonlinear amplifier circuit 2, out-of-band noise generated outside the desired signal band of the output signal of the nonlinear amplifier circuit 2 can be suppressed. This will be described later.

  Then, the adjustment circuit 12 corrects the amplitude of the input signal delayed by the delay circuit 10a with the generated correction coefficient. Note that the delay circuit 10a is set so that the input signal is delayed by the sum of the time for detecting the amplitude of the input signal by the amplitude detection circuit 4 and the time for generating the correction coefficient by the amplitude level nonlinear conversion circuit 6a. ing.

  An adjustment signal generated by the adjustment circuit 12 is shown in FIG. Therefore, the adjustment circuit 12 greatly attenuates the input signal as the gain compression in the input / output characteristics of the nonlinear amplifier circuit 2 with respect to the instantaneous value of the amplitude of the input signal detected by the amplitude detection circuit 4 is increased, and is generated thereby. An adjustment signal can be output. Then, the band limiting circuit 14a band-limits the adjustment signal generated by the adjustment circuit 12 to the desired signal band, and outputs the processed signal generated thereby. The processed signal generated by the band limitation is shown in FIG.

  In the processed signal generated in this way, a sharp increase in amplitude and a severe fluctuation in amplitude are suppressed. For this reason, when the processed signal is input to the nonlinear amplifier circuit 2, the signal amplitude is prevented from instantaneously reaching the saturation region of the nonlinear amplifier circuit 2. For this reason, the nonlinear conversion circuit 1 according to the present embodiment can suppress out-of-band noise that occurs outside the desired signal band of the output signal of the nonlinear amplifier circuit 2. In addition, since the processed signal is band-limited by the band-limiting circuit 14a, the occurrence of distortion due to higher-order mode components can be suppressed. Furthermore, the above-described nonlinear function may be set to a more optimal one in consideration of the temperature characteristics of the input / output characteristics of the nonlinear amplifier circuit 2, the higher-order mode characteristics, and variations among products.

As described above, the nonlinear conversion circuit according to the first embodiment includes the amplitude detection circuit that detects the instantaneous value of the amplitude of the input signal, and the input of the nonlinear amplifier circuit with respect to the detected instantaneous value of the amplitude of the input signal. As the gain compression in the output characteristics increases, the input signal is greatly attenuated, and the amplitude adjustment circuit that outputs the processed signal generated thereby is generated, so that the output signal of the nonlinear amplifier circuit is generated outside the desired signal band. A processed signal obtained by processing the input signal to the nonlinear amplifier circuit so as to suppress the out-of-band noise can be output. Needless to say, the nonlinear conversion circuit according to the present embodiment can also be applied to signals other than the CDMA system as input signals.
“Second Embodiment”

  Hereinafter, the nonlinear conversion circuit according to the second embodiment will be described in detail. FIG. 5 is a diagram illustrating a configuration of a nonlinear conversion circuit according to the second embodiment. FIG. 6 is a diagram illustrating a state of signal processing in the nonlinear conversion circuit according to the second embodiment. In FIG. 5, a non-linear conversion circuit 1b includes an amplitude detection circuit 4, an amplitude level non-linear conversion circuit 6b, a non-linear function setting circuit 8b, a delay circuit 10b, a subtraction circuit 16, and a band limiting circuit 14b that constitute an amplitude adjustment circuit. I have.

  The input signal input to the nonlinear conversion circuit 1b is branched and input to the amplitude detection circuit 4 and the delay circuit 10b. The amplitude detection circuit 4 detects an instantaneous value of the amplitude of the input signal. The instantaneous value of the amplitude of the input signal detected by the amplitude detection circuit 4 is input to the amplitude level nonlinear conversion circuit 6b. The amplitude level nonlinear conversion circuit 6b generates a correction signal for correcting the amplitude of the input signal based on the instantaneous value of the amplitude of the input signal and the nonlinear function set in the nonlinear function setting circuit 8b described later.

  The non-linear function is a non-linear amplifying circuit for the instantaneous value of the amplitude of the input signal detected by the amplitude detecting circuit 4 when the generated correction signal is subtracted from the input signal delayed by the delay circuit 10b described later. The input signal is set to be attenuated more as the gain compression in the input / output characteristic 2 is larger. The band limiting circuit 14b limits the correction signal generated by the amplitude level non-linear conversion circuit 6b to the desired signal band, and outputs a band-limited correction signal.

  The subtracting circuit 16 subtracts the correction signal band-limited by the band-limiting circuit 14b from the input signal delayed by the delay circuit 10b. The delay circuit 10b combines the time for detecting the amplitude of the input signal by the amplitude detection circuit 4, the time for generating the correction signal by the amplitude level nonlinear conversion circuit 6b, and the time for band limiting by the band limiting circuit 14b. The input signal is set to be delayed by time.

  As a result, the subtraction circuit 16 attenuates the input signal more greatly as the gain compression in the input / output characteristics of the nonlinear amplifier circuit 2 is larger than the instantaneous value of the amplitude of the input signal detected by the amplitude detection circuit 4. The processed signal generated by is output. The processed signal generated by the subtraction circuit 16 is shown in FIG.

  In the processed signal generated in this way, a sharp increase in amplitude and a severe fluctuation in amplitude are suppressed. For this reason, when the processed signal is input to the nonlinear amplifier circuit 2, the amplitude of the signal is prevented from instantaneously reaching the saturation region of the nonlinear amplifier circuit 2, and the output signal of the nonlinear amplifier circuit 2 is out of the desired signal band. Can be suppressed. In addition, since the processed signal is band-limited by the band-limiting circuit 14b, the occurrence of distortion due to higher-order mode components can be suppressed.

As described above, in the nonlinear conversion circuit according to the second embodiment, the larger the gain compression in the input / output characteristics of the nonlinear amplifier circuit with respect to the instantaneous value of the amplitude of the detected input signal, A non-linear function for generating a correction signal having a large amplitude is set in advance, a correction signal generating circuit for outputting a correction signal generated based on the non-linear function, and the correction signal is subtracted from the input signal, thereby generating A processed signal for processing the input signal to the nonlinear amplifier circuit so as to suppress out-of-band noise generated outside the desired signal band of the output signal of the nonlinear amplifier circuit. Can be output.
“Third Embodiment”

  Hereinafter, the nonlinear conversion circuit according to the third embodiment will be described in detail. FIG. 7 is a diagram illustrating a configuration of a nonlinear conversion circuit according to the third embodiment. FIG. 8 is a diagram illustrating a state of signal processing in the nonlinear conversion circuit according to the third embodiment. In FIG. 7, a nonlinear conversion circuit 1c includes an amplitude detection circuit 4, a nonlinear function setting circuit 8c, a delay circuit 10c, a band limiting circuit 14c, a subtraction circuit 16, a peak detection circuit 18, and an impulse generation circuit 20 constituting an amplitude adjustment circuit. And.

  The input signal input to the nonlinear conversion circuit 1c is branched and input to the amplitude detection circuit 4 and the delay circuit 10c. The amplitude detection circuit 4 detects an instantaneous value of the amplitude of the input signal. The instantaneous value of the amplitude of the input signal detected by the amplitude detection circuit 4 is input to the peak detection circuit 18.

  The peak detection circuit 18 detects the timing at which the amplitude of the input signal instantaneously peaks from the instantaneous value of the amplitude of the input signal. Note that peak detection can be performed by three-point comparison of instantaneous values of the amplitude of the input signal and differential calculation of the envelope. The peak of the amplitude of the input signal detected by the peak detection circuit 18 is shown in FIG.

  The impulse generation circuit 20 generates an impulse signal at a timing when the amplitude of the detected input signal instantaneously peaks according to the nonlinear function set in the nonlinear function setting circuit 8c. This non-linear function is an instantaneous function of the amplitude of the input signal detected by the amplitude detection circuit 4 when the correction signal generated by the band limiting circuit 14c described later is subtracted from the input signal delayed by the delay circuit 10c described later. With respect to the value, the larger the gain compression in the input / output characteristics of the nonlinear amplifier circuit 2, the greater the attenuation of the input signal.

  Therefore, the impulse generation circuit 20 generates an impulse signal based on a nonlinear function that generates an impulse signal having a larger amplitude as the gain compression in the input / output characteristics of the nonlinear amplifier circuit with respect to the detected instantaneous value of the amplitude of the input signal is larger. And output this. An impulse signal generated by the impulse generation circuit 20 is shown in FIG.

  The band limiting circuit 14c band-limits the input impulse signal with the desired signal band, and outputs a correction signal generated thereby. FIG. 8D shows a correction signal generated by the band limiting circuit 14c.

  The subtracting circuit 16 subtracts the correction signal generated by the band limiting circuit 14c from the input signal delayed by the delay circuit 10c. The delay circuit 10c includes a time for detecting the amplitude of the input signal by the amplitude detection circuit 4, a time for peak detection by the peak detection circuit 18, a time for generating an impulse signal by the impulse generation circuit, and a band limiting circuit 14c. The input signal is set to be delayed by the sum of the time required for band limitation and the total time.

  As a result, the subtraction circuit 16 attenuates the input signal as the gain compression in the input / output characteristics of the nonlinear amplification circuit 2 with respect to the instantaneous value of the amplitude of the input signal detected by the amplitude detection circuit 4 increases, and is generated thereby. The processed signal is output. The processed signal generated by the subtracting circuit 16 is shown in FIG.

  In the processed signal generated in this way, a sharp increase in amplitude and a severe fluctuation in amplitude are suppressed. For this reason, when the processed signal is input to the nonlinear amplifier circuit 2, the amplitude of the signal is prevented from instantaneously reaching the saturation region of the nonlinear amplifier circuit 2, and the output signal of the nonlinear amplifier circuit 2 is out of the desired signal band. Can be suppressed. Further, since the processed signal is band-limited by the band-limiting circuit 14c, the occurrence of distortion due to the higher-order mode component can be suppressed.

  As described above, in the nonlinear conversion circuit according to the third embodiment, the amplitude adjustment circuit detects a timing at which the amplitude of the input signal instantaneously peaks, and the detected input signal. As the gain compression in the input / output characteristics of the nonlinear amplifier circuit with respect to the instantaneous value of the amplitude is larger, a nonlinear function that generates an impulse signal having a larger amplitude is set in advance, and the impulse signal that is generated based on the nonlinear function is output. A signal generation circuit, a band limiting circuit for limiting the band of the impulse signal in the desired signal band, and outputting a correction signal generated thereby, and a process generated by subtracting the correction signal from the input signal Out-of-band generated outside the desired signal band of the output signal of the nonlinear amplifier circuit It is possible to output a processed signal obtained by processing the input signal to the nonlinear amplification circuit so as to suppress the sound.

It is a figure showing the structure of the nonlinear transformation circuit 1 which concerns on this embodiment, and the nonlinear amplification circuit 2 by which the out-of-band noise is suppressed by the processed signal output from the nonlinear transformation circuit. It is a figure showing the structure of the nonlinear conversion circuit which concerns on 1st Embodiment. It is a figure showing the mode of the signal processing in the nonlinear conversion circuit which concerns on 1st Embodiment. FIG. 3 is a diagram showing input / output characteristics of a nonlinear amplifier circuit 2. It is a figure showing the structure of the nonlinear conversion circuit which concerns on 2nd Embodiment. It is a figure showing the mode of the signal processing in the nonlinear conversion circuit which concerns on 2nd Embodiment. It is a figure showing the structure of the nonlinear conversion circuit which concerns on 3rd Embodiment. It is a figure showing the mode of the signal processing in the nonlinear conversion circuit which concerns on 3rd Embodiment.

Explanation of symbols

  1, 1a, 1b, 1c nonlinear conversion circuit, 2 nonlinear amplification circuit, 4 amplitude detection circuit, 6a, 6b amplitude level nonlinear conversion circuit, 8a, 8b, 8c, nonlinear function setting circuit, 10a, 10b, 10c delay circuit, 12 Adjustment circuit, 14a, 14b, 14c Band limiting circuit, 16 subtraction circuit, 18 peak detection circuit, 20 impulse generation circuit.

Claims (3)

A non-linear conversion circuit that outputs a processed signal obtained by processing an input signal to the non-linear amplification circuit so as to suppress out-of-band noise generated outside a desired signal band of the output signal of the non-linear amplification circuit,
An amplitude detection circuit for detecting an instantaneous value of the amplitude of the input signal;
An amplitude adjustment circuit that attenuates the input signal and outputs a processed signal generated thereby, as the gain compression in the input / output characteristics of the nonlinear amplifier circuit with respect to the instantaneous value of the amplitude of the detected input signal is larger,
A non-linear conversion circuit comprising: The nonlinear conversion circuit according to claim 1,
The amplitude adjustment circuit includes:
As the gain compression in the input / output characteristics of the nonlinear amplifier circuit with respect to the detected instantaneous value of the amplitude of the input signal is larger, a nonlinear function that generates a correction signal having a larger amplitude is set in advance, and the correction generated based on the nonlinear function A correction signal generation circuit for outputting a signal;
A processing circuit that subtracts the correction signal from the input signal and outputs a processed signal generated thereby;
A non-linear conversion circuit comprising: The nonlinear conversion circuit according to claim 1,
The amplitude adjustment circuit includes:
A peak detection circuit for detecting the timing at which the amplitude of the input signal instantaneously peaks;
As the gain compression in the input / output characteristics of the nonlinear amplifier circuit with respect to the detected instantaneous value of the amplitude of the input signal is larger, a nonlinear function for generating an impulse signal having a larger amplitude is set in advance, and the impulse generated based on the nonlinear function is set. An impulse signal generation circuit for outputting a signal;
A band limiting circuit that limits the impulse signal in the desired signal band and outputs a correction signal generated thereby;
A processing circuit that subtracts the correction signal from the input signal and outputs a processed signal generated thereby;
A non-linear conversion circuit comprising:

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