JP2003273663A - Predistortion type amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a predistortion type amplifier in which distortion compensation performance is improved by compensating a fine time delay difference based on an analog factor. <P>SOLUTION: The predistortion type amplifier has a means for operating a correlation value from a baseband input signal and a demodulated signal and generating a signal to be increased/decreased corresponding to the time delay quantity of said demodulated signal, and a means for controlling the output signal of a voltage controlled oscillator 15 based upon said generated signal. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifying apparatus, and more particularly to a radio transmitter, and more particularly to a predistortion type amplifying apparatus that enables a power amplifier to operate with low distortion and high efficiency.

[0002]

2. Description of the Related Art In recent years, in an amplification device mounted on a mobile communication base station or the like, in order to achieve downsizing and cost reduction of the device,
It is necessary to operate the power amplifier with a large output that is as power efficient as possible.

However, during high-power operation, the influence of the nonlinear input / output characteristics becomes large, so that nonlinear distortion occurs outside the transmission frequency band and becomes a disturbing wave for other systems. The amount generated is strictly regulated by the Radio Law, and as a result, high-power operation is difficult. In order to solve this problem, various techniques have been devised which are so-called distortion compensation, which reduce the amount of non-linear distortion generated by highly linearizing the power amplifier to enable high output operation.

As a conventional example of the distortion compensation technique, for example, a digital predistortion type distortion compensator disclosed in Japanese Patent Laid-Open No. 10-145146 has been devised. The above-mentioned conventional technique obtains power from an input quadrature baseband signal,
The distortion compensation coefficient is calculated by an approximate expression for distortion compensation using the value as a parameter, and the distortion compensation is performed by performing a complex operation on the input quadrature baseband signal.

[0005]

According to the above prior art, the approximate expression for distortion compensation is calculated based on the difference between the input quadrature baseband signal (digital signal) and the digital quadrature base signal obtained by AD conversion. Therefore, a minute time delay difference based on an analog factor occurs. Therefore, this acts as a disturbance on the device, resulting in deterioration of distortion compensation performance.

An object of the present invention is to provide a predistortion type amplifying device (radio transmitter) capable of compensating for a minute time delay difference based on an analog factor and improving distortion compensation performance.

[0007]

In order to achieve the above object, a predistortion type amplifying device according to the present invention comprises:
A predistortion-type amplifying device for compensating for distortion generated in a transmitting section by controlling an output signal of a voltage controlled oscillator input to an AD converter of a demodulating section, wherein a correlation value is obtained from a baseband input signal and a demodulated signal. And means for generating a signal that increases or decreases according to the time delay amount of the demodulated signal, and means for controlling the output signal of the voltage controlled oscillator based on the signal.

More specifically, the predistortion type amplifying apparatus according to the present invention controls the output signal of the voltage controlled oscillator input to the AD converter of the demodulation section, thereby allowing the first DA converter and the frequency mixer to operate. A predistortion-type amplifier for compensating for distortion generated in a transmission section including a power amplifier, the predistortion type calculating a reverse distortion amount of the distortion based on a baseband input signal and an output signal of the AD converter. A toter, a distributor for extracting the output signal of the transmitting unit by branching, a frequency mixer for converting the output signal of the distributor to a frequency in the baseband, and an AD for converting the output signal of the frequency mixer into a digital signal. A converter; and a first delay device that delays the baseband input signal by an integer multiple of the output signal of the voltage controlled oscillator and outputs the delayed signal.
A second delay device for synchronizing the output signal of the AD converter with the output signal of the voltage controlled oscillator; and a first delay device based on the output signal of the first delay device and the output signal of the second delay device. , A second processing unit for calculating a second correlation signal and subtracting the first and second correlation signals, a second DA converter for converting an output signal of the processing unit into an analog signal, Two
And a filter for smoothing the output signal of the DA converter, and controlling the output signal of the voltage controlled oscillator by the output voltage of the filter.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.
A detailed description will be given with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a radio communication device to which a predistortion type amplification device according to the present invention is applied.

A wireless communication device (for example, a wireless base station) includes an interface unit 10 connected to a public switched telephone network or a packet switched data network, and a baseband unit 1.
1, a radio frequency (RF) unit 12, and an antenna 13
It consists of and.

The RF unit 12 includes a predistortion type amplifying device (radio transmitter) 14 according to the present invention, a demultiplexer 15 for distributing signals, and a reception filter for limiting a band of an output signal from the demultiplexer 15. 16 and reception filter 1
A reception amplifier 17 that amplifies the output signal from 6 and a quadrature demodulator 18 that demodulates the output signal from the reception amplifier 17.
It is composed of an AD converter 19 for converting an output (demodulation) signal from the quadrature demodulator 18 into a digital signal.

FIG. 2 is a block diagram showing the configuration of the first embodiment of the predistortion type amplifying device 14.

Reference numeral 101 is a predistorter, and 102 is
DA converter 103, frequency mixer 104, and power amplifier 10
5, a demodulator 106 including a divider 107, a frequency mixer 108, and an AD converter 109, 110 and 111 delay devices, 112 subtractor, and 113 DA. The converter 114 is a filter 115
Is a voltage controlled oscillator (VCO), 116 is a delay device 11
7, 118, the first and second correlators 119 and 120, and the subtractor 125 are shown. or,
The first correlator 119 includes a multiplier 121 and an integrator 123. The second correlator 120 is composed of a multiplier 122 and an integrator 124.

In the predistortion type amplifying device 14 configured as described above, the AD converter 1 of the demodulating section 106 is used.
09 operates in synchronization with the clock signal CK2 from the voltage controlled oscillator (VCO) 115. Although not shown, other digital signal processing devices (predistorter 101, delay device 111, arithmetic processing unit 116) are
It operates in synchronization with the clock signal CK1.

In the transmitting section 102 of this embodiment, the influence of the nonlinear input / output characteristic becomes large when the power amplifier 105 operates at a high output, so that nonlinear distortion occurs outside the transmission frequency band. The predistorter 101 calculates the inverse distortion amount of the nonlinear distortion based on the signal output from the subtractor 112 (residual signal between the demodulated signal and the output signal of the delay unit 118) and adds it to the baseband digital input signal. Output. The DA converter 103 included in the transmitter 102 converts the digital output signal from the predistorter 101 into an analog signal. The frequency mixer 104 frequency-converts the output signal from the DA converter 103 into a radio frequency band. The power amplifier 105 amplifies the power of the signal whose frequency has been converted by the frequency mixer 104.

The distributor 107 that constitutes the demodulation unit 106 is
By branching a part of the output signal from the power amplifier 105,
Output to the frequency mixer 108. Frequency mixer 108
Converts the output from the distributor 107 into a baseband frequency. The AD converter 109 converts the analog signal frequency-converted by the frequency mixer 108 into a digital signal.

Here, the transmitting unit 102 and the demodulating unit 106 are provided.
It is assumed that the time delay amount generated at is nT + t1. T is a unit sampling period of the digital signal processing system, and t1 is a minute delay less than T. As described above, the AD converter 109 included in the demodulation unit 106 operates in synchronization with the clock signal CK2 different from the clock signal CK1 for operating the other digital signal processing systems. Therefore, it is necessary to synchronize the AD-converted signal with the clock signal CK1. When the output of the AD converter 109 is resampled by the delay device 110, it is assumed that the output frequency of the voltage controlled oscillator 115 is the same as CK1 and the phase is shifted by t2. t2 is less than the unit sampling period T. At this time, as shown in FIG. 3, the AD converter and the delay device cause a time delay of 2T + t2.
Therefore, the total delay time is (2 + n) T + t1 + t2. Here, if τ = t1 + t2, τ becomes a value between 0 and 2T.

Of the total delay time, the delay time ((2 + n) T) that is an integral multiple of the sampling period T is the delay unit 11
A 1 allows the input signal to be corrected by delaying it by (2 + n) T samples.

Next, regarding the small delay τ = t1 + t2,
The method of compensation will be described. Here, the delay device 111
Will be referred to as a reference signal. This reference signal is input to the first correlator 119. Further, the reference signal is delayed by time T by delay devices 117 and 118, respectively, and output to the second correlator 120. First correlator 1
19 is composed of a multiplier 121 and an integrator 123,
A correlation (correlation signal) is obtained from the reference signal and the demodulated signal output from the delay device 110 according to the following equation (1).

[0021]

[Equation 1] Similarly, the second correlator 120 outputs the demodulated signal and the delay 1
A correlation signal is obtained from the output signal of 18. Subtractor 125
Subtracts the correlation signals obtained by the first and second correlators 119 and 120 and outputs the subtracted signals to the DA converter 113.
Therefore, the subtractor 125 can obtain a signal having a polarity and a magnitude corresponding to the magnitude of the delay time of the demodulated signal with respect to the reference signal.

FIG. 4 is a diagram showing the relationship between the delay time τ and the correlation.

In a normal radio design, even if distortion compensation is not performed, the nonlinear distortion power is about the transmission power.
-30dB or less. Therefore, the demodulated signal can be regarded as a waveform very similar to the reference signal. Therefore, in order to clarify the explanation, FIG. 5 shows a case where the demodulated signal and the reference signal have the same waveform and a time delay exists.

Here, in general, the following equation (2) holds for the autocorrelation R relating to a certain waveform. Therefore, τ = 0
At, the autocorrelation takes the maximum value.

[0025]

[Equation 2] Using the above mathematical properties, as shown in FIG. 5, when the delay of the demodulated signal with respect to the reference signal is small, the correlation between the demodulated signal and the reference signal becomes strong, so that the output of the first correlator becomes large. Become. On the contrary, when the delay of the demodulation signal is large with respect to the reference signal, the correlation between the demodulation signal and the output of the second delay device becomes strong, so that the output of the second correlator becomes large. When the demodulated signal is delayed by exactly one sampling period T with respect to the reference signal, the outputs of the first correlator and the second correlator are equal. That is, by subtracting the output of the first correlator from the output of the second correlator, a signal having a polarity and a magnitude corresponding to the magnitude of the delay time of the demodulated signal with respect to the reference signal can be obtained.

The above signal is input to the DA converter 113. The DA converter 113 converts the digital output signal from the subtractor 125 into an analog signal and outputs it to the filter 114. The filter 114 smoothes the output signal from the DA converter 113. The voltage controlled oscillator 115 is controlled by the output voltage of the filter 114, and the demodulation unit 106
The clock signal CK2 is output to the AD converter 109 that constitutes the. Therefore, the output signal of the first correlator and the second correlator
The clock signal CK2 can be controlled so that the difference from the output signal of the correlator becomes zero. In this embodiment, τ
Since T = T, if a signal obtained by delaying the reference signal by T is taken out, this signal has the maximum correlation with the demodulated signal, and a time-synchronized state can be realized. Therefore, according to the present embodiment, the time delay between the reference signal and the demodulated signal can be matched even for a minute delay of less than one sample.

FIG. 5 is a block diagram showing the configuration of the second embodiment of the predistortion type amplifying device 14.

In the second embodiment, in the arithmetic processing unit 116, a multiplier 202 and an integrator 203 are provided after the subtractor 201.
And the arithmetic processing unit 1 in the first embodiment.
It is equivalent to 16 functions. In the second embodiment, the number of multipliers and the number of integrators can each be reduced by one as compared with the first embodiment. In the present embodiment, the multiplier 20
It is also possible to provide the DA converter 113 in the second stage, and the integrator 203 in the latter stage of the DA converter. However,
In this case, the integrator 203 will be realized by an analog circuit.

FIG. 6 is a block diagram showing the configuration of the third embodiment of the predistortion type amplifying device 14.

In the first and second embodiments, the case where the input signal is the real signal has been described, but in the third embodiment, the predistortion type amplification when the complex input signal having the real part and the imaginary part is input. The structure of the apparatus 14 is shown.

In the third embodiment, the conjugate processor 12 for computing the complex conjugate of the complex demodulated signal in the computation processing unit 116.
6 is provided, and between the multipliers 121 and 122 and the integrators 123 and 124 in the first and second correlators 119 and 120,
Real part calculators 127 and 128 for discarding the real part of the correlation signal
Is provided. In this case, the correlation signal is calculated by the following equation (3).

[0032]

[Equation 3] It should be noted that, in general, the real part and the imaginary part of the complex signal may be considered to be uncorrelated, and the imaginary part of the correlated signal may be ignored.

[0033]

As described above, according to the present invention, it is possible to compensate for a minute time delay difference due to an analog factor, so that the distortion compensation performance can be improved.

Further, according to the present invention, it is possible to operate the power amplifier with high efficiency, so that it is possible to reduce the size, power consumption and cost of a wireless communication device such as a wireless base station.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a wireless communication device to which a predistortion type amplifier device according to the present invention is applied.

FIG. 2 shows the first of the predistortion-type amplification device 14.
The block diagram which shows the structure of an Example.

FIG. 3 is a diagram showing output waveforms of an AD converter 109 and a delay device 110.

FIG. 4 is a diagram showing a relationship between delay time τ and correlation.

FIG. 5 is a second part of the predistortion-type amplification device 14.
The block diagram which shows the structure of an Example.

FIG. 6 is a third part of the predistortion type amplifying device 14.
The block diagram which shows the structure of an Example.

[Explanation of symbols]

1 ... Wireless communication device, 10 ... Interface unit, 11
… Baseband unit, 12… RF unit, 13…
Antenna, 14 ... Radio transmitter, 15 ... Demultiplexer, 16 ... Reception filter, 17 ... Reception amplifier, 18 ... Quadrature demodulator, 1
9 ... AD converter, 101 ... Predistorter, 10
2 ... Transmission unit, 103, 113 ... DA converter, 104, 10
8 ... Frequency mixer, 105 ... Power amplifier, 106 ... Demodulator, 107 ... Distributor, 109 ... AD converter, 110, 11
1, 117, 118 ... Delay device, 112, 125, 201
... Subtractor, 114 ... Filter, 115 ... Voltage controlled oscillator (VCO), 116 ... Arithmetic processing unit, 119 ... First correlator, 120 ... Second correlator, 121, 122, 202 ... Multiplier, 123, 124, 203 ... integrator, 126 ... conjugate calculator, 127, 128 ... real part calculator.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shohei Murakami             216 Totsuka Town, Totsuka Ward, Yokohama City, Kanagawa Prefecture             Ceremony Company Hitachi Ltd. Communication Division (72) Norie Hara             216 Totsuka Town, Totsuka Ward, Yokohama City, Kanagawa Prefecture             Ceremony Company Hitachi Ltd. Communication Division (72) Inventor Toshiaki Kurokawa             216 Totsuka Town, Totsuka Ward, Yokohama City, Kanagawa Prefecture             Ceremony Company Hitachi Ltd. Communication Division (72) Inventor Keiichi Kitamura             216 Totsuka Town, Totsuka Ward, Yokohama City, Kanagawa Prefecture             Ceremony Company Hitachi Ltd. Communication Division F term (reference) 5J090 AA01 AA41 CA21 FA20 GN03                       GN07 KA00 KA15 KA26 KA31                       KA32 KA34 KA41 KA55 KA68                       MA20 SA14 TA01 TA06                 5J500 AA01 AA41 AC21 AF20 AK00                       AK15 AK26 AK31 AK32 AK34                       AK41 AK55 AK68 AM20 AS14                       AT01 AT06                 5K060 BB07 CC04 HH06 HH26 LL24

Claims (4)

[Claims] 1. A predistortion type amplifying device for compensating for distortion generated in a transmitting part by controlling an output signal of a voltage controlled oscillator inputted to an AD converter of a demodulating part, the baseband input signal and a demodulating device. A means for calculating a correlation value from the signal and generating a signal that increases or decreases according to the time delay amount of the demodulated signal; and means for controlling the output signal of the voltage controlled oscillator based on the signal. A predistortion type amplification device. 2. Compensation for distortion generated in a transmission section including a first DA converter, a frequency mixer and a power amplifier by controlling an output signal of a voltage controlled oscillator input to an AD converter of a demodulation section. A predistortion type amplification device, wherein a predistorter for calculating an inverse distortion amount of the distortion based on a baseband input signal and an output signal of the AD converter, and an output signal of the transmitter are branched and taken out. Distributor, a frequency mixer for converting the output signal of the distributor to a frequency in the baseband, an AD converter for converting the output signal of the frequency mixer into a digital signal, and the voltage-controlled oscillator for the baseband input signal A first delayer that delays the output signal by an integer multiple and outputs the second delay signal, and a second delayer that synchronizes the output signal of the AD converter with the output signal of the voltage controlled oscillator. Delay unit, and based on the output signal of the first delay unit and the output signal of the second delay unit, first and second correlation signals are calculated, and the first and second correlation signals are subtracted. And a second DA converter that converts an output signal of the arithmetic processing unit into an analog signal, and a filter that smoothes an output signal of the second DA converter. A pre-distortion type amplifying device, wherein an output signal of the voltage controlled oscillator is controlled by an output voltage. 3. A first correlator for calculating a temporal correlation between an output signal of the first delay device and an output signal of the second delay device, wherein the arithmetic processing unit includes the first delay device. Second correlator for calculating the temporal correlation between the signal obtained by delaying the output signal of the correlator by a predetermined time and the output signal of the second delay device, and the output signal of the first correlator and the second correlation The pre-distortion type amplifying device according to claim 2, further comprising a subtractor that calculates a difference between the output signal of the pre-distortion device and the output signal of the pre-distortion device. 4. The predistortion type amplifying apparatus according to claim 2, wherein each of the first and second correlators is composed of a multiplier and an integrator.