JP2002290161A - Predistortion compensation amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize a predistortion compensation amplifier to be used for the transmitting part of a radio base station, in a mobile communication system, and to reduce the cost. SOLUTION: The predistortion compensation amplifier is constituted as a delay unit 1 for delaying a high-frequency input signal, in such a way that an input signal is converted into a lower intermediate frequency by a mixer 11, delayed by a delay means 12 such as a transversal filter with 100 MHz surface acoustic waves, for example, and returned to be a high-frequency signal again by a mixer 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency distortion compensating amplifier, and more particularly to a pre-distortion distortion compensating amplifier used for a radio communication base station or the like.

[0002]

2. Description of the Related Art For example, a mobile communication system of a frequency band equal to or higher than the UHF band, for example, a mobile communication system of a wide band CDMA (WCDCM) system which is being put into practical use as one of radio access systems of a third generation mobile communication system. Various distortion compensation amplifiers have been proposed and put into practical use as distortion compensation techniques for suppressing distortion such as third-order intermodulation distortion due to nonlinear characteristics of a high-output transistor power amplifier of a base station.

A pre-distortion (PD) distortion compensating amplifier is one of them, and a pre-distortion circuit (or pre-distorter: pre-distortion generator) for changing the amplitude and phase is inserted before the amplifier and the amplifier is used. It is configured to cancel the generated distortion.

FIG. 1 is a structural example of a distortion compensating amplifier to which the present invention is applied, and is a specific example of an adaptive pre-distortion distortion compensating amplifier. In the figure, 1 is a delay device, 2 is a predistortion circuit, 21 is a variable attenuator, and 22 is a phase shifter. Reference numeral 3 denotes an amplifier to be subjected to distortion compensation, such as a transmission power amplifier. 4
Is an envelope detector, 5 is a memory storing a correction table, 51 is a variable attenuator table, 52 is a phase shifter table, 6 is a sideband power detector, 7 is an integrator, and 8 is a controller. .

The principle of operation of the adaptive predistortion distortion compensating amplifier shown in FIG. 1 will be described. The high-frequency input signal is input to the delay unit 1 and at the same time its envelope is detected by the envelope detector 4. The output of the delay unit 1 is adjusted in amplitude and phase by a predistortion circuit 2 and input to an amplifier 3. The distortion component generated by the pre-distortion circuit 2 and the distortion component generated by the amplifier 3 are cancelled, and the amplifier 3 outputs a high-frequency transmission signal whose distortion is compensated.

The cancellation of the distortion component depends on whether or not the nonlinearity of the pre-distortion circuit 2 and the amplifier 3 match well. Envelope information of the input signal obtained by the envelope detector 4 is collated in a correction table of a correction table memory 5, and correction data corresponding to the constantly changing envelope information is read out from each of the tables 51 and 52. Then, the attenuation amount and the phase shift amount of the variable attenuator 21 and the phase shifter 22 are controlled.

In order to improve the accuracy of the correction amount and optimize it, the power of a sideband component, which becomes adjacent channel leakage power of the power spectrum of the transmission output of the amplifier 3, is detected by a sideband power detector 6 and the integrator 7 Is integrated at regular time intervals and input to the controller 8. The controller 8 is configured to update the stored value of the table of the correction table memory 5 and to input an optimum correction signal to the pre-distortion circuit 2.

As described above, since a delay time occurs in the control processing of the predistortion circuit 2 based on the envelope information and the sideband power information of the transmission output for the input signal, the input signal is input to the predistortion circuit 2. Before the processing, the delay unit 1 delays the processing time by the same time as the above processing time.

FIG. 3 is a structural example of a conventional delay unit.
(A) is a side view of the coiled delay device 31, and (B) is a configuration diagram in which a linear amplifier 32 is connected to the coiled delay device 31. For example, when the delay time for a high frequency input signal of 2 GHz is 160 nsec, the length is about 30 m and the diameter is about 2 mm.
FIG. 3A shows a coaxial cable for a delay line called a bendable semi-rigid cable whose outer conductor is a copper pipe.
, Or a curve (not shown) that can be accommodated in the space of the housing.

Further, since the coiled delay device 31 as shown in FIG. 3A has an insertion loss of about 10 dB, a linear amplifier 32 is cascaded for gain correction as shown in FIG. In some cases, the delay unit 1 is used.

[0011]

The delay unit 1 in the conventional pre-distortion distortion compensating amplifier is a delay line formed by a coiled delay unit 31 and is expensive and has a large volume. On the other hand, the ratio occupied by the delay line is large, which hinders cost reduction and miniaturization of the amplifier.

Further, the linear amplifier 31 used to compensate for the insertion loss has a further problem of cost and volume in order to achieve good linear characteristics.

Further, in order to adjust the delay time, the length of the coil-shaped delay unit 31 is cut little by little, and each time it is necessary to repeat the measurement, there is a problem that the processing cost increases.

An object of the present invention is to provide a predistortion distortion compensating amplifier in which the size and cost of the conventional delay device are reduced and the size and cost of the distortion compensating amplifier are reduced.

[0015]

A predistortion distortion compensating amplifier according to the present invention includes a delay unit for delaying a high-frequency input signal for a predetermined time, and a predistortion circuit for adjusting the amplitude and phase of the output of the delay unit by using a correction signal. An amplifier that amplifies the output of the predistortion circuit to generate a transmission output; an envelope detector that detects an envelope of the high-frequency input signal and outputs envelope information; and an amplitude corresponding to the envelope information. A correction table memory storing the correction data of the phase and the table, a sideband power detector for detecting the power of a sideband signal serving as leakage power of the transmission output to an adjacent channel, and the sideband power detection. An integrator that integrates the output of the integrator for a certain period of time, and a controller that updates correction data in a correction table of the memory with the output of the integrator. A pre-distortion distortion compensating amplifier provided so that the amplitude and the phase of the signal input to the pre-distortion circuit are adjusted by the correction data read from the memory, and the distortion component generated in the amplifier is cancelled. And the delay device is:
A first mixer for converting the high-frequency input signal into an intermediate frequency having a lower frequency, delay means for delaying an output of the first mixer for a predetermined time, and a second means for converting the output to the frequency of the original high-frequency signal and outputting the same And a mixer.

[0016]

FIG. 2 shows an embodiment of a delay unit applied to a pre-distortion distortion compensating amplifier according to the present invention.
1 is a mixer, 12 is a delay circuit, 13 is a mixer, and 14 is a local oscillator. For example, an input signal in the 2 GHz band of the WCDMA system is converted into an intermediate frequency (IF) signal of several hundred MHz by the mixer 11, for example, and a surface acoustic wave (S
AW), the delay circuit 12 having a transversal filter configuration delays the signal by a predetermined delay time.
The signal is converted back to the original high-frequency signal and output.

As described above, the delay unit 1 of the present invention has a 2G
By converting a high frequency input signal in the Hz band to a low frequency IF, the surface acoustic wave device is used as a delay circuit,
This is for miniaturization and cost reduction.

The delay circuit 12 has a frequency of several hundred MHz.
As the delay means in the above, besides the above SAW filter,
Microstrip line using dielectric ceramic,
Alternatively, it can be realized by a dielectric coaxial resonator or the like.

FIG. 1 is a structural example of a pre-distortion distortion compensating amplifier using the delay unit 1 of the present invention. This embodiment uses the frequency conversion type delay unit 1 shown in FIG. 2, and operates as described in the prior art. Instead of a coiled delay unit of a semi-rigid cable as delay unit 1,
SAW resonators, dielectric microstrip lines, etc.
Since a delay element that can be easily realized in an intermediate frequency band of several hundred MHz is used, miniaturization and cost reduction are achieved.

[0020]

As described above in detail, by implementing the present invention, the pre-distortion distortion compensating amplifier can be downsized, the price can be reduced, the adjustment operation can be facilitated, and the efficiency can be increased. The effect is extremely large.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing an embodiment of a delay unit forming a main part of the present invention.

FIG. 3 is a structural example diagram of a conventional delay device.

[Explanation of symbols]

 Reference Signs List 1 delay device 2 predistortion circuit 3 amplifier 4 envelope detector 5 memory 6 sideband power detector 7 integrator 8 controller 11, 13 mixer 12 delay circuit 14 local oscillator 31 coiled delay device 32 linear amplifier

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Shoji Fujimoto 3-14-20 Higashinakano, Nakano-ku, Tokyo Stock Company Hitachi Kokusai Electric Inc. (72) Inventor Masaki Sudo 3-14-20 Higashinakano, Nakano-ku, Tokyo Stock F-term (reference) in Hitachi Kokusai Electric Co., Ltd.

Claims (1)

[Claims] 1. A delay unit for delaying a high-frequency input signal for a predetermined time, a pre-distortion circuit for adjusting an amplitude and a phase of an output of the delay unit by a correction signal, and amplifying an output of the pre-distortion circuit for transmission Amplifier, an envelope detector that detects an envelope of the high-frequency input signal and outputs envelope information, and a correction table storing correction data of amplitude and phase corresponding to the envelope information. A table memory, a sideband power detector for detecting power of a sideband signal serving as a leakage power of the transmission output to an adjacent channel, an integrator for integrating the output of the sideband power detector for a certain period of time, And a controller for updating the correction data of the correction table of the memory according to the output of the device. A pre-distortion distortion compensating amplifier, wherein a width and a phase are adjusted by correction data read from the memory, and a distortion component generated in the amplifier is canceled, wherein the delay unit converts the high-frequency input signal. It is composed of a first mixer for converting a low-frequency intermediate frequency, a delay means for delaying its output for a predetermined time, and a second mixer for converting its output to the frequency of the original high-frequency signal and outputting it. A pre-distortion distortion compensating amplifier characterized in that: