JPH07336154A - Feedforward amplifier - Google Patents

Abstract

PURPOSE:To improve the distortion compensation amount of a feedforward amplifier which is a kind of a multi-frequency common amplifier. CONSTITUTION:Isolators 6 and 12 for which amplitude frequency characteristics over the entire use frequency band are approximated to the output frequency characteristics of a main amplifier 4 and an auxiliary amplifier 10 are respectively inserted to the delay line 5 of a distortion detection circuit 20 and the delay line 11 of a distortion elimination circuit 30. Thus, extraction and cancellation, in the case of synthesizing two pieces of input in power synthesizers 7 and 13 and performing distortion detection and distortion elimination are improved over the entire band.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feedforward amplifier which is used as a base station or a repeater of a mobile communication system such as a car telephone and which is one of high linear amplifiers for simultaneously amplifying multi-frequency signals. , The improvement of the suppression amount of the distortion detection circuit and the distortion removal circuit.

[0002]

2. Description of the Related Art A base station and a radio relay device in an 800 MHz band car telephone system or the like are provided with a multi-frequency common amplifier for simultaneously amplifying multi-frequency signals. This multi-frequency common amplifier is required to have sufficiently good linearity in order to reduce intermodulation distortion as much as possible, and a compact and highly linear amplifier is used. One of them is a self-adjusting feed forward amplifier (SAFF-A: Self-Ad).
Justing Feed-Forward Ampl
is a common amplifier that compensates for intermodulation distortion and noise generated in the main amplifier by self-adjustment. This feedforward amplifier is composed of a distortion detection circuit and a distortion removal circuit, detects a distortion component other than the input signal with a distortion detection circuit including a main amplifier that is an amplifier to be compensated, and detects the detected distortion component (error component). Is input to a distortion removal circuit including an auxiliary amplifier (error amplifier) to amplify the distortion component, and then is anti-phase combined with the multi-frequency input signal to cancel the distortion component.

FIG. 3 is a block diagram of a conventional self-adjusting feedforward amplifier. In the figure, 1 is a power divider for distributing an input signal, 2 is a variable attenuator, 3 is a variable phase shifter, 4 is a main amplifier, 5 is a delay line, 7 is a power combiner,
8 is a variable attenuator, 9 is a variable phase shifter, 10 is an auxiliary amplifier,
Reference numeral 11 is a delay line, and 13 is a power combiner. Reference numeral 20 is a distortion detection circuit, and 30 is a distortion removal circuit. The multi-frequency input signal is
One multi-frequency signal input to the power distributor 1 and branched into two is amplified by the main amplifier 4 via the variable attenuator 2 and the variable phase shifter 3. The output includes a distortion (error) component generated at the time of amplification, is input to the terminal of the power combiner 7, is branched and output by the power distributor 1, and is input to the terminal of the power combiner 7 via the delay line 5. The distortion component is detected from the terminal after being subjected to reverse phase synthesis with the multi-frequency input signal. Power combiner 7
The multi-frequency input signal output from the terminal of
It is input to the terminal of the power combiner 13 via 1. The distortion component output from the terminal of the power combiner 7 is amplified by the auxiliary amplifier 10 via the variable attenuator 8 and the variable phase shifter 9, is input to the terminal of the power combiner 13, and is input via the delay line 11. The multi-frequency signal including the component is anti-phase combined to cancel the distortion component, and the multi-frequency amplified signal with less distortion is output from the terminal of the power combiner 13.

[0004]

However, in such a circuit, the main amplifier 4 and the auxiliary amplifier 1 are usually used.
The in-band amplitude deviation characteristic of 0 is tuned to the center frequency of the band, and has a characteristic in which the levels at both ends of the band are lowered as shown in (a) and (d). On the other hand, since the delay lines 5 and 11 are realized by a semi-rigid cable or a coaxial cable, they have almost no in-band deviation and have flat characteristics as shown in (b) and (c). Therefore, in the distortion detection circuit 20 and the distortion removal circuit 30, when the power combiners 7 and 11 for canceling the fundamental wave and the distortion component are combined, there is a difference in characteristics near the upper and lower limits of the band as shown in FIG. However, since the amplitude characteristics of all bands do not match, the amount of distortion suppression over the entire band is not uniform. It is an object of the present invention to provide a feedforward amplifier that improves the reduction in distortion suppression amount due to the amplitude deviation at both ends of the band in the distortion detection circuit and distortion removal circuit.

[0005]

A feedforward amplifier according to the present invention branches a multi-frequency input signal by a power divider and outputs one of the signals via a first variable attenuator and a first variable phase shifter. The signal amplified by the main amplifier and the signal whose other signal is timed by the first delay line are subjected to anti-phase combination by the first power combiner to detect the distortion component generated in the main amplifier. A distortion detection circuit, and the first
A signal obtained by amplifying the distortion component output from the power combiner of FIG. 2 by an auxiliary amplifier via a second variable attenuator and a second variable phase shifter, and a main amplifier output from the first power combiner. Distortion that cancels the distortion component generated in the main amplifier and outputs a multi-frequency amplified signal by subjecting the amplified signal and the signal whose timing is adjusted by the second delay line to each other in antiphase combination by the second power combiner. In a feedforward amplifier including a removal circuit, a first isolator that has a frequency characteristic similar to the amplitude frequency characteristic of the main amplifier, is inserted and connected in series with the first delay line, and the amplitude of the auxiliary amplifier. A second isolator having a frequency characteristic similar to that of the second delay line, the second isolator being inserted and connected in series with the second delay line; and the first isolator. It is characterized in that it comprises a first amplifier and the second amplifier instead of data and the second isolator.

[0006]

FIG. 1 is a block diagram showing an embodiment of the present invention. The difference from the conventional configuration shown in FIG. 3 is that isolators 6 and 12 are inserted in the delay lines 5 and 11, respectively. In the distortion detection circuit 20 and the distortion removal circuit 30 of the present invention, attention is paid to the amplitude deviation in order to improve the distortion compensation in the wide band, and the in-band deviation of the inserted isolators 6 and 12 is represented by the characteristics (g) and (h). As described above, by making the frequency characteristics of the main amplifier 4 and the auxiliary amplifier 10 similar to each other, among the amplitude and the phase which are the factors that determine the distortion suppression amount,
This is intended to improve the amount of distortion compensation by correcting the deviation of the amplitude term as much as possible.

As another embodiment of the present invention, instead of the isolators 6 and 12, an amplifier having a frequency characteristic similar to that of the isolator may be provided as shown by a broken line in FIG. Further, by providing an isolator or an amplifier that can obtain a reverse loss, even when the control of the variable attenuators 2 and 8 is incomplete, a loop that flows backward through the delay line 5 of the distortion detection circuit 20 and a distortion removal circuit. Since abnormal oscillation of the loop that flows backward through the delay line 11 of 30 does not occur, an extremely stable common amplification operation is maintained.

FIG. 2 is an explanatory diagram for improving the amount of signal cancellation in the phase deviation and the amplitude deviation. Conventional amplitude deviation is 0.5d
If the B and the phase difference are 0 °, the suppression amount is 25 dB,
According to the present invention, by setting the amplitude deviation to 0.2 dB, the suppression amount becomes 32 to 33 dB, which is improved by about 8 dB. With the improvement of 8 dB, it is clear that the linearity performance of the auxiliary amplifier 11 can be improved, which is economically advantageous. FIG. 5 is a characteristic example diagram of the amplitude, phase imbalance, and signal suppression amount of the feedforward amplifier.

[0009]

As described in detail above, by implementing the present invention, the distortion compensation amount of the feedforward amplifier is improved, and therefore, the effect is extremely large in practical use.

[Brief description of drawings]

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

FIG. 2 is a characteristic explanatory diagram of the present invention.

FIG. 3 is a block diagram of a conventional amplifier.

FIG. 4 is a conventional characteristic explanatory diagram.

FIG. 5 is a characteristic example diagram of a feedforward amplifier.

[Explanation of symbols]

 1 Power Divider 2,8 Variable Attenuator 3,9 Variable Phaser 4 Main Amplifier 5,11 Delay Line 6,12 Isolator 7,13 Power Combiner 10 Auxiliary Amplifier 20 Distortion Detection Circuit 30 Distortion Removal Circuit

Front page continuation (72) Inventor Noriyuki Kagaya 3-14-20 Higashi-Nakano, Nakano-ku, Tokyo Kokusai Electric Co., Ltd.

Claims (2)

[Claims] 1. A signal obtained by branching and outputting a multi-frequency input signal by a power divider, one signal of which is amplified by a main amplifier via a first variable attenuator and a first variable phase shifter, and the other signal. A distortion detection circuit for detecting a distortion component generated in the main amplifier by performing a reverse phase combination of a signal whose timing is adjusted by a first delay line with a first power combiner, and the first power combiner. The distortion component output from the second
, The signal amplified by the auxiliary amplifier via the variable attenuator and the second variable phase shifter, and the signal amplified by the main amplifier output from the first power combiner are timed by the second delay line. A feed-forward amplifier comprising: a distortion removing circuit for canceling a distortion component generated in the main amplifier by outputting a multi-frequency amplified signal by performing anti-phase combination with a signal in a second power combiner; A first isolator having a frequency characteristic close to the amplitude frequency characteristic of the amplifier, inserted and connected in series with the first delay line; and a frequency characteristic close to the amplitude frequency characteristic of the auxiliary amplifier, The second, which is inserted and connected in series with the second delay line
And a feed-forward amplifier. 2. The first isolator and the second isolator
2. The feedforward amplifier according to claim 1, further comprising a first amplifier and a second amplifier each having an equivalent frequency characteristic instead of the isolator.