JP3494957B2 - Feedforward amplifier - Google Patents

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 a kind of highly linear amplifier used for a base station or a repeater of a mobile communication system such as a car telephone and which amplifies multi-frequency signals at the same time, , 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-Adjust).
ing Feed-Forward Amplife
r) 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 an input signal by a distortion detection circuit including a main amplifier which is an amplifier to be compensated, and detects the detected distortion component ( The 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 input to the power distributor 1, and one multi-frequency signal 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.

The multi-frequency input signal output from the terminal of the power combiner 7 is input to the terminal of the power combiner 13 via the delay line 11. 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.

[0008]

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 which can improve a reduction in distortion suppression amount due to an amplitude deviation at both ends of the band in a distortion detection circuit and a distortion removal circuit.

[0010]

A feedforward amplifier according to the present invention branches an input signal by a power divider and outputs one of the signals mainly via a first variable attenuator and a first variable phase shifter. Distortion detection for detecting a distortion component generated in the main amplifier by subjecting the signal amplified by the amplifier and the signal obtained by adjusting the timing of the other signal by the first delay means to each other by anti-phase combining by the first power combiner A circuit, and a distortion variable output from the first power combiner to a second variable attenuator,
A signal amplified by the auxiliary amplifier via the second variable phase shifter and a signal obtained by timing-matching the signal amplified by the main amplifier output from the first power combiner by the second delay means are second. And a distortion removing circuit for canceling the distortion component generated in the main amplifier to output a multi-frequency amplified signal by performing the anti-phase combining in the power combiner of the first delay means. On the route of the desired
In- band deviation characteristic similar to the in- band deviation characteristic of the main amplifier, and the path of the first delay means.
Error due to loop current flowing in a loop circuit that flows backward
And a reverse loss characteristic capable of preventing vibration.
It is characterized by inserting and connecting an isolator .

Further, in the feed-forward amplifier of the present invention, the input signal is branched and output by the power divider, and one of the signals is amplified by the main amplifier via the first variable attenuator and the first variable phase shifter. A distortion detection circuit for detecting a distortion component generated in the main amplifier by subjecting the signal and the signal obtained by timing-matching the other signal by the first delay means to each other by anti-phase combining in the first power combiner; A signal obtained by amplifying the distortion component output from the first power combiner by an auxiliary amplifier via a second variable attenuator and a second variable phase shifter, and a signal output from the first power combiner. The signal amplified by the amplifier and the signal timed by the second delay means are subjected to anti-phase synthesis by the second power combiner to cancel the distortion component generated in the main amplifier and output a multi-frequency amplified signal. And a distortion removal circuit A feedforward amplifier provided with the desired wideband in the path of the second delay means.
Over and is similar to the band deviation characteristic of the main amplifier band
Backflow through the path of the second delay means with the in-region deviation characteristic
To prevent abnormal oscillation due to the loop current flowing through the loop circuit,
A second isolator having a backward loss characteristics that may DOO
It is characterized in that the inserted and connected data.

[0012]

1 is a block diagram showing an embodiment of the present invention. The difference from the conventional configuration shown in FIG. 3 is that
This is the point where the 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, the distortion compensation amount is corrected by correcting the deviation of the amplitude term in the amplitude and the phase, which are the factors that determine the distortion suppression amount. It is intended to improve.

The isolator as the means for correcting the amplitude deviation may be only the isolator 6 of the distortion detection circuit 20, or the isolator 12 of the distortion removal circuit 30 alone, the distortion compensation amount is improved as compared with the conventional case. Needless to say.

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.

[0016]

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 distributor 2,8 variable attenuator 3,9 Variable phase shifter 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. (56) Reference JP-A-60-106209 (JP, A) JP-A-54-137261 (JP, A) Actual development Sho 52-109434 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03F 1/32

Claims (2)

(57) [Claims] 1. An input signal is branched and output by a power divider, one of the signals is amplified by a main amplifier via a first variable attenuator and a first variable phase shifter, and the other signal is 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 the first delay means in the first power combiner, and an output from the first power combiner. A second variable attenuator,
A signal amplified by the auxiliary amplifier via the second variable phase shifter and a signal obtained by timing-matching the signal amplified by the main amplifier output from the first power combiner by the second delay means are second. And a distortion removing circuit for canceling the distortion component generated in the main amplifier to output a multi-frequency amplified signal by performing the anti-phase combining in the power combiner of the first delay means. On the path of the desired broadband
An in- band deviation similar to the in- band deviation characteristic of the main amplifier
Characteristics and a loop circuit that flows backward through the path of the first delay means.
It is possible to prevent abnormal oscillation due to loop current flowing in the road.
A feed-forward amplifier, wherein a first isolator having a reverse loss characteristic is inserted and connected. 2. An input signal is branched and output 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 is 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 the first delay means in the first power combiner, and an output from the first power combiner. A second variable attenuator,
A signal amplified by the auxiliary amplifier via the second variable phase shifter and a signal obtained by timing-matching the signal amplified by the main amplifier output from the first power combiner by the second delay means are second. And a distortion removing circuit for canceling the distortion component generated in the main amplifier to output a multi-frequency amplified signal by performing the anti-phase combining in the power combiner of the second delay means. On the path of the desired broadband
An in- band deviation that is similar to the in- band deviation characteristic of the auxiliary amplifier.
A loop that reverses the difference characteristic and the path of the second delay means.
Because it prevents abnormal oscillation due to loop current flowing in the circuit
A feed-forward amplifier, wherein a second isolator having a reverse loss characteristic is inserted and connected.