JP2943838B2 - 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 feed-forward amplifier which is used as a base station or a relay device of a mobile communication system such as a car telephone and is a kind of a highly linear amplifier for simultaneously amplifying multi-frequency signals. The present invention relates to an improvement for eliminating unstable elements such as unnecessary oscillation.

[0002]

2. Description of the Related Art A base station and a wireless relay device in an 800 MHz band mobile telephone system and the like are provided with a multi-frequency common amplifier for simultaneously amplifying multi-frequency signals. In this multi-frequency common amplifier, it is necessary to sufficiently improve the linearity in order to minimize the intermodulation distortion, and a small and high linearity amplifier is used. One of them is a self-adjustable feedforward amplifier (SAFF-A: Self-Ad).
justifying Feed-Forward Ampl
and a common amplifier that compensates for all intermodulation distortion and noise by self-adjustment. This feedforward amplifier is composed of a distortion detection circuit and a distortion removal circuit, and detects a distortion component other than the input signal with a distortion detection circuit including a main amplifier which is a compensation target amplifier, 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 combined with the multi-frequency input signal in reverse phase to cancel the distortion component.

FIG. 4 is a block diagram of a conventional self-adjustable feedforward amplifier. In the figure, 1 is a drive amplifier for amplifying an input signal Pin, 2 is a power divider for distributing its output, 3 is a variable attenuator, 4 is a variable phase shifter, 5 is a main amplifier, 6 is a delay line, and 7 is power A combiner, 8 is a variable attenuator, 9 is a variable phase shifter, 10 is an auxiliary amplifier, 11 is a delay line, 12 is a power combiner, and 13 is an isolator. 2
0 is a distortion detection circuit, and 30 is a distortion removal circuit. The multi-frequency input signal Pin is input to the power divider 2 via the drive amplifier 1, and one of the two multi-frequency signals is amplified by the main amplifier 5 via the variable attenuator 3 and the variable phase shifter 4. Is done. The output includes a distortion (error) component generated at the time of amplification, and is input to the power combiner 7, branched and output by the power distributor 2, and input to the power combiner 7 via the delay line 6. The distortion component is detected by being combined with the input signal. Power combiner 7
Are output to the power combiner 12 via the delay line 11. The distortion component output from the power combiner 7 is amplified by the auxiliary amplifier 10 via the variable attenuator 8 and the variable phase shifter 9 and is input to the power combiner 12, the polarity is inverted, and is input via the delay line 11. The signal is combined with the signal containing the distortion component to cancel the distortion component, and a multi-frequency common amplification signal with little distortion is output. This output is
, And becomes an output signal Pout. This feed-forward amplifier controls the variable attenuator 3,
8 and the variable phase shifters 4 and 9 are adjusted to perform a desired operation. The drive amplifier 1 at the input end is used when the relay device is placed in a blind spot and the received power from the radio base station is small. When the received power is large, an isolator is used instead of the amplifier.

[0004] Such a feedforward amplifier is
Each block constituting the distortion detection circuit 20 and the distortion removal circuit 30, particularly the main amplifier 5 and the auxiliary amplifier 10, need to have a wide band. The gain of the amplifier 5 is set to G ₁ dB, and the gain of the auxiliary amplifier 10 is set to G ₂ dB. The isolator 13 provided on the output side plays a role of absorbing load fluctuation and protecting the main amplifier 5. Therefore, the isolator 13 may be connected between the main amplifier 5 and the power combiner 7 instead of the output side.

[0005]

However, the above-described conventional circuit configuration has the following problems. Frequency characteristics of the input return loss R ₃ isolator 13, the characteristics of the output return loss R ₂ of the main amplifier 5, and the characteristics of the output return loss R ₁ of driver amplifier 1 on the input side, the main amplifier 5
And the band is narrower than the transmission frequency characteristic of the auxiliary amplifier 10. FIG. 5 is an explanatory diagram of a part of the distortion removing circuit 30 of the conventional circuit. In the distortion removing circuit 30, the loss of the variable attenuator 8 is L ₃ , the loss of the variable phase shifter 9 is L ₄ , the loss of the delay line 11 is L ₇ , the loss of the power combiners 7 and 12 is C ₂ , respectively.
Assuming that C ₃ , the following equation (1) is satisfied inside and outside the band during adjustment by changing the attenuation L ₃ of the variable attenuator 8 to L ₃ ′ (where L ₃ > L ₃ ′). Then, abnormal oscillation occurs in the A loop of the distortion removing circuit 30, and the function as the feedforward amplifier stops.

[Number 1] _{G 2 (dB)> L 3} '+ L 4 + C 2 + C 3 + L 7 + R 2 (dB) ...... (1)

The normal operation condition of the feedforward amplifier is the case of the following equation (2). However, this is a condition within the frequency band of the input power Pin.

G ₂ (dB) = C ₂ + L ₃ ′ + L ₄ + C ₃ −L ₇ (dB) (2)

Similarly, the distortion detection circuit 20 may cause unnecessary oscillation as follows. FIG. 6 is an explanatory diagram of a portion of the distortion detection circuit 20 of the conventional circuit. The output return loss of the drive amplifier 1 is R ₁ , the loss of the power divider 2 is H ₁ (dB), the loss of the variable attenuator 3 is L ₁ , the loss of the variable phase shifter 4 is L ₂ , and the loss of the delay line 6 is Assuming that L ₆ , the loss of the delay line 11 is L ₇ , the loss of the power combiner 7 is C ₂ , and the gain of the main amplifier 5 is G ₁ , an abnormal oscillation occurs in the B loop if the following equation (3) is satisfied. .

G ₁ (dB)> L ₁ + L ₂ + (L ₇ × 2) + L ₆ + C ₂ + H ₁ + R ₁ + R ₃ (dB) (3) Similarly, the following equation (4) holds. Then, normal operation is performed.

G ₁ (dB) = C ₂ + H ₁ + L ₁ + L ₂ + L ₆ (dB) (4) However, this is a condition within the frequency band of the input power Pin.

In each of the loops A and B, the only parameter that does not affect the function of the feedforward amplifier is the return loss of the wide band of R ₁ , R ₂ and R ₃ . That is, from the expressions (1) and (2), ｛(1) −
(2) When｝ is obtained, the following equation (5) is obtained, and the condition of abnormal oscillation is obtained.

0 ≧ L ₃ ′ −L ₃ + R ₂ + R ₃ (5) In a normal use band, R ₂ and R ₃ are 20 dB or more,
Since the variation L ₃ ′ −L ₃ due to the adjustment is −7 dB, it does not satisfy the abnormal oscillation condition. On the other hand, outside the used band, R ₂ ,
R ₃ is about 2 dB, and although the return loss is poor, the in-band transmission characteristics do not deteriorate, but L ₃ ′ −L ₃ is adjusted to −7 dB.
In such a case, the abnormal oscillation condition is satisfied outside the used band.
In particular, when the initial optimum value of the variable element is unknown due to installation adjustment or the like, the amount of attenuation of the attenuators 3 and 8 is greatly changed. Occurs.

It is an object of the present invention to provide a feed-forward amplifier which prevents abnormal oscillation at frequencies outside the band in the above-mentioned conventional circuit.

[0010]

A feedforward amplifier according to the present invention amplifies a multi-frequency input signal by a drive amplifier, branches and outputs the amplified signal at a power divider, and outputs one of the signals to a first variable attenuator and a first variable attenuator. The signal generated by the main amplifier is synthesized by synthesizing the signal amplified by the main amplifier through the variable phase shifter and the signal obtained by adjusting the timing of the other signal by the first delay line by the first power synthesizer. A distortion detection circuit for detecting a component, 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, A signal amplified by the main amplifier output from the first power combiner and subjected to reverse phase synthesis by the second power combiner with a signal whose timing has been adjusted by the second delay line, thereby producing a distortion component generated in the main amplifier. Multi-frequency offset In the feedforward amplifier and a distortion elimination circuit for outputting a width signal, said driving amplifier, and 2 distributes the power of the input signal of the one phase 90
Input-side hybrid 90 ° coupler that changes and outputs
Two amplifiers for respectively amplifying the two divided signals, and the phase of the other signal of the outputs of the two amplifiers is set to 90
And a drive circuit consisting of an output-side hybrid 90 ° coupler that performs in-phase synthesis by changing the main amplifier,
An input-side hybrid 90 ° coupler that splits the power of an input signal into two and changes one of the phases by 90 °, and outputs two amplifiers that amplify the two split signals, respectively;
It is characterized in that the two amplifiers are replaced by a main amplifier circuit composed of an output-side hybrid 90 ° coupler that changes the phase of the other signal of the two amplifiers by 90 ° and performs in-phase synthesis. Further, when the input power is large, the two amplifiers of the drive circuit are replaced with two isolators.

[0011] That is, the output return loss R ₁ of the input-side driving amplifier 1, to increase the input return loss R ₃ output return loss R ₂ and isolator 13 of the main amplifier 5 over a wide band, the drive amplifier 1 to the main amplifier 5 The gist is that a hybrid 90 ° coupler is provided for each of the two distribution amplification configurations.

[0012]

FIG. 1 is a block diagram showing a first embodiment of the present invention. In the figure, reference numerals other than the drive circuit 40 and the main amplifier circuit 50 indicate the same parts as those of the conventional circuit of FIG. FIG. 2A is a diagram illustrating the principle of the drive circuit 40 and the main amplifier circuit 50 of FIG. That is, it shows a distribution / combination amplifier configuration using a hybrid 90 ° coupler. That is, the drive circuit 40 and the main amplifier circuit 50 in FIG. 1 respectively distribute the input power to the two amplifiers A ₁ and A ₂ by the distributor (input-side hybrid 90 ° coupler) H ₁ , and output the respective amplified outputs. configured to combine and output by combiner (output side hybrid 90 ° coupler) H _2. The power of the input signal is supplied to the divider H ₁
And one output signal has a phase difference of 90 ° with respect to the other signal, and is input to _two amplifiers A ₁ and A ₂ having the same gain as the original amplifier. The outputs of the _two amplifiers A ₁ and A ₂ are input to a combiner H ₂ , and the other signals are combined in phase by changing the phase by 90 °.

If this is, for example, a main amplifier circuit 50,
The output (OUT) viewed from the return loss, as indicated by a solid line and a broken line, one of the amplifiers A ₁ and the other amplifier A
_Since the phase difference between the signals of the _two transmission lines is 180 °, the combined return loss increases. In addition, since the 90 ° coupler has a wide band characteristic, for example, a band of 700 to 1100 MHz can be easily realized in a 900 MHz band of a mobile phone system, so that a return loss is wide in a wide range from within a used frequency band to outside the band. growing. This effect is similarly obtained in the case of input return loss. FIG.
The above effect can also be obtained for the drive circuit 40 of FIG.
With the configuration described above, the return loss R ₁ , R ₂ in the equations (1) and (3) can be increased, and the oscillation condition can not be satisfied.

FIG. 2B is a diagram in which the two amplifiers A ₁ and A ₂ in FIG. 2A are replaced with isolators, respectively.
FIG. 9 shows a drive circuit 41 shown in FIG. 3 according to the second embodiment of the present invention instead of the drive circuit 40 shown in FIG. In this case also, the effect of improvement by widening the return loss can be obtained.

As described above, since the return loss can be improved over a wide band outside the used band, even if the attenuation of the variable attenuators 3 and 8 is largely changed at the time of the initial adjustment, the expressions (1) and (1) are obtained. There is no fear that the oscillation condition of (3) is satisfied, and no abnormal oscillation occurs. In the lower and higher frequency bands of the widened and improved frequency band,
Since the gain of the amplifier is reduced, no oscillation occurs even if the return loss is small.

FIG. 3 is a block diagram showing a second embodiment of the present invention, in which the amplifiers A ₁ and A ₂ of the drive circuit 40 of the embodiment of FIG. 1 are replaced with isolators.

[0017]

As described in detail above, by implementing the present invention, a stable feedforward amplifier can be realized which does not cause abnormal oscillation even if the attenuation of the variable attenuator is largely changed at the time of initial adjustment. be able to. For this reason,
The design becomes easy and the practical effect is extremely large.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram of an operation of a main part of the present invention.

FIG. 3 is a block diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of a conventional circuit configuration.

FIG. 5 is a partial configuration example diagram for explaining a drawback of a conventional circuit.

FIG. 6 is a partial configuration example diagram for explaining a defect of a conventional circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 drive amplifier 2 power divider 3,8 variable attenuator 4,9 variable phase shifter 5 main amplifier 6,11 delay line, 7,12 power combiner 10 auxiliary amplifier 13 isolator 20 distortion detection circuit 30 distortion removal circuit 40 drive circuit 50 Main amplifier circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H03F 1/32

Claims (2)

(57) [Claims] 1. A multi-frequency input signal is amplified by a drive amplifier, then branched and output by a power divider, and one of the signals is amplified by a main amplifier via a first variable attenuator and a first variable phase shifter. A distortion detection circuit that detects a distortion component generated in the main amplifier by combining a signal and a signal obtained by adjusting the timing of the other signal by a first delay line with a first power combiner; The distortion component output from the power combiner of
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 matched in timing by a second delay line. A distortion removal circuit that outputs a multi-frequency amplified signal by canceling a distortion component generated in the main amplifier by synthesizing a signal with a second power combiner in an opposite phase. Input-side hybrid 90 that splits the power of the input signal into two, and changes one of the phases by 90 ° to output
A drive comprising a coupler, two amplifiers for respectively amplifying the two distributed signals, and an output-side hybrid 90 ° coupler for changing the phase of the other signal of the two amplifiers by 90 ° and performing in-phase synthesis. An input-side hybrid 90 ° that splits the power of the input signal into two, and changes one of the phases by 90 ° to output the main amplifier.
A coupler, two amplifiers for respectively amplifying the two distributed signals, and an output-side hybrid 9 for performing in-phase synthesis by changing the phase of the other signal of the outputs of the two amplifiers by 90 °
A feed-forward amplifier, which is replaced with a main amplifier circuit comprising a 0 ° coupler. 2. The feedforward amplifier according to claim 1, wherein two amplifiers of said drive circuit are two isolators.