JPH09266427A - Multi-stage amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress fluctuation in a frequency characteristic due to selection of a linear operation and a limiting operation and to reduce the cost by controlling bias voltage control of an amplifier and attenuation control of a variable attenuation in the same direction. SOLUTION: In a transistor amplifier circuit, linearity of the amplifier is increased because a saturation output power is increased as a bias voltage gets higher. Conversely, the saturation output power is reduced by decreasing the bias voltage, the output of the amplifier is saturated at a low input power and then the output power is constant. This characteristic is used to increase the attenuation of a variable attenuator 3 to increase the input power of the amplifier 5 and a bias voltage control circuit 7 is used to increase the bias voltage of the amplifier 5 to allow the multi-stage amplifier to conduct linear operation. Conversely, the attenuation of the variable amplifier 3 is decreased to increase the input power of the amplifier 5 and the bias voltage control circuit 7 is used to reduce the bias voltage of the amplifier 5 so as to allow the multi-stage amplifier to conduct a limiting operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a characteristic improvement and cost reduction in a multistage amplifier having a function of switching between a linear operation and a limiting operation.

[0002]

2. Description of the Related Art FIG. 7 shows an example of a conventional multistage amplifier. In this figure, 1 is a signal input terminal, 2 is a signal output terminal, 3 is an input variable attenuator, 4 is an output variable attenuator, 5 is an amplifier, and 6 is a variable attenuator control circuit.

Next, the operation will be described. The characteristics of the output power output from the output terminal 2 with respect to the input power applied to the input terminal 1 of the multistage amplifier are controlled by the variable attenuator control circuit 6 by the input variable attenuator 3 and the output variable attenuator 4 The characteristics shown in FIG. 8 are obtained depending on the amount of attenuation.
First, when the input variable attenuator 3 has a large amount of attenuation and the output variable attenuator 4 has a small amount of attenuation, a plurality of amplifiers 5 do not saturate in a certain specific input power range and perform linear operation. The amplifier as a whole also operates linearly. on the other hand,
When the attenuation amount of the input variable attenuator 3 is small and the attenuation amount of the output variable attenuator 4 is large, the plurality of amplifiers 5 are completely saturated in the same input power range as above, so that the entire multi-stage amplifier is Performs a limiting operation in which the output power is constant. In this way, the variable attenuator control circuit 6 controls the attenuation amounts of the input variable attenuator 3 and the output variable attenuator 4 to switch between the linear operation and the limiting operation.

[0004]

The conventional multistage amplifier is
As described above, the two variable attenuators are controlled to switch between the linear operation and the limiting operation. Generally, a variable attenuator is often configured by using an element whose impedance changes according to a voltage such as a pin diode, but there is a problem that the frequency characteristic changes when the attenuation amount is switched. Therefore, it is necessary to adjust the matching condition with the circuits before and after so that the frequency characteristic variation becomes equal to or less than the allowable value. Since the input variable attenuator is located in the front stage of the amplifier, the impedance of the circuits connected before and after the linear operation and the limiting operation is constant and the matching adjustment is relatively easy. On the other hand, the variable attenuator for output is located in the latter stage of the amplifier, and the impedance on the output side of the amplifier changes between the linear operation and the limiting operation. Therefore, it is very difficult to obtain matching in both cases. As a result, there has been a problem that the frequency characteristic fluctuates between the linear operation and the limiting operation. Further, since the pin diode is more expensive than semiconductors such as other transistors, there is a problem that the cost of the multistage amplifier becomes high.

The present invention has been made to solve the above problems, and it is an object of the present invention to suppress variation in frequency characteristics due to switching between a linear operation and a limiting operation and to realize a low cost.

[0006]

In the multistage amplifier according to the first invention, the bias voltage of the amplifier can be controlled by a bias voltage control circuit, and the bias voltage control of this amplifier and the attenuation amount control of the input variable attenuator are performed. By controlling in the same direction as each other, the linear operation and the limiting operation are switched.

The multistage amplifier according to the second invention has a variable gain amplifier, a variable gain amplifier control circuit for controlling the variable gain amplifier, and an amplifier whose bias voltage can be controlled by the bias voltage control circuit. The linear operation and the limiting operation are switched by controlling the gain and the bias voltage of the amplifier in opposite directions.

The multistage amplifier according to the third aspect of the invention is an equal power divider, a linear amplifier having a fixed attenuator connected to the input, a limiting amplifier having a fixed attenuator connected to the output, and the like. A power combiner is provided, and switching between the linear operation and the limiting operation is performed by switching the bias voltage supplied to the linear amplifier and the limiting amplifier by the bias control circuit.

The multistage amplifier according to the fourth aspect of the present invention has a non-uniform power divider, a linear amplifier, a limiting amplifier, and a non-uniform power combiner, and a bias control circuit for linear By switching the bias voltage supplied to the amplifier and the limiting amplifier, the linear operation and the limiting operation are switched.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1. FIG. 1 shows a first embodiment of the present invention, in which 1 is a signal input terminal, 2 is a signal output terminal, 3 is an input variable attenuator, 4 is an output variable attenuator, and 5 is an amplifier. , 6 is a variable attenuator control circuit, and 7 is a bias voltage control circuit.

FIG. 2 shows the relationship between the output power and the input power of a general transistor amplifier. The bias voltage shown here means the collector voltage in the case of a bipolar transistor, and the drain voltage in the case of a field effect transistor. The higher the bias voltage, the higher the saturated output power and the stronger the linearity of the amplifier. On the contrary, if the bias voltage is lowered, the saturated output power becomes low, and the output of the amplifier is saturated at a low input power and the output power becomes constant.

By applying this characteristic, the attenuation amount of the variable attenuator 3 is increased, the input power of the amplifier 5 is lowered, and the bias voltage of the amplifier 5 is increased by the bias voltage control circuit 7, so that the multistage amplifier is linearly operated. Can be performed. On the contrary, by reducing the attenuation amount of the variable attenuator 3 to increase the input power of the amplifier 5 and lowering the bias voltage of the amplifier 5 by the bias voltage control circuit 7, the multistage amplifier can perform the limiting operation. It is possible. As a result, the output power output from the output terminal 2 with respect to the input power applied to the input terminal 1 of the multistage amplifier can obtain the same characteristics as in FIG.

As described above, according to the present invention, since it is not necessary to use the variable attenuator for output, it is possible to suppress the fluctuation of the frequency characteristic due to the switching between the linear operation and the limiting operation, and the number of the variable attenuators. Since only one is required, it is possible to realize low cost. Furthermore, since there is only one part where the gain is attenuated, it is possible to reduce the number of amplifier stages required to obtain the same gain, downsizing the circuit, improving functions such as reducing power consumption, and further reducing cost. Is possible.

Embodiment 2 FIG. FIG. 3 shows a second embodiment of the present invention, in which 8 is a variable gain amplifier and 9 is a variable gain amplifier control circuit. In the figure, the same numbers as in FIG. 1 indicate the same items. FIG. 4 shows the relationship between the output power and the input power of a general variable gain amplifier using a dual gate FET or the like. It is possible to control the gain of the amplifier by externally controlling the gain control voltage.

By applying this characteristic, the gain of the variable gain amplifier 8 is reduced, the input power of the amplifier 5 connected in the subsequent stage is lowered, and the bias voltage of the amplifier 5 is increased by the bias voltage control circuit 7 to increase the number of stages. It is possible to make the amplifier perform linear operation. On the contrary, the variable gain amplifier 8
Is increased to increase the input power of the amplifier 5 connected to the subsequent stage and the bias voltage control circuit 7 lowers the bias voltage of the amplifier 5, so that the multistage amplifier can perform the limiting operation. . As a result, the output power output from the output terminal 2 with respect to the input power applied to the input terminal 1 of the multistage amplifier can obtain the same characteristics as in FIG.

As described above, according to the present invention, since it is not necessary to use the output variable attenuator, it is possible to suppress the fluctuation of the frequency characteristic due to the switching between the linear operation and the limiting operation. Further, since it is not necessary to use a variable attenuator using an expensive pin diode or the like, it is possible to realize low cost. Further, since there is no portion for attenuating the gain, it is possible to further reduce the number of amplifier stages required to obtain the same gain as compared with the first embodiment, and to improve the functions such as circuit miniaturization and power consumption reduction. Further cost reduction is possible.

Embodiment 3 5 shows Embodiment 3 of the present invention, in which 10 is an equal power distributor, 11 is an equal power combiner, 12 is a fixed attenuator for limiting, 13 is a fixed attenuator for linear, Reference numeral 14 is a bias control circuit, 15 is a limiting amplifier, and 16 is a linear amplification amplifier. In the figure, the same numbers as in FIG. 1 indicate the same items. Either one of the limiting amplifier 15 and the linear amplification amplifier 16 is selected by the bias control circuit 14 to be in an operating state. When the linear amplification amplifier 16 is set to the operating state, the input signal is distributed by the equal power distributor 10 and then the linear fixed attenuator 1 is used.
Attenuated at 3. After that, it is linearly amplified by the linear amplification amplifier 16 and output via the equal power combiner 11.
On the other hand, when the limiting amplifier 15 is set to the operating state, the input signal is distributed by the equal power distributor 10 and then amplified to the saturated output power by the limiting amplifier 15 to be a fixed attenuator for limiting. 12 and the equal power combiner 11. As a result, the bias control circuit 14 causes the linear amplification amplifier 16 to
By switching the operation of the limiting amplifier 15 and the output power output from the output terminal 2 with respect to the input power applied to the input terminal 1 of the multistage amplifier, the same characteristics as those in FIG. 8 can be obtained.

As described above, according to the present invention, it is not necessary to use a variable attenuator, and the limiting amplifier and the linear amplifying amplifier can be independently adjusted. Therefore, the frequency depending on the switching between the linear operation and the limiting operation. It is possible to suppress variations in characteristics. Further, since it is not necessary to use a variable attenuator using an expensive pin diode or the like, it is possible to realize low cost.

Embodiment 4 6 shows Embodiment 4 of the present invention, in which 17 is a non-uniform power distributor and 18 is a non-uniform power combiner. In the figure, the same numbers as in FIG. 5 indicate the same items. Embodiment 3
Similarly, either one of the limiting amplifier 15 and the linear amplifier 16 is selected by the bias control circuit 14 to be in the operating state. When the linear amplification amplifier 16 is set to the operating state, the input signal is distributed by the unequal power distributor 17, then linearly amplified by the linear amplification amplifier 16, and passed through the unequal power combiner 18. And output. On the other hand, when the limiting amplifier 15 is set to the operating state, the input signal passes through the unequal power distributor 17 and then is amplified to the saturated output power by the limiting amplifier 15 to obtain the unequal power combiner. It is output via 18. As a result, the bias control circuit 14 causes the linear amplification amplifier 16 and the limiting amplifier 1 to operate.
By switching the operation of No. 5, the output power output from the output terminal 2 with respect to the input power applied to the input terminal 1 of the multistage amplifier can obtain the same characteristic as in FIG.

As described above, in the present invention, it is not necessary to use the variable attenuator, and the limiting amplifier and the linear amplifying amplifier can be independently adjusted. It is possible to suppress variations in characteristics. Furthermore, since it is not necessary to use a variable attenuator using an expensive pin diode or the like, low cost can be realized. Also, since the signal is branched by the non-uniform power divider and the non-uniform power combiner, it is not necessary to use a fixed attenuator for level adjustment, and the number of amplifier stages required to obtain the same gain is implemented. It is possible to reduce the number and simplify the circuit as compared with the third mode.

[0021]

According to the first aspect of the present invention, by controlling the attenuation amount of the variable attenuator and the bias voltage of the amplifier in the same direction to switch between the linear operation and the limiting operation, the frequency characteristic at the time of switching is obtained. It is possible to suppress the fluctuation of. Further, the circuit can be simplified and the cost can be reduced.

According to the second invention, the gain of the variable gain amplifier and the bias voltage of the amplifier are controlled in opposite directions to switch between the linear operation and the limiting operation, thereby changing the frequency characteristic at the time of switching. Can be suppressed. Further, the circuit can be simplified and the cost can be reduced.

According to the third aspect of the invention, since it is not necessary to use a variable attenuator and the limiting amplifier and the linear amplifier can be adjusted independently, it is possible to switch between the linear operation and the limiting operation. It is possible to suppress variations in frequency characteristics. Further, since it is not necessary to use a variable attenuator using an expensive pin diode or the like, it is possible to realize low cost.

According to the fourth aspect of the invention, since it is not necessary to use a variable attenuator and the limiting amplifier and the linear amplifying amplifier can be independently adjusted, it is possible to switch between the linear operation and the limiting operation. It is possible to suppress variations in frequency characteristics. Furthermore, since it is not necessary to use a variable attenuator using an expensive pin diode or the like, low cost can be realized. Further, the circuit can be simplified without the need to use a fixed attenuator for level adjustment.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a multistage amplifier according to the present invention.

FIG. 2 is a diagram showing a relationship between output power and input power of a general transistor amplifier.

FIG. 3 is a diagram showing a second embodiment of a multistage amplifier according to the present invention.

FIG. 4 is a diagram showing a relationship between input power and output power of a general variable gain amplifier.

FIG. 5 is a diagram showing a third embodiment of a multistage amplifier according to the present invention.

FIG. 6 is a diagram showing a fourth embodiment of a multistage amplifier according to the present invention.

FIG. 7 is a diagram showing a conventional multistage amplifier.

FIG. 8 is a diagram showing a relationship between output power and input power of a multistage amplifier.

[Explanation of symbols]

1 signal input terminal, 2 signal output terminal, 3 input variable attenuator, 4 output variable attenuator, 5 amplifier, 6 variable attenuator control circuit, 7 bias voltage control circuit, 8 gain variable amplifier, 9 gain variable amplifier control Circuit, 10 equal power distributor, 11 equal power combiner, 12 fixed attenuator for limiting, 13 fixed attenuator for linear, 14 bias control circuit, 15 limiting amplifier, 16 linear amplifying amplifier, 17 unequal division Power distributor, 18 non-uniform power combiner.

Claims (4)

[Claims] 1. A plurality of amplifiers connected in cascade, a bias voltage control circuit for controlling the bias voltage of those amplifiers, a variable attenuator capable of varying the input power of the preceding amplifier, and a variable attenuator of the variable attenuator. In a multistage amplifier composed of a variable attenuator control circuit for setting an attenuation amount, a linear operation and a limiting operation are performed by controlling the bias voltage of the amplifier and the attenuation amount of the variable attenuator in the same direction. A multi-stage amplifier characterized by having a switching function. 2. A plurality of amplifiers connected in cascade, a bias voltage control circuit for controlling the bias voltage of those amplifiers, a variable gain amplifier capable of varying the input power of the preceding amplifier, and a variable gain amplifier of the above. In a multistage amplifier including a variable gain amplifier control circuit for setting a gain, a linear operation and a limiting operation are switched by controlling the bias voltage of the amplifier and the gain of the variable gain amplifier in opposite directions. A multistage amplifier characterized by having functions. 3. An equal power distributor for equally distributing input power,
A fixed linear attenuator that attenuates the distributed signal, a plurality of linear amplification amplifiers that are connected in series to amplify the output of the linear fixed attenuator, and amplifies the other output signal of the equal power distributor. A plurality of limiting amplifiers connected in cascade, a fixed attenuator for limiting which attenuates the output power of the limiting amplifier, and an output power of the linear amplification amplifier and the fixed attenuator for limiting are combined. In a multi-stage amplifier including an equal power combiner and a bias control circuit for switching a bias voltage supplied to the linear amplification amplifier and the limiting amplifier, the linear amplification amplifier and the limiting amplifier by the bias control circuit. Is operated alternately and has a function of switching between linear motion and limiting motion. Amplifier. 4. An unequal power distributor for allocating the input power unequally, a plurality of cascaded linear amplification amplifiers for amplifying one of the distributed signals, and the unequal power distributor. A plurality of cascaded limiting amplifiers for amplifying the other output signal of the above, an unequal power combiner for unequally combining the output powers of the linear amplification amplifier and the limiting amplifier, and In a multistage amplifier composed of a linear amplification amplifier and a bias control circuit that switches the bias voltage supplied to the limiting amplifier,
A multi-stage amplifier having a function of alternately operating the linear amplification amplifier and the limiting amplifier by the bias voltage control circuit to switch between a linear operation and a limiting operation.