JPH0255428A - Microwave agc circuit - Google Patents

Abstract

PURPOSE:To obtain an excellent linearity and a low noise characteristic by varying the overall gain of plural variable attenuators when an input level is fluctuated. CONSTITUTION:When the level of an input signal Sin is going to be a high level and the level of an output signal Sout reaches a prescribed level or above, the circuit applies the control in such a way that the added attenuation of a 1st variable attenuator 4 at the pre-stage is increased by a control signal C1 after the attenuation of the 2nd variable attenuator 8 of the post-stage by a control signal C2 reaches a sufficiently large value. Moreover, when the level of the input signal Sin is low and the level of the output signal Sout reaches a prescribed level or below, first the attenuation of the 1st variable attenuator 4 of the pre-stage is sufficiently decreased by the control signal C1 and the attenuation of the 2nd variable attenuator 8 of the post-stage is decreased by the control signal C2. Thus, the linearity of amplification is kept when the level of an input signal is high and excellent noise index of the low noise amplifier is kept when the level of the input signal is low.

Description

[Detailed Description of the Invention] [Summary] Regarding an automatic gain control AGC circuit for a microwave band receiving device, linearity of amplification is maintained when the input signal level is high,
Aiming at a microwave AGC circuit in which a good noise figure of a low noise amplifier is maintained when the input signal level is low, an amplifier with a low noise figure is installed between a first variable attenuator and a second variable attenuator. AG of a microwave receiving device that amplifies an input signal whose level fluctuates and obtains an output signal of a constant level.
In the C circuit, a priority control signal circuit is provided that generates a control signal that gives priority to the addition of attenuation amount to one of the variable attenuators over the other when the level of the input signal fluctuates and the output signal reaches a certain level. When the level of the output signal becomes higher than a certain level, the attenuation amount of the second variable attenuator is first set to be greater than the attenuation amount of the first variable attenuator. After reaching a sufficiently large value, the attenuation amount of the first variable attenuator is increased, and when the level of the input signal becomes low and the output signal becomes below a certain level, the attenuation amount of the first variable attenuator is increased. The attenuation amount of the second variable attenuator is controlled such that the amount of attenuation becomes small after the attenuation amount is sufficiently small.

[Industrial application field]

The present invention relates to an automatic gain control amplifier (AGC amplifier) for a microwave band receiving device.

In digital microwave receivers, AGC circuits are adopted because it is necessary to ensure linearity to reduce amplifier distortion when the incoming signal level is high, and to ensure a good noise figure of the low-noise amplifier when the incoming signal level is low. ing.

Some multilevel modulation type digital microwave receivers have multi-stage AGC circuits in order to maintain level linearity and a good noise figure in the amplifier.

[Conventional technology]

FIG. 4 shows an example of the configuration of a conventional microwave receiving device. The receiving power Sin is passed through a unidirectional amplifier 18 to a low noise amplifier 2A.
The signal is then amplified by the unidirectional amplifier 28, and is then sent to the first variable attenuator 4A to adjust the amount of attenuation and change the level according to the control signal C from the AGC controller 15A, and then to the unidirectional amplifier 5, the low noise amplifier 6A, After passing through the unidirectional device 78, the attenuation amount is adjusted and the level is changed by the control signal C from the same AGC controller 15A in the second variable attenuator 8A, and the signal is passed through the unidirectional device 9A, the frequency converter 108, and so on. The intermediate frequency amplifier 118 amplifies the signal and outputs an intermediate frequency output signal IF. and output signal IF
The DC voltage Vd obtained by detecting the level of with the detector 12A
is converted into the control signal C by the AGC controller 15A, and supplied to the first variable attenuator 4A and the second variable attenuator 8A, and the amount of attenuation added thereto is changed as shown in the characteristic diagram of FIG. , constitutes an AGC circuit that automatically tries to maintain the output signal IF to the intermediate frequency amplifier 11 within a certain level fluctuation.

As for the noise figure of the microwave receiving apparatus shown in FIG. 4, as the gains of the low-noise amplifiers 2A and 6A are increased, deterioration due to the influence of the subsequent stage becomes less and the noise figure is excellent. Regarding linearity, the smaller the gains of the low-noise amplifiers 2A and 6A are, and the lower the level of the receiving power Sin, the better.

The AGC circuit keeps the output level of the output signal IF of the intermediate frequency amplifier 11A within fluctuations, and when the high level reaches a certain level Lc or more, the first output signal IF is set so that the low noise amplifier 6A, the frequency converter 10A, and the intermediate frequency amplifier 11A are not saturated. The attenuation amounts of the variable attenuator 4^ and the second variable attenuator 8A are controlled to be large. Also, when the low level is below a certain level Lc, the variable attenuator 4 is used to improve the overall noise figure.
A. The attenuation amount of the variable attenuator 8A is controlled to be small.

At this time, the variable attenuator 48 and the variable attenuator 8A are both controlled so that they have the same bias current, and the fifth
As shown in the characteristic diagram in the figure, the amount of attenuation is similar.

[Problem to be solved by the invention]

Focusing on the noise figure, since the first variable attenuator 4A is placed on the input side to the low noise amplifier 6, its influence is due to the second variable attenuator placed on the output side of the low noise amplifier 6A. This is larger than the effect of 8A.

When the receiving power Sin starts to rise, the intermediate frequency amplifier 11A
When the degree level of the output signal IF exceeds a certain level Lc and the attenuation amount of the variable attenuator 4A and the variable attenuator 8^ starts to be controlled to increase, due to the influence on the first variable attenuator 4. , there is a problem that the noise figure starts to deteriorate from a relatively early stage. The present invention aims to solve this problem.

[Means to solve the problem]

This problem consists of the first variable attenuator 4 and the second variable attenuator 8
1, which has a low noise amplifier 6 between them, inputs an input signal Sin whose input level fluctuates, automatically changes the total gain according to a control signal C, amplifies it, and outputs an output signal 5out at a constant level. In the AGC circuit of the microwave receiving device, the level of the input signal Stn fluctuates and the output signal 5
A priority control signal circuit 16 is provided that generates a control signal CLC2 that gives priority to adding attenuation amount to one of the first variable attenuator 4 and the second variable attenuator 8 over the other when out reaches a certain level Lc, When the level of the input signal Sin becomes high and the level of the output signal 5out exceeds a certain level Lc, first, the amount of attenuation of the second variable attenuator 8 in the subsequent stage is made larger than the amount of attenuation of the first variable attenuator 4 in the previous stage. After the amount of attenuation of the second variable attenuator 8 reaches a sufficiently large value, the amount of additional attenuation of the first variable attenuator 4 in the preceding stage is controlled to be increased. In addition, when the level of the input signal Sin becomes low, and when the level of the output signal 5out becomes below a certain level Lc, first the first variable attenuator 4 in the previous stage
This problem is solved by the structure of the present invention, which controls the attenuation amount of the second variable attenuator 8 at the subsequent stage to decrease after the attenuation amount of the second variable attenuator 8 is controlled to be small enough.

In the principle diagram of FIG. 1 showing the configuration of the microwave AGC circuit of the present invention, 4 is a first variable attenuator that provides a variable amount of attenuation to the input signal Sin using a control signal C.

6 is a low noise amplifier that amplifies the output of the first variable attenuator 4 with a low noise figure.

Reference numeral 8 denotes a second variable attenuator that provides a variable amount of attenuation to the output of the low noise amplifier 6 using a control signal C.

15 is a GC controller that outputs a control signal C in accordance with the level L of the output signal Sout of the second variable attenuator 8.

1G means that when the level L of the output signal Sout during the second variable attenuation period is a constant level Lc, the attenuation amount added by one of the first variable attenuator 4 and the second variable attenuator 8 is changed from the attenuation amount added to the other one. This is a priority control signal circuit that generates control signals C1 and C2 that are given priority over addition.

[Effect]

The microwave AGC circuit of the present invention includes a first variable attenuator 4
The input signal Sin is given a variable amount of attenuation by the control signal C and sent to the low noise amplifier 6, and the low noise amplifier 6
The output of the first variable attenuator 4 is amplified with a low noise figure and the second variable attenuator 4 is amplified with a low noise figure.
The signal is sent to the variable attenuator 8.

The second variable attenuator 8 applies a variable amount of attenuation to the output of the low noise amplifier 6 according to the control signal C, and outputs an output signal 5out.
is outputted to the outside and simultaneously sent to the AGC controller 15.

The GC controller 15 outputs the output signal S of the second variable attenuator 8.
A control signal C is output to the priority control signal circuit 16 in accordance with the level L of out.

The priority control signal circuit 16 generates a control signal CLC2 when the level L of the output signal Sout of the second variable attenuator 8 is a constant level Lc, and drives the first variable attenuator 4 with the control signal C1. The second variable attenuator 8 is driven by the control signal C2, and the addition of attenuation amount to one of them is given priority over the other. That is, when the level of the input signal Sin starts to rise and the level of the output signal Sout reaches a certain level Lc or more, first the additional attenuation amount of the second variable attenuator 8 in the subsequent stage is lower than the additional attenuation amount of the first variable attenuator 4 in the previous stage. After the attenuation amount of the second variable attenuator 8 reaches a sufficiently large value, control is performed to increase the attenuation amount of the second variable attenuator 8.
control to increase the amount of additional attenuation. Furthermore, when the level of the input signal Sin becomes low, the output signal Sou
When the level of t becomes below a certain level Lc, first, the attenuation amount of the first variable attenuator 4 at the front stage is controlled to be small, and after the attenuation amount becomes sufficiently small, the second variable attenuator at the rear stage is controlled to reduce the attenuation amount. The amount of attenuation of the device 8 is controlled to be small. Therefore, in the microwave AGC circuit of the present invention, the level of the input signal Sin is high and the level of the output signal Sout is constant level L.
c or more, control is first performed so that the amount of attenuation added by the second variable attenuator 8 in the rear stage is greater than the amount of additional attenuation added by the first variable attenuator 4 in the front stage, and the second variable attenuator 8 After the attenuation amount reaches a sufficiently large value, the additional attenuation amount of the first variable attenuator 4 in the preceding stage is controlled to be increased, so that linearity can be maintained against wide changes in the level of the input signal Sin. It will be done.

Also, the level of the input signal Sin is low and the output signal Sout
When the level of is below a certain level Lc, first
After the attenuation of the variable attenuator 4 is controlled to be small and the attenuation is sufficiently small, the attenuation of the second variable attenuator 8 in the subsequent stage is controlled to be small. The good noise figure of the first variable attenuator 4 and the second variable attenuator 8 is less likely to be adversely affected and deteriorated, and the problem is solved.

〔Example〕

FIG. 2 is a block diagram showing the configuration of a microwave AGC circuit according to an embodiment of the present invention, and FIG. 3 is a characteristic diagram for explaining its operation.

In the block diagram of the embodiment of the present invention shown in FIG. 2, circuits with the same numbers as those in the conventional example shown in FIG. 4 have the same functions as the circuits with the same numbers in the conventional example.

The first variable attenuator 4 applies the control signal C1 to the input signal Sin.
The signal is attenuated by the signal and sent to the low noise amplifier 6.

The low noise amplifier 6 amplifies the output of the first variable attenuator 4 with a low noise figure and sends it to the second variable attenuator 8.

The second variable attenuator 8 applies an attenuation amount to the output of the low noise amplifier 6 using a control signal C2, converts it into an intermediate frequency signal in a frequency converter 10, amplifies it in an intermediate frequency amplifier 11, and outputs an intermediate frequency signal IP. At the same time as outputting the output signal 5out to the outside, the wave detector 12 detects the wave and sends the DC voltage Vc to the AGC controller 15.

The AGC controller 15 outputs the output signal 5 of the second variable attenuator 8.
A control signal C is generated according to the detected voltage Vc of level L at out and output to the priority control signal circuit 16.

The priority control signal circuit 16 is composed of resistors R1, R2, and R3, and the resistor R1 converts the control signal C of the GC controller 15 into a control signal C1 and supplies it to the first variable attenuator 4. The amount of attenuation is added to the receiving human power Sin. Then, the resistor R2,1+3 converts the control signal C from the AGC controller 15 into a control signal C2, supplies it to the second variable attenuator 4, and applies the attenuation amount to the output signal of the low noise amplifier 6. do. Then, when the level L of the output signal Sout of the intermediate frequency amplifier 11 which amplified the output of the second variable attenuator 8 is at a constant level Lc, the above control signal CI.

C2 is generated, and the attenuation amount addition of one of the first variable attenuator 4 and the second variable attenuator 8 is given priority over the attenuation amount addition of the other. That is, when the level of the input signal Sin starts to rise and the level of the output signal Sout reaches a certain level Lc or higher, first, the amount of additional attenuation of the first variable attenuator 4 in the preceding stage by the control signal C1 is greater than the amount of additional attenuation in the first variable attenuator 4 in the preceding stage by the control signal C1. The second variable attenuator 8 is controlled to increase the amount of attenuation added by the second variable attenuator 8 according to the control signal C2.
After the attenuation amount of C1 reaches a sufficiently large value, the control signal C1
control is performed to increase the amount of additional attenuation of the first variable attenuator 4 in the preceding stage. In addition, when the level of the input signal Sin becomes low, when the level of the output signal Sout becomes below a certain level Lc, first, the amount of attenuation of the first variable attenuator 4 in the preceding stage by the control signal CI is reduced. After the amount of attenuation is sufficiently small, the amount of attenuation of the second variable attenuator 8 in the subsequent stage is controlled to be small using the control signal C2. Therefore, the microwave A of the embodiment of the present invention shown in FIG.
In the GC circuit, when the level of the input signal Sin is high and the level of the output signal 5out exceeds a certain level Lc, first the additional attenuation of the first variable attenuator 4 in the previous stage is compared to the second variable attenuator in the subsequent stage.
Control is performed to increase the amount of attenuation added by the second variable attenuator 8, and after the attenuation amount of the second variable attenuator 8 reaches a sufficiently large value as shown in the characteristic diagram A in FIG. first stage
Since the amount of additional attenuation of the variable attenuator 4 is controlled to be large, linearity is maintained over a wide range of changes in the level of the input signal Sin. Furthermore, when the level of the input signal Sin is low and the level of the output signal Sout is below a certain level Lc, first, the attenuation amount of the first variable attenuator 4 in the previous stage is controlled to be small, so that the attenuation amount is sufficiently small. After that, the attenuation amount of the second variable attenuator 8 in the subsequent stage is controlled to be small, so that the attenuation amount of the variable attenuator 4 and 8 is both maximum or minimum as shown in the characteristic diagram of FIG. 3B. In this case, the noise figure is the same as that of the conventional example, and in an intermediate range other than the maximum or minimum attenuation amount, a better noise figure is obtained than that of the conventional example. In other words, there is no problem because the good noise figure of the low-noise amplifier 6 is not adversely affected by the first variable attenuator 4 and the second variable attenuator 8 and deteriorates, and a good noise figure value can be maintained. .

〔Effect of the invention〕

As explained above, according to the present invention, distortion caused by amplification is reduced when the level of the input signal is high, linearity between the input level and the output level is maintained, and the low noise amplifier is improved when the level of the input signal is low. Since a good noise figure is maintained, it is possible to realize a microwave AGC circuit with good linearity and low noise characteristics against large changes in input level.

FIG. 2 is a block diagram showing the configuration of a microwave AGC circuit according to an embodiment of the present invention. FIG. 3 is a characteristic diagram for explaining the operation of the embodiment of the present invention. FIG. 4 is a conventional diagram. FIG. 5 is a block diagram of the microwave receiving device of FIG.

In the figure, 4 is a first variable attenuator; 6 is a low noise amplifier, 8 is a second variable attenuator; 15 is an AGC controller; 16 is a priority control signal circuit.

[Brief explanation of the drawing]

Claims (1)

[Claims] A low noise figure is provided between the first variable attenuator (4) and the second variable attenuator (8) that gives the input signal (Sin) an amount of attenuation that varies depending on the control signal (C). In an AGC circuit of a microwave receiving device that has an amplifier (6) having a variable level and amplifies an input signal (Sin) whose level fluctuates to obtain an output signal (Sout) of a constant level, the level of the input signal (Sin) is The output signal (S
A control signal (C1, C2) that gives priority to adding attenuation amount to one of the first variable attenuator (4) and the second variable attenuator (8) over the other when the output (out) reaches a certain level (Lc). A priority control signal circuit (16) is provided to generate an input signal (
When the level of the output signal (Sin) becomes high and the output signal (Sout) exceeds a certain level (Lc), the additional attenuation of the second variable attenuator (8) is greater than the additional attenuation of the first variable attenuator (4). The second variable attenuator (8) increases the amount of attenuation.
After the amount of attenuation of the input signal (
When the level of the output signal (Sin) becomes low and the output signal (Sout) becomes below a certain level (Lc), the attenuation amount of the first variable attenuator (4) is first controlled to be small, so that the attenuation amount is sufficiently small. Microwave A characterized in that the attenuation amount of the second variable attenuator (8) is subsequently controlled to be reduced.
GC circuit.