JP2000022467A - AGC circuit and automatic gain control method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To increase the response speed when the reception level is equal to or higher than a predetermined value than when the reception level is equal to or lower than a predetermined value. When a difference voltage ΔVL obtained by subtracting a reference voltage V0 from a voltage VL indicating a detection level is positive, a rectifying amplifier circuit 12 amplifies the difference voltage and gives a first-order delay of a time constant τ1 by an integration circuit 14 to the voltage V1. Generate When the difference voltage ΔVL is negative, the rectifying and amplifying circuit 13 amplifies the difference voltage, and the integrating circuit 1
In step 5, a voltage V2 is generated by giving a first-order lag of a time constant τ2 (> τ1). These voltages V1 or V2 are added to the reference voltage VS by the adding circuit 6 to control the gain of the voltage controlled attenuator 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AGC circuit and an automatic gain control method, and more particularly, to an AGC circuit having a variable time constant according to a reception level and an automatic gain control method.

[0002]

2. Description of the Related Art FIG. 2 shows a configuration example of a conventional AGC circuit. This shows a general circuit configuration. Input signal S
IN fluctuates its level due to fading etc.,
In order to keep the level of the output signal SOUT constant even if the level fluctuates, the output of the amplifier circuit 2 is converted into DC by the rectifier circuit 3, amplified by the amplifier circuit 4, and the output level at that time is detected. After passing through the integrating circuit 5, the output voltage VS of the reference voltage setter 7 is added by the adder circuit 6 to obtain a control voltage VC, and the control voltage is used by a voltage control attenuator (hereinafter abbreviated as VCA) 1 by the control voltage. Feedback control of gain.

[0003]

In the above-mentioned AGC circuit, the speed at which the AGC loop follows the level fluctuation of the input signal SIN is substantially determined by the time constant of the integrating circuit 5. The following speed is appropriately determined from the relationship between the stability of the loop and the settling time when the input level changes. However, a circuit (not shown) that performs demodulation, A / D conversion, and the like in response to the output signal SOUT generally has a signal level range (dynamic range) in which the circuit can operate normally. Otherwise, normal operation is impaired.
For this reason, there is a case where it is desired for the AGC circuit to respond as quickly as possible when the input level becomes equal to or higher than the reference value (this is referred to as attack follow-up) and to promptly prevent an increase in the output level. For this purpose, the time constant of the integrating circuit may be reduced. However, if the time constant is reduced, the settling time is increased. Therefore, the response when the input level is equal to or lower than the reference value (this is referred to as “recovery follow-up”) is characteristic degradation. Invite.
As described above, there is a case where it is desired to change the time constant of the AGC loop according to the range of the input level fluctuation, but this cannot be performed by the conventional circuit.

The dynamic range of the AGC, that is, the range to which the input level can be changed, is determined by the variable range of the attenuation of the VCA 1 and the dynamic range of the control voltage for controlling the attenuation. Usually required 4
If the dynamic range is about 0 to 60 dB, VC
Although the variable range of the amount of attenuation of A is sufficient, the control voltage VC needs to be secured by giving a loop gain appropriate for this range. For example, countermeasures such as providing an amplifier on the output side of the adder circuit 6 are taken. It costs.

SUMMARY OF THE INVENTION It is an object of the present invention to set an AGC time constant different between an attack time and a recovery time, and to easily set a wide dynamic range of the AGC.
It is to provide a C circuit and an automatic gain control method.

[0006]

To achieve the above object, the present invention provides a level detecting means for detecting a level of an output signal, a reference voltage setting means, and a level detecting means for detecting a level of an output signal. A subtraction circuit for obtaining a difference voltage obtained by subtracting the set voltage set by the reference voltage setting means from the voltage indicating the level, and when the difference voltage obtained by the subtraction circuit is positive and only when the difference voltage is obtained, A first time constant circuit for amplifying and integrating with a first-order lag element having a first time constant; and amplifying the difference voltage and having a second time constant only when and only when the difference voltage is negative. A second time constant circuit for integrating with a first-order lag element;
A control voltage generating means for generating a control voltage from a sum voltage of output voltages of the first and second time constant circuits, and a gain of which is controlled by the control voltage, and an output of which provides the output signal And an AGC circuit comprising: a variable gain amplifying means.

Further, the present invention generates a difference signal representing a difference between the level of an output signal and a preset level, and when the difference signal is positive, the difference signal is temporarily delayed by a first time constant. And when the difference signal is negative, the difference signal is given a temporary delay with a second time constant different from the first time constant, and the first or second temporary delay is given to the difference signal. To control the amplification factor of the amplifier by using the automatic gain control method.

[0008]

Embodiments of the present invention will be described below. FIG. 1 is a block diagram showing an example of the configuration of an AGC circuit according to the present invention.
2. It comprises a negative-side rectifying amplifier circuit 13, integrating circuits 14, 15, an adding circuit 6, and a reference voltage setting device 7. In this configuration, the reference voltage VO is set by the reference voltage setting unit 11 so as to cancel the output level VL of the rectifier circuit 3 when the level LOUT of the output signal SOUT becomes the reference level LO. The output voltage ΔVL of the subtraction circuit 10 is

## EQU1 ## ΔVL = VL−VO, but the positive side rectifying amplifier circuit 12 inverts and outputs a positive voltage proportional to the magnitude only when ΔVL>, and the negative side rectifying amplifier circuit 13 outputs when ΔVL <0. However, a negative voltage proportional to the magnitude is inverted and output, and the output at other times is zero.

FIG. 3 is a circuit diagram of the integrating circuit 14 or 15, which may be a general one using an operational amplifier. However, the time constants determined by the resistors R1, R2 and the capacitor C1 are τ1, τ2, respectively, which are set to different values.

Next, the operation of the circuit shown in FIG. 1 will be described. First, considering the quasi-stationary state ignoring the transient fluctuation at the time of the level fluctuation, since the integrating circuits 14 and 15 can be regarded as simple coefficient circuits, their output voltages V1 and V2 are as described above.

(Equation 2) Given by Here, the constant K is a combined gain of the positive side or negative side rectification amplification circuit 12 or 13 and the integration circuit 14 or 15 and both are assumed to be equal. The output voltage of the adding circuit 6, that is, the control voltage VC of VCA1 is

## EQU3 ## VC =-(V1 + V2 + VS). When the gain of VCA1 is G1 (dB), the gain of amplifier circuit 2 is G2 (dB), and the levels of input signal SIN and output signal SOUT are LIN and LOUT (dBm).

## EQU4 ## LOUT = LIN + G1 (VC) + G2, and the gain G1 varies with the control voltage VC.
FIG. 4 shows an example of the attenuation characteristic of the VCA with respect to the control voltage. The horizontal axis represents the control voltage VC, and the vertical axis represents the attenuation (= -G1).
It is. In this example, the attenuation increases as the control voltage VC decreases.

First, the output level LOU of the amplifier circuit 2 is
When T becomes equal to the reference value LO, the output voltage ΔVL of the subtraction circuit 10 shown in (Equation 1) becomes 0. At this time, the control voltage VC of (Equation 3) is equal to the inverted value of the polarity of the reference voltage VS. The reference voltage VS is determined so as to be located substantially at the center of the linear portion of the VAC1 characteristic as shown in FIG.

When the output level LOUT becomes larger than the reference value L0, the output voltage .DELTA.
VL is positive. At this time, the output to the rectifying and amplifying circuit 13 is 0 according to (Equation 2), and therefore the output V2 of the integrating circuit 15 is also 0. The voltage of the output V1 = KΔVL> 0 of the integrating circuit 14 is inverted and amplified, and Applied. Therefore, as shown in FIG. 4, the control voltage VC becomes smaller than VS by | V2 |, and the attenuation of VAC1 becomes -GS1 which is larger than -GS when VC = VS. Thus, the output level LOUT of the amplifier circuit 2 decreases, and the feedback control is performed.

On the other hand, when the output level LOUT becomes smaller than the reference value L0, the output voltage ΔVL of the subtraction circuit 10 shown in (Equation 1) becomes negative. At this time, the output of the rectifying and amplifying circuit 12 is 0 from (Equation 2), and therefore the output V1 of the integrating circuit 14 is obtained.
Is also 0, and the voltage of the output V2 = KΔVL <0 of the integrating circuit 15 is inverted and amplified and applied to the adding circuit 6. Therefore, as shown in FIG. 4, the control voltage VC becomes lower than VS by | V1 |, and the attenuation of VCA1 becomes -GS1 smaller than -GS when VC = VS. Thus, the output level LOUT of the amplifier circuit 2 increases, and the feedback control is performed.

Although the above operation has been described as a quasi-stationary state, that is, the integration circuits 14 and 15 are merely coefficient circuits, the operation is basically the same even in consideration of a transient state.
When OUT exceeds its reference level L0, the rectifying amplifier circuit 1
2 and the integrating circuit 14 perform feedback control. When the output level LOUT falls below the reference level L0, the feedback control is performed on the rectifying amplifier 13 and the integrating circuit 15. The response speed at the time of following the attack is determined by the time constant τ1 of the integrating circuit 14, and the response speed at the time of following the recovery is determined by the time constant τ2 of the integrating circuit 15. Therefore, the time constant of the integrating circuit 14 is
If it is set smaller than that of, attack tracking can be accelerated.

Next, consider the dynamic range. In FIG. 4, the dynamic range required for AGC is determined by the control voltage VC.
VSL to VSU. At this time, the output V1 of the integrating circuit 14 may change between 0 and VSU-VS (> 0), and the output V2 of the integrating circuit 15 may change between 0 and VSL-VS (<0). . In the case of the conventional FIG.
Is required to change between VSL-VS to VSU-VS. For this purpose, it is necessary to provide a sufficient gain to the amplifier circuit 4, the integration circuit 5, and the like. On the other hand, as described above, in the circuit of the present invention, this range is divided and divided into two circuits, so that it is not necessary to provide an extra amplifier or the like when implementing with an existing inexpensive IC or the like. In many cases, there is also an advantage that the economical configuration becomes easy.

In the above description, the output level is increased or decreased by controlling the VCA inserted in series with the amplifier. However, this may be achieved by a variable amplification factor mechanism incorporated in the amplifier. Needless to say.

[0017]

According to the present invention, there is an advantage that the speed of the attack response alone can be increased, and the level fluctuation in the receiving circuit or the like can be quickly suppressed to a predetermined value or less to guarantee the normal operation. There is also an advantage that it is easy to generate a control voltage for securing the dynamic range of AGC.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of an AGC circuit according to the present invention.

FIG. 2 is a block diagram showing a conventional AGC circuit.

FIG. 3 is a diagram showing an integration circuit.

FIG. 4 is a diagram illustrating an example of characteristics of a voltage-controlled attenuator.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 voltage controlled attenuator 2 amplifier circuit 3 rectifier circuit 6 adder circuit 7 reference voltage setting device 10 subtraction circuit 11 reference voltage setter 12, 13 rectification amplification circuit 14, 15 integration circuit

Claims (2)

[Claims] A level detection unit for detecting a level of an output signal; a reference voltage setting unit; and a setting voltage set by the reference voltage setting unit from a voltage indicating the level detected by the level detection unit. A subtraction circuit for obtaining a subtracted difference voltage; and when and only when the difference voltage obtained by the subtraction circuit is positive, amplify the difference voltage and integrate it with a first-order lag element having a first time constant. A first time constant circuit; a second time constant circuit for amplifying the difference voltage and integrating only with a first-order lag element having a second time constant when and only when the difference voltage is negative; A control voltage generating means for generating a control voltage from a sum voltage of output voltages of the first and second time constant circuits; and a gain controlled by the control voltage, and an output of the control voltage generating the output signal. AGC circuit comprising: a variable gain amplifying means of the roller. 2. A difference signal representing a difference between a level of an output signal and a preset level is generated, and when the difference signal is positive, a temporary delay is given to the difference signal with a first time constant. When the difference signal is negative, a temporary delay is given to the difference signal with a second time constant different from the first time constant, and amplification of the amplifier is performed by the signal given the first or second temporary delay. An automatic gain control method, wherein the rate is controlled.