JP2003324328A - Agc circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an AGC circuit which performs stable gain control. <P>SOLUTION: A gain control voltage VAGC for controlling the gain of a variable gain amplifier 11 and a reference voltage VREF are compared with each other and when the gain control voltage VAGC is larger than the reference voltage VREF, the gain control voltage VAGC inputted to the variable gain amplifier 11 is switched to the reference voltage VREF. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to AGC (Auto).
The present invention relates to a circuit for a "Magic Gain Control".

[0002]

2. Description of the Related Art FIG. 4 is a diagram showing an example of a general AGC circuit. The AGC circuit shown in FIG. 4 is provided, for example, in a receiving device such as a radio, and has a variable gain amplifier 41 and a control circuit 42 for controlling the gain of the variable gain amplifier 41.
It consists of The variable gain amplifier 41 is, for example,
An amplification circuit including a Gilbert cell circuit. Here, the gain of the variable gain amplifier 41 is proportional to the difference between the reference signal VREF and the gain control signal VAGC. Then, the variable gain amplifier 41 amplifies the input signal IN with this gain and outputs the output signal VOUT. At this time, the control circuit 42
Generates a gain control signal VAGC that keeps the output signal VOUT at a constant value. That is, the variable gain amplifier 41 outputs the output signal VOU of a constant level according to the gain control signal VAGC generated by the control circuit 42.
Output T.

FIG. 5 is a diagram showing the gain characteristic of the variable gain amplifier 41, in which the vertical axis represents the gain and the horizontal axis represents the gain control voltage VA.
GC is shown. As shown in FIG. 5, the gain control signal V
When the potential of AGC (hereinafter, gain control voltage VAGC) is lower than the potential of reference signal VREF (hereinafter, reference voltage VREF), the gain decreases as the gain control voltage VAGC increases, and the gain decreases as the gain control voltage VAGC decreases. Grows. On the other hand, when the gain control voltage VAGC is higher than the reference voltage VREF, the gain increases as the gain control voltage VAGC increases, and the gain decreases as the gain control voltage VAGC decreases. That is, the gain of the variable gain amplifier 41 is such that the gain control voltage VAGC is equal to the reference voltage V
The characteristics that are opposite to each other are shown when the gain control voltage VAGC is higher than REF and when the gain control voltage VAGC is lower than the reference voltage VREF.

[0004]

However, in the AGC circuit having such a configuration, the following problems may occur. That is, for example, when the amplitude of the input signal IN increases when the gain control voltage VAGC is lower than the reference voltage VREF, the control circuit 42 causes the variable gain amplifier 4 to operate.
In order to decrease the gain of 1, the gain control voltage VAGC is increased. However, at this time, if the tracking operation of the feedback system of the AGC circuit is slow, the gain control voltage VAGC exceeds the reference voltage VREF shown in FIG.
There is a possibility that it will be out of the range of C ≦ VREF).
Then, if the gain control voltage VAGC is out of the control range, in the above-mentioned case, the variable gain amplifier 41
If the gain control voltage VAGC is increased in order to reduce the gain, the gain is increased on the contrary, and the AGC operation diverges in some cases. Further, when noise is added to the gain control voltage VAGC, there is a problem that the gain control voltage VAGC exceeds the reference voltage VREF shown in FIG. 5 and is out of the control range.

As described above, in the conventional AGC circuit, the gain control may be unstable. Therefore, it is an object of the present invention to provide an AGC circuit that performs stable gain control.

[0006]

In order to solve the above problems, the present invention employs the following configurations. That is, the AGC circuit of the present invention generates an amplifier that amplifies an input signal with a gain determined based on the first control signal and a predetermined reference signal, and a second control signal based on the output of the amplifier. The first control signal is converted into the second control signal or the reference signal based on the comparison result by the generation means, the comparison means for comparing the second control signal with the reference signal, and the comparison means. And a switching means for switching to either one of the signals.

As a result, since the control signal does not fall outside the control range, stable gain control can be performed. Also, in the AGC circuit, for example, when the second control signal is smaller than the reference signal, the switching means selects the second control signal, and the second control signal is the reference signal. , The reference signal is selected.

As a result, since the control signal does not fall outside the control range, stable gain control can be performed. Further, the AGC circuit of the present invention generates an amplifier that amplifies an input signal with a gain determined based on the first control signal and a predetermined reference signal, and a second control signal based on the output of the amplifier. Generating means, comparing means for comparing the second control signal with the reference signal, and a time constant for adjusting the time constant of the control system including the amplifier and the generating means based on the comparison result by the comparing means. And means.

As a result, the convergence time of the control system in the amplifier can be shortened. In the AGC circuit, for example, when the second control signal is larger than the reference signal, the time constant means sets the time constant of the control system to:
It is made smaller than the time constant of the control system before the second control signal becomes larger than the reference signal.

As a result, the convergence time of the control system in the amplifier can be shortened. Further, the AGC circuit further has a switching means for switching the first control signal to one of the second control signal and the reference signal based on the comparison result by the comparison means. May be.

As a result, the convergence time of the control system of the amplifier can be shortened and the control signal can be kept out of the control range.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an AGC according to an embodiment of the present invention.
3 is a diagram showing a configuration of a circuit 10. FIG. The variable gain amplifier 11 can use a general amplifier, for example,
This is similar to the variable gain amplifier 41 shown in FIG. Therefore, the description of the configuration and operation is omitted.

As shown in FIG. 1, the embodiment A of the present invention is
The GC circuit 10 includes a detection unit 12 that generates and outputs a signal V1 that is a DC voltage corresponding to the output signal OUT output from the variable gain amplifier 11, the voltage of the signal V1, and the AGC circuit 1.
Gain control voltage VAG which is the target voltage of the control system at 0
A gain control voltage VAG for controlling the gain of the variable gain amplifier 11 by comparing with a predetermined reference voltage Vr indicating C.
The comparison control unit 13 that outputs C and the gain control voltage VAGC
Alternatively, the gain control voltage VAGC and the reference voltage VREF are compared with the switch 14 as a switching means for inputting either one of the reference voltage VREF to the variable gain amplifier 11 as a voltage for gain control, and depending on the comparison result. And a collating circuit (comparator) 15 as a comparing means for controlling the switching operation of the switch 14.
The detection unit 12 and the comparison control unit 13 may be combined to be considered as a generation unit that generates the gain control voltage VAGC.

The feature of the AGC circuit 10 of the embodiment of the present invention is that the AGC circuit 10 includes a switch 14 and a matching circuit 15. For example, when the gain characteristic of the variable gain amplifier 11 has a gain characteristic as shown in FIG. 5 and the gain control voltage VAGC is smaller than the reference voltage VREF, the switch 14 is set in the state as shown in FIG. Therefore, the gain control voltage VAGC output from the comparison controller 13 is input to the variable gain amplifier 11. The matching circuit 15 constantly compares the gain control voltage VAGC output from the comparison controller 13 with the reference voltage VREF. Then, in the comparison result, when the gain control voltage VAGC becomes larger than the reference voltage VREF, the switch 14
Is set to a state opposite to the position shown in FIG. 1, and the reference voltage VREF is input to the variable gain amplifier 11 instead of the gain control voltage VAGC. That is, for example, the gain control voltage VAGC and the reference signal VREF input to the variable gain amplifier 11 are used as the first control signal and the reference signal, and the gain control voltage VAGC output from the comparison control unit 13 is used as the second control signal. In this case, the comparison control unit 13 compares the second control signal with the reference signal, and switches the first control signal input to the variable gain amplifier 11 to the second control signal or the reference signal based on the comparison result. .

As described above, when the variable gain amplifier 11 has the gain characteristic as shown in FIG. 5 (control range where VAGC≤VREF), the gain control voltage VAGC is changed to the reference voltage VRE.
When it is smaller than F, the gain control voltage VAGC is in the control range, and the opposite characteristic (for example, the state in which the gain is desired to be lowered but the gain is not lowered) is not obtained. Therefore, the matching circuit 15 outputs the SW control signal V2 to the switch 14 so that the gain control voltage VAGC output from the comparison controller 13 is input to the variable gain amplifier 11. Further, when the gain control voltage VAGC becomes larger than the reference voltage VREF, the gain control voltage VAG
Since the AGC is out of the control range and has the opposite characteristic, the matching circuit 15 outputs the SW control signal V2 for inputting the reference voltage VREF to the variable gain amplifier 11 to the switch 1
4, and the gain control voltage VAGC is set to the reference voltage VREF within the controllable range. Then, the reference voltage VR
EF is input to the variable gain amplifier 11 instead of the gain control voltage VAGC, and the gain of the control system is minimized. Therefore, the output of the variable gain amplifier 11 becomes constant, and the divergence of the control system can be suppressed. Then, after a lapse of a predetermined time, it is preferable that the gain control voltage VAG output from the comparison control unit 13
After C reaches the control range of VAGC ≦ VREF,
The switch 14 returns to the state shown in FIG. 1, and the appropriate gain control voltage VAGC within the control range is input to the variable gain amplifier 11.

As described above, the collation circuit 15 has the switch 14
By controlling the gain control voltage VAGC, the control voltage can be immediately changed to a controllable range even if the gain control voltage VAGC is out of the control range as shown in FIG. It is possible to prevent the reverse control of the gain caused by the delay and noise, the variation of the temperature, the variation of the device, and the change of the use condition such as the power supply voltage, and to perform the stable gain control.

The AGC circuit 11 shown in FIG. 1 can be applied to a variable gain amplifier in which the gain characteristic does not become the opposite characteristic, and such an AGC circuit 11 enables gain control in an arbitrary control range. . Next, an AGC circuit according to another embodiment of the present invention will be described.

FIG. 2 is a diagram showing an AGC circuit 20 of another embodiment. In FIG. 2, the same components as those in FIG. 1 are designated by the same reference numerals, and the description of the operation thereof will be omitted. In FIG. 2, a characteristic point is that the time constant of the detection unit 22 (time constant of the control system in the AGC circuit 20) is changed according to the result of comparison between the gain control voltage VAGC and the reference voltage VREF. That is, for example, when the variable gain amplifier 11 having a gain characteristic as shown in FIG. 5 is applied, when the gain control voltage VAGC becomes larger than the reference voltage VREF, the time constant is controlled to be shortened and VAG is controlled.
It is a point that the original time constant is controlled when the range of C ≦ VREF is satisfied. The variable gain amplifier 11 applied to the AGC circuit 20 of FIG. 2 is a variable gain amplifier 1 having a gain characteristic such that the gain shown in FIG.
It may be 1, and the reference voltage VREF at this time can be set to an arbitrary value.

The conventional AGC circuit has an appropriate time constant so that the control system does not oscillate, but the output signal O
When the gain control signal V1 follows the change of UT slowly, the gain control signal VAGC is out of the control range (VAGC> V
REF) in some cases. Therefore, in the AGC circuit 11 of FIG. 1, when VAGC> VREF, VAGC
The gain control voltage VAGC is controlled so that Vref becomes equal to VREF so that the gain of the variable gain amplifier 11 does not have the opposite characteristic.

In the AGC circuit 21 shown in FIG. 2, the SW control signal V2 output from the matching circuit 15 is further detected by the detector 2.
2, the time constant of the detection unit 22 is switched based on the SW control signal V2. That is,
When the gain control voltage VAGC output from the comparison control unit 13 is larger than the reference voltage VREF, the time constant of the control system is smaller than the time constant of the control system before the gain control voltage VAGC becomes larger than the reference voltage VREF. S to do
The W control signal V2 is output from the matching circuit 15. As a result, the output signal OUT can be made to quickly follow the change in the signal V1, so that the time until the gain becomes constant (convergence time) can be shortened.

In the AGC circuit of FIG. 2, the control signal for varying the time constant of the detector 22 and the control signal for switching the switch 14 are the same SW control signal V2. The control signal for varying the time constant may be generated separately from the SW control signal V2.

The AGC circuit 20 may be constructed so that the matching circuit 15 controls only the time constant of the detection section 22. Also in this configuration, the convergence time of the control system in the AGC circuit 20 can be shortened. FIG. 3 is a diagram showing an example of a circuit diagram of the detection unit 22.

As shown in FIG. 3A, the detection unit 22 is composed of, for example, a detection circuit 31 and a time constant switching circuit 32, and controls the operation of the switch 32-1 based on the SW control signal V2. Then, different time constants 1 or 2 are selected. The detection circuit 31 may be composed of, for example, two capacitors 33a and 33b, a diode 34, and a resistor 35, as shown in FIG.

The time constant switching circuit 32 is, for example, as shown in FIG.
As shown in, the two resistors 36 and 37 having different resistance values may be switched by the switch 38, and the time constant may be changed by making the charging time of the capacitor 39 different. The switch 38 performs the switching operation of the resistor to be used according to the control signal output from the matching circuit 15.

Further, the time constant switching circuit 32, for example, as shown in FIG. 3D, two resistors 36 and 37 having different resistance values, a switch 38, a capacitor 39,
It may be configured with the comparator 40.

[0026]

As described above, according to the AGC circuit of the present invention, the control signal for controlling the gain of the variable gain amplifier is compared with the reference signal, and the control is input to the variable gain amplifying means based on the comparison result. Since the signal is switched to the reference signal, the gain control can be prevented from being controlled outside the control range, and stable gain control can be performed.

Further, according to the AGC circuit of the present invention, the time constant of the control system in the AGC signal from the output signal output from the variable gain amplifier, the control signal for controlling the gain of the variable gain amplifying means, and the reference signal. Since the adjustment is made based on the comparison result, the convergence time of the control system can be shortened.

[Brief description of drawings]

FIG. 1 is a diagram showing an AGC circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing an AGC circuit according to another embodiment.

FIG. 3 is a diagram showing an example of a circuit diagram of a detection unit.

FIG. 4 is a diagram showing a conventional AGC circuit.

FIG. 5 is a diagram showing a gain characteristic of a variable gain amplifier.

[Explanation of symbols]

10 AGC circuit 11 Variable gain amplifier 12 Detection unit 13 Comparison control unit 14 switch 15 Matching circuit 20 AGC circuit 22 Detection unit 31 Detection circuit 32 time constant switching circuit 32-1 switch 33a capacitor 33b capacitor 34 diode 35 resistance 36 Resistance 37 Resistance 38 switch 39 Capacitor 40 comparator 41 Variable gain amplifier 42 Control circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Miyagi             2-5-13 Saijocho, Joetsu City, Niigata Prefecture Niigata             Precision Co., Ltd. F-term (reference) 5J100 JA01 LA00 LA09 LA10 QA01

Claims (5)

[Claims] 1. An amplifier for amplifying an input signal with a gain determined based on a first control signal and a predetermined reference signal, and a generation means for generating a second control signal based on the output of the amplifier. Comparison means for comparing the second control signal with the reference signal and one of the second control signal and the reference signal for the first control signal based on the comparison result by the comparison means. An AGC circuit comprising: switching means for switching to a signal. 2. The AGC circuit according to claim 1, wherein the switching means selects the second control signal when the second control signal is smaller than the reference signal, and the second control signal is selected. An AGC circuit, wherein when the control signal of 2 is larger than the reference signal, the reference signal is selected. 3. An amplifier for amplifying an input signal with a gain determined based on a first control signal and a predetermined reference signal, and a generation means for generating a second control signal based on the output of the amplifier. Comparing means for comparing the second control signal with the reference signal; and time constant means for adjusting the time constant of the control system including the amplifier and the generating means based on the comparison result by the comparing means. An AGC circuit having. 4. The AGC circuit according to claim 3, wherein the time constant means sets the time constant of the control system to the second constant when the second control signal is larger than the reference signal. An AGC circuit, wherein a control signal is made smaller than a time constant of the control system before it becomes larger than the reference signal. 5. The AGC circuit according to claim 3, wherein the first control signal is one of the second control signal and the reference signal based on a comparison result by the comparison means. An AGC circuit having a switching means for switching to.