JPH0691397B2 - Automatic gain control circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an automatic gain control circuit capable of keeping an output signal level constant even if an input signal level fluctuates.

[Prior art]

FIG. 4 is a block diagram showing a configuration of a conventional automatic gain control circuit. As shown, the conventional automatic gain control circuit includes an input terminal 1, a detector 2, a divider 3 and an output terminal 4.

In the automatic gain control circuit having the above configuration, when an AC signal is applied to the input terminal 1, one of the signals is applied to the detector 2 and the other is applied to the denominator input A of the divider 3. The alternating current signal applied to the detector 2 is detected to be a direct current, and is applied to the numerator input B of the divider 3. The divider 3 calculates the division B / A = C of the numerator input B and the denominator input A and outputs the output C to the output terminal 4. When the detection efficiency of the detector 2 is 100%, the denominator input A and the numerator input B of the divider 3 are always equal, so the output C of the divider 3 becomes constant regardless of the input level of the divider 3. Operates as an automatic gain control (AGC) circuit.

However, in the above-mentioned automatic gain control circuit, there is actually no divider 3 which is accurate in frequency characteristics up to high frequencies, and an automatic gain control circuit usable up to high frequencies has not been obtained.

FIG. 5 is a block diagram showing a configuration example of an automatic gain control circuit which eliminates the above-mentioned problems and can be used even in a high frequency range. In the same figure, the parts given the same reference numerals as in FIG. 4 indicate the same or corresponding parts. The same applies to other drawings below. In FIG. 5, 5 is a multiplier and 6 is a reference voltage generator.

In the automatic gain control circuit with the above configuration, when the output voltage of the reference voltage generator 6 is 1V, the denominator input A of the divider 3 and the output C of the divider 3 are 1 / A = C, and the denominator of the divider 3 is This means that the reciprocal of the input A has been obtained.

The input D of the multiplier 5 is the same as the signal at the input terminal 1,
Since the input C of the multiplier 5 is a DC value obtained by calculating the reciprocal of the signal at the input terminal 1, the output E of the multiplier 5 is E = D · 1 / A. Since the input A of the divider 3 and the input D of the multiplier 5 have the same value only in the difference between AC and DC, the output E of the multiplier 5 is constant regardless of the signal level of the input terminal 1. It becomes a level and operates as an automatic gain control circuit. Further, since the divider 3 is a DC voltage calculation, it is not necessary for the frequency characteristic to extend to a high range, while the multiplier 5 can obtain a frequency characteristic extending to a high range.
Unlike the automatic gain control circuit having the configuration shown in FIG. 4, there is no problem that the accuracy deteriorates even in the high frequency region.

[Problems to be Solved by the Invention]

However, in the automatic gain control circuit having the configuration shown in FIG. 5, 1 / A = C when the voltage of the denominator input A is small, so that the output C of the divider 3 is saturated. This saturation voltage is not a fixed voltage as shown by the shaded area in FIG. 6 shows the input level of the input terminal 1 and the divider 3
It is a figure which shows the relationship with the output voltage of.

When used in such a state, there is a drawback that the voltage at the beginning of the automatic gain control is not constant as shown by the hatched portion in FIG. 7. FIG. 7 is a diagram showing the relationship between the input level of the input terminal 1 and the output level of the output terminal 4.

Also, using the divider 3 in a saturated state means that the divider 3
It is also unfavorable in terms of the characteristics and performance of the ICs that compose the.

The present invention has been made in view of the above points, and it is an object of the present invention to eliminate the above-mentioned drawbacks and provide an ideal automatic gain control circuit with high accuracy that can be used up to high frequencies.

[Means for Solving the Problems]

In order to solve the above-mentioned problems, the present invention, as shown in FIG. 1, is provided between the output of the detector 2 and the denominator input of the divider 3 of the conventional automatic gain control circuit shown in FIG. A non-linear circuit 7 having a circuit configuration as shown is inserted. Further, this non-linear circuit 7 has a characteristic that the output voltage of the output terminal 72 becomes constant when the input voltage input to the input terminal 71 is smaller than the reference voltage of the reference voltage generator 75 as described later.

[Action]

By inserting the non-linear circuit 7 between the output of the detector 2 and the denominator input of the divider 3 as described above, the level at which gain control is started becomes the reference voltage of the reference voltage generator 75, and this voltage is stabilized. Since it is easy to perform gain control, the level at which gain control starts is stabilized, and a constant voltage is input to the denominator input A of the divider 3 even when the input signal is smaller than the reference voltage of the reference voltage generator 75. Therefore, since the output of the divider 3 does not saturate, it is possible to realize an ideal automatic gain control circuit that can be used up to a high frequency band and has high accuracy.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an automatic gain control circuit according to the present invention. As shown in the figure, a nonlinear circuit 7 is inserted between the output of the detector 2 and the denominator input A of the divider 3.

FIG. 2 is a diagram showing input / output characteristics of the non-linear circuit 7 of the automatic gain control circuit, and FIG. 3 is a diagram showing a circuit configuration example of the non-linear circuit 7.

In FIG. 3, R _{1 to} R ₆ are resistors, D ₁ and D ₂ are diodes, 71 is an input terminal, 72 is an output terminal, 73 and 74 are operational amplifiers, and 75 is a reference voltage generator. Also, the reference voltage generator
75 of the output voltage is set to -0.1 V, the resistors R ₁ ~ resistor R ₆ are all the same value.

Due to the reference voltage generator 75, constant currents i ₁ and i ₂ flow through the resistors R ₂ and R ₅ . Also, i ₁ =
i ₂

In the non-linear circuit 7 having the above configuration, +0.
When the voltage of 1V is input, the current i ₁ due to the input voltage flows from the resistor R ₁ to the resistor R ₂ and flows into the reference voltage generator 75, but the input terminal voltage and the voltage of the reference voltage generator 75 are reversed. Since the polarities are equal, the voltage at the connection point between the resistors R ₁ and R ₂ is 0V, no voltage is applied to the negative input point of the operational amplifier 73, and the output voltage of the operational amplifier 73 is 0V. Therefore, no current flows through the resistor R ₄ , and the current i ₂ flows through the resistor R _5.
, Which flows from the output of operational amplifier 74 through resistor R ₆ . Since the resistor R ₅ = R ₆ , the output voltage of the amplifier 74 is the same as the voltage value of the reference voltage generator 75, and a voltage of +0.1 V in which only the polarity is inverted is output.

When the voltage value of input terminal 71 is less than + 0.1V,
Since the current flowing through the resistor R ₁ is smaller than the current i ₁ flowing through the resistor R _2, a portion of the current i ₁ is replenished by flow through the diode D ₁ from the output of the operational amplifier 73 to the resistor R ₂ To be done. As a result, the output voltage of the operational amplifier 73 becomes positive and is blocked by the diode D ₂ , and no current flows through the resistor R ₄ . This is the same as when a voltage of +0.1 is applied to the input terminal 71, and therefore the output voltage of the operational amplifier 74 remains +0.1.

On the other hand if the voltage of the large value is applied than + 0.1 V to the input terminal 71, the remaining a part becomes current i ₁ flowing through the resistor R ₂ of the current flowing through the resistor R ₁ is a resistor R ₃ It flows into the output of the operational amplifier 73 through the diode D ₂ . The resistor R _3, every other drop, a connection point between the resistor R ₄ becomes a negative potential. A current corresponding to the potential flows through the resistor R ₄ . This current flows from the output of operational amplifier 74 through resistor R ₆ to resistor R ₄
Is supplied to. The current flowing through resistor R ₆ is
There is a current i ₂ flowing through R ₅ . That is, the sum of the current flowing through the resistor R ₄ and the current flowing through the resistor R ₅ is the resistor R ₆
Flowing through.

Although the current of the current i ₁ from the current of the resistor R ₁ by the voltage applied to the input terminal 71 is pulled value flows respectively and resistor R ₃ to the resistor R _4, the argument is the resistor R ₆ Since the same current as the current value is added as the current i ₂ , the resistor R ₁ and the resistor
The absolute values of the currents flowing through R ₆ become equal, and the voltages at the input terminal 71 and the output terminal 72 become equal.

As described above, when the voltage at the input terminal 71 is less than or equal to the reference voltage value of the reference voltage generator 75, the voltage at the output terminal 72 becomes the same value as when the polarity of the voltage of the reference voltage generator 75 is inverted, When the voltage of the terminal 71 becomes more than the voltage value of the reference voltage generator 75, the voltage of the input terminal 71 becomes equal to the voltage of the output terminal 72,
Operates as a non-linear circuit.

When the circuit having the configuration shown in FIG. 3 is used as the non-linear circuit 7 of FIG. 1, the output voltage of the non-linear circuit 7 becomes a constant DC voltage when the signal level of the input terminal 1 is small. . This value enters the denominator input A of the divider 3, the output C of the divider 3 becomes a constant value, and is input to the input C of the multiplier 5. Then, the level of the input terminal 1 and the level of the output terminal 4 are proportional to each other in the state where they are multiplied by the input signal input to the input terminal 1.

When the input signal level exceeds the voltage value of the reference voltage generator 75 of the non-linear circuit 7 having the configuration shown in FIG. 3, the non-linear circuit 7 becomes a linear circuit, and the operation is the same as that of the automatic gain control circuit in FIG. , Operates as an automatic gain control circuit.

As described above, in the above embodiment, the level at which the gain control is started is the same as the voltage generated by the reference voltage generator 75 in FIG. 3, and this voltage is easy to stabilize. You can get a stable level. Further, unlike the automatic gain control circuit shown in FIG. 5, when the input signal is small, a constant voltage is applied to the denominator input A of the multiplier 3, so that the output of the divider 3 is saturated. Since it is not in a state, it becomes an ideal automatic gain control circuit with high accuracy that can be used up to high frequencies.

〔The invention's effect〕

As described above, according to the present invention, the following excellent effects can be obtained.

That is, since a non-linear circuit is inserted between the output of the detector and the denominator input of the divider to maintain a constant output level when the input signal level is less than or equal to a predetermined value, the gain control will start from that predetermined value. Since it is easy to stabilize this predetermined value, the level at which gain control starts is stable, and a constant voltage is applied to the denominator input of the divider even when the input signal is smaller than the predetermined value. The output of the divider does not saturate. Therefore, it is possible to realize an ideal automatic gain control circuit that can be used up to a high frequency and has high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an automatic gain control circuit according to the present invention, and FIG. 2 is a diagram showing input / output characteristics of a non-linear circuit,
FIG. 3 is a diagram showing a circuit configuration example of this non-linear circuit, FIG. 4 is a block diagram showing a configuration of a conventional automatic gain control circuit, and FIG. 5 is a conventional automatic gain control circuit usable even at a high frequency. Is a block diagram showing an example of the configuration of FIG. 6, FIG. 6 is a diagram showing the relationship between the input terminal level and the output voltage of the divider of FIG.
FIG. 7 is a diagram showing the relationship between the input level and the output level of the automatic gain control circuit of FIG. In the figure, 1 ... input terminal, 2 ... detector, 3 ... divider,
4 ... Output terminal, 5 ... Multiplier, 6 ... Reference voltage generator, 7 ... Non-linear circuit.

Claims (1)

[Claims] 1. A denominator of the divider comprising a detector, a reference voltage generator, a divider and a multiplier, the input terminal of which is connected to one input of the multiplier and the input of the detector. The output of the detector is input to the input, the output of the reference voltage generator is input to the numerator input, the output of the divider is connected to the other input of the multiplier, and the output of the multiplier is output terminal. In the automatic gain control circuit of the configuration connected to, a non-linear circuit is inserted between the output of the detector and the denominator input of the divider when the input signal level is equal to or lower than a predetermined value. And automatic gain control circuit.