JPS5951167B2 - gain control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gain control circuit that is capable of controlling the gain of an amplifier according to changes in the level of an input signal. It is most suitable for use in amplification circuits.

Conventionally, in this type of gain control circuit, the voltage level, etc. of an input signal supplied to the gain control circuit is detected, and the gain of the amplifier is controlled based on this detection signal.

Through this gain control, as shown in FIG. 1, the output signal V2 is amplified in proportion to the input signal V1.

Therefore, if the input signal 1 has a waveform as shown in FIG. 2A, the output signal V2 will have a waveform as shown in FIG. 2B.

The dynamic range of the amplifier circuit, that is, the ratio between the maximum output and the noise level, is maintained at a constant level regardless of sudden changes in the input signal (1).

However, when using such a gain control circuit to amplify the performance sound of various musical instruments, even if there is a sudden level change in the performance sound of the musical instrument, it is amplified within the same dynamic range, making it difficult for the auditory sense. I regret that it lacked a sense of realism.

The present invention is intended to correct the above-mentioned defects.It is an object of the present invention to solve the above-mentioned defects. This is what I did.

With this configuration, for example, when the input signal level rises rapidly, the gain of the amplification circuit is increased based on the time differential signal generated by this level change, thereby increasing the dynamic range of this rise position. This makes it possible to expand the .

Next, an embodiment of the gain control circuit of the present invention is shown in FIGS. 3 to 5B.
This will be explained based on the diagram.

First, regarding the circuit configuration, the input terminal is connected to one input terminal a of the amplifier circuit 2 via a DC blocking capacitor C1 (hereinafter simply referred to as capacitor C1).

The output terminal C of the amplifier circuit 2 is connected to the output terminal 3 via a DC blocking capacitor C2 (hereinafter simply referred to as capacitor C2), and is connected to the other input terminal of the amplifier circuit 1 via a resistor R1. It is connected to the.

Note that the resistors R1, R2, and R3 and the variable resistance circuit 4 connected in parallel to the resistor R3 control the feedback amount of the signal that is negatively fed back from the output terminal C of the amplifier circuit 2 to the other input terminal. It is for deciding.

The amplification circuit 5 is for amplifying the voltage across the resistor R3, and is set to, for example, an amplification degree of 36 CIB.

Also, a capacitor C3 connected to the output terminal of the amplifier circuit 5
constitutes a bypass filter circuit together with resistor R4, and the cut-off frequency is determined by the time constant of capacitor C3 and resistor R4.

Furthermore, the diodes D1 and D2 constitute a voltage doubler rectifier circuit, and the output signal of the amplifying circuit 5 is converted into a direct current and has twice the voltage.

Note that the resistor R5 is for preventing fluctuations in the DC voltage.

The capacitors C4 and C5 and the resistor R6 in the next stage constitute a smoothing circuit, and the capacitor C6 and the resistor R7 constitute a differentiating circuit.

Therefore, when the DC voltage obtained from this smoothing circuit suddenly changes, a differential signal corresponding to this is obtained and supplied to the amplifying circuit 6 at the next stage.

The output terminal of the amplifier circuit 6 is connected to the variable resistance circuit 4 described above.
The resistance value of the variable resistance circuit 4 is changed based on the output signal of the amplifier circuit 6.

Note that a change in the resistance value of the variable resistance circuit 4 means, in other words, a change in the resistance value between both ends of the resistor R3 with respect to the resistors R1 and R2. The amount of feedback from one input terminal to the other input terminal changes.

On the other hand, two feedback circuits are provided between the output terminal and the input terminal of the amplification circuit 6 described above, and the gains of the amplification circuit 6 can be adjusted respectively by these feedback circuits. .

That is, the first feedback circuit is constituted by resistors R8 and R9 and a variable resistor VR, and by adjusting the variable resistor VR, the gain of the amplifier 6 can be changed.

The second feedback circuit includes a DC blocking capacitor C7 (hereinafter simply referred to as capacitor Q) and a diode D3. D4.

This second feedback circuit operates only when the input signal supplied to the amplification circuit 6 becomes excessive, and the output voltage of the amplification circuit 6 momentarily increases due to the excessive input signal. Then, diode D3. D4 is the forward characteristic.

For this reason, the amount of feedback increases, and the amplification circuit 6 does not perform an amplification operation, but is configured to function as a so-called limiter amplifier.

Note that the resistor R1o is for stabilizing the output signal of the amplification circuit 6.

Next, the circuit operation will be explained.

First, to describe the case where there is no sudden change in the input signal Vi (not shown) supplied to the input terminal 1, the output signal Vo (not shown) amplified by the amplifier circuit 2 is connected to the capacitor C2. appears at the output terminal 3 via the signal.

At the same time, the output signal Vo is negatively fed back to the other input terminal of the amplifier circuit 2 via the resistor R1, and the resistor R
2, so the shunted current flows through the resistors R2 and R
Flows through 3.

At this time, a voltage drop occurs across the resistor R3 in response to the current flowing through the resistor R3, and this voltage across the resistor R3 is supplied to the amplifier circuit 5.

Since the output signal amplified by the amplification circuit 5 is cut off by the bypass filter circuits C3 and R4, only the output signal having a frequency equal to or higher than the cutoff frequency is output from the voltage doubler rectifier circuit D1. It is supplied to D2.

As a result, the output signal is rectified and made into a pulsating current, and further converted into a DC signal by the smoothing circuits C4, C5, and R6.

This DC signal is then supplied to the amplification circuit 6 via a differentiating circuit constituted by a capacitor C6 and a resistor R7, so that the DC component is blocked by the capacitor C6 and then supplied to the input terminal 1. Since there are no sudden changes in the input signal Vi, only minute alternating current changes occur in the amplification circuit 6.
will be supplied to

At this time, the output signal of the amplification circuit 6 is supplied to the variable resistance circuit 4, but since the output signal is minute as described above, the resistance value of the variable resistance circuit 4 does not change greatly.

Therefore, the resistance value between both ends of the resistor R3 does not change, and the current flowing through the resistor R3 also remains substantially constant, so the feedback amount of the amplifier circuit 2 does not change either.

As a result, the gain of the amplifier circuit 2 is such that the output signal Vo is proportional to the input signal Vi, as shown in the characteristic f1 of FIG. 4, as in the conventional case described above.

In addition, in FIG. 4, the characteristic f1 is the human power signal V as described above.
The case where there is no sudden change in i is shown, and the characteristic f2. As will be explained in detail later, f3 and f4 indicate the case where the input signal Vi is a signal such as a tone burst signal that changes rapidly only within a specific level range.

Next, a description will be given of the circuit operation when the input signal Vi supplied to the input terminal 1 suddenly changes.

Note that a tone burst signal as shown in FIG. 5A is used as an example of the input signal Vi.

When the human input signal Vi changes rapidly, the output signal VO of the amplification circuit 2 also changes correspondingly.

Then, in response to the rising position of the input signal Vi, the resistor R3
Since the current flowing through the resistor R3 also increases, the voltage across the resistor R3 naturally increases.

Since this voltage across both ends is supplied as is to the amplifier circuit 5, each circuit from the amplifier circuit 5 to the point P in FIG. 3 operates in the same manner as in the case described above.

However, in the differentiating circuit constituted by the capacitor C6 and the resistor R7, a differentiated signal having a level corresponding to the rise position of the input signal Vi is obtained.

This differential signal is supplied to an amplification circuit 6, where it is amplified and then supplied to the variable resistance circuit 4 to reduce its resistance type.

For this reason, the resistance type across the resistor R3 becomes smaller, so the current flowing through the resistor R2 increases, and therefore the amplifier circuit 2
The amount of negative feedback from the output terminal C to the input terminal S decreases.

For this reason, the gain of the amplification circuit 2 increases, and as shown in FIG.
2, and the output signal VO obtained from the output terminal 3 has a waveform whose rising portion overshoots as shown in FIG. 5B.

In the rising portion of the output signal (2)0, the attack time, ie, the rising time t1, is determined by the capacitors C4 and C5 and the resistor R6.

That is, by changing the values of these capacitors C4, C5 and resistor R6, the attack time t□ can be shortened by reducing the time constant of the smoothing circuit. By increasing the time constant, the attack time can be extended.

As a result, the gain of the amplifier 2 is changed correspondingly to the characteristic f3. They can be changed individually like f4.

On the other hand, as shown in FIG. 5B, the time required for the output signal Vo to return from its maximum value to a steady state according to the level of the input signal, that is, the recovery time t2, is determined by the capacitor C6.
and the time constant of R7.

Note that this recovery time t2 is determined by each characteristic f2° f3 . shown in FIG. Time T until f4 returns to its original characteristic f
2. This corresponds to T3°T4.

In this embodiment, in the above operation explanation, only the circuit operation when the input signal Vi suddenly changes is described.
The same operation as described above is performed for a frequency change of the input signal Vi near the cutoff frequency determined by the capacitor C3 and the resistor R4.

That is, since the signals supplied to the differentiating circuits C6 and R7 are significantly attenuated at frequencies lower than the cutoff frequency, the input signal V
A differential signal similar to that obtained when i changes rapidly is obtained near the cutoff frequency, and the variable resistance circuit 4 can be driven based on this.

Therefore, by setting the cutoff frequency to, for example, a frequency corresponding to a certain scale on a piano, the dynamic range around that frequency is expanded, producing an auditory effect as if the piano were being played right in front of the player.

Furthermore, in the above description of the operation, only the case where the input signal Vi rises has been described, but a differential signal can be similarly obtained even when the input signal Vi suddenly decreases.

In this case, the polarity of the differential signal is reversed, so if the variable resistance circuit 4 is driven based on this differential signal, the gain of the amplifier circuit 2 decreases, contrary to the case described above.

As described above, the present invention controls the gain of the amplification circuit based on the time-differentiated signal obtained by time-differentiating the input signal, so that the gain of the amplification circuit is controlled based on the time-differentiated signal obtained by time-differentiating the input signal. The level of the signal can be controlled.

For example, when the level of the input signal rises rapidly, the gain of the amplifier circuit is increased based on the time differential signal generated by this level change, thereby expanding the dynamic range of the rise position.

[Brief explanation of the drawing]

Figures 1 to 2B are for explaining a conventional gain control circuit. Figure 1 is a gain characteristic diagram, Figure 2A is an input signal waveform diagram, and Figure 2B is an output signal waveform diagram. be. 3 to 5B show an embodiment of the gain control circuit of the present invention, in which FIG. 3 is a circuit diagram, FIG. 4 is a gain characteristic diagram, FIG. 5A is an input signal waveform diagram, and FIG. Figure 5B is a waveform diagram of the output signal. In addition, in the symbols used in the drawings, 2 is an amplification circuit, 4 is a variable resistance circuit, C6 is a differential capacitor, R1,
R2 and R3 are gain control resistors, and R7 is a differentiation resistor.

Claims (1)

[Claims] 1. A gain control circuit characterized in that the gain of the amplification circuit is controlled based on a time-differentiated signal obtained by time-differentiating an input signal supplied to the amplification circuit.