JPS5840648Y2 - compression amplifier - Google Patents

Description

[Detailed description of the invention] When amplifying an alternating current signal whose magnitude changes, it may be a problem if the amplifier becomes saturated with a large input signal.

For example, in a differential type photoelectric switch using pulsed light, if an amplifier becomes saturated, changes in the intensity of the pulsed light cannot be detected beyond the amplifier.

To solve this problem, it is sufficient to use a so-called compression amplifier in which the amplification degree of the amplifier decreases as the input signal becomes larger, and a logarithmic amplifier or the like may be used.

However, conventional compression amplifiers of this type have a complicated structure and are expensive, and cannot be used in small and inexpensive photoelectric switches.

In view of the current situation, the present invention aims to provide an inexpensive compression amplifier with an extremely simple configuration.

Briefly explaining the principle of the present invention, the amount of feedback of a feedback amplifier is controlled by the output of the amplifier, and the amplification degree of the amplifier is apparently made smaller as the human input signal becomes larger.

This will be explained below with reference to the drawings.

In FIG. 1, 1 is an AC amplifier circuit that outputs output signals of two forward and reverse polarities in response to an AC input signal, 2 is a rectifier and smoothing circuit that outputs a negative DC voltage in response to a positive input signal, and 3
is a nonlinear circuit whose impedance changes depending on the level of DC input.

The AC input signal given to the input terminal 4 is sent to the AC amplifier circuit 1.
After being amplified by, the output obtained from the forward polarity output terminal is rectified and smoothed by the rectification and smoothing circuit 2 and output from the output terminal 5, and a part of the output is given to the nonlinear circuit 3 to control its impedance.

On the other hand, the AC output obtained from the reverse polarity output terminal of the AC amplifier circuit 1 is fed back to the input terminal of the AC amplifier circuit 1 via the nonlinear circuit 3.

Assuming that the magnitude of the AC input signal applied to the input terminal 4 is constant, the output of the AC amplifier circuit 1 and the DC output of the rectifier and smoothing circuit 2 are constant, and the nonlinear circuit 3 has a certain fixed value due to these constant inputs. The AC output obtained from the opposite polarity output terminal of the AC amplifier circuit 1 is fed back to the input terminal according to the impedance value.

This feedback is performed from the reverse polarity output terminal to the input terminal of the AC amplifier circuit 1, so that it is a negative feedback.

When the AC input signal given to the input terminal 4 increases from this state, the absolute value of each output increases accordingly, the impedance of the nonlinear circuit 3 becomes lower than before, and the amount of negative feedback increases as the AC input signal increases. increase over a minute.

Therefore, the rate of increase in the output obtained from the output terminal 5 is lower than the rate of increase in the AC input signal, and even if the AC input signal increases significantly, the output does not increase much, and the AC input signal is large enough to cause saturation. This means that it is possible to tolerate extremely large values.

FIG. 2 shows a specific example of the present invention that follows the configuration shown in FIG. 1.

In this configuration, the AC amplifier circuit 1 equivalently uses two transistors, and the rectifying and smoothing circuit 2 includes a base-emitter junction of a transistor 21, a capacitor 22, and a resistor 24.

This rectifying and smoothing circuit 2 has a function of detecting changes in the input signal, so it is slightly different from ordinary rectifying and smoothing circuits, and the outline of the rectifying and smoothing action is as follows.

That is, when the forward polarity output terminal of the AC amplifier circuit 1 becomes a high potential, the base of the capacitor 22 and the transistor 21 ~
When a current flows between the emitters and the forward polarity output terminal of the AC amplifier circuit 1 becomes a low potential, the electric charge stored in the capacitor 22 turns off the transistor 21 and resists it in the opposite direction. It begins to flow through 24.

This operation is repeated as long as an AC input signal is applied to the input terminal 4, and if the time constant of the series circuit consisting of the capacitor 22 and the resistor 24 is set appropriately, the capacitor 22 will be connected to the input terminal 4 at that time. A DC voltage corresponding to the strength of the applied AC input signal is obtained with the polarity as indicated in the figure.

Since this voltage includes ripples depending on the AC input signal, it is almost completely smoothed by the smoothing circuit formed by the capacitor 23 and resistor 25.

The nonlinear circuit 3 is mainly composed of a PNP type transistor 31, and the operating point of the transistor 31 is at the resistor 3.
2 and 33.

The base of the transistor 31 is supplied with only an alternating current component from the reverse polarity output terminal of the alternating current amplifier circuit 1 by cutting off the direct current component by a capacitor 9, and is also supplied with a direct current component from the rectifying and smoothing circuit 2 via a resistor 26. .

The resistor 26 functions to prevent the AC component from flowing out toward the capacitor 23 from the reverse polarity output terminal of the AC amplifier circuit 1, and to control the DC current flowing from the capacitor 23 to the base of the transistor 31.

In the above configuration, when an AC input signal of a certain value is given to the input terminal 4, a constant AC output is obtained at the forward polarity output terminal of the AC amplifier circuit 1, and a constant DC voltage is accumulated in the capacitor 23. be done.

The DC voltage stored in the capacitor 23 is applied to the base of the transistor 31 through the resistor 26, causing a base current to flow therethrough, and the transistor 31 exhibits a base-emitter impedance corresponding to the DC voltage.

On the other hand, the AC component from the opposite polarity output terminal of the AC amplifier circuit 1 is
added to the base of transistor 31 and capacitor 2
Negative feedback is provided to the input terminal of the AC amplifier circuit 1 according to the impedance between the base and emitter of the transistor 31 determined by the voltage between the terminals of the transistor 31.

When the magnitude of the AC input signal increases, the capacitor 23
The absolute value of the voltage between the terminals of transistor 31 becomes large.
The base current of transistor 31 increases, and the impedance between the base and emitter of transistor 31 decreases.

At this time, the absolute value of the AC output obtained from the reverse polarity output terminal of the AC amplifier circuit 1 has also increased, and this AC component passes between the base and emitter of the transistor 31, which has become low impedance, and flows into the AC amplifier circuit 1 in large quantities. Negative feedback is provided to the input terminal of.

Therefore, as the AC input signal becomes larger, the amount of negative feedback increases greatly, and the AC input signal given to the input terminal 4 and the output terminal 5
When compared with the output signal obtained from the AC input signal, the characteristics of a compression amplifier are obtained in which the amplification degree decreases as the AC input signal increases, and the output signal does not increase as the AC input signal increases.

In the example shown in FIG. 2, the emitter-collector impedance of the transistor 31 also decreases as the AC input signal increases.

Therefore, the inner portion of the AC input signal flows toward the transistor 31 and also serves to lower the input to the AC amplifier circuit 1, which further enhances the effects of the present invention.

As explained above, according to the present invention, an AC amplifier circuit,
Equipped with a rectifying and smoothing circuit and a nonlinear circuit whose impedance decreases as the absolute value of the DC input increases, the nonlinear circuit is controlled in a DC manner by a part of the output of the AC amplifier circuit via the rectifier and smoothing circuit, and AC amplification is performed. By negatively feeding a portion of the output of the circuit to the input terminal of the AC amplifier circuit via a nonlinear circuit, an extremely simple and inexpensive compression amplifier that can be used in small charging switches and the like can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a compression amplifier according to the present invention, and FIG. 2 is a circuit diagram of a specific example of the compression amplifier according to the present invention. 1.6... AC amplifier circuit, 2,7...
Rectifier smoothing circuit, 3゜8...Nonlinear circuit, 4...
...Input terminal, 5...Output terminal.

Claims (1)

[Scope of utility model registration request] It is equipped with an AC amplification circuit, a rectification smoothing circuit, and a nonlinear circuit whose impedance decreases as the absolute value of the DC input increases, which is mainly composed of PNP transistors, and the forward output end of the AC amplification circuit is connected to the rectification and smoothing circuit. and the input side of the AC amplifier circuit via a nonlinear circuit, and the output end of the AC amplifier circuit in the opposite direction is connected to the nonlinear circuit to increase or decrease the strength of the signal input to the AC amplifier circuit, and to increase or decrease the strength of the signal input to the AC amplifier circuit. A compression amplifier characterized in that an output in the opposite direction is negatively fed back to the signal input side of an AC amplifier circuit.