JPS6257950B2 - - Google Patents

Description

Detailed Description of the Invention The present invention provides an amplitude detection circuit that detects the presence or absence of a special component that exceeds the steady maximum or minimum level of the signal when it is mixed into the signal. The present invention is designed to enable reliable and stable detection with a particularly simple configuration.

An example of the amplitude detection circuit according to the present invention will be explained below with reference to the drawings.

The example shown in the figure is a case where the present invention is applied when some kind of control is to be performed based on the detection output when light exceeding the normal light amount is detected.
A DC power source 1 is grounded through a series circuit of resistors 2 and 3 and a phototransistor 4, and the phototransistor 4 detects light. That is, when light enters the phototransistor 4, it is turned on, and an input signal corresponding to the amount of light is obtained at its collector.

This input signal is connected to the PNP through the coupling capacitor 5.
It is supplied to the emitter of the type transistor 6. A predetermined base bias voltage is applied to this transistor 6 so that it is always turned on.
Therefore, the input signal is obtained at the collector side of the transistor 6 with the same polarity. Then, the input signal obtained at the collector side is supplied to the base of the NPN type transistor 7, and a signal S ₁ whose polarity is inverted with respect to the original input signal is supplied to the collector side as shown by the solid line in Fig. 2. obtain. Here, the portion Sa in the signal _S1 indicates that the phototransistor 4 has detected a light amount exceeding the normal light amount. This polarity-inverted input signal S ₁ is then supplied to the base of a PNP type transistor 9 forming a detection circuit 8 . In this case, the time constant determined by the resistor 10 and capacitor 11 constituting the first time constant circuit of the detection circuit 8 is selected to be relatively small. Therefore, a detection output _S2 as shown by the broken line in FIG. 2 is obtained at the emitter of the transistor 9, and the minimum level of the input signal _S1 is detected. The detected output S ₂ is then supplied to a second time constant circuit 15 made up of a resistor 13 and a capacitor 14 through a unidirectional conduction element such as a diode 12 . Here, this time constant circuit 15
The time constant is selected to be sufficiently larger than the time constant of the detection circuit 8. Therefore, on the output side of the time constant circuit 15, as shown by the chain line in FIG. 2, an output voltage E ₀ is obtained which is equal to the average value of the minimum level of the input signal S ₁ during steady state. That is, in this case, there is a component Sa in the input signal S ₁ and therefore in the detection output S ₂ that exceeds the minimum level in the steady state.
Even if the time constant circuit 1 is
5 is prevented from discharging to the detection circuit 8 side, this component Sa does not appear on the output side of the circuit 15, and the output voltage of the circuit 15 is maintained at the voltage _E0 even in this part. Ru.

Then, using this output voltage E ₀ as the reference voltage, NPN
to the base of a transistor 16. The emitter of this transistor 16 is directly connected to the emitter of a PNP type transistor 17 to form a comparison circuit 18. The input signal S ₁ obtained from the collector of transistor 7 is then supplied to the base of transistor 17 . Therefore, if the forward voltage drop between the base and emitter of transistors 16 and 17 _{is VBE} , transistor 17 is turned on when input signal _S1 becomes a voltage equal to _or lower than _E0-2VBE . Therefore, as mentioned above, if there is a component Sa in the input signal _S1 that exceeds the minimum level in the steady state, the transistor 17
is turned on, and a detection voltage e ₀ is obtained at the output terminal 19 derived from its collector side.

Therefore, in the case of the example shown in the figure, even if the amount of light detected by the phototransistor 4 changes constantly due to ripples in the light source, it is possible to reliably detect light that exceeds the amount of light during normal operation. It will be like that.

In the example shown in the figure, the voltage obtained at the connection point of resistors 2 and 3 is supplied to the base of a PNP type transistor 20, and the emitter of this transistor 20 is supplied to the base of the transistor 20.
A light emitting diode 21 is connected in series with the collector, and when the phototransistor 4 detects light exceeding the normal light intensity, the transistor 20 turns on and the light emitting diode 21 lights up, indicating this state. I'm trying to make it happen.

According to the above-described circuit of the present invention, since the presence or absence of a component exceeding the maximum or minimum level in the signal is detected based on the steady maximum or minimum level in the signal, reliable detection can be performed.
Moreover, even when the level of the input signal _S1 changes due to a change in the power supply voltage, for example, the reference voltage _E0 changes according to the level of the input signal _S1 , so the level of the input signal _S1 and the reference The relative relationship with the voltage E ₀ is constant, and stable operation can be expected even with changes in the power supply voltage.

Note that as a method for detecting this input signal without being affected by background components contained in the input signal, the time constant is switched instead of connecting two time constant circuits as in the present invention. However, with this configuration, the time constant must be changed each time the background component contained in the input signal changes, so although the detection operation is troublesome, sufficient detection accuracy cannot be achieved. In addition, since the input signal can only be detected during a predetermined period after switching the time constant without being affected by background components, intermittent detection is inevitable.

In contrast to this conventional example, the present invention has the advantages of being able to detect an input signal without switching a switch, being able to detect an input signal regardless of level fluctuations in the background component, and being able to perform continuous detection. It is much more useful than the conventional configuration.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram of an example of the circuit of the present invention, and FIG. 2 is a waveform diagram for explaining the same. 1 is a DC power supply, 4 is a phototransistor, 8 is a detection circuit, 15 is a time constant circuit, and 18 is a comparison circuit.

Claims (1)

[Claims] 1. A detection circuit that detects an input signal, a first time constant circuit with a relatively small time constant to which the output of the detection circuit is supplied, and the output of the first time constant circuit is supplied via a diode. It consists of a second time constant circuit with a relatively large time constant, and a comparison circuit that compares the output of the second time constant circuit with the input signal,
An amplitude detection circuit configured to detect only special components exceeding a steady maximum or minimum level in the input signal.