JPS61201121A - Pyroelectric sensor system - Google Patents

Abstract

PURPOSE:To solve latch phenomenon without reducing sensitivity and the like by executing the negative feedback of the output of an amplifying circuit through the resistance or the capacitor to the pyroelectric sensor. CONSTITUTION:At A, the charge generated by a pyroelectric sensor 1 is applied to the gate of an FET 2 and amplified by the voltage. The voltage output is negatively fed back to the pyroelectric sensor 1 at the input side by a capaci tor 4. At such a time, the output is outputted from a resistance RD. At B, the charge of the pyroelectric sensor 1 is inputted from a (-) input of an opera tional amplifier 3 and amplified. The output of the operational amplifier 3 is negatively fed back to the pyroelectric sensor 1 by the capacitor 4. For the method of operating or not operating the function of an amplifier circuit of the operational amplifier 3, a switch 5 may be turned on and off. Thus, by the flowing of the electric current due to the electric current amplifying and the electric current integrating amplifying, the latch phenomenon is solved, and simultaneously, the mechanical chopper to discontinue the infrared light necessary to the pyroelectric sensor system can be made unnecessary.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a pyroelectric sensor system that senses infrared rays.

(Background of the Invention) A blackened film on the electrode surface of a pyroelectric sensor converts infrared energy into heat, causing a centimeter temperature change.

This temperature change generates a charge in the sensor, which generates a voltage across the resistor Rg connected to the same electrode, and the voltage across Rg is F.
The impedance is converted by the ET source-follower circuit and an output signal is generated as a voltage change across the resistor Rs. A problem with this FET source follower circuit is that when there is a large change in ambient temperature, for example, when the temperature rises or falls below 0° C., a latch phenomenon may occur, causing abnormal operation. As a countermeasure for this, the value of Rg is lowered and the discharge time constant is reduced, but this has drawbacks such as a corresponding decrease in sensitivity.

(Object of the Invention) The object of the present invention is to solve the above-mentioned latch phenomenon without reducing sensitivity.

(Structure of the Invention) A pyroelectric sensor system according to the present invention includes a pyroelectric sensor and an amplification circuit. The output of the amplification circuit is negatively fed back to the pyroelectric sensor via a resistor or a capacitor.

The conventional way of thinking was that pyroelectric sensors show a high resistance value when installed, so the only way to think about it was to amplify the voltage. The resistance of the pyroelectric sensor is a static resistance value.

In the present invention, we focused on the dynamic resistance value. In other words, it was noted that the impedance-like or superordinate resistance value is much lower than the static resistance value. This makes it possible to increase the current width, etc. Therefore, current always flows and the latch phenomenon does not occur.

In addition, by making the amplification circuit active and in negative operation, the circuit can be operated stably, and the pyroelectric sensor system can be made mechanically independent.

(Example) The present invention will be described below with reference to the drawings, etc., and FIG. 1 shows a first example of the present invention. The electric charge generated by the pyroelectric sensor 1 is applied to the gate of the FET 2 to amplify the voltage, and this voltage output is negatively fed back to the pyroelectric sensor 1 on the input side through the capacitor 4. The output at this time is output from the resistor RD.

This is different from the conventional method in which the signal was output from the RS end.

FIG. 2 shows a second embodiment according to the invention. The electric charge of the pyroelectric sensor 1 is inputted from the (1) input of the operational amplifier 3 and amplified. The output of the operational amplifier 3 is negatively fed back to the pyroelectric sensor 1 by the condenser 4. The capacitor 4
A high megohm resistor may be used instead (not shown).

The function of the amplifier circuit of the FET or operational amplifier can be activated or negatively activated by turning the switch 5 on and off. Another method (not shown) is to turn on and off a switch (not shown) that charges and discharges the charge in the capacitor 4.

(Effects of the Invention) The present invention solves the latch phenomenon by the current flow due to the current amplification and current integral amplification, and at the same time, the mechanical switch that intermittents (turns on and off) the infrared light, which is necessary for the conventional pyroelectric sensing system, can be used. The present invention has made it unnecessary.

This has made it smaller, has a longer lifespan, and is cheaper.

[Brief explanation of the drawing]

FIG. 1 shows a first embodiment of the present invention. FIG. 2 shows a second embodiment of the present invention. FIG. 3 shows an example of a conventional method. 1. Pyroelectric sensor 2. FET transistor 3. Operational amplifier 4. Capacitor 5. Switch 6. Power supply

Claims (4)

[Claims] (1) A pyroelectric sensor system comprising a pyroelectric sensor and an amplification circuit, wherein the output of the amplification circuit is negatively fed back to the pyroelectric sensor via a negative feedback element. (2) The pyroelectric sensor system according to claim 1, wherein the negative feedback element is a resistor. (3) The pyroelectric sensor system according to claim 1, wherein the negative feedback element is a capacitor. (4) The pyroelectric sensor system according to claim 3, further comprising a circuit that activates and negatively activates the function of the amplification circuit.