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Abstract

The light reception signal circuit for photoelectric switch includes a photoelectric conversion circuit for receiving light from a light emitting part controlled for periodic emission. The photoelectric conversion circuit generates an electrical signal corresponding to the quantity of the received light. A programmable attenuator receives the output electrical signal, and attenuates it in even step in response to a digital control signal. A first comparator compares the output voltage with a predetermined upper bound threshold. The first comparator generates a clock signal when the output voltage exceeds the upper bound threshold. A peak holding circuit for receives an output voltage of the programmable attenuator, and holds the peak value of the output voltage on a time constant that is much longer than an emission period of the light emitting part. A second comparator compares the output voltage of the peak holding circuit with a predetermined lower bound threshold and generates an outgoing signal when the output voltage decreases below the lower bound threshold. A counter counts the clock pulses thereby generating a digital control signal for increasing the attenuation of the programmable attenuator. The counter is reset outgoing signal of the second comparator. A third comparator compares the output voltage of the programmable attenuator with a predetermined decision level to produce the detection output of the photoelectric switch.

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