LIGHT QUANTITY COMPENSATION CIRCUIT

摘要

PURPOSE:To compensate characteristic changes in a light emitting section and a light reception section by providing a control circuit increasing/decreasing stepwise a light quantity to approach the light reception quantity to a reference level to allow one light reception section to attain signal detection and light quantity compensation. CONSTITUTION:A signal for selecting a reference level for setting light reception quantity is given to an input terminal 11 and a selection circuit 9 gives a reference level corresponding to an objective light reception quantity to a non- inverting input of a comparator circuit 5. A signal being the amplification of the light reception signal is given to an inverting input of the circuit 5. The circuit 5 has a Schmitt width DELTAE and decides the inverting input depending on the upper/lower limit of (reference level + or -DELTAE/2). A counter circuit 6 counts so that the output of the amplifier circuit 4 is coincident with the reference level by using the output signal of the circuit 5 and a high-or a low-level signal is outputted from outputs Q0-Qn. A light irradiation current drive circuit 8 outputs a light irradiation current I in response to the output of the circuit 6.