Evaluation electronics for differential photodiodes

摘要

In the case of evaluation electronics for differential photodiodes having a pulse-width-modulated rectangular output voltage, in the case of which a capacitor is charged alternately by means of in each case one photocurrent of the two photodiodes of the receiver up to a comparison voltage and subsequently has its charge changed to a second comparison voltage, the measured value is strictly proportional to the measurement variable, after low-pass filtering. The stability of the capacitor which is to be charged is irrelevant in this case since the same capacitor is charged via the photodiodes in each charging cycle so that said evaluation electronics are suitable for precision applications. The circuit is furthermore characterised by its simple construction, low number of parts, small space requirement and low costs.