High-speed optocoupler detectors

Photodetector circuit includes photodiode, a current to voltage converter, and a voltage change detector which retains the value of the voltage prior to the voltage change. Current generated by photodiode (100) is sensed by transimpedance amplifier (110). Feedback resistor (Rf) couples the output of the amplifier to the negative input, the positive input is grounded. The negative input and the output of the amplifier are connected to the inputs of non-inverting unity-gain buffers (120) and (130) respectively. The outputs from the buffers are connected to opposite ends of a voltage divider which consists of (R1, R2). Positive input to comparator (140) is connected to one end of the voltage divider, in this case the output from buffer (130). The negative is connected to the junction of the divider resistors, and to capacitor (C).