An optical transient sensor circuit includes a photodiode in series with a MOS feedback transistor connected across a voltage difference. An inverting amplifier having its input connected to the common connection between the photodiode and the MOS feedback transistor and its output connected to an output-node for a measure of the incoming irradiance. A charge/discharge circuit, having an input connected to the output of the inverting amplifier, having an output connected to the gate of the MOS feedback transistor and having a first and second output for half-wave rectified and thresholded contrast encoding measures of positive and negative irradiance transients. A capacitor connected between a constant potential and the gate of the MOS feedback transistor.