The HCPL4503M optocoupler consists of an AlGaAs LED optically coupled to a high speed photodetector transistor. A separate connection for the bias of the photodiode improves the speed by several orders of magnitude over conventional phototransistor optocouplers by reducing the base-collector capacitance of the input transistor. The base of the phototransistor is not bonded out to a pin for improved noise immunity. An internal noise shield provides superior common mode rejection of 15kV/s minimum.