Abstract: A TIA protection circuit comprises a TIA bias supply VTIA for applying a bias voltage to the TIA, an APD bias supply VAPD for applying a bias voltage to an APD connected to an input of the TIA, and TIA protection means for reducing the bias voltage applied to the APD to a safe level when the power supplied to the TIA is removed so as to protect the input of the TIA from the application of an excessive voltage. This provides fast protection against high voltages to the input stage of a CMOS-based TIA that is simple and reliable in operation. Due to space limitations and power consumption constraints in small form factor pluggable modules, such as XFP and SFP modules, the circuit must be simple, small and require very low power. Several alternative protection schemes are possible, one using a circuit in parallel with the APD bias supply and one using circuit in series with the APD bias supply.