A fiber optic receiver having a baseline clamp with two clamping diodes. A first diode has a cathode coupled to a source of a first signal, while a second diode has a cathode coupled to a source of a second signal, identical to the first signal but shifted by 180.degree. in phase from the first signal. The anodes of the two diodes are coupled to each other and to a common potential. A first detecting transistor in an AGC detector has a base connected to the first signal source and to the cathode of the first diode. A second detecting transistor in the AGC detector has a base coupled to the second signal source and to the cathode of the second diode, has an emitter coupled to an emitter of the first transistor, and has a collector coupled to the collector of the first transistor.