Patent ID: 6778021
Filing Date: 2004-08-17
Classification: H03F,H03G

Abstract:
A transimpedance amplifier circuit with an amplifier input, the transimpedance amplifier circuit having a controlled low cutoff frequency as average input current to the amplifier input increases, the transimpedance amplifier circuit comprising:an optical device having an optical device input terminal and an optical device output terminal, the optical device for receiving an optical signal at the optical device input terminal, converting the optical signal to an input current, and providing the input current at the optical device output terminal; a forward transimpedance circuit connected to the optical device output terminal, the forward transimpedance circuit for receiving the input current and generating an output signal based on the input current; a feedback circuit that includes: a first circuit that for detecting a low frequency component of the output signal; and a second circuit that is driven by the low frequency component of the output signal and is connected to the forward transimpedance circuit such that the impedance of the second circuit presented at the amplifier input decreases as the output signal increases, the second circuit including: a first pnp transistor having a first base terminal and a first emitter terminal, wherein the first emitter terminal is connected to the amplifier input; and a second pnp transistor having a second base terminal, the second base terminal being connected to the first base terminal, the second pnp transistor having an emitter size that is some factor smaller than an emitter size of the first pnp transistor.