Transimpedance amplifier with automatic gain control
AssigneeVitesse Semiconductor Corporation
InventorBalagopal Mayampurath
Life of this patent
Estimating the term…
Abstract
A transimpedance amplifier in an optical communication system is provided with automatic gain control (AGC) for increasing the input operating range while maintaining high stability. A photodetector is used to convert an optical signal into a differential current for the transimpedance amplifier. An AGC circuit has a gain control device connected across the differential input of the transimpedance amplifier. The gain control device has an impedance that varies as a function of a voltage at the differential output of the transimpedance. Preferably, the gain control device is a FET having a drain coupled to one of the differential inputs, a source coupled to the other differential input, and a gate for receiving an AGC voltage, the AGC voltage being a function of the voltage at the differential output.
Claims11
A differential amplifier with automatic gain control (AGC), comprising:
- a differential amplifier having a differential input and a differential output;
- and
- an AGC circuit comprising a gain control device connected across the differential input, said gain control device having an impedance that varies as a function of a signal on at least one of the differential outputs,
- wherein said gain control device comprises a field effect transistor (FET) having a drain coupled to one of the differential inputs, a source coupled to the other differential input, and a gate responsive to an AGC voltage, said AGC voltage being a function of the signal on said at least one of the differential outputs.
An optical communication link, comprising:
- a photodetector for converting an optical signal into a differential current;
- a differential transimpedance amplifier for converting the differential current to a differential voltage, said transimpedance amplifier having a differential input for receiving the differential current;
- and
- an automatic gain control (AGC) circuit comprising a gain control device connected across the differential input of the transimpedance amplifier, said gain control device having an impedance that varies as a function of the differential voltage.
A differential transimpedance amplifier with automatic gain control (AGC), comprising:
- a differential transimpedance amplifier having a differential input, a differential output, a first feedback resistor connected between one of the differential inputs and one of the differential outputs, and a second feedback resistor connected between the other differential input and the other differential output;
- and
- an AGC circuit comprising a rectifier having an input connected to said one of the differential outputs, and an output, an AGC amplifier having a first input connected to the output of the rectifier, a second input connected to a reference point, and an output, and a field effect transistor having a drain connected to said one of the differential inputs, a source connected to the other differential input, and a gate connected to the output of the AGC amplifier.
Dependencies are inferred from the claim text.