Digitally controlled automatic gain control system for use in an analog front-end of a receiver

摘要

There is disclosed an automatic gain control circuit (AGC) controller for use in a transceiver for operating in a high frequency Ethernet local area network (LAN). The transceiver comprises front-end analog signal processing circuitry capable of transmitting an outgoing analog signal to an external cable via a: transformer, reducing a DC component in an incoming analog signal, and reducing an echo of the outgoing analog signal in the incoming analog signal. The front-end analog signal processing circuitry also comprises an automatic gain control (AGC) circuit for amplifying the incoming analog signal by an adjustable gain factor. The AGC controller comprises: 1) a first circuit for determining an absolute value of an output signal of the front-end analog signal processing circuitry; and 2) comparison circuitry for comparing the absolute value of the output signal to a pre-determined threshold value and generating a gain control signal in response to the comparison. The comparison circuitry sets the gain control signal to a first gain control value if the absolute value exceeds the pre-determined threshold value and sets the gain control signal to a second gain control value if the absolute value does not exceed the pre-determined threshold value. The AGC controller also comprises: 3) a gain adjustment circuit for modifying the adjustable gain factor of the AGC circuit according to the first gain control value and the second gain control value.