CMOS AGC Design Strategies

摘要

The automatic gain control (AGC) circuit is a critical building block in modern wireless transceivers. It is used in both the transmitter (TX) and receiver (RX). In the TX, the AGC is used to regulate the output power level. For example, a well-known issue in a CDMA system is the problem of simultaneously receiving two signals of different strength. If two users transmit to the base station (BS) at the same time, the received power from the close user will be much higher and will jam the signal from the far away user if the power level difference is large. It is desirable to use an AGC to control each TX's output power so that the power received from all users is equal. In the RX, the received signal can vary drastically in a mobile environment. At the same time, the analog-to-digital converter (ADC) requires a fixed input level. An AGC circuitry can be used to stabilize the received power level at the ADC's input.