Design and implementation of a CMOS automatic gain control amplifier

One of the problems faced by communications engineers is the fading of received signals (slow variations in the amplitude of the received carrier). This has led to the design of robust and adaptive automatic gain control (AGC) circuits employed in the front end of a typical radio receiver. An AGC system is a self-adaptive mechanism used to maintain a constant signal level at the output, regardless of the signal variations at the receiver. A complementary metal-oxide semiconductor (CMOS) AGC amplifier is presented in this paper. The amplifier uses a very compact variable gain amplifier (VGA) with an exponential-gain control. It yields an input dynamic range of 36.5 dB and provides a constant output signal of 2 V (peak-to-peak). The proposed system has a low power consumption of 37.3 mW, from a dual power supply of 3.3 V. The system achieves a low settling time of 46.38 ns, which is independent of the input signal voltage. The amplifier operates at a frequency of 200 MHz, using the standard 0.35 μm CMOS process. The simulation results confirm the feasibility of the proposed AGC.