Research And Design Of Automatic Gain Control Circuits For Wireless Communication Applications

The role of Automatic gain control circuit(AGC)is to provide a relatively constant output amplitude when the amplitude of the input signal varies over a wide dynamic range.AGC is widely used in wired and wireless communications,multimedia devices and medical electronic equipment,especially in wireless communication systems,AGC is an important module in the receiver.Due to the different signal transmission distance and the influence of multipath fading,the input signal range of the receiver is greatly changed.To enable the receiver to correctly demodulate,you need to use automatic gain control circuit for different amplitude of the input signals.This paper aims to study and design a high-performance automatic gain control circuit for wireless communication.The main modules of the automatic gain control circuit proposed in this paper include: Variable Gain Amplifier(VGA),intermediate frequency amplifier,peak detector and integrator.The pseudo-exponential method is used to implement the dB linear relationship between the gain of the variable gain amplifier and the control signal.The IF amplifier is based on the existing circuit design to improve,with higher gain and wide bandwidth.The peak detector using differential input with current mirror load structure of the amplifier circuit to achieve the maintenance and tracking signals.The integrator module is composed of a charge pump and an external capacitor.The charge pump charges and discharges the external capacitor and changes the voltage applied to the capacitor,thus controlling the gain of the VGA and adjusting the gain.The design of the AGC circuit proposed in this paper is based on 0.5μm CMOS process,using Hspice tool for simulation and finally complete the layout design.The circuit works under the 3.3V voltage,the proposed overall AGC loop provides-80 ~ 52 dB dynamic range and the loop setting time is 4.3ms.IF circuit can achieve the maximum gain of 80 d B,the circuit power consumption is 2.8mW and the chip area is 1800μm × 1800μm.