基于CMOS工艺的自动增益控制电路研究

Research on Automatic Gain Control Circuit based on CMOS Process

摘要:

在无线接收机中,天线接收的信号强度往往变化很大,自动增益控制环路(automatic gain control,AGC)根据这个信号强度来动态调节控制放大器的增益,向后级基带电路(如ADC)提供幅度恒定的信号,使得接受到的不同强度信号均能被正确接收和解调；为了达到通过识别接收机接收信号的强度动态调节放大器的增益,以实现输出信号幅度恒定的目的,文章基于TSMC90nm CMOS工艺着重论述了针对70 MHz中频信号的AGC电路设计过程,详细设计了AGC各模块电路,并从提高线性度、降低直流失调和提高稳定性等方面对电路进行了优化,主要介绍AGC芯片的版图设计并进行了后仿,给出了整个AGC系统的工作特性和各项指标；在电路设计过程中,针对线性度、输出信号幅度、增益控制范围等进行改进与优化,得到符合设计指标的电路结构；最后对AGC环路的性能进行仿真验证,得到该AGC在满足输出信号幅度和线性度的基础上达到了30 dB的动态范围,满足了接收机系统的要求。

Abstract:

In the wireless receiver, antenna receiving signal strength tend to vary greatly, automatic gain control loop (Automatic Gain Control, AGC) according to the signal strength to dynamically control the gain of the amplifier, backward level baseband circuit (such as ADC) to provide a constant amplitude signal, the different intensity of received signal can be received correctly and demodulation. In order to achieve the dynamic adjustment of the amplifier strength of the signal received by the receiver gain recognition, in order to achieve the output signal amplitude is constant, this paper focuses on the TSMC90nm CMOS process for AGC circuit design process of 70 MHz intermediate frequency signal based on the detailed design of the AGC circuit of each module, and in order to improve the linearity, reduce the DC offset and improve the stability. To optimize the circuit layout design, mainly introduces the AGC chip and the imitation, and gives the characteristics and indexes of AGC system. In the circuit design process, the linearity, the output signal amplitude and the gain control range are improved and optimized. Finally, the performance of the AGC loop is verified by simulation, and the dynamic range of the AGC is achieved on the basis of the output signal amplitude and linearity, which meets the requirements of the 30 dB system.