| Under the condition of large input signal amplitude,the automatic gain control(AGC)amplifier can set the output signal at a fixed potential,or within a small range.It is utilized in the receiver of the wireless communication system to resist to attenuation in radio transmission,guaranteeing a large receiving range and a relatively low error rate as well.Besides,the AGC amplifier also widely emerges in wired communication,hard disk drives,laser,radar and other systems.In this paper,research status at home and abroad has been analyzed in detail.A mixed signal control AGC amplifier has been designed,achieving a large gain control range,medium signal bandwidth and fast settling time,meeting the requirements of several wireless communication systems.Firstly,the overall specifications of the proposed AGC amplifier have been come up,and then the overall architecture has been established.Secondly,the core module variable gain amplifier of the AGC has been designed in detail,including gain-stepping programmable gain amplifier(PGA)and continuous variable gain amplifier(VGA).The proposed PGA adopts resistor multiplex technology,which realizes a constant gain step,omits the decoder and reduces the use of resistors and transistors at the same time.Continuous variable gain amplifier employs the closed-loop whose input and output resistors are the MOSFETs operating in linear region,changing the traditional open-loop structures.This structure realizes continuous tunable gain,meanwhile achieves high-linearity.The exponent gain control circuit achieves the dB-linearity relation between the control voltage and gain.Thirdly,the other modules of the AGC amplifier have been designed,including peak detector,hysteresis comparator,DC offset cancellation circuit,current bandgap,voltage bandgap and so on.The projects have been design with SMIC 0.18 μm CMOS process.The post-simulation results prove that under the 3.3 V supply voltage,the AGC amplifier achieves a gain range of-23.55-61.25 dB,the settling time less than 100 μs,the-3 dB bandwidth of 17.45 MHz,and the power consumption of 28.4 mW.Those parameters can meet the design requirements completely. |
