The Research And Design Of CMOS Variable Gain Amplifier

With the development of various communication devices in modern society,the reconfigurability of various circuit modules in wireless communication systems has become an important research hot-spot.The variable gain amplifier in the receiver used as a typical representatives of reconfigurable amplifiers have been paid more attention.The variable gain amplifier located in the receiver can adjust the gain of the circuit,whose bandwidth affects the data transmission rate,and the channel bandwidth required by the wireless communication transceiver system in different application is different.In addition,the development of semiconductor technology has made the CMOS process a good choice for system-on-chip design which is low-cost and easy-to-integrate,but also challenges the design of variable gain amplifiers.Based on the research status at home and abroad,this paper focuses on the research hot-spot of variable gain amplifier based on CMOS technology,analyzes the principle and classical technology of variable gain amplifier,summarizes the performance of variable gain amplifier,and finally reconfigure two parameters from gain and bandwidth of two variable gain amplifiers.(1)The variable gain amplifier based on the Global Foundries 55nm CMOS process for auto gain control system uses a modified Cherry-Hooper amplifier to achieve wide band and widened gain dynamic range,utilizing the tunable characteristics of the transistor to achieve dB-linear characteristics of gain variation.A high-pass filter with a low cutoff frequency is added to the output to cancell the DC offset.For testing purposes,a buffer is added to the input and output.The simulation result shows an ultra-wide dynamic range of-33.4 dB-46.9 dB.The gain variation has dB-linear characteristics,the 3-d B bandwidth is 1.89 GHz(0.12 MHz-1.9 GHz),the noise figure is 12 dB at the maximum gain mode,the power consumption is 19.68 m W,and the area is only0.006 mm~2.(2)The variable gain amplifier based on the Global Foundries 55nm CMOS process with adjustable bandwidth is adopted.The variable bandwidth part is cascaded with the variable gain part.The variable bandwidth part has double negative feedback network through the improvement of the active feedback structure.Adjusting the negative feedback trans-conductance unit can realize the tunable bandwidth.The variable gain part can continuously adjust the gain through the signal-summing structure.Adding a low-pass filter to the double negative feedback network can reduce the DC offset.The output buffer are designed as a wide-band structure,which does not affect the bandwidth variation of the whole system.The simulation result shows that the bandwidth can changed from 2 GHz to 5 GHz,and the gain dynamic range is-9.31 dB-4.93 dB.The noise figure is 10.6 dB at the maximum gain mode,the power consumption is 8.24 m W,and the area is 0.01 mm~2.