Design Of An Amplification Circuit Suitable For Low-frequency And Small-amplitude Signal

Micro-sensor’s output signal is generally less than10mV, and the frequency islower than100KHz, the ordinary CMOS amplifier’s1/f noise affects the sensitivity ofmicro-sensor seriously, so it has practical application value to design a suitableamplifier circuit for the low-frequency and small-amplitude signal detection.This paper plans to achieve the closed loop amplification more than100times,60dB of1/f noise suppression, less than1%distortion of the target. This amplifier isbased on the “modulation-amplifier-demodulation” idea, and the basic workingprinciple: firstly, the low-frequency and small-amplitude signal goes through mixer,and modulates this signal to the vicinity of the LO signal frequency; then the mixedsignal goes through the amplifier, which can overcomes the1/f noise who comes fromthe ordinary CMOS amplifier; then the signal is demodulated by the mixer to low, atthe same time, the1/f noise of the amplifier is modulated to the vicinity of the LOsignal frequency; finally, the signal goes through the low-pass filter to achieve theseparation from1/f noise.The amplifier circuit includes four parts, the Local Oscillator (LO) unit, themixed unit, the amplifier unit and the filter unit. The LO unit selects the Wien Bridge,which has simple structure and stable performance. The mixed selects Gilbert, whichhas high conversion gain, good isolation characteristics, and strong suppression ofeven-order harmonics. The amplifier selects fully-differential structure, which hashigh gain and high common mode rejection ratio.The circuit is based on CSMC0.5um Mixed Signal technology, using TannerEDA Tools v13.14design, simulation and layout. This structure can realize the closedloop amplification more than200times, and signal distortion is less than0.45%of theoutput signal amplitude, noise suppression ability is at least95dB.The amplifiercircuit has a big advantage in the aspect of noise suppression and eliminatedisturbance.