The Design Of Weak Signal Detection System Analog Front-End

With the rapid development of science and technology,some special signals have attracted widespread attention.This kind of signal strength is low,and the converted voltage signal is generally only on the order of ? v,nv,or even pv,but it plays a vital role in people's lives.Traditional data acquisition systems can only be used for large signal processing,and it is difficult for such weak signals to be submerged in background noise.In response to this problem,a weak signal detection system is proposed.In the field of engineering applications,how to extract signals effectively and design a high-precision acquisition system is still a problem worthy of continuous research.The analog front-end circuit in the weak signal detection system is an important module that determines the performance of the entire system.In this paper,firstly the overall model of the detection system simulation front end based on MATLAB was built.the influence of various factors were analyzed and simulated,and relevant parameters to guide the subsequent circuit design were obtained.Secondly,the circuit construction of the analog front end of the acquisition system is completed,which mainly includes two parts:automatic gain control(AGC)and analog-to-digital converter(ADC).The overall circuit is initialized by a programmable gain amplifier,converted to a digital code by an analog-to-digital converter,then the automatic gain control circuit reads the digital code and automatically selects the programmable gain amplifier range after the operation.The analog-to-digital converter circuit uses a second-order sigma-delta ADC,which is mainly implemented by a switched capacitor integrator,including an integrator,a two-phase non-overlapping clock,a preamplifier latch comparator,and a digital decimation filter.Automatic gain control consists of a variable gain amplifier(VGA)and gain control.The variable gain amplifier uses a resistive feedback programmable gain amplifier which achieves 1-16x linear amplification.The control section implements gain selection based on a lookup table.Based on the adjustment principle of digital AGC,this paper makes full use of the original ADC in the detection system to participate in gain selection.The multiplexed ADC performs both functions simultaneously,effectively reducing the power consumption and area of the system.At the same time,the automatic gain control system is used in the detection system to complete the amplification of the signal.Different amplitudes of the input signal can be used to provide different gain sizes,and the analog-to-digital converter characteristics can be fully utilized to improve the conversion accuracy.The design of the analog front end of the weak signal detection system is based on the smic 0.18 1 m process.The overall circuit operates at 3.3V,the signal bandwidth is 1kHz,and the oversampling rate is 128.After simulation,the circuit signal-to-noise ratio(SNR)is 85.7dB,and the accuracy(ENOB)reaches 13.95bit,which meets the design requirements.