Research And Design Of Preamplifier For Weak Signal Acquisition

With the development of modern science and technology,weak signal detection and analysis technology gradually mature,it promotes the national defense,biomedical science,industrial applications and the process of basic disciplines.The weak signals are converted to electrical signals by various sensors,but the output signal from the sensors is usually weak and the frequency is low.It needs a high performance analog front-end amplifier to process the signal.It is the core module of the weak signal acquisition system.There are many kinds of low-frequency and weak signals in nature.In this paper,the circuit's research object is typical biomedical signal.The purpose of this paper is to design an analog CMOS preamplifier with low noise,low power consumption and low chip area for the purpose of effectively extracting weak signal.Because of the difference of the biomedical signal due to individual differences and acquisition environment,a variable gain amplifier is needed.This paper will design a resistance variable gain amplifier,which uses its gain adjustable characteristics to achieve different gain amplification for different biomedical signals,the amplifier can achieve the EEG signal amplification of 100 times and nerve signal amplification of 1000 times.In order to suppress the DC drift voltage caused by the sampling sensor and improve the power supply rejection ratio,this paper will introduce the famous "AC-Coupled-Capacitive Feedback" instrumentation amplifier,which uses capacitance and high impedance of the NMOS resistor to produce band-pass filter effect.It can also remove low frequency and high frequency noise.The whole preamplifier is cascaded by variable gain amplifier and instrumentation amplifier.This paper will discuss the performance of various cascaded architectures,for biomedical signals with amplitudes ranging from 0.5Hz to 1KHz,such as ECG,the paper will take the most suitable instrumentation amplifier cascade variable gain amplifier architecture,the architecture can achieve a signal amplification of 1000 times,and can achieve good performance.In this paper,the analog preamplifier circuit is designed to operate at 1V and the circuit uses 0.18?m process.The Hspice tool is used to simulate the circuit.The average power dissipation of the whole circuit is 2.9?W,the gain is about 57.6dB,the common mode rejection ratio is 120 dB,The equivalent input noise in the 200 Hz frequency range is 1.59?V.