Analog Front-end Circuit Design For Biomedical Signal Acquisition

In recent years,with the rapid development of bio-microelectronics technology,the combination of integrated circuit and biomedical science is more and more closely.The biomedical signal acquisition chip used in medical diagnosis has attracted wide attention for its broad development prospect and great application value.As a key module in biomedical signal acquisition chip,the performance of the analog front-end circuit can directly affect the precision of the whole signal acquisition chip.Therefore,the design of a good performance analog front-end circuit is very important.By analyzing the characteristics of biomedical signals and bio-potential electrodes,a low-noise,low-power,gain-bandwidth configurable biomedical signal acquisition analog front-end circuit is proposed.The analog front-end integrated circuit designed for biomedical signal acquisition in this paper consists of preamplifier,programmable gain amplifier,low-pass filter and bias circuit.In order to solve the problem of small biomedical signal amplitude and low frequency flicker noise,a closed-loop capacitively coupled chopper modulation preamplifier structure is used,and some improvements such as circuit power,noise and offset have been made to improve the circuit performance:instead of the traditional folded cascode structure,a current-splitting amplifier is proposed to reduce the noise of the circuit;to solve the problem of large layout area which is caused by the capacitance feedback,the T-type feedback capacitor structure is employed,which effectively reduces the capacitance value and chip area;to reduce the large offset voltage introduced by the bio-electrode,an offset voltage cancellation loop is introduced.Programmable gain amplifier is designed to make the circuit having the ability to acquire different kinds of biological signals.The flip-over-capacitor structure is applied to the design of the programmable gain amplifier,so that the switch-off resistance does not appear in the feedback loop,thus can effectively avoiding its influence on low frequency characteristics of the former circuit.In addition,in order to reduce the noise contribution of the programmable gain amplifier to the analog front-end circuit,a low noise current reuse structure is used in the design of programmable amplifier.A low-pass filter is used to filter the noise and offset of the preamplifier which is modulated into high frequency by chopping,and to suppress the out-of-band interference.The cut off frequency of the designed switched capacitor filter can be adjusted precisely,which made the bandwidth of the analog front end configurable.The proposed analog front-end circuit for biomedical signal acquisition is designed under SMIC 0.18?m 2P4M process.The post simulation results are as follows:the total power consumption of the whole circuit is 20.8?W with 1.8V power supply;and the circuit can provide four adjustable gain of 47.8dB?50.8dB?60dB?72.4dB;the tunable low frequency cutoff frequency is 0.3-1.1KHz;the bio-potential electrode offset cancellation capacity is52mV;the input-referred noise is 1.92?Vrms integrated from 0.5Hz to 1KHz,the layout area is 0.2mm~2.All aspects of the circuit performance can meet the design requirements.