The Key Technical Research Of Low-noise High-accuracy Front-end Amplifying Circuit Applied In AFE

In recent years,with the improvement of people's living standards and the development of microelectronics technology,portable medical equipment is widely concerned.Among them,by using the wireless body area network?WBAN?system,timely collection and processing of human body electrical signals makes portable human health monitoring possible.The wireless body area network is a small communication network on the human body composed of several wireless sensors and a central control unit.And the premise of constructing a wireless body area network is that an analog front-end circuit is required to obtain high-quality human biological electrical signals.It is also necessary to ensure the low power consumption,high accuracy,and low noise of the entire signal acquisition system to meet the needs of long-term accurate monitoring.The main task of this paper is to research and design the low-noise high-precision analog front-end circuit.This paper design low-noise preamplifier and variable gain amplifier are used SMIC 65nm CMOS process,to complete the verification and function optimization.The low-noise preamplifier circuit adopts a chopper-modulated full balanced differential difference amplifier?FBDDA?structure,which effectively eliminates higher harmonics and improves the signal anti-jamming performance.The capacitive coupling structure isolates the influence of the DC offset of the electrode;the pre-charging circuit structure is adopted,which increased the input impedance to avoid excessive sampling electrode impedance and loss of the common-mode rejection ratio of the unpaired preamplifier.The simulation results show that the proposed low noise preamplifier circuit has better performance:the equivalent input noise of the low-noise preamplifier is 308.68(1₈),the unity-gain bandwidth is 40.47MHz,the settling time is 1.5?s at 0.5%accuracy,and the input impedance is 313M?.The variable gain amplifier uses a low-power self-biasing unit-cell gain compensation structure.The circuit introduces a RMS detection circuit to achieve automatic gain control of the circuit.The simulation results show that the circuit gain dynamic range is 38.74dB,the maximum gain linear error is 0.8dB,the equivalent input noise is 1.6(1₈),and the minimum unit gain bandwidth is 5.13MHz.Bioelectric signal analog front-end circuit is an interface circuit between biological sampling electrode and portable medical equipment.In addition to low noise preamplifier and variable gain amplifier core design module,this paper also includes third-order Bessel low-pass filter,two-phase non-overlapping clocks generation circuit,a low-offset bandgap reference circuit,and a chopping spike filter.And completed the simulation of the overall circuit.The simulation results show that the low-pass cut-off frequency is adjustable from160Hz to 1.2kHz,the gain is adjustable from 44.1dB to 82.84dB,the equivalent input noise in the band is 2.4(1₈),and the noise energy efficiency factor is 2.8.