Design Of An Analog Front-end For Biological Signal Acquisition With Wired Transmission

People pay more and more attention to their own health,while the existing medical resources still have the problem of insufficiency and uneven distribution.Therefore,a variety of portable,pocket-sized,and intelligent vital sign detection devices that can satisfy people's real-time grasp of their own health status have received widespread attention.The low-noise,low-power consumption,strong anti-jamming biological signal acquisition analog front-end as a key module of the aforementioned equipment has great research value.Compared with the wireless transmission scheme,the wired transmission scheme has stronger anti-interference ability,lower cost,and no battery life problem.According to the widespread popularity of the USB Type-C interface and the current status that the earphone line interface is gradually abandoned,this paper designs a wired front-end biological signal acquisition analog front end based on the USB Type-C interface.The front-end mainly includes four circuit modules such as chopper instrumentation amplifier,programmable gain amplifier,low-pass filter and SAR ADC.The first three circuit modules form a low-noise biosignal amplifier and are taped out.The chopper instrumentation amplifier is composed of the core circuit—capacitively coupled chopper instrumentation amplifier and auxiliary circuits like precharge circuit,driven right leg circuit and digital control DC servo loop.The digitally controlled DC servo loop designed in this paper has a faster calibration speed than the traditional analog DC servo loop.Combined with the programmable gain amplifier that includes a fast recovery circuit,it can completely eliminate the DC offset and achieve the quickly establishment or recover of the entire circuit.The low-noise biosignal amplifier using the digitally controlled DC servo loop can cope with a DC offset of up to ±511m V at the input.And it has such a wide DC offset calibration range and quite good noise performance,unlike the traditional analog DC servo loop,there is no trade-off between offset cancellation range and noise performance.Unlike traditional analog DC servo loop where there is a trade-off between offset cancellation range and noise performance,it has a wide DC offset calibration range as well as fairly good noise performance.In addition,the programmable gain amplifier designed in this paper uses double bias pseudo-resistors to achieve the function of maintaining the frequency characteristics when the gain changes,which can effectively prevent the loss of low-frequency biological signals when the gain changes.In this paper,the circuit design of the analog front end for wired transmission of biological signals is completed under the SMIC 0.18?m 1P6 M standard CMOS process,and the lownoise bio-signal amplifier composed of chopper instrumentation amplifier,programmable gain amplifier and low-pass filter was designed and taped out.The chip area is 1404.6?m×1005.6?m,and the area of core circuit is 849?m×451?m.The post-simulation of the low-noise biosignal amplifier shows that its power consumption is 4.5?W with 1.2V supply voltage.The input impedance is boosted to 2G? by the precharge circuit.The input equivalent noise is related to the calibration voltage generated by the digitally controlled DC servo loop.When the calibration voltage is 0,the equivalent input noise is the smallest(0.67?Vrms).When the calibration voltage is 300 m V(the maximum in practical applications),the equivalent input noise is the largest(1.49?Vrms).The high-pass cut-off frequency of the variable gain amplifier is always maintained at around 0.4 Hz under four gains(20/14/8/6d B).The FFT analysis of SAR ADC shows that the signal-to-noise distortion ratio is 58.35 d B,and the quantized effective number of bits reaches 9.4-bit.