Mobile He Alth Sensor Analog Front-end Integrated Circuit Research

With the desire for a healthy life and an aging population,the existing healthcare system is overwhelmed and there is an urgent need to find a more efficient mode of operation.Mobile health testing devices allow people to check their health status in their daily work and help diagnose relevant diseases in a timely and efficient manner.For example,clinical ECG testing usually uses wet gel to reduce contact impedance and electrode dc offset,which is usually less than ±50 m V.If mobile health testing also uses wet gel,it is likely to cause skin ulceration after prolonged use in chronic patients.Therefore,dry electrodes are needed,but the electrode dc offset of dry electrodes can be as high as ±300m V,which will easily cause the front-end amplifier to saturate and lose amplification capability.For the special characteristics of mobile health electronic devices,this paper designs a low-power,low-noise Capacitively-Coupled instrumentation amplifier with a system covering a ripple suppression loop,an auxiliary path to increase the input impedance,and an electrode dc offset suppression circuit.In order to form a high pass angle with very low frequency characteristics of the dc servo loop to suppress electrode dc offset,it is usually necessary to use a pseudo-resistor with very high resistance value with small layout area.However,the common pseudo-resistor structure has poor linearity,which deteriorates the frequency characteristics of the dc servo loop to some extent.In this paper,common pseudo-resistors such as single MOS pseudo-resistor,symmetric structure and parallel structure pseudo-resistor structure are studied in depth,and the linearity differences exhibited by these pseudo-resistor structures at different voltage polarities are summarized,based on which a streamlined pseudo-resistor structure with better linearity is proposed.Simulation results verify that the proposed pseudo-resistor structure has better harmonic distortion performance compared with other structures.Based on this,an DC electrode offset(EDO)solution with bulk feedback is proposed to suppress ±300m V EDO by using the parasitic capacitance of the amplifier input with the liner bias effect,so the maximum capacitance required for digital electrode offset is 1.37 p F,which reduces the area by 29%compared to the conventional approach.The design of the proposed capacitor-coupled chopper amplifier is verified using a standard 180 nm CMOS process.The post-simulation results show that the system quiescent current is only 5.4 μA at 1.8 V supply voltage,the gain is 40 d B over the bandwidth,the high-pass cutoff frequency can be adjusted within 0.5-49 Hz,the equivalent input detuning voltage is 6.68 μV,the DC input impedance is 449 MΩ The proposed capacitively-coupled chopper amplifier is suitable for mobile health detection applications.