Research On Analog Front-end IC Of Wearable Continuous ECG Monitoring

With the development of society and science,health problems have become the focus of people’s attention.It has become a universal need to be able to know physical condition of oneself and family anytime and anywhere.With the development of the Internet of things and cloud computing,the Internet of things healthcare has become an inevitable trend,and the development of wearable medical devices has attracted more and more attention.Wearable continuous ECG detection equipment can monitor the ECG signal in real time all day,which is one of the best methods to prevent cardiovascular disease.The traditional clinical electrocardiogram monitoring uses wet electrodes,and wet electrodes have lower contact resistance,which is beneficial to the collection of ECG signals.However,the traditional clinical ECG with wet gel electrodes(usually Ag/Ag Cl electrodes)normally requires a galvanic contact to the body and often skin preparation,which may cause skin irritation.Dry electrodes solve this problem by eliminating the need for gel,which in turn enables a faster setup time and improves patients’ comfort.It is the preferred electrode for wearable ECG detection.However,the flaw is its high electrode-skin impedance and electrode offset(EOS).In order to meet the application requirements of dry electrode,the analog front end of the wearable ECG detection must have ultra-high input impedance and large EOS handing range.The frequency of ECG signal is from 0.6Hz to 250 Hz.CMOS technology has serious 1/f noise at this frequency,which makes it impossible to use traditional instrumentation amplifier as preamplifier.In order to overcome the 1/f noise of CMOS process,the low-noise chopper preamplifier is designed.Meanwhile,in order to achieve a better impedance improvement effect,the sampling input stage circuit was proposed,and finally achieved a better impedance improvement effect than the existing positive feedback impedance improvement technology and the auxiliary amplifier impedance improvement technology.It can be seen from the relevant literature that the EOS handing range and system noise are mutually restricted.In order to achieve the large EOS handing range and low noise,an improved digital analog hybrid electrode offset suppression loop is adopted,and a fast recovery loop is added to shorten the recovery time.The design is based on TSMC 0.18 um CMOS technology,and the static power consumption is only 11 u A at 1.8V.the proposed chopper capacitively coupled instrumentation amplifier achieves an ultra-high input impedance of 120GΩ(<0.05 Hz)or 2.1GΩ(0.6～250 Hz),an EOS handing range of ±325 m V and a low noise of 1.9u Vrms at 0.6～250 Hz.It effectively balances the performance of input impedance,EOS range and noise.