Design And Research Of An Analog Front-end For Blood Oxygen Saturation Measurement

With the increasing trend of aging population,real-time monitoring of human blood oxygen saturation can effectively prevent diseases as well as provide useful information for clinical treatment,which can greatly reduce the pressure on the public healthcare system,so,it is of high importance to study a blood oxygen saturation measurement circuit using semiconductor technology.This paper focuses on an analog front-end circuit for blood oxygen saturation measurement to effectively reduce the size,power consumption,and noise of medical instruments.A CMOS 0.18 μm process is used to design an analog front-end circuit for blood oxygen saturation measurement,which is divided into two major modules: a front-end amplifier module as well as a SAR ADC module.This paper begins with a brief introduction to the human pulse signal,the Lambert-Beer law along with the detection principle to obtain a theoretical model for the design of the measurement circuit.Next,the overall circuit structure of the blood oxygen measurement circuit is proposed.For the analysis of the first stage amplification(bandpass amplifier)in the front-end amplifier module,a bandpass amplifier with a modified pseudo-resistor structure and T-type capacitors is proposed,whose characteristics are analyzed and simulated.The capacitance area is effectively reduced compared with the conventional bandpass amplifier.When the second stage amplification(variable gain amplifier)is analyzed,the relationship between distortion and loop gain is obtained.The IM3 of the conventional variable gain amplifier is improved based on the gain boost technique.Then,the SAR ADC is analyzed and designed,the simulation results of each index of SAR ADC are given..In a word,the joint simulation of the front-end amplifier module and SAR ADC is performed,and the overall layout of the bleeding oxygen saturation measurement circuit is given after the layout design steps are introduced.With a supply voltage of 1.2 V at a bandwidth range of 0.4 Hz ～ 24 k Hz,the front-end amplifier module has a gain of 37 dB ～ 53 dB,a sum of equivalent input noise of 22.85 μV,and a power consumption of 15.6 u W.In particular,the front-end amplifier module has the function of amplifying and filtering out-of-band noise to improve the quality of the signal.The SAR ADC has a definition of 10 bits and a measurement rate of 20 k Hz.At an input sine signal of 253.906 Hz,the SNR is 58.51 dB,the SNDR is 58.45 dB,the SFDR is 73.75 dB,the THD is-77.1 dB,the ENOB is 9.42 bit.