A Battery-Less ECG Monitoring System For Wired Audio Transmission

With the development of society and the aging of the population,the demand for health monitoring and medical care has gradually increased.Miniaturization,portability and intelligence have become the development direction of new medical electronic devices.This paper uses the headphone interface to transmit signals,and proposes a battery-less ECG monitoring chip and intelligent system for wired audio transmission.The system proposed in this paper uses the microphone channel in the 3.5mm wired headphone to transmit ECG signals.The left and right channels provide stable and precise supply voltage and local oscillator(LO)signal for the system.The proposed system uses the high-precision audio ADC in the intelligent device to perform analog-to-digital conversion on the transmitted ECG signal,and realizes signal analysis and processing through the inside software.No external battery,LO signal and duplicate modules(ADC,DSP and TX)are required,the proposed system has the advantages of small area,simple structure and portability.The front-end chip converts the sinusoidal signals from two channels into a supply voltage(DC)and a LO signal(square wave),respectively,and implements modulation and amplification of the ECG signal.The proposed chip is implemented in a SMIC 0.18?m standard CMOS process with a chip area of 1.72×1.59mm2.According to the characteristics of audio transmission,a chopper-AM reused mixer amplifier is proposed,which combines chopping with AM modulation and reuses the LO signals.Mixer amplifier includes preamplifier,automatic gain control amplifier,band-pass filter,and output interface circuit.In order to improve the robustness of the circuit,a novel pseudo-resistor structure is proposed as the pre-amplifier's DC feedback resistor.The total gain of the front-end amplifier ranges from 20dB to 47dB,and the gain is automatically adjusted according to the amplitude of the output signals.The band-pass filter has a center frequency of 5 kHz and a bandwidth of 4.25?5.8kHz,and the third harmonic suppression capability of the output signal is-45dB.The energy harvesting circuit realizes the rectification of the sinusoidal signal from left channel,and outputs 1.5V DC voltage to supply power to the system.When the headphone cable is connected,the system consumes 156?W.The local oscillator generation circuit shapes the sinusoidal signal from right channel to a square wave signal(5kHz)as the modulated clock signal.In this paper,the sampling and demodulation of the microphone signals and the generation of the channel signals are realized by the Matlab of the PC.The audio signal is quantized by the audio ADC inside the intelligent device,and then demodulated by software to realize signal restoration.In order to reduce the integration noise,digital filtering is also required,and the low-pass cutoff frequency is set to 200Hz.The test results verify the system function.The third harmonic suppression capability of the demodulated signal is-46dB,and the input reference noise level over the range of 0.1-200Hz is 150nV/?Hz with an integral noise of 2.12?Vrms·...