A Battery-Less Portable ECG Monitoring System With Wired Audio Transmission

This paper proposes a batteryless electrocardiogram (ECG) monitoring chip and intelligent system with wired audio transmission, which can be applied to long-term and real-time ECG monitoring. The ECG signal is modulated and amplified in the front-end chip and then is transmitted through the microphone channel of the 3.5-mm headphone cable. The sinusoidal signals from the left and right channels are converted into a dc supply and a precise local oscillator signal in the front-end chip, respectively. The proposed system samples the signal through the high-precision audio analog-to-digital converter in smart devices and processes it through the internal software. Therefore, no external battery, local oscillator, and complicate modules are required in this system. A chopper/amplitude modulation (AM) reused mixer amplifier is proposed, which combines chopping with AM and reuses the local oscillator signal. The closed-loop gain of the proposed amplifier varies between 20 and 47 dB and can be automatically adjusted according to the amplitude of the output signal. The proposed chip was implemented in a standard 0.18-μm CMOS process and occupies 1.07 × 0.95 mm2 of core area. The power management module outputs a 1.5-V dc voltage to power the system. When connected with the headphone cable load, the chip consumes a total power of 156 μW. The proposed monitoring system has been verified by the audio device and MATLAB in the PC. The test results show that the input reference noise of the demodulated signal is 2.12 μVrms (0.1–200 Hz) and the total harmonic distortion is 0.56%@3 mV input.

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