ECG Measurement System including 10-bit SAR ADC

VLSI Design Lab Project Video from the Spring 2024 ECG Team: Jingyi Huang, Xi Wang, and Xinchang Wang.

See http://www.ee.columbia.edu/~kinget/EE6350_S24/ECG for a full description.

We designed, taped out, and tested a custom integrated circuit (IC or chip) in TSMC 65nm CMOS for an electrocardiogram (ECG) measurement system that includes an instrumentation amplifier and a 10bit SAR analog-to-digital converter (ADC). The project was part of the "EE6350 - VLSI Design Lab" class offered at Columbia University by Prof. Peter Kinget and sponsored by Apple Inc.

We acquire the ECG signal using external electrodes and wires and then amplify it with an instrumentation amplifier (INA) with a gain of 90 dB. A subsequent off-chip band-pass filter with a -60 dB stopband attenuation ensures that only the desired signal within the 0.01 Hz-150 Hz range remains. After the band-pass filtering, the amplitudes of the DC offset and the noise components are significantly reduced. In the next stage, a programmable gain amplifier (PGA) amplifies the clean signal after filtering, ensuring that it reaches the ADC's full input range before entering a 10-bit SAR ADC. This amplification improves the signal-to-noise ratio (SNR). A buffer placed between the ADC and PGA serves as an isolator, ensuring that the stages do not interfere with each other.

We convert the PGA output into a digital signal with a 10Ksps, 10-bit SAR to enable subsequent digital signal processing. The capacitive DAC in the SAR consists of binary-weighted capacitors controlled by individual switches. The charge on each capacitor performs a binary search in conjunction with the comparator and the SAR logic. In the sample-and-hold circuit, we adopt a bootstrapping structure that reduces sampling errors and provides precise on-resistance. This approach minimizes distortion under different input conditions, ensuring higher accuracy in the ECG system.

Overall, we have realized a compact ECG system, which implements the whole process of analog signal acquisition, amplification, and analog-to-digital conversion. We present measurements of our ECG signals from the digital samples and compare it to waveforms obtained with a commercial device.

00:00 Introduction
00:17 Discussion Block Diagram
02:02 Instrumentation Amplifier
03:48 Programmable Gain Amplifier
04:25 10bit Fully Differential SAR ADC
09:24 PCB and Test Setup
10:15 Demo Measurement
11:23 Outro

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