Asynchronous Adaptive Threshold Level Crossing ADC for Wearable ECG Sensors.

Abstract

The level crossing ADC generates digitized samples consisting of the magnitude of input signal and time interval between two consecutive level crossings when the input signal crosses the threshold level. This paper presents a new architecture of low power asynchronous adaptive threshold level crossing (LC) ADC suitable for wearable ECG sensors based on a novel algorithm for determining adaptive threshold. The adaptive threshold was determined by calculating the mean of maximum and minimum values of signal in a predetermined window. Polynomial interpolation was used to reconstruct the signal. A signal to noise distortion ratio of 57.50dB and a mean square error (MSE) measure of 1.368*10-8V2 was achieved by the proposed algorithm for a 1mV, 10Hz input sinusoidal signal in MATLAB. The asynchronous adaptive threshold LC ADC operating from a supply voltage of 0.8V occupied a layout area of 266.33*331.385μm2 when implemented in CADENCE virtuoso using 180nm technology. The designed circuit consumes an average power of 367.6 nW for a 1mVpp, 10Hz input sinusoidal signal when simulated in Virtuoso.