Abstract
Wearable health monitors have required continuous physiological
signal acquisition under severe energy constraints. Conventional
sensor interfaces have consumed significant power due to super
threshold biasing and frequent data conversion. Sub-threshold CMOS
operation has emerged as a viable alternative for achieving ultra–low
energy sensing while maintaining acceptable signal fidelity. Prior
studies have highlighted feasibility, yet practical interface stability and
noise robustness have remained limited. Existing wearable sensor
interfaces have suffered from excessive energy consumption, reduced
battery lifetime, and poor performance under low-voltage operation.
Process variations, thermal noise, and leakage effects have degraded
accuracy when circuits have operated in the sub-threshold region.
These challenges have restricted long-term deployment in body-worn
healthcare systems. This work has proposed a sub-threshold CMOS
sensor interface that has targeted ultra–low-energy wearable
applications. The interface architecture has included a low-noise
transconductance amplifier, an adaptive bias generator that has
regulated operating points, and an energy-efficient analog-to-digital
conversion stage. A calibration mechanism that has compensated
process variations has been integrated. Circuit blocks that which
operate below threshold voltage have been optimized for robustness.
The design has been validated using standard CMOS technology
through post-layout simulations and measured prototypes. The
proposed sub-threshold CMOS sensor interface demonstrates an
average power consumption of 41 nW at a 0.4 V supply after 200
iterations, which represents a reduction of approximately 53%
compared with event-driven sub-threshold designs. Input-referred
noise remains below 4.6 µVrms, while the signal-to-noise ratio exceeds
58 dB. The energy per conversion reaches 16 pJ, and gain drift is
limited to 3.0% under process and temperature variations. These results
confirm that the interface supports stable and ultra–low-energy
wearable health monitoring.
Authors
J. Bridget Nirmala, S. Karpagam, B. Eswara Priya, A. Shinyguruce
St. Michael College of Engineering and Technology, India
Keywords
Sub-Threshold CMOS, Wearable Health Monitors, Ultra-Low Energy Circuits, Sensor Interface, Low-Power Biomedical Electronics