A 0.006 mm2 1.2 $\mu$ W Analog-to-Time Converter for Asynchronous Bio-Sensors

This paper presents a low-power analog-to-time converter (ATC) for integrated bio-sensors. The proposed circuit facilitates the direct conversion of electrode bio-potential recordings into time-encoded digital pulses with high efficiency without prior signal amplification. This approach reduces the circuit complexity for multi-channel instrumentation systems and allows asynchronous digital control to maximize the potential power savings during sensor inactivity. A prototype fabricated using a 65-nm CMOS technology is demonstrated with measured characteristics. Experimental results show an input-referred noise figure of 3.8 $\mu V_{\mathrm{ rms}}$ for a 11-kHz signal bandwidth while dissipating 1.2 $\mu \text{W}$ from a 0.5-V supply and occupying $60\times 80\,\,\mu \text{m}\,\,^{\mathrm{ 2}}$ silicon area. This compact configuration is enabled by the proposed asynchronous readout that shapes the mismatch components arising from the multi-bit quantizer and the use of capacitive feedback.