A 0.5-Hz High-Pass Cutoff Dual-Loop Transimpedance Amplifier for Wearable NIR Sensing Device

This brief describes a fully integrated dual-loop transimpedance amplifier with bandpass response for wearable near-infrared (NIR) sensing operating at low frequency: one loop to lower the lower band cutoff frequency and another loop for self-regulating DC photocurrent to prevent saturation at later stages. The circuit was implemented in a 0.35- $\mu\hbox {m}$ CMOS process and achieved a DC photocurrent rejection ranging from 2.7 to 15 $\mu\hbox {A}$ and a $-$ 3-dB high-pass cutoff frequency from 0.5 to 110 Hz by using on-chip capacitors. Both total harmonic distortion and spurious-free dynamic range are better than $-$ 42 dB. It achieves an improvement of 390 times in capacitor reduction compared with the traditional DC rejection technique.