A Current-Mode Capacitively-Coupled Chopper Instrumentation Amplifier for Biopotential Recording With Resistive or Capacitive Electrodes

This brief presents a high-density, low-noise analog front-end (AFE) for capacitively coupled neural recording applications. Conventional capacitively coupled AFEs, when chopper-stabilized, require large coupling capacitors or servo loops to minimize <inline-formula> <tex-math notation="LaTeX">$ {1/f^{2}}$ </tex-math></inline-formula> input-referred noise and chopper-induced offsets, limiting channel density. In this brief, a current-mode capacitively coupled chopper instrumentation amplifier with embedded delta-sigma analog-to-digital converter (ADC) is presented that enables an area-efficient low-noise design via chopper-stabilized current-mode amplification. In this design, 60 channels are implemented in a <inline-formula> <tex-math notation="LaTeX">$ {2 \times 2}$ </tex-math></inline-formula> mm² 180-nm CMOS chip, and each channel consumes <inline-formula> <tex-math notation="LaTeX">$4~ {\mu }\text{W}$ </tex-math></inline-formula>, achieves an input referred noise of 160 nV/<inline-formula> <tex-math notation="LaTeX">$\sqrt {\text{Hz}}$ </tex-math></inline-formula>, and an ADC effective number of bits of 8.5 bits.