A 96dB DR 3.1GΩ Input Impedance CT-DT ΔΣ Readout Frontend with Level-Crossing Input Range Enhancement for Neural Recordings

This paper proposes a neural recording frontend with a level crossing (LC) style DR-enhancing loop, featuring fast transient response and a wide input range. A dual-Gm input stage together with a differential input single-ended output TIA is exploited, enabling energy efficient LC event detection. The LC capacitive DAC generates a voltage that follows the input, enhancing the DR. A current mode second order CT-DT $\Delta \mathbf{\Sigma}$ modulator follows the dual-Gm stage in the main signal path for data conversion. Prior to the CT-integrator, a common mode current sinking circuit is used to improve the linearity. Designed and simulated in a 55 nm CMOS technology, the proposed frontend supports ± 400mV DC suppression thanks to the DR enhancement. It also achieves a 96 dB DR, a 64.3dB SNDR within the $0.1-10 \mathrm{kHz}$ bandwidth and a $3.1 \mathrm{G} \Omega Z_{\mathrm{in}}$, making it suitable for simultaneously recoding of ECG, EEG and vagus nerve signals.