A micropower delta-sigma modulator based on a self-biased super inverter for neural recording systems

This paper presents a micropower, supply scalable 2^nd order delta-sigma modulator based on a novel self-biased fully differential super inverter for neural recording systems. By employing an enhanced cascode stage and complementary source degeneration, the super inverter achieves 52 dB of differential-mode gain and 42 dB of common-mode rejection ratio, while remaining self-biased at the optimum operating point. The prototype modulator is implemented in a 0.13 μm CMOS process and occupies 0.03 mm² chip area. The fabricated IC achieves 66 dB SNR and 62 dB SNDR over the neural signal bandwidth of 8 KHz, while consuming 20 μW from 1.5 V supply. At 1.2 V supply, it achieves 67 dB SNR and 56 dB SNDR, with only 4.8 μW power consumption. The super inverter-based design methodology can be extended to other low power, high speed, and variation tolerant switched-capacitor circuits.