A differential difference amplifier for neural recording system with tunable low-frequency cutoff

This paper describes a low-noise and low-power architecture of the differential difference amplifier (DDA) for neural recording system. The proposed neural amplifier combines DC offset rejection and low-frequency cutoff tuning without off-chip components. DC offset rejection is carried out by ac coupling which is realized by series connection of a capacitor and a MOS-bipolar pseudoresistor. Low-frequency cutoff tuning permits recording local field potential or neural action potential. Frequency tuning mechanism depends on the feedback capacitor and floating tunable resistor which constructs a low frequency pole nearby 100 Hz. The proposed design is in TSMC 0.18 mum 1P6M CMOS process, which achieves gain of 40.8 dB, passband from 107 Hz to 10.3 kHz, input-referred noise of 4.83 muVrms, power consumption of 25.9 muW, and 0.084 mm² of chip area.