A Novel Variable-Gain Micro-Power Band-Pass Auto-Zeroing Cmos Amplifier

A micropower, low-noise, bandpass amplifier for biomedical implants is presented. Operating at low frequency, the amplifier is fully integrated without any external passive components. Low-frequency noise and offset is reduced through the autozeroing technique. The autozeroing frequency and noise bandwidth is optimized to reduce noise folding. The design consists of a novel variable gain amplifier as the first stage, a low-Gm high-pass filter as the second stage, and a low-pass Gm-C amplifier as the last stage. Subthreshold operation is utilized in all input pair transistors to reduce power consumption, while a low-Gm OTA (Operational Transconductance Amplifier) is realized with a current division technique. A cross-couple parallel pair of source degeneration transistors is utilized to increase the linearity crucial to neural spike detection. The design is realized in a CMOS 0.18um process. It has an offset of 600uV, a variable gain from 42dB to 0dB, and 50 to 900Hz bandwidth while occupying 0.245mm(2) area. The total circuit consumes only 26uW in a 1.8V power supply; the input referred noise is estimated to be 5.6uV(rms).