A low power fully integrated bandpass operational amplifier for biomedical neural recording applications

This paper presents a low power fully integrated bandpass amplifier for a variety of biomedical neural recording applications. A standard two-stage CMOS amplifier in a closed-loop resistive feedback configuration provides stable AC gain of 39.5 dB at 1 kHz. A PMOS input transistor, biased near the sub-threshold region acting as a high value resistor in the range of hundreds of mega ohms, is utilized to clamp the large and random DC open circuit potential that normally exists at the electrode-electrolyte interface. The 3 dB bandwidth of the amplifier is measured to be 26 Hz - 6.5 kHz and the tolerable DC input range is measured to be at least 1 V. The amplifier measures 0.107 mm² in die area and dissipates 133 μW from a 3 V power supply. It is fabricated in MOSIS AMI 1.5 μm double poly double metal n-well CMOS process. Bench tests show complete functionality of the amplifier in both light and dark conditions and for a wide range of recording electrode capacitance.