A Low-Noise Preamplifier with Adjustable Gain and Bandwidth for Biopotential Recording Applications

We have developed a fully differential low-power low-noise preamplifier with multiple adjustable parameters for biopotential and neural recording applications. Common mode feedback has been utilized to guarantee the amplifier functionality by forcing the output DC level to a desired voltage. A switch is added to the output to achieve fast settling time in case the amplifier is saturated. The amplifier has been implemented in the AMI 1.5-μm 2M2P standard CMOS process and occupies 0.201 mm² on chip. The amplifier current consumption is 8 μA at ±1.7 V supply, with two measured AC gains of 39.3 dB and 45.6 dB. The low cutoff frequency is 4-bit programmable from 0.015 Hz to 700 Hz. The high cutoff frequency can be adjusted from 120 Hz to 12 kHz at negligible load and 40 Hz to 4 kHz with a 2 pF active probe loading. The measured input referred noise is 3.6 μV over 20 Hz ~ 10 kHz. The amplifier also provides rail-to-rail input DC range, maximum input offset of 0.7 mV, common mode tuning range of ±600 mV, and output swing of ±0.9 V with minimum distortion.