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This paper describes a micropower low-noise neural front-end circuit capable of recording epileptic fast ripples (FR). The front-end circuit consisting of a preamplifier followed by a 6th-order bandpass filter is designed for signal sensing in a future epileptic deep brain stimulator. A current-splitting technique is combined with an output-branch current scaling technique in a folded-cascode amplifier structure to improve the noise and power tradeoff in the preamplifier. In measurements, the preamplifier exhibits 39.4 dB DC gain, 0.36 Hz to 1.3 kHz of -3 dB bandwidth, and 3.07 μVrms total input-referred noise while consuming 2.4 μW from a 2.8 V power supply provided by an on-chip regulator circuit. A noise efficiency factor (NEF) of 3.09 is achieved with minimal power consumption and is one of the lowest published to date. The 6th-order follow-the-leader feedback elliptic bandpass filter passes FR signals and provides -110 dB/decade attenuation to out-of-band frequency components. In measurements, the entire front-end circuit achieves a mid-band gain of 38.5 dB, a bandwidth from 250 to 486 Hz, and a total input-referred noise of 2.48 μVrms while consuming 4.5 μW from the 2.8 V power supply. The front-end NEF achieved is 7.6. To the authors' knowledge, the proposed epileptic seizure- detection system is the first to achieve the FR-recording functionality. The chip is fabricated in a standard 0.6 μm CMOS process. Die size is 0.45 mm2.
Date of Publication: June 2011