Ricerc@Sapienza

A low-power 6th-order Butterworth bandpass filter has been designed for the front-end of an integrated neural recording system. The passband has been set to 250-500Hz to allow recording the fast ripple (FR) associated with epileptic seizure onset and filter out all other undesired components of the neural signals. The filter is composed of 3 Gm-C biquad stages. Low-power operation is achieved by biasing the MOS devices in the sub-threshold region, and using a dual power supply of ±0.5V.

A low-power class-AB Gm-C biquad stage has been designed using a voltage buffer based on error amplifiers and a push-pull current mirror. The class-AB architecture allows good power efficiency by lowering the required bias current. The biquad stage consumes 250 μA from a 1.2V supply, and achieves a resonance frequency of 2.2MHz with a Q of 2. The SFDR (spurious-free dynamic range) with a two-tone test is 48dB and the SNR (signal-to-noise ratio) is 44.4dB, with a 400mVpp differential input signal.