Fractional-Order Filter Design for Ultra-Low Frequency Applications

The paper presents a novel scheme to implement fractional-order filters for ultra-low frequency applications. The scheme is based on the intrinsic property of the fractional-order filters that the pole frequency can be scaled down to sub-hertz by employing the order if the normal pole frequency of the filter is designed slightly less than one. This is in contrast to the scaling techniques employed in low-frequency integer-order filters where the impedance is scaled to decrease the overall capacitance required for low-frequency design. The functioning of the scheme has been demonstrated by an OTA-based low-pass filter example implemented with 0.35 mu m technology node at +/- 2.1V supply voltage.