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 0.35μm technology node at ± 1.2V supply voltage.