A Widely-Tunable and Power-Scalable MOSFET-C Filter Operating in Subthreshold

A very wide tuning range MOSFET-C filter has been introduced. The wide tuning range in this filter has been achieved without using any switchable components or programmable building blocks, while, the cutoff frequency of the filter can be adjusted simply through a controlling bias current. The filter has a low-pass characteristics with fc = 20Hz to 184kHz while exhibiting a constant power consumption per cutoff frequency over its entire tuning range. The proposed MOSFET-C filter uses PMOS transistors in subthreshold regime for implementing floating and widely adjustable resistors. The ultra high resistivity of the resistances make them very suitable for implementing very low frequency and compact filters. Implemented in 0.18μm CMOS technology, the filter exhibits a relatively constant noise and linearity performance over its entire tuning range. The active area of the proposed MOSFET-C filter is 0.09mm.