Low-Distortion Low-Power MOSFET-C Filter Design Method

S. Takagi, H. Sato (Tokyo Inst. of Techn., Japan)

There have been a lot of methods to realize highly linear filters using MOSFETs with nonlinear voltage-current characteristics\cite{Banu}-\cite{matrix-mrc}. Among them the method proposed inRef. [8] requires small numbers of active elements and capacitors., i.e. filters realized by the method are area-and-power efficient. A problem of the method is requirement of many control voltages which are applied to gate terminals of MOSFETs operating in nonsaturation region. This paper proposes another approach to realize highly linear MOSFET-C filters. The approach is combination of the methods proposed in Ref. [7] and Ref. [8]. Filters realized by the proposed method require only two control voltages as well as the same numbers of active elements and capacitors with the method of Ref. [8]. Thanks to requirement of only two control voltages filters realized by the proposed method can avoid increase in output distortion as shown in simulation results. Furthermore the proposed filter employs the same numbers of operational amplifiers and capacitors and requires the same chip area with the method in Ref. [8]. Simulation results show good agreement with ideal frequency characteristics and sufficiently low harmonic distortions as compared with a matrix MRC-based filter.