Biquadratic high-pass and low-pass single-MOSFET filters

A novel method for analyzing distributed MOSFET filters is presented. The transfer functions of single-MOSFET high-pass and low-pass filters in biquadratic form are obtained using the method. The characteristic frequency and the Q-factor of the high-pass and low-pass filters are directly related to the standard electrical, geometrical, and process parameters of an MOS transistor. It is found that the characteristic frequency of the filter is around three times the intrinsic cutoff frequency of a MOS transistor. To obtain higher-order high-pass and low-pass filters with minimal number of transistors, cascade structures for single-MOSFET filters are proposed. It is shown that MOS transistors in a cascaded chain are required to have a certain channel width ratio to achieve impedance matching. A sixth-order filter can be realized using only three distributed MOS transistors