Low-distortion continuous-time R-MOSFET-C filters

The R-MOSFET-C or R-MOSFET-R structure, which uses a set of passive resistors and current-steering MOS transistors as a variable resistance element, is proposed to implement low-distortion filter or multiplier in CMOS technology. This proposed technique relies on the linearity of passive resistors and the tunability of current-steering MOS transistors in triode. Placing the nonlinear elements inside feedback loops further reduces distortion in the filter implementation. The experimental results of a self-tuned 22 kHz fifth-order Bessel filter confirm the predicted theoretical performance, displaying negligible control voltage feedthrough and -90 dB total harmonic distortion (THD) with a 2 kHz, 4 V_p-p fully-differential signal, in a 5-V system