Switched-resistor tuning technique for highly linear Gm-C filter design

A new tuning technique is proposed to enable highly linear active G_m-C filter design. The transconductance cells of the G_m-C filter are tuned using switched resistors (SRs) which change the equivalent reference resistance of each cell. In the master tuning circuit, a feedback loop containing a continuous-time comparator is used to force the equivalent resistance of an SR branch to be equal to that of a switched-capacitor (SC) branch. Thus, using the output of the loop with an automatically adjusted duty cycle, all time constants of the G_m-C filter can be tuned simultaneously. A second-order low-pass Butterworth filter model was developed and simulated. The result verified the effectiveness and excellent linearity of the proposed tuning method.