Switched-R tuning technique for G m-C filters

A new tuning technique is proposed for G_m-C filters. The transconductance cells are tuned using switched resistors (SRs), which change the equivalent reference resistance of each cell. In the tuning circuit, the equivalent resistance of an SR branch is forced to equal that of a switched-capacitor (SC) branch by a feedback loop containing a continuous-time comparator. Thus, using the output of the loop all time constants of the G_m-C filter can be tuned simultaneously. The simulation of a second-order Butterworth filter is described to verify the effectiveness and excellent linearity of the proposed tuning method.