An adjustable bandwidth analog CMOS Gm-C filter

A fifth order elliptic lowpass Gm-C filter with adjustable bandwidth is presented. This filter consists of cascaded Gm-C integrator and biquadratic sections. We used simple fully differential source degenerated operational transconductance amplifier with folded cascode output stage and common mode feedback circuit for Gin and substrate biased depletion mode MOS gate capacitors. The transconductor gain is constant and the capacitor is variable, so frequency tuning is done using bulk voltage of MOS gate capacitors. The filter has ±2.5V supply voltage and its power consumption is about 34mW for all tuned frequencies. HSPICE simulation results using 0.35μm CMOS process model parameters are given and advantages of this tuning method in comparison with other existing methods are presented.