A low voltage in situ tunable 1.8-18 MHz high-Q fully-differential continuous-time filter

A CMOS low voltage supply filter with in-situ (in place) tuning is presented. Its basic building block is a transconductor comprising an MOS transistor driver operating in the triode region cascoded with an MOS transistor current source at the output. This circuit can be employed in high-frequency continuous-time filters using low power supply voltages (usually less than 3 volts). A second-order high-Q fully-differential bandpass filter with programmable tuning is demonstrated. The filter is tuned by programming the current bias through a switched current memory cell. The overall tuning accuracy is mainly limited by the precision of an external crystal oscillator.