Patent ID: 6903602

Claim:
A calibrated filter comprising: an RC filter having tunable capacitors having a capacitive value responsive to a control code; a fully differential calibration circuit comprising: a differential operational amplifier; a differential voltage source; a first resistor selectively coupled between a first terminal of the differential voltage source and a first integrating capacitor coupled across a first input and a first output of the differential operational amplifier; a second resistor selectively coupled between a second terminal of the differential voltage source and a second integrating capacitor coupled across a second input and a second output of the differential operational amplifier; a logic circuit for: charging the first and second capacitors through the first and second resistors over a first predetermined number of clock periods; discharging the integrating capacitors by a predetermined voltage over a second predetermined number of clock periods; and counting the number of clock periods to needed to discharge the integrating capacitors to a predetermined voltage level to generate the control code for tuning the tunable capacitors.