Transfer-function control in an active filter

A method of filtering comprising:

• forming a filter circuit by feeding a portion of an output of a differential amplifier circuit providing a plurality of poles including a dominant pole to an input of the differential amplifier circuit through a feedback circuit including a feedback capacitor coupled in parallel with a feedback resistor;
• using the feedback capacitor and non-dominant poles of the differential amplifier circuit to provide a controllable increase in an order of a transfer function of the filter circuit;
• and
• forcing coefficients of a transfer function of the differential amplifier circuit to substantially depend solely on at least one of the feedback resistor, the feedback capacitor, and constituent passive circuit elements thereof, the passive circuit elements including at least one of a resistor and a capacitor, to control a dependence of the transfer function of the filter circuit on a gain of the differential amplifier circuit and poles of the differential amplifier circuit.

An integrated circuit comprising:

• an electrical circuit;
• and
• a filter circuit to filter an output of the electrical circuit, the filter circuit comprising:
• a differential amplifier circuit to provide a plurality of poles including a dominant pole;
• a feedback circuit to feed a portion of an output of the differential amplifier circuit to an input of the differential amplifier circuit, the feedback circuit comprising:
• a feedback resistor;
• and
• a feedback capacitor to provide a controllable increase in an order of a transfer function of the filter circuit along with non-dominant poles of the differential amplifier circuit coupled in parallel with the feedback resistor;
• and
• a plurality of passive circuit elements including at least one of a resistor and a capacitor, with coefficients of a transfer function of the differential amplifier circuit being forced to substantially depend solely on at least one of the plurality of passive circuit elements, the feedback resistor, and the feedback capacitor to control a dependence of the transfer function of the filter circuit on a gain of the differential amplifier circuit and poles of the differential amplifier circuit.