A method of operating a circuit includes providing the circuit, the circuit includes an operational amplifier, a plurality of sampling switches, a plurality of holding switches, and a plurality of combined switches. The method further includes: during a first phase, causing the plurality of sampling switches to be closed, the plurality of the holding switches to be open, and the plurality of combined switches to be open; during a second phase, causing the plurality of combined switches to be closed; during a third phase, causing the plurality of sampling switches to be open, the plurality of the holding switches to be closed, and the plurality of combined switches to be open; and during a fourth phase, causing the plurality of sampling switches to be open, the plurality of the holding switches to be closed, and the plurality of combined switches to be closed.