A circuit in accordance with the invention comprises a differential amplifier;
and a direct current (DC) source coupled with the differential amplifier. The DC
source generates a direct current that is communicated in substantially predetermined
portions to multiple inverting input terminals of the differential amplifier. The
direct current is applied so as to shift a common-mode voltage of electrical signals
that are processed by the differential amplifier. The shift in the common-mode
voltage is proportional to the direct current generated by the DC source.
