Analog to digital conversion is performed by sampling an input voltage followed by AD conversion of the sampled voltage. In the sample and hold circuit a differential amplifier output voltage is generated between the first and second output of a differential amplifier in response to the sampled input voltage. A conversion polarity is selected by connecting the one output or the other of the differential amplifier to a circuit node in an AD conversion circuit using a first or second switch. These switches from both outputs of the differential amplifier to the same circuit node of the AD conversion circuit are both made conductive simultaneously prior to making the selected one of the first and second switch conductive. In this way, the amplifier output voltage is reset without requiring a dedicated switch just for this purpose.