Apparatus for determining calibration values of an ADC

An apparatus for determining one or more calibration values of an analog-to-digital converter, ADC, the apparatus comprising:

• a first input configured to receive a first reference signal;
• and
• a second input configured to receive a second reference signal,
• wherein the apparatus is configured to, based on the first reference signal and the second reference signal, apply to the ADC, over four separate signal application periods, the following:
• over a first signal application period, a first ADC input signal comprising the first reference signal;
• over a second signal application period, a second ADC input signal, the second ADC input signal having a substantially equal magnitude and an inverse polarity to the first ADC input signal;
• over a third signal application period, a third ADC input signal comprising the second reference signal;
• and
• over a fourth signal application period, a fourth ADC input signal, the fourth ADC input signal having a substantially equal magnitude and an inverse polarity to the third ADC input signal, and
• wherein the apparatus configured to determine the one or more calibration values based, at least in part, on an ADC output signal of the ADC over the four signal application periods.