The present invention relates to semiconductor integrated circuitry, and in particular to such circuitry where one or a plurality of similar or identical operating units are each operable to carry out an operation dependent on a reference signal. One example of such an operating unit is a sub-ADC unit of analogue-to-digital converter (ADC) circuitry, which employs one or more such sub-ADC units to convert samples of an input analogue signal into representation digital values. Where there are a plurality of sub-ADC units, they may each convert samples of an input analogue signal into representative digital values. They may also operate in a time-interleaved manner so that their conversion rate (from sample to digital value) can be lower than the overall sample rate by a factor of the number of sub-ADC units.