Switched-current analogue-to-digital converter

A current mode pipelined analogue-to-digital converter (ADC) comprising a plurality of serially connected conversion stages (Si) wherein at least one conversion stage comprises, a stage input for receiving a current (ri-1) for conversion, a sample-and-hold (S/H) circuit coupled to sample the current at the stage input during a first time period and to hold the sampled current during a second time period, the S/H circuit having first and second outputs, the first output delivering a mirror of the sampled current during the first time period and a mirror of the held current during the second time period and the second output delivering the held current directly during the second time period, a current comparator means having an input coupled to the first output of the S/H circuit for comparing a current at said input with one or more reference currents, a digital output coupled to an output of the current comparator means for producing a digital signal (D) representing the digital conversion performed by the stage, a digital-to-analogue converter (DAC) having an input coupled to the output of the current comparator means, and a summing means having a first input coupled to an output of the DAC, a second input coupled to the second output of the S/H circuit, and an output for delivering a residual current (ri) during the second time period.