US Patent 10181860 Reducing residue signals in analog-to-digital converters

A residue generation apparatus for use in continuous-time and hybrid ADCs is proposed. The apparatus includes a quantizer for digitizing an analog input to generate a digital output, and means for applying a first transfer function to the digital output from the quantizer to generate a digital input to a feedforward DAC, based on which the DAC can generate a feedforward path analog output. The apparatus further includes means for applying a second, continuous-time, transfer function to the analog input provided to the quantizer to generate a forward path analog output, and a subtractor for generating a residue signal based on a difference between the forward path analog output and the feedforward path analog output. Proposed apparatus allows selecting a combination of the first and second transfer functions so that, when each is applied in its respective path, the residue signal passed to further stages of an ADC is reduced.