Method of applying a dither, and analog to digital converter operating in accordance with the method

A method of operating first and second stages of an analog to digital converter where the first stage forms a residue which is digitized by the second stage, the first stage comprising a first stage analog to digital converter and at least one sampling digital to analog converter, the method comprising:

• receiving a dither value,
• applying the dither value to the first stage analog to digital converter,
• using the first stage analog to digital converter to form a digital code,
• applying the digital code either directly or in a modified form to the at least one sampling digital to analog converter such that the sampling digital to converter outputs an analog residue value, and
• passing the analog residue value to the second stage.

An analog to digital converter (ADC), comprising:

• a stage ADC,
• a digital to analog converter (DAC), and
• a dither generator for generating a first dither,
• wherein:
• the stage ADC is arranged to receive an analog input signal and to form a digital conversion value representing the analog input signal,
• the DAC is arranged to sample a combination of the analog input signal and the first dither, and
• the DAC is further arranged to receive a digital conversion value from which a value of the first dither has been subtracted and to form an analog residue representing a difference between the digital conversion value and the analog input signal.