Patent ID: 7737873

Claim:
A flash analog-to-digital converter for converting an analog input signal to a digital output signal, said converter comprising a cascade of at least two converter stages, the first of said stages comprising means to receive the analog input signal, a resistive reference ladder providing a range of reference voltages, means to compare the input signal with said plurality of reference voltages and deriving therefrom a digital code representing a course quantization of the analog input signal, a digital-to-analog converter stage comprising a plurality of selectors controlled by said digital code and selecting from the plurality of reference voltages an analog representation of said course quantization, means to subtract said analog representation from the analog input signal to obtain a residue signal, characterized in that at each sample of the digital code one selector of a pair of selectors selects a first reference voltage from one half of the range of reference voltages while the other selector selects a second reference voltage from the other half of the range of reference voltages, such that the first and second reference voltages lie symmetrically with respect to the center of the range of reference voltages and that the output signals of said pair of selectors are transferred through a cross-over switch that is arranged to switch at the center of the range of the coarse quantization.