Noise cancellation in a single ended SAR converter. A single ended SAR converter
front end is disclosed with common mode driver noise cancellation. The SAR converter
front end includes a differential amplifier having positive and negative inputs
and an output. A switched capacitor array is provided that is operable in a SAR
data conversion operation to vary the voltage on one of the positive or negative
inputs of the differential amplifier. A common mode driver drives a common mode
node with a low impedance common mode voltage signal to a common mode node, and
switching circuitry then switches the common mode voltage signal on the common
mode node to the positive and negative inputs of the differential amplifier during
a portion of a SAR data conversion cycle. A capacitor reference circuit is attached
to the other of the positive or negative inputs of the differential, amplifier
during at least the portion of the SAR data conversion cycle, the capacitor reference
circuit and the capacitor array during at least the portion of the SAR data conversion
cycle having relative capacitance values that increase the common mode rejection
of any noise introduced to the common mode node at the input of the differential amplifier.