High accuracy analog-to-digital converter with rail-to-rail reference and input voltage ranges

An analog-to-digital converter (ADC) includes successive approximation control logic for generating ten-bit binary numbers, a digital-to-analog converter (DAC) (205) having a resistor string (301) and a weighted-capacitor array (303) for converting the ten-bit binary output of the control logic to a known analog voltage, and an analog comparator (207) for comparing the output of the DAC (205) to a reference voltage provided via a tap (305) to the mid-point of the DAC resistor string (301). The unknown analog voltage input to the ADC and the reference voltage are provided to the capacitor array (303) to precharge the array (303) to a voltage equal to the reference voltage minus the unknown analog voltage. The output of the DAC (205) is equal to the known analog voltage plus the reference voltage minus the unknown analog voltage. The known analog voltage is changed in successive conversion steps such that the output of the DAC (205) converges towards the reference voltage value. High accuracy conversion is achieved over a wide voltage range.