COMBINING A COARSE ADC AND A SAR ADC

A successive approximation register analog to digital converter (SAR ADC) receives an input voltage and a plurality of reference voltages. The SAR ADC includes a charge sharing DAC. The charge sharing DAC includes an array of MSB (most significant bit) capacitors and an array of LSB (least significant bit) capacitors. A zero crossing detector is coupled to the charge sharing DAC. The zero crossing detector generates a digital output. A coarse ADC (analog to digital converter) receives the input voltage and generates a coarse output. A predefined offset is added to a residue of the coarse ADC. A successive approximation register (SAR) state machine is coupled to the coarse ADC and the zero crossing detector and, generates a plurality of control signals. The plurality of control signals operates the charge sharing DAC in a sampling mode, an error-correction mode and a conversion mode.