Successive Approximation Register (SAR) Analog to Digital Converter (ADC) with Switchable Reference Voltage

A method of determining a digital output word having a value corresponding with an analog input value with a successive approximation register (SAR) analog to digital converter (ADC), the method comprising:

• with a SAR logic circuit of the SAR ADC, generating a digital input word;
• with a DAC of the SAR ADC:
• receiving the digital input word and an analog input voltage, and
• generating a first voltage based on the analog input voltage and the digital input word;
• with a comparator of the SAR ADC:
• receiving the first voltage at a first input terminal, and
• receiving a comparison voltage, and
• generating a second voltage based on the first voltage and on the comparison voltage, wherein the second voltage has a value corresponding with a sign of a difference between the first voltage and the comparison voltage;
• with a voltage generator, generating the comparison voltage by selecting the comparison voltage from a plurality of discrete voltage options;
• with the SAR logic circuit of the SAR ADC:
• receiving the second voltage,
• generating the digital input word for the DAC based on one or more comparator output voltages received from the comparator;
• and
• generating the digital output word based on the comparator output voltages, wherein the digital output word represents the value of the analog input voltage.