An analog to digital converter includes a coarse ADC circuit composed of L offset-adjustable comparators and a fine ADC circuit composed of M offset-adjustable comparators. Each offset-adjustable comparator in the coarse ADC circuit has a constant embedded offset. Each offset-adjustable comparator in the fine ADC circuit has an adaptive embedded offset digitally determined by outputs of the coarse ADC circuit. With the constant and adaptive embedded offsets, the analog to digital converter requires no resistor ladder. Therefore, power consumption and area of the analog to digital converter is reduced, and faster conversion speed is achieved.