A 0.8-μW window SAR ADC with offset cancellation for digital DC–DC converters

This letter presents the design of a window successive approximation (SAR) analog-to-digital converter (ADC) using an ultra-fast, offset-cancelled auto-zero comparator for digital DC–DC converters. It is designed in a standard CMOS 0.18 μm process. The ADC has a dynamic reference voltage range to reduce power consumption. The auto-zero scheme of the comparator is realized internally with a preamplifier stage and a latch stage. Post-layout simulation shows that the response time of the comparator from low-to-high and high-to-low is 3.78 ns and 2.47 ns, respectively. The resolution of the proposed window SAR ADC is 7.5 mV. The ADC is fabricated as part of a digital DC–DC converter integrated circuit and measurement results show that an average power consumption of 0.8 μW is achieved. The transient time of the DC–DC converter is within 150 ns for a load current change of 495 mA.