Design of Low Power SAR ADC with Novel Regenerative Comparator

Abstract

This paper introduces two low-power design techniques for a successive approximation register (SAR) analog-to-digital converter (ADC) used in transmitting physiological signals. The first technique is called dual split switching, involving the use of a one-sided charge-scaling digital-to-analog converter (DAC) to minimize switching energy by reducing leakage in a dual transmission gate. The second technique, known as the set and reset phase, determines the amplification and comparison phases of the comparator. This approach reduces the delay time of the comparator through the use of a folded cascode pre-amplifier and a regenerative latch. The design includes a Serial-in-Parallel-Out (SIPO) N-bit register and SAR, implemented using negative edge-triggered D flip-flops (DFFs). To optimize power consumption, the supply voltage of the SAR ADC is set to 500 mV. The concept of a variable threshold is utilized throughout the design to enable operation with this lower supply voltage. The SAR ADC is designed to support a sampling rate of up to 1 Msps (mega-samples per second). The circuit is implemented using standard UMC180nm technology. According to the test results, the power consumption of the SAR ADC is only 29.06 uW, and the achieved sampling rate is 5 Ksps (kilo-samples per second). The maximum differential non-linearity (DNL) is measured to be +0.9/−0.82 least significant bits (LSBs).