A 12-bit 200kS/s subranging SAR ADC with an energy-curve reshape technique

Abstract

This paper presents an energy-efficient 12-bit 200kS/s subranging SAR ADC for multi-touch sensing applications. In order to reduce DAC power consumption, an energy-curve reshape technique is proposed to fit the switching energy curve to the characteristics of Rx signals. An auxiliary polarity quantizer joined with the well-known bottom-plate sampling not only can eliminate the gain mismatch of the subranging architecture but also can be as effective as the top-plate sampling. The ADC low-voltage operation could support the smart wake-up mode in the touch sensing system without using dual reference voltages. A pulse-type self-trigger latch technique is utilized to decrease digital loop power dissipation in the low-voltage environment. This ADC consumes 0.95 μW at 200kS/s under a 0.7V supply in 40nm CMOS technology. It achieves an SNDR of 69.24dB at Nyquist rate and results in an FoM of 2fJ/c.-s.