Ultra-low power 10-bit 50-90 MSps SAR ADCs in 65 nm CMOS for multi-channel ASICs

Abstract

The design and measurement results of ultra-low power, fast 10-bit Successive Approximation Register (SAR) Analog-to-Digital Converter (ADC) prototypes in 65 nm CMOS technology are presented. Eight prototype ADCs were designed using two different switching schemes of capacitive Digital-to-Analog Converters (DACs), based on MIM or MOM capacitors, and controlled by standard or low-power SAR logic. The layout of each ADC prototype is drawn in 60 um pitch to make it ready for multi-channel implementation. A series of measurements have been made confirming that all prototypes are fully functional, and six of them achieve very good quantitative performance. Five out of eight ADCs show both integral (INL) and differential (DNL) nonlinearity errors below 1 LSB. In dynamic measurements performed at 0.1 Nyquist input frequency, the effective number of bits (ENOB) between 8.9-9.3 was obtained for different ADC prototypes. Standard ADC versions work up to 80-90 MSps with ENOB between 8.9-9.2 bits at the highest sampling rate, while the low-power versions work up to above 50 MSps with ENOB around 9.3 bits at 40 MSps. The power consumption is linear with the sample rate and at 40 MSps it is around 400 uW for the low-power ADCs and just over 500 uW for the standard ADCs. At 80 MSps the standard ADCs consume about 1 mW.