A Design of 44.1 fJ/Conv-Step 12-Bit 80 ms/s Time Interleaved Hybrid Type SAR ADC With Redundancy Capacitor and On-Chip Time-Skew Calibration

Abstract

A 12-bit 80 MS/s hybrid type analog-to-digital converter (ADC) for high sampling speed and low power applications is presented in this paper. It has a subranging architecture with a front end of 6-bit Flash ADC with five channels of 6-bit time interleaved synchronous Successive Approximation Register (SAR) ADC. The proposed architecture with a shared 6-bit Flash ADC and time interleaved SAR ADC provides a power and area efficient high speed ADC. The proposed Time-skew calibration is implemented to minimize the discrepancy between the output of Flash ADC and SAR ADC’s channels. To rectify the decision error of the Flash ADC and extract the time-skew information, 1-bit redundancy is included in the CDAC of the SAR conversion. The decision error between the Flash ADC and the SAR ADC is covered with designed redundancy and the mismatch between the ADCs is covered with the time-skew calibration. To reduce the offset mismatch between Flash and SAR ADC and within SAR ADCs, all comparators are calibrated to minimize their absolute offset by utilizing background offset calibration. The modified dynamic strong ARM comparator is used for flash ADC and dynamic latched comparator is used for SAR ADCs. For fine offset calibration and low power consumption, the comparator’s offset calibration circuit is implemented. To reduce the kickback noise and enhance the overall energy efficiency for fast operation of SAR ADCs, rail-to-rail dynamic latch comparator with modified adaptive power control (APC) is implemented. The proposed ADC structure has been implemented in 130 nm CMOS process. The ADC has an effective number of bit (ENOB) of 10.97 bits while consuming 7.08 mW current consumption from the 1.2 V supply voltage.