A 23-mW 24-GS/s 6-bit Voltage-Time Hybrid Time-Interleaved ADC in 28-nm CMOS

Abstract

This paper presents a power- and area-efficient 16-way time-interleaved (TI) analog-to-digital converter (ADC) achieving 24-GS/s conversion speed and 6-bit resolution in 28-nm CMOS. A voltage-time hybrid pipeline technique exploiting the comparator input-voltage-output-time dependency is reported to enhance the throughput of successive-approximation-register (SAR) ADCs. A reference-buffer-free capacitive digital-to-analog (CDAC) converter is utilized to mitigate the crosstalk problem in TI-ADCs. Timing mismatches between individual sub-ADCs are estimated with a reference-ADC dithering technique and corrected by digitally controlled delay lines (DCDL). The techniques collectively enabled a very compact design, obviating any input buffer or hierarchical sampling structures. The ADC core consumes 23 mW and occupies an area of 0.03 mm2. A signal-to-noise plus distortion ratio (SNDR) of 35 dB and a spurious-free dynamic range (SFDR) of 54 dB were measured for a 40-MHz input. For a Nyquist input, the prototype measured an SNDR of 29 dB and an SFDR of 41 dB with all timing mismatch spurs suppressed below −50 dBc after skew calibration.