5. CMOS Ultra-High-Speed Time-Interleaved ADCs

CMOS technologies have been able to fabricate ultra-high-speed time-interleaved (TI) ADCs that achieve a sampling rate over 10 GS/s. The TI architecture relaxes the speed requirement for each A/D channel. It also introduces inter-channel mismatches that cause conversion errors. These errors can be reduced by calibration. An 8-channel 6-bit 16-GS/s TI ADC is presented to illustrate several circuit design and calibration techniques. Each A/D channel is a 6-bit flash ADC. The low-power comparators in the flash ADC are latches with offset calibration. A delay-locked loop generates the 8-phase sampling clocks for the TI ADC. Timing-skew calibration is used to ensure uniform sampling intervals. Both the offset calibration and the timing-skew calibration run continuously in the background. This TI ADC was fabricated using a 65 nm CMOS technology. At 16 GS/s sampling rate, this chip consumes 435 mW from a 1.5V supply. It achieves a signal-to-distortion-plus-noise ratio (SNDR) of 30.8 dB. The ADC active area is \( 0.93 \times 1.58{\text{ m}}{{\text{m}}^2} \)