Asynchronous SAR ADC Research Articles

A 0.47–1.6 mW 5-bit 0.5–1 GS/s Time-Interleaved SAR ADC for Low-Power UWB Radios

This paper presents a 16-channel time-interleaved 5-bit asynchronous SAR ADC for UWB radios. It proposes 400 aF unit capacitors, offset calibration, a self-resetting comparator and a distributed clock divider to optimize the performance. The prototype in 90 nm CMOS occupies only 0.11 mm2 including decoupling capacitors. Two relevant modes for UWB are supported: 0.5 GS/s at 0.75 V supply, and 1 GS/s at 1 V supply with 0.47 mW and 1.6 mW power consumption respectively. With an ENOB of 4.7 and 4.8 bits, this leads to energy efficiencies of 36 and 57 fJ/conversion-step. Compared to prior-art, state-of-the-art efficiency is achieved without relying on complex calibration schemes.

A 550-$\mu\hbox{W}$ 10-b 40-MS/s SAR ADC With Multistep Addition-Only Digital Error Correction

A speed-enhanced 10-b asynchronous SAR ADC with multistep addition-only digital error correction (ADEC) is presented with a straightforward DAC switching algorithm. The capacitor DAC is virtually divided into three sub-DACs for ADEC with negligible hardware overhead. The redundant decision cycles between stages reconfigure the capacitor connection of the DAC. These redundancies guarantee 10-b linearity under 4-b-accurate DAC settling in the MSB decision and the optimally designed ADC enhances the conversion speed by 37%. A prototype ADC was implemented in a CMOS 0.13-μm technology. The chip consumes 550 μW and achieves a 50.6-dB SNDR at 40 MS/s under a 1.2-V supply. The figure-of-merit (FOM) is 50 fJ/conversion-step.

A 26 $\mu$W 8 bit 10 MS/s Asynchronous SAR ADC for Low Energy Radios

This paper presents an asynchronous SAR ADC for flexible, low energy radios. To achieve excellent power efficiency for a relatively moderate resolution, various techniques are introduced to reduce the power consumption: custom-designed 0.5 fF unit capacitors minimize the analog power consumption while asynchronous dynamic logic minimizes the digital power consumption. The variability of the custom-designed capacitors is estimated by a specialized CAD tool and verified by chip measurements. An implemented 8-bit prototype in a 90 nm CMOS technology occupies 228 μm × 240 μm including decoupling capacitors, and achieves an ENOB of 7.77 bit at a sampling frequency of 10.24 MS/s. The power consumption equals 26.3 μW from a 1 V supply, thus resulting in an energy efficiency of 12 fJ/conversion-step. Moreover, the fully dynamic design, which is optimized for low-leakage, leads to a standby power consumption of 6 nW. In that way, the energy efficiency of this converter can be maintained down to very low sampling rates.