Timmy Sundström

Power Dissipation Bounds for High-Speed Nyquist Analog-to-Digital Converters

A very important limitation of high-speed analog-to-digital converters (ADCs) is their power dissipation. ADC power dissipation has been examined several times, mostly empirically. In this paper, we present an attempt to estimate a lower bound for the power of ADCs, based on first principles and using pipeline and flash architectures as examples. We find that power dissipation of high-resolution ADCs is bound by noise, whereas technology is the limiting factor for low-resolution devices. Our model assumes the use of digital error correction, but we also study an example on the power penalty due to matching requirements. A comparison with published experimental data indicates that the best ADCs use about 50 times the estimated minimum power. Two published ADCs are used for a more detailed comparison between the minimum bound and todays designs.

Utilizing Process Variations for Reference Generation in a Flash ADC

This brief presents an experimental study on how to take advantage of the increasing process variations in nanoscale CMOS technologies to achieve small and low-power high-speed analog-to-digital converters (ADCs). Particularly, the need for a reference voltage generation network has been eliminated in a 4-bit Flash ADC in 90-nm CMOS, with small-sized comparators. The native comparator offsets, resulting from the process-variation-induced mismatch, are used as the only source of reference levels, and redundancy is used to acquire the desired resolution. The measured performance of the 1.5-GS/s ADC is comparable to traditional state-of-the art ADCs and dissipates 23 mW.

A Kick-Back Reduced Comparator for a 4-6-Bit 3-GS/s Flash ADC in a 90nm CMOS Process

This paper presents a kick-back reduced comparator based on a sense-amplifier type comparator. The kickback charge and resulting voltage peak is reduced by 6times, which corresponds to a power reduction in the input driver and the resistance ladder of the same magnitude. A 4-6-bit 3-GS/s low-power flash ADC using the proposed comparator has been implemented in a 90 nm CMOS process. The significantly lower requirements on input driver and resistance ladder have reduced the overall ADC power dissipation by 50%.

A 2.5-GS/s 30-mW 4-bit Flash ADC in 90nm CMOS

A 2.5 GS/s flash ADC, fabricated in 90 nm CMOS, avoids traditional power, speed and accuracy trade-offs by using comparator redundancy with power-gating capabilities. Redundancy removes the need to control comparator offsets, allowing the large process-variation induced mismatch of small devices in nanometer technologies. This enables the use of small-sized, ultra-low-power comparators. Measurement results show that the ADC dissipates 30 mW at 1.2 V. With 63 gate-able comparators, the ADC achieves 4.0 effective number of bits.

A 2.4 GS/s, Single-Channel, 31.3 dB SNDR at Nyquist, Pipeline ADC in 65 nm CMOS

This paper presents a high-speed single-channel pipeline analog-to-digital converter sampling at 2.4 GS/s. The high sample rate is achieved through the use of fast open-loop current-mode amplifiers and the early comparison scheme. The bounds on the sub-ADC sampling instance are analyzed based on sufficient settling for a decision as well as metastability. Implemented in a 65 nm general purpose CMOS technology the SNDR is above 30.1 dB in the Nyquist band, being 34.1 and 31.3 dB at low frequency and Nyquist, respectively. This shows that multi-GS/s pipeline ADCs are feasible as key building blocks in interleaved structures.

Reliability study of a low-voltage Class-E power amplifier in 130nm CMOS

This paper presents reliability measurements of a differential Class-E power amplifier (PA) operating at 850MHz in 130nm CMOS. The RF performance of five samples was tested. At 1.1V, the PAs deliver +20.4–21.5dBm of output power with drain efficiencies and power-added efficiencies of 56–64% and 46–51%, respectively. After a continuous long-term test of 240 hours at elevated supply voltage of 1.4V, the output power dropped about 0.7dB.