Design of High‐Speed, Low‐Power, Nyquist Analog‐to‐Digital Converters

Sammanfattning: The scaling of CMOS technologies has increased the performance of general purposeprocessors and DSPs while analog circuits designed in the same process have not been ableto utilize the process scaling to the same extent, suffering from reduced voltage headroom and reduced analog gain. In order to design efficient analog‐to‐digital converters in nanoscale CMOS there is a need to both understand the physical limitations as well as to develop new architectures and circuits that take full advantage of what the process has tooffer.This thesis explores the power dissipation of Nyquist rate analog‐to‐digital converters andtheir lower bounds, set by both the thermal noise limit and the minimum device and feature sizes offered by the process. The use of digital error correction, which allows for lowaccuracy analog components leads to a power dissipation reduction. Developing the bounds for power dissipation based on this concept, it is seen that the power of low‐to‐medium resolution converters is reduced when going to more modern CMOS processes, something which is supported by published results.The design of comparators is studied in detail and a new topology is proposed which reduces the kickback by 6x compared to conventional topologies. This comparator is used in two flash ADCs, the first employing redundancy in the comparator array, allowing for the use of small sized, low‐power, low‐accuracy comparators to achieve an overall low‐power solution. The flash ADC achieves 4 effective bits at 2.5 GS/s while dissipating 30 mW of power.The concept of low‐accuracy components is taken to its edge in the second ADC which oes not include a reference network, instead relying on the process variations to generate the reference levels based on the mismatch induced comparator offsets. The reference‐free ADC achieves a resolution of 3.69 bits at 1.5 GS/s while dissipation 23 mW showing that process variations not necessarily must be seen as detrimental to circuit performance but rather can be seen as a source of diversity.