Design methods for pipeline & delta-sigma A-to-D converters with convex optimization

Abstract

In system LSIs, costs of analog circuits are getting increased relatively for rapid cost reduction of digital circuits. To satisfy given specifications in the analog design, including low power and small area, designers have to select an optimal solution among large combination of the following alternatives: which architecture should be adopted; what type of transistors should be taken; and whether digitally assisting technologies should be used or not, etc. A design based on experience and intuition cannot lead to the optimum in a short time. A comprehensive approach to the optimization, based on circuit theory, is now required. Convex optimization procedure can solve the formulae which represent circuit performance with over hundreds of design variables. We have constructed optimization environments for pipelined and delta-sigma analog-to-digital converters (ADCs) in consideration of the digitally assisting techniques and layout constraints. Both 12-bit pipelined ADCs and a 5th-order delta-sigma modulator were designed with the optimizer, and achieved top-ranked power efficiency.