Based on a new search strategy using circuit simulation and simulated annealing with local search, a design tool is proposed to automate design or tuning process for CMOS operational amplifiers. A special-purpose circuit simulator and some heuristics are used for accomplishing design within reasonable time. For arbitrary circuit topology and specifications, the discrete optimization of cost function is performed through global and local search.
The specifications of operational amplifiers for high-speed pipelined A/D converters is analyzed, and a low-power high-speed fully differential CMOS operational amplifier is designed using this tool. It exhibits a dc gain of 74dB, a unity-gain frequency of 200MHz, and a power dissipation of 11mW at ±2.5 V supply voltages and 1pF load. And applying to the S/H/Gain amplifier with a capacitive load of 0.5pF, the 0.1% settling time of 15 ns for output voltage swing of ±1 V satisfied the design specifications.
Through the comparision of design results and the design of a low-power high-speed fully differential CMOS operational amplifier usable in 10-bit 25-MHz pipelined A/D converters, it was demonstrated that this tool can be used for designing high-performance operational amplifiers with less design knowledge and less design effort.
