An optimization approach to designing OTAs for low-voltage sigma-delta modulators

High performance OTA (Operational Transconductance Amplifier) structures for high-speed, low-voltage, switched-capacitor based sigma-delta modulator applications have been designed utilizing an efficient circuit optimization strategy presented in this paper. The main idea is to use external programs together with a circuit optimizer to construct flexible optimization algorithms. Optimization goals and constraints are derived from analytical equations and application requirements. Using a 0.35 /spl mu/m CMOS processing technology a CFCFC (Complementary Folded Cascode Feedforward Compensated) OTA with 2.5 V supply obtained 470 MHz unity-gain frequency, 350 V//spl mu/s slew rate, over 74 dB gain, and over 70/spl deg/ phase margin using 10 pF load capacitances.