An Unconditionally Stable Three-Stage OTA

• Published in: IEEE solid-state circuits letters Vol. 5; p. 1
• Main Authors: Aminzadeh, H., Ballo, A., Valinezhad, M., Grasso, A. D.
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Capacitors; Circuit stability; frequency compensation; Miller compensation; Operational amplifiers; Operational transconductance amplifier; Resistors; Stability analysis; Topology; Transconductance; Voltage; wide load range
• ISSN: 2573-9603; 2573-9603
• DOI: 10.1109/LSSC.2022.3206892

A three-stage operational transconductance amplifier (OTA) stable for any load capacitor is introduced for the first time in literature. It contains a novel local ac feedback network in the intermediate stage in addition to the cascode-Miller compensation strategy. The final topology is Miller-compensated for the light and CL-compensated for the heavy capacitive loads, and its operation is improved by including a feed-forward stage and a slew-rate enhancer. A prototype of the proposed amplifier was fabricated in a 65-nm standard CMOS process with 1.2-V supply voltage, occupying an active area of 0.0028 mm with 13.07-μA quiescent current. A DC gain of about 100-dB was measured with a unity-gain frequency of 4000, 705, and 22 kHz for 0.03, 0.5 and 100-nF capacitive loads, respectively.