Super class AB OTA without open‐loop gain degradation based on dynamic cascode biasing

• Published in: International journal of circuit theory and applications 2017-12, Vol.45 (12), p.2111-2118
• Main Authors: Pourashraf, Shirin, Ramirez‐Angulo, Jaime, Lopez‐Martin, Antonio J., Carvajal, Ramon G.
• Format: Article
• Language: English
• Subjects: Amplification; analog amplifiers; Cascode transistors; class AB; Degradation; dynamic biasing; low power; Metal oxide semiconductors; Metal oxides; Operational amplifiers; OTA; Semiconductor devices; Transconductance
• ISSN: 0098-9886; 1097-007X
• DOI: 10.1002/cta.2367

Summary A scheme to achieve simultaneously extremely high slew‐rate improvement and avoiding open‐loop gain degradation in one‐stage super class AB op‐amps is introduced. It overcomes the serious shortcoming of super class AB operational transconductance amplifiers that shows very high‐output current enhancement factors at the expense of degrading the open‐loop gain. The proposed scheme uses dynamically biased cascode transistors to avoid gain and slew‐rate degradation. Experimental results of a super class AB operational transconductance amplifier in 180‐nm complementary metal‐oxide semiconductor technology with open‐loop gain of 67 dB, a factor 2 improvement in GBW, and a current enhancement factor of 270 verify the proposed scheme. Copyright © 2017 John Wiley & Sons, Ltd. A scheme to achieve simultaneously extremely high slew‐rate improvement and avoiding open‐loop gain degradation using dynamically biased cascode transistors in super class AB operational transconductance amplifiers is introduced. It overcomes the serious shortcoming of super class operational transconductance amplifiers with very high‐output current enhancement factors at the expense of degrading the open‐loop gain. Experimental results of proposed scheme in 180‐nm complementary metal‐oxide semiconductor technology show open‐loop gain of 67 dB, a factor 2 improvement in GBW and a current enhancement factor of 270.