An overview of feed-forward design techniques for high-gain wideband operational transconductance amplifiers

In this paper, feed-forward techniques are revised and used for the design of high-frequency Operational Transconductance Amplifiers (OTA). For the same power consumption and similar transistor dimensions the two-path and three-path folded-cascode OTAs present both smaller settling error and faster response as compared with the typical folded-cascode topology. Also, a No-Capacitor FeedForward (NCFF) compensation, which uses a high-frequency pole-zero doublet to obtain high gain, high GBW and a good phase margin, is discussed. The settling-time of the NCFF topology can be faster than that of higher miller based OTAs, even if the last topology uses larger transconductance values. Experimental results for the multi-trajectory OTAs fabricated in the AMI 0.5 μm CMOS process demonstrate the feasibility of the feed-forward schemes.