Miller compensated three-stage OTA for a wide range of load capacitors (1 pF to 1 nF)

ABSTRACT

In this work, the miller with a feed-forward capacitor compensated three-stage Operational Transconductance Amplifier (OTA) for a wide range of load capacitors is presented. The proposed OTA can drive a load capacitor with a phase margin of more than ${60}^o$ from a smaller load capacitor of $1\mathit{pF}$ to a larger load capacitor of $1\mathit{nF}$. It is difficult to stabilise multi-stage OTA for a wide range of load capacitors. The OTA needs a good compensator to stabilise the OTA. The proposed compensator uses a miller capacitor along with the small feed-forward capacitor to stabilise the three-stage OTA for a wide range of load capacitors. Usually, the miller compensated multi-stage OTA with more than two stages is unstable for the smaller load capacitors and demands a minimum load capacitor for the OTA to be stable, but the proposed OTA is stable even for a very small load capacitor of $1\mathit{pF}$. The proposed structure uses a slew-rate enhancer (SRE) to enhance the transient performance of the OTA along with the feed-forward transconductors and achieves a settling time of $1.2\mathit{\mu s}$ over the wide range of load capacitors.

KEYWORDS:

• Operational transconductance amplifier
• miller compensation
• feed-forward capacitor
• settling time
• stability

Disclosure statement

No potential conflict of interest was reported by the author(s).