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High current efficiency single-stage bulk-driven subthreshold-biased class-AB OTAs with enhanced transconductance and slew rate for large capacitive loads.

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Title: High current efficiency single-stage bulk-driven subthreshold-biased class-AB OTAs with enhanced transconductance and slew rate for large capacitive loads.
Authors: Ghosh, Sougata1 (AUTHOR) sougata.vlsi@gmail.com, Bhadauria, Vijaya1 (AUTHOR)
Source: Analog Integrated Circuits & Signal Processing. Nov2021, Vol. 109 Issue 2, p403-433. 31p.
Subjects: Operational amplifiers, Power resources
Abstract: This paper introduces two high-performance single-stage bulk-driven (BD) operational transconductance amplifiers (OTA) in weak-inversion with rail-to-rail input and output voltage ranges suited for the excessively low-voltage of 0.5 V supply. The strategy depends on adopting a modified bulk-driven non-tailed input core to achieve high input core transconductance with a minimum power supply and an enhanced input common-mode range. Moreover, a partial positive feedback loop provides an overall improved DC gain and effective transconductance further. The input core of OTA1, named composite class-AB OTA, comprises two combined non-tailed differential pairs as composite differential pairs. The proposed OTA2, named composite super class-AB BD-OTA, exploits a matched bulk-input Flipped voltage follower (FVF) pair to adaptively bias the input core used in the composite class-AB BD OTA. As a result, a significant increase in large-signal input current to the output side due to super class-AB behavior improves the slew rate. The post-layout simulation results using the Cadence Spectre simulator with UMC 0.18 µm process technology confirm that the proposed OTAs have improved small-signal and large-signal performances over the conventional OTA driving a high capacitive load of 5 nF. The proposed composite class-AB and super class-AB BD OTA deliver 2.29 times, and 3.77 times open-loop DC gain, 10.6 times, and 117 times unity-gain bandwidth with 2 times, and 12.03 times slew rate at the expense of almost 0.52 times and 1.21 times power consumed over conventional counterpart, respectively. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:This paper introduces two high-performance single-stage bulk-driven (BD) operational transconductance amplifiers (OTA) in weak-inversion with rail-to-rail input and output voltage ranges suited for the excessively low-voltage of 0.5 V supply. The strategy depends on adopting a modified bulk-driven non-tailed input core to achieve high input core transconductance with a minimum power supply and an enhanced input common-mode range. Moreover, a partial positive feedback loop provides an overall improved DC gain and effective transconductance further. The input core of OTA1, named composite class-AB OTA, comprises two combined non-tailed differential pairs as composite differential pairs. The proposed OTA2, named composite super class-AB BD-OTA, exploits a matched bulk-input Flipped voltage follower (FVF) pair to adaptively bias the input core used in the composite class-AB BD OTA. As a result, a significant increase in large-signal input current to the output side due to super class-AB behavior improves the slew rate. The post-layout simulation results using the Cadence Spectre simulator with UMC 0.18 µm process technology confirm that the proposed OTAs have improved small-signal and large-signal performances over the conventional OTA driving a high capacitive load of 5 nF. The proposed composite class-AB and super class-AB BD OTA deliver 2.29 times, and 3.77 times open-loop DC gain, 10.6 times, and 117 times unity-gain bandwidth with 2 times, and 12.03 times slew rate at the expense of almost 0.52 times and 1.21 times power consumed over conventional counterpart, respectively. [ABSTRACT FROM AUTHOR]
ISSN:09251030
DOI:10.1007/s10470-021-01929-5