Abstract
This paper proposes topological enhancements to increase voltage gain of ultra-low-voltage (ULV) inverter-based OTAs. The two proposed improvements rely on adoption of composite transistors and forward-body-biasing. The impact of the proposed techniques on performance figures is demonstrated through simulations of two OTAs. The first OTA achieves a 39 dB voltage gain, with a power consumption of 600 pW and an active area of 447 μm2. The latter allies the forward-body-bias approach with the benefit of the independently biased composite transistors. By combining both solutions, voltage gain is raised to 51 dB, consuming less power (500 pW) at the cost of an increased area of 727 μm2. The validation has been performed through post-layout simulations with the Cadence Analog Design Environment and the TSMC 180 nm design kit, with the supply voltage ranging from 0.3 V to 0.6 V.
Highlights
The increasing demand for electronic devices supplied by energy-harvesting power sources bring about the need for integrated circuits (ICs) able to properly operate at ultra-low-voltage supply and with ultra-low-power consumption [1,2,3,4,5,6].In this context, the Operational Transconductance Amplifiers (OTAs) are the building blocks of any front-end and signal processing chain that are traditionally unsuitable to operate at very low voltage fulfilling performance like a rail-to-rail input/output voltage swing and high transconductance-gain that are independent by process, supply voltage, and temperature variations [7]
The Operational Transconductance Amplifiers (OTAs) are the building blocks of any front-end and signal processing chain that are traditionally unsuitable to operate at very low voltage fulfilling performance like a rail-to-rail input/output voltage swing and high transconductance-gain that are independent by process, supply voltage, and temperature variations [7]
This paper describes how inverter-based OTAs can benefit from forward-body-biasing to implement common-mode input voltage rejection [21] in single-ended OTAs, balance the charge mobility asymmetry of PMOS and NMOS transistors with parallel and series transistor arrays [19] to save area, and adapt improved composite transistors [22] to enhance voltage-gain
Summary
The increasing demand for electronic devices supplied by energy-harvesting power sources bring about the need for integrated circuits (ICs) able to properly operate at ultra-low-voltage supply and with ultra-low-power consumption [1,2,3,4,5,6]. Push-pull inverter-based OTA topologies [13,14] and their respective ULV variations [15,16] have been proposed, including push-pull based bulk-driven OTAs [17,18], offering a higher power-efficiency, linearity, and voltage gain with low output voltage swing degradation In this framework, the composite transistors [19], such as rectangular arrays [20] and trapezoidal arrays [21], can be used to increase the voltage gain of inverter-based OTAs at the cost of area.
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