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A new configuration of the flipped voltage follower (FVF) offering class-AB operation is presented. The idea uses a bulk-driven transistor instead of the constant current source of the typical FVF topology. This feature enhances the sourcing capability for class-AB operation and the symmetrical slew rate. The key element is changing the basic structure of the original FVF circuit with no additional devices. A detailed analysis of the circuit and simulations using Spice are presented. The experimental results from a manufactured circuit prototype using CMOS 0.35 μm technology demonstrate the feasibility of the proposal.

Abstract:In general terms, it is not possible to establish symbolic explicit analytic expressions of the operating point and transient analysis for circuits containing diodes modelled using an exponential function. Therefore, this work propose replacing the diode for an equivalent circuit obtained by using a power series and a Taylor series consecutively. Finally, we present a symbolic solution for some circuits that include diodes; resulting for the best case: for DC analysis a relative error of 1E-11 and for transient analysis a relative error ≤ 5E-4. Keywords: circuit analysis, nonlinear circuits Classification: Electron devices, circuits, and systems References[1] T. C. Banwell, "Bipolar transistor circuit analysis using the lambert wfunction," IEEE Trans. Circuits Syst. I, Fundam. Theory Appl., vol. 47, no. 11, pp. 1621-1633, Nov. 2000

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During thin film transistor (TFT) operation, gate dielectric is under a bias stress condition. In this work, bias stress effect for CdS TFT using HfO2 as gate dielectric is analyzed. Threshold voltage, Ion/Ioff ratio, and subthreshold slope were studied in order to understand changes produced at the dielectric semiconductor interface. We observed that threshold voltage shift is related with negative charge trapping in the dielectric/semiconductor interface and for this phenomenon we propose a trapping charge model. Finally, the TFT output characteristic was modeled considering a shift in the threshold voltage for each gate voltage curve.

A modified version of the flipped voltage follower (FVF) with class AB operation and very low output resistance is presented. Instead of passing one of the large bidirectional output currents through the voltage following transistor, which considerably degrades the output resistance as in other variations, the proposed circuit maintains a constant current in this device and, hence, a very low output resistance. Complementary-type output transistors that depend on the same signal give the circuit the ability to provide large bidirectional currents at high frequency. The implementation only requires an additional resistor and one connection change, with no additional power consumption. Simulation and experimental results of the fabricated circuit in a 0.5μm technology show an output resistance of the proposed circuit of 12 Ω, with an enhancing factor of 60 with respect to previously reported variations.

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