Negative impedance converter

About: Negative impedance converter is a research topic. Over the lifetime, 5801 publications have been published within this topic receiving 87636 citations.

A Thermodynamic Perspective of Negative-Capacitance Field-Effect Transistors

Abstract: Physical phenomena, underlying operation of negative capacitance field-effect transistors (NCFETs), are treated within a unified simulation framework. The framework incorporates the Landau mean-field treatment of free energy of a ferroelectric (FE) and the polarization dynamics according to Landau–Khalatnikov (LK) equation. These equations are self-consistently solved with the 1-D metal–oxide–semiconductor structure electrostatics and the drift-diffusion solution for currents in the semiconductor channel. Numerical simulations show that, depending on the strength of depolarization field, both regimes of hysteresis switching and of higher on-currents and steeper subthreshold slope with a negligible hysteresis can be delivered by NCFETs under the steady-state condition due to either multiple local energy minima or a single global energy minimum in the free energy landscape. The transient behavior of NCFETs is also studied by the viscosity coefficient in LK equation, and it is found that when the FE response becomes too slow, a significant hysteresis effect on currents shows up even for a free energy landscape with a single global energy minimum. Finally, recent experimental measurements on transient NC in an FE capacitor are discussed. It is shown that those results on transient NC can be due to the mismatch between free charge and polarization driven by the negative curvature of FE thermodynamic energy profile during polarization switching and cannot lead to a transient charge-boost in a hysteresis-free NCFETs.

Adaptive error amplifier clamp circuit to improve transient response of DC/DC converter with current mode control

Abstract: A current mode controlled DC/DC converter that includes an adaptive clamp voltage circuit at an error amplifier output to significantly reduce overshoot in the output of the converter if the target voltage changes rapidly. If a current limiter is active, the clamp level of the adaptive clamp voltage circuit is decreased at an appropriate rate. Similarly, if the current limiter is not activated, the adaptive clamp voltage circuit is restored to an initial clamp level. The operation of the adaptive clamp circuit at the output of the error amplifier enables a relatively faster reduction in both overshoot and the amount of time before the converter's output voltage and output current settle back down to a relatively constant state.

LLAMPÜDKEÑ: A high-current, low-impedance pulser employing an auxiliary exponential transmission line

Abstract: The design and constructional aspects of a novel pulse power generator for use in dense plasma research presently under construction are presented. The generator consists of two Marx capacitor banks, each of 0.25 μF, 480 kV, and 28.8 kJ. Each Marx generator drives a water transmission line, in which the live electrode is the central conductor. The transmission lines consist of a constant impedance section followed by a multielectrode gas line gap followed by an exponential taper to the load section. The novel feature is the use of an auxiliary exponential line coupled at the load. This line controls both the voltage and the effective impedance at the load section. In addition, by leaving this line circuit open, energy not coupled to the plasma in the initial high-impedance phase may be reflected back and deposited into the discharge, increasing the peak current by 50%. Circuit simulations using a real-time-varying load impedance show that the current pulse rises in an approximately linear way to a maximum of 1.2 MA at 250 ns. The current falls to zero in the following 250 ns. The current waveform may be flattened simply by disconnecting the auxiliary line, giving a rectangular pulse of 350 ns with a maximum value of 950 kA. The overall impedance of the entire system may be adjusted by varying the separation between the conductors. The equivalent source impedance at the load is 0.8 Q. This low value is by virtue of the auxiliary line, which limits the voltage at the load section and reduces the insulator constraints. We present simulations of the generator under real load conditions. The model also is checked against analytical solutions of exponential line behavior and against other published models of pulse power generators.

Anodic Oxidation of Formaldehyde on Gold Studied by Electrochemical Impedance Spectroscopy: An Equivalent Circuit Approach

Abstract: The anodic oxidation of formaldehyde on gold in alkaline aqueous solutions was studied by electrochemical impedance spectroscopy. One equivalent circuit was found to mimic all impedance spectra measured for normal formaldehyde and deuterated formaldehyde in various alkaline solutions at various voltages. The resistors and capacitors constituting the circuit depend logarithmically on the voltage applied, and the circuit can be explained in terms of reaction steps proposed in the literature. A negative capacitance (inductive loop) was encountered at low frequencies, which is explained by a rate‐determining C‒H bond rupture step in the overall kinetics of the reaction, as it was more apparent for solutions containing instead of . Data were Kramers‐Kronig transformable and a ‐value of or less was attained in all fits. At least four time constants were revealed by the impedance spectra as a result of positive capacitive, negative capacitive, resistive, and diffusive effects. © 1999 The Electrochemical Society. All rights reserved.

A new VCII based grounded positive/negative capacitance multiplier

Abstract: Capacitive multipliers have found wide applications in capacitive interfaces and other analog circuits requiring large value capacitors. Recently a new active building block (ABB) called second generation voltage conveyor (VCII) has been proved to be useful in many analog signal processing applications. Due to the interesting features offered by VCII, in this paper a new VCII based implementation of grounded capacitance multiplier is proposed employing two VCIIs, two resistors and one grounded capacitor. The circuit can produce both positive and negative multiplication factors in a range of −50 to +50. Its main features are wide frequency range, high resolution, low series resistance, simple structure, low power consumption and maximum percentage error of 7.8%. The circuit enjoys high frequency range up to 10 MHz, even if it employs a floating capacitor in its structure. The behavior of the proposed circuit is analysed by taking into account also the effects of VCII parasitic elements and non-ideal gains. SPICE simulation results using a 0.35 µm CMOS technology parameters are reported. The proposed circuit has been also experimentally tested by using AD844 as VCII. Measurement results on the standalone capacitance multiplier have shown a mean percentage error of 9% across the entire gain range. Finally, the application of the proposed circuit in realizing a low pass filter is also presented to demonstrate the proposed circuit feasibility.