Circuit Potential Research Articles

Versatile wideband impedance matching circuit based on current conveyors

The first active impedance matching circuit for RF applications is introduced. It adapts arbitrary output impedances to values between 50 and 250 Ω, from 0 to 5 GHz, and occupies only 0.005 mm2 in 0.35 µm SiGe-BiCMOS. It is vastly superior to traditional passive-element solutions by being: the first flexible matching circuit to adapt any impedance to any desired value; the smallest matching circuit ever; and a rare example of wideband matching. Application to a low-noise amplifier proves the potential of the new circuit.

Electrochemical Behavior of Titanium in NaOH Solutions

The electrochemical behavior of commercially pure titanium was investigated as a function of NaOH concentration by open- circuit potential (OCP) transients, cyclic voltammograms and galvanostatic method. The OCP value was observed to decrease with increasing NaOH concentration, and the magnitude of the anodic current peaks in cyclic voltammograms becomes higher with increasing NaOH concentration. These results indicate easier anodic dissolution of Ti in more concentrated alkaline solutions in active potential region. The cyclic voltammograms and galvanostatic potential transient curves of Ti showed that protective anodic oxide films are formed on Ti in the passive potential region in all the concentrations of NaOH up to 10 M. The surface film formed anodically on Ti becomes less protective with increasing NaOH concentration up to 3M but it becomes more protective with increasing NaOH concentration above 3M NaOH.

Electrochemical bursting oscillations on a high-dimensional slow subsystem

Experiments are carried out with a chemical burster, the electrodissolution of iron in sulfuric acid solution. The system exhibits bursting oscillations in which fast periodic spiking is superimposed on chaotic, slow oscillations. Regularization of the slow dynamics, i.e., transition from chaotic to periodic bursting oscillations, is investigated through changes in the experimental parameters (circuit potential, external resistance, and electrode diameter). These transitions are accompanied by changes in the fast dynamics; a 'Hopf-Hopf' spiking is transformed to 'homoclinic-Hopf' spiking. The periodic bursting is destroyed through a period lengthening process in which the fast spiking region extends to a large fraction of the slow oscillatory cycle until there is no clear distinction between the fast and slow oscillations. Finally, it is shown that the time-scales of the fast spiking and, to a lesser extent, of the slow oscillations (or the occurrence of fast spiking) can be controlled with periodic perturbation of an experimental parameter, the circuit potential.

Two-way communication for programming and measurement in a miniature implantable stimulator

Implantable stimulators are needed for chronic electrical stimulation of nerves and muscles in experimental studies. The device described exploits the versatility of current microcontrollers for stimulation and communication in a miniature implant. Their standard outputs can provide the required selectable constant-current sources. In this device, pre-programmed stimulation paradigms were selected by transcutaneous light pulses. The potential of a programmable integrated circuit (PIC) was thus exploited. Implantable devices must be biocompatible. A novel encapsulation method that require no specialised equipment and that used two classical encapsulants, silicone and Teflon was developed. It was tested for implantation periods of up to four weeks. A novel way to estimate electrode impedance in awake animals is also presented. It was thus possible to follow the evolution of the nerve-electrode interface and, if necessary, to adjust the stimulation parameters. In practice, the electrode voltage at the end of a known constant-current pulse was measured by the PIC. The binary coded value was then indicated to the user as a series of muscle twitches that represented the binary value of the impedance measurement. This neurostimulator has been successfully tested in vitro and in vivo. Thresholds and impedance values were chronically monitored following implantation of a self-sizing spiral cuff electrode. Impedance variations in the first weeks could reflect morphological changes usually observed after the implantation of such electrodes.

Electrostatic fields and current-flow impact on whisker growth

Tin whisker growth is problematic due to the potential for short circuits in electronic devices. These devices are electrically active, generating electric fields, and transporting current. Controversy continues regarding the propensity for tin whiskers to grow more readily in the presence of an electrical bias, and other researchers have proposed that an electrical field can influence tin-whisker growth directions. The latter would exacerbate the problem of tin whiskers in electronic devices by potentially reducing the effective growth length required to induce electrical shorts. In this paper, we have developed a new test vehicle to examine the roles of electric field and current flow on the tendency to form tin whiskers. Parts have been exposed to various environmental conditions, similar to those proposed by the National Electronics Manufacturing Initiative (NEMI). In summary, the electrical fields used here, bias and current flow, do not significantly affect whisker growth. We will also present some analytical discussion regarding the potential of electromagnetic fields to influence whisker growth directions or deflections.

A multiple-terminal gate charging model

A gate charging model considering charging effect at all terminals of a MOSFET is reported in this letter. The model indicates two distinct charging mechanisms existing in P MOSFETs with a protecting device at their gates during plasma processing. The charging mechanism exists when antenna size at the gate is higher than that at other terminals combined. In contrast, the charging mechanism exists in the case of antenna size at the gate lower than that at other terminals combined. The normal-mode mechanism will dominate the charging event when there is no protecting device at the transistor gate or the protecting device provides very low leakage current. On the other hand, the reverse-mode mechanism becomes dominant if the protecting device provides very high leakage current. The normal-mode charging mechanism is limited by the N-well junction leakage while in the reverse-mode mechanism, it is limited by the leakage of the protecting device. The model also suggests that larger N-well junction gives rise to higher charging damage in the normal-mode mechanism while it is opposite in the reverse-mode mechanism. These were confirmed by experimental data. The model points out that a zero charging damage can be achieved at certain combinations of the gate, source, drain and N-well antenna ratio. The knowledge of these transistor terminal antenna-ratio combinations will maximize the effective usage of the charging protection devices in circuit design. The reverse-mode charging mechanism suggests that the use of a high-leakage device at the transistor gate for charging protection may cause an opposite effect when the transistor terminal antenna ratios run into a condition that triggers this mechanism. This implies that PMOS transistors with gate intentionally pinned at ground or low potential in circuits may be prone to charging damage depending on the connectivity of their source, drain, and NW.

Resonant Control of Electrochemical Oscillations

We report experimental control of complex (periodic and chaotic) oscillatory dynamics in an electrochemical system by applying a nonfeedback control method. By choosing an appropriate frequency for the periodic modulation of an accessible control parameter (e.g., circuit potential) not only are the chaotic dynamics converted to regular periodic behavior (controlling chaos) but also the character of the oscillatory dynamics is altered (for example, 11 → 10). This is different from previously reported experiments involving simple entrainment of oscillatory dynamics, since in our experiments the frequency of sinusoidal modulation is chosen such that the existing unstable dynamics are targeted and subsequently stabilized. Consequently, the maximum amplitude of the control signal is less than ±5% of its base value. Since resonant control strategy can be easily implemented without a complicated precontrol procedure it seems relevant for applications to real systems.

Bis-triazole as a new corrosion inhibitor for copper in sulfate solution. A model for synergistic inhibition action

Bis-[4H-5 hydroxy-1, 2, 4-triazol-3-yl] methane “BHTAM” was tested as a promising new inhibitor for copper corrosion in 0.5 M Na2SO4 solutions using open – circuit potentials and galvanostatic polarization techniques. The results show that, BHTAM is an efficient inhibitor for copper corrosion in neutral medium. The anodic polarization is strongly affected by the presence of BHTAM compound as well as the cathodic polarization but to a lesser extent. The surface condition plays a significant role in the protection of copper. The pre-formed surface cuprous oxide films facilitate inhibitor adsorption as well as precipitation of insoluble [Cu (I) – BHTAM] complex.

神経細胞の電気的等価回路と静止膜電位

神経細胞の電気的等価回路と静止膜電位

A 5-μm-wide 18-cm-long low-loss YBa/sub 2/Cu/sub 3/O/sub 7-δ/ coplanar line for future multichip module technology

Narrow and low-loss YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) coplanar lines, which can be used in multichip module technology for future high-density and high-speed digital circuits, have been developed. Etch-back planarization and a patterning process combining Ar-ion milling and wet-etching enabled us to form an 18-cm-long 5-/spl mu/m-wide YBCO coplanar line without electrical shorts, even for the narrow spacing of 2.5 /spl mu/m. The surface resistance of this line was kept at a level comparable to that of 10- or 25-/spl mu/m-wide YBCO coplanar lines and also comparable to that of unpatterned films. This indicates successful fabrication of the 5-/spl mu/m-wide YBCO coplanar line without notable loss increase resulting from process damage. The 5-/spl mu/m-wide line showed a low-transmission loss of 0.49 dB at 10 GHz and 55 K. This level of loss is similar to that in Cu coaxial cables. No significant increase in transmission loss was observed up to an input power level of 16 mW at 10 GHz and 55 K. This input power is comparable to the power-handling capability required for transmitting high-speed digital signals through the lines with characteristic impedance of 50 /spl Omega/. These results show that the narrow 5-/spl mu/m-wide YBCO coplanar line has great potential for high-density and high-speed digital circuits.

112-GHz collector-up Ge/GaAs heterojunction bipolar transistors with low turn-on voltage

This paper reports small-sized collector-up Ge/Ga/As heterojunction bipolar transistors (HBT's) operating at low power and high frequency. A heavily B-doped Ge base-layer and a newly-developed self-aligned process reduce the base resistance and the parasitic elements. Intrinsic base resistance is 50 /spl Omega///spl square/; this is the lowest value reported for bipolar transistors. With limiting the active emitter area through B ion implantation, these collector-up HBT's with a collector size of 2/spl times/5 /spl mu/m/sup 2/ exhibit a current gain of 60. They exhibit a maximum oscillation frequency f/sub max/ of 112 GHz with an associated current gain cutoff frequency f/sub T/ of 25 GHz. The large value of f/sub max/, exceeding 100 GHz, is attributed to the extremely low base resistance caused by the heavily B-doped base-layer and the self-aligned process and to the low base-collector capacitance expected from the collector-up structure. The turn-on voltage of these HBT's is approximately 0.7 V smaller than that of AlGaAs/GaAs HBT's. These results show that these HBT's have excellent potential for low-power dissipation circuits.

The Limits to Hardening Electronic Boxes to IEMP Coupling

Experimental investigations of the IEMP coupling processes within electronics enclosures have determined that there are practical limits to the effectiveness of IEMP hardening approaches. The use of low-electron-emission coatings or potting compounds and ground planes reduces the IEMP coupling to those processes which occur within the circuit boards themselves. Depending on the thickness of the circuit board, the IEMP coupling may be dominated by the bulk photocurrents emitted within the dielectric or the dipole layer formed over the metallic conductors. Results of this study indicate that IEMP also has a low-impedance coupling mechanism governed by secondary electrons which may be collected by circuit potentials as low as +5 volts.

A valve potentiometer

The usual thermionic valve circuits for amplifying the small measuring current in potentiometric methods cause serious errors due to the appreciable grid current present in valves having high mutual conductance. On the other hand, the use of electrometer valve is attended with lack of sensitiveness. A d.c. amplifier has been described using an electrometer triode coupled to a valve of LP2 type. The drift was considerably less than in a single valve circuit and electrode potentials could be measured to 0·1 millivolt using a unipivot galvanometer. A simple high-insulation switch is designed which enables both the standard and secondary cells to be operated with ease.

Some remarks on the volta force and seat of electro-motive forces questions, and on impressed force and potential in condenser circuits

Some remarks on the volta force and seat of electro-motive forces questions, and on impressed force and potential in condenser circuits