Showing papers on "Negative impedance converter published in 1998"

Negative capacitance effect in semiconductor devices

Abstract: Nontrivial capacitance behavior, including a negative capacitance (NC) effect, observed in a variety of semiconductor devices, is discussed emphasizing the physical mechanism and the theoretical interpretation of experimental data. The correct interpretation of NC can be based on the analysis of the time-domain transient current in response to a small voltage step or impulse, involving a self-consistent treatment of all relevant physical effects (carrier transport, injection, recharging, etc.). NC appears in the case of the nonmonotonic or positive-valued behavior of the time-derivative of the transient current in response to a small voltage step. The time-domain transient current approach is illustrated by simulation results and experimental studies of quantum well infrared photodetectors (QWIPs). The NC effect in QWIPs has been predicted theoretically and confirmed experimentally. The huge NC phenomenon in QWIP's is due to the nonequilibrium transient injection from the emitter caused by the properties of the injection barrier and the inertia of the QW recharging.

Bi-directional DC to DC converters for fuel cell systems

Abstract: This paper first describes the need of a bi-directional DC to DC converter for a fuel cell system. Various combinations of current-fed and voltage-fed converters are explored for the application of different voltage levels. With a preliminary study, putting current-fed on low-voltage side and voltage fed on high voltage side indicated higher efficiency than the other way around. Two low-side circuit topologies were then selected for hardware implementation. One is the L-type half-bridge current-fed converter, and the other is full-bridge current-fed converter. The high-side circuit topology is fixed with a full-bridge voltage-fed converter. Two systems were built and tested to full power. The results indicate that the combination with the full-bridge converter on the low-voltage side is more efficient than the combination with the L-type half-bridge converter on the low-voltage side for both charging and discharging modes.

Gyrator‐based biquad filters and negative impedance converters for microwaves

Abstract: We develop and evaluate a new family of active-RC, gyrator-based, voltage-mode, biquadratic filters capable of realizing all standard second-degree filtering functions at microwave frequencies. Each biquad employs two negative second-generation current conveyors (CCII−s) or, equivalently, two infinite-conductance transistors, and we obtain excellent simulated results by implementing each of these perfect elements as a cascaded pair of MMIC GaAs FETs. The transistors in the simulation are modeled using tabulated S parameters of MB3000 (Phillips) devices. In addition, we catalog all known ideal, two-transistor negative impedance converter (NIC) topologies and we show that some are intrinsically better than others with respect to their performance when the active elements are implemented using MMIC GaAs FET CCII−s. © 1998 John Wiley & Sons, Inc. Int J RF and Microwave CAE 8: 86–101, 1998.

A novel soft-switching high-frequency transformer isolated three-phase AC-to-DC converter with low harmonic distortion

Abstract: A high-frequency transformer isolated, fixed-frequency, 3-/spl phi/ single-stage ac-to-dc converter using a boost-integrated bridge converter that employs a new gating scheme is proposed. This converter enjoys natural power factor correction with low line current harmonic distortion and symmetric high frequency voltage and current waveforms while ensuring zero-voltage switching for all the switches for a wide variation in load and line voltage. Various operating modes of the converter are presented and analyzed. Based on the analysis, design curves are obtained and an optimum design is given. A design example is presented. Results obtained from SPICE simulation and a 500 W output experimental prototype are given to verify the performance of the proposed converter for varying load as well as line voltage.

Start up circuit for DC powered field instrument

Abstract: A direct current (DC) powered process instrument start up circuit includes an energy storage device, a switching regulator circuit, a variable impedance circuit, and a voltage measurement circuit. The energy storage device is coupled between first and second power supply terminals. The switching regulator circuit is coupled to the energy storage device and has a regulated voltage output. The variable impedance circuit is coupled between the energy storage device and the first power supply terminal and has an impedance control input. The voltage measurement circuit has a measurement input coupled to the energy storage device and a measurement output coupled to the impedance control input.

Half-bridge DC to DC converter with low output current ripple

Abstract: A method and apparatus for maintaining relatively low ripple current in a dc-dc converter while minimizing the size of an inductive line filter utilizes a transformer having at least a pair of secondary windings in which the secondary windings are selected to have different numbers of winding turns depending on the specific design of the ideal duty factor at which the converter will be operated. In addition, the converter is provided with an active pre-load which establishes a continuous conduction current when load current is below some selected minimum value in order to provide control stability during light load conditions without converter oscillations. In an illustrated embodiment, the active pre-load circuit comprises a resistor connected in series with a transistor across the voltage output of the converter with the gate terminal of the transistor connected through a zener diode to the control circuit so that when the control voltage feedback signal drops to a selected low value, the transistor is biased into conduction to connect the resistor as a load to maintain a minimum load current. Alternatively, the transistor can be connected across one of the diodes in the transformer secondary and arranged so as to conduct current in a direction opposite to the direction of current through the diode so that under low current conditions, a current loop is formed through the transformer to maintain continuous current flow and allow the converter to operate at very light loads.

Stirling cycle generator control system and method for regulating displacement amplitude of moving members

Abstract: A Stirling cycle machine control system includes an energy converter having a moving member. A detector is operatively associated with the moving member. The detector is configured to detect stroke of the moving member. A converter circuit is coupled with an output of the energy converter and is operative to convert output from AC to DC. A regulator is coupled with the converter circuit and a useful load, and is operative to regulate DC voltage. A controllably variable load member is coupled to the converter circuit and is operative to adjust load to the energy converter. Adjustment of the load to the energy converter regulates power output of the energy converter which in turn controls movement of the moving member. Control circuitry is signal coupled with the detector and the load member. The control circuitry is configured to receive a feedback signal correlated with the detected stroke of the moving member. The control circuitry is operative to dynamically adjust load on the energy converter to limit stroke of the moving member below a threshold level. A method is also provided.

Low frequency negative capacitance behavior of molecular beam epitaxial GaAs n-low temperature-i-p structure with low temperature layer grown at a low temperature

Abstract: The GaAs sample under study is a n-low temperature-i-p structure grown by molecular beam epitaxy with a low-temperature (LT) layer grown at 300 °C and annealed at 620 °C for 1 h. Admittance measurements on this sample reveal a negative capacitance at low frequency. This work analyzes the origin of the negative capacitance and its corresponding frequency-dependent conductance by combining two current components: charging–discharging current and the inertial conducting current. Analysis results indicate that the activation energies and time constants of both current components closely resemble each other and should correspond to the same trap. Based on the results presented herein, we can conclude that the negative capacitance at low frequency provides evidence of a generation-recombination center with an activation energy of 0.77 eV in the LT layer.

Constant current source circuit with variable temperature compensation

Abstract: The constant current source circuit provides current that compensates for changes in performance resulting from changes of temperature. The circuit mixes variable amounts of current having a negative temperature coefficient with current having a positive temperature coefficient. Analog and digital embodiments of the circuit are disclosed. In the analog embodiment, the amount of current having a positive temperature coefficient is added to an amount of current having a negative temperature coefficient as determined by the voltage difference between a variable control voltage input to transistors and a bandgap reference voltage. A transistor in each of two current selectors is connected to the variable control voltage, one of which is connected to ground and the other of which is output; and another transistor in each current selector is connected to the reference voltage, and again one transistor is grounded and the other is output whose current is mixed with the output from the transistor in the first current selector connected to the variable control voltage. A continuous range of temperature coefficients are realizable by varying the control voltage with respect to the bandgap reference voltage. The digital embodiment has a digital-to-analog converter connected to a bias voltage from the current having a positive temperature coefficient and a second digital-to-analog converter connected to a second bias voltage from the current having a negative temperature coefficient. A digital input signal to a corresponding switch determines if its respective transistor in each of the digital-to-analog converters conduct current. The two digital-to-analog converters may be configured in a common centroid arrangement of integrated complementary unit cells. The constant current source circuit can be used to drive off-chip parallel loads such as VCSELs.

Self-excited induction generator controlled by a VS-PWM converter providing high power-factor current to a single-phase grid

Abstract: This paper is concerned with the application of a three-phase cage induction machine as a self-excited hydraulic-turbine driven generator connected to the AC side of a voltage source PWM bi-directional power converter. Frequency and voltage at the three-phase AC load are regulated by the action of the PWM converter. This structure also provides energy to the utility grid via a buck converter and a current inverter connected to a single-phase AC line. The buck converter is controlled by a power factor corrector IC so that a sinusoidal current is sent to the utility with unity power factor. The proposed system is intended to be applied in rural plants as source of three-phase voltage with regulated frequency and amplitude. The generator is intended to be driven by a low-head hydraulic turbine with an unregulated shaft, resulting in a system with relative low-cost.

DC-to-DC converter with transient suppression

Abstract: A DC-to-DC converter includes: a first circuit to sense when the converter output voltage occurs outside a substantially pre-determined range, and a second circuit to adjust the converter load current, based at least in part, upon a signal provided by the first circuit. Alternatively, a circuit to suppress voltage transients for use in a DC-to-DC converter having a primary inductor includes: another circuit inductance lower than the inductance of the primary inductor. The another circuit inductance is coupled in the circuit to be activated when the load voltage of the DC-to-DC converter occurs outside a substantially predetermined range. The another circuit inductance is further coupled in the circuit so that it has the capability to modify the load current during activation.

Dual mode split-boost converter and method of operation thereof

Abstract: A split-boost converter having a main inductor, first and second main switches and floating and fixed outputs and a method of operating the same. In one embodiment, the converter includes an auxiliary diode coupled between the main inductor and a first rail of the floating output, and an auxiliary switch coupled to a node between the main inductor and the auxiliary diode and a second rail of the floating output. The converter is operable in a first mode, when an input voltage of the converter at least equals an output voltage of the converter, in which the auxiliary switch remains open and the first and second main switches are modulated to operate the converter. The converter is further operable in a second mode, when an input voltage of the converter is less than an output voltage of the converter, in which the first and second main switches remain closed and the auxiliary switch is modulated to operate the converter.

Negative capacitance effect in semiconductor devices

Abstract: Nontrivial capacitance behavior, including a negative capacitance (NC) effect, observed in a variety of semiconductor devices, is discussed emphasizing the physical mechanism and the theoretical interpretation of experimental data. The correct interpretation of NC can be based on the analysis of the time-domain transient current in response to a small voltage step or impulse, involving a self-consistent treatment of all relevant physical effects (carrier transport, injection, recharging etc.). NC appears in the case of the non-monotonic or positive-valued behavior of the time-derivative of the transient current in response to a small voltage step. The time-domain transient current approach is illustrated by simulation results and experimental studies of quantum well infrared photodetectors (QWIPs). The NC effect in QWIPs has been predicted theoretically and confirmed experimentally. The huge NC phenomenon in QWIPs is due to the non-equilibrium transient injection from the emitter caused by the properties of the injection barrier and the inertia of the QW recharging.

Novel generation method of current mode Wien-type oscillators using current conveyors

Abstract: A new approach to the generation of current mode Wien-type oscillators using the current conveyor is introduced. The proposed method is based on replacing the generalized current negative impedance converter in the conventional Wien oscillator by a well-known equivalent circuit realized using the current conveyor. A family of four new current mode oscillators employing grounded capacitors derived from the corresponding classical op amp Wien oscillator family is given. The proposed oscillators have the attractive advantage that the condition of oscillation and the frequency of oscillation can be independently controlled without affecting each other. PSpice simulation results supporting the theoretical analysis are given.

Internal voltage generating circuit

Abstract: The present invention relates to an internal voltage generating circuit. The internal voltage generating circuit comprises a reference voltage generating circuit for generating a reference voltage, which does not depend on an external power supply; and a comparator including a first input terminal, to which the reference voltage is supplied, a second input terminal, for comparing the voltages of the first and second input terminals and generating an output voltage according to the difference thereof at the output terminal; and an impedance element, which is selectively inserted between the output terminal and the second input terminal of the comparator according to an operation mode. An internal power supply voltage, which has a constant voltage during normal operation and has an accurate higher voltage during acceleration test, can be generated at the output terminal by inserting or not inserting a suitable impedance element between the second input terminal and output terminal according to the operation mode. The above-described comparator can be realized by a common differential amplifying circuit, for example. Further, a reference voltage value at normal operation can be fine-tuned by subdividing the impedance element. In the same way, the voltage value at acceleration test can be also fine-tuned by subdividing the impedance element.

Performance limitations of random current-sharing parallel-connected converter systems and their solution

Abstract: A study of a random current-sharing power converter system is presented. The system is comprised of many DC/DC power converters connected in parallel. Each power converter has its own single control loop operating in either the voltage regulation or current-limiting mode. Performance limitations are discovered through system simulation. Nonuniform current sharing occurs despite voltage droop characteristics that facilitate near-uniform current distribution. Due to random mismatches in component values, uneven current sharing among power converters exists. This causes system performance characteristics to exhibit large variations and system current sharing is found to be far from uniform, resulting in poor system reliability. The achievement of near-uniform current distribution, stiff system output voltage and the reduction of the output impedance variances are also discussed.

An improved zero voltage switching flyback converter topology

Abstract: An improved zero voltage switching flyback converter topology is presented in this paper. This converter employs an auxiliary circuit that provides ZVS for both the main and auxiliary and it permits the operation of the converter at very high frequencies. Operating principle, steady state analysis, and design procedure for the auxiliary circuit of the proposed converter, are given. A 50 W, 260 kHz prototype converter is built to verify the performance. Experiments of the proposed converter show an improvement of about 2% in the overall efficiency as compared to the previous ZVS flyback converter.

Two Modified for Chaos Negative Impedance Converter Op Amp Oscillators with Symmetrical and Antisymmetrical Nonlinearities

Abstract: Two sinusoidal oscillator circuits, that employ an operational amplifier (op amp) as a current negative impedance converter (CNIC), are modified for chaos using a nonlinear resistor of anti-symmetrical current-voltage characteristics formed by a junction field effect transistor (JFET) operating in the triode region. The internal op amp dominant pole is found to contribute significantly to the chaotic nature of one circuit while the other circuit develops different chaotic attractors when cubic and fifth power odd symmetrical nonlinearities are used. Mathematical models of the two generators are presented. Experimental laboratory results, circuit simulations and numerical simulations of the mathematical models well agree and are included.

Electronic device and associated method for charging an energy storage circuit with a DC-DC converter

Abstract: An electronic device includes an electrical circuitry interface (112) adapted for coupling with an energy source (106), a comparator (138), and a DC-DC converter circuitry (134) having a switch circuit (161) and an energy storage circuit (132). The switch circuit (161) is coupled to the electrical circuitry interface (112) and to the energy storage circuit (132), and is controlled to charge the energy storage circuit (132). A first input (166) of the comparator (138) is coupled to a voltage that varies with a nominal supply voltage of the energy source (106). A second input (168) of the comparator (138) is coupled to a threshold voltage. A comparator output (160) of the comparator (138) is coupled to the switch circuit (161). In operation, the DC-DC converter circuitry (134) charges the energy storage circuit (132) for a certain time period or until the stored voltage is greater then a desired voltage. The DC-DC converter circuitry (134) is controlled to stop charging the energy storage circuit (132) when current demands cause the energy source voltage to exceed a threshold voltage.

Regulated self-oscillating resonant converter with current feedback

Abstract: Lamp voltage or current obtained from a self-oscillating converter is stabilized by a feedback circuit. Gates of the switching transistors are connected to output windings of a current transformer whose input current winding is in series with the resonant load lamp circuit. The lamp voltage or current is sensed, and the resulting signal is used to control current through an auxiliary control winding on the current transformer. Preferably, two opposite conductivity type control transistors are connected in parallel across the control winding, and low-pass filtered DC signals corresponding to the lamp voltage or current bias the control transistors.

Microamp measurement for two-terminal digital meter

Abstract: A two-terminal multimeter capable of both volt/ohm and current measurement employs an input protection circuit with a positive temperature coefficient impedance and a reference impedance, across which an A-D converter takes measurements. A current measurement signal activates a switch to ground one side of the reference impedance for taking current measurements. A controllable clamping switch grounds the positive temperature coefficient impedance in an input overload situation to provide input protection against damage to the meter components.

Gas discharge lamp ballast with output voltage clamping circuit

Abstract: A ballast circuit for a gas discharge lamp includes a d.c.-to-a.c. converter circuit with circuitry for coupling to a resonant load circuit, for inducing a.c. current therein. The converter circuit comprises a pair of switches serially connected between a bus conductor at a d.c. voltage and a reference conductor, the voltage between a reference node and a control node of each switch determining the conduction state of the associated switch. The respective reference nodes of said switches are connected together at a common node through which said a.c. current flows, and the respective control nodes of the switches are connected together. A gate drive arrangement is provided for regeneratively controlling the first and second switches. The arrangement comprises a feedback circuit for providing a feedback signal representing current in the load circuit; a coupling circuit including an inductor for coupling the feedback signal to the control nodes; and a first bidirectional voltage clamp connected between the common node and the control nodes. A second bidirectional voltage clamp is coupled across the inductor in such manner as to limit the positive and negative voltage excursions across the inductor.

Signal converter with a dynamically adjustable reference voltage and chipset including the same

Abstract: A signal converter with a dynamically adjustable reference voltage according to the invention, which can receive different qualities of signals. The signal converter includes an input circuit and a reference voltage generator. The input circuit converts a first digital signal, such as a GTL+ signal, into a second digital signal, such as a TTL or CMOS signal, based on an adjustable reference voltage generated by the reference voltage generator. When a control circuit needs to receive the first digital signal from outside via the input circuit, the control circuit can adjust the reference voltage by controlling the reference voltage generator so as to receive the first digital signal with a different quality.

Simple equivalent circuit for the series-loaded resonant converter with voltage boosting capacitor

Abstract: A simple, fundamental frequency equivalent circuit is derived for the series-loaded resonant converter with voltage boosting capacitor The equivalent circuit permits direct and straightforward calculation of the steady-state resonant current and voltage conversion ratio; previous analyses have used time-domain techniques requiring complex calculation and numerical solution Comparison with results from an idealised time-domain simulation is used to quantify the errors introduced by the fundamental frequency approximation Practical results from a 1 MHz prototype demonstrate the accuracy of the technique for converter design

Method and arrangement in a dc-to-dc converter

Abstract: A method and an arrangement for controlling the output voltage (V2) of a DC-to-DC converter (100). The DC-to-DC converter (100) comprises converting means (101) and regulating means (102). The converting means is fed by a first DC-voltage (V1) from the regulating means. The first DC-voltage (V1) is determined by a feed back portion (VDIV) of the output voltage (V2) from the converting means and a reference voltage (VREF). The reference voltage is derived from a pulse train (PT1). The output voltage (V2) depends on both the first DC-voltage (V1) and the pulse train (PT1). The output voltage (V2) from the DC-to-DC converter is kept constant under varying load and the output voltage level can be adjusted in an easy and flexible manner by the pulse train.

A 2-V 2-GHz BJT variable frequency oscillator

Abstract: A new LC-tuned negative-resistance variable-frequency oscillator (VFO) is described Frequency tuning is accomplished by using a variable-impedance converter (VIC) to simulate the varactor function A negative-impedance converter provides the necessary negative resistance for oscillation and also functions as the voltage level shifters for the VIC A low-voltage translinear circuit is used to linearize the tuning characteristic of the VFO Implemented in a 08 /spl mu/m 12 GHz f/sub T/ BiCMOS technology, the VFO has a tuning range from 155 to 202 GHz, while consuming 15 mA from a -2 V supply

Method and apparatus for gas concentration detection and manufacturing method of the apparatus

Abstract: An A/F sensor generates a current signal corresponding to an air-fuel ratio in response to a voltage applied by a bias control circuit. After a sensor current is received as a voltage signal via a voltage follower, it is outputted to an A/D converter having a predetermined input voltage range, 0 to 5V. A sensor current detection circuit has a plurality of current detection resistors. In order to variably set the resistance value by the sensor current detection circuit, a switch circuit is switched in accordance with the sensor current depending on whether the A/F value to be detected is in the zone near the stoichiometric ratio or in other air-fuel ratio zones.

Amplifier using a single polarity power supply

Abstract: The present invention provides a power amplifier operating with a single power supply. The amplifier includes at least one depletion-mode FET for amplifying an ac signal and a negative voltage generator for providing a bias to the FET. Preferably the amplifier further includes a negative voltage regulator to provide a regulated bias to bias the FET for a class A, AB or B operation. The negative generator includes a multivibrator for producing two clock signals and a charge pump which receives the clock signals and produces a negative voltage. Advantageously the negative voltage is provided as a low reference potential to the multivibrator so that the clock signals it produced include a negative voltage period, which enables the charge pump to operate in a power efficient manner.

Regulated negative voltage supply circuit for floating gate memory devices

Abstract: A technique for regulating a negative voltage charge pump to induce Fowler-Nordheim tunneling in floating gate cells controls applied bias to compensate for variations in the supply potential VDD, temperature, and the gate coupling ratio (GCR) or other characteristics of the memory cells which depend on manufacturing processes. A supply circuit for a negative voltage includes a voltage regulator that is coupled to the negative voltage source to maintain the negative voltage at a regulated level. The regulator includes an element that establishes the regulated level according to the manufacturing processes and temperature of the device. The regulator also comprises a circuit which establishes the regulated level in response to the supply voltage. Thus, where the negative voltage generator is utilized in a floating gate memory device, the element that establishes the regulated level according to manufactured processes and temperatures comprises a floating gate transistor manufactured according to the same processes as the non-volatile memory cells in the array on the device.