Showing papers on "LC circuit published in 1994"

Transponders, interrogators, systems and methods for elimination of interrogators synchronization requirement

Abstract: A Radio Frequency Identification (RFID) system having an interrogator (12) and a transponder (14). The interrogator has a first tuned circuit (28) of a powering frequency for sending a powering burst to a transponder (14), a filter/demodulator (64) for receiving an wireless, modulated RF response from a transponder (14). The interrogator (12) further has a second tuned circuit (29) in electrical communication with a modulator (48), the second tuned circuit (29) having a selected bandwidth about a communication frequency, the selected bandwidth not substantially overlapping the powering frequency and encompassing the bandwidth of the modulated carrier of the RF response. The interrogator also has a controller (16) in electrical communication with the filter/demodulator (64) and the tuned circuits (28,29) and capable of enabling the first tuned circuit (28) to send the powering burst during a first time period and of enabling the modulator (48) in electrical communication with the second tuned circuit (29) to receive the RF response during a second time period. The transponder has a tuned circuit (34), a tuning circuit (54,56) in electrical communication with the tuned circuit (34) for modifying the frequency characteristics of the tuned circuit (34) such that it is can be tuned during the powering burst to the powering frequency and to be tuned during the RF response to the communication frequency. The transponder (14) also includes a demodulator (66) in electrical communication with the tuned circuit (34) for receiving the RF interrogation therefrom and for demodulating data from the RF interrogation.

An analytical method for calculating harmonic currents of a three-phase diode-bridge rectifier with DC filter

Abstract: Commonly, three-phase diode bridge rectifiers with an LC filter at the DC side are often used to convert AC input into a DC voltage. It is well known that they generate large amounts of harmonic currents. This paper proposes an analytical method for calculating the harmonic currents for both the continuous and discontinuous current conductions. The equations for the harmonic currents are derived, taking into account the effects of the DC and AC side impedances. All the calculations are conducted only by algebraic calculation with high accuracy. The validity of the proposed method is demonstrated by comparison to the results of time simulation. >

The two-winding transformer: an experimental method to obtain a wide frequency range equivalent circuit

Abstract: A lumped-component equivalent circuit has been developed by our team to model the electric behavior of any two-winding transformer. This circuit is general: its topology is independent of shape, sizes, and technology chosen. Changing the sample results only in a change of numerical values. Moreover, this circuit is suitable in a wide frequency range: from dc up to, at least, one decade beyond the maximum working frequency of the transformer. The aim of this paper is to present an experimental method which allows all the component values of this equivalent circuit to be determined, using only external impedance measurements. The method is illustrated by one example and, to conclude, Bode plots related to the circuit are compared to the experimental ones. >

High TC superconducting monolithic ferroelectric junable b and pass filter

Abstract: The design of a high Tc superconducting band pass tunable ferroelectric filter (TFF) is presented. The band pass TFF consists of an edge coupled filter on a ferroelectric substrate. Each input and output microstrip line is a quarter wavelength long. Each intermediate microstrip line is a half wavelength long with the first quarter wavelength being coupled to the preceding microstrip line and the remaining quarter wavelength being coupled to the succeeding microstrip line. Each microstrip line is connected, through an LC filter, to a common bias voltage source. Application of a bias voltage changes the frequency of operation of the filter. For matching the impedances of the input and output of the filter to the impedances of an input and output circuit respectively, matching ferroelectric quarter wavelength transformers are provided.

Input Filter Design for PWM Current-Source Rectifiers

Abstract: Pulse-width modulated (PWM) rectifiers are increasingly used because they allow the elimination of low-order harmonics, and therefore a reduction in input filter components. Filtering requirements for PWM current-source rectifiers are usually satisfied through the use of low-pass LC input filters. This paper offers a systematic and user-friendly approach to choosing the filter components. Design of LC filters involves the positioning of the resonant frequency to meet the harmonic attenuation requirements (THD), and introducing damping at the resonant frequency to avoid amplification of residual harmonics. The problem is further complicated by considerations related to cost, power factor, voltage attenuation, system efficiency, and filter parameter variation. The systematic approach proposed in this paper focuses on PWM rectifiers, but can easily be extended to other classes of converters. Practical design considerations are detailed and design equations derived. Simulated results are presented to validate the design approach

Digitally controlled switchmode power supply

Abstract: A digitally controlled switchmode power supply by the use of a pulse width modulated (PWM) controlled field effect transistor, switches an inductor between input and output sides to provide a controllable DC output voltage. The digital processor receives and digitizes the input and output voltages and also the current through the associated inductor and derives a PWM control loop signal driving the associated field effect switching device to switch the inductor. The foregoing compensates for nonlinear changes in the value of the inductance due to changes in inductor currents and also avoids resonance at pole points of the LC circuit in the power supply. In addition a change in buck to boost modes may be accomplished automatically depending on input voltage operating conditions.

Chemical sensor using eddy current or resonant electromagnetic circuit detection

Abstract: An instrument is applied to the measurement of chemical species and concentration through the use of a chemically-sensitive coating on the eddy current coil or in the vicinity of the eddy current coil which produces a change in impedance of the probe through induced eddy currents in the coating. An eddy current or resonance circuit chemical detector is a non-contact sensor for measuring chemical species identity and concentration. The chemical detector is resilient and does not require reference electrodes. The chemical sensor is selective as a result of data available on the change in vector impedance of the probe, the change in resonant frequency of the tuned circuit, and the availability of data to construct a vector response from multiple probes having differing chemistries. The probe is used in extreme temperatures.

A Long Pulse Modulator For Reduced Size And Cost

Abstract: A novel modulator has been designed, built and tested for the TESLA test facility. This e{sup +} e{sup {minus}} accelerator concept uses superconducting RF cavities and requires 2ms of RF power at 10 pps. As the final accelerator will require several hundred modulators, a cost effective, space saving and high efficiency design is desired. This modulator used a modest size switched capacitor bank that droops approximately 20% during the pulse. This large droop is compensated for by the use of a resonant LC circuit. The capacitor bank is connected to the high side of a pulse transformer primary using a series GTO switch. The resonant circuit is connected to the low side of the pulse transformer primary. The output pulse is flat to within 1% for 1.9 ms during a 2.3 ms base pulse width. Measured efficiency, from breaker to klystron and including energy lost in the rise time, is approximately 85%.

Electric vehicle battery charger

Abstract: An on-board electric vehicle battery charger includes a surge limiter circuit, a power factor control circuit, and a resonant inverter circuit. The power factor control circuit includes a boost regulator circuit providing a fixed voltage on an output capacitor. The resonant inverter circuit uses a resonance capacitor and the leakage inductance of an output transformer to establish a resonance frequency at least 500 times the AC input power frequency.

Power selection and protection circuit responsive to an input voltage for providing series or parallel connected inverters

Abstract: An inverter power supply for use with various voltage inputs is provided. The inverter power supply generally receives 208 VAC single-phase, 208 VAC three-phase, 230 VAC three-phase, 230 VAC single-phase, 460 VAC single-phase, or 460 VAC three-phase power and provides a DC output current for welding, heating or cutting applications. The power inverter circuit includes a first tank circuit and a second tank circuit which are configured in serial or parallel according to a particular voltage input. Contactors, relays, or semiconductor switches respond to control signals from an AC sense circuit in order to configure the inverter power supply for the appropriate voltage input.

Dynamic range of high-Q OTA-C and enhanced-Q LC RF bandpass filters

Abstract: Dynamic range limitations of high-Q operational transconductance amplifier capacitor (OTA-C) active bandpass filters are reviewed, and expressions are derived relating the dynamic range to the power consumed by the active circuitry. Similar expressions are then derived for the case of inductor/capacitor (LC) filters whose Q have been increased through active, negative resistance circuitry. It is shown that for a fixed power consumption and bandwidth, the enhanced-Q LC filter realizes a factor of Q/sub 0//sup 2/ improvement in dynamic range over the OTA-C filter, where Q/sub 0/ is the quality factor of the passive LC circuit. The reasons for the improvement are discussed and the importance of the improvement is illustrated for active RF bandpass filters employed in radio receiver applications.

Resonant power factor converter

Abstract: The present invention is directed to a novel converter for interposition between an AC power source and a DC load capable of maintaining a substantially unity power factor independent of the impedance of the load. According to the invention, the converter has rectifying circuit to provide DC power to a DC power output circuit from an AC source, circuit for varying the impedance seen by the AC source in the DC output circuit, and circuit responsive to a shift in AC input current away from an in-phase relation with the voltage of the AC source under loading of the DC power output circuit for controlling said impedance varying circuit in a direction to return the AC current towards in-phase relation with the AC voltage. More particularly, according to the preferred form of the invention, the circuit for varying the impedance seen by the AC source in the DC output circuit includes a resonant circuit interposed between the rectifying circuit and the DC output circuit and connected to deliver DC power thereto. The converter includes a control circuit responsive to the DC voltage of the DC output circuit and the phase between the AC voltage and AC current. The control converter also includes a variable impedance responsive to the resonant circuit current for controlling the phase angle between the resonant circuit current and voltage across the resonant circuit.

Gas discharge lamp ballast circuit with compact starting circuit

Abstract: In accordance with the invention, there is provided a ballast circuit for a gas discharge lamp. The circuit comprises means for providing a d.c. bus voltage on a bus conductor with respect to ground. The circuit includes a resonant load circuit incorporating a gas discharge lamp and including first and second resonant impedances whose values determine the operating frequency of the resonant load circuit. Further included is a converter circuit coupled to the resonant load circuit so as to impress a bidirectional voltage thereacross and thereby induce a bidirectional current in the resonant load circuit. The converter comprises first and second switches serially connected between the bus conductor and ground, and having a common node coupled to a first end of the resonant load circuit and through which the bidirectional load current flows. A current-sensing winding senses at least a portion of the current flowing in the resonant load circuit. A feedback arrangement generates a feedback signal in response to current flowing in the current-sensing winding, and regeneratively controls the first and second switches in response to the feedback signal. A starting circuit superimposes a starting current pulse through the current-sensing winding, so as to achieve the regenerative control of the first and second switches.

Development of circuit for measuring both Q variation and resonant frequency shift of quartz crystal microbalance

Abstract: Although frequency shift is often used for QCM (Quartz Crystal Microbalance) measurement, Q of a resonator also varies when viscous loading occurs. However, it is difficult to measure Q variation in real time in comparison with resonant frequency shift. Furthermore, oscillation frequency shift deviates from real resonant one in case of large viscous loading. Here, the authors have developed the circuit based upon motional admittance method for measuring both Q variation and real resonant frequency shift. It was applied to a quartz resonator gas sensor, and its Q variation was measured by this circuit. Moreover, it was compared with a conventional oscillation circuit and the frequency shift of the former was remarkably different from that of the latter in case of large Q variation. When a quartz resonator coated with PEG20M (PolyEthylene Glycol 20M) membrane was exposed to water vapor, its Q decreased from 38700 to 3650 and a frequency shift of the oscillation circuit was only about one sixth of this circuit. >

Arrangement for protecting telecommunications equipment from voltage transients

Abstract: An arrangement for protecting an electrical circuit such as a telephone circuit from a voltage transient comprises a voltage clamp or foldback device (3) arranged to be connected between a current-carrying line (1) and ground (1'), a capacitor (2) in series with it, and an inductance (4) series connected in the line. During normal operation the arrangement acts as an LC filter whose high frequency break-point is determined by the capacitance of the voltage clamp or foldback device (3) and the value of the inductance (4) which are chosen to give a break point of 1 kHz to 10 MHz. However, when the arrangement is subjected to a voltage transient, the voltage clamp or foldback device (3) fires causing the break-point to fall to a value determined by the values of the capacitor (2) and inductance (4). The arrangement may be used, for example, to protect the circuit against a rapid voltage drop caused by the firing of another circuit protection device such as a gas discharge tube 5.

Lamp ballast circuit characterized by a single resonant frequency substantially greater than the fundamental frequency of the inverter output signal

Abstract: A lamp driving circuit having a series inductor and capacitor (L-C) in which the lamp load is connected in parallel with the capacitor. During pre-ignition of the lamp load, the driving signal supplied by a half-bridge oscillator includes a fundamental frequency and higher odd harmonics including a third harmonic of the fundamental frequency. The resonant frequency of the series connected L-C circuit is at least √5 times greater than the fundamental frequency but not equal to the higher odd harmonic frequencies, preferably less than the third harmonic of the driving signal.

Two-frequency impedance matching circuit for an antenna

Abstract: In order to achieve two-way communications at two different frequencies, an impedance matching circuit is coupled to an antenna. The circuit includes a first inductor which is directly coupled to the antenna. The first inductor induces antenna input impedance to be capacitive at a first resonant frequency and induces the antenna input impedance to be inductive at a second resonant frequency. The first resonant frequency is lower than the second resonant frequency. Further, a first capacitor is coupled to the first inductor. By providing the first capacitor, a reactance component at the first resonant frequency is rendered substantially equal to a reactance component at the second resonant frequency. Further, the circuit includes a second inductor and a second capacitor which are coupled between the second means and a feeder. The combination of the second inductor and the second capacitor is provided to adjust impedance, defined by the antenna and the first inductor and the first capacitor, to characteristic impedance of the feeder at the first and second resonant frequencies.

Ballast for instant-start parallel-connected lamps

Abstract: In an electronic ballast, a half-bridge inverter is powered from a DC voltage and provides a nominal 30 kHz square-wave-like inverter output voltage. The inverter output voltage is applied to a series-resonant LC circuit. Parallel-connected across the tank capacitor of this LC circuit are plural series-combinations, each consisting of an instant-start fluorescent lamp series-connected with a current-limiting capacitor. The magnitude of the high-frequency voltage present across the tank capacitor is controlled by controlling the frequency of the inverter output voltage. Prior to lamp ignition, the magnitude of the high-frequency voltage is controlled to a relatively high level, such as to provide for sufficiently forceful lamp ignition. After the lamps have fully ignited, to enhance overall efficiency, the magnitude of the high-frequency voltage is reduced to a relatively low level. This low level is too low to provide for lamp ignition but sufficiently high to permit proper lamp operation. If, subsequently, one of the lamps were to cease operating, the magnitude of the high-frequency voltage would start pulsing at a 120 Hz rate, spending about 90% of the time at the low level and 10% of the time at the high level.

Single layer YBa2Cu3O7 radio frequency SQUID magnetometers with direct‐coupled pickup coils and flip‐chip flux transformers

Abstract: Our aim has been to further improve the magnetic field resolution, BN, of single‐layer rf SQUID magnetometers operating in liquid nitrogen. Following the approaches recently introduced in dc SQUIDs, we tested designs with direct‐coupled pickup coils having an area Ap=0.6 to 0.8 cm2, and a single‐layer thin‐film flip‐chip flux transformer with Ap=16 cm2. In conditions of still suboptimal coupling between SQUID and the 150 MHz tank circuit, we attained BN≂90 fT/Hz1/2 above 3–4 Hz at Ap=0.8 cm2, and BN≂24 fT/Hz1/2 above 0.5 Hz when Ap=16 cm2. For rf SQUID with lumped‐element tank circuit, we project the lower BN limit to be ≤50 fT/Hz1/2 at Ap≤1 cm2. This might be attainable through further coupling optimization, and increase of tank frequency to the highest possible value of ≥500 MHz.

Capacitively-tapped, variable, wideband bandpass filter

Abstract: A wideband bandpass filter has a tank circuit connected between an input and output tapping circuit. The tank circuit contains a variable capacitor and an inductor in parallel. The tank circuit determines a center frequency for the bandpass filter. The input tapping circuit has an input variable impedance, and the output tapping circuit has an output variable impedance. The input and output variable impedances determine the continuously variable bandwidth of the filter.

High voltage power supply circuit

Abstract: There is provided a resonant circuit incorporating at least a coil L1 therein and a switching circuit for oscillation is connected to the resonant circuit and voltage doubler rectifier circuits 31 and 32 including capacitors C11, C12, C21 and C22 and diodes D11, D12, D21 and D22 are also connected to the resonant circuit. When the switching circuit for oscillation is turned on and off, the resonant voltage V L1 is generated in the resonant circuit and rectified with a voltage doubler amplitude by the voltage doubler rectifier circuits 31 and 32. A switching circuit for output changing over is connected to zero voltage terminals of the diodes D11 and D21 in the voltage doubler rectifier circuits 31 and 32. When the switching circuit for output changing over is turned on and off, an output voltage is selectively generated at output terminals OUT1 and OUT2.

Improving the power consumption characteristics of piezoelectric actuators

Abstract: A study of the application of power factor correction methods to piezoceramic actua tors is performed. The power factor is corrected by adding an inductor both parallel to and in series with the piezoceramic actuator. The actuator consists of two lead zirconate titanate (PZT) patches mounted symmetrically to a cantilever beam. The inductance values were chosen such that each inductor-capacitor (LC) circuit was at resonance at the second natural frequency of the beam. Imple menting the parallel LC circuit reduced the current consumption of the piezoceramic actuator by 75 % when compared to the current consumption of the actuator used without an inductor. Imple menting the series LC circuit produced a 300 % increase in the voltage applied to the actuator com pared to the case when no inductor was used. In both cases, employing power factor correction methods corrected the power factor to near unity and reduced the apparent power by 12 dB. A theo retical model of each circuit was developed, and the analytica...

Method for limiting the frequency of a voltage-controlled oscillator in a control circuit of a resonant converter switched-mode power supply, and control circuit for a resonant converter switched-mode power supply

Abstract: A method for limiting the frequency of a voltage-controlled oscillator in a control circuit of a resonant converter switched-mode power supply includes adjusting a delay time of a delay element disposed in a feedback branch of the voltage-controlled oscillator with a signal indicating a transition from negative to positive values of a current through an oscillating circuit of the switched-mode power supply. A resonant converter switched-mode power supply has an output voltage and an oscillating circuit with a current. A control circuit for the resonant converter switched-mode power supply includes a control amplifier being acted upon by the output voltage and by a reference voltage. A voltage-controlled oscillator is connected to and triggered by the control amplifier. A comparator detects a transition from positive to negative values of the current in the oscillating circuit. A flip-flop has a setting input being connected to and triggered by the voltage-controlled oscillator and has a reset input being connected to and triggered by the comparator. A delay element has a variable delay time and is triggered by a signal indicating a transition from negative to positive values of the current in the oscillating circuit.

Classical analogy to quantum mechanical level repulsion

Abstract: The frequency repulsion in coupled harmonic oscillators can be treated as a classical analogy to the quantum mechanical level repulsion. As an example the inductively coupled LC circuit will be discussed.

Frequency controlled resonant inverter

Abstract: A high-frequency high-voltage generator is provided for x-ray technology that automatically adapts to all load instances and to the coupling network. The inverter is driven dependent on the zero-axis crossing in a series resonant circuit. The capacitor of this series resonant circuit is bridged by an inductance, forming a parallel branch and the control signal for the inverter is acquired from the time delay between the zero-axis crossings in the series resonant circuit in the parallel branch.

Improved capacitance measurement by means of resonance locking

Abstract: We describe a new LC method of capacitance measurement. The method consists of a synthesis of LC resonance and LC oscillator methods. The LC tank circuit is driven by a voltage-controlled oscillator (vco) and is included in an analogue phase-locked loop; the loop is designed to lock with no phase difference between current flow and driving voltage in the tank circuit. The system effectively tracks the resonance peak as the capacitance changes, thus allowing automatic measurement of capacitance by monitoring the vco input voltage or output frequency. The measurement bandwidth is dependent only on phase detector response, and can extend to the range of several MHz. The accuracy of this 'resonance locked loop' is equivalent to that of conventional systems and the dynamic range is considerably improved; a system with measured accuracy of 11 aF and bandwidth of 100 kHz has been constructed, and has been used to measure high-frequency submicrometre movements of piezoelectric actuators.

A low-noise CMOS preamplifier operating at 4.2 K

Abstract: A low-noise CMOS readout preamplifier operating at liquid helium temperatures is described, In conjunction with magnetic field sensors applying SQUIDs (superconducting quantum interference devices) the preamplifier can be used to measure biomagnetic fields of human brain and heart noninvasively. The input of the folded cascode amplifier can be attached directly to a low impedance SQUID output. This way the commonly used discrete LC tank resonator circuit for impedance matching can be omitted. An equivalent noise voltage density of 0.3 nV//spl radic/Hz at 500 kHz has been measured. Despite the occurrence of the kink effect and other abnormalities in MOS transistor characteristics at 4.2 K, during the tests no abnormal operation has been observed. Such a preamplifier circuit is essential in simplifying the expensive shielding currently used in biomagnetic diagnosis systems. >

Oscillator circuit generating oscillation signal responsive to one of resonant element and external clock signal

Abstract: Disclosed herein is an oscillator circuit generating an oscillation signal in response to a resonant element in a first mode and to an external clock signal in a second mode. This oscillator circuit comprises a tri-state inverter circuit and a transfer circuit between the input and output nodes of the tri-state inverter circuit, and the output node of the tri-state inverter circuit is brought into a high impedance condition when an external clock signal is used and into an active state when the resonant element is employed.

Local oscillator frequency multiplier and mixing circuit comprising a squaring circuit

Abstract: In an electronic circuit operable as a local oscillator frequency multiplier and mixing circuit, a squaring circuit is operated in response to a local oscillator frequency signal of a local oscillator frequency and is connected to a constant current circuit or a transistor circuit responsive to an input high frequency signal of a high frequency so as to obtain a frequency equal to a sum of an integral multiple or double of the local oscillator frequency and the high frequency and a difference between the integral multiple of the local oscillator frequency and the high frequency. The squaring circuit may be formed by four transistors connected in pairs while the transistor circuit may be structured by a cross-connected, emitter-coupled transistor circuit, an unbalanced emitter-coupled transistor circuit, or a pair of transistors. A control signal, such as an AGC control signal, may be given to the transistor circuit or the constant current circuit.

Self-generating resonant power supply and method of producing power for transistor switching circuit

Abstract: A resonant power supply for use in conjunction with power transistor switching circuits. In one embodiment, a series-connected LC resonant circuit is coupled to the high voltage pulsed output of the power transistors and designed to draw power from the pulsed output and deliver the same to a low voltage output capacitor at which a low voltage output is provided. The low voltage output is regulated by a zener diode connected in parallel with the output capacitor. A starting resistor of a relatively high value, typically in the Megohm range, supplies initial charge to the output capacitor to permit the first switching event to occur so that the resonant power supply can begin to provide power. The resonant frequency of the LC circuit is significantly higher than the maximum switching frequency of the power transistors, enabling the resonating high frequency wave forms of the LC circuit to supply repeated charge bursts to the output capacitor.