Showing papers on "Output impedance published in 1970"

Simulation of AC System Impedance in HVDC System Studies

Abstract: In some studies of HVDC system design, ac system impedance is represented by its inductance at power frequency. However, for several studies better simulation of the impedance- frequency characteristic (from power frequency to a few kilohertz) of the ac system is important. This paper presents a simple approach to calculating an approximate equivalent network consisting of parallel LCR branches and having an impedance-frequency characteristic similar to that given for the ac system. For given typical ac system impedance diagrams (usually obtained from ac system models and simulators), simulation of an ac system by corresponding equivalent networks during studies of certain HVDC problems would provide a more accurate means of designing HVDC systems.

Microstrip impedance matching circuit with harmonic terminations

Abstract: A microstrip impedance matching circuit has fixed harmonic terminations in the form of a pair of open-circuited stubs, each having a length equal to a quarter wavelength of a different harmonic frequency, connected to the main transmission line to cause the impedance at the harmonic frequencies to be made constant irrespective of the nature of the load impedance at the harmonic frequencies.

Fault current limiter using superconductive element

Abstract: A superconductive impedance element is connected in parallel with a conventional impedance element and is switched from essentially zero impedance to a high impedance during switching operation, thereby to connect the conventional impedance in the circuit to limit the current in the circuit. The impedances switched into the circuit are inductively associated with the superconductive element. A pilot super-conductive element is disclosed for the high accuracy switching of a main superconductive element.

Generalized theory of static power frequency changers

Abstract: The thesis is concerned with static frequency changers, using solid-state switching devices, capable of directly (i.e. without an intermediate dc link) converting polyphase ac power of a given frequency to single or polyphase power of a chosen frequency. The thesis consists of two parts. The first part, comprising five chapters, is devoted to the study of ideal frequency changers operated from ac Sources having zero internal impedance. The second part, comprising two chapters, considers sources with finite internal impedances . Chapter 1 introduces the basic concepts of static frequency conversion, outlines the basic mathematical models representing static frequency changers and defines the output and input performance indicators. Chapter 2 presents a detailed investigation of that class of three-pulse frequency changers which will be studied in the thesis. A large portion of the chapter is devoted to the study of output waveform generation. The mathematical tools of the investigation, existence matrices and modulating functions, are introduced and defined. Analytical expressions for output waveforms corresponding to various practical modulating functions are derived and the related performance indicators are computed. Assuming a given desired output performance, criteria for an optimal modulating function are established. It is proved that only one system can generate an output waveform conforming to the postulated prerequisites. This system is termed the "Unrestricted" Frequency Changer. Expressions for the input current waves are also derived in this chapter and the corresponding input performance indicators are determined . The concept of a new frequency changer having the unique property of providing unity input power factor, regardless of the load, is introduced. This system is termed the "Unity Power Factor" Frequency Changer. In Chapter 3 the previous results are extended to systems having pulse numbers which are integral multiples of three. Chapter 4 is devoted to the study of output voltage control. Three basic methods are analysed and detailed quantitative data for output voltage and input current waves, and the related performance indicators, are presented in graphical form. In Chapter 5 special aspects of static frequency changing are investigated. It is shown that the input displacement factor is variable. The concept of the "Controlled Displacement Factor" Frequency Changer is introduced It is proven that the naturally commutated cycloconvertor is theoretically equivalent to a particular "Controlled Displacement Factor" Frequency Changer. Chapter 6 presents a detailed analysis of the "Unrestricted" Frequency Changer, operated from an ac source with finite internal impedance. The basic conditions are defined and an outline is given of the techniques of symmetrical components used for the analysis. The input current, input terminal voltage and output voltage waveforms are expressed in terms of the input terminal impedance and the positive, negative and zero sequence components of the output currents. The equivalent sequence impedances and the output impedance matrix are derived . The output voltage unbalance is computed under various conditions and presented in graphical form. The relationships between the amplitudes of the unwanted components in the output waveform and the resonant frequency of the input terminal circuit are also graphically presented. The results obtained are verified by computer simulations. In Chapter 7 a similar analysis of the "Unity Power Factor" Frequency Changer is carried out . The computed data are also graphically presented. Again, the results are verified by appropriate computer simulations.

Broadband power amplifier with multiple stages connected by balun transformers

Abstract: Broadband power amplifier including a single ended stage coupled to a plurality of stages by use of balun transformers. Broadband operation is achieved by use of balun transformer having interwinding capacitance which forms a shunt element, and high power is provided by use of a plurality of stages contributing to the load. A first single ended stage may be coupled by a one-toone balun to a pair of push-pull stages, which in turn may be coupled through balun transformer to two pair of push-pull transistor stages. Alternately the single ended stage can be connected by two balun transformers to two pair of push-pull stages, or may be connected by three or more balun transformers to a like number of single ended stages. The outputs can be combined by use of a plurality of balun transformers coupled in series and each providing impedance step-up or by use of transformers, to thereby provide the desired output impedance of the amplifier.

Distortion performance of single-balanced diode modulators

Abstract: The techniques of switching-function analysis are used to extend previous work on the intermodultion and crossmodulation-distortion properties of the ring modulator to include the single-balanced series and shunt configurations. The influence of the local-oscillator source impedance is considered, and excellent agreement is demonstrated between the predicted 3rd-order intermodulation performance of two single-balanced circuits and results obtained for experimental modulators using Schottky-barrier diodes.

Electronic Circuit Analysis and Design by Driving-Point Impedance Techniques

Abstract: By using driving point impedance (DPI) techniques a systematic approach to the analysis of electronic circuits can be developed which helps the engineer gain insight into circuit action. The answers, representing the circuit's currents, voltages, gains, and driving-point impedances, are written down by inspection of the original circuit diagram without resorting to equivalent circuits of flow graphs. The resulting answers are in a most simple form which can be easily interpreted by inexperienced persons since the relative magnitude of each factor is known. Thus, the student rapidly obtains a "feel" for electronic circuits. The method can also be used to complement a computer-aided circuit design and analysis. A tutorial treatment of the fundamental methods is presented and two examples are given. The simple example, which is complex by ordinary standards, has five input signals and three active elements; yet the output signal voltage is written out by inspection with each step explained. The second example, a two-stage transistor feedback amplifier, is used to demonstrate how the fundamental concepts are applied to complex feedback circuits. The gain, input impedance, and output impedance of the feedback amplifier are found and approximations are used to compare the answers to ordinary solutions given for such amplifiers. The answers obtained by DPI analysis methods are also compared to equivalent answers found by node analysis.

Low thermal impedance field effect transistor

Abstract: This disclosure is directed to a Schottky Barrier field effect transistor (FET) having a low thermal impedance and to a process of producing it.

Electric arc furnace control

Abstract: A control system for electric arc furnaces incorporating proportional plus integral control characteristics. The system, which is designed to maintain constant arc impedance, develops an output voltage proportional to input impedance error and then adds a second voltage which increases with time at a rate proportional to the impedance error magnitude. When the combined voltages for a furnace electrode exceed a preset level, the drive motor for that electrode is actuated to move the electrode upwardly or downwardly to maintain the desired arc impedance. In this way, the system will respond quickly to large impedance errors, is insensitive to short term impedance fluctuations, and at the same time has a very high sensitivity to continuing small errors.

Ultrahigh-speed microchannel photomultiplier

Abstract: Use of a microchannel-water electron multiplier makes possible a new, compact photomultiplier with time-resolution capabilities better than can be obtained from classical photomultipliers using cascaded dynode structures. The small thickness of the wafer, together with proximity focusing in the electron optics of the input and output of the wafer, results in reduction of the electron transit-time to about 1 ns. The electron transit-time spread is about 10-10seconds. Short pulses from a mode-locked laser were used to measure the impulse response of the photomultiplier. The experimental value of <500 ps (full width at half maximum) is in good agreement with the predictions of a computer analysis. Other salient characteristics of the new tube are: S 20 photocathode diameter of 11 mm; electron gain of about 105; dark current <10-16amperes (referred to the cathode); and 50-ohm output impedance.

Temperature compensated bias circuit

Abstract: Disclosed is a monolithic voltage regulator having a high current capability, a constant low output impedance from DC to several hundred kilocycles, and a high ripple reduction factor. The regulator has excellent transient response; it provides a wide range of regulated output voltage and has a low temperature drift. The voltage regulator includes a voltage standard or bias source, an input differential amplifier stage having a pair of transistors coupled to a current sink (a current source passing current to ground), and one of the transistors in the pair is connected through a current gain stage to an output terminal. A DC reference shifting circuit is connected to the input of one transistor in the pair and provides a reference voltage to the differential amplifier stage which has been translated to provide the required voltage level at the output terminal. The output terminal is connected directly to the input of the other transistor in the pair in order to achieve a unity feed back factor to provide excellent constant loop performance independent of the output voltage. The direct coupled feedback connection eliminates any undesirable gain loss and phase shifting due to resistance in the input circuits of the differentially coupled transistor pair.

A High Impedance ac Hall Effect Apparatus

Abstract: Measurement of the Hall effect in oxide crystals of high resistivity has been made possible by the use of a very high impedance ac apparatus. The shunt capacitance of leads degrades the input impedance in such a system. However, this effect is minimized by driving the shield of the coaxial line from a low impedance source with a voltage of the same amplitude and phase as that of the input signal. The frequency is chosen sufficiently high to minimize the effects of space charge.

Inductance and capacitance reactance measuring instrument having minimal inclusion of stray reactances

Abstract: An impedance-measuring electrical circuit modulates a high frequency current alternately with the unknown impedance being measured and with a reference impedance. A detector synchronized with the alternation of the modulation detects the resultant modulated current to produce a measure of the resistive and reactive components of the unknown impedance element relative to the corresponding components of the known reference impedance element. The modulating portion of the circuit is constructed with minimal stray reactances that effect the modulated output current, but the other portions of the circuit are essentially free of this restriction.

Analysis of Synchronous Machines under Unbalanced Operation

Abstract: Considering only the fundamental frequency components of currents and voltages, an idealized synchronous machine under any unbalanced load conditions can be represented in phase coordinates, by the sum of a constant impedance matrix and an impedance matrix whose elements are functions of current phase angles. A general method of solving for the unknown current phase angles and hence the total impedance matrix is given when the external impedances are known. The results are shown to be consistent with 1) two-reaction theory for the case of balanced steady- state loads, and 2) symmetrical-component theory using sequence- impedance representation under the assumption of zero resistances in all circuits. Numerical comparison shows that although the current magnitudes can be calculated by the approximate sequence- impedance representation quite accurately, current phase angles could differ, in certain cases, up to about 10°.

A One-Watt CW High-Efficiency X-Band Avalanche-Diode Amplifier (Correspondence)

Abstract: An X-band avalanche-diode amplifier circuit is described which provides accurate and independent in-band impedance control (R and +jx) and orthogonal second-harmonic reactance control. Low-level gains of 13 dB with 500 MHz of bandwidth have been achieved using this circuit. Power outputs of 1 watt CW with 5 dB of gain and 14.7-percent generation efficiency have also been realized by carefully controlling the in-band and second-harmonic load impedance.

Circuit arrangement for correcting the deflection of at least one electron beam in a television picture tube by means of a transductor

Abstract: A circuit arrangement for raster correction in a television picture tube by means of a transductor whose power winding is connected in parallel with at least a portion of the line deflection coils, the line deflection generator having a low internal impedance. In order to increase this impedance a mainly inductive impedance is connected in series with the generator. In a picture tube employing at least two electron beams the series impedance may include the convergence circuit. As a result the convergence in the corners of the picture screen is also improved. The linearity control circuit may likewise form part of the series impedance.

Accurate (2 parts in 107) inductive voltage divider for 20-200 Hz

Abstract: The paper gives the design approach followed for, and the design details of, a 3-decade inductive voltage divider which will realise any 3-digit output/input ratio between 0.001:1 and 0.999:1 to an accuracy of within 2 parts in 107, or better, over the frequency range 20–200Hz. The measurement technique used to establish the errors of the separate decades is described, and it is shown how these can be combined to give the overall error for any ratio setting. It is also shown how the overall output impedance of a multidecade divider can be calculated for any ratio setting from the knowledge of the resistance and leakage inductance per section of the separate decades. A method of compensating for the errors produced by internal admittance loading is also given.

THE CARDlAC ELECTRICAL IMPEDANCE PULSE

Abstract: It is often assumed that individuals interested in bioelectrical impedance are familiar with electrical engineering. In the case of physiologists, this is often a poor assumption. Yet, they are ultimately responsible for the validation of new measuring techniques-devising ultimate biological tests for new methodology. It is important, then, to provide technical information in a manner comprehensible to physiologists. At the same time, we are obliged to present design concepts for the research engineers and biophysicists who develop the equipment. For the sake of brevity, a few comers have been cut, but no excuse could be made if we were not accurate at the same time. The concept of impedance is too complex to explain here. Let it be sufficient to say that from an electrical standpoint, a body can be described by a combination of resistors, inductors, and capacitors. The part of impedance contributed by resistors is called resistive impedance and the part contributed by inductors and capacitors is called reactive impedance. Fortunately, the body does not exhibit impedance qualities related to inductors at impedance-measuring frequencies, so for our work the terms capacitive and reactive impedance are equivalent. The search for an atraumatic method to measure cardiac stroke volume goes back to Max Cremer, who in 1907 recorded the motion of a beating frog heart by electrical capacitance changes between two condenser plates.' This observation, that the beating heart can be monitored without touching a sensor, was applied to man by Atzler and Lehmann 25 years later.2 They noted that capacitance fell with the emptying and rose with the filling phase of the heart, as timed by the electrocardiogram. This work was never followed up with quantitative studies. It may have been that such a technique was too sensitive to chest-wall motion. However, electrical impedance techniques that utilize direct electrode contacts replaced the earlier methods. In clinical investigations, total or resistive impedance changes were correlated with pressure tracings, heart sounds, and cardiac output.3-22 Only two of those investigations correlated the direct measurements of resistive impedance over the chest with cardiac output determinations by the green-dye dilution method. In a study of 10 young men, the employed electrical impedance technique yielded stroke volume values 1.19 higher than obtained by the dye dilution method, while there was a 20% standard deviation from the best fit line.15J6 In a recent report, the correlation coefficient between the two methods was 0.68 in 13 normal subjects and 0.26 in 24 patients with heart disease.22 The electrical impedance measured between electrodes placed on the living body is of a complex nature, since the resistive and reactive components change with frequency and with the size, shape, and orientation of electrodes, as well as with the anatomy of the body. It may be that the inexpensive and improved measuring bridges that are generally available have encouraged resistive impedance measurements. Our experience with resistive and total impedance

The Measurement of a High Impedance Source Having Shunt Capacitance

Abstract: High impedance source with shunt capacitance, discussing periodic output measurement using operational amplifier

Frequency to voltage converter circuit

Abstract: An improved frequency to voltage conversion circuit is described. The unimproved basic circuit comprises a transistor, two capacitors, a resistor, and a diode. The improved circuit includes transistor means connected to the base of the transistor in the basic circuit to provide temperature compensation and to reduce or eliminate transient conditions. Additional transistors, diodes, and resistors are provided to effect protection against supply voltage transients, to provide additional temperature compensation where necessary, to assure the presence of an adequate signal to operate the frequency to voltage converter, and to provide the overall circuit with a high input impedance and a low output impedance.

Proportional only process controller

Abstract: Automatic process controller circuitry for producing an output current which is proportional to a process variable input signal. A differential operational amplifier is connected to receive set point and process variable input signals and provides an output voltage which is proportional to the difference between these two signals. An adjustable proportional band series output impedance is connected between the output of the operational amplifier and a controller circuit output node, and this series impedance converts the output voltage of said amplifier to a current. The voltage developed across this variable series output impedance is differentially fed back via positive and negative feedback loops to the inverting and noninverting inputs of the operational amplifier, and such feedback connection enables the proportional current flowing through the variable series output impedance to be made constant and independent of the output voltage of the operational amplifier. Also, since the load current flowing in the transducer driven by the above controller circuitry can be made equal or proportional to this proportional current, said load current can be adjusted to a value wholly independent of the internal resistance of the driven transducer.

Circuit for switching between two unidirectional voltages

Abstract: An apparatus for switching between high and low dc beam acceleration voltages in a dichromatic cathode-ray tube. The acceleration voltage is applied to the screen of the tube which because it is conductive has a capacitance with respect to ground. The apparatus comprises a switchable voltage generator for switching between the high and low voltages, a charging path for charging the capacitance of the screen of the cathode ray tube, and a discharging path for discharging the capacitance of the screen. The apparatus also includes a control circuit for controlling conduction through said charging and discharging paths. The provision of the charging and discharging paths enables rapid switching of the beam acceleration voltage and thereby the color of the tube with the disadvantages of a voltage generator with a low output impedance.

Coupled inductance impedance measuring circuit with increased sensitivity and frequency independence

Abstract: An impedance measuring circuit having two closely coupled inductances conducting alternating electric excitation from a grounded source through measuring and balancing impedance branches respectively to ground Peak detection circuitry referenced to ground in the impedance measuring circuit gives an indication of the difference in the voltage across the measuring and balancing impedances Where measuring and balancing impedances are capacitive reactances and at source frequencies above resonance of the inductance-capacitance circuit, substantial frequency independence is achieved

Matrix switch with improved transmission characteristics

Abstract: A matrix switch circuit for switching a plurality of output buses to an input bus having the impedance of the input bus substantially lower than the impedance of any one of the output buses, having the output impedance of the line circuit matched to the input bus and with the input bus terminated in its characteristic impedance, thereby reducing the voltage-standingwave ratio, and having means in the input line for reducing the effect of capacitance loading on the input bus resulting from opening or closing of switches electrically connecting the first bus to each of the second buses.

Agc impedance converter and voltage level shifter for high impedance source

Abstract: A signal receiver of a type including an AGC network providing an AGC signal and also of a type employing a varactor tuner is provided with an AGC converter network to convert the AGC output signal to a level and source impedance suitable for use with the tuner.

Feedback amplifier with bridge-stabilized output impedance

Abstract: An impedance-matching arrangement comprising an operational amplifier with a bridge-stabilized output impedance transfers power between circuits having a common ground. The resulting stable gain and impedance extend over a wide frequency range and minimize impedance-matching power losses. The output impedance of the amplifier is modified to incorporate a Wheatstone bridge, three of whose arms are resistive and the fourth is the output impedance of the amplifier. One bridge diagonal feeds the grounded load circuit and the other supplies symmetrical feedback currents to the respective inputs of the amplifier.

Apparatus for particle classification and analysis

Abstract: 1,185,898. Particle counting apparatus. COULTER ELECTRONICS Ltd. (W.H. Coulter). Sept.28, 1967, No.44138/67. Heading G1N. In a "Coulter counter" it has been found that the impedance of different kinds of particle varies with the supply frequency, especially at R.F. The Specification describes at length how this may be used to derive "signatures" for different kinds of particles using pulse counting and phase/ frequency measuring techniques. In a simple case the "gap" may be energized with a single R.F. and measurements made of either the resistive and reactive components using a phase sensitive detector, or the frequency modulation and amplitude modulation components of the signal. Pulses, (due to the passage of a particle), for each component of the signal having an amplitude within predetermined limits may be counted. In a more sophisticated arrangement three frequencies are applied simultaneously e.g. a D.C. or low frequency and two different R. F. S. The signal is analyzed into the amplitude of the D. C. and the quadrature components of each R. F. to provide a detailed signature. Compensation for source impedance may be provided by tuning the sensing zone to anti-resonance at the supply frequency.

Bandpass filters using Wien's bridge

Abstract: Bandpass transfer functions are obtained from an active circuit using Wien's bridge and a single operational amplifier. The Q factor is controllable by a single resistance independently of the resonant frequency, and one version of the circuit has a low output impedance.

Monolithic coupled crystal resonator filter having cross impedance adjusting means

Abstract: A monolithic coupled resonator bandpass filter having pairs of input and output electrodes mounted on a crystal resonator such as quartz. A generator is coupled to the high potential side of the input electrodes via an adjustable input impedance. The high potential side of the output electrodes is coupled to a load via an adjustable output impedance. The low potential sides of the input and output electrodes are coupled to ground via adjustable base impedances. The frequency transfer response of the filter may be adjusted by proper adjustment of the various adjustable impedances. Proper adjustment of the base impedances can adjust the symmetry and ripple of the transfer response curve.