Showing papers on "Output impedance published in 1972"

Regulated dc to dc converter with regulated current source driving a nonregulated inverter

Abstract: A regulated DC to DC converter comprises a switching-type regulated current source driving a non-regulated bridge-type inverter. The output signal of the converter is regulated by pulse width modulating the switching device in the switching regulator. The output impedance of the current source is inductive. This inductive impedance, which comprises the free-wheeling or flyback inductor of the switching regulator, operates as the principal filter inductor of the converter. This regulator-inverter combination advantageously simplifies the switching control of the inverter switching devices and reduces the switching losses therein. It eliminates the switching control problems which normally occur due to switchthrough phenomena and the saturation of the inverter transformer.

Some Characteristics of a 600 kV Flash X-ray Tube

Abstract: The performance of a continuously pumped flash X-ray tube has been studied in the voltage range 250-600 kV Dose, pulse length, beam quality, source size and spatial distribution of the radiation were measured It is shown that the output intensity is maximized if the tube impedance is 23 times the internal impedance of the pulser

Insulated electrocardiogram electrodes.

Abstract: An integrated system consisting of an insulated electrode and an impedance transformer has been fabricated, which can be used for the acquisition of electrocardiographic data. The electrode itself consists of a thin layer of dielectric material which has been deposited onto a silicon substrate. The impedance transformer is a Fairchild μA 740 operational amplifier used in the unity-gain configuration. The input impedance of the impedance transformer is at least 100 MΩ and its output impedance is about 5 Ω. Both electrode and impedance transformer are contained in a plastic housing which is identical to that used with the NASA Apollo-type electrode. The lower cutoff frequency of the electrode system is between 0·01 and 1·0 Hz, depending on the dielectric used and its thickness. Clinical-quality electrocardiograms have been obtained with these electrodes.

Electrically variable impedance utilizing the base emitter junctions of transistors

Abstract: A variable impedance utilizing the diode characteristic of the base-emitter junction of a transistor. The voltage across the base-emitter stays constant so that a control voltage used to change the d.c. emitter current changes the impedance of the junction. When such a diode connected transistor shunts a signal line it attenuates the signal on the signal line. In order to reduce non-linearities in impedance caused by application of the signal, a diode connected transistor has another transistor connected thereto in a differential circuit so that an increase in the emitter current (decrease in impedance) of one due to application of the signal causes a corresponding decrease in emitter current (and increase in impedance) of the other so that the non-linearities cancel out. In another embodiment the two transistors are placed in the feedback loop of a differential amplifier with the impedance of the two transistors serving as the load for the differential amplifier, which further reduces nonlinearities. Several such transistor circuits may be connected in series to provide more junctions and hence a wider range of variable impedance.

Discontinuities in Symmetric Striplines Due to Impedance Steps and Their Compensations

Abstract: The theoretically known magnitude of the series lumped reactance, as a function of impedance step ratio, resulting from an impedance step discontinuity in symmetric stripline is confirmed, and an alternative expression for the inductance is given. A reduction of this reactance has been achieved by splitting the narrower strip at the impedance step junction into a multistrip configuration, while retaining the total characteristic impedance value. A way of compensating the effect of the reactance on the pass-band characteristics of quarter-wave impedance transformers and filters is developed. This is achieved by the introduction of a lumped series capacitance at the impedance step discontinuity.

Automatic noise reduction system

Abstract: An automatic noise reduction system has a signal amplifier, a resistor as a first impedance circuit and a second impedance circuit which comprises resistors, capacitor and a variable resistance element. The frequency response of the second impedance circuit changes according to the resistance value of the variable resistance element and that resistance value is changed by a control circuit. In recording, the resistor constituting the first impedance circuit is connected to the input side of the signal amplifier and the second impedance circuit is connected to the negative feedback loop of the signal amplifier, and the control means provides a D.C. voltage in response to the input signal, so that the signal to be recorded is emphasized. In reproducing, the connection is reversed and the control means provides a D.C. voltage in response to the output signal, so that the reproduced signal is modified with characteristics complementary to the emphasized characteristics and provided with the same wave form as that of the original signal with reduced record medium noises.

Electrical measuring apparatus employing a plurality of condition responsive devices

Abstract: This electrical measuring apparatus includes a plurality of impedance devices such as capacitors for measuring the liquid level in an aircraft fuel tank. The impedance devices are supplied with electrical energy at high frequency (e.g., 10KHz) by a remote power supply. One terminal of each of the impedance devices is connected continuously by means of a shielded conductor to the high voltage output terminal of the power supply. The other terminal of each impedance device is at or near ground potential due to its connection (by an unshielded wire) to an input terminal of an operational amplifier. By shielding the high voltage power supply line, the high frequency signal appears in the same phase at all of the impedance devices. The induction of currents in external impedance devices due to stray electrostatic and electromagnetic fields is prevented by the shielding; and, errors arising from unequal phase shifts in the high frequency lines and from stray fields are thereby avoided.

Circuit using dynamic high impedance load

Abstract: An amplifier comprising a series of field effect transistors is connected to a dynamic high impedance load. The output of the amplifier preferably is taken from the last stage of that load. The dynamic high impedance load may be a constant current source consisting of at least three field effect transistors.

Gain controlled amplifier for integrated circuit applications

Abstract: A gain controlled amplifier circuit in which the amplifying element, such as a transistor, has its emitter-collector circuit connected to a gain control circuit which supplies a constant operating current and changes its AC impedance in accordance with an AGC signal. The gain control circuit includes a first branch having an impedance which varies with the externally applied AGC signal and a second branch having an impedance which varies with the current flow therethrough and which is connected to ground through an AC bypass. These two branches are connected in parallel to a constant current source so that the impedance of the first branch controls the current flow in the second branch and thereby its impedance.

Feedback amplifier circuit

Abstract: A feedback amplifier circuit comprises a high gain amplifier and a negative feedback path including a current source means, e.g. a high output impedance isolation device, for providing feedback current to the amplifier input. In a differential amplifier embodiment, a pair of high output impedance feedback isolation devices provide current to an input impedance means connected between the circuit input terminals. The circuit is largely independent of input voltage level and impedance, and as a result, the aforementioned input impedance means can be varied for changing gain while maintaining a high degree of common mode rejection.

Coaxial cable loop antenna with unidirectional current amplifier opposite the output

Abstract: Disclosed is an antenna system having a second loop disposed immediately adjacent and coupled to the primary field detecting or transmitting loop for neutralizing inductive reactance through the primary loop. Unidirectional current means which is disclosed as a low input impedance, high output impedance, unity gain current amplifier couples the primary and secondary loop for preventing significant current flow through the secondary loop except ina direction opposite that of the current flow through the primary loop, the primary and secondary loop, respectively, being the shield and center conductor of a coaxial cable, the center conductor coupled to signal utilizaton or transmitting means for processing or generating electromagnetic signal waves.

Tristate pulse generator for producing consecutive pair of pulses

Abstract: An improved manually-triggerable pulse generator has a highimpedance output in one operating state and alternate high-andlow-level logic states of low output impedance in remaining operating states for operation as a source of test pulses in digital circuitry.

Improvements in or relating to apparatus for determining the condition of food

Abstract: 1287190 Measuring condition of food NATIONAL RESEARCH DEVELOPMENT CORP 19 April 1971 [25 March 1970] 14394/70 Heading G1N In an arrangement for determining the extent of spoilage in food e.g. fish by measuring the phase angle of an A.C. current flowing through part of the sample as described in Patent 1262749 the effect of the impedance of the measuring electrodes 3a, 3b is compensated for. The A.C. is applied to the sample 1 by electrodes 2a, 2b and the voltage developed between measuring electrodes 3a, 3b after squaring at 11 is compared in phase detector 15 with the A. C. voltage developed across F. E. T. 5. The drain source impedance of F.E.T. 5 is varied so that its impedance is equal to the sum of the electrode 3a, 3b impedances and the sample whereby the amplitudes of the voltages applied to squaring circuits 11, 13 are substantially the same. Control circuit 14 causes a variable bias to be applied to gate 8 of F.E.T. 5 to maintain these amplitudes the same. Thermistor 21 in contact with sample 1 causes the gain in circuit 15 to change to take into account temperature changes.

AC impedance of silicon solar cells.

Abstract: The equivalent source impedance of a solar array is an important parameter in the design and analysis of solar array power conditioning equipment. Laboratory impedance tests have been performed on individual silicon solar cells and the test results have been correlated with P-N junction theory as developed by Shockley. The impedance has been broken into resistive and reactive components. The impedance has been expressed as a function of DC operating point and frequency. A practical application of the individual cell characteristics is presented in a solar array simulator design.

Simulation of Pt-n-p+ silicon punchthrough device

Abstract: The small-signal impedance of a Pt-n-p+ device has been computed using a model which describes in detail the physical mechanisms in the depleted n region. The small-signal negative resistance is shown to be both frequency- and temperature-dependent at a given bias-current density.

A low impedance field effect transistor

Abstract: A junction field effect transistor having non-saturation characteristics like a vacuum tride has been successfully developed. Its output impedance can be decreased to 8 ohms so that it will serve in audio applications or as an impedance transformer. The geometrical structure of this FET is analogous to that of a triode tube and is based on the idea of controlling the resistance between drain and source by a potential applied to a grid-like gate structure. Design considerations that avoid saturation of the drain current will be discussed.

Pulse generator for delivering rectangular pulses having fast rise and fall times

Abstract: A steady voltage applied to a voltage sensitive device such as a Kerr cell or a Pockels cell is caused to be interrupted by a sharp, brief, square pulse, during which the applied voltage is zero, by means of a single d.c. voltage generator operating through a series impedance into two transmission lines of substantially the same characteristic impedance. One line is connected between the generator (i.e., its series impedance) and the load, which is a high impedance, and the other line has one end connected to the generator (i.e., its series impedance) over a switch and its other end connected to a high impedance which acts as an effective open circuit. Closing the switch produces a series of substantially zero voltage intervals across the load, the period being determined by the combined length of the lines and the duty cycle by their relative length, but after the first few pulses the dissipation in the transmission lines and their terminations prevents the voltage from dropping all the way to zero, but for laser triggering only the first pulse is normally needed and the subsequent ones cause no disturbance.

Circuit for controlling the direction of current flow in a load impedance

Abstract: One terminal of a load impedance is connected to the collectors of two transistors of opposite conductivity type. Their emitters are connected to positive and negative power supply terminals to receive direct current, and the emitter-collector circuits of the two transistors are in current-carrying polarity with respect to the direct current terminals. The bases of the two transistors are connected to the arm of a single-pole-double-throw switch. The fixed contacts of the switch are connected to the positive and negative power supply terminals so that in one position the base of one transistor is biased to conductivity to allow current to flow in one direction through the load impedance and the conductive transistor. When the switch is in the opposite position the other transistor is conductive and current can flow in the opposite direction through the latter transistor and the load impedance.

Low output impedance voltage divider network

Abstract: A low output impedance precision dynamic voltage divider network having low power dissipation and particularly suited for fabrication on a monolithic integrated circuit chip.

Audio-communication system having a plurality of interconnected stations

Abstract: An audio-communication system includes a single pair of connecting lines between a master station and a plurality of remote stations. Each station includes a locally powered differential amplifier having a high input impedance and a low output impedance. Switches connect a microphone or a speaker to the amplifier and the lines. The master station includes a D.C. signal source connected to the lines and the remote stations include line reversal circuits responsive to a DC signal to establish a listen condition such that the remote station provides hand-free communication. A line discharge circuit is connected to the lines at the master station and automatically discharges line capacitance when the listen mode is set at the master station.

Impedance measuring bridge circuit

Abstract: Apparatus for measuring the electrical impedance of a variety of materials including an electrode arrangement providing sample data to an impedance bridge, a frequency generator providing a test signal to the impedance bridge, the impedance bridge including a transformer having three separate windings, two of which are highly symmetrical to each other and all three of which have an impedance below 10,000 ohms, and four resistors having resistance values differing from the impedance of the transformer windings but comparable to the unknown impedance, two of the four resistors connected to each of the two symmetrical windings of the transformer. Output devices for displaying the electrical impedance are also disclosed. In one embodiment, a sample box useful in the measurement of the electrical impedance of bulk materials including novel means for mounting an electrode therein is disclosed. Also disclosed in another embodiment is apparatus useful for measuring the electrical impedance of thin sheet material including novel mechanical thermal compensation means.

A transistor realization of the generalized impedance converter

Abstract: A transistor realization of a generalized impedance converter (gic) is developed from an ideal nullor representation The use of gics for realizing low-sensitivity RC-active filters is well established and this new circuit overcomes the requirement for using two operational amplifiers in order to realize a gic The proposed transistor realization is a single-loop structure with the practical advantage of low output impedance; the use of this circuit in the realization of typical elliptic transfer functions is considered

An operational amplifier 4-electrode impedance bridge for electrolyte measurements.

Abstract: A 4-electrode electronic half bridge which utilises solid-state operational amplifiers is described. This system, because of its extremely high input impedance, virtually eliminates the effects of a.c. electrode polarisation impedance in the measurements of the electrical properties of electrolytes. The system finds application in a.c. biological impedance spectroscopy.

Resonant type current regulator providing a continuous regulation

Abstract: A resonant type current regulator in which a controlled inductive impedance is provided in series or in shunt connection with the current path. A control is provided to vary the impedance value of the inductive impedance in response to the load current deviating from a reference value in a manner to stabilize the load current. An antiparallel arrangement of a pair of controlled semiconductor devices can be used for the controlled inductive impedance their control gates receiving control signals at times in each current half period which depend on the magnitude of the current deviation.

Building block for active rc filters

Abstract: A building block for active RC filters including three amplifiers. The output of one amplifier is connected to the input of another amplifier via an impedance. Furthermore, the output of one amplifier is connected to the output terminal of the building block. The inputs of the amplifiers are each via an impedance connected to the input terminal of the building block and via another impedance to the output terminal. Because of the fact that the impedances between the in- and output terminals and the inputs of the amplifiers are triamble, the zeros and the poles of the transfer function can be arbitrarily located in the complex s plane.

Compensation technique for variations in bit line impedance

Abstract: This specification describes a compensation technique for use with storage cells coupled at different points along a resistive sense line to a common sense amplifier so that the position along the sense line effects the impedance between the storage cell and the sense amplifier. The compensation technique involves varying the impedance of a device for coupling and uncoupling the storage element of each cell to the bit line. Where the impedance between the storage cell and the sense amplifier is small the coupling device''s impedance is made large and where the impedance between the device and the sensing circuits is large the device''s impedance is made small. More particularly, the element coupling the cell to the line is a field effect transistor whose length is made longer and shorter to vary its impedance and thereby compensate for impedance differences along the sense line between the storage cell and the sense amplifier.

The Effects of Transmitter Source and Load Impedance on Harmonic Output Spectrum - A New Measurement Method

Abstract: In the recent literature several papers have appeared which discuss the significance of considering the effects of both the transmitter internal impedance and the load impedance when determining the transmitter harmonic output spectrum The considerable variation in the range of predicted harmonic emission levels which accrue from high source and load VSWR and which include the effect of intervening transmission line has been aptly presented1,2,3 It is the purpose of this paper to present the results of recently conducted measurements and analysis aimed at more accurate prediction of these effects in terms of the complex reflection coefficients of both the source and the load impedances which exist at the harmonic frequencies An analysis was made of the constant absorbed-power contours which can be plotted in the complex load reflection coefficient plane for specific complex source reflection coefficients These constant power contours are circles in the load plane, and if superimposed on Smith chart coordinates permit ready determination of the power delivered to any given load impedance at the harmonic frequencies This pictorial representation thus provides particular insight into the effects of source and load reflections on the harmonic power output Measurements were made of the transmitter power delivered to specially designed loads comprising transmission-line sections, tunable stubs, and a linear dummy load These special loads were novel in that they could be tuned to produce a perfect match at the fundamental frequency, while known non-zero reflections were obtained at the several harmonics Thus, in principle, load impedances which are conjugates of the transmitter source impedance are those which absorb maximum power The transmitter load power measurements using these loads were in good agreement with the theoretical load power contours and permitted an indirect determination of transmitter internal impedance at harmonic frequencies An analysis of the transmitter tank circuit was made for both the active and passive conditions of the final amplifier stage These results which will be discussed show that the transmitter internal impedance at harmonic frequencies is the same for both conditions

Slot Impedance of T-Shaped Conductor with Idle Bar

Abstract: A new equivalent circuit is given to simulate the slot impedance of a T-shaped conductor with idle-bar. Calculations are included for the evaluation of slot impedance with single-rectangular conductor, single rectangular conductor with idle-bar, T-shaped conductor and T-shaped conductor with idle-bar respectively. Good agreement was obtained with measured results.

A single-transistor realization of a bilinear RL impedance

Abstract: A realization scheme for a bilinear RL impedance with a single transistor is presented. The parameter relation for the realizability is deduced first and a formal analysis of the circuit is subsequently made with due attention to sensitivity considerations. Practical and theoretical results are compared in graphs.

1 kW microstripline TRAPATT oscillator

Abstract: A microstripline-oscillator circuit capable of operation with one or several stacked TRAPATT diodes is described. Peak power of 1 kW at 1 GHz has been achieved from four diodes operated in series. Experiments have shown the importance of a short-circuited resonant transmission line and a high pulser output impedance for efficient, stable operation of the TRAPATT diode stack.