Showing papers on "Output impedance published in 1975"

Adjustable length center conductor for termination fixtures for electrodeless lamps

Abstract: A light source includes a source of high frequency power, an electrodelsss lamp and a termination fixture for coupling power to the lamp, the fixture having an outer conductor and an inner conductor whose length is adjustable for providing dynamic matching of the impedance of the lamp during the operating mode to the output impedance of the source. Variations in the power level from the source, such as is desirable in providing lamp brightness selectivity, vary both the real and imaginary components of the lamp impedance, and corresponding adjustments of the inner conductor length provide a tuning technique to compensate for these variations.

Microstrip/stripline impedance transformer

Abstract: To eliminate reflections and oscillations when a low impedance level circuit is to be connected to a high impedance level circuit on a printed circuit board, a microstrip/stripline impedance transformer is inserted in between. This transformer is passive and bi-directional, i.e., it can be step-up or step-down. It is made of a continuous folded microstrip (also called a surface etched line) or a continuous folded stripline (also called a buried etched line) wherein each folded section is run in parallel with its preceding one. Because of the mutual coupling between each section with its preceding one, the line impedance of each section will be step-up or step-down depending on the impedance levels at both ends of the interconnection.

Microminiature integrated circuit impedance device including weighted elements and contactless switching means for fixing the impedance at a preselected value

Abstract: A microminiature terminal-adjustable integrated circuit impedance device comprising a substrate, a plurality of impedance elements formed on the substrate with each impedance element having an impedance, a first input terminal, an output terminal, a plurality of electrically permanently alterable contactless switching elements formed on the substrate, each of the switching elements being associated with one of the plurality of impedance elements and having initially a first switching state and being permanently alterable by application of electrical energy to an opposite switching state, an interconnecting means interconnecting the impedance elements and the switching elements in a first circuit configuration between the first input terminal and the output terminal such that the impedance between the first input terminal and the output terminal is of a first value, and a plurality of adjustment terminals each being connected to a different one of the plurality of switching elements for facilitating the application of electrical energy thereto to cause such switching elements to change to the opposite switching state, whereby the application of electrical energy to selected ones of the adjustment terminals causes a second circuit configuration having a preselected second value to be formed between the first input terminal and the output terminal. Each electrically permanently alterable contactless switching element is comprised of fusible conductive links or shortable diodes, singly or in combination. In the preferred embodiment the device comprises resistive elements fabricated with state-of-the-art thin film or monolithic integrated circuit technology and serves as a variable resistor or as a variable voltage divider performing the function of a fixable contactless trimming potentiometer.

Electrodeless light source having improved arc shaping capability

Abstract: An electrodeless lamp is positioned at the end of an inner and outer conductor forming a termination fixture, the inner conductor being shaped such that the arc within the lamp during excitation is isolated from the wall of the lamp envelope. The inner conductor may be formed as a hollow helical element thereby providing both an axial and azimuthal electric field component. Alternatively, the inner conductor may be cup-shaped which has a shielding effect to control the electric field strength at the end of the conductor. The helical or cup element and other features of the inner conductor provide both arc shaping and impedance matching between the complex impedance of the lamp during operation and the output impedance of a high frequency power source which is coupled to the termination fixture.

High frequency excited electrodeless light source

Abstract: A light source includes an electrodeless lamp having an envelope for enclosing a volatile fill material which emits light upon vaporization and excitation, a source of power at a high frequency and a termination fixture coupled to the source. The fixture has inner and outer conductors which have dimensions such that the lamp is located in the high field region at the end of the conductors. When the high frequency power is applied to the fixture, a voltage standing wave is formed which initiates vaporization and excitation of the fill material. The termination load impedance which is that of the lamp changes from a lossy open circuit to a finite value when vaporization and excitation occur. An impedance matching device is provided for matching the running lamp impedance to the output impedance of the source.

Force and electrical Thevenin equivalent circuits and simulations for thickness mode piezoelectric transducers

Abstract: A simple model is reported for thickness‐mode piezoelectric elements used as ultrasonic transducers in measurement systems. The model represents the excitation system and transducer as a Thevenin mechanical equivalent for the transmitting mode and a Thevenin electrical equivalent for the receiving mode. Computer programs based on the model have been developed, and computer simulations to study the effects of backing materials, element areas, and excitation sources are reported. The nature in which the source impedance alters the Thevenin mechanical output impedance and its importance in determining peak transmission frequency and in computing acoustic coating layers for matching was found. A total transfer improvement of 28 dB was shown for epoxy‐backed elements radiating into fluid with the transducer used as both transmitter and receiver by using high values of source and load impedances in contrast to low values. The model was found to agree closely with experimental data of a 2.7‐MHz transducer.Subject Classification: 85.40; 80.70; 85.52.

Electrodeless light source utilizing a lamp termination fixture having parallel capacitive impedance matching capability

Abstract: A termination fixture for use in an electrodeless light source has an input impedance which is matched to the output impedance of a high frequency power source, even though the lamp which forms the termination for the fixture has a complex impedance when the lamp is in an excited state. The fixture has a pair of coaxial conductors of at least a quarter wavelength, the conductors being coupled to the source at one end and to the lamp at the other end. The conductors are shaped to create an impedance which matches the real component of the lamp impedance to the source impedance. A capacitor is formed across the inner and outer conductors at the source coupled end to compensate for the series capacitive reactance part of the lamp impedance at the lamp coupled end of the conductors.

Helical coupler for use in an electrodeless light source

Abstract: A termination fixture for exciting an electrodeless lamp with high frequency power matches a capacitive complex impedance of the lamp in an excited state to the output impedance of the high frequency source coupled to the fixture. The fixture has a pair of coaxial conductors which have a length of one quarter wavelength and which have a ratio of diameters effective to match the real impedance of the lamp to the impedance of the source. A helical coil couples the end of the inner conductor to the lamp. The purpose of the coil is to make the impedance of the lamp, as viewed, electrically, from the end of the inner conductor appear as having only the real component. The quarter wave fixture then matches the real impedance to the source impedance.

Nonideal negative resistors and capacitors using an operational amplifier

Abstract: Negative impedance converters (NIC's) may be used to realize negative driving-point impedances. The effect of the nonideal characteristics of the operational amplifier such as finite frequencydependent gain and output impedance on the performance of the negative impedances is analyzed. Detailed equivalent circuits showing the additional positive or negative inductive impedances due to the nonideal characteristics are given for negative resistance and negative capacitance realizations, and their relative performances are compared. The experimental results confirm the validity of the equivalent circuits. The effect of the slew rate of the operational amplifier on the maximum signal-handling capability (SHC) of the negative impedances at high frequencies is studied. Practical design considerations for achieving wider bandwidth as well as improved SHC are discussed.

An accurate integrated voltage-to-current converter

Abstract: Presents a monolithic integrated differential voltage-to-current converter. The transconductance of the converter is determined accurately by one external resistor. A total error in the conversion factor as low as /spl plusmn/0.5 percent is obtained by using composite transistors and by using the mutual equality of integrated resistors. The transconductance has a nonlinearity of 0.02 percent and a temperature coefficient of 4/spl times/10/SUP -5///spl deg/C. The output impedance is 5 M/spl Omega/. The voltage-to-current converter is a versatile building block. It can be applied as an instrumentation amplifier, a universal current mirror or current follower, etc.

Digital transmitter for data bus communications system

Abstract: Disclosed is an improved digital transmitter for transmitting serial pulse-code modulation (pcm) data at high bit rates over a transmission line. When not transmitting, the transmitter features a high output impedance which prevents the transmitter from loading the transmission line. The pcm input is supplied to a logic control circuit which produces two discrete logic level signals which are supplied to an amplifier. The amplifier, which is transformer coupled to the output isolation circuitry, converts the discrete logic level signals to two high current level, ground isolated signals in the secondary windings of the coupling transformer. The latter signals are employed as inputs to the isolation circuitry which includes two series transistor pairs operating into a hybrid transformer functioning to isolate the transmitter circuitry from the transmission line. An effective increased amplitude, balanced, differential output signal is produced by the transmitter from the serial pcm input data to provide an improved transmitted signal to the transmission line.

Three-phase bridge rectifiers with complex source impedance

Abstract: The operation of uncontrolled and controlled 3-phase bridge rectifiers with resistive and inductive source impedances is investigated. Equations describing the operation of the systems, from open circuit to short circuit on the d.c. side, are given. Results computed from these equations are presented in graphical form. The effect of varying the ratio of source resistance to reactance is demonstrated. Some experimental results obtained from a model system are presented. From the results, it is shown that the resistive component of the source impedance will have a significant effect on the operation of a rectifier system, unless the source reactance is at least an order of magnitude greater than the source resistance. Resistive components of the source impedance have their greatest impact on the high voltage/low current portion of the load characteristic.

Output circuit for charge transfer transversal filter

Abstract: The output circuit includes a high gain differential amplifier having an inverting input terminal, a non-inverting input terminal and an output terminal with a feedback capacitance connected between the output terminal and the inverting input terminal. The input terminals are connected to first and second commonly phased lines of the charge transfer transversal filter. A first switchable impedance means is connected between the first line and the output terminal. A second switchable impedance means is connected between the second line and a d-c source of voltage. The lines are charged periodically to the voltage of the source by the first and second switchable impedance means prior to the transfer of charge in a cycle of operation of the filter and are then isolated from the source during the transfer of charge in the filter by the first and second switchable impedance means.

Electrodeless light source having a lamp holding fixture which has a separate characteristic impedance for the lamp starting and operating mode

Abstract: A lamp holding fixture for exciting an electrodeless lamp by high frequency power has a switchable characteristic impedance for impedance matching the lamp to the power source during both the starting and operating modes. The fixture has an inner conductor and two outer conductors of different dimensions in cross section. During the starting mode the inner conductor and the larger diameter outer conductor form the power coupling conductors for the fixture thereby providing a high characteristic impedance for matching the lamp impedance to the source output impedance. After starting, the smaller diameter outer conductor may be moved along its longitudinal axis until it contacts the power coupling end of the larger diameter outer conductor so that the inner conductor and the smaller diameter outer conductors form the power coupling conductors during the operating mode.

OWL II pulsed‐electron‐beam generator

Abstract: OWL is a water‐dielectric line‐type pulse generator capable of producing ∠100‐nsec electron beams with total energies of as much as 150 kJ. In its present form, OWL II consists of an oil‐immersed, 1/3‐MJ Marx generator charging a 3.9‐Ω coaxial pulse‐forming line which is series switched into either a two‐ or three‐stage impedance transformer. The output impedance is 1.9 or 1.1 Ω, depending upon which transformer is used, and nominal beam outputs in the two cases are 1.3 MV at 0.8 MA and 0.9 MV at 1.2 MA, respectively. The pulse width can be selected at either 60 or 120 nsec (FWHM of power) by interchanging two available pulse lines. Shot‐to‐shot reproducibility in output of ±2% with a mean electron energy ∠1.0 MeV is obtained with the 1.9‐Ω final transformer. A triggered multichannel water switch minimizes the risetime of pulses injected into the transformer section.

Negative impedance network

Abstract: A negative impedance network includes a pair of network terminals, with one terminal connected to the base of an emitter-follower transistor. A current mirror includes one current path connected to supply a first current to a fixed impedance means through the collector-emitter circuit of the transistor and a second current path supplying a second current to the one network terminal in fixed ratio to the first current, such that an effective negative impedance is presented in parallel to an external circuit connected across the network terminals.

Automatic impedance modification of transmission lines

Abstract: An automatic impedance matching network for a transmission line includes an impedance monitor which provides a control signal for two variable compensators. One compensator corrects an impedance mismatch at low frequencies while the second compensates within a higher frequency range. A directional sensor completes a conductive path for the control signal to the variable compensators only for the direction of signal propagation indicative of the impedance of the transmission line being compensated. The disclosed arrangement operates automatically from the intelligence signals transmitted over the line to provide impedance compensation for a variety of cable sizes of different lengths.

Synthetic reactor circuit

Abstract: Communication system interface circuits for bi-directional transmission of signals between terminal sets, each interface circuit comprising a transformer including first winding means coupled through rectifier means and a low-pass filter to a first terminal set and including second winding means having end terminals coupled through diodes to the output of a high frequency inverter and having a center tap coupled through an inductive impedance to a neutral circuit point, a second terminal set being coupled across the inductive impedance. The first terminal set may be connected to a telephone subset with ringing and bias signals being applied in circuit with the inductive impedance. The inductive impedance includes transistor means controlled by an operational amplifier which is controlled from a resistance-capacitance phase-shift means, the impedance being equivalent to that of an inductance and a series resistance.

Microstrip or stripline coupled-transmission-line impedance transformer

Abstract: An electrical transformer for transforming electrical impedances of high transformation ratios including a dielectric substrate having a pair of parallel electromagnetic coupled-transmission lines bonded to one surface of the dielectric substrate. The first of the pair of transmission lines being adapted to be connected to a first impedance at one end with the other end being connected to a ground terminal through a first tuning capacitance which varies the real part of the transformed impedance. The second of the pair of transmission lines being coupled, at its end opposite the first tuning capacitor, through a second tuning capacitance to a second impedance to which the first impedance is to be matched. The second tuning capacitance is utilized to vary the imaginary part of the transformed impedance.

Multi-phase rectifier system

Abstract: Disclosed is a multi-source rectifier system for providing DC power to a load from a plurality of high impedance AC electrical sources connected to a multi-source high voltage transmission system. The system comprises a parallel arrangement of high impedance AC current sources each connected in series with a respective bridge rectifier, the positive output terminals of all bridge rectifiers are connected in parallel to the positive side of a load. The negative output terminals of all bridge rectifiers are connected in parallel to the low side of the load. The individual high impedance AC current sources are completely isolated from one another through their series connected bridge rectifiers, making it possible to simultaneously supply current from more than one high impedance AC current source to the load without significant circulating currents among the sources. The parallel arrangement of high impedance AC current sources connected through bridge rectifiers to the load provides direct current electrical power to the load notwithstanding phase differences between various high impedance AC current sources. A multisource rectifier arrangement when connected to a high impedance AC current source, will yield a level of DC output power greater than what at first might be expected. Only one rectifier may conduct at any given time when voltage sources are used and when the load is resistive, for example, the rectifier conduction angle cannot exceed 120° (60° per half cycle). This is the result of forced commutation of the rectifier by the voltage source. When a current source, e.g. a high impedance AC current source, is used however, the conduction angle with a resistive load, for example, can increase theoretically to 360° (180° per half cycle) and several rectifiers can conduct simultaneously. Further, the failure of any number fewer than all of the high impedance AC current sources will not interrupt power to the load.

Termination fixture for an electrodeless lamp

Abstract: An improved termination fixture for an electrodeless light source matches the complex impedance of an electrodeless lamp during excitation to the output impedance of a high frequency power source coupled to the fixture. The inner conductor of the fixture has a first and a second section. The dimensions of the first section are such as to produce an input impedance whose reactive impedance part is much smaller than the reactive impedance part of the lamp impedance. The dimensions of the second section are such as to match the input impedance to the source output impedance.

Bias circuit for FET

Abstract: A bias circuit particularly adapted for use with a field effect transistor whereby the drain bias current of the field effect transistor is maintained constant in the event of fluctuations in the operating voltage applied to the field effect transistor by a power supply. The bias circuit changes the gate bias voltage applied to the FET as a function of the fluctuations in the operating voltage to thereby restore the drain bias current to a constant value. A variable impedance is included in the bias circuit, the variable impedance being voltage dependent such that its impedance varies as the voltage applied thereto varies in accordance with a hyperbolic relation. The voltage applied to the variable impedance is derived from, and thus includes the fluctuations in, the operating voltage. The hyperbolic relation between the impedance and the voltage applied to the variable impedance effectively matches the relation between the pinch-off voltage VP and the amplification constant μ of the FET.

Spatially distributed transducer for towed line array applications

Abstract: Transducers based on the variable reluctance concept, employing magnetiza, soft, plastic materials. These materials serve as the isolator between the conductors of a coaxial cable. Such materials exist in considerable variety. The magnetization is azimuthal, such as can be generated by electrical currents flowing through the coaxial cable. Any isolated section of the coaxial cable constitutes a transducer, the conductors at one end of which form the terminals, while those at the other end are connected together to provide a closed electrical circuit. Pressure changes, caused, for example, by acoustic signals, on the outer surface of this transducer produce changes in volume, which in turn induce electrical signals due to changes of the magnetic flux. The conductors of the cable transducer can be in the form of wire braids or metal films, neither of which will significantly change the elastic characteristics of the magnetizable plastic material. Transducers of this type exhibit an electrical source impedance which is essentially equal to the resistance of the conductors. This eliminates the need of impedance changing preamplifiers. The output signals can be, therefore, transmitted directly over long distances by simple wires placed in the interior of the central, hollow, inner conductor.

Multiple transistor microwave amplifier

Abstract: An input signal from a microwave source is divided equally between a parallel arrangement of multiple transistors by an input circuit having multiple transmission line center conductors with opposite ends capacitively coupled to a reference potential. The multiple transmission line center conductors of the input circuit are arranged to provide an impedance match between the signal source impedance and the transistor complex input impedance. An output signal from the parallel arrangement of multiple transistors is summed by an output circuit having multiple transmission line center conductors with opposite ends capacitively coupled to a reference potential. The multiple transmission line center conductors of the output circuit are arranged to provide an impedance match between the transistor complex output impedance and a terminating load impedance.

Electronic telephone network

Abstract: An electronic telephone network suitable for use with a two-wire telephone line includes a low-output dynamic microphone coupled to a preamplifier. The output signal of the preamplifier is coupled through a first equalization network which is responsive to an equalization signal which is related to the DC line current to equalize the frequency and amplitude spectrum of the transmitted signal irrespective of the telephone line length or loss. The output of the equalization network is applied to a line-driver amplifier, and as a first input to an electronic signal separator or hybrid. The output of the line-driver is coupled to the two-wire line, and as a second input through the separator by way of an attenuator. The output of the separator is coupled to a receive amplifier by way of a second equalization network which is also responsive to the equalization signal to equalize the frequency spectrum of the receive signal as a function of line length. The loss of the attenuator is selected to be equal to the gain of the line-driver thereby to isolate the transmitted signal and to pass the receive signal to the receive amplifier. In a preferred embodiment, the equalization signal is the DC supply voltage derived from the telephone line itself. The output impedance of the line-driver is lowered during transmit to reduce the sensitivity of the separator isolation and, therefore, the sensitivity of the sidetone signal. The various circuits of the network utilize active loads and other circuitry to provide maximum transmit signal dynamic range even at low line terminal voltages.

High frequency amplifier with frequency conversion

Abstract: A high frequency amplifier comprising an amplifying circuit, an emitter follower which makes the output impedance of the amplifying circuit low and an impedance matching network consisting of a coil and a condenser and connected between the amplifying circuit and the emitter follower, in which an operation voltage for the amplifying circuit is supplied thereto through a bias resistor for the emitter follower and a coil of the impedance matching network.

High impedance voltage probe

Abstract: A high impedance voltage probe with excellent high frequency response and extremely light loading of the circuit under test. The probe uses an IGFET input device having its source connected to a constant current source and to an amplifying device, and its drain connected to a variable voltage source. The output of the amplifying device is connected to a constant current source, to a non-linear voltage translating device and to an output terminal. The voltage translating device is also connected to the variable current source.

Inverters supplying a high frequency alternating current

Abstract: An inverter embodiment provided with an enhanced A.C. output signal frequency upper limit and with an improved circuit protection. This protection operates when the load impedance varies outside permitted limits. In the inverter the number m of pairs of controlled rectifiers and inductances is made equal to 2q, q representing groups of at least two pairs, with each group having the series-connected rectifier and inductance components forming one pair connected in parallel with those forming the other pair, the rectifiers being connected to conduct in opposite directions. In addition, a fault detector is connected via an inductance to the output terminals of the DC source and further is coupled to the output which supplies the load. The value of the Q factor of the coupling means, which means are tuned to the A.C. output signal frequency, depends on the load impedance. A major increase in this impedance results in energy being returned to the source.

Alternating current control circuits

Abstract: A novel circuit is provided for controlling an alternating current supplied to a load which includes a variable impedance element in the form of a low emitter concentration transistor which is bidirectional, and which has a high gain. The impedance of the variable impedance element to the flow of current therethrough is substantially the same in either direction of current flow.

Ground fault protection system including improved impedance detecting means

Abstract: A ground fault protective system in which an impedance responsive oscillator detects low impedance ground faults on the neutral conductor of an electrical distribution circuit and responds thereto to provide a partially or totally attenuated output signal. A demodulator, magnetically coupled to the oscillator, provides a direct current voltage output signal related in value to the magnitude of the oscillator signal. The demodulator output signal may be used by control circuitry to interrupt the distribution circuit.