Showing papers on "Output impedance published in 1973"

Impedance measuring system

Abstract: There is disclosed a constant magnitude alternating current source connected to at least one electrical impedance to be measured. First and second voltage detectors are connected to the electrical impedance to measure voltage across first and second portions of the electrical impedance, respectively, in response to the current conducted from the current source. A computer is attached to the first and second voltage detectors for processing the measured voltage to compute desired characteristics of the electrical impedance.

RF Impedance of Power Lines and Line Impedance Stabilization Networks in Conducted Interference Measurements

Abstract: Impedance measurements were made of 60-Hz commercial ac power sources throughout the LF-HF frequency spectrum and compared to the impedance presented by a typical 5-?H line impedance stabilization network. The results are presented in graphical and tabular form.

Method and apparatus for determining internal impedance of animal body part

Abstract: Apparatus and a method for determining the internal impedance of a portion of an animal body. Two electrical currents of different frequencies are passed through the body portion and the voltage across the body portion corresponding to each current flow is sensed. In-phase coherent detection is performed to remove the out-of-phase signal components and the resulting in-phase voltage signals are subtracted from each other to yield a measure of only the internal impedance of the body portion. The invention is especially suitable for use in measuring the changes in the amount of fluid in the human lung.

Continuous condition measuring system

Abstract: In a system which continuously measures the composition, position or size of materials, the probe has a guard shield which is effective for continuous measurement. The measurement system includes a zero adjusting impedance connected with the variable probe impedance as two adjacent arms of a balanceable bridge. A span impedance is connected between the junction of the adjacent arms and a low impedance AC source. The buffer amplifier has its input connected across the span impedance so that changes in the input impedance of the amplifier do not change the operating point of the system. A guard shield amplifier has its input connected to the output of the buffer amplifier. The guard shield amplifier maintains the guard shield at the same potential as the voltage on the probe electrode continuously for all points of operation, without significantly changing the voltage.

rf impedance of superconducting weak links

Abstract: The rf impedance of a superconducting weak link with negligible capacitance is calculated for a variety of operating conditions. It is shown that the impedance is always real between harmonic steps of the I‐V characteristic. The real part of the impedance is negative under certain conditions of bias for small rf signals, thus indicating the region of self‐oscillation of the weak link.

Impedance plethysmograph having blocking system

Abstract: An impedance plethysmograph has an oscillator for applying constant current to the thorax of a patient. A detector circuit connected to the patient provides an output corresponding to thoracic impedance. Circuits responsive to detected impedance provide signals corresponding to change of impedance and the first time differential of impedance. Means are provided to block the differential signal when it is meaningless, for example, due to respiration.

Electrical sensing circuitry for particle analyzing device

Abstract: The electrical sensing circuitry includes a power supply and a signal-detecting circuit which are coupled through the resistance of an electrolyte in a liquid in an aperture of a particle-analyzing device between sensing electrodes positioned on either side of the aperture. The liquid containing an electrolyte and the passage of a liquidborne particle through the aperture causes a change in the resistance of the aperture thereby generating a signal which is detected by the signal-detecting circuit. The parameters of the circuit elements are chosen to provide circuit relationships which render the particle-generated signal independent of the diameter of the aperture. This is achieved by utilizing a power source having a low output impedance and a signal-detecting circuit which has a low input impedance for both D.C. and A.C., namely, at the signal frequencies of the signals sensed. The electrical circuitry also may include a conductivity monitoring circuit which may utilize one or more of the sensing electrodes and/or additional electrodes for monitoring changes in conductivity of the electrolyte and for relating these changes in conductivity to the particle-generated signals sensed by the signal-detecting circuit to alter those signals so as to render them independent of electrolyte resistivity.

Fast digital computation of 3-phase thyristor bridge circuits

Abstract: The paper describes a digital-computer solution for 3-phase thyristor bridge-rectifier circuits. To cope efficiently with the complex commutation conditions when the source impedance is significant, the solution is based on Kron's method of tensor analysis. Theoretical results are shown to compare closely with experimental results for the same circuit conditions.

Insulated electrocardiographic electrodes

Abstract: Disclosed is an integrated system including an insulated electrode and an impedance transformer which can be assembled in a small plastic housing and used for the acquisition of electrocardiographic data. The electrode may be employed without a paste electrolyte and may be attached to the body for extended usage without producing skin reaction. The electrode comprises a thin layer of a suitable non-toxic dielectric material preferably deposited by radio frequency sputtering onto a conductive substrate. The impedance transformer preferably comprises an operational amplifier having an FET input stage connected in the unity gain configuration which provides a very low lower cut-off frequency, a high input impedance with a very small input bias current, a low output impedance, and a high signal-to-noise ratio. The electrode may be connected directly into a standard monitoring system normally employed with conventional paste-type electrodes.

Communicating over power lines

Abstract: An audiofrequency signal is applied to a power amplifier having an output impedance of considerably less than an ohm that is coupled through a network comprising at least a capacitor that presents a low impedance to this audiofrequency signal and much higher impedance to energy at the 60 Hz power frequency to a power line to provide an amplified signal that is transmitted to a receiver separated from the transmitter by at least one distribution transformer and having a high pass filter for rejecting the 60 Hz power frequency and a number of harmonics thereof while transmitting the audiofrequency signal. The system is especially advantageous for using ordinary power lines for transmitting information in connection with automatic meter reading.

Broadband antenna systems realized from active circuit conjugate impedance matching.

Abstract: : The application of negative impedance converter circuits for use in extremely broadband antenna systems is proposed. The theory of short antennaes, and means of achieving a conjugate impedance match to them, is discussed. Synthesis methods that yield the required converters, uncompensated or compensated, are presented. Lastly, the performance of several of the constructed antenna systems are compared with that of a 12 foot whip.

R-F switching circuit

Abstract: An insulated gate field effect transistor (IGFET) is used selectively to connect a source of radio frequency (e.g., VHF) signal to means for utilizing the radio frequency signal. First and second gate potentials are selectably applied to the IGFET to render its channel conductive and non-conductive, respectively. The first potential is applied from a source impedance appreciably higher than the reactance of the gate-to-channel capacitance of the IGFET for radio frequency signal. This prevents a distributed RC transmission line effect in the IGFET introducing reflections back to the source of radio frequency signals when the IGFET channel is conductive. The second potential is applied from a source impedance appreciably lower than the reactance of the gate-to-source and gate-to-drain capacitances of the IGFET for radio frequency signal, to reduce feedthrough of radio frequency signal when the channel is non-conductive.

Method and apparatus for measuring the impedance of a line

Abstract: A method and apparatus for measuring the impedance of a line in which the resistive and inductive component of line impedance are determined from measured instantaneous values of voltage, current and the rate of current change using a digital computing circuit.

Absorptive pin attenuators

Abstract: Variable attenuators for radio frequency (RF) signals in matched impedance transmission line systems are disclosed. Variable absorptive elements, PIN diodes, are used in shunt with the transmission line at quarter wavelength intervals. The impedance of the diodes which are coupled to input and output terminals is made equal at all attenuation levels to the impedance of the remaining diodes plus the characteristic transmission line impedance so that impedance mismatch with external devices is avoided.

Flyback transformer apparatus

Abstract: A flyback transformer apparatus is provided in which a flyback transformer is provided with a first and second secondary winding with one end of the first secondary winding connected to at least one first rectifier and a second rectifier connected between one end of the second secondary winding and the other end of the first secondary winding, a capacitor is connected to the second secondary winding, and a primary winding of the flyback transformer is inductively coupled with the high-voltage side winding portion of the first secondary winding, whereby the output impedance is reduced and a focusing voltage which does not give rise to defocusing is provided.

Driver circuit for modulating diode

Abstract: A circuit for driving a modulating diode into reverse and forward bias directions. High switching speeds are achieved by connecting a low output impedance driver and a constant current generator to the same terminal of the modulating diode. The current generator provides the entire forward current to the diode when the latter is forward biased. The substantial charge accumulated by the diode during forward bias is swept away at switching time by the low impedance driver.

Flame detection system with compensation for the flame detector

Abstract: A flame detection system utilizes a flame responsive impedance, such as a lead sulphide photocell, and responds to the change in infrared radiation and the flame flicker frequency of the sensed flame. The flame responsive impedance is connected through a variable impedance means to a source of direct current voltage. The voltage between the flame responsive impedance and the variable impedance means is compared by an amplifier to a voltage divider network so that a feedback voltage can be generated by the amplifier to control the variable impedance means. The variable impedance means is controlled by the feedback so as to keep the direct current voltage across the flame responsive impedance constant to compensate for variations in flame background radiation, and cell to cell variation. The system then uses a band-pass amplifier and detector-integrator system to control an output switch.

Tuned oscillator circuit having a tuned filter output

Abstract: A transistor microwave oscillator circuit is provided with a YIG resonator device coupled to one of the transistor terminals. The YIG device resonates at a frequency established by a magnetic field applied thereacross and determines the oscillation frequency of the transistor circuit. Another YIG device is provided as a frequency responsive output transformer and functions as a high Q filter. This YIG transformer is positioned within the same applied magnetic field and has a resonant frequency identical to the YIG resonator. That is, the center frequency of the bandpass filter is the same as the oscillator frequency. As the applied magnetic field is varied, both the oscillation frequency of the transistor and the center frequency of the filter vary an identical amount. This frequency tracking insures that the oscillations are optimally passed by the filter, while off-frequencies are maximally attenuated. Further, the YIG transformer functions as an output impedance matching device. The YIG transformer is loop or coil-coupled to the transistor output terminal and loop-coupled to the load. These coupling coils may easily be modified as to number of turns and proximity to the YIG spheres to effect an optimal impedance match in a manner similar to conventional transformer coupling.

Measuring apparatus utilizing variable impedance elements

Abstract: The measuring apparatus comprises an impedance element which is energized by a reference voltage of a predetermined voltage level and has its impedance varied with variations in the physical properties of an object to be measured, and a negative impedance network, with its input impedance set at a negative value, which includes an amplifier and a positive feedback impedance element connected between the input and output terminals of the amplifier and is connected in series or parallel with the first mentioned impedance element. With the arrangement, the variations in the physical properties of the object can be detected in an extremely enlarged state in the form of a terminal voltage appearing across the first mentioned impedance element or an output voltage appearing across the output terminals of the negative impedance network.

Apparatus and method for tuning a broad bandwidth transducer array

Abstract: A fixed electrical network, in conjunction with an amplifier having varia output impedance, is used to provide each of the transducer elements of an array with a reactance which acts as a large shunt reactance when the amplifier acts as a constant current source, but which acts as a smaller series reactance when the amplifier acts as a constant voltage source. Consequently, the usable bandwidth of the array is greatly increased, without degrading its performance.

Erratum: Rectifier action with constant load voltage: infinite-capacitance condition

Abstract: The paper presents an analysis of a 3-phase fullwave bridge-rectifier system with constant load voltage, and with series resistance and inductance in the a.c. source. It is shown that four different operating modes or conducting patterns may occur, according to the phase angle of the source impedance and the magnitude of the load voltage. The results given include a complete set of output voltage/current characteristics from open circuit to short circuit, for the full range of possible source impedances, together with details of the source and bridge currents.

Drive circuit for pulse width modulated D.C. - D.C. convertors

Abstract: A method of operating a power output transistor comprises interrupting the emitter current of this transistor simultaneously with the base drive current and immediately thereafter allowing the collector current, due to stored charge in the base collector-junction, to flow through the base and thence through a low source impedance during extraction of this stored charge.

Communication system interface circuits

Abstract: Communication system interface circuits for bidirectional 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 inductance 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 indictive 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.

Telephone transmitter circuit

Abstract: A microphone, for example an electret microphone, may be combined with an amplifier to replace a typical carbon telephone transmitter. Such a combination is modified by the addition of a controlled impedance a-c shunt load circuit between the self polarized transmitter and a typical loop circuit. The shunt load circuit co-acts with the output impedance of the amplifier to simulate the conversion efficiency of the typical carbon microphone over a range of loop circuit operating voltages.

Negative impedance converter

Abstract: A semiconductor negative impedance converter device for compensation of insertion losses attributable to the use of high impedance devices such as semiconductor controlled rectifiers in solid state telephone switching networks. The device comprises a double collector PNP transistor and an NPN transistor which can be fabricated in a single semiconductor substrate without the need for isolation of their various regions.

Enhancing impedance characteristics of negative impedance repeaters operating at high gain

Abstract: An alignment procedure for improving the high-gain impedance characteristics of a telephone repeater of the type employing both series-and shunt-connected negative impedance converters. Temporary terminating resistors are connected to each converter such that the repeater is operated at approximately 75-80 percent of its maximum gain with its transmission line terminals connected to a desired nominal image impedance. Using variable decade resistors and a return loss measuring set, small variations in the net terminating resistances of each of the two converters are made until return loss is maximized, thereby determining the values of permanent, fixed-value, impedanceoptimizing resistors which are then interconnected with and become a permanent part of the repeater''s strapping networks.

Sequence amplitude modulated inverters

Abstract: This Static Inverter produces a true stepped waveform from a direct current source, which is symmetrical from one half cycle to the next half cycle. Because of its low output impedance and OC half-wave circulating path for current, the Inverter will deliver rectified, non-linear loads and still operate normally (low distortion) and under extremely poor power factor loads. The method used to obtain this type of stepped waveform was originally developed in 1965. With the advent of integrated circuits, the complexity and cost of the design was considerably reduced. Production of the eight steps of the waveform previously required eight separate volt· age generating sources. Today, through the use of integrated circuits, two or three voltage sources can perform the necessary function of producing eight to twenty-six (or more) steps if desired in a half wave cycle period. Only a fraction of the power (7%) is switched at a high frequency rate as compared with a Pulse Width Modulated technique. The bulk of the power (70%) is generated at the output frequency. The method of inversion discussed here can generate a high quality, high power sine wave voltage that meets most of the desirable character· istics of a high-quality inverter including low output impedance.

Performance of electron beam-semiconductor amplifiers

Abstract: Experimental results obtained with developmental electron beam-semiconductor devices used as video-pulse and RF pulsed amplifiers are discussed. These devices employ a grid-modulated electron beam to control the current in a semiconductor target. Power gains of 26 dB and peak pulse powers of 40 W were obtained at up to 600 MHz with an untuned output impedance of 20 Ω. Peak powers in excess of 30 W were obtained at 600 MHz with a 50-Ω load. Power gains of 20 dB were obtained at up to 860 MHz for both output impedances. Also described is the performance of a video-pulse amplifier with a peak power of 2 kW and a rise time of 2 ns. The experimental results are compared to the theoretically predicted values. A problem of diode deterioration encountered with these developmental devices is discussed and solutions to the problem are presented. The reverse breakdown characteristic of both nonpassivated mesa diodes and silicon dioxide passivated planar diodes using "p on n" material decreased by over 50 percent during the first few hours of operation. "p on n" diodes with phosphorous glass over the silicon dioxide have been operated up to 59 h with little deterioration, and a planar diode with "n on p" construction has been operated satisfactorily for 1000 h.

Electrical power supplies

Abstract: An electrical power supply arranged to provide an alternating voltage output, which includes a pair of transductors or saturable reactors connected in phase opposition in series to the output and provided with means for supplying them with a constant d.c. control current so as to operate in the forced magnetization mode thereby providing a constant current source with a high output impedance, the output current being set by the control current.