Showing papers on "Output impedance published in 1978"

Electrical properties of platinum electrodes: impedance measurements and time-domain analysis.

Abstract: The impedance of small platinum electrodes has been measured as a function of frequency. In the range of 0·1 Hz to 10 kHz, this impedance Z can be described accurately as K/(i2πf)m. The value of K is about 2·5 Mω for a surface are of 0·05 mm2. The values for m are in the order of 0·75. Various step responses are computed based on this expression and are compared to recorded wave forms. All step responses are shown to result directly and consistently from the same expression. The consequences of these results for various models and equivalent circuits of the electrode-medium interface are discussed.

Low-noise amplification of voltage and current fluctuations arising in epithelia.

Abstract: Two low‐noise differential input amplifiers designed for voltage and current fluctuation measurements in epithelia are described. The first one uses a matched pair of low‐noise transistors and is particularly suited for low‐frequency current and voltage noise measurements in frog skin and other preparations with impedances below 1 kΩ. The second one is designed around a matched pair of JFETs and can also be used for higher source impedance. Performance is demonstrated with Na+ current power density spectra obtained from frog skin with the transistor‐input stage.

Compensated pulsed alternator

Abstract: This invention relates to an electromechanical energy converter with inertial energy storage. The device, a single phase, two or multi-pole alternator with stationary field coils, and a rotating armature is provided. The rotor itself may be of laminated steel for slower pulses or for faster pulses should be nonmagnetic and electrically nonconductive in order to allow rapid penetration of the field as the armature coil rotates. The armature coil comprises a plurality of power generating conductors mounted on the rotor. The alternator may also include a stationary or counterrotating compensating coil to increase the output voltage thereof and to reduce the internal impedance of the alternator at the moment of peak outout. As the machine voltage rises sinusoidally, an external trigger switch is adapted to be closed at the appropriate time to create the desired output current from said alternator to an external load circuit, and as the output current passes through zero a self-commutating effect is provided to allow the switch to disconnect the generator from the external circuit.

Multiple band, multiple resonant frequency antenna

Abstract: An antenna (10) suitable for multiple frequency band utilization includes three impedance elements (11,12 and 13). The second impedance element (12), which may also be called a network (12), includes a coil (L 2 ) and at least one other conductor (17) in operative association therewith. The second impedance element may be electrically connected to both a first impedance element (11), which may include a linear conductor (14) coupled to a radio, and a third impedance element (13), which may include a coil (L 1 ). By constructing the network (12) so as to have appropriate dimensions, antenna 10 will have a plurality of natural resonant frequencies substantially within or nearby at least each higher band of frequencies of interest.

Impedance of a circular-disc printed-circuit antenna

Abstract: The driving-point impedance of a printed-circuit antenna consisting of a circular disc separated by a dielectric from a ground plane is investigated experimentally. The impedance is measured as a function of the operating frequency for various disc diameters, thicknesses and permittivities of the dielectric and feed point positions. In addition, a theoretical parallel RLC circuit model is proposed and compared with the experimental data.

Performance limits of a Josephson‐junction mixer

Abstract: We present the results of extensive analog‐computer simulations of a Josephson junction used as a mixer with an external local oscillator. The resistively shunted junction model was used throughout, and the effects of intrinsic junction noise were included. When the source impedance is much greater than the junction resistance R, our simulations permit predictions of conversion efficiency, noise temperature, and saturation level to be made for a wide range of experimental parameters. The possibility of harmonic mixing has also been considered. With a source resistance comparable to R (i.e., conventional ’’matching’’) the behavior of the system is too complicated to permit such general predictions of performance. From the results of simulations for a particular set of parameters, it appears that the best noise temperature will usually be achieved for a source impedance somewhat greater than R. An upper limit for the mixer‐noise temperature is ∼40T over a broad range of junction parameters, where T is the effective temperature of the junction. The conversion efficiency under these circumstances should be comparable to what is potentially available from Schottky‐diode mixers. Our simulations show that with stronger microwave coupling it is possible to obtain conversion gain—i.e., a conversion efficiency exceeding unity. This, however, will probably be at the expense of a higher mixer‐noise temperature. Saturation can be important even for source temperatures ∼300 K. To avoid saturation it is necessary either to restrict the coupling bandwith or use an array of junctions.

Significance of pulmonary input impedance in right ventricular performance

Abstract: Right ventricular adaptation to changes in pulmonary input impedance was studied in open-chest dogs. When identical increases in pulmonary vascular resistance are imposed by two different manoeuvres (lung inflation and clamping of the left pulmonary artery), external power and pressure-time integral of the right ventricle at similar filling pressure are always greater during clamping than during inflation. Further studies demonstrate that, at equal increases in pulmonary input impedance modulus at 0 Hz, the clamping produces a greater change in the sum of the first three harmonics of impedance than the inflation (respectively + 77% and −10% vs control modulus; −82% and +8% vs control phase). These impedance changes could explain the different behaviour of the right ventricle either by better matching of the ventricular internal impedance or by functional modification of the outflow tract.

Hybrid stimulator for chronic experiments

Abstract: A hybrid stimulator is described which combines constant current and constant voltage characteristics. Pulses are delivered with high output impedance to assure the passage of a predetermined amount of current. During the quiescent periods between pulses, the output changes to low impedance, diminishing the post-pulse charge. Electrode erosion and tissue damage are thus minimized, permitting safe, long term excitation.

Design of stepped microstrip components

Abstract: The analysis of the impedance step by the mode matching procedure using a waveguide model for the microstrip line yields an explicit design formula for the frequency-dependent equivalent series inductance. The single-section quarter-wavelength transformer is calculated under the assumption of interacting steps. It turns out that in regard to practical design the neighbouring steps can be considered to be decoupled so that the calculation can be done simply with the results given before. Finally the derived results for the impedance step are used to calculate the scattering matrix of an n-section tapered transmission line. Experimental data show good agreement with theory.

Apparatus for oxygen sensor impedance measurement

Abstract: A vehicle engine exhaust mounted oxygen sensor of the type producing an internally generated signal voltage and having a variable internal impedance is connected in series with a reference impedance and a semiconductor switch, the semiconductor switch having an impedance which may become large when current therethrough is very low. A constant current source is connected to supply current to the junction of the sensor and reference impedance at one sensor terminal and thus guarantee a minimum current and small switch impedance when the sensor impedance is large. Further apparatus samples the magnitudes of the voltage at the one sensor terminal with the semiconductor switch in its conducting and non-conducting states, the ratio of said magnitudes varying with sensor impedance. The ratio can be compared with one or more references to provide a warm sensor signal or control the operation of a sensor heater.

Strain gauge pressure transducer apparatus having an improved impedance bridge

Abstract: A strain gauge pressure transducer apparatus having an impedance bridge of strain gauges formed on a thin wall semiconductor diaphragm to which a pressure to be detected is applied. Each of two arms of the impedance bridge includes two series-connected pressure transducer elements of the semiconductor strain gauges, and is electrically connected at one end thereof to each other. An operational amplifier of an excitation source supplies the impedance bridge with excitation current. That is, the output of the operational amplifier is connected to the junction of the two arms of the impedance bridge, and the inverting input thereof to the other end of one of the two arms. To the non-inverting input of the operational amplifier, a voltage signal varying in accordance with the changing of an ambient temperature is applied. Intermediate nodes of the two arms of the impedance bridge are connected to the inverting and non-inverting inputs of another operational amplifier, respectively. The output of the another operational amplifier is fed back to the other end of the other arm of the impedance bridge.

Signal amplifier system for controlled carrier signal measuring sensor/transducer of the variable impedance type

Abstract: A controlled carrier current measuring sensor/transducer signal amplifier system comprising a carrier oscillator for providing a carrier voltage oscillatory signal of known frequency and fixed voltage magnitude. A differential amplifier has the carrier voltage oscillatory signal supplied to one of its inputs. A reference impedance and a variable impedance sensor transducer are connected in a series circuit across the output of the differential amplifier and a first feedback signal is fed back to a second input of the differential amplifier with the first feedback signal comprising the sum of the voltage across the reference impedance and the variable impedance sensor transducer. A buffer amplifier has its input connected to the juncture of the reference impedance and the variable impedance sensor/transducer for deriving an output voltage representative of the instantaneous value of the voltage across the variable impedance sensor/transducer. The output voltage signal from the output of the buffer amplifier is fed back to a third input to the differential amplifier in opposition to the first feedback signal for regulating the current supplied through the reference impedance and the variable impedance sensor/transducer to a substantially constant value whereby the output voltage signal from the output of the buffer amplifier provides a measure of the impedance of the variable impedance sensor/transduer. Preferably, the system further includes shielded conductors interconnected between the reference impedance and the variable impedance sensor/transducer and between the juncture thereof and the input to the buffer amplifier and the output from the buffer amplifier is fed back to the shielding of the shielded conductors whereby the effects of stray capacitance on any measurement obtained from the variable impedance sensor/transducer are minimized.

Method of and apparatus for enabling soft-failure of modular power converter systems, including RF generator systems, embodying switching components in the power conversion

Abstract: The disclosure is concerned with enabling modular power converter systems, including RF generators or transmitters involving such conversion, employing switching components such as SCRs in the power conversion, to fail in a soft manner as a result of transient electrical or other disturbances so as to permit continued system operation, through the use of individual module d.c. power supplies and circuit design that insures inverter module high output impedance even under SCR failure conditions and that mitigates against SCR failures caused by changes in load phase angle.

A nonlinear macromodel for operational amplifiers

Abstract: A general-purpose nonlinear macromodel of an operational amplifier is presented. All element values can be derived directly from typical specification sheets eliminating any testing to determine model parameters. The model simulates the following characteristics: voltage and current offsets, input impedance, nonlinear input bias currents, gain, multiple poles, nonlinear slew, common-mode gain, voltage and current limiting and output impedance.

Tight tolerance zero crossing detector circuit

Abstract: A zero crossing detector provides an optically coupled output signal with a leading edge which occurs in the vicinity of the zero crossing point of an AC voltage waveform but no later than the zero crossing time. The circuit input includes a filter and rectifier. The filtered and rectified voltage is then applied to a complex impedance circuit with an input and an output, which provides an output lagging its input. A switching device, which may be a light emitting diode, is coupled between the output of the impedance circuit and the rectifier. Thus, when the lagging output voltage of the impedance circuit exceeds the output of the rectifier, the switching device conducts, producing the output signal.

Front-end circuit apparatus for impedance measurements and the like

Abstract: This disclosure is concerned with a novel front-end circuit for impedance measuring circuits and the like, involving separately or alternately operated grounding switches for connecting the free terminals of unknown and standard impedances, series-connected at a common terminal, to ground, for enabling separate selected voltage measurements between the unknown and standard, and with the series-connected impedances fed from a floating transformer; the circuit avoiding errors due to low switch impedances and obviating dependence upon capacitance from either side of the unknown impedance to ground and upon the series impedance involved in connections or leads to the unknown impedance.

Wide band impedance matching device

Abstract: A wide band impedance matching device is described for matching the impedance of an antenna transmission line to a radio transceiver over a wide band of radio frequencies. The device includes an impedance matching network having an inductor and two capacitors that electrically interconnect in either a capacitance "T" mode or a capacitance "π" mode. The device also includes an efficient bypass circuit that is capable of electrically bypassing the impedance matching network to effectively directly interconnect the antenna transmission line to the transceiver.

Method and system for transmission and receipt of measuring ultrasonic wave

Abstract: A measuring ultrasonic wave transmitter comprises a negative immitance converter inserted between an ultrasonic transmitting transducer and a drive amplifier for driving the transmitting transducer. The output impedance of the drive amplifier, the damping impedance of the transmitting transducer and the impedance between the transmitting transducer and the drive amplifier are offset by the negative impedance caused by the negative immitance converter. A measuring ultrasonic wave receiver comprises a negative immitance converter inserted between a receiving transducer and a pre-amplifier for amplifying the output of the receiving transducer. The damping admittance of the receiving transducer and the load admittance of the receiving transducer are offset by the negative admittance caused by the negative immitance converter.

Balancing impedance circuit

Abstract: A class of electronic hybrids is disclosed in which the line balancing impedance is made frequency-sensitive in order to better match the frequency characteristic of the connected line and is made voltage-controlled in order that a single network can be used to match a variety of different gauges of telephone cable pairs. The matching impedances are synthesized utilizing RC networks and the voltage control is realized with two-node Miller effect impedance multiplication circuits realized by long-tailed pairs for synthesizing hyperbolic tangent impedance functions under the control of a voltage.

Arrangement for suppressing high frequency currents in bearings of shafts

Abstract: In order to suppress the high-frequency currents in bearings of shafts, the bearing capacity is arranged in the configuration of an electric quadrupole in such a manner that the high frequency voltage becomes a minimum. In the case of ungrounded shafts, a further impedance is provided between the bearing housing and the housing of the treatment chamber such that the sum of this further impedance and the impedance of the shaft are great compared to the bearing impedance. Additionally, a low resistance in the form of a sliding contact is shunted across the bearing impedance. The further impedance according to one embodiment is a capacitance and in another embodiment is a parallel L-C resonant circuit which is connected in series with the bearing. The capacitance of the L-C circuit is formed by an insulating plate and the inductance by a winding.

Constant distortion volume control

Abstract: A device for maintaining a constant distortion output from a musical instrument amplifier over a volume range of the musical system. The amplifier is set at a predesired volume setting and volume control is provided by a potentiometer control interposed between the output of the amplifier which may, for example, be a guitar amplifier, and the loudspeaker. The potentiometer is connected so that one end is in series with the speaker providing the primary means for controlling volume while the other end is in parallel with the speaker. Because the load that the amplifier sees is a function of both the speaker impedance and the potentiometer setting, there is a calibration scale associated with the control dial of the potentiometer so that the amplifier output impedance can be matched to the impedance of the speaker being used.

Modular motor and control means and method

Abstract: An arrangement of electric motors which are coupled together both mechanically and electrically comprises series pass elements and current sensing devices in the power circuits of the respective motors, each current sensing device having an output voltage which is proportional to its motor current, and which is applied to a respective linear operational amplifier having an output which controls the equivalent resistance of the series pass element (and thereby the magnitude of motor current). A single reference voltage is applied to all the linear operational amplifiers, so that, for example, if the motors are similar, each will transmit the same torque regardless of any difference in its internal impedance.

Integratable driver for liquid crystal displays and the like

Abstract: A solid-state driver circuit having a relatively low output impedance, for supplying proper drive voltage to a liquid crystal display cell and the like, utilizes metal-oxide-semiconductor transistors and avalanche diodes to provide a driver requiring a relatively small area to facilitate integration of a large number of driver circuits upon a single integrated circuit chip.

High voltage leakage and breakdown test circuit

Abstract: A circuit is disclosed for testing electrical apparatus to detect leakage and voltage breakdown failure paths and, furthermore, to indicate if the impedances in the paths are below predetermined levels and thereby to characterize the type and nature of the failure. A feature of the circuit is the use of a high voltage test source which has sufficient internal impedance to prevent hazardous currents if a user should accidentally come into contact with the source output.

Broadband folding amplifier for analogue=digital converter - has differential operational amplifier coupled to four-diode output bridge to provide feedback

Abstract: The broadband folding amplifier, for an A/D converter, has an operational amplifier (2) connected at its output to a balanced Schottky-diode bridge (consisting of 4 diodes) that provides both the output signal (UA) and feedback back to the amplifier's inverting input. A linear decoupling circuit (1) is connected to the amplifier's two inputs to make them high ohmic. The operational amplifier consists of a differential amplifier, current mirrors and an FET output stage. The FET output stage has a high input and a low output impedance.

Laplace Plane Analysis of Skin Impedance: A Preliminary Investigation

Abstract: The impedance and phase angle of skin as functions of frequency were determined by Laplace plane analysis of the time domain current resulting from an external voltage perturbation. Bode plots of these functions established a passive equivalent circuit model for skin impedance which is valid over a wide range of frequencies. Typical values for the model circuit elements are given for ten human subjects. The electrical properties of any biological tissue depend on its intrinsic structure and, for in vivo studies, on the functional state of the organism. For the case of human skin, the impedance can vary with the thickness and moisture content of the stratum corneum, the concentration and activity of sweat glands, localized injury, the age of the subject, and environmental factors such as temperature and humidity. Seasonal and diurnal variations have been measured: For example, the d-c resistance of skin tends to increase during sleep. Short-term fluctuations are the basis for various monitoring techniques, including the electrocardiogra m, electroencephalo gram, and impedance plethysmography. Changes in impedance are also associated with the psychological state of the subject (1). Studies of the a-c impedance of biological systems, including human skin, have generally involved direct measurement of the impedance and phase angle as functions of the frequency of the applied voltage or current (2-5). Any such measurement over a wide range of frequencies tends to be cumbersome and time-consuming. Measurements with an impedance bridge have the additional disadvantage that some a priori assumptions must be made regarding an equivalent circuit for the skin impedance. Other reports have presented approximation methods for deriving the equivalent circuit components from the current response to a square voltage pulse input (6, 7). Burton (8) applied Bode analysis to measurements of the skin impedance and phase angle. By means of this method a passive equivalent circuit can be synthesized for any electrical "black box" from plots of its impedance and phase angle vs. frequency. The only assumption required is that the system consists solely of passive linear lumped circuit elements (8, 9). Even though the resulting model is not necessarily unique (8), it must represent the system accurately in the frequency range studied. By extending this technique one step further, the entire frequency spectrum of any system can be computed by applying a Laplace transformation to the current response to an arbitrary voltage perturbation, thus eliminating the tedious process of point-by-point measurement of the impedance and phase angle.

An integrable precision current-controlled negative impedance converter

Abstract: An easily integrable precision floating current-controlled negative impedance converter is proposed and experimentally demonstrated, The resulting converted negative impedance magnitude is both highly accurate and linear over the entire dynamic range. Either terminal voltage can be referenced. The circuit is stable for capacitive impedance convenions.

Orthogonal components of the impedance of batteries by a simple technique

Abstract: 2. Principle of the method Electrochemical power sources possess an internal impedance whose resistive and reactive (i.e., orthogonal) components are intimately related to the effective area of the electrodes, kinetics of the electrode processes and transport properties of the ions in the system. Interpretation of the

Amplifier for AC voltages - has supply voltage which is switchable, so that amplifier can amplify in either direction

Abstract: The amplifier has several stages connected in cascade, each with semiconductor amplifying component. Supply voltages for emitter (source) and collector (drain) of earthed base (gate) transistors (1) can be switched over, so that the transistor can amplify in one of the two direction, depending on the supply voltage polarity. Terminals are provided in the first and last amplification stage, which serve as signal input or output, depending on the supply voltage polarity, the same in all stages. A four-terminal network (12) is provided between stages. It behaves as a bandpass filter and transforms output impedance of one stage to the input impedance of the following stage.

Analog switch circuit

Abstract: PURPOSE:To achieve high speed and low output and to make suitable for mass production and low cost, by applying the buffer effect of the single and push-pull circuit and the high output impedance condition when the idling current is zero