Showing papers on "Equivalent circuit published in 1970"

New equivalent circuits for elementary piezoelectric transducers

Abstract: New equivalent circuits, having several advantages over previous circuits, are presented for three types of piezoelectric transducer: the thickness-expander plate, the end-electroded bar and the side-electroded bar. Each of the circuits involves an electrical network of frequency-dependent components connected to the centre of an acoustic transmission line.

Application of RF discharges to sputtering

Abstract: The operation of rf discharges is described and the internal distribution of voltages is considered. The significance of this with respect to sputtering, particularly of insulators, is then discussed. An equivalent circuit for the discharge is presented and the influence of such parameters as pressure and magnetic field on the components of this circuit is described. Finally, energy distributions for positive ions, electrons, and negative ions incident at the substrate during deposition are given.

Transient Analysis of Lossless Coupled Transmission Lines in a Non-Homogeneous Dielectric Medium

Abstract: This paper presents an effective method for computing the transient response of an n-conductor, coupled transmission-line system, which is characterized by multiple propagation modes of unequal phase velocities. To derive the computational algorithm, an equivalent circuit consisting of n decoupled transmission lines in conjunction with two congruence transformers was constructed and converted into two disjointed resistive n-ports. It is shown that the electrical behavior of the coupled transmission lines can be completely described by the static capacitance matrices of the conductor system. The experimental result obtained on a three-conductor, microstrip printed circuit was found to be in excellent agreement with the computed result.

Theory of tunneling into interface states

Abstract: A theory of electron tunneling from the metal through the insulator and into the semiconductor of a MIS-structure is developed. Using a square well model, the interface states are represented by a distribution of δ-function potentials, and their wave functions calculated. Following the method of Bardeen, the tunneling matrix element and current are found and used with an extension of Shockley-Read recombination theory to determine a tunnelling time constant, τ To , similar to the surface recombination time constant, τ. Small signal solutions are calculated and presented in the form of equivalent circuits. For a single level state the equivalent circuit consists of the thick insulator, non-tunneling MIS-capacitor plus a tunneling current, j 1 , injected from the metal into the midpoint of the recombination RC circuit. j 1 is made up of three terms caused by modulation of the effective barrier height, and by modulation of the metal and trap occupancy functions. For τ To ⪡ τ , the case of an ideal Schottky barrier, the tunneling current is controlled by the recombination time, τ. If τ To > τ , the tunneling limited case, j 1 is controlled by τ To . This case is discussed in detail. The model's current and conductance characteristics are numerically calculated and graphically presented as a function of interface state density and distribution, interface potential, insulator thickness, and a.c. frequency.

Alternating Current Electrical Properties of Highly Doped Insulating Films

Abstract: Metal‐insulator‐metal systems are discussed in which the insulator is highly doped and in which Schottky barriers exist at the metal‐insulator interface. An equivalent circuit for the system is proposed and the ac electrical characteristics derived. It is shown that the capacitance is extremely temperature and frequency dependent. At high frequencies or low temperatures the capacitance is thickness dependent and equal to the geometric capacitance. At low frequencies and high temperatures it is thickness independent and equal to the Schottky barrier capacitance, which is determined by the doping density. Several methods of determining the activation energy of the donor centers from experimental capacitance versus frequency and temperature curves are suggested. The parallel equivalent conductance is also shown to be extremely frequency and temperature sensitive. It is found to have a pronounced maximum in both cases, which increases in magnitude and occurs at higher temperatures the thicker the insulator.

Microwave properties of Schottky-barrier field-effect transistors

Abstract: The microwave properties of silicon Schottky-barrier field-effect transistor(MESFET'S) with a gate-length of one micrometer are investigated. The scattering parameters of the transistors have been measured from 0.1 GHz up to 12 GHz. From the measured data an equivalent circuit is established which consist of an intrinsic transistor and extrinsic elements. Some of the elements of the intrinsic transistor, notably the transconductance, are strongly influenced by the saturation of the drift velocity. Best performance of the intrinsic transistor is obtained with highly doped and thin channels. The measured power-gain is in good agreement with theoretical values deduced from the equivalent circuit. The best device has a maximum frequency of oscillation fmax of 12 GHz. The investigation reveals that the extrinsic elements, especially the resistance of the gate-metallization and the gate-pad parasitics, degrade the power-gain considerably. Without them a value of fmax close to 20 GHz is predicted.

Physical model for burst noise in semiconductor devices

Abstract: A physical model for burst noise in p−n junction devices is presented. It is proposed that burst noise results when the current through a defect is modulated by a change in the charge state of a single recombination-generation center located adjacent to the defect. The burst noise amplitude and pulse widths are related to the basic properties of the recombination-generation center and the defect. The model leads to a simple interpretation of the equivalent circuit for diodes which exhibit this type of noise.

Square-wave analysis of skin impedance.

Abstract: A method is described for studying skin impedance phenomena, based on analysis of waveforms of current through the skin produced by square voltage pulses. In several experiments, the method is used to provide data relevant to the choice of an appropriate equivalent circuit for skin. Removal of the stratum corneum eliminates the parallel resistive and capacitative elements, and slightly reduces the series or ‘ohmic’ resistance. During healing the source of skin potential recovers before the other electrodermal parameters have returned to normal. The relationship of these parameters to electrode area, current density, and site temperature is studied. It is argued that the capacitance of skin may not vary with the frequency of the measuring current, in contrast to traditional views. The main purpose of the paper is to illustrate and advocate the square-wave method of analysis.

Simplified Analysis of Coupled Transmission-Line Networks

Abstract: A relatively simple method is presented for analyzing coupled transmission-line networks by using network graphs and graph transformations. The network graph symbolism is easy to draw and to manipulate. All the graphs consist only of inductor, capacitor, and transformer symbols, and straight lines, which represent unit elements. The method of analysis is illustrated by several two-wire-line and multiwire-line examples. Also presented are several new useful transmission-line transformations and a graph equivalent for the general coupled transmission-line network. The graph-transformation method has four principal advantages: 1) explicit open-wire-line equivalent circuits of coupled line networks can be obtained relatively easily and without knowledge of network synthesis techniques; 2) the form of equivalent circuits can often be obtained without using any algebra; 3) at each step of the analysis, a positive-real network in graph form is available; consequently, in many analysis problems several equivalent circuits for the same network are derived; and 4) multiport networks are as easily dealt with as two-port networks.

Simulation of AC System Impedance in HVDC System Studies

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

Electrical and Mechanical Loading of a Piezoelectric Surface Supporting Surface Waves

Abstract: The influence of surface loading on the propagation of surface waves on a piezoelectric substrate is analyzed. Both mechanical and electrical loading are described by means of a simple first‐order perturbation theory. General formulas for the perturbation of the surface‐wave phase velocity caused by deposition of a uniform thin film or by electrical interaction with an adjacent conducting or semiconducting medium are developed. The scattering of surface waves from discrete strips is also analyzed. Results from scattering and wave‐propagation analysis are utilized to describe the interdigital surface‐wave transducer. An equivalent circuit for a basic transducer element is developed, and the total transducer is analyzed by means of transmission‐line theory applied to a network of cascade‐coupled elements. The effect of electrode mass loading is specially treated, and the results are compared with measurements made on a Y‐cut Z‐propagation LiNbO3 crystal.

Microwave Equivalent-Circuit Parameters of Gunn-Effect-Device Packages

Abstract: The packages in which Gunn-effect devices are commonly mounted are found to have parasitic reactances which are significant at X-band. An accurate knowledge of the package equivalent circuit is essential. Precision measurements in a coaxial system have therefore been made over a very wide range of frequencies, and a consistent equivalent circuit has been derived. This differs somewhat from previously assumed equivalent circuits. The experimental results are analyzed in terms of a theoretical model based on the known structure of the package.

Isolation and transforming circuit

Abstract: A combination isolating and transforming circuit which consists primarily of three sections, a peak current limiting section and current and voltage isolation sections which electrically isolate the control circuit from the circuit being monitored. The input from the circuit to be measured, either from a bus bar or from a shunt resistor, drives an operational amplifier which controls a variable frequency oscillator. The pulses from this oscillator drive a single-shot multivibrator, the output of which is fed back to the operational amplifier as a negative feedback system. The operational amplifier, in turn, changes its output to adjust the frequency of the oscillator so that duty cycle of the output of the multivibrator has an on-off ratio as a function only of the input signal to the circuit. As this multivibrator switches positive and negative, the pulses are coupled through a pulse transformer to the non-isolated portion of the circuit. This latter circuit includes a flip flop which is driven to follow the multivibrator to produce the same duty-cycle signal in the output circuit as was generated in the circuit electrically connected to the load. The output circuit includes a second operational amplifier which scales and averages this duty-cycle signal and recreates a direct current signal proportional to the incoming voltage. The circuit thus results in a conversion from a voltage to a duty cycle and back to a voltage with very low drift.

Inductive Coupling of Josephson Junctions to External Circuits

Abstract: The inductive coupling between a Josephson junction and a superconducting stripline is calculated. In the overlapping region they share a superconducting film, the structure having superconducting (S) and insulating layers (I) sandwiched S—I—S—I—S. The coupling arises from the magnetic field penetration through the common superconductor. An equivalent circuit representation is exhibited which has the same modes and coupling as the original system. Using the circuit analog, the power transfer is calculated for several cases of interest: (a) power is radiated outward in the stripline from a biased junction and (b) power is absorbed by the junction from a source coupled to the stripline. The criterion for matching the tunnel junction to the stripline is discussed.

Circuit Analysis of Waveguide-Cavity Gunn-Effect Oscillator

Abstract: A simple equivalent circuit using lumped constant elements is developed for the post-coupled-waveguide-cavity Gunn effect oscillator. The circuit is used to predict with high accuracy the tuning characteristics, loaded Q, and mode-switching frequencies for the oscillator. Characteristic capacitance and negative-resistance values for low-n/sub 0/L-product CW devices are also presented.

A thin-film inductance using thermal filaments

Abstract: A particular thin-film structure is analyzed to determine the conditions for thermal filament formation. Assuming that these conditions are satisfied and that the structure is electrically biased so that a thermal filament exists, the current-voltage characteristic and small-signal equivalent circuit for a general conductivity-temperature characteristic in the thin film are determined. It is shown that an abrupt or discontinuous change in conductivity with temperature of the type observed in materials exhibiting semiconductor-metal transitions is not necessary to obtain thermal filaments. It is also shown that if there is no thermal hysteresis in the conductivity -temperature characteristic of the thin film, the filament equivalent circuit for the particular structure analyzed is closely approximated by a resistance in parallel with an inductance. The thin-film prop. erties required for this inductance to be independent of both the ambient temperature and the bias current are defined. If thermal hysteresis exists, the analysis shows that small-signal distortions occur, the inductance will become frequency dependent at low frequencies, and a nonlinear resistance must be added to the equivalent circuit in series with the inductance. Measurements on this structure using VO 2 as the thin-film material are presented and discussed, and are shown to verify the conclusions based on the analysis.

A Compact Broad-Band Thin-Film Lumped-Element L-Band Circulator

Abstract: Impedance matrices including magnetic losses are developed for a number of lumped-element ferrite-loaded symmetrical three-port junctions. The scattering matrix eigenvalues corresponding to these matrices are determined as functions of frequency and circuit parameters and are used to analyze these three-ports with emphasis on their properties as circulators. A very compact broad-band thin-film lumped-element circulator is derived from the idealized equivalent circuit. An experimental model approximately represented by this circuit is shown to have a 20-dB isolation bandwidth of greater than 30 percent with an insertion loss of less than 0.6 decibel. A switchable circulator which requires no magnetic-field switching is treated using this same analytical approach. It is suggested that this type of analysis together with additional experimental refinement of equivalent circuits will lead eventually to a computerized design of lumped-element circulators.

Performance potential of high-frequency heterojunction transistors

Abstract: Assuming a state-of-the-art microwave planar geometry, the maximum frequency of oscillation has been calculated for GaAs-Ge heterojunction transistors utilizing either doped or high-resistivity space-charge-limited emitters. This is compared with a Ge homojunction transistor of the same geometry. A detailed equivalent circuit is used which accounts for the parasitics of the chip. It is shown that if chip parasitics are neglected, GaA-Ge devices should outperform Ge devices by about 4 to 1 in power gain. In the geometry assumed, however both heterojunction and homojunction transistors are limited by wafer parasitics, particularly base contact resistance. The calculated figures of merit of the two types of devices are therefore quite similar.

Testing of nonlinear circuits by comparison with a reference simulation with means to eliminate errors caused by critical race conditions

Abstract: A method and apparatus for testing complex nonlinear binary circuits by applying a bilevel signal pattern, particularly a random pattern, to both a plurality of inputs in the circuit being tested and to a corresponding plurality of inputs in a reference simulation of said circuit, and for comparing corresponding outputs from the circuit and the simulation.

N-Way TEM-Mode Broad-Band Power Dividers

Abstract: An integrative graphical method of designing a broadband TEM-mode power divider of N output ports is presented. Each branch of the divider's circuit consists of cascaded transmission-line segments, and the corresponding segments of each branch are connected by resistors to a common junction. These resistors absorb the reflected signals due to mismatch at any of the output ports; they are therefore isolated from one another. The symmetry of this circuit permits the use of the method of even- and odd-mode excitations at the output ports. It was found that the even-mode circuit is the same as for a stepped-impedance transformer, which is well known. The odd-mode circuit lends itself to the determination of the isolation resistors using the iterative graphical procedure on a Smith chart. Numerical values of the isolation conductance for dividers of bandwidths up to 10:1, the maximum input VSWR, and the minimum isolation among the output ports are given.

The silicon solar cell as a photometric detector.

Abstract: Early in their development, silicon solar cells were recognized to have characteristics desirable for photometric detectors. It is therefore surprising that their use in this way has not become more widespread. Results of an investigation to establish more completely the photometric capabilities of these cells are presented in this paper. An equivalent circuit model is used to predict performance from basic cell parameters and the dependence on illumination level and load impedance is established. When load impedance is low, silicon cells have a small temperature coefficient and the cell current is accurately proportional to illumination. With high impedance loads and high illumination levels, the cell voltage is logarithmically related to illumination and the temperature sensitivity is approximately an order of magnitude greater. Variation of spectral response between unselected cells from the same manufacturer was found to be considerably less than that typically measured for unselected phototubes.

A lumped model for characterizing single and multiple domain propagation in bulk GaAs

Abstract: A study of the nucleation and propagation of single and multiple domains in n-GaAs has led to the development of a circuit oriented lumped model for the representation of this phenomenon. The lumped bulk model accurately predicts device behavior during domain nucleation, modulation and quenching, without indicating domain position within the bulk. The proposed equivalent circuit is developed in a logical fashion and its implications are pursued in some detail. Device studies with the lumped model have produced results exhibiting exceptional agreement with BULK-D, a digital computer program which determines the electric field and carrier distributions in bulk GaAs from current continuity considerations and Poisson's equation.

Large-Signal Equivalent Circuits of Avalanche Transit-Time Devices

Abstract: A large-signal analysis for IMPATT diodes is derived, which allows carrier multiplication by impact ionization to occur at every point in the diode. Therefore, the operating characteristics of IMPATT diodes with a wide range of realistic doping profiles can be investigated. For a given operating frequency, RF voltage, dc bias current, and doping profile, the admittance, power output, efficiency, bias voltage of a diode can be obtained. An equivalent circuit the diode package, microwave circuit mount and diode, is obtained experimentally. Using this circuit, the admittance of the diode is measured by a reflection-type circuit and an oscillator circuit as a function of the RF voltage, dc bias current, and frequency.

Characterization of avalanche diode TRAPATT oscillators

Abstract: The characteristics of a coaxial avalanche diode oscillator circuit are calculated and compared with experimental results. The circuit admittance, as seen at the diode terminals, is calculated in the frequency domain for "optimally tuned" experimental conditions. The impulse response function of the circuit, as obtained from the transformed admittance, is used to obtain time-evolution solutions of the avalanche diode circuit system. The impulse response is more general than the previously employed differential equation characterization of a lumped element equivalent circuit. The simulation presented of the high-efficiency mode of oscillation allowed no adjustable parameters and is in excellent agreement with experiment. The simulation verifies the original TRAPATT [1] explanation for the high-efficiency mode of oscillation.

Characterization of second-harmonic effects in IMPATT diodes

Abstract: We discuss characterization of the tuned-harmonic mode of operation in IMPATT oscillators, and introduce an equivalent circuit which incorporates the large-signal, “single-frequency” oscillator admittances at the fundamental and second-harmonic frequencies. Complete characterization of this mode is equivalent to specifying the behavior of each of the four elements of the equivalent circuit as functions of the oscillation state variables: fundamental voltage and frequency, second-harmonic voltage and relative phase. Using the approximate large-signal analysis of Blue,1 the values of the equivalent circuit elements are presented, as an example, for a 6-GHz IMPATT diode under a variety of oscillation conditions. This equivalent circuit is used to clarify the role played by the fundamental and second-harmonic, single-frequency oscillator admittances in the tuned-harmonic mode. Using an approximation to the equivalent circuit, we investigate the criteria for stable oscillation of the tuned-harmonic mode. It is found that the stability criteria are in general quite restrictive. For the same 6-GHz germanium diode, the range of stable phase is investigated, as a function of the RF parameters, for certain special cases. It is found to be possible to satisfy the stability criteria for the phase which gives an optimum enhancement of the fundamental power output if certain conditions on the external RF circuit are satisfied.

Impedance and admittance matrices of distributed three-layer N-ports

Abstract: The port impedance and admittance matrices of threelayer structures of linear, passive, isotropic materials are defined and their properties briefly investigated. Discrete equivalent circuit representations are given, together with two examples.

Large-Signal Silicon and Germanium Avalanche-Diode Characteristics

Abstract: A technique for measurement of the large-signal single-frequency microwave amplifier admittance of avalanche diodes is described, and results are presented for silicon and germanium avalanche diodes. Single-frequency amplifier operation can provide a unique characterization of diode-admittance variation with RF drive for diodes operated near the optimum transit angle (the case in which all harmonic voltages are negligibly small compared to the fundamental). Such characterization is useful for predicting diode performance for circuits in which the harmonic voltages are not large enough to have an appreciable effect on the diode admittance at the fundamental frequency. A process of matching quadratic forms to the above admittance data which may be used for calculation of diode terminal admittance and power output is discussed. The usefulness of the measurement technique is illustrated by the agreement of the calculated maximum power output with the measured power output in a single-transformer coaxial circuit. The corresponding circuit admittance may be used for circuit-design purposes and for evaluating variations in diode-assembly techniques. The ability to obtain the diode equivalent circuit as a function of incident power allows studies in the design of the associated semiconductor device. For example, one has the capability of obtaining an accurate single-frequency large-signal model near the optimum transit angle, a model which can be studied without building a circuit. With this model it is possible to carry out optimization procedures at considerable savings of time and money.

Characterization of microwave transistors

Abstract: The design, fabrication and evaluation of double-diffused, epitaxial silicon bipolar microwave transistors are discussed. The design approach is intended to maximize the transducer G T = ¦s fe ¦ 2 , MAG and unilateral U power gains. Shallow impurity profiles ( x E = 2000−3000 A , x C = 3000−4000 A ) and narrow emitter strips (h = 1.5−2.0 μm) provide typical current-gain bandwidth width products fT's > 4 GHz and maximum frequencies of oscillation fMAX's > 6 GHz. The electrical performance of the microwave transistor is described by the s-(scattering) parameters which are derived from the T-small-signal equivalent circuit in terms of the physical device parameters. The behavior of the s-parameters vs. frequency for the common-emitter amplifier is predicted and verified experimentally in the frequency range from 1.0 to 6.0 GHz. The physics of the microwave transistor operation is discussed and the fabrication of double-diffused, epitaxial silicon transistors is presented.

Rms voltmeter and log converter

Abstract: An RMS voltmeter and logarithmic converter using electronic mathematical operators for determining the RMS value and its logarithm of an input signal. A source of electrical signals to be measured is connected to the input of an absolute-value circuit. The output from the absolute-value circuit provides the input to a log converter circuit having an output which provides one of the inputs to a summing circuit. The output from the summing network provides the input to an antilog converter circuit. The output from the antilog converter circuit provides the input to an averaging circuit having its output connected to the input of a second log converter circuit. The output from the second log converter circuit is in circuit with the second input to the summing circuit. One of the two inputs to the summing circuit is scaled by a factor of two to achieve the squaring function required by the converter. In an alternative embodiment, means are disclosed for causing the instrument to operate in either the averaging or in the RMS mode to provide either a linear or logarithmic output. In addition, means are disclosed for selecting the time constant of the averaging circuit to accommodate a wide frequency range for the input signals.