Large-signal Behavior Research Articles

The initial transient behavior of a thermoelectric generator

Efficiency and steady-state behavior of thermoelectric devices have been treated in the literature.1?3 More recently, considerable work has been done on the transient behavior of incremental variations about a quiescent operating point.4 The procedure used avoids the inherent nonlinearities of the problem by creating a linearized mathematical model, and it can be extended to many problems of the small-signal case. However, there are certain problems which this method will not handle, the main one of which is large-signal dynamic behavior. A particularly important example is the problem of the start-up transient of a thermoelectric generator under load, which is discussed in this paper.

Recombination Properties of Bombardment Defects in Semiconductors

The theory of recombination via defects having energy levels in the forbidden gap is reviewed. Emphasis is given to those aspects which complicate interpretation of lifetime data, such as the inherent difference between steady state and transient measurements, large-signal behavior, competing recombination mechanisms, trapping, the possible existence of strongly temperature-dependent cross sections, and the properties of multilevel defects. A summary of the known recombination properties of bombardment-produced defects is given.

Silicon transistor performance in a chopper application

THE AVAILABILITY of silicon transistors with low saturation voltages has made possible the development of low-level transistor choppers that are capable of operating over the temperature range of —50 to 150 C (degrees centigrade) with little change in over-all performance. To understand adequately the behavior of silicon transistors in a chopper type of application it is necessary to review the large-signal behavior of junction transistors.

An experimental study of large-signal behaviour in M-type valves in the presence of space charge by the use of an analogue method

The paper is concerned with the use of a new analogue method for the study of the high-frequency bunching in an electron beam in interaction with a slow wave in crossed electric and magnetic fields.For an observer moving at the same velocity and in the same direction as the slow wave, supposed of constant amplitude (case of the magnetron), the electric field of the wave appears as purely static; for this observer, the high-frequency motion in the beam is not modified; and a drift of the total beam parallel to the magnetic field does not introduce any new force or bring any change to the transverse motions of the electrons.The method consists in reconstructing artificially in the laboratory frame of reference the observations made in the moving frame. This is achieved by using a flat or hollow beam subjected to electrostatic fields which simulate the r.f. slow wave and drift parallel to the applied magnetic field (O-type beam). The electrons are intercepted by a fluorescent screen on which the image of the bunching is displayed.

Discussion on “An experimental study of large-signal behaviour in M-type valves in the presence of space charge by the use of an analogue method”

Discussion on “An experimental study of large-signal behaviour in M-type valves in the presence of space charge by the use of an analogue method”

Experiments on the Photomagnetoelectric Effect in Germanium

The photomagnetoelectric (PME) effect in germanium has been investigated over a wide range of light intensity, in both $n$- and $p$-type material. Measurements of PME short-circuit current in conjunction with relative conductance increase agree well with van Roosbroeck's recently developed theory of the PME effect. The predicted large-signal behavior of ambipolar excess-carrier diffusivity is verified. Surface recombination velocities for different surface treatments have been determined with slabs of thicknesses appreciably smaller than a diffusion length. Volume lifetimes have been determined with thicker slabs having high-recombination-velocity dark surfaces. These lifetimes are in substantial agreement with those determined for the same samples by the photoconductivity-decay method.

The Large-Signal Behavior of Crossed-Field Traveling-Wave Devices

A large-signal theory for the interaction between a slow wave and a beam of electrons traveling in crossed dc electric and magnetic fields is formulated. The adiabatic equations of motion are used, space-charge forces are neglected, but phase focusing by the rf field and loss of the beam at the anode and sole plate are taken into account. The limits of validity of the conventional small-signal theory are obtained, and an analog computer is employed to follow the interaction to power saturation. Results are presented for a forward-wave amplifier, backward-wave amplifier, and backward-wave oscillator. It is shown that for very short lengths the backward-wave amplifier may give superior results to the equivalent forward-wave amplifier but that otherwise greater gain and efficiency can be obtained with a forward-wave amplifier. However, it is shown that there is a mode of operation for a backward-wave tube equivalent to an oscillator started by and then locked to the input signal, a condition unlike anything obtained in the equivalent longitudinal twt. Also, it is shown that in a forward-wave or backward-wave tube, the gain is dependent on the input signal and may increase as the input signal level is increased. However, it is apparent that this type of device has inherently a low gain, especially when designed for high efficiency. Consequently, some suggestions which have been made for improving this deficiency are examined.

Large signal behavior of high power traveling-wave amplifiers

The results of an experimental investigation on the large signal behavior of a kilowatt power level helix type traveling-wave amplifier tube are presented. Operation with and without attenuators was investigated using a movable electromagnetic probe to measure power level along the tube. Quite different effects of drive power and beam voltage on the saturation level were found for operation with and without attenuators. The maximum power level is lower for attenuator operation. Also, power levels do not continue to increase with increasing beam voltage and drive power. In contrast, attenuator-less operation produces the highest efficiency, and the power levels continue to rise with increasing beam voltage and drive power. Conversion efficiencies as high as 25 per cent are obtained with an attenuator and as high as 40 per cent without an attenuator. Efficiency calculations based on small-signal theory can be made to agree reasonably well with the experimental attenuator-less operation efficiencies by assuming an appropriate ratio of the ac component of beam current to the dc component of beam current, i/I 0 .

A Large Signal Theory or Traveling-Wave Amplifiers

The large-signal or nonlinear behavior of the traveling-wave amplifier is calculated in this paper by numerically integrating a set of equations of motion, which is essentially that of Nordsieck, but includes the space-charge repulsion between the electrons. The calculations were made assuming a loss-free circuit and a small coupling between the circuit and the beam. A method of computing the space-charge field, by summing the forces between the electrons, is fully described. It is found that in the large signal theory a parameter A is required in addition to the space-charge parameter QC. 1/k measures the range of action of the space-charge forces and is proportional to the beam radius. The other parameters including QC are those defined in the linear theory. Twenty cases covering useful ranges of the design and the operating parameters have been computed. The numerical integrations were done by type 701 IBM equipment. The amplitude and the phase of the circuit wave as functions of the distance are given for all the cases. It is found that the limiting efficiency increases with the electron injection speed, as found by Nordsieck, and increases with the space-charge parameter QC when QC is small, but decreases rapidly for larger QC. The efficiency also increases with the beam radius, or I/k, provided the assumption that the field and the current are uniformly distributed over the cross section is valid. Finally the electron motion in high level operation is analyzed. The effect of QC and of k on efficiency are explained.

Large-Signal Behavior of Junction Transistors

In the consideration of the junction transistor as a switch there are three characteristics of primary interest, the open impedance, the closed impedance, and the switching-time. A generalized two-terminal-pair theory of junction transistors is presented which is applicable, on a dc basis, in all regions of operation. Using this theory, the open and closed impedances of the transistor switch are expressible in terms of easily measurable transistor parameters. For the ideal transistor these parameters are the saturation currents of the emitter and collector junctions and the normal and inverted alphas. The transition of the transistor switch from open to closed, or vice versa, is discussed, including the effects of minority carrier storage. This transition can be expressed in analytic form in terms of the alphas and the normal and inverted alpha cut-off frequencies.

Theory of the Large Signal Behavior of Traveling-Wave Amplifiers

We present results of calculations on the amplification, phase distortion, and harmonic content in an idealized traveling-wave amplifier when excited to levels beyond those for which the device behaves linearly. The idealization consists mainly of neglecting the action on the electron beam of radio-frequency fields due to the space charge in the beam. The limiting efficiency and the phase distortion are given for various values of the beam-to-circuit coupling parameter and of the electron injection velocity. The relative harmonic content of the beam is given to the fifth harmonic frequency, inclusive. The calculations were performed by numerically integrating the equations of motion of typical electrons entering the tube at equal intervals of initial phase. Most of the numerical work was done with IBM equipment, some with desk calculators, and in one case, on the Bell Laboratories relay computer. The results are presented almost entirely graphically, and the reader is referred to figures in main body of the paper for quantitative information.