Madhu S. Gupta

Power gain in feedback amplifiers, a classic revisited

A tutorial review of a classic paper by Samuel J. Mason (1954) is described. That paper contained the first definition of a unilateral power gain for a linear two-port and the first proof that this grain is invariant with respect to linear lossless reciprocal four-port embeddings, thereby making it useful as a figure of merit intrinsic to the device. In this work, that original paper is brought up to date, a tutorial exposition of its contents is presented in a modern form, and its significance and applications in microwave engineering are discussed. The subsequent advances in the subject area are summarized, so that the original paper can be placed within a broader context and understood with a more general perspective. >

Noise Considerations in Self-Mixing IMPATT-Diode Oscillators for Short-Range Doppler RADAR Applications

The influence of the oscillator noise on the minimum detectable signal of a Doppler RADAR with a self-mixing IMPATT-diode oscillator is evaluated. For very short-range RADARs, it is the AM noise which limits the signal-to-noise ratio and thus the range.

Degradation of power combining efficiency due to variability among signal sources

The power combining efficiency of a symmetric n-way power combiner depends on the degree of imbalance among its input signals. The worst-case efficiency is established for a combiner when its input signal amplitudes and phases are uncertain, but constrained to given ranges. This result is used to deduce the permissible tolerance in the uniformity of components used in power combiner construction, given the maximum acceptable efficiency degradation. >

A nonlinear equivalent circuit for IMPATT diodes

Abstract A lumped nonlinear equivalent circuit is developed for Read-type IMPATT diodes, using the carrier transport equations for the device. The validity of this circuit is not restricted to sinusoidal signal waveforms. It can be used for quantitative calculations of device performance as well as for qualitative predictions of the general features of IMPATT diode behavior. The general equivalent circuit is further simplified for the case of sinusoidal excitation and its application is demonstrated by simple examples.

A simple approximate method of estimating the effect of carrier diffusion in IMPATT diodes

Abstract Most large-signal analyses of IMPATT diodes neglect the diffusion of charge carriers in the drift region. A correction can be introduced to include the effect of diffusion in the negative conductance or the efficiency of the IMPATT diode calculated from such analyses. An approximate method of estimating a simple correction factor is presented using the Read model of the diode.

Thermodynamic limits to nonlinearity: Lossless energy‐storing systems

The nonlinearity of the relationship between the extensive and the intensive variables of an ideal energy‐storing thermodynamic system in equilibrium is expressed in terms of the higher‐order moments of the extensive variable, and is thus shown to have both an upper and a lower bound. The bounds are proportional to the size of the system and for most practical systems the upper bound is more restrictive. As an illustration, the bound is applied to the nonlinearity of varactor diode capacitors, and the lower bound is shown to be far from the presently achieved nonlinearity.

Random walk calculation of diffusion coefficient of hot electrons in two‐valley semiconductors

The electric‐field‐dependent longitudinal diffusion coefficient for charge carriers in a two‐valley semiconductor is calculated by modeling the carrier movement as two simultaneous coupled random walks. The first random walk represents carrier scattering from one valley to another, and the second describes the motion of a carrier within a single valley, with the carrier position in the first walk determining the parameters of the second walk. The calculated intervalley transfer diffusion coefficient Dtr contains earlier calculations of Dtr as special cases. An agreement between calculated and measured low‐field diffusion coefficients for electrons in n‐GaAs at room temperature is obtained when the random time interval that a carrier spends in a valley is assumed to have a gamma distribution.

Conductance fluctuations in mesoscopic conductors at low temperatures

This paper is a tutorial introduction to the subject of conductance fluctuations observed in mesoscopic conductors at low temperatures, and the universal conductance fluctuation (UCF) theory proposed to explain them. The discovery of the fluctuations less than a decade ago has been followed by an intensive flurry of research activity, published almost entirely in the journals of solid-state physics. This paper surveys the subject from the viewpoint of a practising electron device engineer, with bias in favor of intuitive appeal rather than rigor, and should be helpful in understanding the primary literature on the subject. The nature of fluctuations and mesoscopic conduction are briefly introduced. Both theoretical and experimental results from the sizable literature on the subject are summarized here, emphasizing the characteristics of the fluctuations, the conditions under which they are observed, the mechanism of fluctuations, and the range of applicability of the UCF theory. >

Microwave Characterization of Silicon BARITT Diodes Under Large-Signal Conditions

Experimental measurements of the small- and large-signal admittance of a silicon BARITT diode are reported. The structural characteristics of the devices are also reported, so that the results provide a basis for evaluating the Iarge-signal analyses of BARITT diodes. A lumped-element frequency-independent equivalent circuit is proposed to represent the terminal characteristics of the device over a broad-frequency range, and is verified by comparison with the measured admittances. Simple approximations are given to describe the dependence of the device admittance on the three operating point parameters: dc bias current, signal frequency, and RF signal level.

Stability measure for negative-resistance amplifiers

A measure of the stability of reflection-type negative-resistance amplifiers is defined as the distance between the actual driving-point immittance of the active one-port and its value that would cause instability. The measure has a simple physical interpretation and demonstrates the gain-stability trade-off.