Small-signal impedance of bulk semiconductor amplifier having a nonuniform doping profile

A convenient method for studying the small-signal impedance of a bulk semiconductor amplifier having a nonuniform doping profile is presented. The small-signal impedance is represented as a two-dimensional sum of the interaction impedance which represents the electrical interaction between various sections in the amplifier due to the transport effect. When the diffusion current is negligible, the two-dimensional plot of the magnitude of the interaction impedance shows which part of it is important. The two-dimensional representation may provide a convenient method of synthesizing the doping profile of a bulk semiconductor amplifier which gives a desired impedance characteristic.     

Calculation of growth rates in oscillators

It is shown that the use of a small-signal real-frequency impedance or Q factor to calculate small-signal growth rates in an oscillator circuit is generally incorrect.     

Simulation of Pt-n-p+ silicon punchthrough device

The small-signal impedance of a Pt-n-p+ device has been computed using a model which describes in detail the physical mechanisms in the depleted n region. The small-signal negative resistance is shown to be both frequency- and temperature-dependent at a given bias-current density.     

Negative resistance in p-n junctions under avalanche breakdown conditions, part II

The small-signal impedance of the space-charge region of p-n junctions under avalanche breakdown conditions is calculated using reasonably realistic dependences of electron and hole ionization rates and drift velocities upon electric field. Two structures are analyzed: one is p⁺νn⁺structure which has a fairly uniform distribution of avalanche multiplication, and the other is a singly diffused junction which is a hybrid of an abrupt and a linear graded junction. Both structures show negative resistance when the transit time of carriers becomes appreciable. A computer program was evolved which requires, as input, the impurity profile and field dependences of ionization rates and drift velocities. The program first calculates the dc field and electron and hole currents and then solves the ac small-signal problem. Both the ac small-signal impedance and theQof the diode are calculated.     

Three-step impedance criterion for small-signal stability analysis in two-stage DC distributed power systems

Small-signal stability analysis methods based on an impedance criterion originate from the minor loop gain method and are gradually utilized in two-stage DC distributed power systems. In this paper, we conclude that the impedance criterion directly dependent on output impedance Z/sub o/(s) of the source subsystem and input impedance Z/sub i/(s) of the load subsystem is possible but gives an incorrect stability analysis for systems with a regulated source subsystem. Through introducing a mapped pure impedance of the load subsystems and the preliminary system, we develop a general three-step impedance criterion, with which a correct small-signal stability analysis can be guaranteed, regardless of the type of source subsystem. Furthermore, we introduce the application of the three-step impedance criterion in two small-signal stability analysis cases and utilize it in an example system to predict the stability shift process arising from the variation on the load resistance and input voltage value.     

The small-signal inductive effect in a long P-I-N diode

The small-signal impedance of the forward-biased p-i-n diode has been calculated. It is found that, for a certain range of bias voltages, the impedance of the intrinsic region can be approximated by a parallel combination of resistance and inductance. If the intrinsic region is sufficiently long the junction impedance becomes negligible in comparision to the i-region impedance and a high Q inductor results at low frequencies. Values of Q up to 18 are calculated.     

A New Extraction Technique for the Complete Small-Signal Equivalent-Circuit Model of InGaP/GaAs HBT Including Base Contact Impedance and AC Current Crowding Effect

In this paper, both ac current crowding and base contact impedance are considered and included in the T-type small-signal equivalent circuit of InGaP/GaAs heterojunction bipolar transistors. The ac current crowding effect and base contact impedance are modeled as a parallel$RC$circuit, respectively. Devices parameters of the equivalent circuit are obtained by a new parameters extraction technique. The technique is to directly analyze the two-port parameters of multibias conditions (cutoff-bias, open-collector, and active-bias modes). The parallel capacitances ($C_B$and$C_ bi$), base resistances ($R_B$and$R_ bi$), and base inductance$(L_B)$are especially determined under the active-bias mode without numerical optimization. In addition, the small-signal equivalent circuits of cutoff-bias and open-collector modes are directly derived from the active-bias mode circuit for consistency. By considering base contact impedance and intrinsic base impedance effects in the presented small-signal equivalent circuit, the calculated$S$-parameters agree well with the measured$S$-parameters. The observed difference in the slope for the unilateral power gain$(U)$versus frequency at high frequency is mainly attributed to the ac emitter current crowding effect and well modeled in this study.     

A.C. response of a saturated ionisation chamber

The small-signal impedance between the electrodes of an ionisation chamber is studied over a range of frequency and ionisation. The impedance is approximately that of an equivalent circuit which has one RC combination for each group of ions in the chamber. More accurate formulas are given. Experimental results support the theory.     

Measurement of differential carrier lifetime in vertical-cavitysurface-emitting lasers

Measurements of differential carrier lifetimes on gain-guided proton-implanted vertical-cavity surface-emitting lasers with device size as a parameter are reported. The lifetimes were obtained from laser impedance measurements and from small-signal modulation optical response at subthreshold currents. A simple small-signal equivalent circuit was used to correct the optical data and to extract the carrier lifetimes from the impedance data. Carrier lifetimes ranged from 4.2 ns at 0.04 mA, to about 0.6 ns at a bias close to threshold. The measured carrier lifetimes were used to calculate the corresponding threshold carrier density (n_th~6×10¹⁸ cm^-3) and recombination parameters     

Electronic tuning effects in the read microwave avalanche diode

Read's theory of the negative-resistance avalanche diode has been examined in detail for the small-signal case. The space-charge wave approach has been used in the analysis leading directly to a simple equivalent circuit and a general expression for the small-signal impedance which includes the significant design and operating parameters. The theory indicates that strong tuning effects will occur through variation of the dc avalanche current. This has been verified experimentally.     

An analysis of small-signal and large-signal base resistances forsubmicrometer BJT's

Small-signal and large-signal base resistances for submicrometer BJT's have been analyzed in detail by using a two-dimensional device simulator. It has been clarified that the small-signal base resistance cannot be obtained from the input impedance semicircle in the complex plane accurately due to the effect of the emitter resistance at low frequencies, and also due to the reduction of the base-emitter junction resistance and the diffusion capacitance at high frequencies. A new method for extracting an accurate value of the small-signal base resistance is proposed. The extracted small-signal base resistance not only differed from the large-signal base resistance extracted from the dc characteristics of a BJT, but also agreed with the differential resistance. It has been shown that, for a 0.6 μm emitter-width BJT, the measured value of the small-signal base resistance is less than half that of the large-signal base resistance in the bias region in which actual BJT circuits operate     

Stabilizing effects for the supercritical GaAs n+nn+-transferred electron amplifier

In this paper effects of importance for the stabilization of supercritical n⁺nn⁺ GaAs transferred electron devices are considered. By small-signal impedance calculations and measurements it is shown that doping- as well as temperature gradients of correct polarity reduce the device negative resistance and enhance stability. It is also found that an increasing doping density reduces the negative resistance. Finally it is demonstrated that relaxation effects have a profound influence on the impedance, and that such effects have to be included in a small-signal analysis in order to give reasonable agreement with measurements.     

State-Space Analysis of General IMPATT Diode Small-Signal Lumped Models

The development of a lumped model for small-signal carrier-field interactions in an IMPATT diode results in a set of state equations. Using state-space analysis techniques, the equations are solved for the small-signal impedance of a general IMPATT diode as a function of dc bias current and frequency. Read, p-n, and p-i-n diodes are studied using realistic values for saturation carrier velocities and carrier-ionization rates. Curves indicating the influence of diode physical properties on the small-signal impedance are presented. By combining state equations describing the behavior of the external microwave circuit with the diode state equations, the small-signal oscillation frequency and threshold dc bias current of a coaxial IMPATT oscillator are determined.     

Monolithic millimetre-wave oscillator using a transmission lineperiodically loaded by QWITT diodes

A small-signal analysis of a travelling-wave structure implemented by periodically loading a parallel-plate waveguide with either resonant tunnelling or QWITT diodes is presented. A small-signal equivalent circuits is used to determine the diode impedance as a function of frequency. The periodicity of the structure, i.e. the distance between adjacent diodes, determines the oscillation (resonant) frequency of the circuit. The analysis shows that change in the oscillation frequency through variation in the design width and thickness of the waveguide is minimal. The physical dimensions of the waveguide facilitate monolithic fabrication of the oscillator circuit     

Transit-time negative resistance in bulk Si structures subjected to avalanche injection

A small-signal analytical model is developed for a bulk silicon device subjected to avalanche multiplication induced by space-charge effects. Results show that transit-time negative resistance may exist, provided the solid is biased near the onset of the dc negative resistance or above it; this ac negative resistance is into the microwave range for practical devices. The main features of this phenomenon and the differences with respect to IMPATT diodes are pointed out by using suitable approximate expressions which can help in finding the overall frequency behavior. A check of the preceding analysis by a computer solution of the small-signal impedance has also been performed.     

Stabilisation of transferred-electron amplifiers with large n0L products

The small-signal stability of a transferred-electron device (t.e.d.) driven with a voltage generator of finite impedance is discussed. It is shown that the series impedance significantly alters the stability condition. Computations for a resistor in series with the t.e.d. show that the maximum n0L product for stable operation increases with increasing series resistance. The practical implications of this result are discussed.     

Electric instability in multibarrier heterostructures: Features of the RF impedance

By mathematical simulation of the electric conduction in multibarrier heterostructures, static voltage-current characteristics (VCCs) whose S-shape is indicative of the corresponding electric instability have been obtained. In order to analyze the dynamic parameters of this instability, an analytical model of the instability under investigation has been constructed with the use of the known approximations of semiconductor physics. The static version of the analytical model also provides an S-shaped VCC that is close to the corresponding results of the numerical simulation. With this closeness considered as a confirmation of the validity of the developed analytical model, the small-signal version of this model is generalized to the case of a harmonic electrical disturbance. A clear physical interpretation of the instability under consideration in terms of a positive feedback in a unit cell of the multibarrier heterostructures under study is proposed. The resulting formula for the frequency dependence of the small-signal impedance shows that the dynamic impedance is negative up to terahertz frequencies.     

Small-signal gain performance of the permeable base transistor at EHF

The small-signal amplifier performance at 40.5 GHz is reported for a GaAs permeable base transistor (PBT) having a base grating of 3200-Å periodicity and 1-mm periphery. The device was embedded in a microstrip circuit with appropriate matching networks and biased for optimal small-signal gain with Vbe= 0.2 V, Vce= 2.0 V, and Ice= 59 mA. The prototype amplifier achieved 11 dB of stable gain at 40.5 GHz. The circuit design was facilitated by the moderate impedance levels and highly unilateral nature of the PBT.     

A generalized analytical model for the quantum well injectiontransit time diode

A generalized small-signal model of the quantum well injection transit time (QWITT) diode derived from the authors' previous large-signal model (see. ibid., vol.35, p.2315-2322, Dec. 1987), which includes not only the carrier space-charge effects but also the velocity transient effects and the carrier diffusion effects is presented. Simple closed forms for the device impedance have been obtained for efficient computation, where only one-dimensional integrations are required. It can be applied to any fashion of time dependence of the velocity transient and diffusivity transient, adopting a Gaussian form for the spatial profile of injected carriers. Using the formulas, the small-signal behavior and the design criteria for the QWITT diode are analyzed. Large-signal impedance of the device can also be estimated by the formulas