The effects of BJT self-heating on circuit behavior

This study demonstrates the circuit and device conditions under which self-heating can significantly affect bipolar junction transistor (BJT) circuit behavior. Simple quantitative measures are supplied that allow estimation of thermally induced errors in BJT small-signal parameters, based on knowledge of the transistor geometry and its Early voltage. It is shown that errors in output admittance and reverse transadmittance can be significant without much power dissipation, especially when the base and emitter driving impedances are small. Other small-signal parameters are less affected unless the power dissipation becomes significant. Thermal effects in large-signal DC analysis can be significant in precision analog circuits that depend on close transistor matching; such circuits can also exhibit long settling-time tails due to long thermal time constants. ECL (emitter-coupled logic) delay is shown to be insensitive to self-heating. These effects are demonstrated through simulations of a variety of circuits using versions of SPICE modified to include physics-based models for thermal impedance     

A large-signal SOI MOSFET model including dynamic self-heatingbased on small-signal model parameters

A new technique for a large-signal SOI MOSFET model with self-heating is proposed, based on thermal and electrical parameters extracted by fitting a small-signal model to measured s-parameters. A thermal derivative approach is developed to calculate the thermal resistance when the isothermal dc drain conductance is extracted from small-signal fitting. The thermal resistance is used to convert the measured dc current-voltage (I-V) characteristics containing the self-heating effects to the isothermal I-V characteristics needed for the large-signal model. Large-signal pulse and sinusoidal input signals are used to verify the model by measurement, and shown to reproduce the observed large-signal behavior of the devices with great accuracy, especially when two or more thermal time constants are used     

Direct extraction of an empirical temperature-dependent InGaP/GaAs HBT large-signal model

A new empirical InGaP/GaAs heterojunction bipolar transistor (HBT) large-signal model including self-heating effects is presented. The model accounts for the inherent temperature dependence of the device characteristics due to ambient-temperature variation as well as self-heating. The model is accompanied by a simple extraction process, which requires only dc current-voltage (I-V) and multibias-point small-signal S-parameter measurements. All the current-source model parameters, including the self-heating parameters, are directly extracted from measured forward I-V data at different ambient temperatures. The distributed base-collector capacitance and base resistance are extracted from measured S-parameters using a new technique. The extraction procedure is fast, accurate, and inherently minimizes the average squared-error between measured and modeled data, thereby eliminating the need for further optimization following parameter extraction. This modeling methodology is successfully applied to predict the dc, small-signal S-parameter, and output fundamental and harmonic power characteristics of an InGaP/GaAs HBT, over a wide range of temperatures.     

A simplified broad-band large-signal nonquasi-static table-basedFET model

In this paper, a simplified nonquasi-static table-based approach is developed for high-frequency broad-band large-signal field-effect-transistor modeling. As well as low-frequency dispersion, the quadratic frequency dependency of the γ-parameters at high frequencies is taken into account through the use of linear delays. This model is suitable for applications related to nonlinear microwave computer-aided design and can be both easily extracted from dc and S-parameter measurements and implemented in commercially available simulation tools. Model formulation, small-signal, and large-signal validation will be described in this paper. Excellent results are obtained from dc up to the device f_T frequencies, even when f _T is as high as 100 GHz     

Modeling of DC–DC Buck Converters for Large-Signal Frequency Response and Limit Cycles

A zeroth-order-hold equivalent discrete-time model of the buck converter for computing its large-signal frequency response is developed and experimentally verified. It is shown that, with a dc bias and a sinusoidal variation of the input duty cycle, the frequency response of the output voltage from the converter shifts from underdamped behavior to damped behavior with increasing amplitude of the input sinusoid. It is observed that, with a given dc input bias and a given input amplitude beyond the range of the state-space linearized small-signal model, the converter behavior varies from exclusively continuous inductor current mode at low frequencies to behavior with continuous and discontinuous inductor current modes at high frequencies. The use of this sinusoidal input large-signal frequency response in predicting limit cycles induced by feedback of the output voltage using proportional and integral controllers for such converters is studied. Experimental results confirming the use of this large-signal frequency response are presented.     

A distributed model of the junction transistor and its application in the prediction of the emitter-base diode characteristic, base impedance, and pulse response of the device

A distributed model for a junction transistor has been analyzed to include both dc and ac biasing effects in the active base region, with particular emphasis on a small-geometry diffused base planar transistor. For such devices with extremely narrow base width, dc biasing effects cannot be neglected. At high frequencies, the response of these devices is greatly modified by ac biasing effects which are accentuated by the significant dc biasing at large emitter current levels. Two-dimensional current flow under these biasing conditions was studied with a distributed model of the active base region. From such a model, the expressions for emitter-base diode characteristic, small-signal and large-signal base resistance, and complex base impedance valid for high frequencies have been deduced in terms of physical parameters of the devices like the geometry, base resistivity, etc. This equivalent base impedance and an ideal diode with its diffusion and emitter-base transition capacitance constitute the lumped model of the emitter-base region. For any particular frequency, the base impedance can be represented exactly by a parallel RC network. The distributed model can also predict the pulse response of the device more accurately than a lumped model and show the sensitivity of the transient response to the physical parameters mentioned above. Experimental verifications of the theoretical expressions are found to be satisfactory, and limitations of the earlier works are pointed out in regard to present devices.     

A new approach to model nonquasi-static (NQS) effects for MOSFETs. Part II: Small-signal analysis

We present a new approach to model nonquasi-static (NQS) effects in a MOSFET in a small-signal situation. The model derived here is based on the large-signal NQS model previously proposed. The derivation of the small-signal model is presented. The small-signal parameters obtained with this model prove to be accurate up to very high frequencies. An excellent match between the new model and device simulation results has been observed even when the frequency is many times larger than the cutoff frequency.     

An investigation of the power characteristics and saturationmechanisms in HEMTs and MESFETs

A method for large-signal transistor analysis is presented. The method is based on the harmonic-balance approach but makes use of input data from measured S-parameters instead of DC or pulsed DC characteristics and a large-signal equivalent circuit with harmonic elements. The topology of this circuit is nearly identical to commonly used small-signal equivalent circuits; its application allows a detailed interpretation of the computed results, which are very precise due to the use of small-signal S-parameters. The large-signal model is applied to HEMTs and MESFETs. Their saturation mechanisms are investigated and the operational difference is discussed. The importance of including higher harmonic signal components in the large-signal analysis is also shown     

IMPATT diode quasi-static large-signal model

A quasi-static large-signal model of an IMPATT diode with general doping profile is derived. The numerical solution of this model has been implemented in a Fortran IV program which executes economically. This model has been used to analyze large-and small-signal admittances of GaAs double-drift and quasi-Read IMPATT diodes. The small-signal results are in good agreement with calculations done using a linearized small-signal model. The large-signal calculations exhibit power and efficiency saturation when reasonable values of parasitic resistance are included and are in good agreement with experimental GaAs diode performance. The generalized quasi-static formulation simplifies analysis of IMPATT structures with arbitrary doping profiles, specifically those with distributed avalanche zones, by providing the correspondence between these devices and the Read diode model.     

Large-signal theory of the effect of dispersive propagation on theintensity modulation response of semiconductor lasers

We have derived an exact large-signal theory of propagation in a dispersive fiber of an optical wave with sinusoidal amplitude and frequency modulation. This has been applied to the study of large-signal direct-modulation of semiconductor lasers. It is shown that the large-signal response can significantly deviate from the predictions of the small-signal theory. In particular, the improvement in modulation response caused by frequency-to-intensity modulation conversion in propagation that occurs with small-signal modulation is no longer achieved with large-signal modulation, which could affect systems such as dispersion supported transmission. Experimental results confirm our theory     

Some limitations of the power output capability of VHF transistors

The power output capability of a VHF transistor is often limited by the RF saturation resistance. The resistance is set up by the constriction of the emitter current to the geometric edges of the device. The contributions of large current densities and high frequencies to current crowding are discussed in this paper. An extension of this discussion leads to an interpretation of the first-order effects for large-signal high-frequency operation. The RF saturation resistance was measured under large-signal conditions and was found to increase by a factor of 2 over a frequency range of 40-200 MHz. This variation was compared to results obtained by a large-dc small-signal analysis. The resulting deviation was less than 20 percent.     

CW microwave amplification from circuit-stabilized epitaxial GaAs transferred electron devices

Stable c.w. reflection-type amplification at C- X-band frequencies has been obtained from circuit-stabilized GaAs transferred electron devices biased as high as three times threshold. An instantaneous fractional bandwidth exceeding 50% and a small-signal linear gain near 10 dB have been realized with a single device for center frequencies from 5.0 to 9.0 GHz. A -1-dB-gain compression-power output typically above 100 mW and a total saturated power output near 1 W have been measured. A narrow-band doubly tuned amplifier response with a linear gain of 40 dB has also been measured. With a noise figure of 15 dB, these amplifiers have a dynamic range in excess of 90 dB. Highly nonlinear effects have been observed for large-signal narrow-band operation. Both gain and hysteresis effects have been observed. Large-signal effects of bias, frequency, and power level on amplifier performance have been measured.     

Improved small-signal equivalent circuit model and large-signalstate equations for the MOSFET/MODFET wave equation

A simple non-quasi-static small-signal equivalent circuit model is derived for the ideal MOSFET wave equation under the gradual channel approximation. This equivalent circuit represents each Y-parameter by its DC small-signal value shunted by a (trans) capacitor in series with a charging (trans) resistor. A large-signal model for the intrinsic MOSFET is derived by first implementing this RC topology in the time domain. Modified state equations are then introduced to enforce charge conservation. Transient simulations with this approximate large-signal model yield results that are compared with reported exact numerical analysis for the long channel MOSFET for a wide range of bias conditions. This unified small- and large-signal model applies to both the three- and four-terminal intrinsic MOSFET in the region of the channel where the gradual channel approximation is applicable. A non-quasi-static small-signal equivalent circuit for the velocity-saturated MOSFET wave equation is also reported     

Noise in IMPATT diodes: Intrinsic properties

The design of low-noise IMPATT diodes has been aided by theories describing the noise generation under small-signal conditions. A major deficiency in this procedure has existed in that there is no apparent connection between the small-signal behavior and the great increases in the noise observed in large-signal operation. As a remedy a theory has been developed for the noise generation at arbitrary signal levels by using a Read diode model. The theory is based on a linearization technique for calculating the spectrum of homogeneous noise with linear damping resulting in a separation of the large-signal and noise problems. The open-circuit noise voltage increases strongly at high signal levels due to nonlinear parametric interactions and gives rise to a rapid increase in the noise measure as a function of the generated microwave power. Operating parameters are derived that optimize the power-noise ratio. A long intrinsic response time is found to be beneficial in achieving high power as well as low noise. Other factors affecting the design and choice of material for IMPATT diodes are discussed. An important feature of the presented theory is that a complete design optimization with respect to the power-noise characteristics can be carried out provided reliable information exists about the ionization rates and the drift velocities. A simpler alternative is to obtain the physical quantities governing the power-noise behavior from small-signal admittance and noise measurements. Good agreement has been obtained with experimental power-noise measurements by this method. As an application of this procedure a state of the art comparison is given for GaAs, Ge, and Si diodes at 6 GHz.     

RF Amplifier Design with Large-Signal S-Parameters

High-power UHF transistors have been characterized through the use of large-signal S-parameters. These S-parameters have been used successfully to design UHF power amplifiers. Waveform measurements show that due to the Q of the package parasitic, most class C operated UHF power transistors have nearly sinusoidal waveforms at their package terminals. Experimental evidence presented shows that the large-signal S-parameters are relatively independent of power once the device is turned on. These two observations make it possible to extend modified small-signal S-parameter design techniques to large-signal power amplifiers.     

A unified model for single/multifinger HBTs including self-heatingeffects

This paper presents a unified analytical large-signal model that includes self-heating effects. The model is applied to a single-finger AlGaAs/GaAs heterojunction bipolar transistor (HBT) and a multifinger InGaAs/GaAs HBT. The self-heating effect in the HBT is simulated as a feedback from the collector current to the base-emitter voltage. The main advantage of the circuit presented here is that additional analysis of coupling between electrical and thermal circuits is not required, as is the case with the existing models. The small-signal HBT model is implemented based on the S-parameters at multiple frequencies measured at multiple bias points. This model is verified by comparing the measured and simulated S-parameters. The large-signal model is based on the forward Gummel plot and is built over the small-signal model. This model is verified by comparing the simulated and measured dc I-V characteristics     

Investigation of SOI-LDMOS for RF-Power Applications Using Computational Load Pull

Small-signal and computational load-pull simulations are used to investigate the effect of substrate resistivity on efficiency in high-power operation of high-frequency silicon-on-insulator-LDMOS transistors. Identical transistors are studied on substrates with different resistivities. Using computational load pull, their high-power performance is evaluated. The results are compared to previous investigations, relating the off-state output resistance to high-efficiency operation. From the large-signal simulation, an output circuit model based on a load-line match is extracted with parameters traceable from small-signal simulations. It is shown that, albeit high off-state output resistance is a good indication, it is not sufficient for high efficiency in a high-power operation. The bias and frequency dependence of the coupling through the substrate makes a more detailed on-state analysis necessary. It is shown that very low resistivity and high-resistivity SOI substrates both result in a high efficiency at the studied frequency and bias point. It is also shown that a normally doped medium-resistivity substrate results in a significantly lower efficiency.      

Prediction of impact-ionization-induced snap-back in advanced Sin-p-n BJT's by means of a nonlocal analytical model for the avalanchemultiplication factor

The authors point out that when a triangular shape for the electric field in the base-collector space-charge region of an n-p-n Si BJT (bipolar junction transistor) is assumed, the electron mean energy can be calculated analytically from a simplified energy-balance equation. On this basis a nonlocal-impact-ionization model, suitable for computer-aided circuit simulation, has been obtained and used to calculate the output characteristics at constant emitter-base voltage (grounded base) of advanced devices. Provided the experimental bias-dependent value of the base parasitic resistance is accounted for in the device model, the base-collector voltage at which impact-ionization-induced snap-back occurs can be accurately predicted     

有射极电阻的基本电路中双极型晶体三极管工作状态的一种判断方法

本文给出含有射极电阻的基本电路中双极型晶体三极管(BJT)工作状态的一种判断方法。对于有射极电阻的基本电路,如果只知道电路中电阻的阻值、BJT的电流放大倍数β和直流电源的电压值,可以先假设其中的BJT处于放大状态,求出BJT在放大状态下的集电极电流IC或基极电流IB,然后与临界饱和状态下的集电极电流ICS或基极电流IBS比较,如果IC相似文献