A Quasi-Linear Approach to the Design of Microwave Transistor Power Amplifiers (Short Papers)

A method of large-signal transistor characterization and power amplifier design is described which allows the designer to predict the load and source terminations required for optimum added-power circuit efficiency, and to see graphically how efficiency and power gain change as a function of the load termination. Experimental results obtained with a 1-W bipolar junction transistor (BJT) amplifier at 1.3 GHz are presented.     

Nonlinear Characterization and Modeling of Carbon Nanotube Field-Effect Transistors

We report for the first time to our knowledge large-signal measurements performed at 600 MHz and in time domain on carbon nanotube field-effect transistors (CNFETs) using a large-signal network analyzer. To overcome the very high mismatch between the high CNFET impedance and the basic 50-$Omega$ configuration of the setup, the output impedance was matched with the help of an experimental active load–pull configuration. Hence, we were able to observe under large-signal conditions the nonlinear behavior of CNFETs. Static measurements and continuous-wave ${ S}_{ ij}$-parameter measurements were made for many different biases. They were used in order to determine a nonlinear electrical model that has been validated thanks to the nonlinear measurements. The developed model opens the way for electrical CNFET circuit simulation and nonlinear applications of these devices.      

Accurate pHEMT nonlinear modeling in the presence of low-frequency dispersive effects

Low-frequency (LF) dispersive phenomena due to device self-heating and/or the presence of "traps" (i.e., surface state densities and bulk spurious energy levels) must be taken into account in the large-signal dynamic modeling of III-V field-effect transistors when accurate performance predictions are pursued, since these effects cause important deviations between direct current (dc) and dynamic drain current characteristics. In this paper, a new model for the accurate characterization of these phenomena above their cutoff frequencies is presented, which is able to fully exploit, in the identification phase, large-signal current-voltage (I-V) measurements carried out under quasi-sinusoidal regime using a recently proposed setup. Detailed experimental results for model validation under LF small- and large-signal operating conditions are provided. Furthermore, the I-V model proposed has been embedded into a microwave large-signal pseudomorphic high electron-mobility transistor (pHEMT) model in order to point out the strong influence of LF modeling on the degree of accuracy achievable under millimeter-wave nonlinear operation. Large-signal experimental validation at microwave frequencies is provided for the model proposed, by showing the excellent intermodulation distortion (IMD) predictions obtained with different loads despite the very low power level of IMD products involved. Details on the millimeter-wave IMD measurement setup are also provided. Finally, IMD measurements and simulations on a Ka-band highly linear power amplifier, designed by Ericsson using the Triquint GaAs 0.25-/spl mu/m pHEMT process, are shown for further model validation.     

A parameter extraction method using cutoff measurement for alarge-scale HSPICE model of HBT's

We present an accurate parameter extraction method for the HBT large-signal equivalent circuit model in which several extrinsic parasitics are connected to HSPICE BJT model. The measured Gummel plot are used to extract DC model parameters of HBT using HSPICE. Capacitances are then obtained from S-parameter measurements of the HBTs biased to cutoff. The other parameters are determined from the active device S-parameters. The large-signal modeled Gummel plot and S-parameters show good agreement with the measured ones, respectively     

RF electro-thermal modeling of LDMOSFETs for power-amplifier design

A new approach for the electro-thermal modeling of LDMOSFETs for power-amplifier design that bypasses pulsed-IVs and pulsed-RF measurements is presented in this paper. The existence of low-frequency dispersion in LDMOSFETs is demonstrated by comparing pulsed IVs with iso-thermal IVs. The modeling technique uses iso-thermal IV and microwave measurements to obtain the temperature dependence of small-signal parameters. Optimized tensor-product B-splines, which distribute knots to minimize fitting errors, are used to represent the small-signal parameters and extract the large-signal model as a function of voltages and temperature. The model is implemented on ADS and is verified by simulating and measuring the power harmonics and IMD large-signal performance of a power amplifier. The impact on the model of temperature-dependent drain and gate charge is investigated. The presented model is found to compare well and, in some cases, exceed the existing MET model for LDMOSFETs     

A new approach to the RF power operation of MESFETs

A large-signal numerical model for a MESFET is described which allows investigations of the behavior of these devices at X-band frequencies under large-signal conditions. The authors of numerical simulations are compared with those of the measurements and provide on improved understanding of the behavior of GaAs MESFETs that operate at microwave frequencies and with high power requirements. The analysis yields some indications about the optimum design of these devices     

Large-signal behavioral modeling of nonlinear amplifiers based on load-pull AM-AM and AM-PM measurements

This paper presents an improved behavioral modeling technique that generates large-signal models for nonlinear amplifiers or devices based on load-pull AM-AM and AM-PM measurement datasets. The generated behavioral model characterizes the incident and scattering waveforms at two ports in the frequency domain based on the large-signal scattering function theory. The advantage of this technique is that it is derived entirely from load-pull measurements and provides an analytic method to utilize the load-pull measurements in practical designs. Examples are given to demonstrate the ability of the behavioral models to predict the load-related nonlinearities of the device-under-test.     

Large-signal capabilities and analysis of distributed amplifiers

In the letter experimental results are presented which show that distributed amplifiers can be used for power applications. These results are verified by comparing an analytic model predicted using SPICE 2 simulation with measurements between 0.3 and 12 GHz. It appears that a very broad band can be achieved and that the distributed amplifiers keep their self matching properties even under large-signal operation. Distributed-amplifier characteristics, under small-signal operations, are now well known.1?4 However, recent improvements in GaAs FET technology have created new prospects in large-signal and high-frequency conditions. To our knowledge, although some experimental results have been published3, no theoretical study has been carried out for large-signal conditions. The letter provides such a study.     

Simple formula for AM-detector transfer factor

A simple approximate formula for the AM-detector transfer factor, which is valid for small-signal modes as well as for large-signal ones is proposed. This formula allows one to model analytically (or numerically at the behavioural level) an AM-detector in the large-signal and small-signal modes taking into account the nonlinearity of its transfer factor. Formula validation is made by comparison with measurements and PSPICE simulation data     

Mildly Nonquasi-Static Two-Port Device Model Extraction by Integrating Linearized Large-Signal Vector Measurements

This paper introduces a new procedure, based on linearized large-signal vector measurements, for extracting a nonlinear behavioral model for two-port active microwave devices. The technique is applied to a model structure that assumes a short-term memory condition and is formulated as a parallel connection of a limited number of frequency-weighted static nonlinearities. The proposed method consists of integrating the time-varying linear characterization of the device driven into a nonlinear state by a large signal. The experiment design and measurement setup are based on a large-signal network analyzer and are discussed in detail. In the second portion of this paper, insight is provided on the most meaningful model parameters, along with an extensive independent experimental validation, which considers a GaAs pHEMT as a case study and includes two-tone large-signal data, a wideband code division multiple access signal, bias-dependent -parameters, and dc data.     

Nonlinearity and cross modulation in field-effect transistors

It is shown that present large-signal models are inadequate for cross modulation in field-effect transistors, but the cross-modulation performance can be accurately predicted from a power-series approximation to the measured l.f. transfer characteristic of the device. The cross modulation for typical field- effect transistors is essentially independent of frequency up to about 100 MHz. A large-signal h.f. model of the field-effect transistor is proposed for the prediction of cross modulation and related phenomena at very high frequencies. Computer predictions of cross modulation based on this model agree well with experimental measurements.     

Error-corrected large-signal waveform measurement system combiningnetwork analyzer and sampling oscilloscope capabilities

A large-signal automatic stepped CW waveform measurement system for nonlinear device characterization is presented that combines the high accuracy of a vector network analyzer with the waveform measurement capabilities of a sampling oscilloscope. A large-signal error model and a corresponding coaxial calibration procedure are proposed to describe the systematic errors of the measurement setup. The error parameters and the correction algorithm are independent of the properties of the RF generator. System accuracy is investigated by Schottky diode verification measurements with different offsets from the reference plane. GaAs MESFET reflection and transmission response measurements with error correction extended to the planar device under test (DUT) reference planes are given     

Noise in IMPATT oscillator at large r.f. amplitudes

The noise-current generator of a large-signal IMPATT oscillator is shown to be inversely proportional to the avalanche starting current. This is verified by a numerical study of a large-signal model of an IMPATT oscillator.     

Optimization of Third-Order Intermodulation Product and Output Power from an X-Band MESFET Amplifier Using Volterra Series Analysis

A third-order analysis for accurately predicting large-signal power and intermodulation distortion performance for GaAs MESFET amplifiers is presented. The analysis is carried out for both single- and two-tone input signals using the Volterra series representation and is based only on small-signal measurements. Simple expressions for the nonlinear power gain frequency response, the output power, the gain compression factor, and the third-order intermodulation (IM/sub 3/) power are presented. The major sources of gain compression and intermodulation distortion are identified. Based on the developed nonlinear analysis in conjunction with the device nonlinear model, a systematic procedure for designing a MESFET amplifier under large-signal conditions for optimum output power and IM/sub 3/ performance is proposed. The method utilizes out of band computed matching compensation through a nonlinear model of the amplifier. The accuracy of the device large-signal and IM/sub 3/ distortion characterization and the practicability of the proposed method are illustrated through comparison between measured and predicted results.     

A comprehensive analysis of IMD behavior in RF CMOS power amplifiers

This paper presents a comprehensive analysis of nonlinear intermodulation distortion (IMD) behavior in RF CMOS power amplifiers (PAs). Separate analyses are presented for small- and large-signal operation regimes. Especially, a new, simple, large-signal behavioral IMD analysis method is presented that allows the mechanisms dominant for IMD generation to be identified and their individual contributions to be studied. By combining these analyses, typical IMD versus input power characteristics of MOSFET PAs can be predicted and understood for different classes of operation. Various measurements made on a 950-MHz RF CMOS PA are used to demonstrate typical behavior and validate the proposed theory. Prediction of IMD using a standard CMOS transistor model is also evaluated and is shown to give good agreement with the measurements.     

Straightforward and accurate nonlinear device model parameter-estimation method based on vectorial large-signal measurements

To model nonlinear device behavior at microwave frequencies, accurate large-signal models are required. However, the standard procedure to estimate model parameters is often cumbersome, as it involves several measurement systems (DC, vector network analyzer, etc.). Therefore, we propose a new nonlinear modeling technique, which reduces the complexity of the model generation tremendously and only requires full two-port vectorial large-signal measurements. This paper reports on the results obtained with this new modeling technique applied to both empirical and artificial-neural-network device models. Experimental results are given for high electron-mobility transistors and MOSFETs. We also show that realistic signal excitations can easily be included in the optimization process.     

Consistent modeling of capacitances and transit times of GaAs-based HBTs

This paper investigates how time delays and capacitances observed under small-signal conditions can be consistently accounted for in heterojunction bipolar transistor (HBT) large-signal models. The approach starts at the circuit level by mapping the large-signal equivalent circuit (which consists of charge and current sources) to the well-known small-signal circuit (which consists of capacitances, transit-time, and resistances). It is shown that and how bias dependent charge sources at either pn-junction impact transit-time, base-collector capacitance, and their mutual dependence. It is demonstrated for the example of a GaAs-based HBT that the interrelation of the elements is observed in measurements as predicted. The results of the investigation enhance understanding of HBT model characteristics and provide a criterion to check model consistency.     

RF Characterization of Microwave Power Fet's

The large-signal S-parameter S/sub 22/ and the optimum load for maximum output power are two parameters commonly used in the RF characterization of microwave power FET's. Using a nonlinear circuit model of the device, the dependence on RF power of each of these parameters is investigated. A method is given for computing the optimum load from the Iarge-signal S/sub 22/. Equivalent load-pull data can thus be obtained without the need for load-pull measurements. The gain compression characteristics of the transistor for arbitrary load can be computed from large-signal S/sub 21/, and S/sub 22/ data.     

Modeling and small-signal analysis of controlled on-time boostpower-factor-correction circuit

A large-signal average model for the controlled on-time boost power-factor-correction (PFC) circuit is developed and subsequently linearized, resulting in a small-signal model for the PFC circuit. AC analyses are performed using the small-signal model, revealing new results on the small-signal dynamics of the PFC circuit. The analysis results and model predictions are confirmed with experimental measurements on a 200-W prototype PFC circuit     

A nonlinear integral model of electron devices for HB circuitanalysis

A technology-independent large-signal model of electron devices, the nonlinear integral model (NIM), is proposed. It is rigorously derived from the Volterra series under basic assumptions valid for most types of electron devices and is suitable for harmonic-balance circuit analysis. Unlike other Volterra-based approaches, the validity of the NIM is not limited to weakly nonlinear operation. In particular, the proposed model allows the large-signal dynamic response of an electron device to be directly computed on the basis of data obtained either by conventional measurements or by physics-based numerical simulations. In this perspective, it provides a valuable tool for linking accurate device simulations based on carrier transport physics and harmonic-balance circuit analysis algorithms. Simulations and experimental results, which confirm the validity of the NIM, are also presented