RF I-V waveform measurement and engineering systems are now finally enabling practical waveform engineering to be directly undertaken with systems capable of supporting continuous wave stimulus reaching a high level of maturity. On-going research and development activities are presently addressing the multitone requirement. The availability of RF I-V measurement and engineering capability extends the characterization opportunities for both high-frequency/speed transistor technology developers and circuit/system designers; terminal waveforms are the unifying theoretical link between transistor technology, circuit design, and system performance. Design support can involve the direct utilization of such a measurement system in the design investigation/evaluation loop of either power transistor technology or PAs. This eliminates the black box design processes and allows for the development of new intelligent design processes that are completely founded on theoretical waveform analysis. Alternatively, it can also indirectly support the amplifier investigation/evaluation loop by supporting the development or improving the accuracy of nonlinear transistor models or by providing CAD-accessible behavioral or behavioral model parameter datasets. W can now only hope that, triggered by the availability of RF waveform measurement and engineering systems, we will see a renaissance in theoretical waveform mathematical analysis addressing not only power and efficiency but also design sensitivity and linearity.

Practical waveform engineering

Methods and apparatus for calibrating a vector network analyzer (VNA) and characterizing a device under test. In one example, a device fixture including a pair of embedded device adapters provides an interface between a device under test (DUT) with non-coaxial connectors and the coaxial connectors of the VNA, and moves the calibration reference plane from the coaxial connectors of the VNA to a DUT reference plane at the leads/connectors of the DUT. A through fixture having a pair of similar through adapters is used to establish the DUT reference plane and to facilitate characterizing the device adapters such that they can be de-embedded from measurements of the device fixture.

Method and apparatus for calibrating a test system for measuring a device under test

Good transistor models are essential for efficient computer-aided-design (CAD) of nonlinear microwave and RF circuits, monolithic microwave integrated circuits (MMICs), power amplifiers (PAs), and nonlinear RF systems. Increasingly complicated demands of the various semiconductor technologies (e.g., GaAs pHEMTs, InP double heterojunction bipolar transistors (DHBTs), silicon on insulator (SOI), LDMOS, GaN HFETs, etc.), and their applications in terms of power and frequency of operation and complexity of applied signals (e.g., modern communication signals with high peak-toaverage ratios) have placed commensurate requirements on the accuracy and generality of the device models used for design. New semiconductor material systems (e.g., GaN) have been developing at such a fast rate that conventional compact modeling approaches may not be able to keep up. These and other challenges have spawned much research into the advanced nonlinear device modeling techniques that are the focus of this article.

Future Device Modeling Trends

X-parameters are the mathematically correct supersets of S-parameters valid for nonlinear (and linear) components under large-signal (and small-signal) conditions This work presents an automated application combining a nonlinear vector network analyzer (NVNA) instrument with automated load-pull measurements that extends the measurement and extraction of X-parameters over the entire Smith Chart The augmented X-parameter data include magnitude and phase as nonlinear functions of power, bias, and load, at each harmonic generated by the device and measured by the NVNA The X-parameters can be immediately used in a nonlinear simulator for complex microwave circuit analysis and design This capability extends the applicability of measurement-based X-parameters to highly mismatched environments, such as high-power and multi-stage amplifiers, and power transistors designed to work far from 50 ohms It provides a powerful and general technology-independent alternative, with improved accuracy and speed, to traditional large-signal device models which are typically slow to develop and typically extrapolate large-signal operation from small-signal and DC measurements

/pdf/load-pull-nvna-enhanced-x-parameters-for-pa-designs-with-236xca2nn5.pdf

Load-pull + NVNA = enhanced X-parameters for PA designs with high mismatch and technology-independent large-signal device models

Power amplifier (PA) behavior is inextricably linked to the characteristics of the transistors underlying the PA design. All transistors exhibit some degree of memory effects, which must therefore be taken into account in the modeling and design of these PAs. In this paper, we will present new trends for the characterization, device modeling, and behavioral modeling of power transistors and amplifiers with strong memory effects. First the impact of thermal and electrical memory effects upon the performance of a transistor will be revealed by comparing continuous wave and pulsed RF large-signal measurements. Pulsed-RF load-pull from the proper hot bias condition yields a more realistic representation of the peak power response of transistors excited with modulated signals with high peak-to-average power ratio. Next, an advanced device modeling method based on large-signal data from a modern nonlinear vector network analyzer instrument, coupled with modeling approaches based on advanced artificial neural network technology, will be presented. This approach enables the generation of accurate and robust time-domain nonlinear simulation models of modern transistors that exhibit significant memory effects. Finally an extension of the X-parameter (X-parameter is a trademark of Agilent Technologies Inc.) behavioral model to account for model memory effects of RF and microwave components will be presented. The approach can be used to model hard nonlinear behavior and long-term memory effects and is valid for all possible modulation formats for all possible peak-to-average ratios and for a wide range of modulation bandwidths. Both the device and behavioral models have been validated by measurements and are implemented in a commercial nonlinear circuit simulator.

/pdf/new-trends-for-the-nonlinear-measurement-and-modeling-of-3itq2ogw0j.pdf

New Trends for the Nonlinear Measurement and Modeling of High-Power RF Transistors and Amplifiers With Memory Effects

A new unified theory and methodology is presented to characterize and model long-term memory effects of microwave components by extending the Poly-Harmonic Distortion (PHD) Model to include dynamics that are identified from pulsed envelope X-parameter measurements on an NVNA. The model correctly predicts the transient RF response to time-varying RF excitations including the asymmetry between off-to-on and on-to-off switched behavior as well as responses to conventional wide-bandwidth communication signals that excite long-term memory effects in power amplifiers. The model is implemented in the ADS circuit envelope simulator.

Extension of X-parameters to include long-term dynamic memory effects

X-parameters, also referred to as the parameters of the Poly-Harmonic Distortion (PHD) nonlinear behavioral model, have been introduced as the natural extension of S-parameters to nonlinear devices under large-signal drive [1]-[3]. This paper describes a new approach to X-parameter characterization and nonlinear simulation - including large-signal experimental model validation - of a commercially available GSM amplifier. A specially configured Nonlinear Vector Network Analyzer (NVNA) and procedure for measuring, for the first time, X-parameters under pulsed bias conditions is presented. The measured pulsed bias X-parameters are then used with the PHD framework to enable accurate nonlinear simulation of device behavior, including harmonics (magnitude and phase) under pulsed bias large-signal conditions with mismatch. Independent NVNA measurements validate the predictions of the X-parameter simulations of output match under drive, and show the inadequacy of "Hot S22" techniques to predict such device performance.

/pdf/x-parameter-measurement-and-simulation-of-a-gsm-handset-5b46irwq7h.pdf

X-Parameter Measurement and Simulation of a GSM Handset Amplifier

A test system and methods (400) using the test system correlate measurements of a device under test (DUT) regardless of which test fixture is used for in-fixture testing of the DUT. The test system (400) includes test equipment (410), a test fixture (430A or 43OB), that interfaces the DUT to the test equipment a computer (440) and a computer program (450) executed by the computer (440). The computer program (450) includes Instructions that implement determining a port-specific difference array for test fixtures (430A, 430B) used with the test system (400). The difference array describes a difference between the test fixtures (430A, 430B) at a corresponding test port thereof. The method includes determining the difference array, measuring a performance of the DUT in a second test fixture, and applying the difference array such that the measured performance approximates a hypothetical DUT performance for the DUT as if mounted in a first test fixture.

Correcting test system calibration and transforming device measurements when using multiple test fixtures

Predictable measurement-based large-signal design has been demonstrated with a unique set of interoperable commercially available nonlinear technologies for measurement, simulation, and design of nonlinear components. The new NVNA instrument, automated X-parameter measurements and extraction, and auto-configurable compiled PHD component in ADS, together enable design of nonlinear circuits entirely from fully calibrated nonlinear component data.

Measurement-based large-signal simulation of active components from automated nonlinear vector network analyzer data via X-parameters

A method is presented where the phase trace is offset for each sweep such that the first point is always at zero degrees. The resulting traces are then averaged. The average reduces the noise in the phase trace and results in a less noisy group delay trace.

Test method for frequency converters with embedded local oscillators

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