Lawrence Dunleavy

Modeling GaN: Powerful but Challenging

As GaN technology has developed, first in research laboratories and more recently in multiple commercial device manufacturers, the demand for improved nonlinear models has grown alongside the device process improvements. The need for improved models for GaN is twofold: first, GaN devices have unique nuances in behavior to be addressed; second, there is a desire for improved accuracy to take full advantage of the performance wins to be gained by GaN HEMT performance in the areas of high efficiency and high-power operation.

Design and characterization of FET based cold/hot noise sources

Innovative design, modeling, and characterization methods are described for FET cold noise sources. A developed InP HEMT cold/hot noise source demonstrates 105 K in the 18-22 GHz range; the highest reported frequency for a FET cold noise source. Measurements confirm variable source temperature from 105 K to over 1000 K.

Resolving capacitor discrepancies between large and small signal FET models

A novel solution is presented for the well known capacitor discrepancy problem between large and small signal FET models. The discrepancy arises due to the two-parameter bias voltage dependence of the intrinsic FET model capacitances. The resolution is enabled by the proper choice of partial-integration constants associated with the transformation of a charge source in the large signal model to a capacitor in the small signal model.<<ETX>>

Direct measurement of thermal circuit parameters using pulsed IV and the normalized difference unit

New methods are presented for direct extraction of thermal resistance and capacitance from pulsed IV measurements. Because thermal effects are frequency dependent, a thermal circuit is used in many models to characterize the device channel temperature as a function of frequency. Thermal resistance is determined using pulsed IV data sets taken at varied ambient temperature, while the thermal capacitance is found through use of a new normalized difference unit (NDU) for IV data. Determination of thermal subcircuit parameters from readily available pulsed IV measurements reduces the complexity of electrothermal model development for microwave transistors.

Math methods in transistor modeling: Condition numbers for parameter extraction

Condition numbers expressing the sensitivity of computed circuit element values to inaccuracies in S-parameter measurements are derived and evaluated for a standard small-signal MESFET model. The condition numbers shed light on the common difficulty experienced by transistor modelers in extracting accurate values for the input resistance. Other elements are also classified according to their sensitivity.

On-wafer calibration using space-conservative (SOLT) standards

In this paper the accuracy of on-wafer calibration using space-conservative (SOLT) standards is evaluated. The calibration approach relies on measurement-based standard definitions. Results are presented using CPW standards with 50 and 300 micron offsets, over the range from .045-65 GHz. In comparing to a multi-line TRL, the magnitude of the difference between the S-parameters is less than 0.05 up to 40 GHz, and below 0.1 up to 65 GHz.

Educating tomorrow's RF/microwave engineer: a new undergraduate laboratory uniting circuit and system concepts

This paper describes recent advancements made at the University of South Florida for educating undergraduate electrical engineering students in the fields of wireless circuits and systems. The foundation for the program is an innovative lecture/laboratory course which guides students through wireless component and subsystem analysis and design using a case-study approach. While providing a broad exposure to the wireless arena, students also gain hands-on experience with state-of-the-art instrumentation and computer-aided engineering software.

Temperature-dependent modeling of gallium arsenide MESFETs

A complete temperature-dependent small signal model extraction methodology is used to achieve accurate circuit level simulations of metal semiconductor field-effect transistor (MESFET) amplifier performance over temperature. The procedure applies a previously described field-effect transistor (FET) modeling approach to predict the performance of a small signal amplifier over a -55/spl deg/C to 100/spl deg/C temperature range. This work includes a description of the MESFET equivalent circuit element thermal coefficients along with an amplifier simulation. Therefore, for the first time, a clear correspondence between circuit level simulation and measured results over temperature are published together. A new comparison of published temperature-dependent data shows a common agreement for amplifier gain variations of 0.015 dB//spl deg/C/Stage for a broad range of designs from 400 K down to cryogenic levels (77 K).

Stability measurements on noise sources

We report results of stability and repeatability measurements performed on a selection of different noise sources for selected frequencies between 12 GHz and 26.5 GHz. Measurements cover intervals classified as intermediate term (about 1 week) and long term (about 1 year or more). Noise sources measured include a commercial diode source, a gas-discharge source constructed by NIST, a specially modified commercial diode source, and a variable-temperature FET-based source. All sources exhibit excellent stability, typically consistent with zero drift in noise temperature within the uncertainty of the tests.

A table-based bias and temperature-dependent small-signal and noise equivalent circuit model

A new algorithm is presented for construction of an accurate table-based bias and temperature dependent FET small-signal and noise model. The algorithm provides orders of magnitude data reduction over the alternate approach of storing multiple S-parameter and noise parameter data files (to represent different bias and temperature conditions). The algorithm performs 2-D linear interpolation on a single stored data table to quickly produce accurate bias and temperature dependent model simulations.<<ETX>>