A.J. Panks

Electrothermal modeling and measurement for spatial power combining at millimeter wavelengths

In this paper, the first completely physical coupled electrothermal model, suitable for large-signal simulation of MESFET- and HEMT-based MMICs and MMIC arrays, on a timescale suitable for computer-aided design, is presented. The model is validated experimentally by high-resolution thermal imaging of a MMIC 38-GHz three-stage balanced amplifier, mounted on a Cu/FR-4 substrate and cooled entirely by natural convection and radiation into free space.

Thermal transients in microwave active devices and their influence on intermodulation distortion

A fully physical transient thermal model is used to investigate the effects of temperature on the intermodulation distortion performance of microwave devices. A 24 mm, 60 finger PHEMT is used to compare measurements with predictions from the model. Results are in very good agreement and are a strong indication of thermally induced intermodulation distortion.

Electro-Thermal Modelling of Monolithic and Hybrid Microwave and Millimeter Wave IC's

The first completely physical electro-thermal model is presented that is capable of describing the large signal performance of MESFET- and HEMT-based, high power microwave and millimeter wave monolithic and hybrid ICs, on timescales suitable for CAD. The model includes the effects of self-heating and mutual thermal interaction on active device performance with full treatment of all thermal non linearities. The electrical description is provided by the rapid quasi-2D Leeds Physical Model and the steady-state global thermal description is provided by a highly accurate and computationally inexpensive analytical thermal resistance matrix approach. The order of the global thermal resistance matrix describing 3-dimensional heat flow in complex systems, is shown to be determined purely by the number of active device elements, not the level of internal device structure. Thermal updates in the necessarily iterative, fully coupled electro-thermal solution, therefore reduce to small matrix multiplications implying orders of magnitude speed-up compared to the use of full numerical thermal solutions capable of comparable levels of detail and accuracy.

Fully physical coupled electro-thermal simulations and measurements of power FETs

A fully physical coupled electro-thermal model is presented. It is fast, efficient, suitable for CAD applications and capable of describing power FETs, MMICs and MMIC arrays. Results are presented which show the model gives good agreement with measurements for large power devices.

Electro-thermal modelling of microwave transistors and MMICs for optimised transient and steady-state performance

The influence of the physical layout of MESFET-based MMICs, on active device temperature and I-V characteristics, is investigated. These transient and steady state simulations represent the first reported, fully physical, coupled electro-thermal studies on CAD timescales. Calculated temperature rises are compared against experimental results obtained by thermal imaging.

Global electrothermal CAD of complex nonlinear 3-D systems based on a fully physical time-dependent compact thermal model

An original spectral domain decomposition approach is presented for the time-dependent thermal modelling of complex, nonlinear, 3-dimensional systems. This fully analytical approach immediately gives rise to compact models of nonlinear distributed thermal subsystems, without requiring approximation by a lumped element RC network, or nodal reduction. In combination with any thermally self-consistent models of analogue, digital, RF and microwave, microelectromechanical or photonic devices, it supplies a CAD timescale description of mutual thermal interaction between power dissipating and temperature sensitive elements. It therefore has the potential for thermal description of the whole system-in-package. In combination with microwave circuit simulator, Transim (NCSU), the thermal model is applied to the self-consistent global electrothermal harmonic balance simulation of a spatial power combining power FET array. The model is validated by comparison of electrothermal simulation of a power HEMT against experimentally obtained thermal images.

Fully coupled electro-thermal simulation of MMICs and MMIC arrays based on a physical model

The first completely physical coupled electro-thermal model, suitable for large signal simulation of MESFET and HEMT based MMICs and MMIC arrays, on a timescale suitable for CAD, is presented. The model is validated experimentally by high resolution thermal imaging of a MMIC 38 GHz 3-stage balanced amplifier, mounted on a Cu/FR-4 substrate and cooled entirely by natural convection and radiation into free space.

Electro-thermal modelling and measurement of thermal time constants and natural convection in spatial power combining grid arrays

The first theoretical study of thermal time constants in MMIC grid arrays is presented, indicating the significance of time dependent thermal effects for spatial power combining. Model validation against thermal images of passive grid arrays provides the first experimental demonstration of the impact of natural convection on grid array beam forming.

The synthesis of microwave and MM-wave transistor oscillators based on physical modelling

A new fast and efficient large-signal time domain circuit design routine for MMIC and M3IC oscillators has been developed by combining a quasi-two-dimensional MESFET/HEMT physical model with lumped element circuit models. The main objective is to synthesise microwave and mm-wave two terminal negative conductance devices, which can then be applied to the optimal design of oscillators. Common source, drain or gate configurations can be used in this synthesis procedure along with series and/or shunt feedback arrangements. This is the first time that the synthesis of a two terminal negative conductance has been achieved using a physical model for the active device.