Accurate Distortion Prediction for Thermal Memory Effect in Power Amplifier Using Multi-Stage Thermal RC-Ladder Network

Yukio TAKAHASHI  Ryo ISHIKAWA  Kazuhiko HONJO  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E90-C   No.9   pp.1658-1663
Publication Date: 2007/09/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e90-c.9.1658
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Microwave and Millimeter-Wave Technology)
Category: Active Devices/Circuits
Keyword: 
thermal memory effect,  thermal resistance,  thermal capacitance,  thermal RC-ladder network,  IMD3,  

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Summary: 
Distortion characteristics caused by the thermal memory effect in power amplifiers were accurately predicted using a multi-stage thermal RC-ladder network derived by simplifying the heat diffusion equation. Assuming a steep gradient of heat diffusion near an intrinsic transistor region in a semiconductor substrate, the steady state temperature, as well as the transient thermal response at the transistor region, was estimated. The thermal resistances and thermal capacitances were adjusted to fit a temperature distribution characteristic and a step response characteristic of temperature in the substrate. These thermal characteristics were calculated by thermal FDTD simulation. For an InGaP/GaAs HBT, a step response characteristic for a square-wave voltage signal input was simulated using a large-signal model of the HBT connecting the multi-stage thermal RC-ladder network. The result was verified experimentally. Additionally, for an RF-amplifier using the HBT, the 3rd-order intermodulation distortion caused by the thermal memory effect was simulated and this result was also verified experimentally. From these verifications, a multi-stage thermal RC-ladder network can be used to accurately design super linear microwave power amplifiers and linearizers.