...under perpetual construction.
This page contains some notes about LDMOS devices modeling; while the concepts discussed are general, the main focus is on obtaining models for low/medium power amplifiers for the HF/VHF amateur radio bands.
At first, the small-signal model extraction is discussed and a method is presented that allows to obtain an estimate of the main parameters. The values obtained can then be used as a starting point for an optimization procedure, in order to obtain a model which fits even better the measured data provided as input. Of course, to obtain a better model, a measure of the model quality has to be defined first; as discussed in  several different choices are possible.
Some practical examples of commonly used RF LDMOS are also presented on their own pages (see menu on the left): these model were optimized using the S-parameters Error Vector Magnitude (EVM) as error measure .
The Z-parameters of this equivalent circuits can be easily determined after some tedious calulations; the general idea is first to compute the Y parameters of the intrinsic part and then add the contributions of the extrinsec resistors and capacitors 
Assuming the Z-parameters are where
There are a number of different methods to determine parameters values of the small signal model circuit ("parameters extraction"); one of the most general is described in . The Z-parameters above are rewritten as a ratio of polynomials whose coefficient can be determined by fitting these rational functions to the measured Z-parameters; Note that some of the Z-parameters equations may need to be multiplied by so that all are non-zero and . An important feature of this method is that a least-square fit can be determined directly, without any interative optimization needing an initial starting point close enough to the optimal values to converge properly.
For the circuit above, still assuming , the Z-parameters are rewritten as note that the denominator of all the expressions is the same. In the equations above so that
|||B. Grossman, E. Fledell and E. Acar, "Adventures in Measurement: A Signal Integrity Perspective to the Correlation Between Simulation and Measurement," IEEE Microwave Magazine, vol. 14, no. 3, pp. 94-102, May 2013.|
|||L. Vestling, "Design and Modeling of High-Frequency LDMOS Transistors," Ph.D. Thesis, ISBN 91-554-5210-8, Uppsala University, Feb.2002.|
|||G. Dambrine, A. Capy, F. Heliodore and E. Playez "A new method for determining the FET small-signal equivalent circuit," IEEE Trans. Microwave Theory and Techniques, vol. 36, no. 7, pp. 1151-1159, 1988.|
|||S. Lee, H.K. Yu, C.S. Kim, J.G. Koo and K.S. Nam "A novel approach to extracting small-signal model parameters of silicon MOSFET's," IEEE Microwave and Guided Wave Letters, vol. 7, no. 3, pp. 75-77, 1997.|
|||C. Fager, J. C. Pedro, N. B. de Carvalho and H. Zirath "Prediction of IMD in LDMOS transistor amplifiers using a new large-signal model," IEEE Trans. Microwave Theory and Techniques, vol. 50, no. 12, pp. 2834-2842, Dec. 2002.|
|||S. Lai, C. Fager, D. Kuylenstierna and I. Angelov "LDMOS Modeling," IEEE Microwave Magazine, vol. 14, no. 1, pp. 108-116, Jan.-Feb. 2013.|