LASIMO LARGE AND SMALL SIGNAL MODELING

Accurate model generation is becoming a progressively more important part of the computer-aided design process. Of special importance are large signal models capable of accurately predicting the performance of nonlinear circuits.

LASIMO, part of the MMICAD Suite of software solutions, further expands the data acquisition and modeling capabilities of the MMICAD Version 3 simulator by the fitting of large signal modeling parameters to measured DC and RF data.

This is accomplished in three steps:

Measuring transistor S-parameters (corresponding to I-V characteristics) from Vector Network Analyzers;
Extracting a bias-dependent small signal model;
Optimizing the bias-dependent parameters (IDS, GM, RDS, CGS, CGD, etc.) to agree with either built-in or user-defined nonlinear large signal models.

LASIMO Features

LASIMO is designed to seamlessly integrate with the MMICAD Version 3 Linear Simulator, but can also be operated stand-alone.

LASIMO facilitates the development of large-signal models by simplifying procedures for the extraction of MESFET and HEMT model parameters. The program provides the designer with a set of proven transistor models as well as the capability to incorporate user-defined models and subsequently model these as required.

Model parameters are optimized to match actual transistors by fitting the measured and modeled bias dependence of the device characteristics. In the user-defined model version of LASIMO, provisions were made for 5 DC and 5 Capacitance user-defined large signal models. The user-defined models were implemented as dynamic link libraries (DLLs) created and added outside LASIMO, and linked to the program at run time. Each of the dynamic link libraries is generated from a set of project files written in the "C" language and loaded into a C compiler. The default DC model is the Curtice model, and the default capacitance model is the Basic Semi-Junction Model. The designer has only to edit a single function that computes the nonlinear parameters. This function receives a set of arguments from LASIMO and the function returns the required nonlinear parameters. The user is able to define and access up to 13 large signal parameter coefficients to be optimized for each DC model and up to 15 large signal parameters for each Capacitance model. These DC and Capacitance large signal model parameters can be selected by the user to suit various nonlinear simulators.

7 large signal bias-dependent MESFET models
2 large signal bias-dependent HEMT models
4 small signal MESFET and HEMT models
10 user-defined models
5 user-reconfigurable large signal models
3 small signal analysis modes: Unique technique which combines extraction algorithms for the intrinsic elements and inductances, requiring only the three extrinsic resistances R_s, R_d, and R_g to be optimized. Extraction of the intrinsic elements each with a custom frequency specification and two independent weights. Multi-bias intrinsic elements extraction.
4 versatile optimizers with unique solution search algorithms.

Large signal model parameter export to SPICE.

Bias-dependent small-signal model export to the MMICAD Linear Simulator.

LASIMO includes the capabilities of CAMFET.

Supported Small Signal Models
11, 12, 13, 15 and 16 element components.

Supported Large Signal Models
Alpha Own Model, Advanced Curtice, Curtice, Curtice-Ettenberg, Lehovic-Zuleeg, Materka-Kacprzak, Raytheon, Triquint.

BUILT-IN STANDARD MODELS Ids MESFET Models:
Model 1:     Curtice
Model 2:     Statz (Raytheon)
Model 3:     Materka-Kacprzak
Model 4:     Triquint Own Model
Model 5:     Advanced Curtice
Model 6:     Curtice-Ettenberg
Model 7:     Lehovic Zuleeg
Cgs and Cgd MESFET Models:
Model 1:     Junction Model
Model 2:     Statz (Raytheon)
Model 3:     A physically based model
Ids HEMT Models:
Model 1:     Curtice
Model 2:     Advanced Curtice
Cgs and Cgd HEMT Models:
Model 1:     A physically based model
RECONFIGURABLE MODELS
Model 1,2:   DC Curtice and Basic Semi-Junction Capacitance
Model 3:     TOM3 (room temperature)
Model 4:     Alpha Own Model (AOM)
Model 5:     TOM3 (with temperature dependence)
USER -DEFINED MODELS
Model 1-5:   User assignable. Can also be substituted for the reconfigurable models.
Details on Advanced Models

Alpha Own Model
AOM is a comprehensive model for GaAs MESFETs which expands upon aspects of the Triquint Own Model (TOM) to account for dispersion, self-heating effects, and charge conservation. A set of capacitance and charge equations are used for consistent small- and large-signal models. Transconductance and output conductance dispersion are modeled by combining a feedback network and a subcircuit which describes the self-heating effects. The new model accurately predicts the I-V, CV, bias-dependent S-parameter, waveform, power, and linearity characteristics of the MESFET. This model has been implemented in PSPICE.

Triquint Own Model, Level 3
TOM3 is also a comprehensive model for GaAs MESFETs. It was developed to improve existing MESFET capacitance models for SPICE using conservation of charge in the implanted layer. The capacitance model calculates the gate charge from the drain current and the gate capacitance from the drain conductances. Relating the gate charge to the channel current creates gate capacitances dependent upon the channel current derivatives linking the small-signal model to the large-signal equations. Drain dispersion and self-heating effects are modeled by a GD model using a set of device equations and a specific subcircuit in SPICE.

Triquint Own Model, Level 3, Modified
A variant of the TOM3 model is also provided where the parameters assigned to temperature are not included. For many applications the model can be used quite effectively without the temperature parameters. Speed of extraction is improved.

References:

[1] Optotek Limited, "GaAs MESFET and HEMT Model Extraction Software", Microwave Journal, Vol 38 No 4, April 1995, pp. 274-276

[2] Optotek Limited, "Large-Signal Modelling of MESFETs and HEMTs", Microwave Journal, Vol 40, No 11, November 1997, pp. 162-166).

[3] "C.J. Wei, Y.A.Tkachenko, D. Bartle, S. Dindo, and D. Kennedy, "A Compact Large-Signal Model of a GaAs MESFET", Microwave Journal, Vol 40, No 12, Dec 1997, pp. 22-34

[4] C.J. Wei, Y.A. Tkachenko, and Dylan Bartle, "An Accurate Large-Signal Model of GaAs MESFET which Accounts for Charge Conservation, Dispersion, and Self-Heating", IEEE Transactions on Microwave Theory and Techniques, Vol. 46, No. 11, November 1998.

[5] R.B. Hallgren and P.H. Litzenberg, "TOM3 Capacitance Model: Linking Large- and Small-Signal MESFET Models in SPICE", IEEE MTT, Vol. 47, No. 5, May 1999, pp. 556-561.

[6] R.B. Hallgren and D.S. Smith, "TOM3 Equations", Triquint report dated 14 September, 1998.

Pricing

Contact sales@optotek.com.