• Analog Custom Design & Analysis Examples

opt_ex07 : VBIC Bipolar Model Extraction

Requires: Utmost IV, SmartSpice, SmartView

Minimum Versions: Utmost IV 1.10.6.R, SmartSpice 4.10.2.R, SmartView 2.28.2.R

This example describes how to extract a VBIC model for a bipolar transistor. To extract the model, typical forward and reverse operation DC characteristics and reverse bias capacitance characteristics of each junction are required.

The project file opt_ex07.prj and the data file opt_ex07.uds for this example should be loaded into your database. When opened, the project will look as shown in opt_ex07_01.png and when plotted, the example measured data will look as shown in opt_ex07_02.png .

The optimization sequence, which fully automates the extraction of this VBIC bipolar model example, has five sections. The objective of each section is to isolate a device characteristic and then to optimize only those model parameters which account for this device behaviour.

The VBIC bipolar model couples the capacitance and the charge equations together. Therefore, it is important to extract the capacitance parameters first to avoid having to readjust the DC model parameters later.

The first section extracts the CJE , PE , ME , CJC , PC , MC , CJCP , PS , and MS model parameters which describe the reverse bias capacitance characteristics of all three transistor junctions.

Once the capacitance parameters are extracted, the second section will extract the reverse Gummel parameters IS , NR , IBCI , IBCN , NCN , IKR , RCI , and RBI . Then the third section will extract the reverse output characteristic parameters VER and IKR .

As the forward operation of the transistor is more important than the reverse, these model parameters are extracted last. In this way, the goodness of fit to the reverse data can be sacrificed if necessary to achieve the best fit to the forward data.

The fourth section extracts the parameters IS , NF , IBEI , IBEN , NEN , RE , IKF to fit to the forward Gummel data and finally the fifth section extracts the model parameters IKF and VEF to fit to the forward output characteristics.

If the overall fit to the data is not acceptable at this point, it may be necessary to repeat the sequence multiple times. Also, if there is a marked difference in forward and reverse saturation current ( IS ) values, it is possible to use an extension to the VBIC model which utilizes the parameter ISRR which represents the ratio between the saturation current in forward and reverse. This parameter should be added to the rgummel1 optimization setup in place of the IS parameter and must be extracted after IS has already been extracted for the forward data.

On completion of the sequence, the measured versus simulated characteristics should be as shown in opt_ex07_03.png . The model card can then be exported into an external model library file as shown in the output file opt_ex07.lib.

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