Hints, Tips and Solutions


Volume 11, Number 4, April 2000

Q. How can I extract VBIC bipolar model parameters using UTMOST III?

A. UTMOST III Bipolar module can be utilized to extract and optimize the VBIC model parameters for bipolar devices.

The VBIC model extraction strategy is similar to the Gummel-Poon model parameter extraction. For DC modeling the measured data should be collected using routines "RC_sat" (For RC and RE extraction), and ALL_DC (forward and reverse characteristics should be collected). The RB extraction can be accomplished using the DC or AC methods. However the extracted RB results usually requires further optimization.

The user should load the VBIC model parameters and their default values using the "Spice Model File". The Spice Model File is located under the working directory of "<user_home_directory/ vyper_data/ utmost_data/bip/" For the UTMOST III version of 16.3.0.R the Spice Model File name would be: BIP.16.3.0.R.s. The Spice Model File can be loaded by selecting the Spice Model File menu option from the files menu of UTMOST III.

The RC_sat routine uses the flyback method to extract the constant part of the RC (RCX) and RE for the VBIC model. The RC has two parts in the VBIC model. The parameter RCX is the constant extrinsic collector resistance and RCI is the intrinsic modulated collector resistance. After the data collection the user can press the "fit" option to extract both parameters RCX and RE. The results will be copied to the "parameters" screen. (Figure 1.) The parameter RCI will be used later for quasi-RC region modeling.

Figure 1. RC_sat routine graphics screen.


The ALL_DC routine can be used to extract some of the fundamental DC parameters of the VBIC model. The forward and reverse characteristics of the bipolar device should be measured ( The "All DC" selection in the "set measurement/To Model" button selection). After the data collection the "fit" button should be pressed to extract the DC parameters (Figure 2.). The extracted parameters will be copied to the parameters screen.

The extracted parameters are:


Figure 2. ALL_DC routine with extracted VBIC parameters.


In order to model the substrate current, the ALL_DC or Gummel routine data should be collected with Isub_flag in the measurement setup screen set to "1". When this flag is set to "1" the gummel curves will include the measured substrate current (Figure 3.)

Figure 3. Measured Gummel curves including the substrate current.


For NPN devices the substrate current will be more dominant under reverse bias operation. Therefore the reverse bias gummel curves should also include the substrate current. The following parameters should be optimized on the reverse gummel curve with substrate current:


The VBIC model can be utilized to model the avalanche effect on IC/VCE characteristics. Parameters AVC1 and AVC2 should be optimized at the high VCE region where the avalanche effect becomes visible (Figure 4.)

Figure 4. IC/VCE measured vs simulated data.


The quasi saturation region modeling can also be accomplished using the VBIC model parameters RCX, RCI, GAMM and HRCF. These parameters should be optimized using the IC/VCE characteristics which demonstrates the Quasi-RC effect (Figure 5).

Figure 5. IC/VCE measured versus simulated (including the Quasi-RC effect)


The parameter values used for this example are:

RCI = 22

RCX = 55

VO = 0.4

GAMM = 1E-10

HRCF = 111


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