Spectrum Software
Industrial Strength Simulation




Spectrum Software has released Micro-Cap 11, the eleventh generation of our SPICE circuit simulator.

For users of previous Micro-Cap versions, check out the new features available in the latest version. For those of you who are new to Micro-Cap, take our features tour to see what Micro-Cap has to offer.




Diode Materials Temperature Parameter Values


When modeling a diode at the nominal temperature of 27C, the actual material of the diode is irrelevant. As long as the diode parameters that have been defined for the model can appropriately simulate the current and capacitance curves, the resulting model will be applicable to the simulation. If the simulation is running at a temperature other than 27C, then the EG and XTI diode temperature parameters must be defined with respect to the semiconductor material of the diode being modeled.

The EG parameter defines the energy gap of the diode in electronvolts. This parameter is completely dependent on the semiconductor material being used in creating the diode. The XTI parameter defines the temperature exponent for the IS current. At 27C, neither of these parameters will have an effect. At other temperatures, the EG and XTI parameters should be defined according to the semiconductor material as shown below:

Material EG XTI
Silicon 1.11 3
Schottky .69 2
Germanium .67 3
GaAs 1.43 3
GaP 2.26 3
To demonstrate the effect that these two temperature parameters have on a diode, the schematic below has been created in order to produce the basic If-Vf curve of the diode. The top circuit consists of a battery that will drive the D1 diode that is in series with it. The battery voltage in the schematic has been set to 5V, but that will be overwritten when the DC sweep is performed. The bottom circuit has an NFV source that duplicates the battery voltage in order to drive a second diode, D2. The only difference between the two diode models is that the D2 diode has had its T_ABS parameter set to 27. This diode will always run at 27C no matter what the temperature defined in the analysis limits is. This will provide us a baseline If-Vf curve to compare to.

Diode I-V Schematic

To produce the desired If-Vf curve, a DC analysis is run. In the DC Analysis Limits dialog box, the V1 battery is swept from 0V to 1V in .001V increments. A linear step method is chosen for this example. The temperature field has been set to 50C so that the temperature parameters will influence the results. Both the EG and the XTI parameters of the D1 diode are set up to be stepped. The EG parameter is stepped through the list '1.11,.69,.67,1.43,2.26' and the XTI parameter is stepped through the list '3,2,3,3,3'. These two parameters are stepped simultaneously so that there will be five curves in the analysis with each curve simulating one of the materials shown in the table above.

The resulting If-Vf curves are displayed below. The red waveform displays the If-Vf curve of the diode when it is running at 27C. At this temperature, the semiconductor material doesn't have an effect. The other five curves simulate the If-Vf curve at a temperature of 50C for each of the semiconductor materials that are in the table. Each curve is labelled with the semiconductor material that it represents. The germanium and Schottky curves are nearly on top of each other since the EG parameters each uses are nearly equivalent. As expected, the GaP semiconductor material shows the greatest divergence from the nominal curve due to it having the largest energy gap. The default temperature parameters for the diode model are set to model silicon.

Stepping Eg and Xti Diode Parameters

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