Temperature Characteristics of a Resistor

When you place a resistor part called R () jn your circuit, you are using an ideal resistor that is, the resistor has no tolerance and no temperature dependence. The resistor is exactly the value you specify and the resistance does not change as the temperature changes. In practice, all resistors have tolerance and temperature variations. If you use a 1 k 2 resistor with 5% tolerance, the resistor will not be exactly equal to 1000 2. Its value could be anywhere between 950 2 and 1050 2. Temperature variations are anywhere from 50 parts per million (ppm) to 400 ppm. In PSpice we can specify both temperature variations and resistor tolerance. Tolerance will be covered in Part 9. 

PSpice has three ways to specify temperature dependence. Three model parameters named TCI, TC2, and TCE are available. TCI and TC2 may be used together. If you use TCE, then TCI and TC2 are ignored. Suppose we have a resistor with a resistance equal to Rval. If TCE is specified, then the resistance is  

TCE is called the exponential temperature coefficient. If TCE is specified, then the values of TCI and TC2 are ignored. If TCE is not specified, then the resistance is 

TCI is referred to as the linear temperature coefficient and TC2 is referred to as the quadratic temperature coefficient. Tnom is the nominal temperature. Its default value is 27°C. 

The default values of TCE, TCI, and TC2 are zero. Thus, if you do not specify any of the coefficients, there will be no temperature dependence. In all of our previous simulations the resistors had no temperature dependence. Thus, if we varied temperature in any of the simulations, the resistors would not be affected. To add temperature dependence we must specify the temperature coefficients. 

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