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When you run a simulation in Multisim, all the elements of the circuit are assumed to be measured at the nominal temperature of 27°C. This temperature can be changed by customizing the SPICE options. However, using Temperature Sweep Analysis, you can quickly verify the operation of your circuit by simulating it at different temperatures. The effect is the same as simulating the circuit several times, once for each temperature. You control the temperature values by choosing start, stop and increment values.
When you configure a Temperature Sweep Analysis in Multisim, you can define the temperature values to be swept and the type of analysis to be run at the various swept temperatures. There are three types of sweeps: DC Operating Point , Transient Analysis , and AC Analysis.
The assumptions depend on the selected analysis as follows:
In order to simulate circuits at various temperatures, the components of the circuit must have variation in their values, however, you must have in mind that Temperature Sweep Analysis affects only components whose model includes temperature dependency. In this tutorial we will focus on resistors.
In Multisim, the resistance of a resistor instance is calculated using the following equation:
R = The resistance of the resistor.
Ro = The resistance of the resistor at temperature To.
To = Nominal temperature = 27°C.
TC1 = First order temperature coefficient.
TC2 = Second order temperature coefficient.
T = Temperature of the resistor.
Before running a Temperature Sweep Analysis, you must specify the desired values for TC1 and/or TC2. The temperature coefficient is usually expressed in ppm/°C (parts per million per degree Centigrade) units.
Consider the common-emitter (CE) amplifier shown in Figure 1. This configuration offers a high gain, however the gain depends on the temperature and bias current. In this exercise you will vary the temperature of the emitter resistor (RE) to see its effect on the amplifier’s gain.
Figure 1. Common-emitter amplifier
Complete the following steps to configure and run a Temperature Sweep Analysis:
Figure 2. Specifying the Temperature Coefficient (TC1).
Table 1. Parameters used in Temperature Sweep Analysis
Sweep Variation Type
Dictates how to calculate the interval between the start and stop temperatures. Temperature Sweep Analysis plots the appropriate curves sequentially. The number of curves is dependent on the type of sweep as shown below:
Analysis to sweep
Select the analysis to sweep. There are four options:
You can set the analysis parameters by clicking the Edit Analysis button.
Note: In SPICE, the command that performs a Temperature Analysis has the following form: .TEMP T1 <T2 … TN> Where .TEMP initializes a Temperature Analysis; T1 is the first temperature at which the circuit is to be simulated, TN is the Nth temperature at which the circuit is to be simulated. Note that these parameters are similar to those defined in Table 1.
Figure 3. Analysis parameters for the Temperature Sweep Analysis.
Figure 4. Sweep of Transient Analysis window.
Refer to the Transient Analysis tutorial for more details on how to configure the Analysis Parameters tab.
Figure 5. Output variable for the Temperature Sweep Analysis.
Figure 6. Temperature Sweep Analysis results.
As you can see, as the temperature increases, the output of the CE amplifier decreases. Use the Cursors to obtain precise measurements. You can also perform nested sweeps, combining various levels of device/model parameter sweeps.
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