General procedure

The general way of calibration is summarized below as follows:

• The basic concept of calibration is measuring the voltage across the sensor device at two different temperatures. The sensitivity coefficient is usually measured in [mV/K] units and can be derived as voltage difference/temperature difference. The JEDEC standard defines an inverse K factor for sensitivity, measured in [K/mV].
  
  
• It is a good practice to measure the two points near to the ends of the temperature range that will be used and to measure one or two additional points inside for checking whether the calculated sensitivity value is correct. Calculating a correct regression is even better.
  
  
• The sensitivity depends on the operating point where the device is used. For achieving low noise and smooth curves the T3Ster^® transient measurement is 'on-line', the current is not switched off for the measurement time. This means, the calibration has to occur at the operating current, which can be sometimes high. For details, see the actual cases below.
  
  
• The easiest way to measure device sensitivity is using the T3Ster thermostat unit (see section 7.4). If this device is installed the only thing you have to do is setting a proper current through the device in the Set Measurement Parameters menu and then selecting Auto thcoeff measurement in the Thermostat menu of the T3Ster software. The calibration process will be carried out automatically in the given temperature range and the result will be presented in the form as shown in Figure 7-6. The measured sensitivity value will be automatically fed into the appropriate input field of the Channel Attributes window (see Figure 7-3).
  
  
• You may also use some general sensitivity values known from literature instead of really measuring it (1-2 mV/K for p-n junctions, depending on the current density). Then you will have measured curves, which are scaled in some quasi-temperature so giving a good approximate picture. You can also measure the actual sensitivity later. You can get then correct temperature values then by editing the sensitivity value in the .par and .raw/.rec files (see T3Ster Measurement Control and Evaluation Tool User's Manual, Appendix A .) and re-evaluating the project. Low power levels should be used at the measurement in case you do not know the actual sensitivity because you may destroy the devices by excessive power if you are not aware that maximum temperature values (120 - 150 °C for silicon devices) have been reached.