AN 769: Intel FPGA Remote Temperature Sensing Diode Implementation Guide

ID 683139
Date 4/06/2022

3.2. Series Resistance Error

The series resistance on the P and N pins contributes to temperature measurement error.

The series resistance can be from:

  • The internal resistance of the P and N pin of the temperature diode.
  • The board trace resistance, for example, a long board trace.

The series resistance causes additional voltage to drop at the temperature sensing path and results in measurement error, affecting the accuracy of the temperature measurement. Typically, this situation happens when you perform temperature measurement with a 2-current temperature sensing chip.

Figure 3. Internal and On-Board Series Resistance

To explain the temperature error incurred when the series resistance increases, some temperature sensing chip manufacturer provides the data for the remote diode temperature error versus the resistance.

However, you can eliminate the series resistance error. Some temperature sensing chip has built-in series resistance cancellation feature. The series resistance cancellation feature can eliminate the series resistance from a range of a few hundred Ω to a range exceeding a few thousand Ω.

Intel recommends that you consider the series resistance cancellation feature when you select the temperature sensing chip. The feature automatically eliminates the temperature error caused by the resistance of the routing to the remote transistor.

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