AN 769: Intel FPGA Remote Temperature Sensing Diode Implementation Guide

ID 683139
Date 4/06/2022

2. Implementation Overview

The external temperature sensing chip connects to the Intel® FPGA remote TSD. The remote TSD is a PNP or NPN diode-connected transistor.
Figure 1. Connection Between Temperature Sensing Chip and Intel® FPGA Remote TSD (NPN Diode)

Figure 2. Connection Between Temperature Sensing Chip and Intel® FPGA Remote TSD (PNP Diode)

The following equation forms the temperature of a transistor in relation to the base-emitter voltage (VBE).

Equation 1. Relationship Between Temperature of Transistor to Base-Emitter Voltage (VBE)


  • T—Temperature in Kelvin
  • q—the electron charge ( )
  • VBE —base-emitter voltage
  • k—Boltzmann constant ( )
  • IC —the collector current
  • IS —the reverse saturation current
  • η—the ideality factor of the remote diode

Rearranging Equation 1, you get the following equation.

Equation 2. VBE

Typically, the temperature sensing chip forces two consecutive well-controlled currents, I1 and I2 on the P and N pins. The chip then measures and averages the change of the VBE of the diode. The delta in VBE is directly proportional to the temperature, as shown in Equation 3.

Equation 3. Delta in VBE


  • n—forced current ratio
  • VBE1 —base-emitter voltage at I1
  • VBE2 —base-emitter voltage at I2

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