Remote temperature sensors measure the temperature of an external transistor by measuring the base-emitter voltage (V_BE) of the BJT, which depends on temperature. One method of determining a transistor base-emitter voltage is the two current method, using the difference of two voltage measurements to calculate temperature, as shown in Figure 1-1. However, thermal diode signals can be sensitive to noise, series resistance, and variation in transistors’ η-factors and betas can introduce additional errors if not accommodated.

Figure 1-1 ΔV_BE Measurement with Two Currents