Silicon I.C. temperature sensors all operate on the same basic principal: voltage through the base-emitter is proportional to temperature. Two current sources are used to null out any unknowns or sources of error in the temperature equation shown here where N = current ratio of I1/I2, k = Boltzmann’s constant, q = charge on an electron, and T = temperature in Kelvin. Analog Devices has parts that give temperature results as an output voltage or current (Delta VBE gained up), or digitized data (read back temperature over I2C, SPI, PWM).