Cold Junction Compensation Technique of Thermocouple Thermometer Using Radiation-Hardened-by-Design Voltage Reference for Harsh Radiation Environment

This article introduces a radiation-hardened-by-design (RHBD) cold junction compensation (CJC) circuit to compensate for the voltage variation at the cold junction of a thermocouple used in a nuclear power plant (NPP) to detect the reactor temperature. The key idea of the RHBD circuit is to cancel the error induced by radiation, subtracting two reference voltages. In this design, two conditions should be satisfied to realize the first-order cancellation. First, the two voltages should have similar changes according to temperature and radiation. Therefore, two identical voltage generators are used in the proposed circuit. Second, the two reference voltages might have different values. The proposed circuit was fabricated using general purpose 0.18-
$\mu \text{m}$
complementary metal–oxide–semiconductor (CMOS) technology with a shallow trench isolation (STI) process. The RHBD CJC circuit showed a reference voltage of 275 mV at room temperature. The final output voltage variation was 5.2 mV under irradiation up to 2 Mrad, and the temperature coefficient (TC) was 2.9 ppm/°C in a range of 20 °–110 °C without additional trimming and annealing. The proposed circuit showed improvements of 60% and 90% for the radiation effect and temperature variation, respectively, compared with the conventional reference circuit. The active area and power consumption were 0.035 mm2 and 1.716 mW, respectively.