Single current source Tj control

Tj control using single current source was successfully developed to replace Tcase control for testing microprocessor. Tj control uses diode junction temperature feedback whereas Tcase control uses case temperature (temperature at the die surface). In single current source Tj control, the single current source is employed to measure diode junction temperature. A simple circuitry is designed to supply a constant current to junction diode and its temperature-dependant forward-biased voltage is obtained and amplified before feeding into the PID controller. The thermocouple input signal in Tcase control is replaced with amplified voltage signal. An auto on-line diode characterization program is designed to determine mathematical relation between diode voltage and junction temperature, referred as the characteristic equation, before the start of every production lot. Its purpose is to minimize error in temperature measurement due to change in the characteristic equation which is different for different wafer lots and also is affected by changes in material and silicon fabrication process. Calibration accuracy is improved substantially with a new calibration jig.