Modern CPUs with increasing core frequency and power are rapidly reaching a point that the CPU frequency and performance are limited by the amount of heat that can be extracted by the cooling technology. In mobile environment, this issue is becoming more apparent, as form factors become thinner and lighter. Often, mobile platforms trade CPU performance in order to reduce power and manage the box thermals. Most of today's high performance CPUs provide thermal sensor on the die to allow thermal management, typically in the form of analog thermal diode. Operating system algorithms and platform embedded controllers read the temperature and control the processor power. In addition to full temperature reading, some products implement digital sensors with fixed temperature threshold, intended for fail safe operation. Temperature measurements using the diode suffer some inherent inaccuracies : ? Measurement accuracy - An external device connects to the diode and performs the A/D conversion. The combination of diode behavior, electrical noise and conversion accuracy result with measurement error ? Distance to the die hot spot - Due to routing restrictions, the diode is not placed at the hottest spot on the die. The temperature difference between the diode and the hot spot varies with the workload and the reported temperature dose not accurately represent the die max temperature. This offset is increasing as power density of the CPU increase. multiple core CPUs introduce harder problem to address as the workload and the thermal distribution changes with the different active cores. ? Manufacturing temperature accuracy - Inaccuracies in the test environment induce additional temperature inaccuracy between the measured temperature vs. the actual temperature. As a result to these effects, the thermal control algorithm requires to add temperature guard bend to account for the control feedback errors. These impact the performance and reliability of the silicon. In order to address the thermal control issues, the Intel® CoreTM Duo has introduced a new digital temperature reading capability on die. Multiple thermal sensors are distributed on the die on different possible hot spots. An A/D logic built around these sensors translates the temperature into a digital value, accessible to operating system thermal control S/W, or driver based control mechanism. Providing high accuracy temperature reading requires a calibration process. During high volume manufacturing, each sensor is calibrated to provide good accuracy and linearity. The die specification and reliability limitation is defined by the hottest spot on the die. In addition the calibration of the sensor is done at the same test conditions as the specification testing. Any test control inaccuracy is eliminated because the part is guaranteed to meet specifications at max temperature, as measured by the digital thermometer. As a result, the use of integrated thermal sensor enables improved reliability and performance at high workloads while meeting specifications at ant time. In this paper we will present the implementation and calibration details of the digital thermometer. We will show some studies of the temperature distribution on die and compare traditional diode based measurement to the digital sensor implementation
