Small footprint synthesizable temperature sensor for FPGA devices

In this paper, a novel synthesizable temperature sensor for FPGA devices, which uses DSP-slices instead of LUTs, is presented. The correlation between the delay of the critical path and the temperature of a DSP-slice is exploited to implement a ring oscillator, whose oscillation frequency is used to estimate the local die temperature. In contrast to previously proposed synthesizable temperature sensors based on ring oscillators implemented with LUTs, the proposed DSP-based temperature sensor has a smaller footprint. The complete synthesizable temperature sensor, including the ring oscillator and the required time-to-digital converter, only requires three DSP-slices. An evaluation using a programmable climate chamber and a Virtex-6 FPGA evaluation board is presented. The DSP-based temperature sensor provides similar accuracies (i.e., ±0.5 °C) than LUT-based temperature sensors, while greatly improving the resolution and temperature sampling rates depending on the selected configuration. Finally, by using the proposed temperature sensors together with several internal hardware heat generators, a maximal temperature gradient of 9 °C was measured on the FPGA die.