Thermal testing on programmable logic devices

In this work, an FPGA-oriented temperature monitoring scheme is presented. A control circuit enables a ring-oscillator during a short period and measures its output frequency, a magnitude that is a function of the die temperature. Several sensors have been constructed using Xilinx chips, obtaining sensitivities between 17 kHz per degrees C and 77 kHz per degrees C. The characterization of self-heating, matching between identical sensors, power supply dependence and detection of signal contentions has also been performed. The usefulness of other chip resources as thermal transducers, like the built-in OSC4 cell or the IOB clamping diodes, has also been verified. The use of ring-oscillators convert the FPGAs in a powerful tool for researchers interested in thermal modeling of integrated circuits. Just the possibility of "moving" a sensor (or an array of them) over the die, in a simple, fast, and inexpensive way, is almost impossible in any other VLSI technology.