According to Byte.com, AMD is going to solve the problem of temperature monitoring in the upcoming versions of Athlon and Duron cores: Palomino and Morgan. As is known, Athlon and Duron do not have the built-in thermal sensor unlike Intel Pentium III and Celeron, which makes it a hard task to measure their actual temperature. Moreover, AMD CPUs very often suffer from overheating. That is why AMD decided to integrate a thermal diode and to implement a special thermal control circuit in its new cores.
The thermal diode will allow monitoring the actual die temperature and the thermal control circuit will prevent the CPU from overheating. Although the working principles of the new circuit are still unclear. It may simply stop the CPU just like a similar solution in Intel Pentium III. Or it may act like the solution implemented in Pentium 4 processor: as soon as the temperature exceeds the dangerous limit, the circuit will modulate the strobe signal in order to stop the CPU for a short while, so that the temperature could drop down a bit.