[hwg]

I doubt that you would find those kind of specs published. And there's no way I know of to modify or tweak those internal timing parameters. They are what they are, and you live with it. You are right, the only things you have control of are temperature and voltage.

I'm starting to understand where you're coming from with the low temp, low voltage. (I told you I'm new to this...) Low temp gives you less thermal noise (background noise that all semiconductors produce). Lower thermal noise allows you to use lower voltages, since there is less error on the switching threshold. And lower voltages allow the chip to run faster, since the switching time of a transistor is limited by its slew rate, or dv/dt. For instance, if the transistor can change at 10V/ns, and it only has to change by 2V (0V to 2V), then it can switch in 0.2ns. If it has to change by 3V, it will take 0.3ns, since the rate of change is the same (roughly). So all those things are working for you as you go colder. But the one thing that may be working against you is the one you can't see or control, and that is the internal timing. It may be optimized for a much higher temperature, and it might get worse as you go colder. But there's nothing you can do about that. You just have to find the the optimum temperature where things work best. My only point is that "optimum" might not equal "as cold as you can make it". Maybe it is.

Your comment about "stabilizing such a high frequency" has me thinking. The clock that is fed into the CPU is not 8GHz, but a much lower frequency. The CPU has a PLL (phase locked loop), or something similar inside to generate the internal higher-rate clock. A PLL is basically a feedback circuit with a phase detector, charge pump, and a VCO (voltage controlled oscillator). These things are all in silicon. But there are usually a couple of external components, a resistor and a capacitor, which make up the "loop filter", and set the natural frequency range of the PLL. Sometimes there is only a capacitor, as the resistor is on-chip. Sometimes there are no external loop filter components at all. If the CPU you are trying to overclock has an external loop filter, I wonder if it might make it easier to stabilize the clock by changing the component values in the loop filter (different C and/or R). The PLL will be designed to run at the CPU's normal clock rate. Maybe you could tweak it to shift the frequency up so that the clock will more easily stabilize at higher frequencies. You will still ultimately be limited by how fast the VCO will run, internal timing, etc., but at least the PLL would be more optimized for higher frequency operation.

If I can find a data sheet for an Intel CPU, I will have a look at this and see what I can find out. Or maybe you guys have already looked into this.


hwg