High Speed Processor Clock Oscillators

[xgoat]

Does anyone know how the fast oscillators for pc processors work? They tend to use crystals, but that's all I know about them. Does anyone have any documents regarding crystal oscillators?

 

[mitgrace]

What 's frequency , Do u use it ? And what procee do you use ? I do many crystal oscillator , But I need some information , that I can solve these problem

 

[flatulent]

The internal clock is a two stage operation. There is a crystal oscillator in the nx10 MHz range and then a phase locked loop with a divider in the feedback loop locked to the nx10 MHz crystal oscillator output. This is how they get the GHz internal clocks.

 

[pisoiu]

As flatulent stated, the first stage is a pll onboard. Most common crystal value is 14,31818MHz. A PLL will generate high clock frequencies, around hundreds of MHz, depending on FSB parameters. For CPUs with cores running at gigahertz, usually, another PLL, this time on chip, is implemented. This have two reasons: one is that it is impossible to route gigahertz range clocks and signals over a PC PCB (considering the size and complexity). The second one is compliance related. Higher the clocks and signals, then higher EMI will result. Large traces carying high frequencies clocks will increase dramatically generated EM fields , and it will be difficult to shield them. A special tehnique used to cut some interference generated by high speed clocks is called clock spread spectrum. Basically, the high clock freq. is modulated with a low freq. component, thus spreading the main radiated frequency and reducing its peak energy.

/pisoiu