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Altera_Forum's avatar
Altera_Forum
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15 years ago

pll reconfiguration and CP/LF parameters

Documentation describing the pll scan chain is clear enough for the settings of the m,n,cx counters. However, it is not clear to me how the charge-pump and loop-filter parameters should be calculated...
Altera_Forum's avatar
Altera_Forum
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15 years ago

That's how I proceeded until now.

I recently got a request to generate freqs with a certain offset with respect to the base freq.

Even though the mega wizard is still a (heavy) option, it is not very flexible and seems to generate frequencies not as optimal as if I find the m, n, cx parameters myself.

Altera's documentation (eg. AN367) states that "You can also change the charge pump and loop filter components, which dynamically affects the PLL bandwidth". OK, but without clear indication on how to set the CP/LF params,

this statement is useless.

In Altera's docs, there are formulas to compute the phase shifts. Having formulas to compute the PLL bandwidth would be very helpful tough, as deriving them from the PLL filter diagram is not a doable task (for me).