At this time PLLatinum Sim does not assign output frequencies to specific output ports on
the device with the intention to minimize cross-coupled spurs and jitter. The user can make
some educated re-assignment of outputs when using the EVM programming tool to configure the
device registers appropriately.
In an effort to optimize device configuration for best jitter performance, consider the following guidelines:
- The clock outputs intended to clock high-data
rates require the lowest possible jitter, therefore assigning 156.25 MHz to outputs 0
and 1 and assign 125 MHz to outputs 2 and 3 is best.
- To minimize cross coupling between PLLs, select PLL2 VCO to operate at 5 GHz and PLL1 VCO to operate 4.8 GHz.
- Coupling between outputs at different frequencies
appear as spurs at offsets that are at the frequency difference between the outputs and
the harmonics. Typical SERDES reference clocks must have low integrated jitter up to an
offset of 20 MHz. Therefore, to minimize cross coupling between output 3 and output 4,
assigning 100 MHz to outputs 4 and 5 is best.
- The 133.3333 MHz can then be assigned to output 6.
- The 1.8-V LVCMOS clock at 66.6667 MHz is assigned
to output 7 and selecting complementary LVCMOS operation is best. This helps to minimize
coupling from this output channel to other outputs.