Forum Discussion
Occasional ContributorCyclone V: Dynamic phase shift
Super ContributorHi,
consider the relation between dynamical and programmable phase shift. Both have the same phase resolution. Review respective handbook paragraph:
"Programmable Phase Shift
The programmable phase shift feature allows the PLLs to generate output clocks with a fixed phase offset.
The VCO frequency of the PLL determines the precision of the phase shift. The minimum phase shift
increment is 1/8 of the VCO period. For example, if a PLL operates with a VCO frequency of 1000 MHz,
phase shift steps of 125 ps are possible.
The Intel Quartus Prime software automatically adjusts the VCO frequency according to the user-specified
phase shift values entered into the IP core."
Getting 360° phase shift in 64 steps means that output frequency is 1/8 of vco frequency.
Regards
Frank
MikexxMany thanks for your reply.
I can see that with a VCO frequency of 1000MHz and a phase shift of 125ps this will give an increment of 1/8 of the VCO period., Such that phase shifts would be incremented of 45 degrees.
I don't understand the phrase "The Intel Quartus Prime software automatically adjusts the VCO frequency according to the user-specified phase shift values entered into the IP core." I thought the frequency is set by "Desired Frequency" in the MegaWizard Plugin Manager where I can also introduce an initial phase shift, or delay.
However, in my case I have a 50MHz reference clock and 50MHz output clocks. I can confirm the frequency is independent of the phase shift I introduce using the port signals mentioned in my OP.
On closer inspection I believe there might be a total of 72 increments to implement 360 degrees. However I don't understand, "Getting 360° phase shift in 64 steps means that output frequency is 1/8 of vco frequency." The VCO frequency is 50MHz and the output frequency is also 50MHz, independent of the phase shift I introduce.
I still can't see where or understand how I can predict the phase shift for a phase increment.
