I have used Altera FPGAs from last year and I would like to know how the PLLs inside works. Mainly, really have any kind of analog circuitry inside in order to measure phase-offset between VCO and external signal? This pretty pieces are so reliable along wide freq range (currently 100MHz and beyond even on cheapest models) that I am impressed.

  • \$\begingroup\$ One good idea would be to read the device documentation, like the handbook for example. \$\endgroup\$ – quantum231 May 15 '13 at 13:28

It's a conventional PLL with a VCO, a PFD, filter and dividers:

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    \$\begingroup\$ I must admit that the brevity of some of your answers annoys me. You could at least explain what a PFD is for users not familiar with PLLs! \$\endgroup\$ – Federico Russo Jul 15 '11 at 16:38
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    \$\begingroup\$ @Federico Russo: Basically, the answer is suggesting that the FPGAs do indeed have analog circuitry for phase detection, etc. and that there isn't anything magic about FPGA PLLs that makes them really different from any other sort. \$\endgroup\$ – supercat Jul 16 '11 at 3:28
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    \$\begingroup\$ @supercat: yes, but an answer like this screams "I'm too lazy to give a full answer". But then Leon Heller's answers are very often brief. \$\endgroup\$ – Federico Russo Jul 16 '11 at 10:04
  • \$\begingroup\$ @Federico: Leon's answer may be brief, but it still contains meaningful information. Remember that people answering here are volunteers and are not obligated to answer at all. You may wish for additional information, but that's a problem on your end. As long as the information that is given addresses the question and is correct, I think downvoting it is unfair. After all, he is the only one that answered at all, making his answer better than everyone else's, and you're not downvoting all them. \$\endgroup\$ – Olin Lathrop Jul 16 '11 at 15:35
  • \$\begingroup\$ conventional PLL are even impressing me too. =P \$\endgroup\$ – Jairo Andres Velasco Romero Jul 19 '11 at 21:28

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