We have designed a PLL for an operating range of 11-14 GHz. The output of the VCO goes directly to the amplifier, and then to a divider, see the picture.

enter image description here

Is there anything that affects PLL locking time or performance because we are placing an amplifier in it?

Can anyone please please clarify this?

  • \$\begingroup\$ Have you simulated it before asking this question. If so, what was problematic? If you haven't simulated it, then my advice is that you should. \$\endgroup\$
    – Andy aka
    Jan 12 at 10:34
  • \$\begingroup\$ @Dinesh Is there a reason why you need an amplifier in the control loop? \$\endgroup\$
    – Don
    Jan 12 at 17:59
  • \$\begingroup\$ Yes, Don. Output power of VCO is not enough power to drive the N-DIVIDER input for dividing.That is the reason we kept it amplifier in between. Is there any anything phase will affect? \$\endgroup\$
    – Dinesh
    Jan 13 at 4:39

1 Answer 1


I'm not an PLL design expert, but you can get Amplitude noise to phase noise conversion.

If the amplifier is too noisy this can be translated into jitter, thus your output signal might not follow your input signal properly, and this noise can be translated to other blocks in your system. It'll be very jittery.

  • \$\begingroup\$ I really appreciate your response @ErnestoG. Which means you are saying placing amplifier in between VCO and N-Divider is not good option. Definitively, phase will affect right? \$\endgroup\$
    – Dinesh
    Jan 13 at 9:09
  • \$\begingroup\$ @Dinesh I'm not saying is bad, but I'd suggest you do a system simulation assuming different noise values for your amplifier to check how jitter is affected. It could be that it doesn't matter because your oscillator phase noise is orders of magnitude more important, I don't know. Just saying you should take it into account before concluding is important or not. \$\endgroup\$
    – ErnestoG
    Jan 13 at 9:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.