Bonsoir, Perhaps we can take profit from ITU-T and ETSI specifications for clocks that are build with PLL. I just read that this evening, and I forgot it was writen like this. For example, in G.813 about SEC (SDH equipment clock). Today, this type of clock is also used in synchronous Ethernet, with the term EEC (Ethernet equipment clock). G.813 � 9 Noise transfer: �The SEC can be viewed as a low-pass filter for the differences between the actual input phase and the ideal input phase of the reference. The minimum and maximum allowed bandwidths for this low-pass filter behaviour are based on the considerations described in Appendix II and are indicated below� The minimum bandwidth requirement for a SEC is 1 Hz. The maximum bandwidth requirement for a SEC is 10 Hz�. And I have a reply to my question concerning the bandwith. Thanks also to YTach for these words. Best regards, Michelot
PLL Basics
Started by ●February 13, 2009
Reply by ●February 14, 20092009-02-14
Reply by ●February 14, 20092009-02-14
On Feb 13, 2:30�pm, Jerry Avins <j...@ieee.org> wrote:> Muzaffer Kal wrote: > > On Fri, 13 Feb 2009 11:36:50 -0500, Jerry Avins <j...@ieee.org> wrote: > > >> Of course filters are used in a PLL implementation. That doesn't mean a > >> PLL is a filter, any more it is a VCO. > > > I'm curious as to how you make the distinction. What makes a PLL a > > non-filter? It has an H(s), it takes a noisy periodic signal and > > produces cleaned up, frequency shaped version of it. How is that > > qualitatively different from an RC filter? > > It's also a signal generator, no? The OP asked a a simple,question that > (it seemed to me) embodied a misconception that I tried to dispel. To > answer your question, a simple RC filter isn't bandpass. > > Jerry > -- > Engineering is the art of making what you want from things you can get. > �����������������������������������������������������������������������Furthermore, a PLL produces an output signal when the input is zero. Is that different enough? John
Reply by ●February 14, 20092009-02-14
Glen Herrmannsfeldt <gah@ugcs.caltech.edu> writes:> [...] > I probably believe that different people have legitimately different > definitions of what is and isn't a filter. In the DSP context, it might > be a little more restrictive than in other contexts.I would define a filter as any LTI system; as someone else said, anything with a T(s) is a "filter." That includes linear control systems, of which a PLL is a type.> Would you consider a half wave rectifier a filter?I would not. This thread is interesting because it seems that a PLL isn't a filter (that's what I was thinking at first). I now believe it is. -- % Randy Yates % "Bird, on the wing, %% Fuquay-Varina, NC % goes floating by %%% 919-577-9882 % but there's a teardrop in his eye..." %%%% <yates@ieee.org> % 'One Summer Dream', *Face The Music*, ELO http://www.digitalsignallabs.com
Reply by ●February 14, 20092009-02-14
Randy Yates <yates@ieee.org> wrote:>I would define a filter as any LTI system; as someone else said, >anything with a T(s) is a "filter." That includes linear control >systems, of which a PLL is a type.I like this definition, but I'm not so sure a voltage-controlled oscillator is a linear component. It has output frequencies that do not appear at its inputs. I'll have to think about this one a little more. :-) Steve
