Reply by robert bristow-johnson●September 22, 20092009-09-22
On Sep 22, 1:12�pm, Jerry Avins <j...@ieee.org> wrote:
> robert bristow-johnson wrote:
> > On Sep 21, 12:37 pm, Eric Jacobsen <eric.jacob...@ieee.org> wrote:
> >> On 9/21/2009 4:00 AM, JAlbertoDJ wrote:
>
> >>> I am reading and you are confuse me. Differents between PLL ans FLL??
> >>> None.
> > ...
> >> PLL is not equal to FLL. � PLLs can be used to track frequency, but FLLs
> >> don't lock phase. �PLLs do lock phase. �The distinction can be very
> >> important.
>
> > there is an inherent integrator in the loop in a PLL that is not in
> > the FLL. �so the closed loop tracking behavior (step response,
> > whatever) for the PLL is different than the FLL.
>
> > my $0.02 . (i hadn't done a regular ol' PLL since my college daze.
> > but i have done an ASRC that has something similar in the loop. �ya
> > know, maybe an ASRC *does* have a PLL in it. �the step or stride
> > length is sorta like instantaneous frequency.)
>
> http://tinyurl.com/lo39fn?
>
hmmm. i added (or suggested) "Asynchronous Sample Rate Converter" to
the list.
r b-j
Reply by Jerry Avins●September 22, 20092009-09-22
robert bristow-johnson wrote:
> On Sep 21, 12:37 pm, Eric Jacobsen <eric.jacob...@ieee.org> wrote:
>> On 9/21/2009 4:00 AM, JAlbertoDJ wrote:
>>
>>
>>
>>> I am reading and you are confuse me. Differents between PLL ans FLL??
>>> None.
> ...
>> PLL is not equal to FLL. PLLs can be used to track frequency, but FLLs
>> don't lock phase. PLLs do lock phase. The distinction can be very
>> important.
>
> there is an inherent integrator in the loop in a PLL that is not in
> the FLL. so the closed loop tracking behavior (step response,
> whatever) for the PLL is different than the FLL.
>
> my $0.02 . (i hadn't done a regular ol' PLL since my college daze.
> but i have done an ASRC that has something similar in the loop. ya
> know, maybe an ASRC *does* have a PLL in it. the step or stride
> length is sorta like instantaneous frequency.)
http://tinyurl.com/lo39fn ?
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by robert bristow-johnson●September 22, 20092009-09-22
On Sep 21, 12:37�pm, Eric Jacobsen <eric.jacob...@ieee.org> wrote:
> On 9/21/2009 4:00 AM, JAlbertoDJ wrote:
>
>
>
> > I am reading and you are confuse me. Differents between PLL ans FLL??
> > None.
>
...
>
> PLL is not equal to FLL. � PLLs can be used to track frequency, but FLLs
> don't lock phase. �PLLs do lock phase. �The distinction can be very
> important.
there is an inherent integrator in the loop in a PLL that is not in
the FLL. so the closed loop tracking behavior (step response,
whatever) for the PLL is different than the FLL.
my $0.02 . (i hadn't done a regular ol' PLL since my college daze.
but i have done an ASRC that has something similar in the loop. ya
know, maybe an ASRC *does* have a PLL in it. the step or stride
length is sorta like instantaneous frequency.)
r b-j
Reply by Tim Wescott●September 21, 20092009-09-21
On Mon, 21 Sep 2009 09:37:15 -0700, Eric Jacobsen wrote:
> On 9/21/2009 4:00 AM, JAlbertoDJ wrote:
>> I am reading and you are confuse me. Differents between PLL ans FLL??
>> None.
>>
>> In a PLL, VCO output is the frecuency recover, then you have a FLL.
>>
>>
>> I have done an AFC with a PLL. Error signal is get of this form:
>>
>> x=FFT previous
>> y=FFT current
>>
>> z = (complex conjugate of x) * y
>>
>> frecuency estimated= (arg of z) * Fs / (2*pi)
>>
>> Frecuency error= frecuency estimated - frecuency of bin FFT
>>
>>
> You deleted the context, so there's no way to tell where this question
> came from.
>
> PLL is not equal to FLL. PLLs can be used to track frequency, but FLLs
> don't lock phase. PLLs do lock phase. The distinction can be very
> important.
And in the context of AFC for something like FM radio reception you don't
even have to lock the frequency - you just need to pull it in close
enough to the design center of the receiver to make things work correctly.
--
www.wescottdesign.com
Reply by Eric Jacobsen●September 21, 20092009-09-21
On 9/21/2009 4:00 AM, JAlbertoDJ wrote:
> I am reading and you are confuse me. Differents between PLL ans FLL??
> None.
>
> In a PLL, VCO output is the frecuency recover, then you have a FLL.
>
>
> I have done an AFC with a PLL. Error signal is get of this form:
>
> x=FFT previous
> y=FFT current
>
> z = (complex conjugate of x) * y
>
> frecuency estimated= (arg of z) * Fs / (2*pi)
>
> Frecuency error= frecuency estimated - frecuency of bin FFT
>
You deleted the context, so there's no way to tell where this question
came from.
PLL is not equal to FLL. PLLs can be used to track frequency, but FLLs
don't lock phase. PLLs do lock phase. The distinction can be very
important.
--
Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.abineau.com
Reply by JAlbertoDJ●September 21, 20092009-09-21
I am reading and you are confuse me. Differents between PLL ans FLL??
None.
In a PLL, VCO output is the frecuency recover, then you have a FLL.
I have done an AFC with a PLL. Error signal is get of this form:
x=FFT previous
y=FFT current
z = (complex conjugate of x) * y
frecuency estimated= (arg of z) * Fs / (2*pi)
Frecuency error= frecuency estimated - frecuency of bin FFT
Reply by ●March 21, 20062006-03-21
Hi, thanks all you guys' help.
Actually, I have the same feeling as u said, in different references
and from different people, AFC experesses different meaning of
demodualtion. It depends...
So if I try to recover the carrier for QPSK demoduation in UHF channel,
can PLL system do this job? I think the answer is affirmative, right?
But some experts told me only AFC can achieve this. I feel confused and
therefore post my question here.
Anyway, thx your kindness.
Reply by john●March 20, 20062006-03-20
shellte@hotmail.com wrote:
> By the way, I asked some experts about this question, one said PLLs are
> only useful for frequency tracking if there is some carrier power in
> the spectrum of the received signal like AM, while AFC really refers to
> carrrier recovery even though there is not carrier present.
> The major difference between them is that AFC can achieve complete
> carrier recovery, no matter which modulation technique is involved.
> What do u think about that?
What AFC does is reduce the frequency error to a level that the
demodulator can handle. It does not "recover" the carrier, present or
not.
I would also point out that a PLL can in fact lock onto an absent
carrier. Look up the Costas PLL for an example.
John
Reply by Randy Yates●March 20, 20062006-03-20
Jerry Avins <jya@ieee.org> writes:
> shellte@hotmail.com wrote:
>> By the way, I asked some experts about this question, one said PLLs are
>> only useful for frequency tracking if there is some carrier power in
>> the spectrum of the received signal like AM, while AFC really refers to
>> carrrier recovery even though there is not carrier present.
>> The major difference between them is that AFC can achieve complete
>> carrier recovery, no matter which modulation technique is involved.
>> What do u think about that?
>
> You can see that people interpret these acronyms differently. Instead
> of bogging down in names for circuits, we should discuss the circuits
> themselves. Then the answer to your question becomes clear: it depends.
I second that. What we call something is important, but it seems the
more important question is, "What do you want to do?"
--
% Randy Yates % "Ticket to the moon, flight leaves here today
%% Fuquay-Varina, NC % from Satellite 2"
%%% 919-577-9882 % 'Ticket To The Moon'
%%%% <yates@ieee.org> % *Time*, Electric Light Orchestra
http://home.earthlink.net/~yatescr
Reply by Jerry Avins●March 20, 20062006-03-20
shellte@hotmail.com wrote:
> By the way, I asked some experts about this question, one said PLLs are
> only useful for frequency tracking if there is some carrier power in
> the spectrum of the received signal like AM, while AFC really refers to
> carrrier recovery even though there is not carrier present.
> The major difference between them is that AFC can achieve complete
> carrier recovery, no matter which modulation technique is involved.
> What do u think about that?
You can see that people interpret these acronyms differently. Instead of
bogging down in names for circuits, we should discuss the circuits
themselves. Then the answer to your question becomes clear: it depends.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������