On Thu, 13 Sep 2007 07:31:26 -0700, fpga.vhdl.designer@gmail.com
wrote:

>hi
>
>now it works quasi properly under simulink
>
>but i have at the ouput of the farrow filter (the input interpoled) a
>magnitude of +/- 1.5 and the input of this filter is +/-1 (before
>fixed sampling)
>
>i don't think that is because when the loop is locked, u = 0.5
>
>do you have idea ?

Just a comment not an answer: From your comment, you're testing the
case for no frequency difference; with frequency difference between
the two sides, loop locked case will have a constant speed u change,
not a fixed u, to accomodate the drift.

Reply by John●September 13, 20072007-09-13

On Sep 13, 10:26 am, Clay <phys...@bellsouth.net> wrote:

> On Sep 13, 3:22 am, Andor <andor.bari...@gmail.com> wrote:
>
>
>
> > julius <juli...@gmail.com> wrote:
> > > On Sep 12, 12:29 pm, "mnentwig" <mnent...@elisanet.fi> wrote:
>
> > > > How about this?
>
> > > >http://www.signumconcepts.com/IP_center/paper018.pdf
>
> > > > -mn
>
> > > It's ironic how the author misspelled the name of the
> > > inventor who inspired the entire paper [1].
>
> > > [1] C. W. Barrow, "A continuously variable digital delay
> > > element," ICAS-88.
>
> > That's odd. Here on comp.dsp, everybody talks about the Farrow filter.
> > In the title, the author also calls it the Farrow filter, and in the
> > reference it is attributed to Barrow. That seems to be strange
> > misspelling ...
>
> A single letter typo - The original paper is by C.W. Farrow of AT&T
> June 1988. Harris in his conference paper has the author's name
> properly spelled in the 1st reference. The mistake showed up in his
> regular paper a few months later. However, "Farrow" is the correct
> term.
>
> Clay

As in the actress, not the Alaskan town. I've heard both are cold
though.
John

Reply by ●September 13, 20072007-09-13

hi
now it works quasi properly under simulink
but i have at the ouput of the farrow filter (the input interpoled) a
magnitude of +/- 1.5 and the input of this filter is +/-1 (before
fixed sampling)
i don't think that is because when the loop is locked, u = 0.5
do you have idea ?

Reply by Clay●September 13, 20072007-09-13

On Sep 13, 3:22 am, Andor <andor.bari...@gmail.com> wrote:

> julius <juli...@gmail.com> wrote:
> > On Sep 12, 12:29 pm, "mnentwig" <mnent...@elisanet.fi> wrote:
>
> > > How about this?
>
> > >http://www.signumconcepts.com/IP_center/paper018.pdf
>
> > > -mn
>
> > It's ironic how the author misspelled the name of the
> > inventor who inspired the entire paper [1].
>
> > [1] C. W. Barrow, "A continuously variable digital delay
> > element," ICAS-88.
>
> That's odd. Here on comp.dsp, everybody talks about the Farrow filter.
> In the title, the author also calls it the Farrow filter, and in the
> reference it is attributed to Barrow. That seems to be strange
> misspelling ...

A single letter typo - The original paper is by C.W. Farrow of AT&T
June 1988. Harris in his conference paper has the author's name
properly spelled in the 1st reference. The mistake showed up in his
regular paper a few months later. However, "Farrow" is the correct
term.
Clay

Reply by Jerry Avins●September 13, 20072007-09-13

Andor wrote:

> julius <juli...@gmail.com> wrote:
>> On Sep 12, 12:29 pm, "mnentwig" <mnent...@elisanet.fi> wrote:
>>
>>> How about this?
>>> http://www.signumconcepts.com/IP_center/paper018.pdf
>>> -mn
>> It's ironic how the author misspelled the name of the
>> inventor who inspired the entire paper [1].
>>
>> [1] C. W. Barrow, "A continuously variable digital delay
>> element," ICAS-88.
>
> That's odd. Here on comp.dsp, everybody talks about the Farrow filter.
> In the title, the author also calls it the Farrow filter, and in the
> reference it is attributed to Barrow. That seems to be strange
> misspelling ...

Try this: A secretary did the bilbiography. He used a spell checker.
Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Reply by John Sampson●September 13, 20072007-09-13

fpga.vhdl.designer@gmail.com wrote:

> I don't understand how the Interpolator Farrow filter works with
> Gardner synchronizer loop.
>
> First, I have a fixed sampling rate, then the Farrow filter, then the
> second sampler, then the TED, Loop filter, NCO and the ouput of the
> NCO is sent to the second sampler.
>
> The TED, loop filter and NCO tends to acquire the symbol frequency.
> And the Farrow filter allows to sampling to the correct timing with
> interpolation.
>
> What is the signal u that control the delay in the Farrow filter ?
> This u signal shoud be beetwen 0 and 1 with my first order linear
> Farrow interpolator : y^(n-u)=y(n)+u[y(n-1)-y(n)]
>
> Where can I found a genreral scheme of this Gardner loop with the
> Farrow filter ?
>
> Thanks.
>
>

Think of the NCO as a non-saturating down counter. Before you decrement
the NCO, test if it will wrap around zero if decremented (current NCO <
decrement). If a wrap will occur, then it's time to generate an output.
The fraction u is the current NCO value (before decrement) divided by
the decrement value.
John

Reply by Steve Underwood●September 13, 20072007-09-13

fpga.vhdl.designer@gmail.com wrote:

> I don't understand how the Interpolator Farrow filter works with
> Gardner synchronizer loop.

The Gardner algorithm is only a timing error *detector*. You need to
combine it with something like the analogue tuning of an ADC's timing,
or a digital variable delay filter to form a synchroniser loop. The
Farrow structure is a popular way to realise that variable delay. Others
exist.

> First, I have a fixed sampling rate, then the Farrow filter, then the
> second sampler, then the TED, Loop filter, NCO and the ouput of the
> NCO is sent to the second sampler.

You have a loop filter filter in this signal chain, but you haven't
identified a loop that it is filtering.

> The TED, loop filter and NCO tends to acquire the symbol frequency.
> And the Farrow filter allows to sampling to the correct timing with
> interpolation.

The symbol frequency usually varies over a very narrow band. Your focus
has to be on the *phase* rather than the frequency of the symbols. You
need to home in your sampling, so you are hitting the middle of the
symbols (and possibly the edges or other well defined points, if your
next stage works at say T/2 or T/3). The continuous tracking of this
phase will deal with any minor difference between your notion of symbol
frequency, and the sender's.

> What is the signal u that control the delay in the Farrow filter ?
> This u signal shoud be beetwen 0 and 1 with my first order linear
> Farrow interpolator : y^(n-u)=y(n)+u[y(n-1)-y(n)]

The direction of error comes from that expression. You use this to nudge
the delay produced by the Farrow filter, such that the error from the
Gardner expression tends to zero. That is the control loop.

> Where can I found a genreral scheme of this Gardner loop with the
> Farrow filter ?

Gardner himself wrote good material on this topic. You can find it on
the IEEE web site.
Steve

Reply by ●September 13, 20072007-09-13

I don't understand how the Interpolator Farrow filter works with
Gardner synchronizer loop.
First, I have a fixed sampling rate, then the Farrow filter, then the
second sampler, then the TED, Loop filter, NCO and the ouput of the
NCO is sent to the second sampler.
The TED, loop filter and NCO tends to acquire the symbol frequency.
And the Farrow filter allows to sampling to the correct timing with
interpolation.
What is the signal u that control the delay in the Farrow filter ?
This u signal shoud be beetwen 0 and 1 with my first order linear
Farrow interpolator : y^(n-u)=y(n)+u[y(n-1)-y(n)]
Where can I found a genreral scheme of this Gardner loop with the
Farrow filter ?
Thanks.

Reply by Steve Underwood●September 13, 20072007-09-13

Andor wrote:

> julius <juli...@gmail.com> wrote:
>> On Sep 12, 12:29 pm, "mnentwig" <mnent...@elisanet.fi> wrote:
>>
>>> How about this?
>>> http://www.signumconcepts.com/IP_center/paper018.pdf
>>> -mn
>> It's ironic how the author misspelled the name of the
>> inventor who inspired the entire paper [1].
>>
>> [1] C. W. Barrow, "A continuously variable digital delay
>> element," ICAS-88.
>
> That's odd. Here on comp.dsp, everybody talks about the Farrow filter.
> In the title, the author also calls it the Farrow filter, and in the
> reference it is attributed to Barrow. That seems to be strange
> misspelling ...
>

Yes, Barrow is a wheely odd spelling spelling for Farrow. He made a bit
of a pig's litter of his spelling.
Steve

Reply by Andor●September 13, 20072007-09-13

julius <juli...@gmail.com> wrote:

> On Sep 12, 12:29 pm, "mnentwig" <mnent...@elisanet.fi> wrote:
>
> > How about this?
>
> >http://www.signumconcepts.com/IP_center/paper018.pdf
>
> > -mn
>
> It's ironic how the author misspelled the name of the
> inventor who inspired the entire paper [1].
>
> [1] C. W. Barrow, "A continuously variable digital delay
> element," ICAS-88.

That's odd. Here on comp.dsp, everybody talks about the Farrow filter.
In the title, the author also calls it the Farrow filter, and in the
reference it is attributed to Barrow. That seems to be strange
misspelling ...