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Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??
From: |
Charles Swiger |
Subject: |
Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ?? |
Date: |
Fri, 17 Mar 2006 11:06:00 -0500 |
On Thu, 2006-03-16 at 19:55 -0500, Robert McGwier wrote:
> phase is ALWAYS computed in an NCO by phase = phase + freq so this says that
>
> phase_new = (phase_old + GAIN_FOR_PHASE*measured-phase-err) +
> NewFrequency. SO Something is amiss. You just turned your second
> order phase locked loop into a first order loop. It is NOT a typo.
>
> >>>> It's way over my head but is d_freq supposed to be in the d_phase
> >>>> calculation, 2nd line? phase is mod_2pi but freq can be a very big
> >>>> number, like mod_2pi(100000 + 1.572849). That is I'm USING very big
> >>>> numbers for max_freq and min_freq - don't suppose they're normalized
> >>>> somehow.
> >>>>
> >>> OK. I can see why that would be a problem. mod_2pi is optimized for
> >>> the expected "close in case" (symmetric around zero), thus the phase
> >>> isn't *really* getting folded down to [-pi,pi].
> >>>
> >>> Try changing mod_2pi to make the bounds check and then compute the
> >>> modulus if it needs to using division, floor, multiplication and
> >>> subtraction. It's not cheap, but it'll probably compute the right
> >>> answer.
> >>>
> >>>
Ok, I start to see - d_phase is an accumulator in (supposedly) mod_2pi
bounds - so d_freq would indeed be the derivitive of phase (the steeper
the phase, the greater the frequency) - and a 2nd order control loop has
a proportional and a derivitive component. Then d_phase is converted
to sin/cos for output.
It just seeemd strange to me that a very large number, d_freq, which is
bounds limited to between d_min_freq and d_max_freq, is inside a
function trying to limit it's output to between +PI and -PI.
if(100e3 > M_PI)
return(100e3-M_TWOPI)
or 99993.7168... error can get close to zero, but frequency will
never be less than d_freq_min.
--Chuck
- [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Charles Swiger, 2006/03/16
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Eric Blossom, 2006/03/16
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Charles Swiger, 2006/03/16
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Eric Blossom, 2006/03/16
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Charles Swiger, 2006/03/16
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Eric Blossom, 2006/03/16
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Robert McGwier, 2006/03/16
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??,
Charles Swiger <=
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Eric Blossom, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Charles Swiger, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Charles Swiger, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, ldoolitt, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Eric Blossom, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Charles Swiger, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Matt Ettus, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Robert McGwier, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Eric Blossom, 2006/03/20
- Re: [Discuss-gnuradio] fixing gr_pll_*_c[cf], Charles Swiger, 2006/03/22