Re: Narrow pll loop filter
- From: Vladimir Vassilevsky <antispam_bogus@xxxxxxxxxxx>
- Date: Sun, 02 Dec 2007 11:15:29 -0600
ElectricQuadrupole@xxxxxxxxx wrote:
Hello,
I'm trying to design a PLL with narrow loop filter, about 10Hz.
What do you mean exactly? Is 10Hz a desired close loop noise bandwidth or what?
The
most popular (2nd order)
designs are active PI filter and pasive RC filter, but calculations
gives me mF capacitors and mOhm
resistors.
Looks like the excessive open loop gain, so the poles have to be located at very low frequency.
I see, that phase shift for DC very low freq. in by PI
filter is
about 90 deg. I think that Bessel or Czebyshev (with slowly changing
phase shift, without instant "phase jump")
filter would be great, but these filters produces different phase
shifts for near-DC component and I don't know,
if phase loop will work.
Avoid the higher order filters in the PLL unless you really need them. It complicates the situation dramatically.
Does anyone know, how to build shuch a filter?
Try dropping the loop gain.
Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
.
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