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pll - active loop filter - RF Cafe Forums
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Ghada
Post subject: pll - active loop filter Posted: Wed Sep 28,
2005 7:30 am
Hi ,
Do any one have a design or example circuit
of active loop filter ?
and what are the advantages of the active
over the passive filter and how does it effect the vtune ?
Thank
you ....
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YZ-Israel
Post subject: active filterPosted:
Wed Sep 28, 2005 12:51 pm
hello,
Active filter is useful
in a case when the tunning voltage from
the IC PLL\Phase detector
is not fit to the tunning voltage of the VCO.
In that case you must
use Active filter to amplified the voltage.
but, it will increase
your phase noise (~6dB) in the loop BW.
I dont have an exemple
but you may find one at the demo`s from the
RF software like EagleWare
, AWR etc.
YZ-Israel
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Todd
Post subject:
Posted: Wed Sep 28, 2005 2:32 pm
check out National Semiconductors
for starters, in case you already haven't.
I'm sure you can find
good app-notes on this website.
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guest
Post
subject: active loop filtersPosted: Wed Sep 28, 2005 3:03 pm
1.
Active PLL filters look very much like classical op-amp integrators,
except there are one or more added resistors to set the frequency response.
2. One advantage is that you can get higher-order loops. This
gives you the possibility of tracking a changing frequency better. This
may also give you more reduction of the spurious frequencies that appear
at a delta of the reference frequency above and below the oscillator's
output frequency. These are sidebands, and are undesired garbage that
you try to minimize.
3. Another advantage that you can (but don't
necessarily) get is the ability to drive the phase error to zero.
4. The effect on noise depends on the noise level of the amplifier
used in the active filter. There are some amazingly quiet opamps available
these days!
Good Luck!
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Guest
Post
subject: Posted: Mon Oct 10, 2005 12:32 pm
ADISimPLL from Analog
Devices is a program that will help you simulate the effects of using
an active loop filter.
The Analog parts are generally better
than the national parts I also find...
Posted 11/12/2012
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