Message-ID: <014601c0c46c$ba6d2100$0301a8c0@steve>
From: "Steve Olney" <ollaneg@zeta.org.au>
To: rsgb_lf_group@blacksheep.org
References: <3.0.1.16.20010328085558.2f57efaa@mail.cc.kuleuven.ac.be>
Subject: LF: Re: Soft phase switching...
Date: Sat, 14 Apr 2001 08:54:34 +1000
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G'day Rik,

>
> BTW,  another idea :
> What happens if you send a BPSK (instant phase switching) as reference
> signal to a PLL ?
> The reaction time of the PLL would depend on the feedback circuitery,
maybe
> this could also be used to get 'soft phase transistions'.
> At 136kHz the whole PLL could be incorporated in a single CMOS4046, just 1
> cheap IC and half a dozen resistors/capacitors might do the job.
>

What a fascinating idea !!   I have been struggling with a way to reduce the
BW of the simple hard-phase switching from an XOR gate (used for generating
FDK signals).    I had tried all sorts of complicated ways of generating a
suitable signal (PWM with high switching frequency, stepped phase change,
etc) not much different from previous ideas from others.    Your idea of a
PLL captured (:-) my interest.

I did a couple of spectrum analyses using Excel for both the hard-switched
case (see Wanjina.gif attached - 3kB) and for a slow-phase case (see
Wanjina_Slow.gif attached - 3kB).

The hard-switched case shows the expected spectrum.    The slow-switched
case shows the appearance of the "carrier" frequency between the two mains
sidebands and the close-in sidebands are of the same order of magnitude as
the hard-switched case.    The gain comes from the rapid roll-off further
out.

Looks promising.    When I get a round tuit I will implement this using a
CD4046 as suggested.    There are two phase detectors.    One which uses an
XOR gate and locks to a phase difference of 90 degrees.    This one is not
suitable as it seems to lock to +/-90 degrees, therefore I suspect for an
180 degrees shift it would only momentarily hiccup but not actually switch
phase.    The other phase detector locks to a zero phase difference and so
would switch.    The only disadvantage is that it has less noise immunity.
This should not be an issue here as there are no S/N considerations (or very
little).

A great piece of lateral thinking Rik !!

73s Steve Olney (VK2ZTO/AXSO - QF56IK : Lat -33 34 07, Long +150 44 40)
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