Message-ID: <15263.200012151513@gemini>
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: rsgb_lf_group@blacksheep.org
Date: Fri, 15 Dec 2000 15:17:11 +0000
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Subject: LF: Phase Modulator
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Reply-To: rsgb_lf_group@blacksheep.org
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Dear Andy, LF Group,

To generate linear phase shift, how about a PWM:

Generate a sawtooth at carrier frequency, feed into one input of a 
comparator. Other comparator input is analogue "phase" signal. 
The higher the "phase" voltage, the later in the cycle the 
comparator changes state, ie more phase lag. You could get a 
square wave back again by dividing by 2; this would also limit the 
phase shift to 180 degrees, which is probably what you want.

Main problem might be that you would have to design the circuit so 
that a transition would definitely occur somewhere on the cycle, 
whatever the analogue input voltage was - otherwise you would 
lose the carrier altogether.

Cheers, Jim Moritz
73 de M0BMU