constant phase shifts

Magnus Danielson magnus at
Wed Mar 25 22:05:35 CET 1998

>>>>> "DM" == David MOYLAN <moylan at> writes:

 DM> I'm wondering if anyone knows of a realistic
 DM> way to get constant phase shifts across
 DM> the frequency spectrum.  That is, a shifter
 DM> which is not frequency dependent.  More
 DM> specifically I'm trying to do it with triangle
 DM> waves.  Any thoughts?  Thanks.  dave moylan

Well, for generic signals you must use a allpass filter dimensioned to
have a maximum flat phase change. These will never be totally flat
since the problem is kind of hard to say the least... the better
approximation the more expensive it gets... and you can't forget
stability and noise issues here either...

However, for certain signals one migth use various tricks which
achives the same thing basicall.

One trick is to build a PLL (Phase Locked Loop) where one will add the
phase difference wanted just after the phase detector. With such a
device would one use a VCO that generated a suitable waveform.
CV controlable PLLs could BTW be a cool thing to use in some
cases... have anyone ever heard about such a thing, I know that PLLs
been used before... but CV adjustable PLLs?

PLLs is BTW very CV oriented...

Back on Track!

For the special cases of triangle and sawtooth I think I could dream
up a phase adjusting cursuit out of a fairly small bunch of op-amps
and resistors.

Hmm... quadrature saw/tri oscillators isn't common, are they?

Has Juergen any thougths on this?


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