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Adjustable phase shift?

Discussion in 'Electronic Design' started by Don A. Gilmore, Jan 3, 2004.

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  1. Hi kids:

    I've got a signal from a sensor that I convert to a simple, clean square
    wave at an audio frequency (anywhere between about 20 and 5000 Hz). I would
    like to be able to shift the phase of this wave by variable amounts. In
    other words, if we consider the conditioned square wave as starting at 0
    deg. is there a way to set up a circuit so that I can shift the wave
    infinitely up to +/- 90 deg. (relative to the input wave) by turning a knob
    (like a pot)?

    Any responses are greatly appreciated.

  2. Such as an allpass filter ?

  3. Jim Thompson

    Jim Thompson Guest

    You could make a variable *delay*, but anticipators are in short
    supply ;-)

    ...Jim Thompson
  4. Fred Bloggs

    Fred Bloggs Guest

    Since you are working with square waves, one approach would be a PLL
    with a phase-shifting DC bias summed with the PD output driving a
    PI-loop filter- this will force the VCO to advance/retard its phase
    relative to your input reference to compensate for the bias- pot controlled.
  5. Since you don't know the frequency of the signal, you can't adjust the phase
    accordingly. If I had to do what you seem to wnat, I would use a
    microcontroller. One part of the code determines the frequency semi real
    time and adjusts the phase accordingly. May I ask why you need such a delay?


  6. Genome

    Genome Guest

    Perhaps you should learn the delicate art of sucking cock first. Having
    mastered that one, from your own perspective, you might graduate to a bit of
    the oral on your girl/boy friend or wife.

    Hint, there are other parts that are part of the experience. Try shoving
    your thumb up your bum. It's a more severe form of stroking your ring piece
    with your index one.

    Now you've learnt how to ask nicely you might try having a look at one of
    those phase locked loop things, unless them's been discontinued, 4046 or

    Once you have figured out how to make one lock and be stable you might move
    on and think what will happen if you dribble a DC offset into the input of
    the VCO.

    Make sense?


    Well, shouldn't have fucked your cluster on the first try.


  7. It would be easy enough to do digitally, but of course your estimate
    of required edge timing would be, at best, as good as the most
    measurement of the period and position of the signal edge. This is an
    unusual requirement. What are you trying to do?

    Best regards,
    Spehro Pefhany
  8. Jim Thompson

    Jim Thompson Guest

    For square waves ?:)

    ...Jim Thompson
  9. I read in that Don A. Gilmore
    You can't phase-shift a square wave without using heroic means. What you
    can do is to introduce a time-delay. A precision monostable with
    adjustable period is one way of doing it.
  10. Fred Bloggs

    Fred Bloggs Guest

    No- he has to keep DC away from the VCO input for that 250:1 range- he
    has to apply the offset bias to an error integrator, and then to the
    VCO- the VCO phase output is the integration of the control input
    voltage offset from the DC value required to settle on the reference
    frequency-and you don't know what that is....
  11. Jim Thompson

    Jim Thompson Guest

    On the S.E.D/Schematics page of my website, see:


    The SyncRingOsc could be embellished to tap outputs from the shift

    ...Jim Thompson
  12. Genome

    Genome Guest

    No, no, no, no, no.

    Mr PD goes so many volts per degree. Mr DC offset...... offsets it. The rest
    of the bucket dunt matter..... caveat, as long as it's stable including the
    method of offsetting.

    I will not be having your babies!

  13. Hi John:

    Hey, I like this idea. It's simple. I'm guessing that I can use a pot with
    the timer to control the delay and thus the phase shift.

    Is there a particular timer that you recommend? I take it an ordinary 555
    would be inadequate.

    Thanks again for your input.

  14. Fred Bloggs

    Fred Bloggs Guest

    It's simple- but not very good- the PLL makes the phase adjust frequency
    independent- the timer does not. What kind of sensor is this anyway?-and
    why do you need adjustable phase shift?
  15. Fred Bloggs

    Fred Bloggs Guest

    Well- still working on the laser project- you condescendingly posted:

    "Hi kids:

    I'm trying to sense fairly fast (about 5000 Hz) pulses from a laser beam and
    keep it cheap for a comsumer-type application."

    Now for the +/- phase shift- not talking about your big secret design
    you're "gonna" make millions on-and looking for free advice from SED...
  16. I read in that Don A. Gilmore
    For the frequencies you cite, a 555 may be OK, but to be sure a 4047 or
    more modern device would be better.
  17. James Meyer

    James Meyer Guest

    I would start with the original signal. If it isn't close to a sine
    wave, I'd band-pass filter it to make it so. Then I'd pass the sine wave
    through another filter that had an adjustable phase delay associated with it.

    THEN I'd convert the signal to a square wave.

  18. Mark Zenier

    Mark Zenier Guest

    What about a monostable driven by an adjustable current source that
    is set by measuring the duration of the previous cycle.

    (Hey, whatever the customer wants. ;-) )

    Mark Zenier Washington State resident
  19. Baphomet

    Baphomet Guest

    I'm not sure you have provided sufficient information to effect a realistic
    solution. For example, is the frequency of the input square wave
    continuously changing? If so, how fast? Do you really need infinite
    resolution of the phase shift (time delay) or if not, what resolution would
    be acceptable? How much phase jitter can your circuit tolerate? It would
    really be nice to know the end application because not knowing is like
    shooting in the dark without night vision. Then again, perhaps I'm just not
    understanding the problem as stated.
  20. Mike

    Mike Guest

    I knew you were going to say that.

    -- Mike --
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