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Phase shifter question

Discussion in 'Electronic Design' started by alan, Feb 11, 2008.

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  1. alan

    alan Guest

    The phase shifter described in H&H has a phase that starts at 0 at DC
    and then goes to negative 180 at high freq. (excuse me if I got the
    definition of phase backwards) Is there a phase shifter that shifts
    phase the other direction with respect to freq, i.e. start at -180 at
    low freq and increases to 0?
     
  2. MooseFET

    MooseFET Guest


    The phase shifter that exists shifts the phase later with higher
    frequencies. Later in phase is minus values of degrees. The phase
    goes from 0 to -180 as frequency increases.

    The phase shifter you want poses a bit of a problem. It requires that
    the phase go earlier with higher frequencies. Over a limited band
    this can be done but not without also having a variation in gain.
    This is because, in real life, only information from the past can be
    used in creation of the output.
     
  3. Joerg

    Joerg Guest


    Then how about those time machines?
     
  4. John Larkin

    John Larkin Guest

    Just invert the output.

    John
     
  5. Jim Thompson

    Jim Thompson Guest

    Or learn to read ?:)

    -180° is _always_ lagging.

    ...Jim Thompson
     
  6. Tim Wescott

    Tim Wescott Guest

    Technically that will yield a phase shifter that goes from -180 degrees
    to -360 -- the endpoints will be right, but if the OP needs a positive
    slope then he needs to find the contact information for Non-Causal
    Systems, Inc. to get the parts. (their number is in next year's phone
    book).

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Do you need to implement control loops in software?
    "Applied Control Theory for Embedded Systems" gives you just what it says.
    See details at http://www.wescottdesign.com/actfes/actfes.html
     
  7. Jim Thompson

    Jim Thompson Guest

    If the OP is referring to H&H figure 2.29, just reverse inputs phi1
    and phi2.

    Or as I would designate them (as shown in H&H)...

    phi1 => +ein

    phi2 => -ein

    180° phase difference between inputs +ein and -ein.

    ...Jim Thompson
     
  8. ehsjr

    ehsjr Guest

    Or he could use those dilithium capacitors that JL
    figured the guy in the other thread uses.

    Ed
     
  9. Joel Koltner

    Joel Koltner Guest

    Oh, come oh, the digital guys use non-casual filters all the time.

    You just to overlook the input-output latency involved and designs can be as
    non-casual as you'd like. :)
     
  10. krw

    krw Guest

    You'd be lagging at -180° too.
     
  11. Guest

    Yes and no. Let's say you have a differential signal.


    in out
    + ----C-----+
    - ----C----- +

    +----L------ -
    - ----L ---- +

    So feed the low frequency with crossed inductors and feed the high
    frequency is non-crossed capacitors.

    Assuming source and load resistors, this should end up as an all-pass
    network with phase shift.
     
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