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+- 90 phase shifter

Discussion in 'Electronic Design' started by greysky, Jun 18, 2013.

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  1. greysky

    greysky Guest

    Anyone know how to make a phase shifter that will shift a sine wave +- 90
    degrees without distorting it in the process?
    Thanks.
     
  2. Joerg

    Joerg Guest


    Unless you do it digitally that will only work over a limited frequency
    range. Check our Hilbert transform circuitry. Usually consist of lots of
    precision R's and C's. There are also tricks how to do those with
    switched capacitor filters. Mostly used in ultrasound, Radar and
    somewhat ancient ham radio gear.
     
  3. Guest

    ¨
    Audio ?

    Microwave ?
     
  4. tm

    tm Guest

    The right length of coax? For just one frequency.
     
  5. Jamie

    Jamie Guest

    Sure, one be long piece of wire, or what ever the freq you are working
    with. calculate the wave length in free space and then apply the
    velocity factor to shorten that figure up a bit. Of course it depends
    on what you're using as a conductor, you''ll also need to worry about
    matching the line to avoid reflection distortion.

    THen again, you could always use a delay line

    Jamie
     
  6. No, but yes, kinda.

    Any circuit, even as simple as a single conductor distorts its input
    to some degree, adding, if nothing else, noise. As your circuit
    increases in complexity, it will have distortions in amplitude, and
    delay that vary based on the incoming signal.

    Engineering is all about defining the parameters of that distortion
    that are acceptable to your application, described in one of several
    domains, and developing a circuit that meets those parametrs.

    The circuit I think you're looking for is often called an "all passs"
    filter in the analog domain, or a Hilbert Transform.

    For a signal of a single frequency, it is nothing more than a fixed
    delay. If your signal can take one of many frequencies, you need a
    delay that is variable based on frequency, such that the delay is
    always the time that represents 90-degrees at each frequency.

    The implementation I'm thinking of has one input and two outputs, that are
    each delayed from the input, but one is delayed 90 degrees more than
    the other over some range of frequencies.

    Putting it in the concrete -- if I want to create a single-sideband
    signal to carry Voice Modulation, I can use a phase splitter that
    gives me 0 and 90-degree shifts over a limited band from roughly 300
    to 3000 hertz.
     
  7. Phil Allison

    Phil Allison Guest


    ** Completely ambiguous question.

    Why don't people just SAY what it is they are trying to do.



    .... Phil
     
  8. Joerg

    Joerg Guest

    Well, if it was just one frequency all you need is one inductor and one
    capacitor, not a whole PLL :)
     
  9. Bill Sloman

    Bill Sloman Guest

    M.J. Gingell “Single Sideband Modulation using Sequence Asymmetric Polyphase Networks” Electrical Communication 48 21-25 (1973). See also http://traktoria.org/files/electronics/networks/polyphase_networks.pdf

    describes an approach that provides a close approximation to a 90 degree phase shift over an appreciable range of frequencies. It's in the second edition of "The Art of Electronics" by Horowitz and Hill (ISBN 0-521-37095-7) in section 5.17 as a "phase sequence filter".
     
  10. Hey, could you stick a divider before the mixer, lock to 1/2 the freq. and get
    the full 180? (I guess you'd need a divider after the VCO too.)

    George H.
    So would integrator or
     
  11. Yeah, a long piece of wire with a tap... how can you make the velocity really low?
    For microwave frequecies, we had this trombone like thing at the FEL.
    (not cheap!!!)

    George H.
     
  12. miso

    miso Guest

    Are you generating this sine wave? If so, just generate it in quadrature.

    IIRC a biquad implementation of a bandpass filter has a 90 phase
    difference between the op amps. But that is a narrow band solution.

    I recall a project where I needed a wide band 90 degree phase shift and
    ended up using a paper out of the IRE journal. (RE as in Radio
    Engineers). It was a SSB phase splitter filter.
     
  13. Robert Baer

    Robert Baer Guest

    Act ignorant and use a L-C network..
     
  14. Robert Baer

    Robert Baer Guest

    Too simple for management..
     
  15. As well as the other suggestions, analog configurations with all-pass
    filters can give you 90 degree phase shift over a range of
    frequencies, practical up to maybe the entire audio range (lots of
    op-amps and resistors and capacitors).

    Or, assuming audio, maybe consider a DSP with a Hilbert filter
    algorithm.
     
  16. Jamie

    Jamie Guest

    Freq of interest would help immensely. We use coax phase matching.
    Just roll up some turns according to what you need and there you are..

    Just remember what one famous person said.

    "No matter where you go, there you are"

    Jamie
     
  17. Guest

    If its analog audio, you can do it with two parallel paths of allpass filters that approximate a 90 degree phase difference over some frequency range.The closer you want to get to DC , the more filter sections you will need.To design this you may need to use an optimizer of some sort. Same approach can be used in digital, but with another restriction that you can't get 90 degrees at Fs/2, and the harder you try the more filter sections you willburn.
    Bob

    Bob
     
  18. whit3rd

    whit3rd Guest

    Howzabout... make a 20F oscillator, use flip/flops to divide it down
    to a 5F quadrature pair/quartet of signals, and upmix your X with one of those
    then downmix the 5F + X with a different phase?

    If the X signal is narrowband, and you filter the result well, it is a sine wave
    at X with phase according to the chosen downmix signal.
     
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