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design of a 120 degree phase shifter

Discussion in 'Electronic Design' started by rony, Oct 10, 2007.

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  1. rony

    rony Guest

    can anyone tell me how to implement a 120degree phase shifter for
    using in a high power circuit and possibly a opamp model that can be
    used for the same pls also let me know anyalternate methhods for
    implementing the same with some other components instead of op amps
  2. D from BC

    D from BC Guest

    F range??
    D from BC
  3. HardySpicer

    HardySpicer Guest

    You need an RLC circuit. An RC would attenuate the signal too
    much.Take the output at the cap and put all three in series. The phase
    shift is easy to calculate.Take the Laplace Transform and find the
    transfer function - then work out the phase using arctan(imag/Real).
    The solution is not unique of course. Watch the ratings of the
    cap,inductor and resistor and stand well back when switching on!

  4. neon


    Oct 21, 2006
    take an op-amp amplify if need be add an rc network to get what you want. and amplify again use AND gates cross couple to generate square wave OR USE COMPARATORS
  5. Tom Bruhns

    Tom Bruhns Guest

    What's the signal source? What frequency range? Do you need a 3-
    phase output (0--120--240 degrees) or only a 120 degree shift? Do you
    need the output to be 120 degrees from the input, or can you use a
    circuit that takes an input and provides two outputs separated by 120
    degrees? (Or three outputs, 0--120--240 from each other?) What will
    the load be on the output(s)?

    If you're operating on a fixed frequency, it's relatively easy to use
    a fixed LC circuit to get the phase shift you want, but if you need it
    to operate over a range of frequencies, it likely will be easier if
    you can use a set of three outputs that maintain a particular
    relationship to each other, but a variable phase relative to the
    input. This assumes you want the amplitudes to be held close to each

    A more complete description in the question is likely going to get you
    a better answer...


  6. Jim Thompson

    Jim Thompson Guest

    Easiest way to make an adjustable phase shifter without amplitude
    variation is push-pull drive....

    / Variable R
    o----> Output
    --- C

    ( -E is 180° out-of-phase from +E )

    ...Jim Thompson
  7. A bit OT, but around 1980 I built a sound card to
    go off a TRS-80 Output, using this,

    (I used a transistor instead of an Op-Amp).

    Using the output I programmed the resistor
    values, (IIRC it was 8 bit O/P, maybe 16),
    using CMOS switches, latched.
    Anyway the tone was nearly perfect sinsodial
    and sounded great pumped through a big old
    Hi-Fi. (I don't like square wave audio).

    Phase-shift oscillators are great for Audio.
  8. John Fields

    John Fields Guest

    View in Courier:

    ..[CLOCK]--+--[COUNTER]--+--[LUT 0°]--[DAC]--[LPF]--> 0° OUT
    .. | | |
    .. +-----------------------------------+
    .. | |
    .. | +--[LUT 120°]--[DAC]--[LPF]-> 120° OUT
    .. | |
    .. +-------------------------------------+
  9. Tom Bruhns

    Tom Bruhns Guest

    Yes, indeed--but the phase shift of that circuit depends on frequency,
    so we need to know if the OP wants the circuit to operate over a range
    of frequencies or only at one frequency. It will help to know what
    the load is, too, and if the load is stable.

  10. Jamie

    Jamie Guest

    if you were talking about a steady CW, I would say a
    PLL OSC so that it's 120 degree's offset.
    But, I don't think we're talking about the same thing here
    are we?
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