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  1. #1
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    Phase shifter 90 degrees

    Page 6 and 7 of the attached document, the figure 6C is a variable phase shifter (90 degrees). Do the shunt capacitors need to be tuned at the same capacitance value both or it can be different?
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    Re: Phase shifter 90 degrees

    They need to be the same value to keep the impedances of the I and Q branches equal. Note that the shift changes with frequency so simple RC or LC delays are only suitable for a very narrow range of frequencies and ideally need tuning for exact 90 degrees at each frequency used.

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    Re: Phase shifter 90 degrees

    Hi,

    I agree with: both C should have the same value.

    But doesn't shift one path to positive phase, while the other shifts to negative phase.
    ...in a way that the phase difference between both paths is always 90°? In a wide range of frequency..

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    Re: Phase shifter 90 degrees

    Actually the example attached (with Xc=XL=50ohm) shows that the phase response is not wide range.

    And to keep the impedance constant you have to change not only the values of C but also of the value of L, which makes the circuit pretty hard to tune.



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    Re: Phase shifter 90 degrees

    Hi,

    I was mistaken, I referred to figure 6A.

    Klaus
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