Phase shifter 90 degrees

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neazoi

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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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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.

Brian.
 
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..

Klaus
 

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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Hi,

I was mistaken, I referred to figure 6A.

Klaus
 

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