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How to make a 90º shifter in 25-40MHz

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manuel_trekker

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Hello,

I have to make a 90º shifter in 25-40MHz.
I'll use it as I/Q baseband signals of an I/Q modulator.

On I/Q modulator, the phase difference and amplitude balance between I signal and Q signal are very important. For optimum performance, this phase difference and balance must be low, less than 3degrees and 0.5dB for at least -30dBc of sideband supression.

The simplest circuit is a RC - CR, but for this wideband it's not adecuate on phase and amplitude performance.

Another option is use operational amplifier. I'm not sure, but I think that it's to high frequency.

Can anyone help me?

Thanks in advance.

MANUEL
 

If this signal is a single tone you can generate it at 4x frequency and use a johnson counter to get the two signals at 1x frequency.

Look at Electronic Filter Design Handbook by Williams and Taylor third edition chapter 7 section 5. They have several circuits active and passive.

If you do not need good phase accuracy you can make a lumped equivalent to coupled lines with a 1:1 transformer. Put it common mode in the two wires from your source to your load. This means that each winding is connected to the source on one end and the load on the other. Shunt the left and the right two terminal pairs with capacitors.

This is a simple enough circuit that you can do hand calculations and SPICE simulations to fine tune the design.
 

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