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ADL5380 I/Q driving capability

Question asked by limni on Feb 12, 2012
Latest reply on Mar 4, 2012 by Qui

Hi,

 

in my adl5380 application BB I/Q max freq is 190MHz.

ADL5380 should be connected  with either a 2¨1 balun (100Ω -->50Ω)  or a 4:1 balun (200Ω-->50Ω)

A  microstrip 100Ω differential line of aproax 12cm long connects al5380 with the balun.

Balun could not be placed at adl5380 side.

 

adl5380--> 100Ω microstrip 12cm long diff line --> balun  --> passive network

passive network Zin=50Ω

Balun 4:1 or 2:1

 

In order for adl5380 to see a load impedance >=200Ω, I'm considering the following interface options:

 

1. Use a resistive impedance transformation network near adl5380 to implement a 200Ω (adl5380 load)-->100Ω transformation, driving differential line with 100Ω source impedance and use a 2:1 balun at the end of the line. That solution will yield to the optimum matching , adl5380 driving scheme, but will have a rather large pwr loss.

2. place two 75Ω resistors in series with I,I', Q,Q' outputs , and a 4:1 balun at the and of diff. line. There will be an impedance mismatch at the adl5380-diff line side , adl5380 load impedance will be >200Ω, pwr loss will be less  than choice 1.

3. As choice 2 , but using 25Ω resistors , not creating impedance mismatch at adl5380 side.

 

Could ADL5380 drive directly a 100Ω diff line terminated at its end with a 200Ω impedance?

Which is the recomended interface option?

Which are the pros & cons for each 3 solutions?

would be any problem selecting choices 2 or 3 as far as adl5380 is concerned?

 

Thank you

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