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ADRF6850 Differential RF Input Balun Question

Question asked by USVARobRoy on Mar 10, 2011
Latest reply on Mar 11, 2011 by TimM

Hello;

 

In the ADRF6850 Rev 0 datasheet, for a differential input, the RFCM pin guidance is as follows:

 

In Table 5, When driving the input differentially using a balun, connect this pin to the common terminal of the output coil of the balun. Decouple RFCM to the ground plane.

On page 20/36 under Variable Gain

To drive differentially, use a balun with the RFI and RFI pins driven by the balanced outputs of the balun, and connect the RFCM pin to the common balun output terminal. Decouple RFCM to ground.

On page 32/36 under RF Input

When driving the input differentially using a balun, connect this pin to the common terminal of the output coil of the balun.

 

My problem is I dont know anything about baluns or differential inputs. I assume that this means a balun (or rf transformer) that has three pins on the output coil, with the RFCM connected to the center tap pin? Like this one: http://www.minicircuits.com/pdfs/JTX-4-10T.pdf

 

My questions:

1. Does this part require a 3 pin output coil on the balun and is my understanding of the common pin correct?

2. If so, how is the decoupling cap determined? Am I just looking to sink the RF to ground at this pin so I am looking for low impedance to the RF range?

3. If a two pin output balun can be used, how would I wire the RFCM pin and what are the pitfalls or negative aspects of doing this?

 

Thanks for the help, this is for an American manufacturer of equipment that builds in the USA and I am proud to help them and scared stiff that I might miss something and not get it right for them.

 

Rob

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