Balun

Hello,

I have a doubt about how to use the baluns. I have seen in aplication notes that, in the evaluation boards, if you have a SMA conector (like an input or output to the PCB) it's used the balun to convert the unbalanced input (ANNTENA) to a balanced input (a differential input in a CI).

My question is: ¿Can I use a balun, inside the PCB, to convert the unbalanced output of an IC in a balanced signal (that is the input of the next IC in the chain)?

For example:

if I want to connect the output of the ADL5373 (I/Q Modulator) with the ADL5330 (VGA), I will have to convert from un-balanced to balanced. ¿Is a good idea to do that? If you see the document AN-826 the describe in the Figure 15 to connect the single-ended output with the low pin of the differential input, INLO (with ac-coupling) and the INHI (with ac-coupling too) to the ground. ¿When can I use this kind of connection?¿Has it any problem?

Thank you in advance!

585340006AN_826.pdf
  • 0
    •  Analog Employees 
    on Jun 6, 2011 7:19 PM

    Hi!,

    You are on the right path. Although AN826 shows ac coupling between the modulator and ADL5330, for best performance, we recommend that a balun (MaCom ETC1-1-13 works good) be used here instead. The balun will help suppress even order harmonics coming from the modulator. If your performance requirements are not great, then you may be able to use the ac coupling caps but for best performance you will need the balun,

    Steve

  • 0
    •  Analog Employees 
    on Jun 6, 2011 7:21 PM

    Balun is the common product to convert single-ended(un-balanced) signal to differential(balanced) signal or vice versa. Usually balanced differential driving give better performance at common-mode, even-order performance than single-ended driving and so differential driving is recommended in terms of performance. But single-ended driving allows simple interface and it would be OK as long as performance is acceptable. So either balanced driving with balun or single-ended(unbalanced) driving is OK for the ADL5373-ADL5330 interface as mentioned at Fig 33 of ADL5330 datasheet, AN-826.