How to do differential input matching?

[boy]

Differential matching

Hi, I got a differential input (actualy it is the input of active mixer IC), they gave the differential S11. HOw can I match that input? I do need a transformer to a single end but I have no idea how to do the matching. Also, any tutorial on dfferential input will be very appreciated.

 

[flyhigh]

Re: Differential matching

Hi,

I have never been involved in any differetial matching but I collected some papers about it as it was a very interesting area. The larger application area is in mixed (analog and digital) chips and highly integrated hybrid modules. The issue is that digital circuits are making the environment noisy for analog parts. The analog is then made differential, so common mode, sensitive to noise, is suppresed.

This is not what you were asking, so here is your paper. Hope this will help.

flyhigh

 

[boy]

Differential matching

Thank you, after that reading application note i know how to do the matching. I still have a litle question. what is the different between using a transformer with center tap and without center tap? I know only one reason of using a center tap transformer which is biasing open collector output of the device. Ortherwise, why some circuits connect the center tap to ground even it is used for balun function.

 

[DJ]

Re: Differential matching

Usually the differential devices help to reduce common noise as mentioned and for high speed pulses. One can match between differential to defferential as described in the paper or has to use a balun and then to match a single port. The center tape is used for DC return and in order to define the vertual ground between the + and - input ports. It is important for DB diode mixers for example.

 

[Mazz]

Re: Differential matching

If I can add a contribution to the discussion, I will advise you not to trust too much in ideal characteristics of baluns, ask for their s-parameters and verify the matching network in a simulator before implement it.
BR
Mazz