Measuring the impedance of the balance port of balun chip

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btom

Joined: 11 Sep 2008
Posts: 4

02 Jul 2009 19:30 impedance balance -patent

Hi,

Can someone provide some pointers on, if possible, to measure the impedance of the balance port of a balun chip with a 2-port network analyzer? Thanks.

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FvM

Joined: 22 Jan 2008
Posts: 5154
Helped: 766
Location: Bochum, Germany

03 Jul 2009 7:50 common mode rejection balun measurement

Basically, you can connect another (auxilary) balun to the VNA and perform a calibration at it's balanced side (using a suitable termination resistor). There may be a considerable error due to the limited common mode rejection of the aux balun. Also the results for the D.U.T possibly depend on the actual common mode termination. This would mean, that the D.U.T can't be characterized completely by a single differential impedance.

btom

Joined: 11 Sep 2008
Posts: 4

03 Jul 2009 18:17 Re: Measuring the impedance of the balance port of balun chi

FvM,

Thanks for the reply. However, I am not very clear what you are suggesting. In some of app notes that I have found shows (1) insertion loss measurement with two baluns with the balanced ports connected together and the unbalanced port of each balun going to the VNA, and (2) Return loss mesaurement with the one balun with unbalanced port going to the VNA and a resistor across the balanced ports.

I know that the unbalanced port is 50ohms, but I do not any of the characteristics of the balanced port. . Thanks.