In Baluns

A while ago we wrote a product feature for Microwave Journal for our isolation baluns. Basically we showed why they were better than 4 port VNAs for high speed differential testing.

Check out the article here.

These baluns are now available up to 67 GHz:





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  • Pedram Kermani

    Hi Doug,

    I need a setup to measure the output of a differential amplifier which has unbalanced DC offset on it. I want to measure the width band noise of DC to 100Mhz on the output and only considering the power level. Can I use the BAL-0003 in combination with DC blocker in the input (if needed), and then connect the output of the Balun to the spectrum analyzer? FYI: the output of the amplifier is 130mV only.

    Kind regards,
    Pedram Kermani

    • Doug Jorgesen

      Hi Pedram,

      Whether or not you can use the BAL-0003 comes down to your amplifier.

      First the DC. The BAL-0003 is DC short to ground on all ports. It does not require a DC block, but your amplifier probably does (to keep the bias) so I would recommend a DC block. The positive and negative sides need to be phase matched, so you should put DC blocks on both sides.

      Next the RF. Because the isolation of the BAL-0003 is only around 8 dB, this means that the positive and negative sides of the amplifier will see 8 dB of crosstalk between them. Will this affect your noise? I don’t know. The way that I would conduct the experiment is to measure the noise using the BAL-0003 like you suggest (into the spectrum analyzer) and then measure it again with phase matched 3 dB pads on both the positive and negative ports. If the noise level drops by 3 dB then you know that you have a good measurement. If it drops by more (or less) then you know that the feedthrough is causing some kind of noise contribution.

      At 3 GHz I wouldn’t worry too much about phase matching the components as any two identically constructed components should be close to phase matched.

      Finally you can measure the single ended noise from the positive and negative side and compare them with the balanced noise as a sanity check. The difference will be the common mode noise that is rejected by the balun, so the balanced noise should be lower.



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