How to make differential input signal balanced?

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cmosbjt

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Hi,

I make a PCB to test a chip. I need differential sine waves input, the signal is 1 GHz and the amplitude is 1.6V. I use a transformer/ balun and draw the PCB trace very symmetric and very short (less than 1 inch), but when I test the board, I found the two signal are very unbalanced. One amplitude is much larger than the other one. Since the chip is not my design, I only know the input circuit is an inverter. In this case how to make the input signal balanced?

BTW, someone suggest me to measure the s-param and do the matching, but I think that is not correct since the signal I apply is large signal, small signal S-param is not valid in this case.
 

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