ziller
Member
I'm having some difficulty understanding how an input transformer operates, in terms of CMRR. I've read over the excellent info in the Meta threads, along with lots of other info (maybe have info overload). In particular, I've been reading the Jensen artilcle
http://www.jensen-transformers.com/an/an002.pdf
and am hoping someone can explain some of the concepts in the paper. For instance, it states that symmetry has nothing to do with noise cancellation... But don't the signals of each line have to be 180 deg out of phase, lest the signal itself be canceled in the transformer? Or is it saying that it doesn't matter in terms of CMRR, but it does matter in terms of signal transfer to the secondary? Did I just answer my own question?
Also, on some schematics, the center tap in the primary on the input transformer is tied to one end of the secondary winding. In the Jenson schematics, there is no primary center tap, and the signals just float. Seems like that would make a difference, but I'm not sure what it is...
If it's the case that the signals have to be 180 out of phase, and the primary is not center tapped, then I think I get how any CM signal would be canceled in the transformer: both ends of the primary would be at the same voltage and so no current flows in the primary, and so no mutual induc to the secondary.
I think I'm missing something basic here, but can't pin it down...
Thanks.
http://www.jensen-transformers.com/an/an002.pdf
and am hoping someone can explain some of the concepts in the paper. For instance, it states that symmetry has nothing to do with noise cancellation... But don't the signals of each line have to be 180 deg out of phase, lest the signal itself be canceled in the transformer? Or is it saying that it doesn't matter in terms of CMRR, but it does matter in terms of signal transfer to the secondary? Did I just answer my own question?
Also, on some schematics, the center tap in the primary on the input transformer is tied to one end of the secondary winding. In the Jenson schematics, there is no primary center tap, and the signals just float. Seems like that would make a difference, but I'm not sure what it is...
If it's the case that the signals have to be 180 out of phase, and the primary is not center tapped, then I think I get how any CM signal would be canceled in the transformer: both ends of the primary would be at the same voltage and so no current flows in the primary, and so no mutual induc to the secondary.
I think I'm missing something basic here, but can't pin it down...
Thanks.