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RE: "differential bridged output " balanced or not?

Posted by Ugly (A) on September 7, 2017 at 21:00:03

In Reply to: RE: "differential bridged output " balanced or not? posted by Charles Hansen on September 7, 2017 at 13:08:17:

"the marrow definition of "balanced" you used was extremely limited and defined only one aspect of true differential balanced circuitry."

My interpretation was the OP only asked whether his proposed circuit can be considered balanced or not.

I didn't interpret his post to be an inquiry about the signal integrity merits of using differential signaling in a balanced circuits of varying topology.

That's why I was only talking about whether his circuit would end up with a balanced output, not whether it could be considered "true differential balanced circuitry"

Maybe I misunderstood the OP, I don't know.

"A balanced circuit is a two-conductor circuit in which both conductors and all circuits connected to them have the same impedance with respect to ground and to all other conductors. The purpose of balancing is to make the noise pickup equal in both conductors, in which case it will be a common-mode signal which can be made to cancel out in the load." - Bill Whitlock Jensen Transformers

It seems that Bill is more eloquent than me, but this sure sounds familiar.

I still argue being balanced or not is about impedance as "seen" by common mode signal and would also add that the signaling type or circuit topology type makes no difference. For example, signaling on balanced lines/circuitry does not have to be differential for the line/circuit to be balanced. All that matters is characteristic impedance of one line of the signal is as close to equal to characteristic impedance of the other line of the signal as they are both related to the common mode signal reference. This allows common mode signal to cancel at the inputs of whatever load the signal is intended to be driving, ie input of ADC, next amp stage, speaker, etc.

The wiki link below also seems to echo the impedance to common mode noise thing.

"In a balanced line the two signal lines are of a matched impedance to help ensure that interference induced in the line is common-mode and can be removed at the receiving end by circuitry with good common-mode rejection." -from Wikipedia

• https://en.wikipedia.org/wiki/Balanced_circuit   (Open in New Window)

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