User:Jordsan/sandbox


 * The expressions are correct with respect to common-mode noise, if the impedance to ground at V+ and V- are the same (as stated on the second paragraph in the balanced circuit article). Which should be an stated requirement just the way it is mentioned that the output impedance of the driving amplifier is zero. The expressions are not correct with respect to Vin, so again the voltage divider equations do not hold as written.


 * A better approach might be stating that the impedance seen by common-mode noise is the same all along the line including the impedance looking both into the transmitting side (which is zero on both legs) and into the receiving amplifier (Zv+ and Zv- to ground are assumed to be equal). Therefore it doesn't matter where the noise is injected or what happens when it reaches one end or the other. By inspection of the circuit we know that the voltages at V+ and V- with respect to Vin are different. We don't need an equation for that. The signal is being fed to only one leg.


 * This is not the most appropriate way to prove that the line signal is not balanced. It is not required for V- to be much smaller than V+ only that they are different.