Balun: voltage & current relation; voltage vs power balun

[vlsi_design2]

1. The following tutorial says that ideal_balun in analogLib of virtuoso has these voltage and current relations
Vd=Vp - Vm
Id=1/2( Ip - Im )
Why the current relation is not Ip-Im?

https://www.designers-guide.org/Analysis/diff.pdf


2. What is difference between voltage & power balun. I think in voltage balun, unbalanced output voltage is half and in power balun power is half i.e. unbalaned voltage is 0.7 times diff. I want to know what is the hardware difference in them?

 

[sarge]

Hi,

for case 1:

Pd = Vd^2/Rin = Pp + Pm = Vd^2/2Rout, so Rin = 2Rout

Next, id = Vd/Rin, ip - im = Vp/Rout + Vm/Rout = Vd/2Rout + Vd/2Rout = Vd/Rin + Vd/Rin = 2Vd/Rin = 2id, or id = 1/2(ip-im)

 

[Tomsin yin]

sarge's explannation is very well.

 

[D.A.(Tony)Stewart]

The quick answer is because ;
- potentials and electric fields are averaged while currents and fluxes are summed.


Like a bunch of same cell voltage batteries in parallel gives the average voltage but the max current capacity adds ( don't try this on LiPo unless <=2% matched)


Thus vc = ½(vp + vn) ....
thus the common mode current ( which are in opposite direction) is the net sum or...

ic = ip + in

 

[vlsi_design2]

Hi Sarge,
Thank you for the mathematical solution.

Hi SunnySkyGuy,
Thank you for the elegant intuitive explanation. The common mode results i.e. Vc and Ic are conceivable.
But how do you intuitively explain the differential results? especially Id=1/2(Ip-In)