discrete balun

Can anybody help me in analysing the below circuit (mainly Balun design and adjacent filter). I couldn't able to understand how the values of these components were selected.
If I talk on Balun the formula says

√Rout*Rin/2*pi*f = L121 = L131
& 1/2*pi*f*√Rout*Rin = C122 = C132

But it doesn't matches to the real values mentioned in the datasheet of C2500 (BOM attached).

C2500 has Differential Load Impedance =80 + 74j = Rout (extracted from the datasheet)

Component values are

[/img]


Thanks

It is a lumped element phase shifter. One arm give 90 degrees, and the other arm gives -90 degrees. So they are supposed to combine the differential output into a single ended without throwing away half the power.

I have used these things before, and they seem to work OK, but they are very load dependent, and pretty narrow band. I wish they would just make these chips with a single ended output and allow us to get rid of all this garbage.

They probably tweaked the actual component values to optimize the impedance in the lab. The published impedance of chipcon parts is not too believable.

Thanks biff44,

What you said is the definition of Balun but can we calculate the value of the components involved ? If yes, How ?

Where do you get those formulae.
It is always better to check with the simulator like ADS , AWR etc.
I has two sections, one is balun i.e. LC which is one side connected to device with differential ports through coupling caps C121, C131. the other end of balun is connected to C123.

This balun matches the impedance with IC on one side and it is not 50 ohm on the other side. Which you need to find.
Let say it as z'
I am sure that C123, C124 with L122 is matching to this z' on balun side with the 50 ohm on the other side.

kspalla,
I got these formulas from an application note but don't know how to use it with the Balanced pins of the IC.

I tried to get the application note that has these formulae but failed.
May I ask to share the link? or file if possible.

I am sory for late response,
Here is one article from www.rfdesign.com, figure 3 shows Discrete Balun with along with the formula.

From the above article
http://rfdesign.com/mag/408rfdf1.pdf
it shows for single tranfer of impedance from Rsouce and R load.
in your case its RL is complex also you have additional pi section.
once again I repeat
It is always better to check with the simulator like ADS , AWR etc.
I has two sections, one is balun i.e. LC which is one side connected to device with differential ports through coupling caps C121, C131. the other end of balun is connected to C123.

This balun matches the impedance with IC on one side and it is not 50 ohm on the other side. Which you need to find.
Let say it as z'
I am sure that C123, C124 with L122 is matching to this z' on balun side with the 50 ohm on the other side.

elexlearner wrote
kspalla wrote

I think this is the formula for constructing a LC balun to convert a differential signal to a single-ended signal , a balanced to an unbalanced transformation or vice-versa.

There is a similar formula found inside the application note attached below.