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Impedance 2.4 GHz balun

Sorry to bother you all with a basic quastion:

I like to use a balun like the Murata LDB212G4005C-001 for a Zigbee project.

The balun is described as a 50 / 50 Ohm device.

On the balanced side it has 2 balanced connections and a centre tap.

Question: what is actually 50 Ohm on the balanced side?

  1. Centre tap to each of the balanced connections (so total impedance (if terminated correctly at unbalanced side) is ~*200* Ohms?)

  1. Balanced connection to other balanced connection?

As the Zigbee device has a balanced output with complex impedance ~approx. 200 Ohms, it seems a 200 to 50 Ohm balun would be in order (give or take a few extra L's / C's to match and filter), yet the manufacturer provides an example around a 50/50 ohm balun.

The datasheet is utterly unhelpful, as is the datasheet of the HHM1517, which is a similar part.

Insights welcome! TIA

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 - René
Reply to
René
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Balun: Balanced to Unbalanced transformation ! The fact that these devices can be used to provide impedance transformation as well is a bonus!

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Baron:
Reply to
Baron

I don't see anything about a centre-tap on this page

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The balun you mention is a 1:1 ratio. They also have 1:2 and 1:4 devices for the same frequency.

Reply to
Andrew Holme

René wrote: : I like to use a balun like the Murata LDB212G4005C-001 for a Zigbee : project.

I happened to use those same baluns together with a MAX2701 downmixer instead of the LDB15C500A2400's specified in the MAX2701 eval kit datasheet. I believe the device is a Guanella-style balun, and any of the GND's in the package drawing do not refer to a centre tap, but to the ground plane of the transmission lines (which is also the GND for the unbalanced port of course). They are 1:1, i.e. 50ohm-50ohm devices.

Regards, Mikko

Reply to
Mikko S Kiviranta

That's another thing. If one sees how these parts are used in actual cicrcuits, 2 is the center tap (hf ground and port bias), while 5 is the unbalanced ground for pin 1.

Indeed this is not to be derived from the datasheet, but pins 2 and 5 are *not* interconnected, pin 2 has DC contact with 3 and 4 only.

If I read you right, pins 3-4 and 1-5 are 1:1? If so, what do you consider the impedance 2-3 and 2-4 individually (unbalanced side terminated with 50 ohms)- 25 Ohms...or 12.5 Ohms? :-)

For the other poster: I would use the balun for both balance / unbalance conversion as well as impedance transformation. It seems that my theoretical calculations clash with actual application as I find it in working evaluation samples. No doubt I got it wrong, but I like to understand it....

Thanks for reacting!

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 - René
Reply to
René

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