Maker Pro
Maker Pro

Impedance 2.4 GHz balun

R

René

Jan 1, 1970
0
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?)

2. 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
 
B

Baron

Jan 1, 1970
0
René said:
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?)

2. 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

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

Andrew Holme

Jan 1, 1970
0
René said:
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?)

2. 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

I don't see anything about a centre-tap on this page
http://www.murata.com/catalog/k99/es0800.pdf

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

Mikko S Kiviranta

Jan 1, 1970
0
: 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
 
R

René

Jan 1, 1970
0
I don't see anything about a centre-tap on this page
http://www.murata.com/catalog/k99/es0800.pdf

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

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!
 
Top