CC2520 balun

Hello,

Can I have additionnal information about the impedance matching at the output of the CC2520. Please correct me if I am wrong.

If we have a look at the schematic of the CC2520 EM_2_1, we have:

1. C171 and C191, used as most probably as DC blocking capacitors. Is there any reasons to have 2 differents values: 39pF and 82 pF respectively ? At these frequencies, they are supposed to be short-circuits.

2. C172, C91 and 2 TLin's (shunt and series), used as the LC-CL balun. So if my understanding is correct, we can replace the micro strip inductors  by 1.2nH inductors. Is it right ?

3. C173, C174 and 1TLin. What is the purpose of this network ? Is it used as a filter or to match the impedance ? Can we drop it on our board for space reason ?

Chris

You might want to consider the easier approach of an integrated ceramic device, such as the Murata LDB182G4510C-110.

Along with a 3.9nH 0402 inductor between RF_P and RF_N, it should give you 50Ohm on 4 layers FR4 (1.6mm thick).

Thanks a lot for your answer !

I think that we need to add a least a dc block capacitors between the balun and the CC2520. Could you confirm this ?

This is the schematic we use.

You can short the 1.5nH and remove the 2.2pF for ~1dB increase in output power.

This is the schematic that we used in the lab. If you do remove the low pass filter just make sure that you are compliant with the conducted / radiated harmonic requirements that you are targetting.

Regards, Richard.

I have a question on the CC2520 Murata Balun Solution:The schematic shows pins 4 and 6 as the balanced inputs to the Murata Balun network comming from the CC2520 chip. The Murata data sheet however shows pins 3 an 4 as balanced inputs (pin 6 seems to be Not Connected)! Pin 3 is according to data sheet a balanced port pin. Is there a mixup in pins numbers, or is the schematic right anyway?

There are 2 versions of the component, C and G, with different pinout.  In the schematic, version C was used.

All of the TI reference designs mention to follow the design explicitly, which is usually only 2 layer designs.  However what are the effects of additional layers on the board, thicknesses, and different PCB material (FR4, FR406, 370HR, etc.)? 

Also I like that someone listed replacement discrete inductors for the transmission line inductors in the cc2520 balun in the reference design, but what were the values of the T-line inductors we were originally supposed to use?  I'm new to designing RF PCBs, is there a formula for calculating the inductance of a PCB trace using the H, W, L, dielectric constant, etc.? 

Thanks.

Richard,

Sorry, I realize this is a fairly old post but I've got a new question.

The post that preceded this one in the thread showed a Balun schematic for the CC2520 using the Murata LDB182G4510C-110 LTCC Balun plus some passive components.

I think that your reply following that post - "This is the schematic that we used in the lab" - refers to that Murata Balun circuit. [I'd attach a picture of that schematic but can't remember how to cut and paste using keystrokes only. ]

Assuming that schematic does represent what you used, do you recall or have documented elsewhere, how well this Balun worked in terms of insertion loss in transmit and (more importantly) receive mode? I basically just need find out the typical receiver sensitivity and output power with this particular Balun+passives in place.

Thanks,

Mark

Richard,

Here's another CC2520 Balun question. I can find many more LTCC Baluns qualified for use with the CC2530 than I can with the CC2520.  Are the RF sections of both chips similar enough that a Balun designed for operation with the CC2530 would also (with slight tweaking) work with the CC2520?

Thanks,

Mark

Gribo, just for information: the 10nF decoupling capacitor is needed in order for the CC2520 to work properly? Should RF_P and RF_N be DC decoupled?

Thank you for your help,
R.