R or L, missing part, schematic errors at Application Note of CR95HF demo board

[Tamas Novak]

Posted on February 03, 2017 at 16:21

What is the role of 0ohms in demo CR95HF reader (application note AN3394). Demo gerbers call these 0 ohm shorts not Resistor but 'L01' and 'L02'. Are they neccessary?

On the picture of the PCB (page  6/29 of the same AN3394 Doc ID 018754 Rev 5)   R12 is not seated. Is it neccessary?

On the same figure (page 6/29 AN3394) C17 seems to be NOT parallel to C3, but R1-C17-R5 circuit is 'above' C3 track. In theory 229pF is needed where parallel  200pF+15pF is used. Do I need to 'finetune' capacitance this way if 220pF is only +/-10%.  Is this so sensitive?

#doc-id-018754-rev-5 #cr95hf #an3394

[Dennis Jump]

Posted on February 03, 2017 at 19:47

The 'L' designation does imply a inductor, however, an inductor might not be required at that point at this time, so a 0 ohm resistor is there to replace it and complete the RF circuit. At some later date, or in your own design, you may need some inductance at that location for optimal tuning and the pads are there for adding a real inductor.

[Tamas Novak]

Posted on February 04, 2017 at 11:49

Thanks, Dennis,

I only need 5 mm sensing distance, so well tuned antenna may not be so important for me. On the other hand my design is only a test board, so I'm going to have those inductors/shorts on my PCB, and we'll see.

Is it the same case with R12 (~2K2) parallel to the antenna? Can be omitted?

[Dennis Jump]

Posted on February 04, 2017 at 18:52

I don't have the schematic or layout in front of me, but inductors come

in most of the standard sizes - certainly 0402 through 1206 - so finding

a 0 ohm resistor of the same size is a matter of selecting the matching

one from the catalog.

In any kind of reasonable quantity (more than 10), the prices start to

become reasonable and shouldn't break the budget. I never buy a single

resistor or capacitor of any value from a distributor - I always take a

quantity price. It is often the rule that 10 will cost the same as 4

items (give or take, the math is easy to see). Then on a second project,

you won't have to buy any.

Dennis

[Peter Boringer]

Posted on January 15, 2018 at 13:19

Hello Tamas,

L are ferrite bead with at least same characteristics as Wurt Electronik  referenced 74279042 on the demo Board.

They are used to set up an EMI filter on top of the antenna matching circuitry. For a test bench those can be replaced by a 0 ohms resistors and capacitors bead left open, in that case EMI filtering is not mandatory.

Regards