CC2640 on flexible PCB

Hiren Shah

Other Parts Discussed in Thread: CC2640

Hi,

We are working on CC2640 BLE for some medical application.

My issue is that we are going to make final design on flexible PCB. Now , How can I design antenna on flexible size.

i would like to have as small as possible with least components for antenna. distance is not very crucial for me. Range can be of 5 -10 mtr will be ok with us.

Max PCB size is 35 x 13 mm !!

if you can guide or share antenna design , it will be very helpful.

Hoping for earliest reply.

Regards,

Hiren Shah

over 8 years ago

0 CHS over 8 years ago

TI__Mastermind 18780 points

For small designs, I would recommend a chip antenna for instant from Fractus or Johanson. Also I would recommend looking at our antenna selection guide for some more antenna advices, www.ti.com/.../swra161b.pdf

0 Hiren Shah over 8 years ago in reply to CHS

Intellectual 355 points

Dear Charlotte,

I have gone through that doc.

I think you are right I need to use chip antenna for compact design.

But I am new to anteena design , so I would lie to know how do design antenna traces on flexible PCB for this chip.
Dielectric constant must be different for FR4 1.6 mm material and of flexible PCB.

Can I have some application note for this design.

Regards,
Hiren I Shah

0 CHS over 8 years ago in reply to Hiren Shah

TI__Mastermind 18780 points

For a small design, I would also go for a single ended design or chip balun (for instant from Murata) to reduce the number of components. The components should be placed as close as possible to the RF pins. The distance between the top layer and the GND layer underneath is the most important. We have 0.73 mm as in our 2-layer designs and 175 um in our 4-layers designs both using the same BOM so you do have some flexibility. Also note that if the distance between the end of the RF filter and antenna is less than 1/10th of the wavelength, it is not regarded as a transmission line and a 50 ohm trace is not that important. Also, I would recommend looking at the following links, one of the presentations also gives you a tool to calculate transmission lines.
Our wiki page processors.wiki.ti.com/.../Category:BluetoothLE.
Here you find layout considerations processors.wiki.ti.com/.../CC26xx_HW_training_Layout_Considerations.pdf and more info on the front-end configurations processors.wiki.ti.com/.../CC26xx_HW_training_Layout_Considerations.pdf

0 Hiren Shah over 8 years ago in reply to CHS

Intellectual 355 points

Dear CHS,

Thank you for sharing details.

I am going to use 0.32mm double side flexible pcb. So distance between top n bottom will we 320 um. Will that ok?

Additionally we are going to use 2.4 ghz so distance 2.4/10 ?

Regards,

Hiren shah

0 CHS over 8 years ago in reply to Hiren Shah

TI__Mastermind 18780 points

320um should be fine. It is 1/10 th of the wavelength, not the frequency, to make it a transmission line. If you have long traces, making a 50 ohm line is always a good practice anyway, and as said, in one of the links provided earlier include a tool to calculate widths of transmission lines.

0 Hiren Shah over 8 years ago in reply to CHS

Intellectual 355 points

Hi CHS,

Wavelength of 2.4GHz is around 4.35 inch ?

so should we have transmission line of 0.435 inch? is it true?

Regards,
Hiren Shah

0 Hiren Shah over 8 years ago in reply to Hiren Shah

Intellectual 355 points

Hi CHS,

Can you send me some reference design or rough sketch of antenna design.

in reference design and on dev kit trace is 20 mm long which is not feasible for my design.

Also suggest some Murata antenna part and other BOM.

Reagrds,
Hiren Shah

0 CHS over 8 years ago in reply to Hiren Shah

TI__Mastermind 18780 points

sounds right.

0 CHS over 8 years ago in reply to Hiren Shah

TI__Mastermind 18780 points

We have several antenna design available. I would recommend looking at the Antenna Selection Guide , www.ti.com/.../swra161b.pdf, the CC-antenna DK and the antenna selection quick start guide www.ti.com/.../swra351a.pdf. Both Johanson, Fractus and Murata (and more) have good chip antennas.

0 Hiren Shah over 8 years ago in reply to CHS

Intellectual 355 points

Dear CHS,

Thank you for helping me through out design process.

We are finalizing to use antennna due to its smaller size and lower profile.

Please let me know if I have chosen right antenna.

Also , as per TI recommendation schematic filters and all are different then what Johnson is recommending. So, I am confuse for which one to be followed.

Second , can I make shorter transmission line then shown in link attached? Can I cut down copper poring from what is shown in attached link?

Thank and Regards,

Hiren Shah

0 pixbroker over 8 years ago in reply to Hiren Shah

Genius 5820 points

We have done CC2640 on 2 layer FPC with Fractus FR05-S1-N-0-110 and it worked out great. We did a single ended design with internal bias and just used the recommended match values from the fractus app note (6.8nH and 1.5p) for a total of 3 external components including the chip antenna.

0 Hiren Shah over 8 years ago in reply to pixbroker

Intellectual 355 points

Hi Pixbroker,

Thank you for motivating me!!

I have only one question that can make transmission line of 7 mm long? i.e length from CC2640 to Antenna?

I can't afford to make transmission line longer. After this length 4 mm will be for CC2640 and after that other all components will be placed. So is this ok?

What was the thickness for your FPC PCB?

Can you share antenna design part or pic?

Regards,
Hiren I Shah

0 CHS over 8 years ago in reply to Hiren Shah

TI__Mastermind 18780 points

The antenna looks fine. The components suggested for the antenna are antenna matching components and needs to come in addition to the filter suggested from TI. The antenna matching components suggested by the antenna manufacturer is for that board and size of ground plane and will most likely need to be tuned to your board for optimal performance. You can also ask the antenna manufacturer for some advice as they know this product the best. The transmission line is 50 ohm so it can be shorter or removed if wanted, the important point is that the antenna looks like a 50 ohm load from the 50 ohm point in our ref design (after the filter/ DC block).

0 pixbroker over 8 years ago in reply to Hiren Shah

Genius 5820 points

Our polyamide core was only 50um thick, so theoretically the feed line should have been 0.08mm trace width, which was below our manufacturing specifications. we did the trace line at 0.125mm thickness and kept it as short as possible and it worked out ok. We don't have access to a network analyzer all the time so we did not tune the matching components yet but we are getting acceptable performance. Good luck.

0 Hiren Shah over 8 years ago in reply to pixbroker

Intellectual 355 points

Hi Pixbroker,

Thank you very much, Mine PCB is is also polyamide 0.1 mm. So my trace width come around 0.2 mm with 25 micron copper.

if I have 15mm x 35 mm PCB and I am leaving 7.5mm x 5 mm area for antenna as per recommendation.

Now can i use remaining 7.5 mm area on 15 mm side for CC2640 ( 4x4 mm package)? or should leave unoccupied with copper pouring?

Thanks and regards,
Hiren I Shah

0 pixbroker over 8 years ago in reply to Hiren Shah

Genius 5820 points

Typically the bottom layer would be used as a ground plane, so you should try to keep the copper pour as uninterrupted as possible. With your small size that will be a challenge, as you will have to do most of the routing on the top layer. I assume your FPC needs to ben somehow so you need to keep that in mind as well, as the bend lines and radii will further restrict your routing. We have no copper pour on the top layer, only on the bottom.

0 Hiren Shah over 8 years ago in reply to pixbroker

Intellectual 355 points

hi , friends. This is my final design for 0.2 um flexible pcb.

can you suggest if i have done right design.

please suggest correction if required.

Thanks,

Hiren Shah

0 pixbroker over 8 years ago in reply to Hiren Shah

Genius 5820 points

It's hard to see all the details from your picture. It might also be helpful for you to upload the schematic so we may comment on it. Personally i would have rotated the chip antenna by 90deg (CCW) so it is horizontal. As stated before, one thing to keep in mind for FPC about are the bend lines. It's not visible from your picture where they are. Just be mindful that your assembled FPC will still bend the way you need it to bend.

0 Hiren Shah over 8 years ago in reply to pixbroker

Intellectual 355 points

HI ,

I am uploading my sch picture for antenna.

I have used CC2640 ref for single ended antenna.

0 pixbroker over 8 years ago in reply to Hiren Shah

Genius 5820 points

That seems fine.

FYI, for our FPC project, we removed the bias and filter to save space. we only had 2 0402 components for matching between the RF pin and the chip antenna and our performance ended up being enough.

0 Fredrik K over 8 years ago in reply to pixbroker

TI__Guru** 106705 points

Hi Pixbroker,

Can you share the performance of your design? I am curious to know what output power you acheived and what the levels of the 2nd and 3rd harmonic was. I tested one of our eval boards without any filtering and the harmonic emission ended up being above FCC limits.

Cheers,
Fredrik

0 Hiren Shah over 8 years ago in reply to Fredrik K

Intellectual 355 points

HI Pixbroker and Fredrik and CHS,

I am also concern about harmonic emission.

We are also planning export from India , so it has to be under FCC limit.

Can you please check my layout and let me know if it OK.

This ca be good thread for flexible PCB , antenna and communication.

Thank you for every motivational reply.

Regards,
Hiren Shah

0 CHS over 8 years ago in reply to Hiren Shah

TI__Mastermind 18780 points

It is quite hard to see the details from your picture, can you please provide gerbers for a layout review?

0 Hiren Shah over 8 years ago in reply to CHS

Intellectual 355 points

Hi CHS,

Can I have your mail id?

So that I can send you Gerber files.

Regards,
Hiren Shah

0 CHS over 8 years ago in reply to Hiren Shah

TI__Mastermind 18780 points

send me a friend request so we can take it off line:)

0 Hiren Shah over 8 years ago in reply to CHS

Intellectual 355 points

Hello guys,

We first make 0.5mm PCB for testing.

Antenna and communication is working fine.

We are getting 10 feet range.

Regards,
Hiren Shah

0 Fredrik K over 8 years ago in reply to Hiren Shah

TI__Guru** 106705 points

Hi Shah,

Good to hear that your HW is working as expected!

Cheers,
Fredrik

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CC2640 on flexible PCB