CC2541: Half Harmonics

Tim Harvey84

Part Number: CC2541
Other Parts Discussed in Thread: CC2592

We made several boards with the CC2541 and CC2592 front end. All got FCC approval and the CE mark back in 2016.

Now we are getting them re-certified and are seeing half harmonics to boards that did not change.

Most of the filtering is done in the CC2541 and CC2592s. There are PI filters and other passives.

Where are places to look for a solution? What causes half harmonics when you use the Continuous Wave tone and the Modulated counterpart?

2.402GHz unmodulated has the smallest half harmonic. 2.44GHz unmodulated and 2.48GHz unmodulated have half harmonics almost as large as the main signal. Modulated is worse for all.

Thanks, Tim.

over 5 years ago

0 PM over 5 years ago

TI__Mastermind 27145 points

Hi,

If we compress CC2592 heavily then it may generate Half harmonic.

Please set the Tx power on CC2541 to < -3dBm and also check your design matches with our CC2592 reference design ( please use exact component values).

Thanks,

0 Tim Harvey84 over 5 years ago in reply to PM

Prodigy 180 points

PM,

We can look at that. Strange that it wasn't an issue, and now it is a big issue, with no design changes. THe FCC test reports had no half harmonics, now they are huge.

Would the passives between the CC2592 and the antenna have that much effect on the half harmonics?

Thanks,

TIm.

0 PM over 5 years ago in reply to Tim Harvey84

TI__Mastermind 27145 points

Hi,

Yes, they will effect the performance. Please make sure you use the recommended components in our Reference design.

Thanks,

0 Tim Harvey84 over 5 years ago in reply to PM

Prodigy 180 points

PM.

If one of the caps in the Pi filter went from a low ESL cap to a similar cap in every parameter except not listed as low ESL, could that cause half harmonics?

The reference designs usually just list caps as general use caps.

What about the DC blocking cap going from low ESL to general?

Thanks,

Tim.

0 PM over 5 years ago in reply to Tim Harvey84

TI__Mastermind 27145 points

Hi,

Please see the following picture. All the componen

ts from Pin-10 to Antenna are important. Please don't change any value.

Yes, you can use the equivalent values from the other Vendors.

Thanks,

0 Tim Harvey84 over 5 years ago in reply to PM

Prodigy 180 points

Did anything Change in the CC2541 or CC2592 in the last 4 years that could affect this?

Thanks,

Tim

0 PM over 5 years ago in reply to Tim Harvey84

TI__Mastermind 27145 points

Hi Tim,

No, nothing has been changed in the chips, which affects the performance.

Thanks,

0 Tim Harvey84 over 5 years ago in reply to PM

Prodigy 180 points

PM,

Your Reference Design is for connecting it to a 50 ohm load/antenna or a PC mounted antenna. Right?

What would we change if we just connected a 1/4 wave wire? (About 30mm)

That should look like a 377 ohm load. Right?

Thanks,

Tim.

0 PM over 5 years ago in reply to Tim Harvey84

TI__Mastermind 27145 points

Hi,

You can add a PI Network in between C3110 and Antenna for Antenna matching. Then this PI network can be used for matching the Antenna.

Please note that the Antenna matching must be done on a complete unit ( with casing).

Please refer to SWRA640 for Antenna matching.

Thanks,

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CC2541: Half Harmonics