TRF7960A: Choosing ASK modulation depth

Phil Salisbury

Part Number: TRF7960A

I am using the TRF7960A in a product where the antenna is close to the path of a moving aluminum plate. The plate can be near or far from the antenna during data exchange. The Pri/Aux RSSI values are typically around 2/5 when the plate is far, and 4/4 when near so it is clear that plate position changes antenna tuning. I have been using OOK modulation and on a few rare occasions communication cannot occur. I have looked at technical discussions of ASK vs OOK and learned that ASK has higher SNR and lower error rates than OOK. The TRF796x supports 7%, 8.5%, 10%, 13%, 16%, 22%, 30% ASK. I found using 30% ASK almost always solves it in the field. I took a guess on 30% in the field but 7% works in my lab too so maybe 7% would be even better? Can you give me a few words on how to choose modulation depth based on application factors?

Thanks

Phil

over 6 years ago

0 Helfried Vollbrecht over 6 years ago

TI__Mastermind 18265 points

Hello Phil,

I do not have any knowledge in this case that can help with this issue. Even this is a little bit beyond our level of support I will try to get information from other sources and will come back to you the next days.

Best regards,

Helfried

0 Helfried Vollbrecht over 6 years ago in reply to Helfried Vollbrecht

TI__Mastermind 18265 points

Hello Phil,

just had a discussion with a colleague about your problem. From our experience the effect of aluminum is a change in the resonance frequency of the tag. This will lead to a reduced energy transfer to the tag.

From the modulation OOK should give the best result. You wrote that ASK has a better SNR but this is only relevant if you expect a noise problem in your setup.

Best regards,

Helfried

0 Phil Salisbury over 6 years ago in reply to Helfried Vollbrecht

Prodigy 240 points

Thanks for the reply.

There is some electro-magnetic interference from switching power supply and motors in the vicinity of the antenna so that may be a contributing factor.

Can you give me application scenarios where one would choose ASK 30% over 7% and 7% over 30%?

Thanks

Phil

0 Helfried Vollbrecht over 6 years ago in reply to Phil Salisbury

TI__Mastermind 18265 points

Hello Phil,

I do not see any application advantage for the lower modulation index. The 30% should be more robust because of the higher level of the sidebands.

The 7% to 30% is the range the standard requires for the cards to operate and so it is also required for the reader to operate.

One possible scenario could be a high power reader that will fall out of the regulatory limits for the sideband levels when using a higher modulation index.

Best regards,

Helfried

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TRF7960A: Choosing ASK modulation depth