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Antenna and interference

Antenna and interference

Antenna and interference

Hi everyone,

I have a problem and i hope someone can help me,
I am designing a system comprising the following (RFID system(13.56Mhz) - TFT LCD (alike to the one in smartwatch))
The antenna used in the RFID system is inductive loop antenna,

if i put the antenna as in the assembly shown in the image attached,
Will this affect the performance of the antenna, or the LCD in a negative manner,

Thanks in advance,
Ahmed Tarek

RE: Antenna and interference

I'll post your image inline.

RE: Antenna and interference

Image provides no info, except arrangement.

One could retune the antenna, if it's even resonant to begin with. Adjust the parallel capacitor if applicable.

EMI on circuits could be modelled, or just take some commonsense E3 precautions and build a rough prototype. Try it.

One could also use the embedded software to blank the display when transmitting, and vice versa.

RE: Antenna and interference

You'll have antenna EMI on the LCD data/control signals, and A/C LCD signals plopped right in the middle of an antenna. Definition of "negative" is up for debate.

Dan - Owner

RE: Antenna and interference

Why not just do some testing? Surely, you already have RFIDs floating around; you can see if it interferes with any displays that you have. RFID power is so low that I doubt that you'd even have recognizable interference.

TTFN (ta ta for now)
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RE: Antenna and interference

Is RFID power really low?

I understood that the excitation to power-up the passive RFID tags was a significant challenge. The limiting factor for range.

If there's enough to power-up the RFID tag, then there's certainly enough RF to generate noticeable voltages on unprotected circuitry in the middle of the coil.

Just asking, curious. smile

RE: Antenna and interference

Expect a typical transmitter to be around 10dBm to a 50-ohm load (=/-, depending upon frequency), so let's just call it 2V peak-to-peak.

Dan - Owner

RE: Antenna and interference

That's surprisingly (to me) low. I had assumed that higher powers were required to illuminate a passive RFID tag.

Another ref: The specs for the TI TRF7960A state "Programmable Output Power: +20 dBm (100 mW) or +23 dBm (200 mW)".

That's close enough that your "around 10dBm" statement is perfectly correct. Thank you for adjusting my assumptions.

Yes, that is a fairly low power. So addressing the EMI risks or issues should be quite easy.

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