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TRF7960: TX Pulse length ISO14443A 106 kbps

Part Number: TRF7960

Dear sir or madam

 

We are using the TRF7960 for many years.

Accidentally we stumbled upon an issue regarding the default TX modulation pulse  length in ISO14443A mode (Bit rate 106 kbps).

The datasheet states, that the preset for ISO14443A with 106 kbps is 2.36 µs (Table 5-16 TX Pulse Length Control). But in contrast we measured a TX pulse length of only ~1,2 µs, which is theoretically way to short compared to the definition in ISO14443 standard, which defines a pulse length not less than 2 µs.

Selecting a  pulse length of ~ 2,36 µs  "manually" by writing 20h to TX Pulse Length Control register 06h results in a correct measured pulse length of ~ 2.35 µs.

So obviously the preset value seems to be not correct.

Anyhow we never encountered any problems with any ISO 14443A Tags when using the preset and therefore the short pulse length.

But we still wonder, if this is a known issue for the TRF7960.

Maybe you can shed some light on this observation.

Best regards

Burkhard Bröhl

  • Hello Burkhard,

    thanks for sharing your observation. I was not aware of such a device behavior so far. There is some note in chapter 6.3.3.1 of the datasheet, saying that the TX pulse depends on the Q factor of the antenna and correction can be done with the TX Pulse Length register. So you did a great job by adjusting it to the desired value.

    Best regards,

    Andreas.

  • Hello Andreas

    Thanks a lot for the quick response

    We are aware that antenna Q has influence on the pulse length, but we also measured the pulse length with an purely ohmic dummy load attached, to eliminate antenna influence and found the same result. Furthermore, writing the same value as the stated preset value (~ 2,3 µs) "manually" into the TX length register results in a different (correct) pulse length.

    So obviously the preset value stated in the datasheet seems to be not correct.

    Anyhow, as I mentioned, we never faced a problem with any ISO14443A TAG using the preset value so far. So maybe it ain't be a problem due to the admissible tolerance of the TAGs (I think you would have heard about it earlier, if anyone faced a problem).

    Also we already found (as you mentioned) the workaround by setting the length manually in case we will face any problem in the future. So there is no need for further investigation now.

    We just wondered, if this is a known errata in the datasheet and obviously it isn't yet. Maybe it can be corrected in future datasheet versions, if it turns out, that there is a mistake indeed.

    Thanks again and best regards

    Burkhard