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impedance matching of eZ430-TMS37157 Palfi

mochou liao
Prodigy 130 points
Other Parts Discussed in Thread: TMS37157

Dear all,

I have a question about the impedance matching. I was wondering why there is no impedance matching circuit in the eZ430-TMS37157 Palfi, so I searched in the forum. I found the answer that for the signal ended transmitter, the matching circuit is required, however the eZ430-TMS37157 Palfi is differential drive transmitter which should not implement the impedance matching circuit. I understand what is single ended and differential data transfer, but I don't understand the architecture of those two kinds of transmitter. And why the differential one doesn't need matching circuit? 

I was trying to search information on internet, but couldn't find any useful information. Hope someone in the forum can help me.

Kind regards,

Mochou Liao

  • 0
    TI__Guru* 91086 points

    this device is using almost pure resonance - this i am sure you are familiar with - once the true inductance of the coil is found, then it must be tuned and trimmed to accommodate both the high and low bit frequencies

    please see the datasheet and app notes (on the topic of antenna for the TMS37157) here: 

  • 0 in reply to Josh Wyatt
    Prodigy 130 points
    Dear Josh,
    I don't really understand your explanation. This picture shows how to trigger transponder antenna to the desired frequency, but my question is the impedance matching between transmitter and transponder. If they have the same impedance then the maximal power can be transferred. But for the differential transmitter, you said it is not necessary to make the impedance matching circuit. I don't understand why? Here is the your previous post: e2e.ti.com/.../848621
    Kind regards,
    Mochou Liao
  • 0 in reply to mochou liao
    TI__Guru* 91086 points

    the picture shows only the tag. the coupling factor between the tag and the reader is what governs the power transfer. Read up on Lenz's law and Faraday's law and you can understand the fundamentals. then understand that the tuning of the tag is such that it is resonant @ 134.2kHz and responds using 123.2kHz and 134.2kHz, to indicate a 1 or a 0, while the transmitter is off. (this is HDX operation, using FSK)

    HF tags and readers use FDX, and signal back to the reader using subcarriers, while the transmitter is still on. Please see the documents and then come back with questions related to them and the devices themselves. this would be most productive for you.

    and see the attached for how LF HDX works

    3771.FDX VS HDX.pdf

    6013.TMS37157 PaLFI_Technical_Training_03_29_2010.pdf