[SI-LIST] Imbalance in outout from single ended drivers driving RF (13.56 MHz) antenna
- From: Bharathkumar Raju <bharathrajupcb@xxxxxxxxxxx>
- To: Signal Integrity <si-list@xxxxxxxxxxxxx>
- Date: Fri, 20 Feb 2009 20:14:35 +0530 (IST)
Dear List memebrs,
   We use NxP (Philips) chip MFRC531 in our RFID card reader. I am
measuring the output at the Tx1 & Tx2 pins when both pins are left open. I use
TDS 7154 Tek scope and in spectral mode I measure the output. The out put from
these pins is digital 5 volts @ 13.56 MHz.
    At 13.56 MHz the outputs are equal and reasonably balanced between
them. But as I try to measure the output at higher frequecnies I find mismatch
between the outputs. At some haromincs of 13.56 MHz Tx1 output is higher and at
some other harmonics Tx2 output is higher.
    Will this imablance bring any issues? How to reduce the mismatch? I
request your expert guidance here.
   We have a LC filter between the pins and ground where the single ended
output of the Tx pins get converetd to differntial signal. Output of this LC
filter goes to the antenna matching circuitry and the 13.56 loop antenna in the
PCB as trace.
BharathÂ
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