[SI-LIST] Re: Imbalance in outout from single ended drivers driving RF (13.56 MHz) antenna
- From: olaney@xxxxxxxx
- To: bharathrajupcb@xxxxxxxxxxx
- Date: Fri, 20 Feb 2009 09:40:32 -0600
This is not a matching problem like making sure you have good edges.
Here, you want only the fundamental to reach the antenna. To do that the
bandpass filter must MAXIMIZE the mismatch at all harmonic frequencies.
Since you are (hopefully) not using the harmonic energy, it doesn't
matter whether harmonics levels are the same at both pins or not, just
the fundamental.
Orin Laney
On Fri, 20 Feb 2009 20:14:35 +0530 (IST) Bharathkumar Raju
<bharathrajupcb@xxxxxxxxxxx> writes:
> Dear List memebrs,
> Â Â Â 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.
> Â Â Â 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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