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Measuring RFID Tag Voltages (DC)

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Referring to your original question about wireless measurement - you can put zero bias diodes connected as bridge . These diodes capasitance is fraction of picof and that is nothing compared to RFID capacitor value . But you will get measurement errors for voltage range closed to diode forward voltage . From test instructions you could see that Hmin Hmax required voltage to be induced on coil about 3V and can add estimated diode forward voltage to get final result, which of coruse does not tend to be as accurate as you will measure it with right equipment.

Test standard to use is selected based on by chip used in tag.
 

rautio said:
What R and C will work best depends on the diode you use. I would think 300 nF is too small. Seems like you would want the C to be significantly larger than the off-state C of your diode.
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Surely, if I use a larger capacitance for the RC then it would affect the resonance of the tag itself?
 

Is it right that in order to choose the right tuning capacitance I need to actually measure the capacitance of my chosen capacitors at 13.56 MHz.

For example the so called 100pF capacitor I have actualy has a much higher value of C at 13.56MHz (around 400pF).

So basically, all of the components I use on my test circuit must have the required values of L or C or R at 13.56MHz (which is not the same as the quoted values on the packaging)


Can anyone please shed light on this?

Regards :)


Cat
 
In fact, does this apply to any RF circuit?
 

Hello :),

I was thinking of modifying this idea to include a means of wirelessly transmitting the measured DC voltage to a PC instead of connecting an oscilloscpe directly to the circuit which cud affect the reading.

Can anyone give me advice on where to start with this idea?
Would it interfere much with the accuracy?

Would be nice to hear some opinions


Kind Regards

Cat

:)
 

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