Hello, how do we know that the carrier cancelation is correct in my board?

[MSilv.3]

I developed a board with the same carrier cancelation circuit as the ST25-EVAL board, but I'm having some different measures regarding the reception power. I would like to know if it is correct or if something is wrong.

EVAL measurements :

Ptx = 28.95dbm

Prx = -8.671dbm

Measurements of my board:

Ptx = 29.34dbm

Prx = 5.23dbm

I really don't know about there value are correct.

Please, help me and Thanks!

[Bart Herse · Accepted solution]

Hello MSilv.3,

a reflected power of 5.23 dBm after running carrier cancellation is too high.

Which carrier cancellation algorithm variant was run/has been implement?

Note: The Fast algorithm attempts to find a minimum of reflected power starting from the current configuration of the three tunable capacitors. While this algorithm is fast it might get stuck in a local minimum and therefore not yielding the lowest obtainable reflected power. Best use the Fast algorithm for re-tuning and for initial tuning only if the current tunable capacitor settings are already known to be close to optimal.

Otherwise use the Slow or Medium algorithm for improved accuracy in finding a carrier cancellation circuit configuration yielding a low reflected power.

For more details on the various carrier cancellation algorithm please refer to the user manual of the GUI SW which can be found on ST.COM

Also watch out for the values of the three tunable capacitors after running any algorithm: None of the three capacitor values should end up at their minimum or maximum value as this indicates that the algorithm would have liked to change the tunable capacitor further in this direction but couldn't since its range limit was reached. If this is the case change the lumped component next to the respective tunable capacitor at the carrier cancellation circuit.

Cheers,

B

[MSilv.3]

Hello Bart Herse,

I was use the Fast algorithm. So now I used the SLOW algorithm, but I had this result that you can see in this figures below.

I think this tunable capacitors not work very well.

This is tx sign.

And then, this is rx sign.

When I read the tunable capacitors these are the result: cin= 0x02 clen= 0x0 cout=0x1b.

So, Can you help me please?

[Bart Herse]

Hello MSilv.3,

What is the measurement procedure here?

The images shared suggest that first the carrier cancellation algorithm is run

and then the spectrum analyzer (SA) is connected for a measurement.

Note that when introducing the SA and any measurement cable and adaptors to the RFID circuit the carrier cancellation is void and any value measured with the SA is an incorrect value.

Important is the result of the reflected power that was measured by the reader IC because this is the point where the reflected power should be cancelled.

What reflected power value do you seen when measured by the reader IC?

Cheers,

B

[MSilv.3]

Hello, Bart Herse

This values was about transmissition power and reception power, but like you sad this values were wrong. Thanks for helping me understand this.

So, the values of I and Q can be seen in the figure below. Soon the calculated reflection power value is around 3,22dbm. I think there value are wrong.

Cheers,

Monalisa

[Bart Herse]

Dear MSilv.3,

since this output seems to be specific to you implementation can you please elaborate on how the data was formated/converted?

This should help to interpret the I and Q readings from the reader IC

Cheers,

B