ST25RU3993-HPEV sensitivity

[Fma.1]

Hi,

We tested the receiving sensitivity of the RFID reader evaluation kit ST25RU3993-HPEV, and the actual measurement is -66dBm, but the sensitivity given in each document is -77dBm.

The sensitivity given here(-77dBm) is the sensitivity of the ST25RU3993 chip or the reader evaluation kit?

Thanks in advance.

[Bart Herse]

Hi Fma.1,

what was the RX gain setting in the GUI when the measurement was performed - was it left at the default or was it set to the maximum?

The max. sensitivity of the evaluation kit is -77 dBm according to the 2020 update of the ISO 18046-3 measurement standard which takes both tag response side-bands into account.

Cheers,

B

[Fma.1]

The RX gain setting of the GUI during the test is the default setting.Is the measurement result -66dBm reasonable?

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Does the carrier�?cancellation circuit have any effect on the receiving gain?

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In addition, is there a more detailed document about the carrier�?cancellation circuit on the HPEV board except AN5532?

​

Thanks.​

[Fma.1]

Thanks.​

[Bart Herse]

Dear Fma.1,

for the default RX gain setting -66 dBm of sensitivity is expected, hence reasonable.

Please find additional information regarding the carrier cancellation in the schematics and layout of the PCB as well in the available SDK (containing source code).

If there any specific questions concerning the carrier cancellation, let us know.

Cheers,

B

[Fma.1]

Dear Bart，

​

I adjusted the RX gain to 19dBm, and the receiving sensitivity is indeed -77dBm.

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There is no LNA circuit in the receiving link, so where does the change of the RX gain play its role? In the ST25RU3993 chip data manual, it is said that the receiver system includes an automatic gain control system. Does the receiver gain parameter play a role in this system?

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In addition, can the internal protocol source code of ST25RU3993 be open for use?

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Thanks.​

[Bart Herse]

Dear Fma.1,

the internal RX mixer has a gain stage that can be activated which is the case if the RX gain slider is moved all the way to the right.

The automatic gain control reduces the RX gain if needed. So the RX gain slider defines the max. RX gain and the AGC reduces the gain if the tag response is getting too strong.

The source code of the ST25RU3993-HPEV and the former ST25RU3993-EVAL are all open source.

Just load the SDK from ST.COM/ST25RU.

It includes source code examples for Windows, Linux and an embedded STM32L4 device.

It also provides Java, C# and Python SW wrappers.

Here's the link

Cheers,

B

[Fma.1]

We measured the reading distance of the reader in the microwave anechoic chamber to only about 3 m.

After the receiving sensitivity is increased to -77dBm, the reading distance of the tag remains the same.

Why?Thanks.​

[Bart Herse]

Hi FMa.1,

there could be a number of reasons.

-what output power is set?

-what antenna is used?

-EIRP?

-what tag is used?

-how is the tag oriented in relation to the reader antenna

-on which material type is the tag attached to

When you mention that despite the increased RX sensitivity the tag was still not being detected, I am wondering if the tag is responding at all?

Have you checked that the tag is powered and able to respond beyond the 3 meters distance?

Cheers,

B

[Fma.1]

Hi Bart,

​

Sorry,here is our latest test results.

When the RX gain is 3dB, the receiving sensitivity is -63dBm, and the reading distance of the ISO standard tag is 3m.

When the RX gain is 19dB, the receiving sensitivity is -79dBm, and the reading distance of the ISO standard tag is 4m.

The reading distance is the distance at which the tag can hardly be read.​Beyond this distance,the tag the can only be read for a few seconds and can no longer be read.

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The test conditions are as follows.

The output circuit is external PA , the output power is 30 dBm.

The antenna is a ​circular polarized attenna whose gain is 6 dBi.

The tag is a ISO standard tag, that is hung in the air with paper tape.

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Can you analyze why the reading distance is so close?

Thanks.

​

[Bart Herse]

Dear Fma.1,

best would be to check if the tag is responding to the reader commands at a distance >4m as mentioned in my previous post.

Btw. what are the dimensions of the anechoic chamber you are testing in?

Cheers,

B

[Fma.1]

Hi Bart,

When the RX gain is 3dB and the distance between the tag and the reader is about 3.5m, the tag will respond briefly for about ten seconds, but when the distance is greater than 4m, the GUI displays no response.

The dimensions of the microwave anechoic chamber is about 8m*3m*3m.

Thanks,

Ma

[Bart Herse]

Dear Fma.1,

thanks, I thing I understand the situation your are facing.

What I am trying to explain is that you should check if the tag is responding at distances >4 m.

I acknowledge that I have assumed that the concept how to do this was clear and therefore did not explain it in detail.

So while the reader is scanning for tags, place the tag at a distance >4m.

At the same time you could check with a second antenna, that is for instance connected to a spectrum analyzer, if a tag response is present.

You could check this in the frequency or in the time (zero-span) domain.

• If you see a tag response happening then it would mean the reader's sensitivity is to low.
• If there is no tag response and you see only the reader's modulated spectrum then the tag has most probably insufficient power to turn ON.

Your observation that at 3.5m the tag can be detected only for ten seconds might be an indication that the tag has insufficient power.

A possible explanation is that when the reader starts to operate (and the reader is cold), TX power is the highest.

When the reader continues to operate is gets warm the TX power drops a little bit.

Maybe at 3.5m the tag is marginally powered and just a bit less TX power shuts the tag OFF.

You could also place the tag at 3.5m and slightly reduce the TX power in the reader settings. If the tag is then never responding at all it indicates that TX power is responsible.

I hope this explanation was helpful to you.

Cheers,

B