Sensitivity and RFID read range are related but are not the same thing. Understand what you are looking for in your RFID chip.

One of the key things you are probably thinking about when selecting your RFID tag chip to develop your next IoT solution is RFID read range.

You may have done some research in the RFID industry and figured out that you want a solution where your RFID read range is around 10 meters. It’s not a guess game, you’ve already seen RFID tags working at those ranges.

You may even have gotten a little bit further. You have figured out that the RFID chips that are used in the solutions with the 10 meters have a sensitivity of around -20dBm. You’re probably going to ask for that value in the chip you will use for your development.

Long RFID read range inlays

Standard ID tag inlay with long RFID read range from Trace Tech ID

Unluckily, there are some things that are not completely right in this analysis.

RFID read range is not RFID chip sensitivity

While the chip sensitivity plays a big role in the read range of your solution, the RFID solution depends on the reader you are using, the reader antenna, the tag antenna and the tag chip.

The sensitivity of the chip is the minimum amount of power it needs to switch on the internal circuits and reply to the reader. It does not tell you anything about how that power gets to the chip (reader output power, duty cycle, reader antenna and tag antenna).

RFID chip sensitivity in different RFID solution types

That being said, there’s a second critical thing to take into account in your sensing solution development: sensitivity.

Yes, sensitivity once again. Why is that? Well, on top of sensitivity not being the only factor that impacts the RFID read range, you need to consider the nature of your RFID tag.

We said that sensitivity was the lowest power you need to switch on the tag. You may be able to switch on a simple circuit to reply with a unique ID number with -20dBm. However, for a sensor solution, you will probably need some more energy. You have some sensors to power up, right?

This takes the discussion into ‘should I have the sensitivity of the RFID chip or the sensitivity of the complete tag into account?’ The correct answer is you have to take into account both and consider very carefully the dynamic power consumption of your design.

Actually, I believe RFID chips for battery free device development should differentiate between sensitivity for ID only and sensitivity for an specific load. This would give you a lot more information about what to expect from the RFID chip.

Higher supply voltage forces a lower sensitivity

On top of that, RFID chips for identification purposes only can work at very low voltage levels. They only require power for a digital circuit so working at 1V or even lower is feasible.

Once you start thinking about using external devices you are probably going to need a higher supply voltage. Sensors for example typically work at 2.5V or 1.8V the lowest.

The need for the RFID chip to generate those voltage levels greatly reduces the sensitivity you can obtain. It also reduces the RFID read range of course.

As a summary, if you are really focusing on solutions with battery free RFID devices, I recommend you understand the differences between RFID chips for identification and RFID chips for extra capabilities.

As we discussed with the master vs. slave SPI feature, chip sensitivity is another of the key differences between RFID chips. You will do well by trying to find the chip with the highest sensitivity but make sure you do not get a -20dBm sensitivity chip that does not provide you with a power output you can actually use in your design.

If you haven’t done so yet, you can download the free eBook on read range for RFID sensor systems. You’ll find some extra information there and you can contact us directly at sales@farsens.com.