The dynamic range of phase change in an RU3993

[NKhal]

Hi,

I am using one of the evaluation boards to test 3993. My objective is to determine the change in the phase of the reflected signal. For this reason, I use the movement detection mode that shows the Phase of the tag using the linear I & Q RSSI values.

My tag is attached with a phase shifter that shifts the phase of the reflected back signal. The shifter can be adjusted to delay the signal from 0 up to 100 degrees. Which I can confirm using a VNA of even Oscilloscope.

When operating in the system, where I use Reader to determine the phase of the reflected signal, from my tag which has a phase shifter attached with, I don't see as much phase delay as I can see on the VNA. The maximum phase change that I see is 5 degrees, which was expected to be instead 80 degrees. There are some configurations of distance/pathloss, gain of transmitted signal, sensitivity of the receiver and AGC mode where I get more dynamic range of up to 30 degrees. However, that is a very impractical case.

I have tried calibrating and turning on AGL mode as well, which sometimes show some improvements, however, a small increase or decrease in the pathloss kills the dynamic range of the phase detector at the reader.

I am unable to determine the reason behind this. Can someone please help me in resolving this issue? Should you need any further clarifications, please don't hesitate to ask.

Thanks in advance.

[Bart Herse · Accepted solution]

Hello Nkhalid,

you mention the movement detection mode - which GUI version and FW version are you running with the EVAL board?

Note that from the IC you will be able to see a maximum of 90° phase change. In addition you should observe the phase bit which indicates if I and Q are in-phase or in anti-phase.

Cheers,

B

[NKhal]

Hi Bart,

Thank you for your reply.

I found that the problem was with my system. I was able to solve it by making some changes in it.

On the other hand, I found the phase bit to be very unstable. moreover, the value it shows is usually wrong. Especially when we are approaching 10 degrees or 80 degrees. I can anticipate this by changing the frequency and observing if the phase increases or decreases to see if one is leading or lagging. Is there a way to make it more stable?