TIDA-00524

Hi Martin,

When the D1 and D2 rectification diodes are placed, there is some reverse leakage current from the diodes(few uA).  Please not that the default configuration is to have D1 and D2 unpopulated(DNI).  These should only be populated if the design were to be implemented to be RF field powered. 

To confirm the RF field power could leak back into the battery causing issues/damage? 

If D1 and D2 are populated, it is possible that the RF power could cause issues with the battery.  Due to the low current consumption of the circuit without the diodes(less than 1uA in standby) in place, I recommend using the logger without the rectification diodes.  If you want to do instantaneous measurements or use a super cap/rechargeable battery, the diodes could be used to harvest some energy.  

Thanks, the link was very helpful. The adjusted delays made the difference with the tablet. I found that the 100uF cap does take some time to charge for the initial read, so will try with the suggestion I saw in the thread of using a 47uF cap instead for quicker charge times. 

Thanks, Martin. 

Hello, I had one follow up question. We don't have access to Altium Designer (even evaluation). Is there a way to get the NC drill file as part of the gerbers for this board? The board house is also concerned about the distance from the out er traces to the board outline. They like to have 15mil from the edge and are asking if there would be any issue increasing the board size by ~20mils. 

Thanks, Martin

Thank you. Have sent address in a private message. 

Regards, Martin

Martin,

Yes, please see the attached document for using a VNA. 

Also, I recently created a 3D printed rig for the two coils to be wrapped in.  Let me know if you are interested and have a 3d printer and I can provide my design files and specifications. 

3683.How to use Network Analyzer to measure resonant.ppt

Would very much appreciate the 3d printer files. I had put together a very simple test fixture (closer to the mini one) that I'd seen documented in the rf430frl152h guide.

Also, what gauge is the wire for coil and is it shielded magnet wire? 

I did not realize I could use the same fixture for the VNA as well as the SA.

When performing the thru calibration, I assume you just had the fixture attached, rather than connecting both ports?

Thanks, Martin

Martin,

I have attached my .stl file for the print.  I used 18 gauge copper wire for the single turn larger coil and 2 turns of 22 gauge for the smaller top coil.  I used a short SMA coax cable to connect from the top coil to VNA port 2.  The bottom coil is connected directly to an SMA connector which goes to port 1.  It may actually be easier to use a slightly thinner wire for the single turn coil as I had some trouble soldering the SMA since the thick gauge wire caused some tension.  We just want to have a thicker gauge for the larger coil and something thinner for the two turn coil.

  Helm3.stl

Thank you. This test fixture seems to be working quite well both with the VNA and the SA now. 

When harvesting power rather than running the TIDA-00524 on battery, what effect does that ultimately have on the tuning? Does the antenna need to be tuned differently, or is the goal still around 13.56Mhz measured on the fixture? 

On the TIDA-00524 running on battery, I currently see a resonant frequency of ~13.50Mhz and a BW of ~600kHz. 

Regards, Martin. 

Martin,

You will still want to tune for ~13.56Mhz.  If you are adding the schottky diodes for energy harvesting field power, make sure that you tune with the diodes populated as they will adjust the tuning as well.

Martin,

If you are doing this on FR4, the attached calculator will give good results for two layer coils.  If you are using a thin PCB substrate like flex PCB, the inductance will end up being a bit higher than the calculation.  It is somewhere on the order of 1.5x the inductance.  8540.Calculate_L.zip

Yes, I suggest treating it as a single coil since it really is a single coil.  Sum the number of turns on both top and bottom and input that into the flat rectangular coil tab.  It could be more accurate by using the gap between traces as well, but it won't make a huge difference and will get you close enough for tuning without this parameter.