Other Parts Discussed in Thread: FDC2214,
Hello,
I would like to ask you a question about temperature drift od FDC2214 chip. I am using FDC2214 Evaluation Module and while testing it I notised that there is significant measurement drift between channel pairs. In application where I am going to use FDC2214 chip, I need to receive at most independent capacitance measurement results from temperature as possible (my device is dedicated to work outside in different weather conditions). At first I have read capacitance value in room temperature from Sensing Solutions EVM GUI. In the second step, I have warmed up Evaluation board to about 60 degrees Celcius and read results again. The test was performed without touch sensor board.
Channel. Room temp. Afret heating DeltaCap[pF]
0 18.419998 20.361565 1,941567
1 17.273549 19.138614 1,865065
2 18.425148 19.908471 1,483323
3 18.087430 19.507414 1,419984
As we can see, the difference in capacitance between channels 0,1 and 2,3 is about 0.5pF. I am going to use FDC2214 chip in liquid level measurents, where I would like to connect Enviroment electrode to channel 0 and Reference electrode to channel 2. With such big temperature drift, the ratiometric algorithm that should be used to get liquid level in cointainter can not work properly. On schematic placed in datasheet, we can see that output channels are switching by multiplexer to the core, so each channel should be measured the same way. The only thing which comes to my mind is that oryginally on 0 and 1 channels there where attached capacitive buttons and the tracks on this channels ale a little bit longer than in 2 and 3 channel but I need confirmation.
Could you explain to me, where this difference is comming from?
