This thread has been locked.
If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
Part Number: FDC2114EVM
I am using the FDC2114 chip for a university senior project, and I want to make sure that I understand the technical side of what the sensor is actually doing, because this is not clear from the datasheet.
As I understand it, the capacitor is fully charged (in the attached diagram it would be done by closing S1 and reopening after charging), then the charged capacitor is connected in series to an inductor (in this diagram, closing S2, though there are other ways to achieve this), and then an ADC measures the frequency across the inductor as Vout oscillates between +V and -V. This should be the resonant frequency, from which it backs out the capacitance from sqrt(LC).
Is this the general idea behind what the FDC2114 does, even if there is some extra circuitry to clean up the signal?
Evan, That method would work, but it isn't what the FDC2114 does. Instead of charging up the capacitor one time, the device uses a current source to drive the circuit at its resonant frequency. It can detect the resonant frequency by monitoring INxA and INxB. You can think of it as a pendulum. You push in one direction, then when it crosses the center, you start pushing in the other direction. Later, it measures the frequency of this signal which can be used to calculate the capacitance.
We are glad that we were able to resolve this issue, and will now proceed to close this thread.
If you have further questions related to this thread, you may click "Ask a related question" below. The newly created question will be automatically linked to this question.
In reply to Clancy Soehren:
So just to make sure I'm understanding you correctly, does this diagram (and calculations) represent the mechanism that is going on in the FDC2114? (technically speaking, the frequency output would be the reciprocal of the resonant frequency, but the parameters can still be detected)
In reply to Evan Archibald Meikleham:
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.