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FDC2112: Fdc2112 sensor device advice?

Part Number: FDC2112

Hello,


may I use a gain amplifier to increase sensor excitation voltage.

if yes, when i increase the voltage, is measurement more precisely.

  • Hello,

    my main problem is that;

    The measurement value is proportional with capacitor value.  why i cant measure right value in single ended mode.

    If i double excitation current may i read capacitor value more precisely.

  • In reply to jack22:

    Hi Jack,
    I've got your request. Allow me some time to think about this and get back to you.

    Best Regards,
    Bala Ravi
  • In reply to Bala Ravi:

    Hello;

    I do more test. I wait for your reply.

    I use FDC2112 to measure capacitor with single ended mode. I read data from fdc and calculate frequency value. Also I measure frequency value with scope.

    The frequency value is equal to each other. But when I convert to capacitor to frequency value, the cap value is wrong.

    I use 22pF, 33pF, 47pF and 100pF ceramic capacitor for this test. In adition I measure this capacitor with LCR meter to lear exact value.

    As you see all value is up. But calculated value with FDC data is wrong. You may see an scope screen below.

    When I  use to calculate above formula all result is wrong. It looks like tank capacitor change with frequency.

    Please help.

    Best Regards.

  • In reply to jack22:

    As a result the FDC count frequency right. I think problem is LC circuit. Resonant frequency effect of some sort of thing.

    When I add difference capacitor to the circuit, the frequency changes is not proportional.

    What is reason of this effect.

    What can i do eleminate to disturbance effect.

    Best Regards.
  • In reply to jack22:

    Hi Jack,
    Sorry about the delayed response. Have you tried differential measurement by any chance? Differential mode is known to be more accurate compared to single-ended measurement. Are you providing the ref clock signal? This difference in cap value measured could be due to parasitic capacitance. Have you tried measuring the capacitance without a cap on, to see if there is any parasitic capacitance?

    The gain amplifier shouldn't cause any measurement resolution issues as long as there isn't too much offset at the inputs of the op-amp. If resolution is your issue, you can increase the sensor size (to get more precise measurements).

    I would also run a SNR analysis, to make sure the disturbance is not coming from there. Amplifying the signal also amplifies the disturbances, which could be more visible after amplification.

    Best Regards,
    Bala Ravi
  • In reply to Bala Ravi:

    Hi Bala;

    I must use single-enden mode for my aplication.
    I connect external clock to FDC
    Yes, firstly I measure parasitic cap, when any external cap connect.
  • In reply to jack22:

    Hi Jack,
    I understand that differential measurement will not work for you. Allow me some time to test this in lab and get back to you.

    Best Regards,
    Bala Ravi
  • In reply to Bala Ravi:

    Hi Jack,
    Are you using our FDC2114EVM? If so can you please share a picture of your setup?

    Best Regards,
    Bala Ravi
  • In reply to Bala Ravi:

    Hi Jack,
    I am going to close this thread for now. If you have any further questions, please start a new thread.

    Best Regards,
    Bala Ravi