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FDC2214: About the specification of the offset

user5929126
Prodigy 150 points
Part Number: FDC2214
Other Parts Discussed in Thread: FDC2114,
The offset range is described in the data sheet as 16-bit, but what is the setting value, from pF to pF?
-16384 pF to +16383 pF?
  • 0
    TI__Genius 17440 points

    Hello,

    Please note that the FDC2214 is our 28-bit capacitive sensor, which does not have an offset capability. The FDC2114 is our 12-bit capacitive sensor which does have an offset setting. 

    Because the FDC2114 uses a resonant architecture (see this blog post for more information), its measurements are actually in units of Hz and the change in capacitance must be calculated (if needed). This means the offset is also in units of Hz. Table 8 in the datasheet shows how to calculate the offset values. 

    Best Regards,

  • 0 in reply to Kristin Jones93
    Prodigy 150 points
    Hello.
    Thank you for answering.
    Does it mean that offset is not necessary because the measurement range is wide?
    When using the FDC2214, does it mean that the changed capacity of the measurement object connected to the sensor can be measured, but the capacity of the measurement object itself can not be measured accurately?
    In that case,
    the pattern capacity from the IC to the measurement target is measured and subtracted from the capacity up to the sensor, right?
    Also, is the input range of this IC 0 to 250 nF?
    Best Regards,
    Koji Kuboyama
  • 0 in reply to user5929126
    TI__Genius 17440 points

    Hello Kuboyama-san,

    The FDC2214 measures capacitance by measuring the resonant frequency of an LC tank. When the sensor capacitance changes, the resonant frequency also changes, and the FDC2214 can measure this very precisely. The FDC2214 outputs a digital representation of the sensor frequency. Knowing the sensor frequency and the values of the inductor and the capacitor in the LC tank, the capacitance between the sensor and the target can be calculated. However, most applications do not require this additional calculation and can work with just the digital output codes.

    The input capacitance range of the device (up to 250nF) is defined for a given inductor and sensor frequency. A different inductor and sensor frequency would have a different maximum input capacitance. The more important limitation is the sensor frequency. The FDC2214 can drive sensor frequencies between 10kHz to 10MHz. As long as the sensor frequency is within this range, most sensor capacitances can be accommodated by shifting the inductor value.

    The offset is used in the FDC2114 to maximize the dynamic input range. It is not required, but we recommend using it for applications with very small shifts in capacitance.

    Best Regards,

  • 0 in reply to Kristin Jones93
    TI__Genius 17440 points

    Hello Kuboyama-san,

    I haven't heard from you in a while, so I'm assuming you found the answer to your question. If this is not the case, please feel free to post a new thread.

    Best Regards,