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LDC1000 Rp resolution

I have problem: i could not see improvement in resolution when i narrow my Rp range. I'am looking at LDC1000 EVM inductance graph and no matter if Rp range is ~1kΩ to ~4MΩ, or ~1kΩ to ~16kΩ i could not see LSB amplitude change (0.002uH LSB)

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  • Hi,

    The Rp range is applicable to Rp measurement. The L measurement is not affected.

    Don

  • So when i choose Rp range, Rp results are 16 bit resoulution in that range? Also proximity, because its derivate from Rp.

    L measurement is derivate from resonant frequency, and L range depends on Rp range:

    L_MAX = Rp_MAX*C*Rs

    L_MIN=Rp_MIN*C*Rs ( datasheet page 9)

    Am I wrong?

    I' am trying to measure small change in low inductance (~2uH absolute inductance, changing 0.001uH -0.1uH).

    What's better to work in small Rp range (with series inductance 20uH, Cp = 4700pF) (therefore huge resolution), but low Q tank circuit. Or to go with high Q (series inductance 1mH, Cp = 100pF), but also high Rp ( therefore lower resolution).

    Anyway hardly can get output in Rp range  0.798kOhm - 1.347kOhm, because output is very noisy.

    P.S. I adjust the CFB pin every time i change tank to get proper amplitude. I noticed that sometimes LDC1000 is working fine even there is no oscillation on CFB.

  • Hi Tomas,

    The L range is not derived from the RP range. You will need to have a reference frequency on the TBCLK pin to measure inductance- the higher the reference frequency, the better (up to the 8MHz maximum input).