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Impact of Cmod and Ctank values on proximity sensing performance – KBA237252

Impact of Cmod and Ctank values on proximity sensing performance – KBA237252

Ritwick_S
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Community Translation: Cmod と Ctank の値が近接センシング性能に与える影響 – KBA237252

1.1  Cmod capacitor value


1.1.1. Decreasing the Cmod capacitor value

The signal strength increases as the Cmod value is decreased, but the width of the flat spot is inversely proportional to the Cmod value because the modulator causes nonlinearity as Cmod is decreased. Therefore, proximity detection works if the calibration is accurate. If the flat spot width is large due to a small value of CMod, proximity detection is inaccurate.

1.1.2  Increasing the Cmod value


Increasing the Cmod value has the following adverse effects:

  • Increases the noise
  • Reduces the initialization time
  • Decreases the signal strength

As a result, the proximity sensing distance decreases.

1.2  Ctank capacitor value

1.1.2. Increasing the Ctank capacitor value


When the shield electrode is enabled, a Ctank capacitor is required. It increases the shield's drive strength, allowing the shield signal to settle to the sensor voltage faster.

As long as the Ctank value can completely charge and discharge the Cp (shield), increasing the Ctank value does not change the proximity sensing distance.

1.2.2 Decreasing the Ctank capacitor value

If the Ctank cap value is decreased and the capacitor is unable to fully charge and discharge the Cp (shield), the proximity distance decreases because more noise is induced and the signal strength is reduced.

For example, if a 10-nF Ctank capacitor can fully charge and discharge the Cp (shield), increasing the Ctank value does not improve the proximity sensing distance. However, decreasing the Ctank value reduces the proximity sensing distance.

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