DocID024789 Rev 2

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AN4310

Capacitor characteristics

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Capacitor characteristics

The most common short comings of capacitors are the following:

•

Series resistance

•

Series inductance

•

Parallel resistance (leakage current)

•

Non-zero temperature coefficient

•

Dielectric absorption (DA) or soakage

•

Dissipation Factor

The three most important characteristics that need to be examined are non-zero

temperature coefficient, dissipation factor and dielectric absorption (DA). The effect of these

non-ideal characteristics on the operation of the system will be briefly examined in the

following sections.

2.1

Dielectric absorption or soakage

Dielectric absorption (DA) or soakage can be detrimental to the operation and accuracy of

capacitive sensors that rely on a stable reference capacitor.

DA is caused by the charge that is soaked-up in the dielectric and remains there during the

discharge period. The charge then trickles back out of the dielectric during the relaxation

creates a memory effect in the capacitor. The size of the offset voltage is dependent on the

Figure 1. Model of dielectric absorption

This offset voltage influences the sensitivity of the system by reducing the number of

transfers needed to reach the internal reference voltage threshold and may cause false

proximity detections to occur.

By choosing a capacitor with a low dielectric absorption factor, a higher sensitivity level can

be selected, ensuring a more stable and reliable design with improved proximity detections.

Refer to Table 2 for a comparison of dielectric absorption factors for the different types of

capacitor dielectrics.