Calculating the Resolution for CY8C21x34 CapSense CSD - KBA82521
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Mar 07, 2011
12:39 PM
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Mar 07, 2011
12:39 PM
Version: **
Question: How do you calculate the resolution of a capacitive touch sensing application designed using the CY8C21x34 CapSense® CSD?
Answer:
Resolution is equal to the inverse of sensitivity. Sensitivity is calculated using the following formula:
Where:
Counts = Digital capacitance measurement result returned by the User Module N = Resolution of the User Module RB = Bleed resistor value FSW-AVG = Average switching frequency of the sensor RefVal = Reference value of the User Module |
For example, given the following User Module settings:
N = 14 RB = 10 kΩ FSW-AVG = 375 kHz (Prescaler = 15) RefVal = 0 |
Resolution = 0.00543 pF
Note: Although the calculation indicates that a change as small as 0.00543 pF can be detected, raw-count noise limits the use of such high resolution. CapSense is not recommended for measuring absolute capacitances.
Note: The “sensitivity” calculated above is the capacitive measurement module sensitivity, not the system sensitivity to button/sensor activation.
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