Design Considerations
AN64846 - Getting Started with CapSense
®
Doc. No. 001-64846 Rev. *X
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Figure 3-29. Median Filter (16-Sample) Finger Touch
For more information about how to implement a median filter, see the code example
CSA Software Filters with EzI2Cs
3.4.4 Jitter Filter
3.4.4.1 Jitter Filter for Noisy Slider Data
The centroid function is used to estimate finger position on a slider. When the signal level is low, usually because of
thick overlay on the slider, the estimate of finger position will appear to shake and jitter even when the finger is held at
a fixed position. This jitter noise can be removed using a jitter filter. To do this, the previous input is stored in a buffer.
The current input is compared to the previous output. If the difference is greater than ±1, the output is changed by ±1
(matching sign), as shown in Equation 21. This is a nonlinear filter.
𝑦[𝑖] = 𝑥[𝑖] − 1, 𝑖𝑓 𝑥[𝑖] > 𝑦[𝑖 − 1] + 1
Equation 21
𝑦[𝑖] = 𝑥[𝑖] + 1, 𝑖𝑓 𝑥[𝑖] < 𝑦[𝑖 − 1] − 1
𝑦[𝑖] = 𝑦[𝑖 − 1], 𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒
shows the results of applying a jitter filter applied to noisy centroid data.
Figure 3-30. Jitter Filter Applied to Noisy Centroid Data
Unfiltered
Filtered
