User guide

Getting Started with CapSense Document No. 001-64846 Rev. *A 39
3.4.2 IIR Filter
Infinite Impulse Response filters (IIR) produce a step response similar to RC filters. IIR filters attenuate high
frequency noise components and pass lower frequency signals, such as finger touch response waveforms.
Figure 3-14. IIR Filter Step Response
The general equation for a first-order IIR filter is:

[

]
=


(
[

]
+ (
(
  1
)
× 
[
  1
]
)) Equation 14
Figure 3-15 and Figure 3-16 on page 40 illustrate the results of using a first-order IIR filter on real CapSense data
using the filter equation with k = 16:

[

]
=


(
[

]
+ (15 × 
[
  1
]
)) Equation 15
Figure 3-15. IIR Filter Noise