Cypress CapSense CY8C20x36 Guia do Utilizador descarregar pdf (Página 42)

42 Document No. 001-64846 Rev. *I Getting Started with CapSense

Figure 3-13. Average Filter Noise (16 Samples)

Unfiltered

Filtered

Unfiltered

Filtered

Figure 3-14. Average Filter Finger Touch (16 Samples)

The previous examples are representative of power supply noise. The filter works well in this example because the

period of the noise is close to the length of the filter (N = 16). For more information about how to implement an

average filter, see the code example CSA Software Filters with EzI2Cs Slave on CY8C20xx6.

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.

1 2 ... 37 38 39 40 41 42 43 44 45 46 47 ... 74 75

Getting Started with CapSense 1
Contents 3
1. Introduction 6
1.4 Document Conventions 9
2. CapSense Technology 10
2.1.2 Mutual-Capacitance 11
2.3.1 Sensing Methods 12
CY8C21x34/B 13
= External Connection 14
2.4 CapSense Tuning 15
2.4.3 Measuring SNR 16
2.4.4.1 What is SmartSense? 17
2.5 Sensor Types 19
2.5.1.2 Matrix Buttons 20
2.5.2.1 Linear Sliders 20
2.5.2.2 Diplexed Sliders 21
Area contacted by finger 22
Proximity Sensor 22
2.6 Sensor Construction 23
2.7.1 Visual Feedback 24
OFFON OFF 26
2.7.2 Haptic Feedback 28
2.7.3 Audible Feedback 29
2.8 Water Tolerance 31
CapSense Controller 32
3. Design Considerations 33
3.2 ESD Protection 34
Non Conductive 35
Material 35
3.2.2 Redirect 36
3.2.3 Clamp 36
3.3.1.1 Ground Plane 37
3.3.1.2 Series Resistor 37
3.3.1.3 Trace Length 37
3.3.1.4 Current Loop Area 37
CapSense 38
Controller 38
3.3.2 Radiated Emissions 39
3.4 Software Filtering 41
3.4.2 IIR Filter 42
Equation 18 43
3.4.3 Median Filter 44
3.4.4 Jitter Filter 45
Unfiltered 46
Filtered 46
3.5 Power Consumption 47
3.6 Pin Assignments 48
3.7 PCB Layout Guidelines 51
3.7.5 Slider Design 52
3.7.8 Trace Routing 53
3.7.9 Crosstalk Solutions 53
3.7.10 Vias 54
3.7.11 Ground Plane 54
Sensor-1 55
Shield Electrode 56
Guard Sensor 56
Sensor Pads 56
4.1.1.1 CY8CMBR20xx 57
4.1.1.2 CY8C201xx 57
4.1.2.1 CY8C20x34, CapSense 57
5. CapSense Selector Guide 59
Design Requirements 60
7. Resources 65
7.4.5 Evaluation Pods 66
7.5 Demonstration Kit 67
7.6 PSoC Designer 67
7.7 PSoC Programmer 68
C-to-USB Bridge Kit 69
7.10 Design Support 71
8. Appendix 72
Introduced Capacitance, pF 73
8.1.4 Design Examples 74

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