CAPSENSE™入门指南：电容式触摸按键设计

触摸按键

硬件电路设计

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"电容式触摸按键设计参考 - 触摸感应按键设计指南" 本文档是Infineon Technologies的Application Note AN64846，主要针对电容式触摸感应（CAPSENSE™）技术，旨在为初次接触CAPSENSE™解决方案的硬件设计师提供指导。文档覆盖了从基础技术理解到实际设计考虑的多个方面，包括电路图设计、布局以及电磁干扰（EMI）的管理。此外，它还帮助用户选择适合自己应用的合适设备，并提供了CAPSENSE™设计的相关资源。文档的目标受众是使用或对使用CAPSENSE™设备感兴趣的用户。CAPSENSE™技术是一种基于电容原理的触控技术，通过检测人体与传感器间的电容变化来识别触摸事件，常用于无物理按键的现代电子设备中，如智能手机、家电和工业控制面板。在文档中，读者将了解到CAPSENSE™技术的基本工作原理，以及在设计过程中需要注意的关键因素。例如，设计时要考虑传感器的灵敏度、噪声抑制、抗干扰能力，以及如何优化电路布局以减少EMI的影响。同时，文档还涵盖了器件选择的指导，帮助用户根据应用需求挑选合适的CAPSENSE™芯片。此外，为了辅助设计，Infineon提供了专门针对CAPSENSE™设备家族的设计指南，这些指南通常包含更详细的技术规格、设计实例和实用工具。对于寻求代码示例的开发者，可以通过Infineon的在线代码示例网页获取不断更新的PSoC™代码库，也可以通过视频培训库深入学习。文档的目录通常会包含各个主题的章节，如理论介绍、设计流程、器件选型、硬件实施、软件配置以及故障排查等，这些章节将逐步引导读者完成一个完整的CAPSENSE™触摸按键设计项目。通过这份指南，工程师不仅可以掌握CAPSENSE™技术的基础，还能获得实践经验，从而有效地开发出稳定、可靠的触摸感应按键系统。对于那些希望提升产品用户体验，采用先进触控技术的设计师来说，这是一份非常有价值的参考资料。

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Application Note 16 of 146 001-64846 Rev. *Z

2022-08-17

Getting started with CAPSENSE™

CAPSENSE™ technology

2.4 Comparison of CAPSENSE™ architecture in different devices

The fourth-generation CAPSENSE™ functionality in PSoC™ 4 S-Series, PSoC™ 4100S Plus, PSoC™ 4100PS, and

PSoC™ 6 devices is an improved version of the previous generation. The main differences between the two

generations of CAPSENSE™ architecture are listed in Table 1.

Table 1 Comparison of CAPSENSE™ architecture

Feature

Third-generation

CAPSENSE™

Fourth-generation

CAPSENSE™

Advantages of fourth-generation over

third generation CAPSENSE™

For CSD

For CSX

Sensor parasitic

capacitance (C

)

range

5 pF – 60 pF

5 pF – 200 pF

Supports high-C

design applications

Sensing modes

Self-Cap and

Mutual-Cap

modes

Self-Cap, Mutual-

Cap, and ADC

modes

The CAPSENSE™ hardware block can be

used as a 10-bit ADC when CAPSENSE™

sensor scanning is not in progress

Refer CSDADC component/middleware

datasheet for detailed ADC specifications

REF

1.2 V

0.6 V to VDDA-0.6 V

Higher Vref allows

improved SNR

IDAC LSB size

1.2 µA, 2.4 µA

37.5 nA, 300 nA, 2.4

µA

Improved sensitivity, small IDAC for

improved tuning

Split IDAC

capability

Requires two

IDACs

Requires one IDAC

Requires fewer

resources to achieve the

same performance and

frees up one IDAC for

general-purpose use

EMI reduction –

digital

Supports only PRS

method

Supports

additional spread

spectrum clock

(SSC) method

More options to control the sense/Tx clock

frequency spread for EMI reduction

Modulator clock

frequency range

Lower

Higher

Higher modulator-clock

frequency implies faster

scans

Higher

modulator-clock

frequency

implies increased

sensitivity and

accuracy

Hardware state

machine

Yes

Initiation of sensor scanning is less

dependent on CPU; there are fewer critical

sections during scan initialization

PSoC™ 4100 family does not support CSX sensing method since it does not have UDB resources which is required to implement CSX for

this family.

The CAPSENSE™ component automatically selects the VREF voltage depending on the VDDA voltage specified in the cydwr window.

Require one IDAC if compensation and modulation IDAC split is 50-50; if it is not 50-50, it requires two IDACs.

The hardware state machine is a logic which controls the CAPSENSE™ block and sensor scanning.

Application Note 18 of 146 001-64846 Rev. *Z

2022-08-17

Getting started with CAPSENSE™

CAPSENSE™ technology

Table 2 PSoC™ device family and CAPSENSE™ architecture

PSoC™ device family

CAPSENSE™ architecture

PSoC™ 4

Third-generation CAPSENSE™

PSoC™ 4-M

PSoC™ 4100-BLE

PSoC™ 4-L

PSoC™ 4 S-Series

Fourth-generation CAPSENSE™

PSoC™ 4100S Plus

PSoC™ 4100PS

PSoC™ 6 MCU

2.5 CAPSENSE™ tuning

Optimal CAPSENSE™ system performance depends on the board layout, button dimensions, overlay material,

and application requirements. In addition to these factors, switching frequency and threshold levels must be

carefully selected for robust and reliable performance. Tuning is the process of determining the optimum

values for these parameters. Tuning is required to maintain high sensitivity to touch and to compensate for

process variations in the sensor board, overlay material, and environmental conditions.

Many of the CAPSENSE™ devices support SmartSense, Infineon’s Auto-tuning algorithm, which automatically

sets parameters for optimal performance and continuously compensates for system, manufacturing and

environmental changes. See SmartSense auto-tuning for more information.

This section gives an introduction about the tuning process. For details on all the parameters involved in

CAPSENSE™ operation and the step-by-step tuning procedure, see the device-specific Design Guide. Infineon

provides many tools to make tuning and data monitoring easy. See Data monitoring tools to learn more about

these tools.

The following section defines some terms that will help you understand the tuning process.

2.5.1 Definitions

• Raw count: As seen in Figure 19, sensor capacitance is converted into a count value by the CAPSENSE™

algorithm. The unprocessed count value is referred to as raw count. Processing of the raw count results in

ON/OFF states for the sensor.

• Baseline: The raw count value of a sensor may vary gradually due to changes in the environment such as

temperature and humidity. Therefore, the raw count is low-pass filtered to create a new count value known

as baseline that keeps track of and compensates for the gradual changes in raw count. The baseline is less

sensitive to sudden changes in the raw count caused by a touch. Therefore, the baseline value provides the

reference level for computing the signals (explained below). Figure 15 shows the concept of raw count,

baseline and signal.

Application Note 20 of 146 001-64846 Rev. *Z

2022-08-17

Getting started with CAPSENSE™

CAPSENSE™ technology

2.5.2 SmartSense auto-tuning

2.5.2.1 What is SmartSense?

Tuning the touch sensing user interface is a critical step in ensuring proper system operation and a pleasant

user experience. The typical design flow involves tuning the sensor interface in the initial design phase, during

system integration, and finally production fine-tuning before the production ramp. Because tuning is an

iterative process, it can be time-consuming. SmartSense Auto-Tuning helps to simplify the user interface

development cycle. In addition, the method is easy to use and reduces the design cycle time by eliminating the

tuning process throughout the product development cycle, from prototype to mass production.

2.5.2.2 What does SmartSense do?

SmartSense tunes each CAPSENSE™ sensor automatically at power-up and then monitors and maintains

optimum sensor performance during runtime. The number of parameters to be tuned is reduced from 17 in

CSD to 4 with SmartSense.

• Power-up tuning: SmartSense tunes the parameters of each sensor based on the individual sensor parasitic

capacitance to get the desired sensitivity for the sensor.

• Runtime tuning: Noise in the system is measured dynamically. The thresholds are adjusted accordingly for

each sensor to overcome false triggering due to dynamic variations in noise in the CAPSENSE™ system.

2.5.2.3 How and where is SmartSense helpful?

SmartSense technology adapts for manufacturing variations in PCBs, overlays, and noise generators, such as

LCD inverters, AC line noise, and switch-mode power supplies and automatically tunes them out. SmartSense

handles changes in system environment, such as temperature, humidity, and noise sources such as RF, SMPS,

LCD Inverter, and AC line noise.

The following sections describe scenarios in which SmartSense is instrumental in adapting to the external

noise. By maintaining a robust signal-to-noise ratio, the false triggering of buttons is prevented.

Different noise levels in different designs

SmartSense technology dynamically tunes itself (adjusts noise and finger thresholds) for different noise

environments. In Figure 17, Design A and Design B have different noise levels. To maintain a minimum SNR of

5:1, you must adjust the dynamic threshold. SmartSense does this automatically, allowing seamless transition

from one model to another with minimal or no tuning required.

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