区分噪声与实际触摸——鲁棒电容传感的关键

　　区分噪声与实际触摸——鲁棒电容传感的关键

　　电容感应正在成为一种流行的接口替代开关和旋钮在消费电子，前面板显示应用，以及许多工业和汽车传感器。本文描述了影响各种电容传感技术的各种噪声，以及在不同环境条件下可以克服各种噪声的方法。

　　电容式传感可以降低成本、健壮性、灵活性和直观的用户界面，而不会破坏与现有形式因素和特征集的兼容性。电容感应还使其他创新的用户界面（UI）功能，如邻近效应和LED（发光二极管）调光和褪色效果。所有这一切都依赖于具有强大的电容传感性能。一个强大的电容传感性能的关键方面是区分噪声和一个真正的信号（即来自手指触摸）。电容传感技术的鲁棒性取决于如何做到这一点，以避免在恶劣、嘈杂的环境中错误地按下按钮。

　　Capacitive sensing basics

　　At the heart of any capacitive-sensing system is a set of conductors on a PCB which interact with electric fields. Placing a finger near fringing electric fields adds capacitance to the system. As shown in Figure 1 below， the additional charge storage capacity added by the finger is known as CF （finger capacitance）。 The capacitance of the sensor without a finger present is denoted as CP （parasitic capacitance）。 The measurement system determines the variation in CX （total capacitance） due to the addition of CF for the detection of the finger. This variation in capacitance due to a finger is in the range of less than 1 pF. External noise affecting the sensors either has roots in charge or voltage， and this produces noise at the digital output that looks like capacitance change on the input. This induces a challenge in terms of avoiding any noise， which can also cause the same amount of capacitance change.

　　Sensor Capacitance = CX

　　CX = CP + CF