How does surface capacitive touch technology drive a new revolution in human-machine interfaces? （1） 4

Surface capacitive touch technology

The SCT panel consists of a uniformly coated ITO layer, with four connection lines (UR, UL, LR, LL) at the four corners of the panel linked to the SCT controller. To accurately detect the touch point, the SCT controller must first establish a uniform electric field on the panel, which is achieved by the drive circuit within the IC charging the panel. When a finger touches the screen, a small current flows; at this moment, the sensing circuit inside the IC analyzes the current on the four connection lines respectively and calculates the XY coordinates of the touch point using the formula shown in Figure 3. To mitigate interference effects, the calculated coordinate values can be processed using hardware or software filters.  diode

Figure 3: Block diagram of the SCT panel and controller.

The biggest difference between PCT and SCT lies in the fact that PCT can achieve multi-touch, while SCT is limited to single-touch. On this basis, PCT appears superior to SCT, but in reality, this is not entirely the case.

Market Status of Capacitive Touch Technology

The working principle of PCT is not complicated, so providing a demonstrative prototype is not difficult; however, when engineers attempt to convert the PCTDemoSet into a mass production plan for large-scale replication, various technical challenges emerge. The main challenges include the following three aspects.  diode

The signal to be detected is weak (rendered in bold) and susceptible to environmental interference, leading to inconsistent sensitivity in touch functionality and potential false actions. The capacitance changes induced by touch are highly sensitive to temperature and humidity. The current common solution is to employ periodic automatic calibration to mitigate this issue. Additionally, other active electrical devices or the device's own non-touch functions (such as a phone's RF) can interfere with signal measurement. This aspect requires efforts to improve SNR through software or hardware methods, though IC designers still have room for improvement in this area as of now.