Average power consumption refers to the average power consumption of the touch screen system, including the controller working time (scanning, processing, communication, sleep, etc.) and the time for the main processor to receive and interpret touch data. Power consumption is a very common performance parameter. Regarding the power consumption of the touch screen, a more precise calculation formula is required, because different usage modes will produce different power consumption. The standby time of the mobile phone depends on the current consumed in the standby or sleep mode of the touch screen.
When the touch screen is working, it can be divided into many modes, for example, wake-on-touch (WOT), cheek detection (Cheek Detect), such as answering a call for 5 minutes, while viewing or entering a phone number, the phone may switch to touch mode for up to 10s , And then switch to WOT or cheek detection mode to remind the call. Even when sending text messages (SMS), it is still mixed WOT mode and actual finger contact. When pressing a button or thinking, the controller will switch between various sleep modes.
If these power consumption modes are not considered, it is easy to be misled by the power consumption of the system. In most cases, the touch screen is switched to cheek detection mode and touch wake-up mode 90 percent to 99 percent of the time. Some systems allow users to set the ratio of processing time to sleep mode, even when the finger is still on the panel. If the system only detects that the finger is placed in the same position, it does not need a picture update rate of 200MHz. If you want to develop a high-performance touch screen, you must use a low-power system in sleep mode and work with innovative sleep and wake-up modes.
When designing a capacitive touch screen system, system developers must consider many other important factors:
1) Finger capacitance. Finger capacitance refers to the capacitance measured between the finger and a single sensor component. When measuring finger capacitance, a real finger is used instead of a metal mechanical finger to ensure that the measured data conform to the actual conditions. The factors affecting the feedback capacitance (CF) include the thickness of the lens covering the upper layer and the dielectric constant of the material covering the outer layer.
2) System background noise. The noise floor of the system refers to the noise measured at the output of the capacitor-to-digital converter, which is the input (capacitance) value of the data converter.
3) Signal-to-noise ratio. The signal-to-noise ratio (SNR) is the ratio of the finger signal measured by the sensor to the measured noise. This is an important parameter, and designers must have a deep understanding of it in order to develop a high-efficiency touch screen. The system must be able to adjust, adapt and filter out parasitic noise in the mobile system. In order to obtain high signal and very little noise, consider adopting accurate analog front-end components for touch screen function.
Products such as the True Touch series programmable solutions provide many excellent mechanisms for filtering noise. PSoC programmable analog components can be reconfigured to integrate signals that last for a period of time to filter out noise.
