| The basic principle of capacitive touch key technology is to measure the introduced additional capacitance from one's finger to ground. This additional capacitor is paralleled with the charge and discharge capacitor of a relaxation oscillator, and the touch capacitance can be measured by detecting the output changes in frequency or duty cycle of the oscillator. Capacitive touch key has many significant advantages in consumer electronics and home appliances, such as beautiful and diverse styles, slip resistant, waterproof, dustproof and so on. As prices continue going down, capacitive touch key technology is more and more widely used.This paper describes the principle of a touch key capacitive sensing chip with self-calibration mechanism, as well as introduces the design of analog and digital circuit part, simulation, layout design, and application in products of the chip. The core architecture of this touch key capacitive sensing chip consists of two relaxation oscillators which are constructed in the same substrate, and connect to a digital frequency difference detector. When touching action occurs, the detector reads out frequency deviation between two signals, and then enables the output. |
