1. Field of the Invention
The present invention generally relates to a device and a method for reducing input noise and, more particularly, to a device and a method for reducing input noise using a noise reduction device turned on and connected to a ground or a voltage so that a plurality of charges stored in an equivalent capacitor of a turned off analog switch are released or accumulated to zero or a specific value.
2. Description of the Prior Art
The conventional user interface uses mechanic buttons as its input devices. For example, the input devices for telephones, electronic calculators, induction cookers, electric rice cookers are implemented using buttons. However, such input devices have problems such as button bouncing, poor contacts and usage wear. Therefore, touch switches have become more and more popular due to the rapid advancement in development to overcome the problems related to mechanic buttons. In the process for making a touch switch, pads for GND and VDD are disposed around the touch switch on the printed circuit board (PCB) to reduce noise. These pads occupy area. When the area is limited by the circuitry or structure, considerable noise is generated due to insufficient area for GND or VDD.
FIG. 1 is a conventional touch switch PCB 100. In FIG. 1, the meshed portion 110 is covered by pads for GND or VDD. The small black circles are contacts 120 for touch switches surrounding each of the touch switches. These increase the area occupied by the layout on the PCB 100. However, the aforesaid technology is not suitable for reducing input noise when the buttons are used as a user interface. FIG. 2 is an equivalent circuit showing an equivalent capacitor when the analog switch is turned off. The touch switch 200 is connected to an analog input unit 210 (or an analog input switch). Before the analog input unit 210 is turned on, an equivalent capacitor 220 has already existed. The amount of charges stored in the equivalent capacitor 220 depends on where the equivalent capacitor 220 appears and on the operation time of the analog input unit 210. Because of the input noise, the user has to set the software parameters according to practical use. Moreover, the error tolerance of the back-end timer/counter has to be larger, which leads to the need in a timer/counter of a larger number of bits.
Therefore, there exists a need in providing a device and a method for reducing input noise using a noise reduction device turned on and connected to the ground or a voltage so that a plurality of charges stored in the equivalent capacitor are charged or discharged to zero or a specific value. Thereby, the noise in a touch switch is reduced and the cost of layout on the PCB is saved.