On-chip capacitive touch key system

Abstract

The invention discloses an on-chip capacitive touch key system. The system comprises a soc chip and an off-chip system, the soc chip comprises a trimming bias circuit K, an MOS tube Q1, an MOS tube Q2, a digital circuit, a comparator U1, a comparator U2 and a pad switching circuit. The off-chip system comprises a plurality of off-chip equivalent capacitors; the pad switching circuit comprises a switch circuit and a PAD circuit. According to the invention, a set of complete correction closed control circuit is designed, the system can realize dynamic tracking of touch key frequency change and suppress noise interference of a random frequency band, and meanwhile, an oscillation circuit is shared, so that time division multiplexing of a plurality of keys is realized, and the hardware cost isgreatly reduced. Due to the fact that the system can accurately judge whether the keys are pressed or not, software work is reduced, and the working efficiency of the whole system is greatly improved.

Description

technical field [0001] The invention relates to the technical field of touch, in particular to an on-chip capacitive touch key system. Background technique [0002] Compared with traditional mechanical keys, capacitive touch keys have many advantages, such as: almost unlimited number of key presses, no key failure due to mechanical wear, beautiful appearance, low cost, waterproof and dustproof functions, so the capacitive touch key system Widely used in consumer electronics, Internet of Things, home appliances and other occasions. [0003] The basic principle of capacitive touch buttons is to detect the extra capacitance generated by human finger touch, and this extra capacitance is connected in parallel to the charge and discharge capacitor of the oscillator. When the capacitance changes due to human finger touch, the frequency or duty of the oscillator ratio will change. [0004] Traditional on-chip button systems such as figure 1 As shown, the core principle of the sys...

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Problems solved by technology

But we can also clearly find that with the change of voltage V and temperature T, no touch and touched will change, but judge Freq is a constant value because it is obtained by the system self-test after the chip starts, and will not change with V, T change, when V, T is at some random value, it is very easy to misjudgment

At the same time, the touch system does not have the ability to suppress frequency noise, and is easily disturbed by certain frequencies, resulting in misjudgment by the system

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