TWI411789B - Capacitance touch contorl element - Google Patents

Abstract

The present invention provides a capacitance touch control element, which includes a variable capacitor, an integrator and a detector. The variable capacitor varies its capacitance according to a touch event on the capacitance touch control element. The integrator is coupled to the variable capacitor and a reference signal, and implemented for generating an output signal according to the capacitance of the variable capacitor and the reference signal. The detector is coupled to the integrator, and implemented for receiving the output signal and generating a touch event detection result according to the output signal.

Description

Capacitive touch element

The invention relates to a touch panel, in particular to a capacitive touch element using an integrator.

Among the diverse electronics, touch panels provide a user-friendly and easy-to-use interface. Traditional touch panels are often implemented with capacitors and op amps. Please refer to FIG. 1 , which is a schematic diagram of a conventional capacitive touch element 100 . The capacitive touch element 100 includes a current source I, a capacitor C ₁ , an operational amplifier 110 , a switch 120 , and a control module 130 . Under normal circumstances, the current source I will continuously charge the capacitor C ₁ to form an input voltage V _X , while an output voltage V _out at the output of the operational amplifier 110 is fed back to the first of the operational amplifier 110 via the switch 120. The input terminal (-) causes the input voltage V _X to be equal to the output voltage V _out . When the input voltage V _X exceeds the input voltage V _BG of a second input terminal (+) of the operational amplifier 110, the switch 120 turns off the operational amplifier 110. The first input (-) is connected to the output, and the first input (-) is grounded to reset the input voltage V _X . After the input voltage V _X is reset, the switch 120 is coupled to the first input (-) and output of the operational amplifier 110, and the current source I charges the capacitor C ₁ again, repeating the above steps. In other words, the input voltage V _X will have a fixed slope ( Raising until it is equal to the input voltage V _BG , then resetting the input voltage V _{X to} zero, repeating the above steps to form a periodic triangular wave, and the output voltage V _OUT will keep track of the value of the input voltage V _X . Thereafter, the operational amplifier 110 transmits the output voltage V _OUT to the control module 130 to determine whether a condition of a touch event is reached.

Referring to FIG. 2, FIG. 2 is a schematic diagram showing changes in capacitance values seen by the first input terminal (-) of the operational amplifier 110 in the conventional capacitive touch element 100 when a touch event occurs. When the touch event occurs, an object (for example, a user's finger) contacts the panel to form a parasitic capacitance C _f , and at this time, the current source I charges the capacitor C ₁ and the parasitic capacitance C _{f to} make the input voltage. V _X is fixed at a lower slope than the previous one ( Rising up to the input voltage V _BG and then resetting to zero, repeating the above steps to form a longer triangular wave of another period. Please refer to Figure 3. When no touch event occurs, the input voltage V _X will be ( The slope of the curve forms a triangular wave, and when there is a touch event, the input voltage V _X will be ( The slope of the curve forms a triangular wave with a long period, and the control module 130 determines whether the touch event occurs according to the triangular wave of different periods, for example, calculating the number of the triangular wave within a predetermined time or calculating a predetermined number of the triangular wave. The time required for the number cycle.

As can be seen from the above description, when it is determined whether a touch event occurs, the conventional capacitive touch element 100 needs to wait for a plurality of triangular wave periods for a period of time, so a long reaction time is required, and the capacitor C ₁ needs to be implemented. Larger areas often result in increased production costs. Furthermore, in practice, one panel needs to use multiple sensing components, and each sensing component is inevitably inputted by the printed circuit board (PCB) and the circuit. The stray capacitance formed by the output pad (Input/Output pad) causes an error in the determination of the touch event and a crosstalk between the respective sensing elements. Please refer to FIG. 4 , which is a partial circuit diagram of a conventional capacitive touch panel. Only the six conventional capacitive touch elements 100a-100e are shown in FIG. 4, and the structure and operation thereof are the same as those of the capacitive touch element 100 shown in FIG. 1, so no further details are provided herein. When the touch point is at the node A, the conventional capacitive touch element 100a will have a different stray capacitance than when the touch point is at the node B, so even if both are in the conventional capacitive touch On the sensing axis X ₁ processed by the component 100a, the judgment result of the touch point at the last output is slightly different, and the larger the area of the panel, the longer the sensing axis will be, which leads to different touches. The difference in the judgment result obtained by the point becomes more and more serious, which affects the detection determination of the touch element.

Therefore, one of the objects of the present invention is to provide a capacitive touch element to improve the correctness and speed of the touch event determination and to overcome the influence of stray capacitance on the touch event determination.

According to an embodiment of the present invention, a capacitive touch element includes: a variable capacitor, an integrator, and a detector. The variable capacitor changes its capacitance value according to a touch event on the capacitive touch element. The integrator is coupled to the variable capacitor and a reference signal for generating an output signal according to the capacitance value of the variable capacitor and the reference signal. The detector is coupled to the integrator for receiving the output signal and generating a touch event detection result according to the output signal.

According to another embodiment of the present invention, a capacitive touch element is provided, including: a signal detector and a slope detector. The signal detector generates an output signal according to a touch event on the capacitive touch element. The slope detector is coupled to the signal detector for generating a touch event detection result according to a slope of the output signal.

Please refer to FIG. 5, which is a schematic diagram of an embodiment of a capacitive touch element of the present invention. The capacitive touch component 500 includes, but is not limited to, a variable capacitor C _R , an integrator 510 , and a detector 520 . The variable capacitor C _R represents the equivalent capacitance seen by the integrator 510 at one input, including the line parasitic capacitance of the printed circuit board, the stray capacitance formed by the input/output pads in the circuit, and the like. When the capacitive touch element 500 has a touch event, the variable capacitor C _R changes its capacitance value according to the touch event, for example, when an object (for example, a user's finger) contacts the panel to form A parasitic capacitance C _f increases the equivalent capacitance seen at the input. The integrator 510 is coupled to the variable capacitor C _R and a periodic reference signal V _REF, according to the capacitance value of the reference signal V _REF variable capacitance C _R of generating an output signal V _OUT '. The detector 520 is coupled to the integrator 510 to receive the output signal V _OUT ^' and generate a touch event detection result TR according to the received output signal V _OUT '. In this embodiment, the reference signal V _REF is a periodic square wave for driving the integrator 510. In addition, the integrator 510 includes an operational amplifier 5101 and a feedback capacitor C _fb , and the operational amplifier 5101 has a first An input terminal (-) is coupled to the variable capacitor C _R and a second input terminal (+) is coupled to the reference signal V _REF and generates an output signal V _OUT ' to the detector 520 at an output terminal V_OUT. The feedback capacitor C _fb is coupled between the first input terminal (-) and the output terminal V_OUT, and the output signal V _OUT ' is fed back to the first input terminal (-) of the operational amplifier 5101. The operation of the integrator 510 can be illustrated by the following equation:

I ₁ * dT = I ₂ * dT = C _fb *( V _{OUT '} - V _- )=( C _f + C _R )*( V _- ) (1)

Wherein I ₁ is the current flowing through the variable capacitor C _R and the parasitic capacitor C _f , and I ₂ is the current flowing through the feedback capacitor C _fb . Since the operational amplifier 5101 is an ideal operational amplifier, the first input terminal (-) is not Any current will pass, so I ₁ = I ₂ . Within a predetermined time dT, the current I ₁ and the variable capacitance C _R the amount of charge charged by the parasitic capacitance C _f is _{(C f + C R) *} (V -), and the current I ₁ pair of return feedback capacitor C _fb The amount of charge charged is C _fb *(V _OUT' -V _- ). Another equation (2) can be obtained from the above equation (1):

And further obtain an equation (3) by the equation (2):

In equation (3), It represents the slope of the output signal V _OUT ' on the time axis.

Therefore, when no touch event occurs, C _f =0, so V _OUT ' will have a smaller slope And rise; and when a touch event occurs, V _OUT ' takes a larger slope rise. Compared with the prior art, the output signal V _OUT of the capacitive touch element 100 of FIG. 1 is proportional to the presence or absence of a touch event, respectively. , The slope of the output of the capacitive touch element 500 of the present invention is proportional to the output signal V _OUT ' , The slope of the rise is based on the characteristics of the integrator, so that the slope of the output signal V _OUT ' is only related to the ratio of the capacitance value. In practice, large-area capacitors can be avoided, and only the ratio between the capacitors needs to be adjusted. Yes, so you can save on the cost of production.

In addition, since the integrator 510 is driven by the periodic reference signal V _REF , when a plurality of sensing elements of the present invention (for example, the capacitive touch element 500 shown in FIG. 5 ) are used on the same panel, each Each of them is periodically driven by the reference signal V _REF , so the stray capacitance seen at different touch points on the sensing axis processed by each capacitive touch element is equivalently the same, so at the end There is not much difference in the judgment results of the touch points, and the interference between the respective sensing elements is lower than that of the prior art.

The detector 520 receives the output signal V _OUT ' generated by the integrator 510 and generates a touch event detection result TR according to the slope of the output signal V _OUT '. For example, the detector 520 can detect whether the amplitude change amount ΔV of the output signal V _OUT ' is increased within a predetermined time T ₁ to determine the touch event detection result TR. Please refer to FIG. 6 , which is a waveform diagram of a reference signal V _REF and an output signal V _OUT ' of the capacitive touch element 500 in FIG. 5 . When the amplitude variation ΔV does not change much or is zero, the detector 520 determines that the touch event has not occurred; however, when the amplitude variation ΔV exceeds a threshold, the detector 520 determines the touch. The hit event has occurred.

In another embodiment, the detector 520 can detect whether the output signal V _OUT ' exceeds a predetermined threshold value V _TH within a predetermined time T ₁ to determine the touch event detection result TR. When the output signal V _OUT ' fails to exceed the predetermined threshold value V _TH , the detector 520 determines that the touch event has not occurred; however, when the output signal V _OUT ' exceeds the predetermined threshold value V _TH , the detector 520 will A determination has been made that a touch event has occurred.

Compared with the prior art, the advantage of applying the slope to generate the touch event detection result of the present invention is that it only requires a very short reaction time, and it is not necessary to wait for the output signal to pass through a plurality of cycles to judge as in the prior art. Furthermore, the circuit of the printed circuit and the stray capacitance formed by the input/output pads in the circuit increase the slope of the output signal due to the characteristics of the integrator, thereby accelerating the determination of the touch event.

It is to be understood that the above-described embodiments are merely illustrative of the invention and are not intended to limit the scope of the invention. For example, the detector 520 in FIG. 5 does not have to be paired with the integrator 510, and can be separately used with a conventional capacitive touch element to detect the rate of an output signal to generate a touch. The event detection result, this design change is also within the scope of the present invention. Please refer to FIG. 7 , which is a schematic diagram of another embodiment of a capacitive touch element according to the present invention. The capacitive touch component 700 includes, but is not limited to, a signal detector 702 and a slope detector 704. The signal detector 702 can be implemented by using any conventional capacitive touch element for generating an output signal V _out " according to a touch event on the capacitive touch element 700, and the slope detector 704 is The signal detector 702 is coupled to receive the output signal V _out " and according to a slope of the output signal V _out " to generate a touch event detection result TR'. For example, as the detector 520 Operation (refer to Fig. 6), the slope detector 704 can detect whether the output signal V _OUT "is a large amount of amplitude change within a predetermined time to determine the touch event detection result TR", or to detect the output signal Whether V _OUT " exceeds a predetermined threshold value for a predetermined time determines the touch event detection result TR'.

In summary, the present invention provides a capacitive touch element that uses the characteristics of an integrator to obtain an output signal, and then determines whether a touch event occurs via the slope of the output signal. The use of the integrator can reduce the unnecessary capacitance area, thereby reducing the manufacturing cost. In addition, applying the slope to determine the touch event can increase the reaction speed of the capacitive touch element, and the present invention applies the periodic signal to drive the integrator. It can also effectively overcome the influence of stray capacitance on the determination of touch events.

The above are only the preferred embodiments of the present invention, and all changes and modifications made to the scope of the present invention should be within the scope of the present invention.

100, 100a~100e, 500, 700. . . Capacitive touch element

110, 5101. . . Operational Amplifier

120. . . switch

130. . . Control module

510. . . Integrator

520. . . Detector

702‧‧‧Signal Detector

704‧‧‧Slope detector

C ₁ ‧‧‧ capacitor

C _R ‧‧‧Variable Capacitor

C _f ‧‧‧Parasitic capacitance

C _fb ‧‧‧Responsive capacitance

I‧‧‧current source

FIG. 1 is a schematic diagram of a conventional capacitive touch element.

Figure 2 is a schematic diagram showing the change in capacitance seen at the input of the operational amplifier in Figure 1 when a touch event occurs.

FIG. 3 is a waveform diagram of the output signals of the conventional capacitive touch elements in FIG. 1 in the presence of a touch event and a non-touch event.

FIG. 4 is a schematic diagram of a part of a circuit of a conventional capacitive touch panel.

FIG. 5 is a schematic diagram of an embodiment of a capacitive touch element of the present invention.

Figure 6 is a waveform diagram of a reference signal and an output signal of the capacitive touch element in Figure 5.

FIG. 7 is a schematic view of another embodiment of the capacitive touch element of the present invention.

500. . . Capacitive touch element

510. . . Integrator

520. . . Detector

5101. . . Operational Amplifier

C _R . . . Variable capacitance

C _f . . . Parasitic capacitance

C _fb . . . Feedback capacitor

I ₁ , I ₂ . . . Current

Claims (8)

A capacitive touch component includes: a variable capacitor that changes a capacitance value according to a touch event on the capacitive touch component; an integrator coupled to the variable a capacitor and a reference signal for generating an output signal according to the capacitance value of the variable capacitor and the reference signal; and a slope detector coupled to the integrator for receiving the output signal and according to the output A slope of the signal produces a touch event detection result. The capacitive touch element of claim 1, wherein the reference signal is a periodic signal. The capacitive touch element of claim 1, wherein the integrator comprises: an operational amplifier having a first input coupled to the variable capacitor and a second input coupled to the The reference signal generates the output signal at an output; and a feedback capacitor is coupled between the first input and the output. The capacitive touch element of claim 1, wherein the slope detector detects an amplitude change of the output signal for a predetermined time to generate the touch event detection result. The capacitive touch sensor of claim 1, wherein the slope detector detects whether the output signal exceeds a predetermined threshold for a predetermined time to generate the touch event detection result. A capacitive touch component includes: a signal detector for generating an output signal according to a touch event on the capacitive touch component; and a slope detector coupled to the The signal detector is configured to generate a touch event detection result according to a slope of the output signal. The capacitive touch element of claim 6, wherein the slope detector detects an amplitude change of the output signal for a predetermined time to generate the touch event detection result. The capacitive touch sensor of claim 6, wherein the slope detector detects whether the output signal exceeds a predetermined threshold for a predetermined time to generate the touch event detection result.