Method of driving a touch screen and touch control circuit thereof

Abstract

A method for driving a touch screen includes applying a touch drive signal to the touch screen for touch sensing, wherein an amplitude of the touch drive signal gradually rises and falls.

Description

TECHNICAL FIELD

[0001] The present application relates to a touch driving technology, and in particular, to a method for driving a touch screen and a touch control circuit associated therewith. BACKGROUND

[0002] In recent years, the application of touch screens has gradually entered the field of vehicle electronics. Due to the safety of vehicle drivers, the problem of electromagnetic interference (EMI) should be considered in more detail for touch screen products in vehicle electronics. In addition, modern touch screens usually adopt touch and display driver integration (TDDI) technology, and the touch driving signal is applied in combination with a load-free driving signal. In other words, signals with the same phase, amplitude and frequency are applied to all control lines and components on the touch screen, thereby reducing the load caused by the parasitic capacitance on the touch screen. However, simultaneous output of the touch driving signal and the load-free driving signal can exacerbate the problem of electromagnetic interference.

[0003] Please refer to Figure 1 , Figure 1 is a waveform diagram of one state of a touch driving signal and its frequency spectrum distribution. As shown in Figure 1 , the touch driving signal S1 includes several chord wave signals, and each chord wave signal has a small time interval between them. For a pure chord wave signal S2, the frequency spectrum distribution has a high peak value at the signal frequency and low energy at other frequencies. However, considering the case where there are several chord wave signals in a long period of time, the frequency spectrum distribution can become more complex and distributed in a larger frequency range. As shown in the lowermost graph of Figure 1 , assuming that the region of interest (ROI) in the frequency domain is 0.1 MHz to 0.16 MHz (this segment of the frequency spectrum distribution is enlarged in the figure), in the region of interest, the intensity of electromagnetic interference is required to be lower than 40 dBuV / m, even if the swing frequency of the chord wave signal is lower than the frequency of the region of interest, the touch driving signal S1 can still produce multiple energy peaks exceeding the critical range required by electromagnetic interference in the long run.

[0004] Therefore, it is necessary to propose a new touch driving technology to reduce the electromagnetic interference caused by the touch driving signal. SUMMARY

[0005] Therefore, the main purpose of the present application is to provide a method for driving a touch screen and a touch control circuit associated therewith to solve the above problems.

[0006] An embodiment of the present application discloses a method for driving a touch screen. The method includes applying a touch driving signal to the touch screen for touch sensing. The amplitude of the touch driving signal gradually increases and decreases.

[0007] Another embodiment of the present application discloses a touch control circuit. The touch control circuit includes a digital control circuit and a digital-to-analog converter (DAC). The digital control circuit is configured to generate a series of data codes. The digital-to-analog converter is coupled to the digital control circuit and configured to convert the series of data codes into a touch driving signal. The amplitude of the touch driving signal gradually increases and decreases.

[0008] Another embodiment of the present application discloses a touch control circuit. The touch control circuit includes a pulse generator, a voltage selector and a voltage switching circuit. The pulse generator is configured to generate a pulse signal with a series of first pulses. The voltage selector is configured to output a plurality of voltage selection signals. The voltage switching circuit is coupled to the pulse generator and the voltage selector and configured to receive the pulse signal and the plurality of voltage selection signals to generate a touch driving signal with a series of second pulses. Each second pulse in the series of second pulses has a voltage level determined according to a voltage selection signal in the plurality of voltage selection signals. The amplitude of the touch driving signal gradually increases and decreases. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 A waveform diagram of a state of a touch driving signal and its frequency spectrum distribution.

[0010] Figure 2 A waveform diagram of a touch driving signal of an embodiment of the present application.

[0011] Figure 3 A waveform diagram of a comparison of a touch driving signal and its corresponding frequency spectrum distribution.

[0012] Figures 4 to 7 A schematic diagram of a state of a touch driving signal of an embodiment of the present application.

[0013] Figures 8 to 10 A schematic diagram of a touch control circuit of an embodiment of the present application.

[0014] Figure 11 A flowchart of a touch driving process of an embodiment of the present application.

[0015] In the drawings, the following reference signs apply:

[0016] S1, S3, S4, DRV, DRV' touch driving signal

[0017] S2 Sine wave signal

[0018] VSYNC Vertical synchronization signal

[0019] DP Display period

[0020] TP Touch period

[0021] TS Time slot

[0022] 80, 90, 100 Touch control circuit

[0023] 802 Digital control circuit

[0024] 804 Digital-to-analog converter

[0025] 812, 814 Digitally controlled oscillator

[0026] 816 Multiplier

[0027] D1 Data code

[0028] P1, P2 Discrete periodic signal

[0029] 902 Pulse generator

[0030] 904 Voltage selector

[0031] 906 Voltage switching circuit

[0032] PUL Pulse signal

[0033] V SEL Voltage selection signal

[0034] VO1-VO6 Alternative voltage

[0035] 1002 Signal adjuster

[0036] 110 Touch driving flow

[0037] 1100-1104 Step DETAILED DESCRIPTION

[0038] In order to reduce electromagnetic interference (EMI) caused by the touch driving signal, the waveform of the touch driving signal can be modified so that the amplitude of the touch driving signal gradually rises and falls. More specifically, in a time interval for outputting a touch driving signal, the amplitude of the touch driving signal can be gradually increased in the early stage of the time interval, and the amplitude of the touch driving signal can be gradually decreased in the late stage of the time interval.

[0039] Please refer to Figure 2 , Figure 2This is a waveform diagram of the touch driving signal according to Embodiment 1 of the present invention. Figure 2 As shown, a typical sine wave signal can be combined with an envelope to generate a touch driving signal. Specifically, in the touch driving signal, the first sine wave has a minimum level, the next sine wave rises to a higher level, and so on, gradually increasing until the maximum amplitude. Then, the amplitude of the sine waves decreases symmetrically, reaching a minimum level in the last sine wave.

[0040] It is worth noting that the sine wave signal with gradually rising and falling amplitudes is only one of many embodiments of the present invention. In another embodiment, the touch driving signal may also be composed of square waves, triangular waves, or other types of periodic oscillation signals, and is not limited thereto. As long as the signal can oscillate to different levels to achieve gradually rising and falling amplitudes, its signal state is applicable to the touch driving signal of the present invention.

[0041] Please refer to Figure 3 , Figure 3 This is a waveform diagram comparing the touch drive signal and its corresponding spectral distribution. For example... Figure 3 As shown, the touch drive signals S3 and S4 have gradually rising and falling amplitudes, which are related to... Figure 1 The existing sine wave signal S2 is compared to the sine wave signal S2 shown. As mentioned above, the spectral distribution of the sine wave signal with several time intervals spans a large frequency range. In contrast, the electromagnetic energy of the touch drive signal S3, whose amplitude gradually increases and decreases, is less than that of the sine wave signal S2, especially at higher frequencies. The touch drive signal S4 has a slower rate of amplitude increase and decrease, and its electromagnetic energy is smaller and more concentrated at the frequency of signal oscillation. In this case, the problem of electromagnetic interference can be mitigated by reshaping the touch drive signal to have a gradually and slowly increasing and decreasing amplitude. If the amplitude of the touch drive signal increases and / or decreases at a slower rate, more optimized efficiency in reducing electromagnetic interference can be achieved.

[0042] It should be noted that the envelope used to form the rise and fall of the signal amplitude can be implemented in any way. In this invention, the envelope used to reshape the touch drive signal can follow functions such as the Hanning window, Hamming window, Blackman window, or ramp signal, but is not limited thereto.

[0043] Please refer to Figure 4 , Figure 4 This is a schematic diagram illustrating one state of the touch driving signal according to an embodiment of the present invention. Figure 4As shown, touch drive signals can be used in touchscreens that integrate display and touch functions to enable touch sensing on the touchscreen. Generally, display and touch can be performed in a time-sharing manner, and a display frame time (controlled by the vertical sync signal VSYNC) can be divided into one or more display periods DP and one or more touch periods TP. The display period DP is the period during which display data is output to the touchscreen, while the touch drive signal is output during the touch period TP. Figure 4 A long horizontal blank (H-blank) mode is shown, where the touch panel (TP) is arranged within a horizontal blank area during touch. The touchscreen may include an array of touch-sensing electrodes, and touch drive signals can be transmitted to one or more touch-sensing electrodes within a touch period on the TP. Figure 4 As shown, the touch drive signal located within a touch period TP has a variable amplitude, wherein the amplitude gradually increases slowly in the early part of the touch period TP and gradually decreases slowly in the later part of the touch period TP.

[0044] Please refer to Figure 5 , Figure 5 This is a schematic diagram illustrating another state of the touch drive signal according to an embodiment of the present invention. In this example, the touchscreen operates in a long V-blank mode, wherein the touch panel (TP) is positioned within the vertical blank area during touch. Figure 5 As shown, the touch period TP includes multiple time slots TS, each of which is allocated to transmit a touch drive signal to one or more touch sensing electrodes. All touch sensing electrodes on the touchscreen can be scanned within one or more touch periods TP. The touch drive signal located within a time slot TS of the touch period TP has a variable amplitude, wherein the amplitude gradually increases slowly in the first part of the time slot TS and gradually decreases slowly in the second part of the time slot TS.

[0045] In another embodiment, an envelope used to generate the rising and falling amplitudes can be applied to multiple time slots TS, such as Figure 6 As shown. In this example, one or more touch drive signals can be output within two consecutive time slots TS, reshaped by the same envelope, wherein the amplitude gradually increases slowly in the first time slot TS and remains at its maximum level, then gradually decreases slowly in the second time slot TS. The touch drive signals located within these consecutive time slots TS can be transmitted to the same or different touch sensing electrodes. It should be noted that the sine wave of the touch drive signal can oscillate continuously across the time slots TS, or the touch drive signal can be spaced at the boundaries between the time slots TS, such as... Figure 6 As shown. In another embodiment, the touch drive signal can also be reshaped using the same envelope within three or more time slots TS, and the number of time slots TS corresponding to the envelope is not a limiting condition of the present invention.

[0046] Please refer to Figure 7, Figure 7 FIG. 8 shows a schematic diagram of another embodiment of a touch control signal according to the present application. As shown, the touch control signal is a negative voltage signal, which can also be reshaped in a similar manner to achieve a gradually increasing and decreasing amplitude at the negative voltage level. In this case, the amplitude of the touch control signal gradually increases in the negative voltage direction at the beginning of the touch period TP and gradually decreases at the end of the touch period TP. Note that the above embodiments regarding the implementation of the touch control signal can be implemented in the negative voltage domain. Figure 7

[0047] In another embodiment, the touch control signal during a touch period can include a positive voltage for a period and a negative voltage for another period, as long as the amplitude of the signal swing gradually and slowly increases and / or decreases to reduce the electromagnetic interference energy of the touch control signal, and the related driving method should be within the scope of the present application.

[0048] Please refer to Figure 8 , Figure 8 FIG. 9 shows a schematic diagram of a touch control circuit 80 according to an embodiment of the present application. As shown, the touch control circuit 80 includes a digital control circuit 802 and a digital-to-analog converter (DAC) 804. The digital control circuit 802 can be used to generate a series of data codes D1. The digital-to-analog converter 804 can convert the data codes D1 into a touch control signal DRV. More specifically, the data codes D1 outputted by the digital control circuit 802 can include a series of discrete values, which are used to represent the waveform of the high-frequency signal swing (i.e., the waveform of the touch control signal DRV to be generated) with gradually increasing and decreasing amplitude, and the digital-to-analog converter 804 converts the discrete values into the touch control signal DRV. Figure 8

[0049] The data codes D1 can be generated by a numerically controlled oscillator (NCO), which can be used to generate discrete values corresponding to a periodic signal (e.g., a sine wave signal). In an embodiment, the digital control circuit 802 can include two numerically controlled oscillators 812 and 814 and a multiplier 816, as shown in FIG. 10. The numerically controlled oscillator 812 can be used to generate a series of discrete values corresponding to a sine wave signal, and the numerically controlled oscillator 814 can be used to generate a series of discrete values corresponding to a cosine wave signal. The multiplier 816 can be used to multiply the discrete values outputted by the numerically controlled oscillator 812 and the numerically controlled oscillator 814 to generate a series of data codes D1, which are used to represent the waveform of the high-frequency signal swing (i.e., the waveform of the touch control signal DRV to be generated) with gradually increasing and decreasing amplitude. Figure 8 ​​As shown. Digitally controlled oscillator 812 generates and outputs a discrete periodic signal P1, which includes discrete values ​​representing a high-frequency signal to establish signal oscillation in the touch drive signal DRV. Digitally controlled oscillator 814 generates and outputs another discrete periodic signal P2, which includes discrete values ​​representing the envelope to reshape the amplitude of the touch drive signal DRV. The envelope can be a sine wave signal with a lower frequency than the frequency of signal oscillation in the touch drive signal DRV. Multiplier 816, coupled to the outputs of digitally controlled oscillators 812 and 814, multiplies the discrete periodic signals P1 and P2 to generate a data code D1. The series of discrete values ​​included in the data code D1 can be used to represent the waveform of a high-frequency signal oscillation with gradually rising and falling amplitudes based on the envelope.

[0050] It is worth noting that touch drive signals with gradually increasing and decreasing amplitude can also be achieved through other methods. Please refer to [reference needed]. Figure 9 , Figure 9 This is a schematic diagram of another touch control circuit 90 according to an embodiment of the present invention. Figure 9 As shown, the touch control circuit 90 includes a pulse generator 902, a voltage selector 904, and a voltage switching circuit 906. The pulse generator 902 generates a pulse signal PUL, which includes a series of pulses. The voltage selector 904 outputs a voltage selection signal V_SEL. The voltage switching circuit 906 is coupled to the pulse generator 902 and the voltage selector 904, and receives the pulse signal PUL from the pulse generator 902 and the voltage selection signal V_SEL from the voltage selector 904 to generate a touch drive signal DRV. The touch drive signal DRV has a series of pulses corresponding to the pulses of the pulse signal PUL, wherein the voltage level of each pulse in the touch drive signal DRV is determined according to the corresponding voltage selection signal V_SEL.

[0051] For example, the voltage switching circuit 906 may be configured to have several alternative voltages (e.g., VO1 to VO6), and the amplitude of each pulse in the touch drive signal DRV output by the voltage switching circuit 906 is selected from one of the alternative voltages VO1 to VO6 according to the voltage selection signal V_SEL. In one embodiment, the voltage selection signal V_SEL includes a periodic numerical sequence that instructs the voltage switching circuit 906 to select an appropriate voltage for each pulse. Alternatively, the voltage selector 904 may include a counter that outputs a counting result as the voltage selection signal V_SEL transmitted to the voltage switching circuit 906, and the voltage switching circuit 906 may select a voltage value corresponding to the counting result for each pulse. In this way, according to the voltage selection signal V_SEL, signal pulses with gradually rising and falling amplitudes can be generated as the touch drive signal DRV.

[0052] It is worth noting that the rising edge and the falling edge of the pulse in the touch driving signal DRV can still cause electromagnetic interference energy that cannot be ignored. To solve this problem, further processing can be performed on the touch driving signal DRV. Please refer to Figure 10 , Figure 10 is a schematic diagram of another touch control circuit 100 according to an embodiment of the present application. As shown in Figure 10 , the circuit structure of the touch control circuit 100 is similar to that of the touch control circuit 90, so signals or components with similar functions are denoted by the same symbols. The difference between the touch control circuit 100 and the touch control circuit 90 is that the touch control circuit 100 further includes a signal adjuster 1002 coupled to the output of the voltage switching circuit 906, which can be used to smooth the rising edge and / or the falling edge of each pulse in the touch driving signal DRV to generate a touch driving signal DRV'.

[0053] As shown in Figure 10 , in the touch driving signal DRV', not only the amplitude of the pulse gradually rises and falls slowly, but also the rising and falling speed of each pulse is slowed down. In an embodiment, the signal adjuster 1002 can include a low-pass filter that can be used to make the rising edge and the falling edge smooth. Alternatively or additionally, the signal adjuster 1002 can include a slew rate controller that can be used to reduce the rising and falling speed of the pulse. In an embodiment, the slew rate controller can be implemented using an operational amplifier, which can be set to have a lower slew rate or driving capability, so as to output a touch driving signal DRV' with a pulse having a smoother rising edge and a falling edge.

[0054] The touch control circuits 80, 90 and 100 can be implemented in an integrated circuit (IC), which can be a touch driving integrated circuit with touch driving and sensing functions, or a touch and display driver integration (TDDI) integrated circuit with both touch driving / sensing functions and display functions. The detailed operation of touch driving and sensing using the touch driving signal should be well known to those skilled in the art, and will not be described here.

[0055] It is noted that the present application aims to provide a touch driving signal with gradually rising and falling amplitude for a touch screen. Those skilled in the art can make modifications or changes accordingly without being limited thereto. For example, the method of reshaping the touch driving signal to have gradually rising and falling amplitude can be applied to the signal of self-capacitance touch sensing and / or mutual capacitance touch sensing. In addition, in the above embodiments, Figures 4 to 7 The above embodiments show that the touch driving signal can be used for several envelope patterns. According to the arrangement during touch, different patterns can be combined. In one embodiment, the rising and falling of the touch driving signal amplitude can be asymmetric. For example, the rising and falling of the touch driving signal amplitude can follow different functions. In one embodiment, the touch driving signal amplitude can rise slowly but fall quickly, or rise quickly but fall slowly. In another embodiment, the touch driving signal amplitude can rise slowly at the beginning of a touch period and maintain at the maximum level without falling until the end of the touch period. Alternatively, the touch driving signal amplitude can be at the maximum level at the beginning of a touch period without gradually rising, and then slowly fall before the end of the touch period.

[0056] It is further noted that the touch driving signal of the present application can be applied to various types of touch screens. In one embodiment, the touch screen can be a panel integrating touch and display functions, in which touch and display operations are performed in time division. In another embodiment, the touch screen can be a touch pad without display function, for example, on a vehicle instrument panel with touch sensing function, the touch driving signal can be applied to the active area of the touch screen, or to the buttons around the touch screen.

[0057] The above operation of outputting the touch driving signal can be summarized as a touch driving flow 110, as shown in Figure 11 The touch driving flow 110 can be implemented in a touch driving circuit, such as the above-mentioned touch driving circuits 80, 90 or 100, in which the touch driving circuit can output the touch driving signal to control the touch operation on the touch screen. As shown in Figure 11 The touch driving flow 110 includes the following steps:

[0058] Step 1100: Start.

[0059] Step 1102: Apply a touch driving signal to the touch screen to perform touch sensing, in which the amplitude of the touch driving signal gradually rises and falls.

[0060] Step 1104: End.

[0061] Detailed implementation and variations of the touch driving procedure 110 can refer to the above-mentioned descriptions, and will not be repeated here.

[0062] In summary, the present application proposes a method for generating and outputting a touch driving signal, which can be applied to a touch screen for touch sensing. The amplitude of the touch driving signal gradually increases and decreases slowly, so as to reduce the electromagnetic interference energy generated by the touch driving signal. In an embodiment, a general touch driving signal with high-speed signal swing can be combined with an envelope to generate the touch driving signal, so that the amplitude of the touch driving signal gradually increases in the early stage of a touch period and gradually decreases in the late stage of the touch period. The touch driving signal can be generated by a touch control circuit, which can be implemented by a digital control circuit and a digital-to-analog converter in an embodiment, wherein the digital control circuit includes a digital control oscillator that can be used to generate a discrete periodic signal representing the high-frequency signal swing, and another digital control oscillator that can be used to generate a discrete periodic signal representing the envelope, the output results of the digital control oscillators can be combined with each other, and then converted by the digital-to-analog converter to generate the touch driving signal; in another embodiment, the touch control circuit can be implemented by a pulse generator for generating a pulse signal, each pulse on the pulse signal can provide a voltage level by a voltage selector, thereby generating a touch driving signal with gradually increasing and decreasing amplitude. The slow change of the amplitude of the touch driving signal can effectively improve the electromagnetic interference problem on the touch screen.

[0063] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of driving a touch screen, characterized by, Comprising: outputting, by a touch control circuit, a touch driving signal to the touch screen for touch sensing, the touch driving signal having a plurality of pulses, wherein each pulse has a peak; wherein the amplitude absolute value of the peak gradually increases and decreases during a touch period; wherein the peaks of the plurality of pulses have different amplitude absolute values.

2. The method of claim 1, wherein, The touch driving signal comprises a plurality of sine waves or square waves output through the same channel, and at least two of the plurality of sine waves or square waves have different levels.

3. The method of claim 1, wherein, The amplitude absolute value of the peak gradually increases in the early stage of a time interval and gradually decreases in the later stage of the time interval.

4. The method of claim 3, wherein, The time interval is a time slot within the touch period for outputting the touch driving signal to the touch screen.

5. The method of claim 3, wherein, The time interval is the touch period for outputting the touch driving signal to the touch screen, and the touch period is arranged between two display periods for outputting display data.

6. The method of claim 3, wherein, The time interval includes a plurality of time slots for outputting the touch driving signal, wherein the amplitude absolute value of the peak gradually increases in a first time slot of the plurality of time slots and gradually decreases in a second time slot of the plurality of time slots.

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