Touch data acquisition system and capacitive screen scanning method

Abstract

The invention discloses a touch data acquisition system and a capacitive screen scanning method. The touch data acquisition system comprises an SP I transceiver module, a front-end control module, a driving and data acquisition module, an ADC module and a data decoding module. According to the touch data acquisition system, a touch strategy that a self-capacitance working mode with low power consumption is used under the non-touch condition and a mutual capacitance working mode with high power consumption but capable of detecting multi-point touch is used under the touch condition is adopted, so that the power consumption of touch detection is effectively reduced. According to the touch data acquisition system disclosed by the invention, a plurality of channels are taken as driving channels when mutual capacitance works by using a parallel driving method of coding segmentation, so that the signal-to-noise ratio of touch detection is effectively improved.

Description

Technical Field

[0001] The invention belongs to the field of touch control and relates to a touch data acquisition system and a capacitive screen scanning method. Background Art

[0002] Projected capacitive screen is a touch screen that uses projected capacitive touch technology. The capacitive touch screen glass surface uses ITO to form horizontal and vertical electrode arrays. These horizontal and vertical electrodes form self-capacitance with the ground, and the horizontal and vertical electrodes form mutual capacitance with each other. When a finger touches the capacitive screen, the capacitance of the finger will be superimposed on the capacitance of the screen. At this time, the self-capacitive screen determines the horizontal coordinates and vertical coordinates respectively according to the changes in capacitance before and after the touch by detecting the horizontal and vertical electrode arrays, and then combines them into the touch coordinates of the plane.

[0003] When the self-capacitive touch system is working, each electrode only needs to be detected once in a single scanning cycle, that is, the number of scans in a single scanning cycle is equal to the number of electrodes, which makes the scanning cycle of the self-capacitive touch system shorter and has a higher touch refresh rate. However, in the case of multi-point touch, the self-capacitive operation has the "ghost point" phenomenon.

[0004] When the mutual capacitance touch system is working, the horizontal electrodes send out excitation signals in sequence, and all the vertical electrodes receive the signals at the same time, so that the capacitance value of all the intersection points of the horizontal and vertical electrodes can be obtained, that is, the capacitance value of the two-dimensional plane of the entire touch screen. Therefore, the mutual capacitance touch system has a true multi-touch function. However, the mutual capacitance touch system has the disadvantages of a long scanning cycle and high power consumption.

[0005] In traditional touch control systems, a time-division-based scanning drive method is usually used, that is, by sending drive signals column by column, each row receives the response signals of each column after the drive signals pass through each capacitor node in multiple times, and converts the capacitance data into voltage data through a charge amplifier at the receiving end for subsequent quantization equipment to quantify the capacitance change of the capacitor node. However, this method is greatly affected by noise and has a low signal-to-noise ratio. Summary of the invention

[0006] In order to overcome the deficiencies of the prior art, the present invention provides a touch data acquisition system and a capacitive screen scanning method.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A touch data acquisition system, comprising:

[0009] SPI transceiver module, used to receive drive configuration parameters and data acquisition configuration parameters from an external MCU and send decoded capacitance data to the MCU;

[0010] The front-end control module is used to receive and store the drive configuration parameters and data acquisition configuration parameters output by the SPI transceiver module, and generate control signals for controlling the drive and data acquisition modules;

[0011] The driving and data acquisition module is used to receive a control signal to configure any channel of the capacitive screen as a driving channel or a data acquisition channel, send a driving square wave with configurable polarity, frequency, and quantity to the capacitive screen through the driving channel, and collect capacitance data through the data acquisition channel;

[0012] ADC module, used to convert capacitance data into digital signals;

[0013] The data decoding module is used to decode the digital signal and send it to the SPI transceiver module.

[0014] Furthermore, the control signal of the front-end control module to the driving and data acquisition module also includes: controlling the driving square wave polarity of the driving channel, controlling the driving square wave frequency of the driving channel, controlling the driving square wave quantity of the driving channel, and controlling the acquisition time of the data acquisition channel.

[0015] Furthermore, the driving and data acquisition module encodes the driving signal by driving a plurality of driving channels and configuring different polarities respectively.

[0016] Furthermore, the SPI transceiver module is connected to the front-end control module, the front-end control module is connected to the drive and data acquisition module, the drive and data acquisition module is connected to the ADC module, the ADC module is connected to the data decoding module, and the data decoding module is connected to the SPI transceiver module.

[0017] A capacitive screen scanning method comprises the following steps:

[0018] Step 1: Perform a self-capacitance scan for 1 frame and proceed to step 2;

[0019] Step 2: Determine whether a touch event occurs in the self-capacitance scanning result. If a touch event occurs, go to step 3; if no touch event occurs, go to step 1.

[0020] Step 3: Perform mutual capacitance scanning for 1 frame and proceed to step 4;

[0021] Step 4: Determine whether a touch event occurs in the mutual capacitance scanning result. If a touch event occurs, extract the touch position information and go to step 3. If no touch event occurs, go to step 1.

[0022] Furthermore, in step 1 to step 2, the front-end control module configures the channel of the capacitive screen to a driving state during the high-level time period of the self-capacitance scanning cycle, and continuously outputs a high level. In the low-level time period of the self-capacitance scanning cycle, the channel of the capacitive screen is configured to a data acquisition state, and the self-capacitance value of each channel is collected. The self-capacitance value is converted into a digital value and decoded and sent to the MCU for determining whether a touch event occurs.

[0023] Furthermore, in step 3 and step 4, the transverse electrodes and the longitudinal electrodes of the capacitive screen form a mutual capacitance matrix in the X direction and the Y direction; the front-end control module configures the channel in the X direction as a driving channel, and the driving channel continuously transmits a square wave of a set frequency, a set polarity, and a set number to the capacitive screen; the channel in the Y direction is configured as a data acquisition channel, and mutual capacitance data is collected once in the first half cycle and the second half cycle of the square wave according to the frequency of the driving square wave, and the mutual capacitance data is converted into a digital quantity and decoded and sent to the MCU for determining whether a touch event occurs.

[0024] Furthermore, the external MCU sends the configuration parameters to the front-end control module through the SPI transceiver module for parameter storage. The external MCU sends a self-capacitance scan start signal or a mutual capacitance scan start signal through the SPI transceiver module. After the front-end control module detects the corresponding signal, it controls the drive and data acquisition module to perform corresponding self-capacitance scan or mutual capacitance scan.

[0025] In summary, the present invention is beneficial in that:

[0026] The present invention uses a self-interconnected touch data acquisition system and a scanning strategy. In the absence of touch, a self-capacitance working mode with lower power consumption is used. In the presence of touch, a mutual capacitance working mode with higher power consumption but capable of detecting multi-point touch is used. This effectively reduces the power consumption of the touch system while ensuring the accuracy of the touch and ensuring that no "ghost points" appear during multi-point touch.

[0027] The present invention uses a parallel driving method of coding segmentation and simultaneously uses multiple channels as driving channels when mutual capacitance works, thereby effectively improving the signal-to-noise ratio of touch detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of the touch data acquisition system of the present invention.

[0029] Figure 2 It is a flowchart of the capacitive screen scanning method of the present invention.

[0030] Figure 3 Schematic diagram of the channel structure of the capacitive touch screen in the embodiment of the present invention.

[0031] Figure 4Schematic diagram of a matrix structure of 4*4 channels in a parallel driving method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0033] The present invention provides a touch data acquisition system based on a capacitive touch screen, referring to Figure 1 As shown, it includes an SPI transceiver module, a front-end control module, a drive and data acquisition module, an ADC module, and a data decoding module. The SPI transceiver module is connected to the front-end control module, the front-end control module is connected to the drive and data acquisition module, the drive and data acquisition module is connected to the ADC module, the ADC module is connected to the data decoding module, and the data decoding module is connected to the SPI transceiver module.

[0034] The main function of the SPI transceiver module is to communicate with an external MCU. As a slave of the SPI protocol, the module receives the driver parameters and the receiver parameters that need to be configured from the MCU, and sends the decoded capacitance data collected on the touch screen to the MCU.

[0035] The main function of the front-end control module is to store the drive configuration parameters and the data acquisition configuration parameters, and generate the control signal for controlling the drive and data acquisition modules according to the configuration parameters provided by the MCU obtained by the SPI transceiver module. The control signals of the front-end control module to the drive and data acquisition modules are as follows: controlling a channel as a drive channel or a data acquisition channel, controlling the driving square wave polarity of the drive channel, controlling the driving square wave frequency of the drive channel, controlling the number of driving square waves of the drive channel, and controlling the acquisition time of the data acquisition channel. The driving signal can be encoded by controlling the driving square wave polarity of the drive channel.

[0036] The main functions of the driving and data acquisition module are as follows: the module can configure any channel of the capacitive touch screen as a driving channel or a data acquisition channel. The channel configured as a driving channel can send a square wave with configurable polarity, frequency, and number of square waves to the capacitive screen, and the channel configured as a data acquisition channel can collect capacitance data from the capacitive screen according to the configured time. When the mutual capacitance is working, the driving and data acquisition module can work under the control of the front-end control module based on the parallel driving method of coding segmentation, that is, by driving different driving channels at the same time and configuring different polarities for them to realize the encoding of the driving signal. At this time, a capacitance data after all the drives are compounded will be obtained in each data acquisition channel.

[0037] The main function of the ADC module is to convert the capacitance data collected by the driving and data acquisition modules into digital signals.

[0038] The main function of the decoding module is to decode the digital signal of the composite driving capacitor obtained by the data acquisition channel.

[0039] Based on the above touch data acquisition system, the present invention also provides a scanning method for a capacitive touch screen.

[0040] Among them, capacitive touch screens are made of a layer of transparent conductive material, usually coated on a glass surface. This layer of conductive material is divided into tiny capacitive electrodes or sensing units, usually arranged in a matrix. In a non-touch state, these capacitive units distribute the charge evenly. When a position on the screen is touched with a finger or a capacitive object, the charge distribution between the capacitive electrodes changes, and part of the charge is transferred to the internal capacitor of the drive and data acquisition module, causing the voltage across the internal capacitor to change. This change is sensed, so that the control circuit determines the change in capacitance through the voltage and determines the location of the touch point.

[0041] The horizontal and vertical electrode positions in the capacitive touch screen form a mutual capacitance matrix densely distributed in the X and Y directions. By inputting square waves to the electrodes in the X direction, the driving and data acquisition modules connect the electrodes in the Y direction to obtain the mutual capacitance. When a finger or other capacitive material touches the screen, the mutual capacitance near the coordinate will change. The specific position of the touch point can be obtained through calculation.

[0042] As an embodiment of a preferred capacitive touch screen structure in the present invention, refer to Figure 3As shown in the figure, the first direction is set to the positive direction of the X-axis, the second direction is set to the negative direction of the Y-axis, the X-axis direction is the mutual capacitance drive channel, the number of which is 40, and the Y-axis direction is the mutual capacitance data acquisition channel, the number of which is 72. When performing a full-screen scan, all channels are first scanned for self-capacitance, and self-capacitance information of 112 channels will be obtained. When a touch is detected, a mutual capacitance scan is performed, all drive channels are driven in parallel with coding, and all data acquisition channels output signals in parallel. Each time slice will obtain information from 72 data acquisition channels, and 72*40 mutual capacitance data will be obtained after 40 time slices.

[0043] Based on the above preferred embodiment, the scanning method comprises the following steps:

[0044] Step 1: The external MCU sends the configuration parameters to the front-end control module through the SPI transceiver module for parameter storage. Furthermore, the external MCU sends a self-capacitance scan start signal through the SPI transceiver module. After the front-end control module detects the self-capacitance scan start signal, it controls the drive and data acquisition modules to perform self-capacitance scanning. During the self-capacitance scanning process, the front-end control module configures 112 channels to the drive state during the high-level time period of the self-capacitance scanning cycle, and continuously outputs a high level; during the low-level time period of the self-capacitance scanning cycle, the 112 channels are configured to the data acquisition state, and the self-capacitance value of each channel is collected. The self-capacitance value is sent to the ADC module for analog-to-digital conversion to obtain its digital value. After the self-capacitance digital value is briefly stored in the data decoding module, it will be sent to the external MCU through the SPI transceiver module.

[0045] Step 2: The MCU will determine whether there is a touch event based on the self-capacitance information. If there is no touch event, the self-capacitance scan start signal will be resent to start a new frame of self-capacitance scan; if there is a touch event, the mutual capacitance scan start signal will be sent to perform mutual capacitance scan.

[0046] Step 3: If the self-capacitance scan finds a touch event, the front-end control module receives the mutual capacitance scan start signal, and the front-end control module controls the drive and data acquisition modules to perform mutual capacitance scanning. During the mutual capacitance scanning process, the front-end control module configures 40 channels in the X direction as drive channels and 72 channels in the Y direction as data acquisition channels. Based on the parallel drive method of encoding segmentation, for the drive channel, a square wave will be continuously sent to the capacitive screen during the mutual capacitance scan. The frequency, polarity and number of square waves generated are determined by the configuration parameters. There are three polarities, including -1, 0, and +1. The square wave with -1 polarity is high level first and then low level; the square wave with +1 polarity is low level first and then high level; the 0 polarity is a continuous output of low level. For the data acquisition channel, during the mutual capacitance scan, the mutual capacitance data will be collected once in the first half cycle and the second half cycle of the square wave according to the frequency of the driving square wave. Further, the collected mutual capacitance data is sent to the ADC module for analog-to-digital conversion to obtain the digital value of the mutual capacitance. Since the polarity of the square wave is introduced at the driver end, it is equivalent to encoding the driver. Therefore, the collected mutual capacitance digital quantity needs to be sent to the data decoding module for decoding. The decoded data will be sent to the MCU through the SPI transceiver module.

[0047] Step 4: The MCU will extract the touch coordinates and determine whether a touch event has occurred through the mutual capacitance information. If a touch event occurs, the mutual capacitance scan start signal will be resent to start a new frame of mutual capacitance scan; if there is no touch event, the self-capacitance scan start signal will be sent to perform self-capacitance scan and wait for the touch event to be sent.

[0048] In some embodiments, the code segmentation-based parallel driving method in the mutual capacitance scanning in step 3 includes:

[0049] like Figure 4 As shown in the upper right, the horizontal channels are used as driving channels, which are TX0, TX1, TX2, and TX3 from top to bottom; the vertical channels are used as data acquisition channels, which are RX0, RX1, RX2, and RX3 from left to right; a 4*4 mutual capacitance scan requires 4 time slices. Figure 4As shown in the upper left, in the first time slice, the polarities of TX0, TX1, TX2, and TX3 are -1, +1, +1, +1 respectively; assuming that the mutual capacitance of the capacitive screen is exactly the same, the values ​​detected on RX0, RX1, RX2, and RX3 are 2, 2, 2, and 2 respectively; similarly, in the second time slice, the values ​​detected on RX0, RX1, RX2, and RX3 are -2, -2, -2, and -2 respectively; in the third time slice, the values ​​detected on RX0, RX1, RX2, and RX3 are -2, -2, -2, and -2 respectively; in the fourth time slice, the values ​​detected on RX0, RX1, RX2, and RX3 are -2, -2, -2, and -2 respectively. Thus, after four time slices, a 4*4 matrix M can be obtained at the data acquisition end. RX ,like Figure 4 As shown in the lower right, the mutual capacitance matrix with a coefficient of 4 can be obtained by decoding the matrix in the decoding module.

[0050] The specific formula is as follows:

[0051]

[0052] Among them, M RX is the 4*4 matrix obtained by the data acquisition end, is the transposed matrix of the driving matrix of the driving channel, M C互 is the decoded mutual capacitance matrix.

[0053] The process of the data acquisition channel collecting the mutual capacitance value after the encoding drive can be seen from the result of multiplying the transposed matrix of the driving matrix with the mutual capacitance matrix. In the decoding module, as long as the inverse matrix of the transposed matrix of the driving matrix is ​​multiplied with the matrix M obtained by data acquisition, RX By multiplying, we can get the mutual capacitance matrix M on the capacitive screen with coefficients C互 .

[0054] Since there is noise when the touch control system is working normally, the above formula (1) is the data sampling matrix under the ideal noise-free condition. Let M RX0 is the matrix collected by the data acquisition channel under ideal conditions, M C互0 is the actual mutual capacitance matrix, then the noise matrix is ​​N = M RX -M RX0 .

[0055] So we can get:

[0056]

[0057] Among them, M C互 is the decoded mutual capacitance matrix, M C互0 is the actual mutual capacitance matrix, The smaller the value of , the higher the signal-to-noise ratio. The standard deviation of all elements in the matrix. The smaller the standard deviation, the smaller the demodulation result jump is, and the better its anti-noise performance is.

[0058] Taking 8 driving channels as an example, the data noise when the Hardamard matrix is ​​used as the driving matrix is ​​9db lower than the data noise when the unit matrix is ​​used as the driving matrix. The unit matrix is ​​equivalent to the scanning driving method based on time division. Therefore, the parallel driving method based on coding division has a significant improvement in signal-to-noise ratio compared with the scanning driving method based on time division.

[0059] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

Claims

1. A touch data acquisition system, characterized in that: include: SPI transceiver module, used to receive drive configuration parameters and data acquisition configuration parameters from an external MCU and send decoded capacitance data to the MCU; The front-end control module is used to receive and store the drive configuration parameters and data acquisition configuration parameters output by the SPI transceiver module, and generate control signals for controlling the drive and data acquisition modules; The driving and data acquisition module is used to receive a control signal to configure any channel of the capacitive screen as a driving channel or a data acquisition channel, send a driving square wave with configurable polarity, frequency, and quantity to the capacitive screen through the driving channel, and collect capacitance data through the data acquisition channel; ADC module, used to convert capacitance data into digital signals; The data decoding module is used to decode the digital signal and send it to the SPI transceiver module.

2. A touch data acquisition system according to claim 1, characterized in that: The control signal of the front-end control module to the driving and data acquisition module also includes: controlling the driving square wave polarity of the driving channel, controlling the driving square wave frequency of the driving channel, controlling the driving square wave quantity of the driving channel, and controlling the acquisition time of the data acquisition channel.

3. A touch data acquisition system according to claim 1, characterized in that: The driving and data acquisition module encodes the driving signal by driving a plurality of driving channels and respectively configuring different polarities.

4. The touch data acquisition system according to claim 1, characterized in that: The SPI transceiver module is connected to the front-end control module, the front-end control module is connected to the drive and data acquisition module, the drive and data acquisition module is connected to the ADC module, the ADC module is connected to the data decoding module, and the data decoding module is connected to the SPI transceiver module.

5. A capacitive screen scanning method, characterized in that: The following steps are involved: Step 1: Perform a self-capacitance scan for 1 frame and proceed to step 2; Step 2: Determine whether a touch event occurs in the self-capacitance scanning result. If a touch event occurs, go to step 3; if no touch event occurs, go to step 1. Step 3: Perform mutual capacitance scanning for 1 frame and proceed to step 4; Step 4: Determine whether a touch event occurs in the mutual capacitance scanning result. If a touch event occurs, extract the touch position information and go to step 3. If no touch event occurs, go to step 1.

6. A capacitive screen scanning method according to claim 1, characterized in that: In step 1 to step 2, the front-end control module configures the channel of the capacitive screen to a driving state during the high-level time period of the self-capacitance scanning cycle, and continuously outputs a high level. In the low-level time period of the self-capacitance scanning cycle, the channel of the capacitive screen is configured to a data acquisition state, and the self-capacitance value of each channel is collected. The self-capacitance value is converted into a digital value and decoded and sent to the MCU to determine whether a touch event occurs.

7. A capacitive screen scanning method according to claim 1, characterized in that: In step 3 to step 4, the transverse electrodes and the longitudinal electrodes of the capacitive screen form a mutual capacitance matrix in the X direction and the Y direction; the front-end control module configures the channel in the X direction as a driving channel, and the driving channel continuously transmits a square wave of a set frequency, a set polarity, and a set number to the capacitive screen; The channel in the Y direction is configured as a data acquisition channel. Mutual capacitance data is collected once in the first half cycle and the second half cycle of the square wave according to the frequency of the driving square wave. The mutual capacitance data is converted into digital quantity and decoded and sent to the MCU to determine whether a touch event occurs.

8. A capacitive screen scanning method according to claim 1, characterized in that: The external MCU sends the configuration parameters to the front-end control module through the SPI transceiver module for parameter storage. The external MCU sends a self-capacitance scan start signal or a mutual capacitance scan start signal through the SPI transceiver module. After the front-end control module detects the corresponding signal, it controls the drive and data acquisition modules to perform the corresponding self-capacitance scan or mutual capacitance scan.

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