CN112332828A - Charging circuit, analog receiving circuit and charging method based on self-capacitance touch screen - Google Patents
Charging circuit, analog receiving circuit and charging method based on self-capacitance touch screen Download PDFInfo
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- CN112332828A CN112332828A CN202010963940.6A CN202010963940A CN112332828A CN 112332828 A CN112332828 A CN 112332828A CN 202010963940 A CN202010963940 A CN 202010963940A CN 112332828 A CN112332828 A CN 112332828A
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
- H03K17/96—Touch switches
- H03K17/962—Capacitive touch switches
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
- G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
- G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
- G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
- G06F3/044—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means by capacitive means
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/22—Modifications for ensuring a predetermined initial state when the supply voltage has been applied
Abstract
The invention discloses a charging circuit, an analog receiving circuit and a charging method based on a self-capacitance touch screen, wherein an input end A of a charge amplifier of the charging circuit is connected with a feedback capacitor, two ends of the feedback capacitor are connected with a switch Ca _ rst in parallel, the input end A of the charge amplifier is connected with one end of a screen body capacitor after sequentially passing through a switch P3 and a switch P1-1, a circuit between the switch P3 and the switch P1-1 is provided with a switch P1-2 and a switch P2-1, the switch P2-1 is connected with the input end B, correspondingly, one end of the switch P1-3 is connected with the input end B, the other end of the switch P2-2 is connected with the switch P2-2, and the other end of the switch P2-2 is grounded, the application range is wider.
Description
Technical Field
The invention relates to the technical field of charging circuits, in particular to a charging circuit, an analog receiving circuit and a charging method based on a self-capacitance touch screen.
Background
As is well known, an electronic system with touch sensing function includes a touch area for a user to touch with a finger or a stylus. The capacitive touch technology is mostly used in touch screens with medium and small sizes, and becomes the mainstream technology with the largest application amount in the market.
A touch screen using capacitive touch technology generally includes a touch panel superimposed on the screen for a user to touch with his or her hand or a touch pen, wherein the touch panel includes a plurality of wires each coupled to a touch sensing circuit in a touch sensing device.
Capacitive touch technologies are mainly classified into two types, one is a self-capacitive touch technology, and the other is a mutual capacitive touch technology. Both techniques rely on the change in capacitance on a wire when a finger or stylus is brought close to the wire of the touch pad, and the position of the touch point is known by measuring the voltage drop of the driving potential.
The capacitance of the screen body is detected by detecting the energy transmitted by the capacitance, one end of the capacitance of the screen body is grounded, and the signal detection processing circuit is connected to the other end of the capacitance of the screen body and judges the position of the capacitance change according to the signal level of a receiving point (as shown in figure 1).
When the touch screen is started, the screen capacitor needs to be charged first, charges are stored, the charges stored in the screen capacitor can be changed when a finger or a touch pen contacts the touch screen, and output can also be changed.
As shown in fig. 3, the first idea of the basic working principle of capacitive screens is: when a user touches the screen, because the screen body is self-capacitance, when the human body touches the screen body, the capacitance of the screen body is increased, but a part of charges are absorbed, namely the charges in the capacitance of the screen body are reduced. The function of the charge amplifier is to convert this reduced charge into a reduction in the output voltage.
At present, most of used touch screens are small screens such as mobile phones and flat panels, the capacitance of a screen body is small, and the capacitance can be transferred to the capacitance through an internal adjusting capacitance with a capacitance value close to that of the touch screen, so that the capacitance of the screen body is charged.
In the traditional self-capacitance screen capacitor charging, an internal adjusting capacitor with the capacitance value equal to that of a screen capacitor is designed inside an Integrated Circuit (IC) control chip, the internal adjusting capacitor is charged firstly, and the charges are transferred to the screen capacitor after reaching the requirement.
For a touch screen with a small screen, charges can be filled in the screen capacitor through the internal adjusting capacitor, but if the screen is too large, the screen capacitor is also correspondingly increased, the size of the internal capacitor is limited by the area of a chip, and the charges stored in the built-in capacitor are transferred to the screen capacitor, so that the potential of the upper electrode plate of the screen capacitor is not close to or equal to the required potential.
Disclosure of Invention
The purpose of the invention is as follows: in order to overcome the defects of the prior art, the invention provides a charging circuit based on a self-capacitance touch screen, which can solve the problems of overlarge chip area and narrow application range caused by the limitation of capacitance potential of a screen body, and also provides an analog receiving circuit and a charging method obtained according to the charging circuit.
The technical scheme is as follows: the invention provides a charging circuit based on a self-capacitance touch screen, which is connected with one end of a screen body capacitor, the other end of the screen body capacitor is grounded, the charging circuit comprises a charge amplifier, a switch P1-3, a switch P2-2, an internal adjusting capacitor and a switch P4, the charge amplifier comprises an input end A, an input end B and an output end, the input end A of the charge amplifier is connected with a feedback capacitor, two ends of the feedback capacitor are connected with a switch Ca _ rst in parallel, the input end A of the charge amplifier is connected with one end of the screen body capacitor after sequentially passing through a switch P3 and a switch P1-1, a circuit between the switch P3 and the switch P1-1 is provided with the switch P1-2 and the switch P2-1, the switch P2-1 is connected with the input end B, correspondingly, one end of the switch P1-3 is connected with the input end B, the other end of the switch P, the other end of the internal adjusting capacitor is grounded, two ends of the internal adjusting capacitor are respectively connected to a line between a switch P1-2 and a switch P2-1 and a line between a switch P1-3 and a switch P2-2, one end of the switch P4 is connected to a line between the screen capacitor and the switch P1-1, and the other end of the switch P4 is grounded.
Further, the method comprises the following steps:
the B input end inputs a reference voltage V1。
Further, the method comprises the following steps:
the switch P1-1, the switch P1-2 and the switch P1-3 are all controlled by a first signal, the switch P1-2 and the switch P2-1 are all controlled by a second signal, and the first signal and the second signal are absolutely opposite.
On the other hand, the invention also provides an analog receiving circuit, which comprises the charging circuit based on the self-capacitance touch screen, a filter and an analog-digital converter, wherein the output end of the charging circuit is connected with the input end of the filter, and the output end of the filter is connected with the input end of the analog-digital converter.
Finally, the invention provides a charging method realized by a charging circuit based on a self-capacitance touch screen, which comprises the following steps:
(1) determining the capacitance of the screen body and the capacitance of the internal adjusting capacitor;
(2) determining the time T for charging the internal adjusting capacitor once to reach the required charging voltage, the time T for transferring the charge of the internal adjusting capacitor to the screen body capacitor once, and the times n for charging and charge transfer;
(3) setting a square wave with a period of (T + T) and a duration of n x (T + T) for controlling a corresponding switch to charge a screen capacitor so that the internal charge of the screen capacitor is filled to a required value;
(4) and after the charging is completed, starting the touch screen.
Further, the method comprises the following steps:
in the step (3), the screen capacitor is charged to fill the internal charge of the screen capacitor to a required value, and the method specifically includes:
(31) closing the switch P2-1, opening the switch P2-2, the switch P4, the switch Ca _ rst, the switch P1-1, the switch P1-2, the switch P1-3 and the switch P3, charging the internal adjusting capacitor to enable the potential of the internal adjusting capacitor to reach the reference voltage V1, wherein the charge on the internal adjusting capacitor is Q;
(32) switch P1-1, switch P1-2, switch P1-3 closed, switch P2-1, switch P2-2, switch P3 and switchP4 is turned off, switch Ca _ rst is turned on, the screen capacitor is connected with the internal adjusting capacitor, the lower plate of the internal adjusting capacitor is connected to the reference voltage V1Starting to transfer charges to the screen capacitor until the charges of the screen capacitor are the same as the charges Q of the internal adjusting capacitor in the step (31);
(33) repeating the steps (31) and (32) until the charge on the capacitance charge of the screen body reaches the value nQ of the required charge, and finishing charging the capacitance of the screen body;
(34) when the electric charge in the screen body capacitor reaches the required value nQ, namely the voltage V2 of the screen body capacitor is basically equal to the reference voltage V1, the switch P3, the switch P1-1, the switch P1-2 and the switch P1-3 are closed, the switch P2-1, the switch P2-2 and the switch P4 are opened, the switch Ca _ rst is opened, the circuit is opened, and the touch screen starts to work.
Further, the method comprises the following steps:
the method for calculating the number n of times of charging and charge transfer comprises the following steps:
the internal tuning capacitor is charged once according to the formula Q ═ C × U, and the resulting charge Q ═ C is generatedb*V1The voltage of the screen capacitor can be obtained by transferring the charge Q into the screen capacitor
Finally, the voltage of the screen capacitor is made to be equal to the reference voltage V1Are substantially equal, then obtain
n is Cs/CbRounding up the value, where CsIs the capacitance value of the screen body capacitance, CbThe capacitance value of the capacitor is adjusted for the inside.
Has the advantages that: (1) the charging circuit and the charging method can solve the problem that the screen body capacitance of any self-capacitance touch screen can not reach the required potential, are suitable for any self-capacitance touch screen, and have wider application range; (2) the invention does not limit the internal adjusting capacitance to be basically the same as the screen capacitance, and can be much smaller than the screen capacitance, thereby reducing the internal adjusting capacitance CbCorrespondingly, the chip area can be reducedAnd (4) accumulating.
Drawings
FIG. 1 is a schematic diagram of a touch screen IC control chip according to an embodiment of the invention;
FIG. 2 is a schematic diagram of an analog receiver circuit according to the present invention;
FIG. 3 is a schematic diagram of a capacitive screen according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a charging circuit according to an embodiment of the present invention;
FIG. 5 is a circuit diagram illustrating the charging of the internal tuning capacitor according to the present invention;
FIG. 6 is a circuit diagram illustrating a charge handling process according to the present invention;
FIG. 7 is a circuit diagram illustrating the charge accumulation during multiple charging operations according to an embodiment of the present invention;
FIG. 8 is a flow chart of the charge variation of the panel capacitance according to an embodiment of the present invention;
FIG. 9 is a diagram illustrating the effect of the amount of charge in the capacitor of the shield on the output of the charge amplifier according to an embodiment of the present invention;
fig. 10 is a circuit diagram of a start-up circuit according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, the present invention provides a capacitive touch screen with an integrated circuit embedded therein, wherein the integrated circuit includes an analog receiving end, a digital AFE module, i.e. analog front end, and a screen capacitance CsOne end of the screen capacitor is grounded, the other end of the screen capacitor is connected with the analog receiving end, the analog receiving end is connected with the digital AFE, the digital AFE module is used for setting square waves and controlling a switch corresponding to the inside of the chip to charge the screen capacitor, so that the inside of the screen capacitor is enabled to be chargedThe charge is filled to the required value.
Specifically, be analog receiving circuit in the analog receiving end, analog receiving circuit specifically includes:
as shown in fig. 2, the charging circuit, the filter and the analog-to-digital converter based on the self-capacitance touch screen have an output terminal connected to an input terminal of the filter (filter) and an output terminal connected to an input terminal of the analog-to-digital converter (ADC).
As shown in FIG. 4, in the present embodiment, the charging circuit based on the self-capacitance touch screen comprises a charge amplifier, a switch P1-3, a switch P2-2, and an internal adjusting capacitor CbAnd the switch P4, the internal adjusting capacitor not only has the function of charging the screen body capacitor, but also mainly adjusts the offset of the charge amplifier, so as to increase the input dynamic range of the ADC and thus increase the variation.
The charge amplifier comprises an input end A, an input end B and an output end, wherein the input end A of the charge amplifier is connected with a feedback capacitor CfThe two ends of the feedback capacitor are connected with a switch Ca _ rst in parallel, and the A input end of the charge amplifier passes through a switch P3 and a switch P1-1 in sequence and then is connected with a screen capacitor CsOne end of the internal adjusting capacitor is connected, a circuit between the switch P3 and the switch P1-1 is connected with a switch P1-2 and a switch P2-1, the switch P2-1 is connected with the input end B, correspondingly, one end of the switch P1-3 is connected with the input end B, the other end of the switch P2-2 is connected with the switch P2-2, the other end of the internal adjusting capacitor is grounded, two ends of the internal adjusting capacitor are respectively connected to a circuit between the switch P1-2 and the switch P2-1 and a circuit between the switch P1-3 and the switch P2-2, one end of the switch P4 is connected to a circuit between the screen capacitor and the switch P1-1, and the.
The switch P1-1, the switch P1-2 and the switch P1-3 are controlled by the same signal, the signal is a first signal, the switch P1-1, the switch P1-2 and the switch P1-3 are collectively called as a switch P1, the switch P2-1 and the switch P2-2 are controlled by the same signal, the signal is a second signal, the switch P2-1 and the switch P2-2 are collectively called as a switch P2, the signals of the first signal and the second signal are absolutely opposite, and the reference voltage V is input into the B input end1。
As shown in fig. 8, the present invention provides a charging method based on a charging circuit, including:
(1) the capacitance of the screen body is determined through a physical measurement means, the capacitance value of the internal adjusting capacitor is determined, the capacitance values of the screen body and the internal adjusting capacitor can be set randomly according to the needs of a user, and the capacitance values are not necessarily set to be basically the same;
(2) determining the time T for charging the internal adjusting capacitor once through simulation to reach the required charging voltage, the time T for transferring the charge of the internal adjusting capacitor to the screen body capacitor once, and the number n of times of charging and charge transfer;
the number n of times of charging and charge transfer is calculated as follows:
the internal tuning capacitor is charged once according to the formula Q ═ C × U, and the resulting charge Q ═ C is generatedb*V1The voltage of the screen capacitor can be obtained by transferring the charge Q into the screen capacitor
Finally, the voltage of the screen capacitor is made to be equal to the reference voltage V1Substantially equal, then approximately the number of transfers required is
Wherein, CsIs the capacitance value of the screen body capacitance, CbAfter the rough times are determined for the capacitance value of the internal adjusting capacitor, the obtained rough times are rounded up through an rounding-up function ROUNDUP (n, 0) to obtain times n, and the times n are verified through analog simulation.
(3) Setting a square wave with a period of (T + T) and a duration of n x (T + T) for controlling a corresponding switch to charge a screen capacitor so that the internal charge of the screen capacitor is filled to a required value;
charging the screen capacitor to fill the internal charge of the screen capacitor to a required value, specifically comprising:
(31) as shown in FIG. 5, switches P2, P4 are closed, P1 and P3 are open, switch Ca _ rst is closed, and capacitor C is adjusted for internalbCharging is carried out to make the internal adjusting capacitor CbReaches the reference voltage V1Rear magnificationThe device is now a follower with an output of V1The charge on the internal adjusting capacitor is Q;
(32) as shown in FIG. 6, switch P1 is closed, P2, P3 and P4 are open, switch Ca _ rst is closed, and screen capacitor C is closedsAnd an internal regulation capacitor CbConnected to each other, and internally adjusting the capacitance CbIs connected to V1Starting to the screen capacitance CsTransferring the charges until the charges of the screen capacitor are the same as the charges Q of the internal adjusting capacitor in the step (31);
(33) screen capacitor CsThe change of internal charge is caused by an internal regulating capacitance CbCharging time t and charge transfer to screen capacitance CsThe time T of (2) may result in a panel capacitance C if the charging time is insufficient or the charge transfer time is insufficient, as shown in FIG. 7sInsufficient internal charge will result in V2Less than V1The deviation is large, which affects the output of the charge amplifier, as shown in fig. 9, therefore, steps (31) and (32) are repeated until the charge on the screen capacitor charge reaches the value nQ of the required charge, and the charging of the screen capacitor is completed;
(34) as shown in FIG. 10, when the charge in the panel capacitor reaches the required value nQ, i.e. the voltage V2 of the panel capacitor and the reference voltage V1When the voltage is basically equal to each other, the switches P3 and P1 are closed, the switches P2 and P4 are opened, the switch Ca _ rst is opened, the starting circuit is opened, and the touch screen starts to work.
(4) And after the charging is completed, starting the touch screen.
The invention controls the switch to be turned off and on through the digital control signal, and adjusts the capacitor C inside for multiple timesbCharging and transferring charge to the screen capacitor CsAfter the charges are conveyed, the charges reach the required potential, the charges are connected into the charge amplifier, the charge amplifier is connected into the feedback capacitor, the circuit is started successfully, and finally when the touch screen is touched by fingers, the human body capacitor is connected with the screen body capacitor in parallel to change the size of the capacitor, and then the charge change quantity can be accurately amplified through the amplifier.
It will be apparent to those skilled in the art that various modifications and variations can be made in the embodiments of the present invention without departing from the spirit or scope of the embodiments of the invention. Thus, if such modifications and variations of the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to encompass such modifications and variations.
Claims (7)
1. A charging circuit based on a self-capacitance touch screen is characterized in that the charging circuit is connected with one end of a screen body capacitor, the other end of the screen body capacitor is grounded, the charging circuit comprises a charge amplifier, a switch P1-3, a switch P2-2, an internal adjusting capacitor and a switch P4, the charge amplifier comprises an input end A, an input end B and an output end, the input end A of the charge amplifier is connected with a feedback capacitor, two ends of the feedback capacitor are connected with a switch Ca _ rst in parallel, the input end A of the charge amplifier is connected with one end of the screen body capacitor after sequentially passing through a switch P3 and a switch P1-1, a circuit between the switch P3 and the switch P1-1 is provided with the switch P1-2 and the switch P2-1, the switch P2-1 is connected with the input end B correspondingly, one end of the switch P1-3 is connected with the input end B, and the other end of the, the other end of the internal adjusting capacitor is grounded, two ends of the internal adjusting capacitor are respectively connected to a line between a switch P1-2 and a switch P2-1 and a line between a switch P1-3 and a switch P2-2, one end of the switch P4 is connected to a line between the screen capacitor and the switch P1-1, and the other end of the switch P4 is grounded.
2. The self-capacitance touch screen-based charging circuit according to claim 1, wherein the B input end inputs a reference voltage V1。
3. The self-capacitance touch screen-based charging circuit according to claim 2, wherein the switch P1-1, the switch P1-2 and the switch P1-3 are all controlled by a first signal, the switch P1-2 and the switch P2-1 are all controlled by a second signal, and the first signal and the second signal are absolutely opposite.
4. An analog receiving circuit, comprising the self-capacitance touch screen based charging circuit, the filter and the analog-digital converter of any one of claims 1-3, wherein the output terminal of the charging circuit is connected to the input terminal of the filter, and the output terminal of the filter is connected to the input terminal of the analog-digital converter.
5. A charging method implemented by the charging circuit based on the self-capacitance touch screen according to claim 2 or 3, characterized by comprising the following steps:
(1) determining the capacitance of the screen body and the capacitance of the internal adjusting capacitor;
(2) determining the time T for charging the internal adjusting capacitor once to reach the required charging voltage, the time T for transferring the charge of the internal adjusting capacitor to the screen body capacitor once, and the times n for charging and charge transfer;
(3) setting a square wave with a period of (T + T) and a duration of n x (T + T) for controlling a corresponding switch to charge a screen capacitor so that the internal charge of the screen capacitor is filled to a required value;
(4) and after the charging is completed, starting the touch screen.
6. The charging method according to claim 5, wherein in the step (3), the step of charging the screen capacitor to fill the internal charge of the screen capacitor to a desired value specifically comprises:
(31) closing the switch P2-1, opening the switch P2-2, the switch P4, the switch Ca _ rst, the switch P1-1, the switch P1-2, the switch P1-3 and the switch P3, charging the internal adjusting capacitor, and enabling the potential of the internal adjusting capacitor to reach the reference voltage V1The charge on the internal adjusting capacitor is Q;
(32) switch P1-1, switch P1-2, switch P1-3 are closed, switch P2-1, switch P2-2, switch P3 and switch P4 are opened, switch Ca _ rst is closed, the screen capacitor is connected with the internal adjusting capacitor, the lower plate of the internal adjusting capacitor is connected with a reference voltage V1Starting to transfer charges to the screen capacitor until the charges of the screen capacitor are the same as the charges Q of the internal adjusting capacitor in the step (31);
(33) repeating the steps (31) and (32) until the charge on the capacitance charge of the screen body reaches the value nQ of the required charge, and finishing charging the capacitance of the screen body;
(34) when the electric charge in the screen body capacitor reaches the required value nQ, namely the voltage V2 of the screen body capacitor is basically equal to the reference voltage V1, the switch P3, the switch P1-1, the switch P1-2 and the switch P1-3 are closed, the switch P2-1, the switch P2-2 and the switch P4 are opened, the switch Ca _ rst is opened, the circuit is opened, and the touch screen starts to work.
7. The charging method according to claim 6, wherein the number of times n that the charging and the charge transfer are required is calculated by:
the internal tuning capacitor is charged once according to the formula Q ═ C × U, and the resulting charge Q ═ C is generatedb*V1The voltage of the screen capacitor can be obtained by transferring the charge Q into the screen capacitor
Finally, the voltage of the screen capacitor is made to be equal to the reference voltage V1Are substantially equal, then obtain
n is Cs/CbRounding up the value, where CsIs the capacitance value of the screen body capacitance, CbThe capacitance value of the capacitor is adjusted for the inside.
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| CN202010963940.6A CN112332828A (en) | 2020-09-15 | 2020-09-15 | Charging circuit, analog receiving circuit and charging method based on self-capacitance touch screen |
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| CN202010963940.6A CN112332828A (en) | 2020-09-15 | 2020-09-15 | Charging circuit, analog receiving circuit and charging method based on self-capacitance touch screen |
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