High-speed driving shield circuit for touch and method thereof

Abstract

The application discloses a high-speed driving shielding circuit for touch and a method thereof, which comprises a basic follow-up circuit, a negative feedback branch, a charging follow-up unit and a migration follow-up unit. The basic follow-up circuit comprises a two-stage amplifier and a load capacitor, an input is followed by a signal, and an output drives a shielding signal. The negative feedback branch comprises a first switch and a negative feedback capacitor. The charging follow-up unit comprises a second switch and a power supply. The load capacitor is electrically connected to the power supply through the second switch, and the second switch is controlled by a charging migration control signal. The migration follow-up unit comprises a monitoring unit and a logic control unit which are connected in sequence. The input end of the monitoring unit is electrically connected to the followed signal and the driving shielding signal. The output end of the logic control unit is electrically connected to the first switch, and the logic control unit is controlled by the charging migration control signal. The application solves the problem of slow voltage follow-up speed of the driving shielding circuit, can realize fast and accurate follow-up effect, fully improves the charge migration signal-to-noise ratio, and improves the touch detection sensitivity.

Description

Technical Field

[0001] This invention belongs to the field of hybrid integrated circuit design, specifically relating to a high-speed driving shielding circuit and method for touch. Background Technology

[0002] Charge migration touch button detection typically utilizes the additional parasitic capacitance generated by a human finger to determine if a button has been pressed. However, PCB trace capacitance and the inherent parasitic capacitance of the button significantly affect the sensitivity of the touch button. Existing solutions involve touch buttons with driver shielding, but as the number of buttons increases, the processing time of a single button becomes shorter, PCB layouts become more compact, and the mutual capacitance between buttons and the button's own capacitance increases. This means that the load on the driver shielding unit becomes increasingly larger, and the required load-carrying capacity and response speed of the driver also increase, posing a significant challenge to the design of the driver shielding unit.

[0003] The working principle of existing touch driver shielding technology is as follows: Figure 1 As shown, taking three buttons as an example, the inherent capacitances of buttons 1, 2, and 3 are C1, C2, and C3 respectively. The mutual capacitances between the buttons are C12, C13, and C23, and the external capacitor is Cx. Typically, Cx is much larger than C1, and C12, C13, and C23 are also much larger than C1. Assuming the drive shielding unit is perfectly ideal, V1 and V3 follow V2, i.e., Vy follows Vx. When button 2 is not pressed, SWA2 is connected to the power supply VDD to charge C2. SWA1 and SWA3 are disconnected, the drive shielding switch SWB2 is disconnected, and SWB1 and SWB3 are turned on. The switches SWC1, SWC2, and SWC3 connected to the external capacitor Cx are disconnected. Due to the ideal drive shielding unit, both C1 and C3 are charged to VDD. Then, SWA2 is disconnected, SWC2 is turned on, and button 2 shares charge with the external capacitor Cx. After N such operations, the voltage at the external capacitor C2 is Vx1 = Vx1 is approximately equal to VDD is the power supply voltage. When button 2 is pressed, assuming the capacitance of the finger is Cf, similarly, after N times, Vx2 is approximately equal to... Signal-to-noise ratio (SNR) = However, in reality, the drive shielding unit is not perfectly ideal; the voltage following process of a traditional drive shielding circuit is as follows: Figure 2 When the driving shield is not ideal, that is, during the migration process, V1 and V3 cannot fully keep up with V2. After each charging and migration process, a difference voltage Vos will be generated between Vx and Vy. That is, C1 and C2 will participate in the charge sharing process. Considering the most extreme case, SNR = Based on the above analysis, the load capacity and speed of the driver unit will significantly affect the touch SNR.

[0004] Based on the characteristics of charge-transfer touch, the driving shielding unit does not need to make Vy follow Vx in real time, and the voltage characteristics of Vx over time are known, i.e. Figure 2 The waveform of Vx is divided into charging and migration processes. The drive shielding circuit usually plays a role in the migration process. Traditional drive shielding circuits are implemented by voltage followers, generally unity-gain negative feedback systems. Their characteristics are high tracking accuracy; under sufficient tracking time, the input-output difference can be ignored. However, their disadvantage is that the response speed is very slow. Figure 3 This is a schematic diagram of the time-domain response of a traditional drive shielding circuit with negative feedback. Compared to the response curve of positive feedback, the response speed of negative feedback is slower and the response time is longer. Negative feedback can be approximated as... Positive feedback can be approximated as Where t is time and Vout is the output voltage. Positive feedback is typically used in oscillator or latch designs and cannot be used as a voltage follower, so traditional solutions use negative feedback to achieve voltage following. Furthermore, the settling time is proportional to its unity-gain bandwidth (GBW). Traditional driver shielding circuits use a two-stage amplifier; assuming the op-amp load is CL and the negative feedback capacitor is Cc... For the first stage transconductance of the amplifier, The second stage transconductance of the amplifier has a unity-gain bandwidth of GBW. , The time constant is used to ensure the small-signal stability of the driving shielding circuit. Much larger This requires sacrificing a significant amount of hardware current consumption.

[0005] In summary, traditional touch button driver shielding circuits suffer from problems such as slow voltage following speed, long response time, and unsatisfactory following effect. Summary of the Invention

[0006] Purpose of the invention: In order to solve the problem of slow following speed in the driving shielding circuit for touch in the prior art, the present invention provides a high-speed driving shielding circuit and method for touch.

[0007] Technical solution: A high-speed driving shielding circuit for touch, comprising:

[0008] The basic follower circuit includes two stages of amplifiers and a load capacitor. The signal to be followed is input from the input terminals of the two stages of amplifiers. The output terminals of the two stages of amplifiers are electrically connected to the load capacitor and output a drive shield signal.

[0009] The negative feedback branch includes a first switch and a negative feedback capacitor, with the first switch and the negative feedback capacitor connected in series; one end of the negative feedback branch is electrically connected to the intermediate node of the two-stage amplifier, and the other end is electrically connected to the drive shield signal.

[0010] The charging follower unit includes a second switch and a power supply. The load capacitor is electrically connected to the power supply through the second switch, and the second switch is controlled by a charging migration control signal.

[0011] The migration follower unit includes a monitoring unit and a logic control unit connected in sequence. The input terminal of the monitoring unit is electrically connected to the followed signal and the drive shielding signal. The logic control unit is electrically connected to the first switch and is controlled by the charging migration control signal.

[0012] Furthermore, when the charging migration control signal is the first control signal, the second switch is turned on and the monitoring unit is in a reset state; when the charging migration control signal is the second control signal, the second switch is turned off and the monitoring unit switches to the working state.

[0013] Furthermore, when the driving shielding signal is greater than the followed signal, the monitoring unit outputs the first state signal, the logic control unit outputs the first signal, and the first switch is turned off; when the driving shielding signal is less than the followed signal, the monitoring unit outputs the second state signal, the logic control unit outputs the second signal, and the first switch is turned on.

[0014] Furthermore, in the migration following unit, the monitoring unit includes a comparator, the logic control unit includes a flip-flop, the first input terminal of the comparator is electrically connected to the followed signal, the second input terminal of the comparator is electrically connected to the drive shielding signal, the output terminal of the comparator is electrically connected to the input terminal of the flip-flop, the output terminal of the flip-flop is electrically connected to the first switch, and the enable terminal of the flip-flop is controlled by the charging migration control signal.

[0015] Furthermore, the comparator is a comparator with a fixed offset.

[0016] Furthermore, the offset value of the comparator is Where VDD is the power supply voltage, td is the response time of the monitoring unit, and τ is the time constant. Let the voltage of the followed signal be Vx and the voltage of the driving shield signal be Vy. When Vy < Vx + Vos, the comparator output flips.

[0017] Furthermore, the trigger is a D trigger or an RS trigger.

[0018] A high-speed drive shielding method for touch, employing the aforementioned high-speed drive shielding circuit for touch, includes the following steps:

[0019] During the charging phase, the charging migration control signal is set to the first control signal, the second switch is turned on, and the power supply charges the load capacitor; the logic control unit is in a reset state; and the first switch is turned off.

[0020] During the migration phase, the charging migration control signal is set to the second control signal, and the second switch is turned off; the logic control unit is in the working state, the monitoring unit outputs the first state signal, the logic control unit outputs the first signal, the first switch remains in the off state, and the basic follower circuit operates in the positive feedback mode; the drive shielding signal continuously decreases until the output of the monitoring unit flips and outputs the second state signal, the logic control unit outputs the second signal, the first switch switches to the on state, and the basic follower circuit operates in the negative feedback mode.

[0021] Repeated cycle of charging migration operation.

[0022] Furthermore, when the voltage of the driving shield signal is less than the voltage of the followed signal, the output of the monitoring unit flips.

[0023] Furthermore, let the voltage of the followed signal be Vx, and the voltage of the driving shield signal be Vy. When Vy < Vx + Vos, the output of the monitoring unit flips, where Vos is the offset value of the comparator. Where VDD is the power supply voltage, td is the response time of the monitoring unit, and τ is the time constant.

[0024] Compared with the prior art, the high-speed driving shielding circuit and method for touch provided by the present invention have the following beneficial effects:

[0025] By fully utilizing the characteristics of the voltage being followed during charge migration on touch buttons and the relationship between the driving shielding signal and the voltage being followed, the driving shielding circuit in the charge migration process has been improved and the circuit structure optimized. The entire following process is divided into two stages, which can improve the response speed and ensure the following accuracy without consuming too much hardware current. This significantly improves the charge migration signal-to-noise ratio and enhances the detection sensitivity of touch buttons. In particular, it can meet the requirements of the increasing number of buttons, the reduction of processing time for a single button, and the more compact PCB layout. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the working principle of the driver shielding used for touch.

[0027] Figure 2 This is a schematic diagram of the voltage follower of the driving shielding circuit in the prior art;

[0028] Figure 3 This is a schematic diagram illustrating the time-domain establishment of negative and positive feedback;

[0029] Figure 4 This is a schematic diagram of the drive shielding circuit in Embodiment 1;

[0030] Figure 5 This is a voltage follower schematic diagram of the drive shielding circuit in Embodiment 1;

[0031] Figure 6 This is a schematic diagram of voltage overshoot in the drive shielding circuit of Embodiment 1;

[0032] Figure 7 This is a schematic diagram of the drive shielding circuit in Embodiment 2;

[0033] Figure 8 This is a schematic diagram of the voltage overshoot of the drive shielding circuit in Embodiment 2;

[0034] In the diagram, VDD is the power supply voltage; C1, C2, and C3 are the inherent capacitances of buttons 1, 2, and 3, respectively; C12, C13, and C23 are the mutual capacitances of buttons 1 and 2, buttons 1 and 3, and buttons 2 and 3, respectively; Cx is the external capacitor; Cf is the finger capacitance; CL is the load capacitance; Cc is the negative feedback capacitor; SW1 is the first switch; SW2 is the second switch; Vx is the followed signal; Vy is the drive shield signal; SWA1, SWA2, and SWA3 are the charging switches of buttons 1, 2, and 3, respectively; SWB1, SWB2, and SWB3 are the drive switches of buttons 1, 2, and 3, respectively; and SWC1, SWC2, and SWC3 are the charge transfer switches of buttons 1, 2, and 3, respectively. Detailed Implementation

[0035] The present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments.

[0036] Example 1:

[0037] A high-speed drive shielding circuit for touch, such as Figure 4 As shown, it includes:

[0038] The basic follower circuit includes two-stage amplifiers gm1 and gm2 and a load capacitor CL. The signal to be followed, Cx, is input from the input terminals of the two-stage amplifiers. The output terminals of the two-stage amplifiers are electrically connected to the load capacitor CL and output a drive shield signal Cy.

[0039] The negative feedback branch includes a first switch SW1 and a negative feedback capacitor Cc, with the first switch SW1 and the negative feedback capacitor Cc connected in series; one end of the negative feedback branch is electrically connected to the intermediate node Vo1 of the two-stage amplifier, and the other end is electrically connected to the drive shielding signal Vy.

[0040] The charging follower unit includes a second switch SW2 and a power supply VDD. The load capacitor CL is electrically connected to the power supply through the second switch SW2. The second switch SW2 is controlled by a charging migration control signal.

[0041] The migration follower unit includes a monitoring unit and a logic control unit connected in sequence. The input terminal of the monitoring unit is electrically connected to the followed signal Vx and the drive shielding signal Vy. The output terminal of the logic control unit is electrically connected to the first switch SW1. Whether the logic control unit works is controlled by the charging migration control signal.

[0042] When the charging migration control signal is the first control signal (i.e., indicating that the current stage is charging), the second switch SW2 is turned on, and the logic control unit is in the reset state; when the charging migration control signal is the second control signal (i.e., indicating that the current stage is migration), the second switch SW2 is turned off, and the logic control unit switches to the working state.

[0043] During the migration phase, the logic control unit outputs corresponding signals to control the on / off state of the first switch based on the output of the monitoring unit. When the drive shielding signal Vy is greater than the followed signal Vx, the monitoring unit outputs a first status signal, the logic control unit outputs a first signal, and the first switch SW1 is turned off; when the drive shielding signal Vy is less than the followed signal Vx, the monitoring unit outputs a second status signal, the logic control unit outputs a second signal, and the first switch SW1 is turned on.

[0044] In one specific implementation, the monitoring unit includes a comparator, and the logic control unit includes a flip-flop. The first input of the comparator is electrically connected to a followed signal Vx, the second input of the comparator is electrically connected to a drive shield signal Vy, the output of the comparator is electrically connected to the input CLK of the flip-flop, the output of the flip-flop is electrically connected to a first switch SW1, and the enable terminal RB of the flip-flop is controlled by a charge migration control signal. Alternatively, other specific circuit structures can be used to implement this.

[0045] The trigger may be a D trigger, such as... Figure 4 As shown, an RS flip-flop can also be used, as can other devices with the same function. The main purpose is to output different signals according to the output of the comparator. When the comparator output flips, the flip-flop output will also reverse, thereby realizing the control of the first switch SW1.

[0046] A high-speed drive shielding method for touch, employing the aforementioned high-speed drive shielding circuit for touch, includes the following steps:

[0047] During the charging phase, the charging migration control signal is set to the first control signal, the second switch SW2 is turned on, and the power supply VDD charges the load capacitor CL; the logic control unit is in the reset state; and the first switch SW1 is turned off.

[0048] During the migration phase, the charging migration control signal is set to the second control signal, and the second switch SW2 is open; the logic control unit is in the working state, the monitoring unit outputs the first state signal, the logic control unit outputs the first signal, the first switch SW1 remains open, and the basic follower circuit operates in positive feedback mode; the drive shielding signal Vy continuously decreases until the output of the monitoring unit flips and outputs the second state signal, the logic control unit outputs the second signal, the first switch SW1 switches to the conducting state, and the basic follower circuit operates in negative feedback mode.

[0049] Repeated cyclical charging migration operations, the charging migration process is as follows: Figure 5 As shown.

[0050] The overall working process of this embodiment is as follows: During the charging stage, the charge migration control signal is set to a high level (it can be set to a high level or a low level according to actual needs). An inverter is set as needed. As shown in the figure, the second switch SW2 is closed under the action of the inverter. At this time, the power supply VDD charges the load capacitor CL through the second switch SW2. At this time, the D flip-flop is in the reset state, and the output terminal QN of the D flip-flop is at a high level. The first switch SW1 is open. After the charging is completed, the charge migration stage begins. At this time, the charge migration control signal is switched to a low level. As shown in the figure, the second switch SW2 is opened under the action of the inverter. The first switch SW1 remains open. At this time, the closed-loop follower unit composed of the two-stage amplifier of the basic follower circuit is in an unstable state, that is, the positive feedback mode. Vy will rapidly change to Vx. This stage is the positive feedback stage. Once Vy is lower than Vx, the comparator output flips, the output QN of the D flip-flop changes from high to low, controls the first switch SW1 to close, drives the shielding circuit to switch to the negative feedback mode, and tends to a stable state. Vy gradually approaches Vx. However, in reality, since the monitoring unit's response time is td, a certain delay time td is required. During this time, Vy will continue to decrease, resulting in a downward overshoot. The overshoot voltage can be approximated as... After the time limit (td), the driver will switch to negative feedback mode only after the time limit has elapsed, thus affecting the tracking speed. For example... Figure 6 The diagram shown is a schematic of voltage overshoot in the drive shielding circuit in this embodiment.

[0051] Traditional drive shielding processes operate only in negative feedback mode. Limited by GBW (Gross Voltage Regulator), the output Vy slowly follows Vx, resulting in a long follow-up time and slow speed. In this embodiment, during charging, the second switch SW2 forces Vy to follow Vx. During the charge transfer process, a comparator monitors and a D flip-flop controls the charge transfer process in the drive shielding, dividing it into positive and negative feedback components. Positive feedback offers the advantage of fast following, but its disadvantage is instability and inability to accurately track the input and output voltages. Once the comparator detects that Vy is lower than Vx, the D flip-flop immediately generates a control signal, switching the drive shielding to negative feedback mode for accurate following. This significantly reduces the overall following time, even under heavy loads, enabling accurate following in a short time, fully utilizing the drive shielding circuit, and improving the charge transfer signal-to-noise ratio.

[0052] Example 2:

[0053] The difference between Example 2 and Example 1 is that the comparator in Example 2 is a comparator with a fixed offset, for example, a fixed offset value Vos at the first input terminal of the comparator (the input signal being followed). Figure 7 As shown. The comparator's offset value is... Where VDD is the power supply voltage, td is the response time of the monitoring unit, and τ is the time constant. Let the voltage of the followed signal be Vx, and the voltage of the driving shield signal be Vy. When Vy < Vx + Vos, the comparator output flips. Theoretically, a fixed offset value -Vos can also be added to the second input of the comparator.

[0054] like Figure 8 This is a schematic diagram illustrating voltage overshoot in the drive shielding circuit of this embodiment. When Vy approaches Vx with a phase difference of approximately Vos, the comparator begins to respond. After time td, the system completes the switch from positive feedback mode to negative feedback mode. Figure 8 and Figure 6 As can be seen from the comparison, the drive shielding circuit in this embodiment will enter the negative feedback mode earlier, so that Vy can follow Vx faster, thereby shortening the overall following time.

[0055] This embodiment addresses the characteristics of the followed voltage Vx in the driver shielding circuit of a touch application and the relationship between Vy and Vx. Specifically, Vx needs to be charged before decreasing from high to low, and Vx must decrease before Vy before Vy gradually decreases to intersect with Vx. A special comparator with fixed offset is specifically selected, which, compared to Embodiment 1, allows the circuit to switch to the negative feedback state earlier, thereby achieving Vy to Vx tracking more quickly. This is more conducive to solving the problems of slow tracking speed and low efficiency, significantly improving the charge transfer signal-to-noise ratio, and enhancing the detection sensitivity of touch buttons.

Claims

1. A high-speed drive shielding circuit for touch, characterized in that, include: The basic follower circuit includes two stages of amplifiers and a load capacitor. The signal to be followed is input from the input terminals of the two stages of amplifiers. The output terminals of the two stages of amplifiers are electrically connected to the load capacitor and output a drive shield signal. The negative feedback branch includes a first switch and a negative feedback capacitor, with the first switch and the negative feedback capacitor connected in series; one end of the negative feedback branch is electrically connected to the intermediate node of the two-stage amplifier, and the other end is electrically connected to the drive shield signal. The charging follower unit includes a second switch and a power supply. The load capacitor is electrically connected to the power supply through the second switch, and the second switch is controlled by a charging migration control signal. The migration follower unit includes a monitoring unit and a logic control unit connected in sequence. The input terminal of the monitoring unit is electrically connected to the followed signal and the drive shielding signal. The logic control unit is electrically connected to the first switch and is controlled by the charging migration control signal.

2. The high-speed drive shielding circuit for touch according to claim 1, characterized in that, When the charging migration control signal is the first control signal, the second switch is turned on and the monitoring unit is in a reset state; when the charging migration control signal is the second control signal, the second switch is turned off and the monitoring unit switches to the working state.

3. The high-speed drive shielding circuit for touch according to claim 1 or 2, characterized in that, When the drive shielding signal is greater than the followed signal, the monitoring unit outputs a first status signal, the logic control unit outputs a first signal, and the first switch is turned off; when the drive shielding signal is less than the followed signal, the monitoring unit outputs a second status signal, the logic control unit outputs a second signal, and the first switch is turned on.

4. The high-speed drive shielding circuit for touch according to claim 1 or 2, characterized in that, In the migration following unit, the monitoring unit includes a comparator, the logic control unit includes a flip-flop, the first input terminal of the comparator is electrically connected to the followed signal, the second input terminal of the comparator is electrically connected to the drive shield signal, the output terminal of the comparator is electrically connected to the input terminal of the flip-flop, the output terminal of the flip-flop is electrically connected to the first switch, and the enable terminal of the flip-flop is controlled by the charging migration control signal.

5. The high-speed drive shielding circuit for touch according to claim 4, characterized in that, The comparator is a comparator with a fixed offset.

6. The high-speed drive shielding circuit for touch according to claim 5, characterized in that, The offset value of the comparator is Where VDD is the power supply voltage, td is the response time of the monitoring unit, and τ is the time constant. Let the voltage of the followed signal be Vx and the voltage of the driving shield signal be Vy. When Vy < Vx + Vos, the comparator output flips.

7. The high-speed drive shielding circuit for touch according to claim 4, characterized in that, The trigger is a D trigger or an RS trigger.

8. A high-speed drive shielding method for touch, employing the high-speed drive shielding circuit for touch as described in any one of claims 1-7, characterized in that, Includes the following steps: During the charging phase, the charging migration control signal is set to the first control signal, the second switch is turned on, and the power supply charges the load capacitor; the logic control unit is in a reset state; and the first switch is turned off. During the migration phase, the charging migration control signal is set to the second control signal, and the second switch is turned off; When the logic control unit is in operation, the monitoring unit outputs a first status signal, the logic control unit outputs a first signal, the first switch remains open, and the basic follower circuit operates in positive feedback mode. The drive shielding signal continuously decreases until the output of the monitoring unit flips and outputs a second status signal. The logic control unit outputs a second signal, the first switch switches to the on state, and the basic follower circuit operates in negative feedback mode. Repeated cycle of charging migration operation.

9. The high-speed drive shielding method for touch according to claim 8, characterized in that, When the voltage of the drive shielding signal is less than the voltage of the followed signal, the output of the monitoring unit flips.

10. The high-speed drive shielding method for touch according to claim 8, characterized in that, Let the voltage of the followed signal be Vx, and the voltage of the driving shield signal be Vy. When Vy < Vx + Vos, the output of the monitoring unit flips, where Vos is the offset value of the comparator. Where VDD is the power supply voltage, td is the response time of the monitoring unit, and τ is the time constant.

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