A touch screen channel-based charge compensation circuit and method

Abstract

The application belongs to the technical field of integrated circuit touch screen control, and discloses a charge compensation circuit and method based on a touch screen channel. The charge compensation circuit comprises a clamping operational amplifier module, a charge compensation module and a charge transmission module. The clamping operational amplifier module is used for clamping the voltage of a compensation node to a reference voltage. The charge compensation module comprises a first charge compensation unit and a second charge compensation unit. The first charge compensation unit and the second charge compensation unit are respectively responsible for charge compensation in different directions, and generate compensation charges through a switched capacitor method. The charge transmission module is connected with the first charge compensation unit and the second charge compensation unit. Compared with a traditional current compensation method, the application generates compensation charges in a capacitor voltage mode, does not depend on multi-stage replication of a current mirror, thereby significantly reducing the mismatch degree of charge compensation between different touch screen channels, and improving the uniformity of compensation precision.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit touch screen control technology, and in particular to a charge compensation circuit and method based on touch screen channels. Background Technology

[0002] In capacitive touchscreen systems, the touch channel operates in mutual capacitance sensing or self-capacitance sensing mode for touch detection. During sensing, a significant amount of charge enters the sensor module. The base capacitance of the touch electrodes is typically large, resulting in a base charge that is far greater than the charge change during a touch. If the sensor module directly quantizes all the charge, it would reduce the measurement sensitivity and resolution.

[0003] To prevent the sensor module from carrying a large charge for quantization, charge compensation is typically required. Existing charge compensators in the industry usually employ current compensation, generating a compensation charge I0×t0 by charging or discharging a reference channel for a time t0. This compensation current is then transferred to each touchscreen channel via a current mirror circuit for sensor compensation.

[0004] However, existing current compensation methods suffer from current mismatch. During the multiple mirroring transfers of the compensation current to various touchscreen channels, the current mirroring circuit cannot achieve perfectly accurate current replication due to non-ideal factors such as process variations in MOS transistors and channel length modulation effects. This current mismatch accumulates at each stage, leading to significant differences in the compensation current between different touchscreen channels, affecting the uniformity and accuracy of touch detection.

[0005] Furthermore, existing current compensation methods introduce significant current thermal noise. The compensation current generates thermal noise as it flows through the MOS transistor, and this noise power is proportional to the current magnitude. To achieve sufficient charge compensation in a short time, the compensation current typically needs to be set relatively large, which significantly increases the power of the thermal noise, reduces the system's signal-to-noise ratio, and greatly impacts the sensor's operation.

[0006] Furthermore, existing current compensation methods struggle to balance compensation range and accuracy. Achieving a wide compensation range requires a larger compensation current, but this leads to more severe mismatch and noise issues. Conversely, improving compensation accuracy necessitates reducing the compensation current or extending the compensation time, which in turn limits the compensation range or slows down the system response. Summary of the Invention

[0007] The purpose of this invention is to provide a charge compensation circuit and method based on a touch screen channel, which solves the technical problems of current mismatch, compensation range and accuracy that exist in existing current compensation methods.

[0008] To address the aforementioned technical problems, in one aspect, the present invention provides a charge compensation circuit based on a touchscreen channel, comprising:

[0009] The clamping operational amplifier module is used to clamp the voltage of the compensation node to the reference voltage;

[0010] The charge compensation module includes a first charge compensation unit and a second charge compensation unit;

[0011] The first charge compensation unit is connected between the first voltage and the second voltage, and is connected to the clamping operational amplifier module, and is used to generate a first compensation charge after the touch screen channel voltage changes in the direction of the first voltage.

[0012] The second charge compensation unit is connected between the second voltage and the third voltage and is connected to the clamping operational amplifier module, and is used to generate a second compensation charge after the touch screen channel voltage changes in the direction of the third voltage.

[0013] A charge transfer module is connected to the first charge compensation unit and the second charge compensation unit respectively, and is used to output the first compensation charge or the second compensation charge to the touch screen channel at a preset multiple.

[0014] The first charge compensation unit and the second charge compensation unit generate compensation charge by switching capacitors.

[0015] Furthermore, the first charge compensation unit includes a first compensation capacitor, a first switch, a second switch, a first current limiting resistor, a first PMOS transistor, and a second PMOS transistor;

[0016] The first compensation capacitor and the first switch are connected in parallel. One end of the first compensation capacitor and the first switch are both connected to the first voltage, and the other end of each is connected to the drain of the first PMOS transistor through the second switch and the first current limiting resistor.

[0017] The source of the first PMOS transistor is connected to the drain of the second PMOS transistor, and the gate is connected to the first bias voltage signal.

[0018] The gate of the second PMOS transistor is connected to the second bias voltage signal and is also connected to the clamping operational amplifier module, while the source is connected to the second voltage.

[0019] Furthermore, the second charge compensation unit includes a second compensation capacitor, a third switch, a fourth switch, a second current-limiting resistor, a first NMOS transistor, and a second NMOS transistor;

[0020] The second compensation capacitor and the third switch are connected in parallel. One end of the second compensation capacitor and the third switch are both connected to the second voltage, and the other end of both are connected to the drain of the first NMOS transistor through the fourth switch and the second current limiting resistor.

[0021] The source of the first NMOS transistor is connected to the drain of the second NMOS transistor, and the gate is connected to the third bias voltage signal;

[0022] The gate of the second NMOS transistor is connected to the fourth bias voltage signal and is also connected to the clamping operational amplifier module, while the source is connected to the third voltage.

[0023] Furthermore, the charge transfer module adopts a current mirror structure, including a first receiving unit;

[0024] The first receiving unit includes a third PMOS transistor, a fourth PMOS transistor, and a fifth switch;

[0025] The gate of the third PMOS transistor is connected to the first bias voltage signal to form the first mirror control node of the current mirror, and the drain is connected to the touch screen channel through the fifth switch to form the first output branch of the current mirror.

[0026] The gate of the fourth PMOS transistor is connected to the second bias voltage signal, forming the second mirror control node of the current mirror. The drain is connected to the source of the third PMOS transistor, and the source is connected to the second voltage.

[0027] Furthermore, the charge transfer module also includes a second receiving unit;

[0028] The second receiving unit includes a third NMOS transistor, a fourth NMOS transistor, and a sixth switch;

[0029] The gate of the third NMOS transistor is connected to the third bias voltage signal to form the third mirror control node of the current mirror, and the drain is connected to the touch screen channel through the sixth switch to form the second output branch of the current mirror.

[0030] The gate of the fourth NMOS transistor is connected to the fourth bias voltage signal, forming the fourth mirror control node of the current mirror. The drain is connected to the source of the third NMOS transistor, and the source is connected to the third voltage.

[0031] Furthermore, the clamping operational amplifier module includes a first clamping operational amplifier and a second clamping operational amplifier;

[0032] The non-inverting input terminal of the first clamping operational amplifier is connected to the drain of the first PMOS transistor, the inverting input terminal is connected to the reference voltage, and the output terminal is connected to the gate of the second PMOS transistor.

[0033] The non-inverting input of the second clamping operational amplifier is connected to the drain of the first NMOS transistor, the inverting input is connected to the reference voltage, and the output is connected to the gate of the second NMOS transistor.

[0034] Furthermore, the internal structure of the first clamping operational amplifier and the second clamping operational amplifier adopts the ClassAB architecture.

[0035] On the other hand, the present invention provides a charge compensation method based on a touch screen channel, comprising the following steps:

[0036] The voltage of the compensation node is clamped to the reference voltage by the clamping operational amplifier module;

[0037] The direction of charge compensation is determined based on the voltage change state of the touch screen channel under the action of the working clock.

[0038] Select the appropriate charge compensation unit for charge compensation based on the charge compensation direction;

[0039] The compensation charge is output to the touch screen channel through the charge transfer module at an adjustable transfer ratio, so that the amount of compensation charge output to the touch screen channel compensates the voltage of the touch screen channel to the target voltage range.

[0040] Furthermore, determining the direction of charge compensation based on the voltage change state of the touchscreen channel under the operation of the clock includes:

[0041] When the touch screen channel voltage switches to the first voltage direction, a compensation charge in the first direction is generated through the first charge compensation unit;

[0042] When the touchscreen channel voltage switches to the third voltage direction, a compensation charge in the second direction is generated through the second charge compensation unit.

[0043] Furthermore, when the touchscreen channel voltage switches to the first voltage direction, the first charge compensation unit generates a compensation charge in the first direction, specifically including:

[0044] Before the touch screen channel voltage switches to the first voltage direction, the two ends of the first compensation capacitor are connected to the same first voltage through the control switch group in the first charge compensation unit, so that the first compensation capacitor is in a charge balance state.

[0045] When the working clock triggers the touch screen channel voltage to switch to the first voltage direction, the connection state of the control switch group is changed so that one end of the first compensation capacitor is kept at the first voltage and the other end is connected to the first compensation node through the current limiting resistor.

[0046] Under the action of the clamping operational amplifier module, the voltage of the first compensation node changes from the first voltage to the reference voltage within a set time, and a first voltage change is generated on the first compensation capacitor. The first voltage change is equal to the difference between the first voltage and the reference voltage.

[0047] The first compensation charge generated on the first compensation capacitor is equal to the product of the value of the first compensation capacitor and the first voltage change.

[0048] Compared with the prior art, the present invention has at least the following beneficial effects:

[0049] This invention generates compensation charge using a capacitor voltage method. A first compensation charge and a second compensation charge are generated by a first charge compensation unit and a second charge compensation unit, respectively. The amount of compensation charge is determined by the product of the compensation capacitor value and the voltage change. Compared to traditional current compensation methods, the capacitor voltage method does not rely on multi-stage replication of current mirrors. The matching accuracy of the capacitor is much higher than that of the current mirror, thus significantly reducing the mismatch between different touchscreen channels and improving the uniformity of compensation accuracy. Simultaneously, the capacitor voltage method primarily achieves charge transfer through the charging and discharging of the capacitor, eliminating the need for continuous high current flow, significantly reducing the impact of current thermal noise, and improving the signal-to-noise ratio. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of a charge compensation circuit in one embodiment of the present invention;

[0051] Figure 2 This is a schematic diagram of the ClassAB architecture in one embodiment of the present invention;

[0052] Figure 3 This is a schematic flowchart of a charge compensation method in one embodiment of the present invention;

[0053] Figure 4 This is a timing diagram of charge compensation in one embodiment of the present invention.

[0054] Reference numerals: C1, First compensation capacitor; C2, Second compensation capacitor; Rd1, First current-limiting resistor; Rd2, Second current-limiting resistor; S1, First switch; S2, Second switch; S3, Third switch; S4, Fourth switch; S5, Fifth switch; S6, Sixth switch; Q1, First PMOS transistor; Q2, Second PMOS transistor; Q3, First NMOS transistor; Q4, Second NMOS transistor; Q5, Third PMOS transistor; Q6, Fourth PMOS transistor; Q7, Third NMOS transistor; Q8, Fourth NMOS transistor; Op1, First clamping operational amplifier; Op2, Second clamping operational amplifier; VDD_CS, First voltage; VSSA, second voltage; VDDA, third voltage; VCM, reference voltage; VBNC_0, first bias voltage signal; VBN_0, second bias voltage signal; VBP, third bias voltage signal; VBPC, fourth bias voltage signal; Vcap1, first compensation node; Vcap2, second compensation node; ck_tx, operating clock; RX_up, pull-up control signal; RX_dn, pull-down control signal; sw_com_up, switch pull-up control signal; sw_com_dn, switch pull-down control signal; V_RX, touchscreen channel voltage; Tcom, compensation time. Detailed Implementation

[0055] Based on the teachings of this specification, those skilled in the art can form new technical solutions by combining different implementation methods without creating technical contradictions. Such variations should be considered to fall within the protection scope of this patent.

[0056] The present invention will now be described in more detail with reference to the schematic diagrams, which illustrate preferred embodiments of the invention. It should be understood that those skilled in the art can modify the invention described herein while still achieving its advantageous effects. Therefore, the following description should be understood as being of general knowledge to those skilled in the art and is not intended to limit the invention.

[0057] The invention is described more specifically by way of example in the following paragraphs with reference to the accompanying drawings. The advantages and features of the invention will become clearer from the following description. It should be noted that the drawings are in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0058] Example 1

[0059] like Figure 1 As shown, this embodiment of the invention proposes a charge compensation circuit based on a touch screen channel, including a clamping operational amplifier module, a charge compensation module, and a charge transfer module.

[0060] The clamping operational amplifier module is used to clamp the voltage of the compensation node to the reference voltage VCM. During the operation of the touch screen channel, the voltage of the compensation node will change due to the inflow or outflow of charge. The clamping operational amplifier module monitors the voltage of the compensation node in real time through a negative feedback control mechanism and stabilizes it at the reference voltage VCM level. This clamping effect provides a stable reference for subsequent charge compensation, making the generation of compensation charge deterministic and repeatable.

[0061] The charge compensation module includes a first charge compensation unit and a second charge compensation unit. The first charge compensation unit and the second charge compensation unit are responsible for charge compensation in different directions, enabling the circuit to cope with bidirectional changes in the touch screen channel voltage V_RX.

[0062] The first charge compensation unit is connected between the first voltage VDD_CS and the second voltage VSSA, and is also connected to the clamping operational amplifier module. It generates a first compensation charge after the touchscreen channel voltage V_RX changes towards the first voltage VDD_CS. The first voltage VDD_CS is the power supply voltage for the touchscreen channel, and the second voltage VSSA is typically analog ground. The connection between the first charge compensation unit and the clamping operational amplifier module enables precise control of the compensation charge amount, stabilizing the voltage difference across the compensation capacitor at a preset value, thereby generating a specific amount of compensation charge.

[0063] The second charge compensation unit is connected between the second voltage VSSA and the third voltage VDDA and is also connected to the clamping operational amplifier module. It generates a second compensation charge after the touchscreen channel voltage V_RX changes towards the third voltage VDDA. The third voltage VDDA is typically the power supply voltage. Through the coordinated operation of the first and second charge compensation units, the circuit can cope with various voltage changes in the touchscreen channel, achieving comprehensive charge compensation.

[0064] In this design, both the first and second charge compensation units generate compensation charge using a switched capacitor method. The switched capacitor method relies primarily on the charging and discharging of capacitors, eliminating the need for continuous high current flow, thus resulting in significantly lower thermal noise compared to the current source method. The amount of compensation charge in the switched capacitor method can be flexibly adjusted by changing the capacitance value or voltage variation, achieving both a wide compensation range and high compensation accuracy. The working principle of the switched capacitor method is simple and straightforward, resulting in a relatively simple circuit structure, reducing design complexity and chip area.

[0065] The charge transfer module is connected to both the first charge compensation unit and the second charge compensation unit, and is used to output the first or second compensation charge to the touch screen channel at a preset multiple. Since different touch screen channels may require different amounts of compensation charge, the charge transfer module uses a current mirror structure to replicate and scale the compensation charge. The preset multiple can be set according to actual needs, such as 1x, 2x, or 0.5x. The charge transfer module can also dynamically adjust the output amount of compensation charge according to the real-time operating status of the touch screen channel, improving the flexibility and adaptability of compensation.

[0066] In this embodiment, the first charge compensation unit includes a first compensation capacitor C1, a first switch S1, a second switch S2, a first current limiting resistor Rd1, a first PMOS transistor Q1, and a second PMOS transistor Q2.

[0067] The first compensation capacitor C1 and the first switch S1 are connected in parallel. One end of both the first compensation capacitor C1 and the first switch S1 is connected to the first voltage VDD_CS, and the other end is connected to the drain of the first PMOS transistor Q1 through the second switch S2 and the first current-limiting resistor Rd1. The source of the first PMOS transistor Q1 is connected to the drain of the second PMOS transistor Q2, and the gate is connected to the first bias voltage signal VBNC_0. The gate of the second PMOS transistor Q2 is connected to the second bias voltage signal VBN_0, and is also connected to the clamping operational amplifier module. The source is connected to the second voltage VSSA.

[0068] In this embodiment, the second charge compensation unit includes a second compensation capacitor C2, a third switch S3, a fourth switch S4, a second current limiting resistor Rd2, a first NMOS transistor Q3, and a second NMOS transistor Q4.

[0069] The second compensation capacitor C2 and the third switch S3 are connected in parallel. One end of both the second compensation capacitor C2 and the third switch S3 is connected to the second voltage VSSA, and the other end is connected to the drain of the first NMOS transistor Q3 through the fourth switch S4 and the second current-limiting resistor Rd2. The structure of the second charge compensation unit is similar to that of the first charge compensation unit, except that an NMOS transistor is used instead of a PMOS transistor to achieve reverse charge compensation. The third switch S3 is connected in parallel with the second compensation capacitor C2, which can short-circuit the two ends of the second compensation capacitor C2 to the second voltage VSSA, so that the second compensation capacitor C2 is in a charge balance state. The second current-limiting resistor Rd2 is used to limit the instantaneous current during the reverse charge transfer process. The source of the first NMOS transistor Q3 is connected to the drain of the second NMOS transistor Q4, and the gate is connected to the third bias voltage signal VBP. The gate of the second NMOS transistor Q4 is connected to the fourth bias voltage signal VBPC, and is also connected to the clamping operational amplifier module, and the source is connected to the third voltage VDDA.

[0070] In this embodiment, the charge transfer module employs a current mirror structure, including a first receiving unit. A current mirror is a commonly used current replication and scaling structure in analog integrated circuits, capable of replicating a reference current to one or more output branches at a specific ratio. By adjusting the size ratio of the transistors within the current mirror, different multiples of current replication can be achieved. Furthermore, the current mirror has high output impedance, providing a stable current output that is less susceptible to load variations.

[0071] Specifically, the first receiving unit includes a third PMOS transistor Q5, a fourth PMOS transistor Q6, and a fifth switch S5. The first receiving unit is responsible for outputting the compensation charge generated by the first charge compensation unit to the touch screen channel according to a preset ratio.

[0072] The gate of the third PMOS transistor Q5 is connected to the first bias voltage signal VBNC_0, forming the first mirror control node of the current mirror. Its drain is connected to the touchscreen channel via the fifth switch S5, forming the first output branch of the current mirror. The third PMOS transistor Q5 and the first PMOS transistor Q1 in the first charge compensation unit form a current mirror relationship. Both transistors have their gates connected to the first bias voltage signal VBNC_0, forming a common-gate structure. Since the gate voltages and source voltages of the first PMOS transistor Q1 and the third PMOS transistor Q5 are the same, accurate current replication can be achieved. When it is necessary to replenish charge to the touchscreen channel, the fifth switch S5 closes, and the compensation current flows into the touchscreen channel; when compensation is not needed, the fifth switch S5 opens.

[0073] The gate of the fourth PMOS transistor Q6 is connected to the second bias voltage signal VBN_0, forming the second mirror control node of the current mirror. Its drain is connected to the source of the third PMOS transistor Q5, and the source is connected to the second voltage VSSA. The fourth PMOS transistor Q6 and the second PMOS transistor Q2 in the first charge compensation unit form another set of current mirrors. The fourth PMOS transistor Q6 and the third PMOS transistor Q5 are cascaded together to form the complete current path of the first receiving unit. This dual-layer current mirror structure provides more precise current control and higher output impedance.

[0074] In this embodiment, the charge transfer module further includes a second receiving unit. The second receiving unit is structurally symmetrical to the first receiving unit and is responsible for outputting the compensation charge generated by the second charge compensation unit to the touch screen channel according to a preset ratio.

[0075] Specifically, the second receiving unit includes a third NMOS transistor Q7, a fourth NMOS transistor Q8, and a sixth switch S6. The second receiving unit uses NMOS transistors to form a current mirror structure, which is complementary to the PMOS current mirror of the first receiving unit.

[0076] The gate of the third NMOS transistor Q7 is connected to the third bias voltage signal VBP, forming the third mirror control node of the current mirror. Its drain is connected to the touchscreen channel via the sixth switch S6, forming the second output branch of the current mirror. The third NMOS transistor Q7 and the first NMOS transistor Q3 in the second charge compensation unit form a current mirror relationship. Both transistors have their gates connected to the third bias voltage signal VBP, forming a common-gate structure. The drain of the third NMOS transistor Q7 is connected to the touchscreen channel via the sixth switch S6, which controls the timing of the reverse compensation charge output. When charge replenishment is needed, the sixth switch S6 is closed, and the compensation current flows out from the touchscreen channel; when compensation is not needed, the sixth switch S6 is open.

[0077] The gate of the fourth NMOS transistor Q8 is connected to the fourth bias voltage signal VBPC, forming the fourth mirror control node of the current mirror. Its drain is connected to the source of the third NMOS transistor Q7, and the source is connected to the third voltage VDDA. The fourth NMOS transistor Q8 and the second NMOS transistor Q4 in the second charge compensation unit form a current mirror relationship. The fourth NMOS transistor Q8 and the third NMOS transistor Q7 are cascaded together, forming a complete current path for the second receiving unit.

[0078] Through the coordinated operation of the first and second receiving units, the charge transfer module enables bidirectional charge compensation output. When the touchscreen channel needs to replenish charge, the first receiving unit operates, the fifth switch S5 closes, and the sixth switch S6 opens, allowing compensation current to flow from the first receiving unit into the touchscreen channel. When the touchscreen channel needs to absorb charge, the second receiving unit operates, the sixth switch S6 closes, and the fifth switch S5 opens, allowing compensation current to flow from the touchscreen channel into the second receiving unit. The two receiving units do not operate simultaneously, avoiding current conflict. The adjustable proportional characteristic of the current mirror structure allows for flexible adjustment of the compensation charge amount to adapt to the compensation needs of different touchscreen channels.

[0079] In this embodiment, the clamping operational amplifier module includes a first clamping operational amplifier Op1 and a second clamping operational amplifier Op2. The clamping operational amplifier module controls the voltages of the first compensation node Vcap1 and the second compensation node Vcap2 through two independent operational amplifiers, thereby realizing a dual-channel independent voltage clamping function.

[0080] The first clamping operational amplifier Op1 has its non-inverting input connected to the drain of the first PMOS transistor Q1, its inverting input connected to the reference voltage VCM, and its output connected to the gate of the second PMOS transistor Q2. The second clamping operational amplifier Op2 has its non-inverting input connected to the drain of the first NMOS transistor Q3, its inverting input connected to the reference voltage VCM, and its output connected to the gate of the second NMOS transistor Q4. The first clamping operational amplifier Op1, the first PMOS transistor Q1, and the second PMOS transistor Q2 form a first clamping operational amplifier loop, which precisely clamps the voltage of the first compensation node Vcap1 to the reference voltage VCM through a negative feedback mechanism. The second clamping operational amplifier Op2, the first NMOS transistor Q3, and the second NMOS transistor Q4 form a second clamping operational amplifier loop, which precisely clamps the voltage of the second compensation node Vcap2 to the reference voltage VCM through a negative feedback mechanism. This allows the first and second clamping operational amplifier loops to provide a reliable basis for the proportional mirroring of the subsequent charge transfer module.

[0081] In this embodiment, as Figure 2 As shown, the internal structures of the first clamping op-amp Op1 and the second clamping op-amp Op2 both adopt the Class AB architecture operational amplifier. M0-M3 shown in the figure are all MOS transistors, and Cc1 and Cc2 are capacitors inside the clamping op-amp.

[0082] The clamping operational amplifier contains multiple bias voltage nodes: VBP_1, VBPC_1, VBNC_1, VBAP, and VBAN. These voltages are generated by an external bias circuit. The ClassAB architecture operational amplifier is primarily designed to improve output load capacity, ensuring sufficient drive capability when the bias voltage VBP / VBN point is connected to the MOSFET gate. The ClassAB architecture maintains a low quiescent current and provides a fast response and sufficient source and sink current capabilities when a large output current is required.

[0083] The reference voltage VCM is typically set at the midpoint of the touchscreen channel's operating voltage, i.e., VCM = VDD_CS / 2. This setting ensures consistent compensation charge and simplifies the control logic.

[0084] Example 2

[0085] like Figure 3 As shown, this embodiment provides a charge compensation method based on a touchscreen channel, including the following steps:

[0086] The voltage of the compensation node is clamped to the reference voltage VCM by the clamping operational amplifier module.

[0087] The direction of charge compensation is determined based on the voltage changes of the touchscreen channel under the influence of the operating clock. The touchscreen channel periodically switches between different voltage states under the control of the operating clock. The charge compensation circuit needs to determine which direction of compensation is required based on the operating clock signal and the direction of change of the touchscreen channel voltage V_RX.

[0088] Based on the direction of charge compensation, select the appropriate charge compensation unit for charge compensation.

[0089] The compensation charge is output to the touch screen channel through the charge transfer module at an adjustable transfer ratio, so that the amount of compensation charge output to the touch screen channel compensates the touch screen channel voltage V_RX to the target voltage range.

[0090] In this embodiment, determining the direction of charge compensation based on the voltage change state of the touchscreen channel under the action of the working clock includes:

[0091] When the touchscreen channel voltage V_RX switches towards the first voltage VDD_CS, a compensation charge in the first direction is generated through the first charge compensation unit. In other words, when the operating clock instructs the touchscreen channel to switch from a low voltage state to a high voltage state, i.e., to the first voltage VDD_CS, positive charge compensation is required.

[0092] When the touchscreen channel voltage V_RX switches to the direction of the third voltage VDDA, a compensation charge in the second direction is generated through the second charge compensation unit.

[0093] When the operating clock indicates that the touch screen channel is switching from a high voltage state to a low voltage state, that is, switching towards the third voltage VDDA, reverse charge compensation is required.

[0094] This adaptive bidirectional charge compensation, achieved by selecting the appropriate compensation unit based on the switching direction of the touchscreen channel voltage V_RX, can cope with various working states of the touchscreen channel.

[0095] In this embodiment, when the touchscreen channel voltage V_RX switches towards the first voltage VDD_CS, the generation of compensation charge in the first direction by the first charge compensation unit specifically includes:

[0096] Before the touchscreen channel voltage V_RX switches towards the first voltage VDD_CS, the two ends of the first compensation capacitor C1 are connected to the same first voltage VDD_CS via a control switch, ensuring that the first compensation capacitor C1 is in a charge balance state. Before the touchscreen channel voltage V_RX switches, the first switch S1 is closed, while the second switch S2 and the fifth switch S5 are open. After the first switch S1 is closed, both ends of the first compensation capacitor C1 are connected to the first voltage VDD_CS, and the voltage difference across the capacitor is zero. At this time, the net charge stored on the first compensation capacitor C1 is zero, and it is in a charge balance state. This eliminates any residual charge that may have remained on the first compensation capacitor C1 from the previous compensation cycle, providing a clean initial condition for the new round of charge compensation.

[0097] When the operating clock triggers the touchscreen channel voltage V_RX to switch towards the first voltage VDD_CS, the first switch S1 changes from closed to open, and the second switch S2 and the fifth switch S5 change from open to closed. After the switch state changes, one end of the first compensation capacitor C1 remains connected to the first voltage VDD_CS and is kept at a high voltage; the other end is connected to the drain of the first PMOS transistor Q1 through the second switch S2 and the first current-limiting resistor Rd1. At this time, the voltage of the first compensation node Vcap1 is reduced from the first voltage VDD_CS to the reference voltage VCM through the first clamping operational amplifier loop. The voltage difference ΔV1 generated by the first compensation capacitor C1 is VDD_CS - VCM, and the resulting first compensation charge Q_1 is ΔV1 × C1 = (VDD_CS - VCM) × C1. Simultaneously, the first compensation charge Q_1 flows into the first receiving unit, and after being mirrored by the current mirror (assuming the mirror ratio is M), the final charge reaching the channel is Qcom_1 = M × C1 × (VDD_CS - VCM), thus effectively compensating the touchscreen channel.

[0098] Similarly, when the touchscreen channel voltage V_RX switches towards the third voltage VDDA, the second charge compensation unit generates compensation charge in the second direction using the same working principle. Before the switch, the third switch S3 and the sixth switch S6 are closed, and the two ends of the second compensation capacitor C2 are connected to the second voltage VSSA, in a state of charge balance. When the switching signal arrives, the third switch S3 opens, and the fourth switch S4 and the sixth switch S6 close. One end of the second compensation capacitor C2 remains at the second voltage VSSA, and the other end is connected to the drain of the first NMOS transistor Q3 through the second current-limiting resistor Rd2. At this time, the voltage of the second compensation node Vcap2 is changed from the second voltage VSSA to the reference voltage VCM through the second clamping operational amplifier loop. The voltage change ΔV2 = VCM - VSSA is generated across the second compensation capacitor C2, and the second compensation charge Q_2 generated on the second compensation capacitor C2 is Q_2 = ΔV2 × C2 = (VCM - VSSA) × C2. Meanwhile, the second compensation charge Q_2 flows into the second receiving unit, and after being mirrored by the current mirror (assuming the mirror magnification is M), the charge that finally reaches the channel is Qcom_2=M×C2×(VCM-VSSA), thus effectively compensating the touch screen channel.

[0099] It should be noted that the operating timing of the charge compensation circuit of this invention is synchronized with the operating clock of the touch screen channel. In self-capacitance detection mode, when there is a press signal on the touch sensing channel, charge compensation in different directions will be triggered on the rising and falling edges of the operating clock.

[0100] Please refer to Figure 4 Before the rising edge of the operating clock ck_tx arrives, the pull-up control signal RX_up is high, at which point the touchscreen channel voltage V_RX is pulled up to the first voltage VDD_CS. Assuming the capacitance of the first compensation capacitor C1 and the second compensation capacitor C2 is Cs, if we want to compensate the touchscreen channel voltage V_RX to near the reference voltage VCM for subsequent quantization, then the amount of charge to be compensated is Qrx_1 = Cs × (VDD_CS - VCM).

[0101] Simultaneously, the first switch S1 is closed, while the second switch S2 and the fifth switch S5 are open. At this time, both ends of the first compensation capacitor C1 are pulled to the first voltage VDD_CS, the voltage difference across the capacitor is zero, the amount of charge stored in it is zero, and it is in a state of charge balance.

[0102] When the operating clock ck_tx changes from 0 to 1, the pull-up control signal RX_up goes low, and the switch pull-down control signal sw_com_dn goes high. At this time, the first switch S1 is open, and the second switch S2 and the fifth switch S5 are closed. Under the action of the first clamping operational amplifier loop, the voltage of the first compensation node Vcap1 is pulled down from the first voltage VDD_CS back to the reference voltage VCM within the compensation time Tcom.

[0103] During this process, the voltage change across the first compensation capacitor C1 is equal to the difference between the first voltage VDD_CS and the reference voltage VCM, i.e., ΔV1 = VDD_CS - VCM, and the first compensation charge Q_1 = ΔV1 × C1 = (VDD_CS - VCM) × C1.

[0104] The first compensation charge Q1 is mirrored into the touch screen channel through the current mirror formed by the third PMOS transistor Q5 and the fourth PMOS transistor Q6 in the first receiving unit. If the mirroring factor is M, then the compensation charge Qcom_1 that finally reaches the touch screen channel is Qcom_1 = M × C1 × (VDD_CS - VCM).

[0105] Since both the mirror ratio M and the first compensation capacitor C1 are adjustable, simply setting M×C1=Cs will completely compensate for the charge generated by the touch channel, and the signal generated by the touch press can be quantized by the subsequent ADC.

[0106] Before the falling edge of the operating clock ck_tx arrives, the pull-down control signal RX_dn goes high, at which point the touchscreen channel voltage V_RX is pulled down to the second voltage VSSA (ground voltage 0V). The amount of charge to be compensated is Qrx_2 = Cs × (reference voltage VCM - second voltage VSSA).

[0107] At the same time, the third switch S3 is in the closed state, while the fourth switch S4 and the sixth switch S6 are in the open state. At this time, both ends of the second compensation capacitor C2 are pulled to the second voltage VSSA, the voltage difference across the capacitor is zero, the amount of charge stored in it is zero, and it is in a state of charge balance.

[0108] When the operating clock ck_tx changes from 1 to 0, the pull-down control signal RX_dn goes low, and the switch pull-up control signal sw_com_up goes high. At this time, the third switch S3 opens, and the fourth switch S4 and the sixth switch S6 close. Under the action of the second clamping operational amplifier loop, the voltage of the second compensation node Vcap2 is pulled back from the second voltage VSSA to the reference voltage VCM within the compensation time Tcom.

[0109] During this process, the voltage change across the second compensation capacitor C2 is equal to the difference between the reference voltage VCM and the second voltage VSSA, i.e., ΔV2 = VCM - VSSA, and the second compensation charge Q_2 generated on the second compensation capacitor C2 is ΔV2 × C2 = (VCM - VSSA) × C2.

[0110] The second compensation charge is mirrored into the touchscreen channel through the current mirror formed by the third NMOS transistor Q7 and the fourth NMOS transistor Q8 in the second receiving unit. The second compensation charge Q_2 generated on the second compensation capacitor C2 is Q_2 = ΔV2 × C2 = (VCM - VSSA) × C2. If the mirroring factor is M, then the amount of compensation charge that finally reaches the touchscreen channel is Qcom_2 = M × C2 × (VCM - VSSA).

[0111] Simply setting M×C2=Cs will completely compensate for the amount of charge generated by the touchscreen channel.

[0112] The first charge compensation unit and the second charge compensation unit operate alternately and will not start simultaneously. When the touch screen channel voltage V_RX changes towards the first voltage VDD_CS, the first charge compensation unit operates, the fifth switch S5 closes, the sixth switch S6 opens, and the first receiving unit injects the first compensation charge into the touch screen channel. When the touch screen channel voltage V_RX changes towards the third voltage VDDA (equal to the first voltage VDD_CS), the second charge compensation unit operates, the sixth switch S6 closes, the fifth switch S5 opens, and the second receiving unit absorbs the second compensation charge from the touch screen channel.

[0113] This time-division multiplexing operation avoids current conflicts between the two compensation units, improving the controllability and reliability of the compensation process. Simultaneously, the first clamping operational amplifier Op1 and the second clamping operational amplifier Op2 in the clamping operational amplifier module independently control the first compensation node Vcap1 and the second compensation node Vcap2, respectively. The two clamping loops do not interfere with each other, improving system stability.

[0114] In summary, this invention generates compensation charge using a capacitor voltage method. A first compensation charge and a second compensation charge are generated through a first charge compensation unit and a second charge compensation unit, respectively. The amount of compensation charge is determined by the product of the compensation capacitor value and the voltage change. Compared to traditional current compensation methods, this invention completes charge distribution using only one set of current mirrors, reducing mismatch accumulation and significantly improving linearity. Furthermore, the capacitor voltage method does not rely on multi-stage replication of current mirrors; the matching accuracy of the capacitor is much higher than that of the current mirror, thus significantly reducing the degree of mismatch in charge compensation between different touchscreen channels and improving the uniformity of compensation accuracy. Simultaneously, the capacitor voltage method primarily achieves charge transfer through the charging and discharging of the capacitor. The circuit requires only two sets of compensation units to achieve bidirectional compensation, resulting in a simple topology, small chip area, and ease of integration and mass production.

[0115] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A charge compensation circuit based on a touchscreen channel, characterized in that, include: The clamping operational amplifier module is used to clamp the voltage of the compensation node to the reference voltage; The charge compensation module includes a first charge compensation unit and a second charge compensation unit; The first charge compensation unit is connected between the first voltage and the second voltage, and is connected to the clamping operational amplifier module, and is used to generate a first compensation charge after the touch screen channel voltage changes in the direction of the first voltage. The second charge compensation unit is connected between the second voltage and the third voltage and is connected to the clamping operational amplifier module, and is used to generate a second compensation charge after the touch screen channel voltage changes in the direction of the third voltage. A charge transfer module is connected to the first charge compensation unit and the second charge compensation unit respectively, and is used to output the first compensation charge or the second compensation charge to the touch screen channel at a preset multiple. The first charge compensation unit and the second charge compensation unit generate compensation charge through a switched capacitor method. The first charge compensation unit connects both ends of the compensation capacitor to the first voltage before the touch screen channel voltage is switched by controlling the switch. After switching, one end of the compensation capacitor is kept connected to the first voltage and the other end is connected to the first compensation node. Under the action of the clamping operational amplifier module, the voltage of the first compensation node changes from the first voltage to the reference voltage to generate the first compensation charge. The operation mode of the second charge compensation unit is symmetrical to that of the first charge compensation unit. The charge transport module adopts a current mirror structure, and the mirror control node of the current mirror structure is connected to the gate of the corresponding MOS transistor in the charge compensation module.

2. The charge compensation circuit based on the touchscreen channel as described in claim 1, characterized in that, The first charge compensation unit includes a first compensation capacitor, a first switch, a second switch, a first current limiting resistor, a first PMOS transistor, and a second PMOS transistor; The first compensation capacitor and the first switch are connected in parallel. One end of the first compensation capacitor and the first switch are both connected to the first voltage, and the other end of each is connected to the drain of the first PMOS transistor through the second switch and the first current limiting resistor. The source of the first PMOS transistor is connected to the drain of the second PMOS transistor, and the gate is connected to the first bias voltage signal. The gate of the second PMOS transistor is connected to the second bias voltage signal and is also connected to the clamping operational amplifier module, while the source is connected to the second voltage.

3. The charge compensation circuit based on the touchscreen channel as described in claim 2, characterized in that, The second charge compensation unit includes a second compensation capacitor, a third switch, a fourth switch, a second current-limiting resistor, a first NMOS transistor, and a second NMOS transistor; The second compensation capacitor and the third switch are connected in parallel. One end of the second compensation capacitor and the third switch are both connected to the second voltage, and the other end of both are connected to the drain of the first NMOS transistor through the fourth switch and the second current limiting resistor. The source of the first NMOS transistor is connected to the drain of the second NMOS transistor, and the gate is connected to the third bias voltage signal. The gate of the second NMOS transistor is connected to the fourth bias voltage signal and is also connected to the clamping operational amplifier module, while the source is connected to the third voltage.

4. The charge compensation circuit based on the touchscreen channel as described in claim 3, characterized in that, The charge transfer module adopts a current mirror structure, including a first receiving unit; The first receiving unit includes a third PMOS transistor, a fourth PMOS transistor, and a fifth switch; The gate of the third PMOS transistor is connected to the first bias voltage signal to form the first mirror control node of the current mirror, and the drain is connected to the touch screen channel through the fifth switch to form the first output branch of the current mirror. The gate of the fourth PMOS transistor is connected to the second bias voltage signal, forming the second mirror control node of the current mirror. The drain is connected to the source of the third PMOS transistor, and the source is connected to the second voltage.

5. The charge compensation circuit based on the touchscreen channel as described in claim 4, characterized in that, The charge transfer module further includes a second receiving unit; The second receiving unit includes a third NMOS transistor, a fourth NMOS transistor, and a sixth switch; The gate of the third NMOS transistor is connected to the third bias voltage signal to form the third mirror control node of the current mirror, and the drain is connected to the touch screen channel through the sixth switch to form the second output branch of the current mirror. The gate of the fourth NMOS transistor is connected to the fourth bias voltage signal, forming the fourth mirror control node of the current mirror. The drain is connected to the source of the third NMOS transistor, and the source is connected to the third voltage.

6. The charge compensation circuit based on the touchscreen channel as described in claim 1, characterized in that, The clamping operational amplifier module includes a first clamping operational amplifier and a second clamping operational amplifier; The non-inverting input terminal of the first clamping operational amplifier is connected to the drain of the first PMOS transistor, the inverting input terminal is connected to the reference voltage, and the output terminal is connected to the gate of the second PMOS transistor. The non-inverting input of the second clamping operational amplifier is connected to the drain of the first NMOS transistor, the inverting input is connected to the reference voltage, and the output is connected to the gate of the second NMOS transistor.

7. The charge compensation circuit based on the touchscreen channel as described in claim 6, characterized in that, The internal structure of the first clamping operational amplifier and the second clamping operational amplifier adopts the ClassAB architecture.

8. A charge compensation method based on a touchscreen channel, characterized in that, Includes the following steps: The voltage of the compensation node is clamped to the reference voltage by the clamping operational amplifier module; The direction of charge compensation is determined based on the voltage change state of the touch screen channel under the action of the working clock. Select the appropriate charge compensation unit for charge compensation based on the charge compensation direction; The compensation charge is output to the touch screen channel through the charge transfer module at an adjustable transfer ratio, so that the amount of compensation charge output to the touch screen channel compensates the voltage of the touch screen channel to the target voltage range. The first charge compensation unit connects both ends of the compensation capacitor to the first voltage before the touch screen channel voltage is switched by a control switch. After the switch, one end of the compensation capacitor is kept connected to the first voltage and the other end is connected to the first compensation node. Under the action of the clamping operational amplifier module, the voltage of the first compensation node changes from the first voltage to the reference voltage to generate the first compensation charge. The operation mode of the second charge compensation unit is symmetrical to that of the first charge compensation unit. The charge transport module adopts a current mirror structure, and the mirror control node of the current mirror structure is connected to the gate of the corresponding MOS transistor in the charge compensation module.

9. The charge compensation method based on a touchscreen channel as described in claim 8, characterized in that, Determining the direction of charge compensation based on the voltage change state of the touchscreen channel under the action of the working clock includes: When the touch screen channel voltage switches to the first voltage direction, a compensation charge in the first direction is generated through the first charge compensation unit; When the touchscreen channel voltage switches to the third voltage direction, a compensation charge in the second direction is generated through the second charge compensation unit.

10. The charge compensation method based on a touchscreen channel as described in claim 9, characterized in that, When the touchscreen channel voltage switches to the first voltage direction, a compensation charge in the first direction is generated by the first charge compensation unit, specifically including: Before the touch screen channel voltage switches to the first voltage direction, the two ends of the first compensation capacitor are connected to the same first voltage through the control switch group in the first charge compensation unit, so that the first compensation capacitor is in a charge balance state. When the working clock triggers the touch screen channel voltage to switch to the first voltage direction, the connection state of the control switch group is changed so that one end of the first compensation capacitor is kept at the first voltage and the other end is connected to the first compensation node through the current limiting resistor. Under the action of the clamping operational amplifier module, the voltage of the first compensation node changes from the first voltage to the reference voltage within a set time, and a first voltage change is generated on the first compensation capacitor. The first voltage change is equal to the difference between the first voltage and the reference voltage. The first compensation charge generated on the first compensation capacitor is equal to the product of the value of the first compensation capacitor and the first voltage change.

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