Driver circuit and method for driving a capacitive load

Abstract

An apparatus and method for a voltage driver circuit, where the path between the ground node and the output node includes an inductor and / or another energy storage element and an energy transfer circuit including at least two switching elements (e.g., transistors) and at least two valve elements (e.g., diodes). The energy transfer circuit is used to discharge a capacitive load (e.g., output capacitor) into the energy storage element and facilitate the conversion from low voltage to high voltage while improving efficiency. An additional ground path can be included via another switching element to prevent cross-talk and hold the output at ground potential.

Description

Background Technology

[0001] Electronic devices, particularly tablets or smartphones, can accept input via handheld peripherals such as pens or styluses, and can then act as host devices for those peripherals. A stylus can be manually held by a user relative to the display screen of a digitizer (e.g., a touchscreen) to provide input to the electronic device. The stylus's position on the display screen is related to the virtual information depicted on the screen. Position detection and data transfer (i.e., communication) are achieved via capacitive coupling between the stylus and the digitizer's display screen (and vice versa). More specifically, driver circuitry is configured to generate binary information (bits) by applying a voltage to the tip electrodes of the stylus to generate a current through the capacitance between the tip electrodes and the digitizer's display screen. This current can be sensed by the digitizer. Similarly, such driver circuitry can also be located at the digitizer to transmit data to the stylus via the tip electrodes. Summary of the Invention

[0002] This disclosure is provided to present a selection of concepts in a simplified form, which are further described in the following detailed description. This disclosure is not intended to identify key or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter. The claimed subject matter is also not limited to implementations that address any or all of the shortcomings indicated herein.

[0003] In some embodiments, this disclosure relates to a driver circuit for providing a drive signal to a capacitive load via an output terminal, wherein the driver circuit includes:

[0004] Energy storage components; and

[0005] An energy transfer circuit is configured to transfer charge from the capacitive load to the energy storage element at a first edge of the drive signal, and to transfer charge from the energy storage element to the capacitive load at a second edge of the drive signal.

[0006] According to one aspect of some embodiments, a stylus includes driver circuitry configured to provide drive signals to the tip electrodes of the stylus.

[0007] According to another aspect, a host device includes the aforementioned driver circuit, wherein the driver circuit is configured to provide drive signals to a sensor array of a touch-sensitive display.

[0008] According to another aspect, a method of providing a drive signal to a capacitive load via an output terminal includes controlling an energy transfer circuit to transfer charge from the capacitive load to an energy storage element at a first edge of the drive signal, and to transfer charge from the energy storage element to the capacitive load at a second edge of the drive signal.

[0009] This enhanced driver circuit and drive control method provide high efficiency for high-voltage drivers with highly capacitive loads, significantly reducing power consumption.

[0010] Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as commonly known to those skilled in the art. While similar or equivalent methods and materials to those described and materials herein may be used to practice or test embodiments of this disclosure, exemplary methods and / or materials are described below. Furthermore, the materials, methods, and examples are illustrative only and are not intended to impose any necessary limitations. Attached Figure Description

[0011] To aid in understanding this disclosure and to illustrate how these embodiments can be implemented, reference is made to the accompanying drawings by way of example only, in which:

[0012] Figure 1 This is a schematic block diagram of an example system including a stylus and a host device.

[0013] Figure 2 This is a schematic circuit diagram of an example driver circuit, which has a push-pull circuit for applying a voltage to the tip of the stylus.

[0014] Figure 3 This is a schematic waveform diagram, an example signal with a driver circuit.

[0015] Figure 4 This is a schematic block diagram of an example driver circuit with energy transfer circuitry for improved efficiency.

[0016] Figure 5 This is a schematic flowchart of an example driver procedure used to control energy transfer circuits.

[0017] Figure 6 This is a schematic circuit diagram of a driver circuit, featuring a first example of an enhanced push-pull circuit for improved efficiency.

[0018] Figure 7 This is a schematic waveform diagram of an example signal from a first example of an enhanced push-pull circuit.

[0019] Figure 8 This is an example of a waveform of a signal measured at the falling edge of the voltage at the tip of the stylus, representing a first example of an enhanced push-pull circuit.

[0020] Figure 9 This is an example of a waveform of a signal measured at the rising edge of the voltage at the tip of the stylus, representing a first example of an enhanced push-pull circuit.

[0021] Figure 10 This is a schematic circuit diagram of a driver circuit, with a second example of an enhanced push-pull circuit for improving efficiency and reducing crosstalk.

[0022] Figure 11 This is a schematic waveform diagram of an example signal from a second example of an enhanced push-pull circuit.

[0023] Figure 12 The waveform of the signal measured is an example of a second example with an enhanced push-pull circuit at the falling edge of the voltage at the tip of the stylus.

[0024] Figure 13 The waveform of the signal measured is an example of a second example with an enhanced push-pull circuit at the rising edge of the voltage at the tip of the stylus.

[0025] Figure 14 The waveform of the signal measured is an example of a second example of a push-pull circuit with an enhanced push-pull circuit, during a relatively long period of time until a steady state is reached. Detailed Implementation

[0026] This disclosure relates to a driver circuit for driving a capacitive load, which can be provided in the touchscreen controller of a stylus and / or digitizer, or in any other electronic device configured to provide an output signal to a capacitive load.

[0027] Handheld stylus peripherals (“styluses”) used with electronic devices (including smartphones, tablets, watches, desktop computers, gaming devices, wearable devices, televisions, video conferencing systems, etc.) can be used to transmit user input to electronic devices (“host devices”). Some host devices include a display with a built-in digitizer for sensing signals transmitted from the stylus (e.g., an “active stylus”). In these electronic devices, a user interacts with the digitizer system by positioning and moving the stylus on the system’s sensing surface (e.g., a tablet and / or touchscreen). The position of the stylus relative to the sensing surface is tracked by the digitizer system and interpreted as user commands. In some technologies, the position of the stylus can be determined based on the detection of capacitive coupling between the electrodes of the stylus and one or more electrodes of the digitizer. For example, the device display may include a digitizer with multiple X and Y oriented conductors or resistive films to receive signals transmitted from the electrodes of an active stylus. In some technologies, to accurately identify the tip position, the transmission electrodes are physically positioned within the writing tip of the stylus.

[0028] Styluses can be classified as passive or active styluses. Passive styluses utilize a sensing method based on changes in the capacitive coupling between sensor electrodes deposited on a touchscreen sensor and an input object (such as a rubber-tipped stylus or a finger). In contrast, active styluses drive a unique modulated signal between the stylus's tip electrode (antenna) and the electrode grid or array of a touchscreen sensor (e.g., a digitizer system) and utilize a sensing method based on changes in the capacitive coupling between the sensor electrodes. The digitizer system detects at least one position of the stylus based on the emitted signal, and the detected position provides input to an electronic device (e.g., a computing device) associated with the digitizer system. The detected position can then be interpreted as a user command. Typically, the digitizer system is integrated with a display screen, for example, to form a touch-sensitive display device.

[0029] An active stylus can generate a modulated signal that can be detected by a digitizer. This signal can be encoded with information such as device identification, operating mode (e.g., writing, erasing), pressure / force information, tilt information, and other information. This information can be assigned to various locations on the signal.

[0030] Figure 1 This is a schematic diagram of an example system including a host device (e.g., a touch-sensitive display device) 20 and a stylus 10 with driver circuitry 120. Driver circuitry 120 applies an output signal to the tip electrode 100 (output electrode) of the stylus 10 and receives input signals from the host device via capacitive coupling between the tip electrode 100 and the touchscreen (TS) 200 or another type of touch-sensitive display of the host device 20. The touchscreen 200 is controlled by a touchscreen controller (TSC) 220, which provides an interface between the capacitive touchscreen sensor array (e.g., a grid or matrix of electrodes) of the touchscreen 200 and the controlled host device 20. The touchscreen controller 220 can be connected to the touchscreen sensor array of the touchscreen 200 and the host device 20 via a serial connection such as RS232 or Universal Serial Bus (USB). The capacitive touchscreen sensor array can be placed on a special panel coated, for example, with indium tin oxide and configured to conduct a continuous current through the sensor array to detect changes in capacitance.

[0031] The touchscreen controller 220 can be configured to apply voltages to the rows and columns of the touch sensor array that constitutes the touchscreen. When stimulating the rows and columns, the touch sensor array can be scanned by testing the rows and columns. Testing may involve detecting the impedance of the circuitry by measuring the voltage amplitude across the touch sensor array at each coordinate. This can be achieved using a differential amplifier and an analog-to-digital converter (typically a successive approximation type). This information is then transmitted to the host device 20 for analysis.

[0032] Note that, for the sake of simplicity, Figure 1 and the following Figure 2 , 4 Figures 6 and 10 show only those system components that are useful for explaining the specific example operation of the example embodiments. Furthermore, unless otherwise stated, components or signals having the same or similar reference numerals have the same or similar function and / or structure and may be described only once in this disclosure.

[0033] Figure 2 It has a push-pull circuit 122 and is used to... Figure 1 A schematic circuit diagram of an example driver circuit for applying a dynamically changing voltage Vtip (e.g., a rectangular binary signal) to the tip electrode 100 of the stylus 10.

[0034] Alternatively, driver circuitry can be provided at one or more output terminals of the touchscreen controller 220 for applying voltage to the touchscreen sensor array.

[0035] The input impedance of the touchscreen 200 is represented by a capacitive load C2 and a resistive load R1. The capacitive load C2 represents a first capacitance (e.g., approximately 30 picofarads (pF)) between the tip electrode 100 and ground (reference potential) and a second capacitance (e.g., approximately 30 femtofarads (fF)) between the tip electrode and the touch sensor array of the touchscreen 200. Given its small value, the second capacitance can be ignored when determining the capacitive load C2. Furthermore, the parallel resistive load R1 is very high, and therefore its effect on the dynamic behavior of the impedance of the drive signal (e.g., tip voltage Vtip) provided via the tip electrode 100 in the considered frequency range (up to approximately 1 megahertz (MHz) in the kilohertz (kHz) range).

[0036] Figure 2 The push-pull circuit 122 includes two controllable switching elements SW1 and SW2, which are connected between a high-voltage Vhv power supply terminal and a reference potential (e.g., ground) and can be implemented by a drive control circuit ( Figure 2 Semiconductor switches (e.g., transistors) controlled by (not shown in the image).

[0037] Figure 3 This is a schematic waveform diagram, with... Figure 2 Example signals for the driver circuit. More specifically, Figure 3 The upper waveform represents the peak voltage Vtip, the middle waveform represents the control signal for the first switching element SW1, and the lower waveform represents the control signal for the second switching element SW2. The control of the first and second switching elements SW1 and SW2 is configured such that a high control signal closes the corresponding switching element, while a low control signal opens the corresponding switching element.

[0038] like Figure 3 As shown, during the positive half-wave or pulse of the rectangular tip voltage Vtip, the first switching element SW1 is closed and the second switching element SW2 is open, while during the negative half-wave or pulse of the rectangular tip voltage Vtip, the first switching element SW1 is open and the second switching element SW2 is closed. Therefore, the capacitive load C2 is charged via the first switching element SW1 at the rising edge of the tip voltage Vtip and discharged to ground via the second switching element SW2 at the falling edge of the tip voltage Vtip.

[0039] Therefore, push-pull circuit 122 is used to generate a tip voltage Vtip at the tip electrode 100 of the stylus, which has binary information (e.g., data bits) and a high voltage value (e.g., 20 volts (V)). Tip voltage Vtip generates a current through the capacitance between the tip electrode 100 and the touchscreen of the digitizer in the host device. This current can be sensed by the digitizer to determine the position of the stylus and / or additional information conveyed by tip voltage Vtip.

[0040] A high tip voltage Vtip is desirable for increasing the signal power and efficiency of the driver circuitry because the current through the capacitor between the tip electrode 100 and the touchscreen of the digitizer in the host device is very low. However, typically at frequencies in the kHz range, the capacitive load C2 at the tip electrode 100 results in considerable energy loss by discharging the energy stored in the capacitive load C2 to ground at each falling edge of the tip voltage Vtip. These energy losses depend on the tip voltage Vtip, the capacitance value, and the frequency, and can, for example, reach approximately 30% of the total power consumption of the driver circuitry.

[0041] Figure 4 This is a schematic block diagram of an example driver circuit 120 with an energy transfer circuit (PP) 124 for improving power efficiency. The energy transfer circuit 124 is arranged at a reference terminal at a reference potential 150 (e.g., ground potential) and an output terminal 140 (e.g., the tip electrode 100 of the stylus 10 or...). Figure 1 The path between the output electrodes of the touchscreen controller 220. The driver circuit 120 includes an energy storage element (SE) 130 (e.g., at least one inductive element, such as an inductor or coil) or a combination of at least one inductive element and at least one capacitive element (e.g., a capacitor, a MOS transistor, or a varactor diode) for temporarily storing the charging energy of the capacitive load C2. The energy transfer circuit (PP) 124 may include an arrangement having at least two switching elements (e.g., semiconductor switching elements, such as transistors, thyristors, etc.) and at least two valve elements (e.g., diodes, transistors, etc.) and may be integrated on a semiconductor chip.

[0042] Furthermore, the energy transfer circuit 124 is controlled by a control signal generated by the driver control circuit (DC) 110 to direct the energy discharged from the capacitive load C2 to the energy storage element 130 and recharge the capacitive load C2 before the next discharge cycle. The driver control circuit 110 can be implemented by integrated or discrete hardware circuitry (e.g., digital logic circuitry, analog circuitry, application-specific integrated circuit (ASIC), or digital signal processor (DSP)) or a software-controlled microcontroller (e.g., a central processing unit (CPU) integrated on the same chip or the same circuit board as the driver circuit 120 and / or the energy transfer circuit 124). Therefore, the energy transfer circuit 124, controlled by the driver control circuit 110, discharges and charges the capacitive load C2 (e.g., the output capacitor) and facilitates the voltage transition from a low value to a high value at the output terminal 100, thereby reducing energy loss and improving the efficiency of the driver circuit 120.

[0043] Figure 5 It is used to control energy storage elements with switching (e.g.) Figure 4 A schematic flowchart of an example driver control procedure for the energy transfer circuit of the energy storage element 130.

[0044] The driver control program can be implemented using software routines stored in memory and used to control the driver control circuitry (e.g., Figure 4 The processor or controller in the driver control circuit 110) applies control signals to control the energy transfer circuit (e.g., Figure 4 Energy transmission circuit 124).

[0045] In S310, the procedure controls the power transfer circuit at the output terminal of the driver circuit (e.g., the output terminal (tip electrode) 100 of the driver circuit 120 of the stylus 10) and / or Figure 1 The capacitive load C2 is charged at the rising edge of the output voltage at the output terminal of the driver circuit of the touch screen controller 220. Subsequently, in S320, the energy transfer circuit is controlled to discharge the capacitive load C2 into the energy storage element of the driver circuit at the falling edge of the output voltage, so as to temporarily store energy in the energy storage element.

[0046] In S330, the power transfer circuit can be optionally controlled to intermittently connect (pull down) the output terminal to a reference potential (e.g., ground potential) of the output voltage for a predetermined time period (e.g., between the falling edge and the next rising edge of the output voltage) to reduce crosstalk and / or other noise.

[0047] In S340, the energy transfer circuit is controlled to recharge the capacitive load C2 using the energy stored in the energy storage element before the next rising edge of the output voltage used to further charge the capacitive load to the maximum value of the output voltage.

[0048] Through the aforementioned driver control procedure, the charge stored in the capacitive load is temporarily stored in the energy storage element and then transferred back to the capacitive load C2, thereby enhancing efficiency and reducing power loss in the driver circuit.

[0049] refer to Figures 6 to 14 The stylus driver circuitry is described in more detail (e.g.) Figure 1 Non-limiting examples of possible arrangements of switching elements (e.g., SW1 to SW4) and valve elements (e.g., diodes D1 and D2) in the power transfer circuit of the driver circuit 120 of the stylus 10. Figure 6 and Figure 10 The switching element shown can optionally be implemented as a controllable semiconductor switch (e.g., PMOS, NMOS, or CMOS transistor).

[0050] Figure 6 This is a schematic circuit diagram of a driver circuit, with a first more detailed example of an energy transfer circuit configured as an enhanced push-pull circuit 126 to improve efficiency when the output voltage has a voltage swing around zero (e.g., -9V to +11V or -18V to +20V) (e.g., the positive and negative half-waves of the rectangular output voltage of the driver circuit).

[0051] exist Figure 6 In the example, the parallel connection of the second and third switching elements SW2 and SW3, each with anti-parallel diodes D1 and D2 connected in series, is connected in series between the first switching element SW1 and the inductor L1 in the circuit path between the terminal of the supply voltage Vhv and the reference potential 150 (e.g., ground potential) of the tip voltage Vtip at the tip electrode 100 of the stylus. The tip electrode 100 is connected between the first switching element SW1 and the second and third switching elements SW2 and SW3, as well as the parallel connection of the first and second diodes D1 and D2.

[0052] Note that the switching states of the first to third switching elements SW1 to SW3 can be determined via... Figure 6 The driver control circuit (e.g., DC 110, not shown) Figure 4 Control is achieved by applying corresponding control signals.

[0053] Furthermore, inductor L1 can be provided as an external circuit element, while the first to third switching elements SW1 to SW3 and the first and second diodes D1 and D2 can be integrated into the chip of the enhanced push-pull circuit 126 or one or more chip modules or the entire driver circuit. Additionally, note that for Figure 6 In a driver circuit, if inductor L1 is connected to a reference potential 150, for example, 10V instead of ground, a voltage around, for example, 10V can be generated. Of course, other values ​​for the reference potential 150 can also be applied.

[0054] Figure 7 This is a waveform diagram, showing the waveform from top to bottom. Figure 6 The waveforms of the tip voltage Vtip, the control signal of the first switching element SW1, the control signal of the second switching element SW2, the control signal of the third switching element SW3, and the inductor current IL1 are shown in the first example of the enhanced push-pull circuit. The values ​​and signs of the control signals are selected based on the corresponding types of the first to third switching elements SW1 to SW3. At the falling edge, for example, the transition of the rectangular tip voltage Vtip from high voltage to low voltage, the second switching element SW2 is controlled to close for a predetermined time period (the corresponding positive pulse of the control signal) (and the current path is turned on) until the tip voltage Vtip becomes low voltage, so that the capacitive load C2 is discharged into the inductor L1 via the first diode D1 (valve element). This is indicated by the positive pulse in the waveform of the inductor current IL1. Due to the magnetic field (stored magnetic energy) generated by the inductor L1, the current IL1 continues to flow through the inductor L1 after the capacitive load is fully discharged, so as to pull the potential at the tip electrode 100 to a negative value. The valve effect of the first diode D1 in the current path prevents the current IL1 from changing direction, thereby suppressing the oscillation between the inductor L1 and the capacitive load C2.

[0055] Shortly before the subsequent rising edge (e.g., the transition of the tip voltage Vtip from low to high voltage), the capacitive load C2 is charged with a negative voltage via the second switching element SW2 during the discharge phase, and the closing of the third switching element SW3 (e.g., a positive pulse of the corresponding control signal) causes the capacitive load C2 to discharge into the inductor L1, which pulls the tip voltage Vtip to a positive value. This is indicated by a negative pulse in the waveform of the inductor current IL1. The switching timing of the third switching element SW3 is selected according to the desired waveform of the tip voltage. Afterwards, the first switching element SW1 closes at the rising edge of the tip voltage Vtip, causing the capacitive load C2 to charge via the first switching element SW1 to the value of the supply voltage Vhv, while the second and third switching elements SW2 and SW3 are open. For example, the second switching element SW2 can be open (non-conductive) for the entire rising edge of the tip voltage Vtip. During this rising edge, the third switching element SW3 can be closed (conductive). After the inductor L1 has charged the capacitive load C2, the first switching element SW1 can be closed (conductive). The second diode D2 allows the first switching element SW1 to be closed when the third switching element SW3 is closed, but this is an optional feature.

[0056] Figure 8 These are waveform diagrams of different measured waveforms of the tip voltage Vtip, the control signals of switching elements SW1 and SW2, and the inductor current IL1 through inductor L1. These waveforms serve as a first example of an enhanced push-pull circuit. Figure 6 This was obtained from simulation results at the falling edge of the stylus tip voltage Vtip. In this example, the tip voltage Vtip varies in a roughly rectangular manner between approximately +20V and approximately -17V.

[0057] like Figure 8 As shown, the inductor current IL1 is generated as a positive pulse at the falling edge of the tip voltage Vtip, and includes some small parasitic oscillations until the second switching element SW2 subsequently turns on. These small parasitic oscillations are also reflected at the beginning of the negative half-wave of the tip voltage Vtip when the second switching element SW2 closes and couples the inductor L1 to the tip electrode 100. These small parasitic oscillations are caused by the non-ideal behavior of diode D1 and are therefore dependent on the circuit design. The first and second diodes D1 and D2 can be replaced by corresponding control loops that close the corresponding switching elements when the current reaches zero. Figure 9 These are waveforms of different measured waveforms of the tip voltage Vtip, the control signals of switching elements SW1 and SW3, and the inductor current IL1 through inductor L1. These waveforms are a first example of an enhanced push-pull circuit. Figure 6 Simulation at the rising edge of the stylus tip voltage Vtip.

[0058] like Figure 9 As shown, the inductor current IL1 is generated as a negative pulse at the rising edge of the tip voltage Vtip and includes some small parasitic oscillations (attributed to imperfect diode behavior) until the third switching element SW3 subsequently turns on. These small parasitic oscillations are also reflected at the beginning of the positive half-wave of the tip voltage Vtip when the third switching element SW3 closes and couples the inductor L1 to the tip electrode 100. However, in this example, due to residual energy loss during the charging and recharging process via the inductor L1, the recharging of the capacitive load C2 using the stored charge in the inductor L1 through the inductor current IL1 during the closed state of the third switching element SW3 is insufficient to reach the maximum value of the tip voltage Vtip (+20V) again. As can be seen from the waveform diagram, the capacitive load C2 is first recharged to an intermediate maximum value of approximately +15V. Thereafter, when the first switching element SW1 subsequently closes, the original maximum value of the tip voltage Vtip (+20V) is reached, and the capacitive load C2 is charged to the full value of the supply voltage Vhv. In this way, the supply voltage Vhv is used to charge the capacitive load C2 from +15V to +20V, instead of charging it from 0V to +20V as in a conventional push-pull circuit. Therefore, for the same peak-to-peak value of the peak voltage Vtip, Figure 2 A conventional push-pull circuit will require more Figure 10 The exemplary driver circuit has approximately four times more power. Therefore, from a design perspective, the driver circuit and its supply voltage Vhv can be designed to meet the peak-to-peak requirements of the tip voltage Vtip with less power loss.

[0059] Figure 10 This is a schematic example circuit diagram of the driver circuit, in which a more detailed second example of the energy transfer circuitry is implemented as an enhanced push-pull circuit 128 to improve efficiency while maintaining the output voltage in a positive voltage range (e.g., 0V to +20V) above ground potential and achieving a stable state. Furthermore, the fact that the tip voltage Vtip and other circuit voltages are positive voltages above ground potential is advantageous for chip design. This positive voltage range reduces the complexity of the input / output (I / O) circuitry measures required for electrostatic discharge (ESD) protection.

[0060] Furthermore, crosstalk reduction can be achieved by providing an additional path to a reference potential 150 (e.g., ground potential) via an additional fourth switching element SW4, which can also be controlled by a driver circuit. Figure 10 (Not shown) Controls are used to couple the tip electrode 100 to the reference potential 150 for a temporary period.

[0061] In this example, similar to Figure 6The second and third switching elements SW2 and SW3, each having diodes D1 and D2 connected in series, are connected in parallel between the first switching element SW1 and the inductor L1 in the circuit path between the terminal of the supply voltage Vhv and the reference potential (e.g., ground potential) of the tip voltage Vtip at the tip electrode 100 of the stylus. Furthermore, the tip electrode 100 is also connected between the first switching element SW1 and the second and third switching elements SW2 and SW3, as well as the parallel connection of the first and second diodes D1 and D2.

[0062] However, with Figure 6 Unlike the first example, a fourth switching element SW4 is connected between the tip electrode 100 and the reference potential 150. Furthermore, an additional energy storage capacitor C3 is connected in series between the inductor L1 and the reference potential 150 to store the steady-state DC component of the rectangular tip voltage Vtip. The additional energy storage capacitor C3 provides the advantage of preventing the need for additional voltage supply structures (e.g., rails) and associated costs. Figure 10 In the example, the additional energy storage capacitor C3 is charged to half of the supply voltage Vhv in steady state.

[0063] Note that the switching states of the first to fourth switching elements SW1 to SW4 can also be determined via... Figure 10 The driver control circuit (e.g., not shown) Figure 4 The control is achieved by applying the corresponding control signals from the DC 110. These control signals are also adapted for the corresponding types of switching elements SW1 to SW4.

[0064] In addition, inductor L1 and / or energy storage capacitor C3 can be provided as external circuit elements, while the first to fourth switching elements SW1 to SW4 and the first and second diodes D1 and D2 can be integrated on the chip of the enhanced push-pull circuit 128 or one or more chip modules or the entire driver circuit.

[0065] Figure 11 This is a schematic waveform diagram, showing the waveform from top to bottom. Figure 10 The waveforms of the tip voltage Vtip, the control signal of the first switching element SW1, the control signal of the second switching element SW2, the control signal of the fourth switching element SW4, the control signal of the third switching element SW3, and the inductor current IL1 in the second example of the enhanced push-pull circuit.

[0066] At the falling edge, for example, the transition of the rectangular tip voltage Vtip from high to low voltage, the second switching element SW2 is controlled to close (and the current path is opened) for a predetermined period of time less than half the cycle of the tip voltage Vtip (corresponding to a positive pulse of the control signal) to discharge the capacitive load C2 through the inductor L1 to the energy storage capacitor C3 via the first diode D1 (example valve element). This is indicated by a positive pulse in the waveform of the inductor current IL1. Due to the use of inductor L1, there is only a small amount of residual energy loss caused by the parasitic resistance of the switching elements SW1 to SW4, diodes D1 and D2, inductor L1, and energy storage capacitor C3. Without inductor L1, not all the energy stored in the capacitive load C2 will be transferred to the energy storage capacitor C3, and therefore the power loss will increase.

[0067] When the fourth switching element SW4 subsequently closes for a predetermined time period before the subsequent rising edge of the tip voltage Vtip, the tip electrode 100 is pulled down and held at a reference potential 150 (e.g., ground potential), thereby preventing crosstalk and / or other noise or interference. The valve effect of the first diode D1 in the current path prevents a change in the direction of current IL1, thereby suppressing oscillations between the inductor L1, the energy storage capacitor C3, and the capacitive load C2.

[0068] Shortly before the subsequent rising edge (e.g., the transition of the tip voltage Vtip from low to high voltage), under the control of the driver control circuit, the closing of the third switching element SW3 (corresponding to a positive pulse of the control signal) causes the charge of the energy storage capacitor C3 to be transferred to the capacitive load C2 via the second diode D2 and the third switching element SW3. This is indicated by a negative pulse in the waveform of the inductor current IL1. Thereafter, the first switching element SW1 closes at the rising edge of the tip voltage Vtip, causing the capacitive load C2 to be charged to the supply voltage Vhv via the first switching element SW1, while the second, third, and fourth switching elements SW2 to SW4 are turned on.

[0069] Figure 12 The waveforms are obtained from simulations of the stylus tip voltage Vtip, the voltage VC3 across the energy storage capacitor C3, the control signals for switching elements SW1, SW2, and SW4, and the inductor current IL1 through inductor L1 and energy storage capacitor C3. These waveforms are the result of simulations at the falling edge of the stylus tip voltage Vtip, which serves as a second example of an enhanced push-pull circuit. In this example, the tip voltage Vtip varies in a generally rectangular manner between approximately +20V and 0V.

[0070] like Figure 12As shown, the inductor current IL1 is generated as a positive pulse at the falling edge of the tip voltage Vtip, and includes some small parasitic oscillations until the second switching element SW2 turns on again. These small parasitic oscillations are also reflected in the tip voltage Vtip and the voltage VC3 across the energy storage capacitor C3, which stores a value of approximately +13V in its fully charged state. Figure 13 The waveforms are waveforms of the tip voltage Vtip, the voltage VC3 across the energy storage capacitor C3, the control signals of the switching elements SW1 and SW3, and the inductor current IL1 through the inductor L1 and the energy storage capacitor C3. These waveforms are a simulation of the second example of the enhanced push-pull circuit at the rising edge of the stylus tip voltage Vtip.

[0071] like Figure 13 As shown, the inductor current IL1 is generated as a negative pulse at the rising edge of the tip voltage Vtip and includes some small parasitic oscillations until the third switching element SW3 turns on again. These small parasitic oscillations are also reflected in the tip voltage Vtip and the voltage VC3 across the energy storage capacitor C3, which is discharged to approximately +7V during its discharge state. However, due to residual energy losses during the charging and recharging process via inductor L1, the recharging of the capacitive load C2 using the stored charge in inductor L1 through the inductor current IL1 during the closed state of the third switching element SW3 is insufficient to reach the maximum tip voltage Vtip (+20V) again. As can be seen from the waveform, the capacitive load C2 is almost completely recharged to the maximum supply voltage value of approximately +20V based on the charging of the energy storage capacitor C3. This illustrates the relatively small energy loss in this example embodiment that includes the energy storage capacitor C3. Figure 14 The waveforms are waveforms of the tip voltage Vtip, the voltage VC3 across the energy storage capacitor C3, the control signals of the switching elements SW1 to SW4, and the inductor current IL1 through the inductor L1 and the energy storage capacitor C3. These waveforms are measured over a longer period of time until a steady state is reached in the second example of an enhanced push-pull circuit.

[0072] like Figure 14 As shown, in some implementations, the energy storage capacitor C3 needs to undergo multiple (e.g., three) charge / discharge cycles until a steady state is reached where the voltage VC3 across the energy storage capacitor C3 is at its constant maximum value. Figure 10In the example, assume that the energy storage capacitor C3 is larger than the capacitive load C2. Therefore, in the small initial period before reaching steady state, it will take some time until enough energy is transferred from the smaller capacitive load C2 to charge the larger energy storage capacitor C3 to its steady-state voltage (e.g., 10V). Thereafter, during steady state, the voltage at the energy storage capacitor C3 remains near its steady-state value (assuming that the average high and low times of the binary waveform of the tip voltage Vtip are the same, which is true for any digital communication).

[0073] An apparatus and method for a voltage driver circuit are described, wherein the path between a ground node and an output node includes an inductor and / or another energy storage element and an energy transfer circuit comprising at least two switching elements (e.g., transistors) and at least two valve elements (e.g., diodes). The energy transfer circuit is used to discharge a capacitive load (e.g., an output capacitor) into the energy storage element and facilitates the conversion from low voltage to high voltage while improving efficiency. An additional ground path may be included via another switching element to prevent crosstalk while maintaining the output at ground potential.

[0074] By utilizing the novel design of the driver circuit with power transfer circuitry according to the above-described example embodiment, the total power consumption of the driver circuit can be significantly reduced (e.g., from approximately 2.5 mW to approximately 0.2 mW), thereby improving battery life and efficiency. Furthermore, compared to alternative solutions (such as Collpits oscillators or thermal insulation circuits), the proposed driver circuit can be used over a wider frequency range and at higher voltages, allowing complete control over the high and low times of the driver output voltage, and thus enabling baseband-level digital data as well as advanced modulation in frequency and phase. The higher voltage allows for smaller electrodes with lower capacitive loads (e.g., at the tip of a stylus or the touch sensor of a digitizer), and thus allows for more precise determination of the stylus position.

[0075] It will be understood that the above embodiments are described by way of example only.

[0076] More generally, according to one aspect disclosed herein (A1), a method for transmitting via an output terminal (e.g., output terminal 100, Figure 4 ) to capacitive load (e.g., C2, Figure 4 The driver circuit that provides the drive signal (e.g., driver circuit 120) Figure 4 The driver circuit includes:

[0077] Energy storage elements (e.g., SE 130, Figure 4 );as well as

[0078] Energy transfer circuits (e.g., PP 124, Figure 4It is configured to transfer energy from the capacitive load to the energy storage element at a first edge of the drive signal, and to transfer energy from the energy storage element to the capacitive load at a second edge of the drive signal.

[0079] (A2) In the embodiment of A1, the energy transfer circuit is controlled to intermittently connect the output terminal to a reference potential of the output voltage (e.g., Figure 4 , 6 The grounding potential (150) in 10 reaches the predetermined time period.

[0080] (A3) In embodiments A1 or A2, the energy storage element includes at least one inductive element (e.g., inductor L1, Figure 6 ), at least one capacitive element (e.g., capacitor C3, Figure 10 (or a combination of at least one inductive element and at least one capacitive element.)

[0081] (A4) In the embodiments of A1-A3, the energy transfer circuit includes at least two switching elements (e.g., SW2 and SW3). Figure 6 ) and at least two valve elements (e.g., D1 and D2, Figure 6 ) layout.

[0082] (A5) In the embodiments of A1-A4, the energy transfer circuit includes anti-parallel valve elements (e.g., D1 and D2) having their respective series connections. Figure 6 The parallel connection of the second and third switching elements is connected in series between the first switching element and the energy storage element in the circuit path between the power supply voltage terminal and the reference potential of the drive signal at the output terminal, wherein the output terminal is connected between the first switching element and the parallel connection.

[0083] (A6) In the embodiment of A5, in conjunction with the first edge (e.g., falling edge) of the drive signal, the second switching element is controlled to be closed for a predetermined time period to pass through the first valve element (e.g., D1). Figure 6 Discharge the capacitive load into the energy storage element.

[0084] (A7) In the embodiment of A5 or A6, in conjunction with the second edge (e.g., rising edge) of the drive signal, the third switching element is controlled to be closed to discharge the capacitive load into the energy storage element, and wherein, thereafter in conjunction with the second edge of the drive signal, the first switching element is closed and the third switching element is opened, such that the capacitive load is charged via the first switching element while the second and third switching elements are open.

[0085] (A8) In the embodiments of A4-A7, the fourth switching element (e.g., SW4, Figure 10It is connected between the output terminal and the reference potential.

[0086] (A9) In the embodiments of A1-A8, the energy storage element includes an inductor and a capacitor (e.g., capacitor C3, Figure 10 () are connected in series, and in which capacitors are used as energy storage elements.

[0087] (A10) In the embodiments of A1-A9, the energy transfer circuit is integrated on a chip or one or more chip modules, and the energy storage element is arranged as a non-integrated external circuit element.

[0088] (A11) In the embodiments of A4-A10, in conjunction with the second edge (e.g., rising edge) of the drive signal, the third switching element is controlled to be closed, so that energy is drawn from the energy storage element (e.g., Figure 10 C3 in the middle) is transmitted via a second valve element (e.g., Figure 10 The first switching element is controlled to be closed so that the capacitive load is charged from the first level to the second level via the first switching element, wherein the transfer of the third switching element to the capacitive load is made in conjunction with the second edge (e.g., rising edge) of the drive signal.

[0089] According to another aspect disclosed herein, a stylus (e.g., stylus 10) is provided. Figure 1 The stylus includes a driver circuit according to any embodiment disclosed herein (e.g., A1-A11), wherein the driver circuit is configured to provide a drive signal to the tip electrode of the stylus.

[0090] According to another aspect disclosed herein, a host device (e.g., host device 20) is provided. Figure 1 The present invention includes a driver circuit according to any embodiment disclosed herein (e.g., A1-A11), wherein the driver circuit is configured to provide a drive signal to a sensor array of a touch-sensitive display.

[0091] According to another aspect disclosed herein, a method is provided for providing a drive signal to a capacitive load via an output terminal, wherein the method includes controlling an energy transfer circuit to transfer energy from the capacitive load to an energy storage element at a first edge of the drive signal, and to transfer energy from the energy storage element to the capacitive load at a second edge of the drive signal. In various embodiments, the method includes controlling a push-pull circuit according to any embodiment disclosed herein (e.g., A1-A11).

[0092] According to another aspect disclosed herein, a computer program implemented on computer-readable storage (e.g., within memory, such as random access memory (RAM) or read-only memory (ROM)) is provided, the computer program including code configured to perform the methods of any of the embodiments disclosed herein when run on one or more processors.

[0093] The examples and embodiments described herein can be implemented as logical steps in one or more computer systems. Logical operations can be implemented as: (1) a sequence of processor-implemented steps executed in one or more computer systems; and (2) interconnected machines or circuit modules within one or more computer systems. The implementation is a matter of choice depending on the performance requirements of the computer system used for implementation. Therefore, the logical operations constituting the various examples or embodiments described herein may be referred to differently as operations, steps, objects, or modules. Furthermore, it should be understood that logical operations can be performed in any order, added as needed, or omitted unless expressly stated or required by the language of the claims.

[0094] Once this disclosure is given, other variations and applications of the disclosed technology will become apparent to those skilled in the art. The scope of this disclosure is not limited to the embodiments described above, but is defined only by the appended claims.

Claims

1. A driver circuit for providing a drive signal as a rectangular tip voltage to a capacitive load via an output terminal, wherein the driver circuit comprises: Energy storage components; as well as An energy transfer circuit is configured to transfer energy from the capacitive load to the energy storage element at a first edge of the drive signal and from the energy storage element to the capacitive load at a second edge of the drive signal. The energy transfer circuit includes a parallel connection of second and third switching elements having respective series-connected anti-parallel valve elements. This parallel connection is connected in series between a first switching element and the energy storage element in a circuit path between a terminal of the supply voltage and a reference potential of the drive signal at the output terminal. The output terminal is connected between the first switching element and the parallel connection, and a fourth switching element is connected between the output terminal and the reference potential. The energy storage element includes at least one inductive element or a combination of at least one inductive element and at least one capacitive element, wherein the at least one capacitive element is directly connected in series between the at least one inductive element and a reference potential to store the steady-state DC component of the rectangular tip voltage.

2. The driver circuit according to claim 1, characterized in that, The energy transfer circuit is controlled to intermittently connect the output terminal to the reference potential of the output voltage for a predetermined time period.

3. The driver circuit according to claim 1 or 2, characterized in that, The energy transmission circuit includes an arrangement of at least two switching elements and at least two valve elements.

4. The driver circuit according to claim 3, characterized in that, In conjunction with the first edge of the drive signal, the second switching element is controlled to be closed for a predetermined period of time to discharge the capacitive load into the energy storage element via the first valve element.

5. The driver circuit according to claim 3, characterized in that, In conjunction with the second edge of the drive signal, the third switching element is controlled to be closed to discharge the capacitive load into the energy storage element, and wherein, subsequently in conjunction with the second edge of the drive signal, the first switching element is closed and the third switching element is opened, such that the capacitive load is charged via the first switching element, while the second and third switching elements are open.

6. The driver circuit according to claim 3, characterized in that, The energy storage element includes an inductor and a capacitor connected in series, wherein the capacitor is used as an energy storage element.

7. The driver circuit according to claim 1, characterized in that, The energy transfer circuit is integrated on a chip or one or more chip modules, and the energy storage element is arranged as a non-integrated external circuit element.

8. The driver circuit according to claim 6, characterized in that, In conjunction with the second edge of the drive signal, the third switching element is controlled to be closed such that the capacitive load is charged to a first level via the transfer of energy from the energy storage element through the second valve element and the third switching element to the capacitive load, and wherein thereafter, in conjunction with the second edge of the drive signal, the first switching element is controlled to be closed such that the capacitive load is charged from the first level to a second level via the first switching element.

9. A stylus comprising a driver circuit according to any one of claims 1 to 8, wherein the driver circuit is configured to provide the drive signal to the tip electrode of the stylus.

10. A host device comprising a driver circuit according to any one of claims 1 to 8, wherein the driver circuit is configured to provide the drive signal to a sensor array of a touch-sensitive display.

11. A method for providing a drive signal as a rectangular tip voltage to a capacitive load via an output terminal, wherein the method includes controlling an energy transfer circuit to transfer energy from the capacitive load to an energy storage element at a first edge of the drive signal, and to transfer energy from the energy storage element to the capacitive load at a second edge of the drive signal, the energy transfer circuit including a parallel connection of second and third switching elements having respective series-connected anti-parallel valve elements, the parallel connection being connected in series between a first switching element and the energy storage element in a circuit path between a terminal of the supply voltage and a reference potential of the drive signal at the output terminal, wherein the output terminal is connected between the first switching element and the parallel connection, and a fourth switching element is connected between the output terminal and the reference potential. The energy storage element includes at least one inductive element or a combination of at least one inductive element and at least one capacitive element, wherein the at least one capacitive element is directly connected in series between the at least one inductive element and a reference potential to store the steady-state DC component of the rectangular tip voltage.

12. A computer-readable storage medium storing a computer program including code configured to perform the method of claim 11 when the code is run on one or more processors.

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