Compensation circuit for touch sensors

Abstract

Device comprising: an integrator circuit (305); a compensation circuit (315) separate from and connected to the integrator circuit (305), wherein the compensation circuit (315) comprises: a driver (400); a resistor (405) coupled to the driver (400); a capacitor (410) coupled to the resistor (405); and a demultiplexer (415) coupled to the capacitor (410), where the driver (400) can be used for this purpose: during a first time interval, a positive charge is supplied to the integrator circuit (305) through the resistor (405), the capacitor (410), and the demultiplexer (415), wherein the integrator circuit (305) is operable to integrate a signal and the positive charge to generate a first readout signal, the signal being based on a charge at an electrode of a touch sensor (102); and during a second time interval, a negative charge is supplied to the integrator circuit (305) through the resistor (405), the capacitor (410), and the demultiplexer (415), wherein the integrator circuit (305) can further be operated to integrate the signal and the negative charge in order to generate a second readout signal; and a readout circuit (310) that can be operated to detect a touch based on the first readout signal and the second readout signal.

Description

[0001] This disclosure relates generally to touch sensor technology.

[0002] In an example scenario, a touch sensor detects the presence and position of an object (e.g., a user's finger or a stylus) within a touch-sensitive area of ​​the touch sensor pad, e.g., overlaid on a display screen. In a touch-sensitive display application, a touch sensor pad allows a user to interact directly with what is on the screen, rather than indirectly with a mouse or touchpad. A touch sensor is mounted on, or incorporated into, a desktop computer, laptop computer, tablet computer, personal digital assistant (PDA), smartphone, satellite navigation device, portable media player, portable game console, kiosk computer, point-of-sale device, or other device. A control panel of a household appliance or other device may include a touch sensor.There are a number of different types of touch sensors, such as resistive touch sensors, surface acoustic wave touch sensors and capacitive touch sensors.

[0003] In one example, when an object physically touches a touch screen within a touch-sensitive area of ​​a touch sensor of the touch screen (e.g., by physically touching a cover layer overlying a touch sensor array of the touch sensor) or comes within a detection distance of the touch sensor (e.g., by hovering over the cover layer overlying the touch sensor array of the touch sensor), a capacitance change occurs within the touch screen at a position of the touch sensor of the touch screen that coincides with the position of the object within the touch-sensitive area of ​​the touch sensor. A touch-sensor controller processes the capacitance change to determine the position of the capacitance change within the touch sensor (e.g., within a touch sensor array of the touch sensor).

[0004] An active integration circuit is described in US 2012 / 0 256 869 A1. Short description of the drawings

[0005] For a better understanding of the present disclosure and its advantages, reference is made to the following description taken in conjunction with the accompanying drawings in which: Fig. 1 illustrates an example system including a touch sensor, according to an embodiment of the present disclosure; Fig. 2 illustrates an example device housing the touch sensor, according to an embodiment of the present disclosure; Fig. 3A illustrates an exemplary touch sensor controller, according to an embodiment of the present disclosure; Fig. 3B illustrates an exemplary touch-sensor controller, according to an embodiment of the present disclosure; Fig. 4 illustrates an exemplary compensation circuit, according to an embodiment of the present disclosure; Fig. 5 illustrates an exemplary signal diagram showing a first exemplary precharge of an integrator circuit using a compensation circuit according to an embodiment of the present disclosure; Fig. 6 illustrates an exemplary signal diagram showing a second exemplary precharge of an integrator circuit using a compensation circuit according to an embodiment of the present disclosure; and Fig. 7 illustrates an example method for detecting a touch according to an embodiment of the present disclosure. Description of the exemplary embodiments

[0006] Touch sensors can detect touches and / or objects by monitoring electrical signals generated by an array of electrodes within the touch sensor. Each electrode is associated with a charge that generates an electrical signal through the electrode. When a touch occurs and / or an object comes close to the electrode, the charge associated with the electrode changes, and as a result, the electrical signal generated by that charge also changes. The touch sensor monitors the electrical signal to determine when that electrical signal changes. When the touch sensor detects that the electrical signal has changed, the touch sensor determines that there is a touch and / or an object near the electrode.

[0007] One way to monitor electrical signals is to integrate them over a monitoring cycle. During each cycle, the touch sensor integrates the electrical signal over that cycle and compares the integrated signal to a baseline to determine if a change has occurred. If a change has occurred, the touch sensor can conclude that there is a touch and / or an object near the electrode.

[0008] One problem that degrades touch sensor performance is the parasitic capacitance of the touch sensor components. These parasitic capacitances create fixed and / or direct current (DC) components in the electrical signal transmitted through the electrodes. When these DC components are amplified and / or integrated, they degrade the accuracy of the touch sensor by reducing the margin available for monitoring the touch sensor's integrated signals. As a result, the touch sensor's signal-to-noise ratio is reduced.

[0009] This disclosure relates to a touch sensor that uses a compensation circuit to remove the fixed components and / or the DC components generated by the parasitic capacitances. The compensation circuit adds and / or removes a charge from an input of an integrator circuit to cancel and / or reduce the DC component of the electrical signal. As a result, the amount of headroom available for monitoring the integrated signal is increased. Furthermore, the signal-to-noise ratio is also increased. The touch sensor is generally implemented using the Fig. 1 and Fig. 2. In detail, the touch sensor is configured using the Fig. 3 to 7.

[0010] Fig. 1 shows an example system 100 including a touch sensor 102 according to an embodiment of the present disclosure. The touch sensor 102 includes a touch sensor panel 106 and a touch sensor controller 108. The touch sensor panel 106 and the touch sensor controller 108 detect the presence and position of a touch or the proximity of an object within a touch-sensitive area of ​​the touch sensor panel 106.

[0011] The touch sensor panel 106 includes one or more touch-sensitive areas. In one embodiment, the touch sensor panel 106 includes an array of electrodes disposed on one or more substrates made of a dielectric material. Reference herein to a touch sensor panel may include both the electrodes of the touch sensor panel 106 and the substrate or substrates on which they are disposed. Alternatively, reference to a touch sensor panel may include the electrodes of the touch sensor panel 106 but not the substrate or substrates on which they are disposed.

[0012] In one embodiment, an electrode is a region of conductive material that forms a shape, such as a circular disk, a square, a rectangle, a thin line, another shape, or a combination of these shapes. One or more cuts in one or more layers of a conductive material create (at least in part) the shape of an electrode, and the area of ​​the shape is (at least in part) defined by these cuts. In one embodiment, the conductive material of an electrode covers approximately 100% of the area of ​​its shape. For example, an electrode is made of indium tin oxide (ITO), and the ITO of the electrode covers approximately 100% of the area of ​​its shape (sometimes referred to as 100% fill). In one embodiment, the conductive material of an electrode covers less than 100% of the area of ​​its shape. An electrode may, for example, consist of fine lines of metal or other conductive material (FLM), such asof copper, silver, or a copper- or silver-containing material, and the fine lines of conductive material may cover approximately 5% of the area of ​​their shape in a cross-hatched, reticulated, or other pattern. Reference to FLM includes such materials. Although this disclosure contemplates certain electrodes composed of certain conductive materials forming certain shapes with certain fill percentages in certain patterns, this disclosure contemplates, in any combination, electrodes composed of other conductive materials forming other shapes with different fill percentages in a different pattern.

[0013] The shapes of the electrodes (or other elements) of a touch sensor panel 106 define, in whole or in part, one or more macro-features of the touch sensor panel 106. One or more properties of the implementation of these shapes (such as the conductive materials, fills, or patterns within the shapes) define, in whole or in part, one or more micro-features of the touch sensor panel 106. One or more macro-features of a touch sensor panel 106 may define one or more properties of its functionality, and one or more micro-features of the touch sensor panel 106 may define one or more optical features of the touch sensor panel 106, such as transmissivity, refraction, or reflection.

[0014] Although this disclosure describes a number of example electrodes, the present disclosure is not limited to these example electrodes, and other electrodes may be implemented. Furthermore, although this disclosure describes a number of example embodiments that include particular configurations of particular electrodes forming particular nodes, the present disclosure is not limited to these example embodiments, and other configurations may be implemented. In one embodiment, a number of electrodes are arranged on the same or on different surfaces of the same substrate. Additionally or alternatively, different electrodes may be arranged on different substrates.Although this disclosure describes a number of example embodiments that include certain electrodes arranged in certain example patterns, the present disclosure is not limited to these example patterns, and other electrode patterns may be implemented.

[0015] A mechanical stack includes the substrate (or multiple substrates) and the conductive material forming the electrodes of the touch sensor panel 106. The mechanical stack may, for example, include a first layer of optically clear adhesive (OCA) beneath a cover panel. The cover panel may be clear and made of a material resistant to repeated touches, such as glass, polycarbonate, or poly(methyl methacrylate) (PMMA). This disclosure contemplates cover panels made of any material. The first layer of OCA may be disposed between the cover panel and the substrate containing the conductive material forming the electrodes. The mechanical stack may also include a second layer of OCA and a dielectric layer (which may be made of PET or another material similar to the substrate containing the conductive material forming the electrodes).Alternatively, a thin coating of a dielectric material may be applied in place of the second layer of OCA and the dielectric layer. The second layer of OCA may be disposed between the substrate with the conductive material forming the electrodes and the dielectric layer, and the dielectric layer may be disposed between the second layer of OCA and an air gap to a display of a device containing the touch-sensor panel 106 and the touch-sensor controller 108. For example, the cover panel may have a thickness of approximately 1 millimeter (mm); the first layer of OCA may have a thickness of approximately 0.05 mm; the substrate with the conductive material forming the electrodes may have a thickness of approximately 0.05 mm; the second layer of OCA may have a thickness of approximately 0.05 mm; and the dielectric layer may have a thickness of approximately 0.05 mm.

[0016] Although this disclosure describes a particular mechanical stack having a particular number of particular layers composed of particular materials and having particular thicknesses, this disclosure contemplates other mechanical stacks having any number of layers composed of any materials and having any thicknesses. For example, in one embodiment, a layer of adhesive or dielectric may replace the dielectric layer, the second layer of OCA, and the air gap described above, so that no air gap is present in the display.

[0017] One or more portions of the substrate of touch sensor panel 106 may be made of polyethylene terephthalate (PET) or another material. This disclosure contemplates any substrates with portions made of any materials. In one embodiment, one or more electrodes in touch sensor panel 106 are made entirely or partially of ITO. Additionally or alternatively, one or more electrodes in touch sensor panel 106 are made of fine lines of metal or another conductive material. For example, one or more portions of the conductive material may be copper or copper-containing and have a thickness of approximately 5 micrometers (µm) or less and a width of approximately 10 µm or less. In another example, one or more portions of the conductive material may be silver or silver-containing and similarly have a thickness of approximately 5 µm or less and a width of approximately 10 µm or less.This disclosure encompasses any electrodes made of any materials.

[0018] In one embodiment, touch sensor panel 106 implements a capacitive form of touch sensing. In a mutual capacitance implementation, touch sensor panel 106 may include an array of drive and sense electrodes forming an array of capacitive nodes. A drive electrode and a sense electrode may form a capacitive node. The drive and sense electrodes forming the capacitive node are positioned close to each other but do not make electrical contact with each other. In response to a signal applied, for example, to the drive electrodes, the drive and sense electrodes are instead capacitively coupled to each other across a gap between them.A pulsed or alternating voltage applied to the drive electrode (by the touch-sensor controller 108) induces a charge on the sense electrode, and the amount of induced charge is sensitive to external influences (such as a touch or the proximity of an object). When an object touches or comes close to the capacitive node, a capacitance change may occur at the capacitive node, and the touch-sensor controller 108 measures the capacitance change. By measuring the capacitance change across the array, the touch-sensor controller 108 determines the position of the touch or proximity within the touch-sensitive areas of the touch-sensor array 106.

[0019] In a self-capacitance implementation, touch-sensor array 106 may include an array of electrodes of a single type, each of which may form a capacitive node. When an object touches or comes close to the capacitive node, a change in self-capacitance may occur at the capacitive node, and the touch-sensor controller measures the change in capacitance, e.g., as a change in the amount of charge implemented to increase the voltage at the capacitive node by a predetermined amount. As with the mutual-capacitance implementation, by measuring the changes in capacitance across the array, touch-sensor controller 108 determines the position of the touch or proximity within the touch-sensitive areas of touch-sensor array 106. This disclosure contemplates any form of capacitive touch sensing.

[0020] In one embodiment, one or more drive electrodes together form a drive line that runs horizontally or vertically or in another orientation. Similarly, in one embodiment, one or more sense electrodes together form a sense line that runs horizontally or vertically or in another orientation. In a specific example, the drive lines run substantially perpendicular to the sense lines. Reference to a drive line herein may include one or more drive electrodes forming the drive line, or vice versa. Reference to a sense line herein may optionally include one or more sense electrodes forming the sense line, and vice versa.

[0021] In one embodiment, touch-sensor panel 106 includes drive and sense electrodes arranged in a pattern on one side of a single substrate. In such a configuration, a pair of drive and sense electrodes capacitively coupled to each other across a gap between them forms a capacitive node. In the example of a self-capacitance implementation, electrodes of a single type are arranged in a pattern on a single substrate. In addition or alternatively to having the drive and sense electrodes arranged in a pattern on one side of a single substrate, touch-sensor panel 106 may have drive electrodes arranged in a pattern on one side of a substrate and sense electrodes arranged in a pattern on another side of the substrate.Furthermore, touch sensor panel 106 may have drive electrodes arranged in a pattern on one side of a substrate and sense electrodes arranged in a pattern on a side of another substrate. In such configurations, an intersection of a drive electrode and a sense electrode forms a capacitive node. Such an intersection may be a location where the drive electrode and sense electrode "cross," or are closest to each other in their respective planes. The drive and sense electrodes do not make electrical contact with each other, but are capacitively coupled to each other via a dielectric at the intersection. Although this disclosure describes particular configurations of particular electrodes forming particular nodes, this disclosure contemplates other configurations of electrodes forming nodes.Furthermore, this disclosure encompasses other electrodes arranged on any number of substrates in any pattern.

[0022] As described above, a change in capacitance at a capacitive node of touch-sensor panel 106 may indicate a touch or proximity input at the location of the capacitive node. Touch-sensor controller 108 detects and processes the change in capacitance to determine the presence and location of the touch or proximity input. In one embodiment, touch-sensor controller 108 then communicates information about the touch or proximity input to one or more other components (such as one or more central processing units (CPUs)) of a device that includes touch-sensor panel 106 and touch-sensor controller 108, which may respond to the touch or proximity input by initiating a function of the device (or an application running on the device).Although this disclosure describes a particular touch-sensor controller 108 having particular functionality with respect to a particular device and a particular touch sensor 102, this disclosure also encompasses other touch-sensor controllers having other functionality with respect to any devices and any touch sensors.

[0023] In one embodiment, the touch-sensor controller 108 is implemented in the form of one or more integrated circuits (ICs), such as general-purpose microprocessors, microcontrollers, programmable logic devices or arrays, or application-specific integrated circuits (ASICs). The touch-sensor controller 108 includes any combination of analog circuitry, digital logic, and digital non-volatile memory. In one embodiment, the touch-sensor controller 108 is disposed on a flexible printed circuit (FPC) mounted on the substrate of the touch-sensor array 106, as described below. The FPC can be active or passive. In one embodiment, multiple touch-sensor controllers 108 are disposed on the FPC.

[0024] In one example implementation, the touch-sensor controller 108 includes a processing unit, a drive unit, a readout unit, and a storage unit. In such an implementation, the drive unit applies a drive signal to the drive electrodes of the touch-sensor panel 106, and the readout unit senses charges at the capacitive node of the touch-sensor panel 106 and provides measurement signals to the processing unit that represent capacitances at the capacitive nodes. The processing unit controls the drive unit's application of the drive signals to the drive electrodes and processes the measurement signals from the readout unit to detect and process the presence and location of a touch or proximity input within the touch-sensitive areas of the touch-sensor panel 106.The processing unit can also track changes in the position of a touch or proximity input within the touch-sensitive areas of the touch-sensor panel 106. The storage unit stores programs for execution by the processing unit, including programs for controlling the drive unit to apply the drive signals to the drive electrodes, programs for processing the measurement signals from the readout unit, and other programs. Although this disclosure describes a particular touch-sensor controller 108 having a particular implementation with particular components, this disclosure also encompasses touch-sensor controllers having other implementations with different components.

[0025] Traces 110 of conductive material disposed on the substrate of touch sensor panel 106 connect the drive and sense electrodes of touch sensor panel 106 to connection pads 112, which are also disposed on the substrate of touch sensor panel 106. As described below, connection pads 112 enable coupling of traces 110 to touch sensor controller 108. Traces 110 can extend around the outside (e.g., at the edges) of the touch-sensitive areas of touch sensor panel 106 or into them.In one embodiment, certain traces 110 provide drive connections for coupling the touch-sensor controller 108 to the drive electrodes of the touch-sensor panel 106, through which the drive unit of the touch-sensor controller 108 applies drive signals to the drive electrodes, and other traces 110 provide sense connections for coupling the touch-sensor controller 108 to the sense electrodes of the touch-sensor panel 106, through which the sense unit of the touch-sensor controller 108 senses charges at the capacitive nodes of the touch-sensor panel 106.

[0026] The conductive traces 110 consist of fine lines made of metal or another conductive material. The conductive material of the conductive traces 110 can be, for example, copper or copper-containing and have a width of approximately 100 µm or less. In another example, the conductive material of the conductive traces 110 can be silver or silver-containing and have a width of approximately 100 µm or less. In one embodiment, the conductive traces 110 can also be made entirely or partially of ITO, in addition to or alternatively to the fine lines made of metal or the other conductive material. Although this disclosure describes certain conductive traces made of certain materials with certain widths, this disclosure encompasses conductive traces made of other materials and / or other widths.In addition to the conductive traces 110, the touch sensor pad 106 may include one or more ground lines that terminate at a ground connector (which may be a bonding pad 112) at an edge of the substrate of the touch sensor pad 106 (similar to the conductive traces 110).

[0027] The connection pads 112 may be located along one or more edges of the substrate outside a touch-sensitive area of ​​the touch sensor panel 106. As described above, the touch-sensor controller 108 may be located on an FPC. The connection pads 112 may be made of the same material as the conductive traces 110 and may be connected to the FPC using an anisotropic conductive film (ACF). In one embodiment, the connections 114 include conductive lines on the FPC that connect the touch-sensor controller 108 to the connection pads 112, which in turn couple the touch-sensor controller 108 to the conductive traces 110 and the drive or sense electrodes of the touch sensor panel 106. In another embodiment, the connection pads 112 are connected to an electromechanical connector (such as a zero-insertion wire-to-board connector).The connection 114 may, but need not, include an FPC. This disclosure encompasses any connections 114 between the touch-sensor controller 108 and the touch-sensor panel 106.

[0028] Fig. 2 shows an example device 200 housing a touch sensor 102, according to an embodiment of the present disclosure. The device 200 is any personal digital assistant, a mobile phone, a smartphone, a tablet computer, or the like. In one embodiment, the device 200 includes other types of devices, such as an ATM, home appliances, personal computers, or other such devices with a touch screen. In the illustrated example, the components of the system 100 reside within the device 200. Although this disclosure describes a particular device 200 having a particular implementation with particular components, this disclosure includes any devices 200 having any implementations with any components.

[0029] A specific example of device 200 is a smartphone that includes a housing 201 and a touch screen 202 covering a portion of a surface 204 of the housing 201 of the device 200. In one embodiment, the housing 201 is a housing of a device 200 that contains certain internal components (e.g., internal electrical components) of the device 200. The touch sensor 102 may be directly or indirectly coupled to the housing 201 of the device 200. The touch screen 202 may cover a substantial portion of a surface 204 or the entire surface 204 (e.g., one of the largest surfaces 204) of the housing 201 of the device 200. Reference to a touch screen 202 includes cover layers that overlay the actual display and touch-sensing elements of the device 200, including a top cover layer (e.g., a glass cover layer).In the illustrated example, surface 204 is a surface of the top cover layer of touch screen 202. In one embodiment, the top cover layer (e.g., a glass cover layer) of touch screen 200 is considered part of housing 201 of device 200.

[0030] In one embodiment, the large dimensions of touch screen 202 enable touch screen 202 to display a wide variety of data, including a keyboard, a numeric keypad, program or application events, and various other interfaces. In one embodiment, a user interacts with device 200 by touching touch screen 202 with a finger, a stylus, or other object to interact with device 200 (e.g., to select a program to execute or type a letter on a keyboard displayed on touch screen 202). In one embodiment, a user interacts with device 200 using multiple touches to perform various operations, such as zooming when viewing a document or image. In some embodiments, such asIn household appliances, the touch screen 202 does not change or changes only slightly during operation of the device and only detects single touches.

[0031] Users can interact with device 200 by physically interacting with surface 204 (or another surface) of housing 201 of device 200, represented as interaction 206, using an object 208, such as one or more fingers, one or more styluses, or other objects. In one embodiment, surface 204 is a cover layer overlaid on touch sensor panel 106 and a display of device 200. As described above, users may perform a series of physical actions (e.g., double-tap, triple-tap, or another implemented series of actions) to initiate a transition of the touch sensor 102 (e.g., the touch-sensor controller 108) from a first power mode (e.g., a low power mode) to a second power mode (e.g., to wake up the touch sensor 102 (e.g., the touch-sensor controller 108) of the device 200).The impact sensor 104 detects impacts 206 and transmits an output signal indicative of the detected impacts 206. The touch-sensor controller 108 (e.g., a monitoring component of the touch-sensor controller 108) receives the output signal from the impact sensor 104 and, based on the output signal corresponding to a predetermined impact pattern (e.g., a double-tap for a predetermined period of time), initiates the transition of the touch sensor 102 (e.g., the touch-sensor controller 108) from the first power mode to the second power mode.

[0032] Device 200 includes buttons 210 that may perform any function related to the operation of device 200. One or more buttons 210 (e.g., button 210b) may serve as a so-called "home button," indicating to the device, at least in part, that a user is about to provide input to touch sensor 102 of device 200. As described in more detail below, an embodiment of the present disclosure may reduce or eliminate various reasons for providing a "home button."

[0033] Fig. 3A shows an exemplary touch-sensor controller 108 according to an embodiment of the present disclosure. As shown in Fig. As shown in Figure 3A, touch-sensor controller 208 includes an integrator circuit 305, a readout circuit 310, and a compensation circuit 315. In one embodiment, compensation circuit 315 increases the margin available for readout circuit 310 to monitor electrical signals from integrator circuit 305 by applying and / or removing charge to an input of integrator circuit 305. As a result, the electrical signals from integrator circuit 305 can experience a larger voltage change before reaching a threshold voltage (either ground or supply voltage). The ability of touch sensor 102 to detect a touch is therefore improved.

[0034] The integrator circuit 305 is coupled to the touch sensor panel 106. The integrator circuit 305 receives an electrical signal from an electrode of the touch sensor panel 106. The electrical signal is based on a charge on the electrode. The integrator circuit 305 integrates the electrical signal to generate two readout signals (e.g., a positive readout signal and a negative readout signal). These two readout signals are then monitored by the readout circuit 310 to determine if a touch has occurred. For example, if one or more of the two signals deviates from a known or preselected baseline signal, it may be determined that a touch has occurred near the electrode. In another example, if a difference between the two signals deviates from a known or preselected distance, it may be determined that a touch has occurred near the electrode.

[0035] Readout circuit 310 receives the two readout signals generated by integrator circuit 305. Readout circuit 310 monitors the two readout signals from integrator circuit 305 to determine whether a touch has occurred near the electrode of touch sensor pad 106. For example, readout circuit 310 may first establish a baseline for each of the two readout signals. Readout circuit 310 then monitors the two readout signals to see if they deviate from the baseline by a selected threshold. If one or more of the two signals deviate from the baseline by more than the threshold, readout circuit 310 determines that a touch has occurred near the electrode. In another example, readout circuit 310 may establish a differential baseline and / or a difference between the two readout signals.The readout circuit 310 then monitors the difference between the two transmitted signals; if this difference deviates from the baseline difference by more than a selected threshold, then the readout circuit 310 determines that a touch has occurred near the electrode.

[0036] According to one example scenario, the performance and / or accuracy of readout circuitry 310 may be degraded by parasitic capacitances of components of touch sensor 110. These parasitic capacitances create DC components in the electrical signal transmitted by the electrodes of touch sensor pad 106. When these DC components are integrated, they reduce the amount of margin over which readout circuitry 310 can monitor the two readout signals generated by integrator circuitry 305. In other words, the DC components bring the two readout signals closer to threshold voltages (e.g., ground or supply voltage). The amount of voltage change the readout signal can undergo before reaching a threshold voltage is therefore reduced (less margin), allowing the gain of integrator circuitry 305 to be increased, thereby increasing the magnitude of the touch signal.Because the reduced voltage change may be more difficult to detect, the readout circuit 310 may not necessarily detect a touch under these circumstances. By removing the DC components, the readout signal can experience a larger voltage change before reaching a threshold voltage (more headroom), allowing the gain of the integrator circuit 305 to be increased, thereby increasing the magnitude of the touch signal. As a result, the signal-to-noise ratio of the two readout signals is increased, improving the touch detection capabilities of the touch sensor 102.

[0037] The touch sensor controller 108 includes a compensation circuit 315 that adds or removes charge to compensate for and / or reduce the effect of the DC component caused by the parasitic capacitances of the touch sensor 102. As shown in Fig. 3A, the compensation circuit 315 is coupled to an input of the integrator circuit 305. The compensation circuit 305 adds and / or subtracts a charge to / from the signal generated by the touch-sensor pad 106 before that signal is integrated by the integrator circuit 305 (and / or during the integration phase(s). As a result, the charge added and / or removed by the compensation circuit 315 compensates and / or reduces the DC component of the amplified signal. By reducing and / or removing the DC component, the two readout signals generated by the integrator circuit 305 provide additional margin for the readout circuit 315 to monitor the two transmitted signals, thereby allowing the system gain to be increased (e.g.,there is additional margin in which the readout circuit 315 can monitor the actual touch signal, thereby increasing the system gain.) The operation of the compensation circuit 315 is described in detail in connection with the . Fig. 4 to 7. This disclosure understands the addition or removal of charge in the sense of applying a positive and a negative charge. For example, a charge can be added by applying a positive charge, and a charge can be removed by applying a negative charge, or vice versa.

[0038] Compensation circuit 315 receives input via power supply line 325 and control lines 330. Power supply line 325 supplies a charge to compensation circuit 315. In some embodiments, this charge is added to and / or removed from integrator circuit 305. A signal from controller 330 controls whether compensation circuit 315 adds or removes charge.

[0039] In one embodiment, the compensation circuit 315 is powered by a ground-referenced reference voltage that is substantially constant over an operating temperature range (e.g., a 5°C range) of an operating temperature of the touch sensor 102. Furthermore, the ground-referenced reference voltage is substantially independent of a supply voltage supplied to the integrator circuit 305. The ground-based reference voltage deviates, for example, by less than 1% over a 145°C range (e.g., from -40°C to 105°C) of the operating temperature of the touch sensor 102. In another example, the ground-based reference voltage deviates by less than 1% from a change in the supply voltage supplied to the integrator circuit 305.

[0040] Fig. 3B shows an exemplary touch-sensor controller 108 according to an embodiment of the present disclosure. The touch-sensor controller 108 includes a current amplifier circuit 300, an integrator circuit 305, a readout circuit 310, a compensation circuit 315, and a built-in self-test circuit 320. The addition of the current amplifier circuit 300 improves the operation of the touch sensor 102 by enabling scaling of the input signal. The built-in self-test circuit 320 reduces the testing time and production costs of the touch sensor controller 108 by requiring less interaction with external test equipment. Furthermore, the operation of the touch sensor 102 is improved because the built-in self-test circuit 320 enables runtime calibration or diagnostic testing. The operation of the exemplary touch-sensor controller 108 of Fig. 3B substantially resembles the operation of the exemplary touch sensor controller 108 Fig. 3A with a few differences.

[0041] As in Fig. 3B, current amplifier circuit 300 is coupled to touch sensor panel 106 and integrator circuit 305. Current amplifier circuit 300 receives an electrical signal from an electrode of touch sensor panel 106. The signal is based on a charge on the electrode. Current amplifier circuit 300 amplifies the electrical signal. This disclosure contemplates current amplifier circuits 300 that include any number of components, such as one or more current amplifiers and / or one or more differential amplifiers, configured to amplify the electrical signal from touch sensor panel 106. Furthermore, each electrode of touch sensor panel 106 is contemplated to carry an electrical signal that is amplified by current amplifier circuit 300.In one embodiment, amplifying the electrical signal from the electrode makes small changes and variations in the electrical signal caused by a touch and / or an object near the electrode easier to detect. The current amplifier circuit 300 can be tuned and / or adjusted so that the current amplifier circuit 300 applies a certain gain to an electrical signal at a first time and, based on the tuning and / or adjustment, applies a different gain at a different time. The integrator circuit 305 receives the amplified electrical signal from the current amplifier circuit 300 and integrates the amplified electrical signal to generate the two readout signals.It is further provided that the amplifier circuit 300 can have a gain factor less than one, so that the amplifier circuit 300 operates as an attenuator.

[0042] Additionally, compensation circuit 315 is also coupled to an input of current amplifier circuit 300. In this manner, compensation circuit 315 adds and / or removes charge from the electrical signal received by current amplifier circuit 300. As a result, any DC component in the electrical signal transmitted by an electrode of touch sensor pad 106 can be reduced and / or removed before it is amplified by current amplifier circuit 300.

[0043] Furthermore, compensation circuit 315 is also coupled to an input of a built-in self-test circuit 320 in one embodiment. Compensation circuit 315 adds and / or removes charge at an input of built-in self-test circuit 320. The line over which compensation circuit 315 removes or adds charge from built-in self-test circuit 320 is referred to as a built-in self-test bus. In this way, the charge added and / or removed by compensation circuit 315 can be tested using built-in self-test circuit 320. As a result, a self-test of compensation circuit 315 can be performed by built-in self-test circuit 320, thereby simplifying manufacturing testing of touch sensor 102.Furthermore, the built-in self-test circuit 320 can be used to perform diagnostic checks of the touch sensor 102 during operation of the touch sensor 102. In one embodiment, the compensation circuit 315 can be used to test other circuit blocks by applying a charge signal to the other blocks. The built-in self-test circuit 320 provides a bus that connects the compensation circuit 315 to the other blocks. An input of another integrator circuit (if there are multiple integrators in the touch controller 108) can be connected to the compensation circuit 315 via the built-in self-test circuit.

[0044] In addition, the compensation circuit 315 receives an additional input via the control line 335. A signal from the control line 335 controls where the compensation circuit 315 adds / removes charge (e.g., the current amplifier circuit 300, the integrator circuit 305, and / or the built-in self-test circuit 320).

[0045] Additionally, in one embodiment, current amplifier circuit 300 includes an input for a positive reference voltage and a negative reference voltage. The magnitude of the positive reference voltage and the magnitude of the negative reference voltage are substantially equal to the magnitude of the ground-based reference voltage used to operate compensation circuit 315. The magnitude of the positive reference voltage and the magnitude of the negative reference voltage may, for example, differ by less than 1% from the magnitude of the ground-based reference voltage. As a result, the ground-based reference voltage, the positive reference voltage, and the negative reference voltage are maintained independent of the supply voltage at which integrator circuit 305 is operated, thereby eliminating the effects of supply voltage variations (e.g., over temperature ranges or battery lifetimes, etc.).) and supply voltage noise on the ground-based reference voltage, the positive reference voltage and the negative reference voltage.

[0046] Fig. 4 illustrates an exemplary compensation circuit 315 according to an embodiment of the present disclosure. As in Fig. 4, the compensation circuit 315 includes a driver 400, a resistor 405, a capacitor 410, and a demultiplexer 415. In one embodiment, the compensation circuit 315 adds and / or removes charge at various components of the touch-sensor controller 108 to increase the margin available for the readout circuit 315 to monitor a first readout signal and a second readout signal generated by the integrator circuit 305.

[0047] The driver 400 supplies a positive charge or a negative charge through the compensation circuit 315. The driver 400 receives a charge via the supply line 325 and a control signal via the control line 330. Based on this control signal, the driver 400 decides whether the driver 400 supplies a positive charge or a negative charge. For example, if the control signal indicates that the driver 400 should add charge, then the driver 400 will supply the charge received via the supply line 325. If the control signal indicates that the driver 400 should remove charge, the driver 400 will instead pull charge to ground. In one embodiment, the supply line 325 carries a reference voltage set by a ground-based reference system. The output of the driver 400 is switched between the supply line 325 and ground to supply the positive and negative charges (e.g.,from ground to supply line 325 to provide a positive charge, and from supply line 325 to ground to provide a negative charge). In one embodiment, the control signal is provided by the touch-sensor controller 108 rather than a component external to the controller 108. The control signal, in one embodiment, is based on a phase of the integrator circuit 305. For example, during a negative integration phase of the integrator circuit 305, the control signal causes the driver 400 to provide a positive charge through the compensation circuit 315. In another example, during a positive integration phase of the integrator circuit 305, the control signal causes the driver 400 to provide a negative charge or to remove charge from the compensation circuit 315.In one embodiment, driver 400 uses a ground-based reference voltage as the supply voltage to avoid effects of device main supply voltage drift.

[0048] Resistor 405 and capacitor 410 are connected in series with driver 400. An input of resistor 405 is coupled to an output of driver 400, and an input of capacitor 410 is coupled to an output of resistor 405. Resistor 405 and capacitor 410 influence how quickly charge is added and / or removed by compensation circuit 315. For example, an impedance or resistance of resistor 405 influences how quickly electrical energy is transferred to or from capacitor 410, and a capacitance of capacitor 410 influences how much energy is stored by capacitor 410. In one embodiment, resistor 405 is an adjustable resistor whose impedance / resistance can be adjusted. Furthermore, in one embodiment, capacitor 410 is an adjustable capacitor whose capacitance can be adjusted.By making resistor 405 and / or capacitor 410 variable, compensation circuit 315 can be configured to add and / or remove different amounts of charge at different rates depending on the state of touch sensor 102. For example, compensation circuit 315 can be configured to add a certain amount of charge during a negative integration phase of integrator circuit 305 and remove a different amount of charge during a positive integration phase of integrator circuit 305. In another example, compensation circuit 315 can be configured to add a certain amount of charge when compensation circuit 315 adds charge to an input of current amplifier circuit 300 and remove a different amount of charge when compensation circuit 315 removes charge from an input of integrator circuit 305.

[0049] The demultiplexer 415 switches the output of the compensation circuit 315. An input of the demultiplexer 415 is coupled to an output of the capacitor 410. Furthermore, the demultiplexer 415 receives a control signal via the control line 335. In one embodiment, the control signal is provided by the touch sensor controller 108, rather than an external component of the controller 108. The demultiplexer 315 includes several outputs: an output for the current amplifier circuit 300, an output for the integrator circuit 305, and an output for the built-in self-test circuit 320. Depending on the control signal received via the control line 335, the demultiplexer 315 sends the output of the capacitor 410 to one of these outputs. For example, during a diagnostic self-test, the control signal causes the demultiplexer 415 to direct the output of the capacitor 410 to the built-in self-test circuit 320.In another example, during an integration phase of the integrator circuit 305, the control signal causes the demultiplexer 415 to direct the output of the capacitor 410 to the integrator circuit 305 and / or the current amplifier circuit 300.

[0050] Fig. 5 shows an exemplary signal diagram for precharging an integrator circuit 305 using a compensation circuit 315 according to an embodiment of the present disclosure. As in Fig. 5, charge may be added and / or removed from an input of the integrator circuit 305 during initialization of the integrator circuit 305.

[0051] After initialization of the integrator circuit 305, a negative integration phase and a positive integration phase occur. During this phase, the integrator circuit 305 integrates an input signal provided by the touch-sensor panel 106 and / or the current amplifier circuit 300 to generate a first readout signal 500 and a second readout signal 505. Initialization prepares the integrator circuit 305 and the touch-sensor controller 108 to detect touches on or near the touch-sensor panel 106. This disclosure includes initializations that occur before the touch-sensor controller 108 takes measurements for a touch.

[0052] As in Fig. 5, charge is added and / or removed from the signal before the integrator circuit 305 enters the negative integration phase and the positive integration phase. For example, the compensation circuit 315 adds charge to the signal before the negative integration phase. After the charge is added, the integrator circuit 305 performs a negative integration on the signal to generate a first readout signal 500. The signal starts at half the supply voltage. Then, just before the negative integration phase, the voltage of the signal increases due to the added charge. Then, the signal gradually decreases to one-quarter the supply voltage during the negative integration phase. The integrator circuit 305 then maintains the first readout signal 500 at one-quarter the supply voltage.As a result, the available margin in the first readout signal 500 increases, allowing for a larger system gain factor, which increases the magnitude of the touch signal and makes it easier to detect.

[0053] To generate the second readout signal 505, the integrator circuit 305 performs a positive integration during the positive integration phase. Before the positive integration phase, the compensation circuit 315 removes charge from the signal. As shown in Fig. 5, the signal starts at half the supply voltage. Then, before the positive integration phase, the signal falls with the removed charge. The integrator circuit 305 then performs the positive integration on the signal, and the signal gradually rises to three-quarters of the supply voltage. The integrator circuit 305 then maintains the second readout signal 505 at three-quarters of the supply voltage. As a result, the available headroom in the second readout signal 505 is increased, allowing for a higher system gain, which increases the magnitude of the touch signal and makes it easier to detect.

[0054] In one embodiment, the signal on control line 330 is used to add and / or remove an amount of charge that compensates for offset errors in current amplifier circuit 300. Current amplifier circuit 300 may add and / or remove an amount of error charge during the integration phase due to an internal offset. Compensation circuit 315 and the control line may cancel this error charge so that the effect of the offset in current amplifier circuit 300 is not visible at the output of integrator circuit 305.

[0055] Fig. 6 shows an exemplary signal diagram for precharging an integrator circuit 305 using a compensation circuit 315 according to an embodiment of the present disclosure. As in Fig. 6, instead of adding and / or removing charge on the electrical signal before the negative integration phase and the positive integration phase, the compensation circuit 315 may add and / or remove charge during the negative integration phase and the positive integration phase.

[0056] As in Fig. As can be seen in Figure 6, the first readout signal 500 is generated by performing the negative integration and adding charge to the signal during the negative integration phase. As shown in Fig. As shown in Figure 6, the electrical signal begins at half the supply voltage, and then negative integration is performed during the negative integration phase. Furthermore, charge is added to the electrical signal during the negative integration phase. As a result, the first readout signal 500 still ends at a quarter of the supply voltage. As a result of charge compensation, the system gain can be increased without the first readout signal 500 reaching a threshold voltage (e.g., ground or supply voltage) during the integration phase.

[0057] Similarly, the second readout signal 505 is generated by performing positive integration and removing charge during the positive integration phase. As a result, the electrical signal begins at half the supply voltage, and then positive integration is performed during the positive integration phase. Furthermore, charge is removed from the electrical signal during the positive integration phase. As a result, the second readout signal 505 ends at three-quarters of the supply voltage. As a result of charge compensation, the system gain can be increased without the second readout signal 505 reaching a threshold voltage (e.g., ground or supply voltage) during the integration phase.

[0058] This disclosure also includes integrator circuits 305 and compensation circuits 315 in which the Fig. 5 and Fig. 6 may be executed each time before the readout circuit 310 measures the first readout signal 500 and the second readout signal 505 to determine whether a touch has occurred. For example, after the readout circuit 310 determines that no touch has occurred, the integrator circuit 305 may reset the first readout signal 500 and the second readout signal 505 to half the supply voltage. The compensation circuit 315 adds and / or removes charge, and the negative and positive integration phases begin again. The readout circuit 310 may then remeasure the first readout signal 500 and the second readout signal 505 to determine whether a touch has occurred.

[0059] Although this disclosure describes integrator circuitry 305 as generating a first readout signal 500 at one-quarter of the supply voltage and a second readout signal 505 at three-quarters of the supply voltage, this disclosure contemplates integrator circuitry 305 that generates a first readout signal 500 and a second readout signal 505 at arbitrary voltages. For example, integrator circuitry 305 could generate a first readout signal 500 at one-third of the supply voltage and a second readout signal 505 at two-thirds of the supply voltage. This disclosure also contemplates compensation circuitry that adds and / or removes arbitrary amounts of charge to components of touch-sensor controller 108.

[0060] Fig.7 shows an example method 700 for detecting a touch, according to an embodiment of the present disclosure. In one embodiment, the touch-sensor controller 108 performs the method 700. By performing the method 700, the touch-sensor controller increases the margin over which the touch-sensor controller 108 monitors a first and a second read signal, thereby improving the accuracy of the touch sensor 102. For example, an actual touch may change the voltage at which the first read signal 500 and / or the second read signal 505 terminate (e.g., one-quarter of the supply voltage or three-quarters of the supply voltage). The increased margin allows for a wider signal range available for detecting the touch signal.

[0061] In step 705, the control unit 108 resets an integrator circuit to half the supply voltage. By resetting the integrator circuit to half the supply voltage, two readout signals are generated at half the supply voltage. In step 710, the control unit 108 then applies a positive charge to an input of the integrator circuit. In step 715, the control unit 108 performs a negative integration on an input signal of the integrator circuit and the positive charge to generate a first readout signal. In one embodiment, the first readout signal is reduced from half the supply voltage to one-quarter the supply voltage as a result of the negative integration.

[0062] In step 720, the controller 108 applies a negative charge to the input of the integrator circuit. In step 725, the controller 108 then performs a positive integration on an input signal of the integrator circuit and the negative charge to generate a second readout signal. In one embodiment, the second readout signal increases from half the supply voltage to three-quarters the supply voltage as a result of the positive integration. The controller 108 terminates the method in step 730 by detecting a touch on a touch sensor using the first readout signal and the second readout signal. In one embodiment, by performing method 700, the controller 108 increases the margin available for detecting a touch using the first readout signal and the second readout signal.

[0063] In one embodiment, a device includes an integrator circuit, a compensation circuit, and a readout circuit. The integrator circuit integrates a signal to generate a first readout signal and a second readout signal. The signals are based on a charge on an electrode of a touch sensor. The compensation circuit includes a driver, a resistor, and a capacitor. The resistor is coupled to an output of the driver. The capacitor is coupled to the resistor and an input of the integrator circuit. The readout circuit is coupled to an output of the integrator circuit. The readout circuit detects a touch using the first readout signal and the second readout signal.In one embodiment, the compensation circuit further includes a demultiplexer coupled to the capacitor, and the capacitor is further coupled to an input of a current amplifier circuit via the demultiplexer. The current amplifier is coupled to an input of the integrator circuit. In one embodiment, the compensation circuit further includes a demultiplexer coupled to the capacitor, and the capacitor is further coupled to a built-in self-test bus. In one embodiment, the capacitor is a variable capacitor. In one embodiment, the resistor is a variable resistor. In one embodiment, the first readout signal is generated during a negative integration phase of the integrator circuit, and the second readout signal is generated during a positive integration phase of the integrator circuit.In one embodiment, the device includes a current amplifier circuit coupled to the input of the integrator. The compensation circuit is powered by a ground-based reference voltage that is substantially constant over an operating temperature range of the touch sensor 102 (e.g., -40 to 105°C) and is substantially independent of a supply voltage with which the integrator circuit is operated. The current amplifier circuit includes an input for a positive reference voltage and a negative reference voltage. The magnitude of the positive reference voltage and the magnitude of the negative reference voltage are substantially equal to the magnitude of the ground-based reference voltage.In one embodiment, the compensation circuit adds charge to the amplified signal before a negative integration phase of the integrator circuit, and the compensation circuit removes charge from the amplified signal before a positive integration phase of the integrator circuit. In one embodiment, the compensation circuit adds charge to the amplified signal during a negative integration phase of the integrator circuit, and the compensation circuit removes charge from the amplified signal during a positive integration phase of the integrator circuit.

[0064] In one embodiment, a non-transitory computer-readable medium includes logic that, when executed by a processor, causes the processor to apply a positive charge to an input of an integrator circuit via a compensation circuit. The integrator circuit integrates a signal transmitted by an electrode of a touch sensor and the positive charge to generate a first readout signal. The signal is based on a charge at an electrode of a touch sensor. The logic further causes the processor to apply a negative charge to the input of the integrator circuit via the compensation circuit. The integrator circuit integrates the signal and the negative charge to generate a second readout signal. The logic also causes the processor to detect a touch using the first readout signal and the second readout signal.In one embodiment, the logic further causes the processor to apply a positive charge to an input of a current amplifier circuit coupled to the input of the integrator circuit via the compensation circuit and to apply a negative charge to the input of the current amplifier circuit via the compensation circuit. In one embodiment, the logic further causes the processor to apply a positive charge to a built-in self-test bus via the compensation circuit and to apply a negative charge to the built-in self-test bus via the compensation circuit. In one embodiment, the first readout signal is generated during a negative integration phase of the integrator circuit, and the second readout signal is generated during a positive integration phase of the integrator circuit.In one embodiment, the positive charge is applied to the input of the integrator circuit before a negative integration phase of the integrator circuit, and the negative charge is applied to the input of the integrator circuit before a positive integration phase of the integrator circuit. In one embodiment, the positive charge is applied to the input of the integrator circuit during a negative integration phase of the integrator circuit, and the negative charge is applied to the input of the integrator circuit during a positive integration phase of the integrator circuit.

[0065] Embodiments of the present disclosure provide one or more technical advantages. For example, one embodiment improves the accuracy of touch sensor 102 by increasing the margin available for monitoring the first and second read signals, thereby also improving the signal-to-noise ratio of the electrical signals provided by a touch-sensor array. In another example, one embodiment enables runtime self-tests and diagnostic testing of touch-sensor controller 108 via a built-in self-test bus. Certain embodiments of the invention may include none, some, or all of the above technical advantages. One or more other technical advantages may be apparent to those skilled in the art from the figures, the description, and the claims appended hereto.

[0066] A computer-readable, non-transitory storage medium may include one or more semiconductor-based or other integrated circuits (ICs) (such as field-programmable gate arrays (FPGAs) or application-specific integrated circuits (ASICs)), hard disk drives (HDDs), hybrid drives (HHDs), optical disks, optical disk drives (ODDs), magneto-optical disks, magneto-optical drives, floppy disks, floppy disk drives (FDDs), magnetic tapes, solid-state drives (SSDs), RAM drives, SD cards or drives, or other computer-readable, non-transitory storage media, or any combination of two or more thereof. A computer-readable, non-transitory storage medium may be volatile, non-volatile, or a combination of volatile and non-volatile.

[0067] As used herein, “or” is inclusive and not exclusive, unless explicitly stated to the contrary or the context otherwise indicates. “A or B” therefore means “A, B, or both,” unless explicitly stated to the contrary or the context otherwise indicates. Furthermore, “and” means both individually and collectively, unless explicitly stated to the contrary or the context otherwise indicates. “A and B” therefore means “A and B, both individually and collectively,” unless explicitly stated to the contrary or the context otherwise indicates. Furthermore, components that have been described as “coupled” include those components regardless of whether they are directly or indirectly coupled with each other.

[0068] This disclosure encompasses numerous changes, substitutions, variations, alterations, and modifications to the example embodiments given herein that one skilled in the art would contemplate. Similarly, the appended claims, where appropriate, encompass all changes, substitutions, variations, alterations, and modifications to the example embodiments given herein that one skilled in the art would contemplate.A reference in the appended claims to a device or system, or a component of a device or system, that is adapted, capable of, configured, or operable to perform a particular function includes that device, system, or component, regardless of whether that particular function is activated, turned on, or unlocked, as long as that device, system, or component is adapted, capable of, configured, or operable to perform those functions.

Claims

[1] Device comprising: an integrator circuit (305); a compensation circuit (315) separate from the integrator circuit (305) and connected to the integrator circuit (305), the compensation circuit (315) comprising: a driver (400); a resistor (405) coupled to the driver (400); a capacitor (410) coupled to the resistor (405); and a demultiplexer (415) coupled to the capacitor (410), wherein the driver (400) is operable to: supplying a positive charge through the resistor (405), the capacitor (410), and the demultiplexer (415) to the integrator circuit (305) during a first period of time, the integrator circuit (305) being operable to integrate a signal and the positive charge to generate a first readout signal, the signal being based on a charge on an electrode of a touch sensor (102); and supplying a negative charge through the resistor (405), the capacitor (410) and the demultiplexer (415) to the integrator circuit (305) during a second period of time, the integrator circuit (305) further operable to integrate the signal and the negative charge to generate a second readout signal; and a readout circuit (310) operable to detect a touch based on the first readout signal and the second readout signal. [2] The device of claim 1, wherein the resistor (405) is a variable resistor. [3] The device of claim 1, wherein the capacitor (410) is a variable capacitor. [4] The device of claim 1, wherein the driver (400) uses a ground-based reference voltage as a supply voltage to remove an effect of a drift in a main supply voltage. [5] The apparatus of claim 1, wherein an output of the demultiplexer (415) is coupled to the integrator circuit (305), and an input of the demultiplexer (415) is coupled to the capacitor (410). [6] The apparatus of claim 1, wherein an output of the demultiplexer (415) is coupled to a current amplifier circuit (300), and an input of the demultiplexer (415) is coupled to the capacitor (410). [7] The apparatus of claim 1, wherein an output of the demultiplexer (415) is coupled to a built-in self-test bus, and an input of the demultiplexer (415) is coupled to the capacitor (410). [8] The apparatus of claim 1, further comprising a current amplifier circuit (300) coupled to the integrator circuit (305) and the compensation circuit (315). [9] The apparatus of claim 1, further comprising a built-in self-test bus coupled to the compensation circuit (315). [10] Device comprising: a touch sensor panel (106); an integrator circuit (305); a compensation circuit (315) separate from the integrator circuit (305) and connected to the integrator circuit (305), the compensation circuit (315) comprising: a driver (400); a resistor (405) coupled to the driver (400); a capacitor (410) coupled to the resistor (405); and a demultiplexer (415) coupled to the capacitor (410), wherein the driver (400) is operable to: supplying a positive charge through the resistor (405), the capacitor (410), and the demultiplexer (415) to the integrator circuit (305) during a first period of time, the integrator circuit (305) being operable to integrate a signal and the positive charge to generate a first readout signal, the signal being based on a charge on an electrode of the touch sensor panel (106); and supplying a negative charge through the resistor (405), the capacitor (410) and the demultiplexer (415) to the integrator circuit (305) during a second period of time, the integrator circuit (305) further operable to integrate the signal and the negative charge to generate a second readout signal; and a readout circuit (310) operable to detect a touch based on the first readout signal and the second readout signal. [11] The apparatus of claim 10, wherein the resistor (405) is a variable resistor. [12] The apparatus of claim 10, wherein the capacitor (410) is a variable capacitor. [13] The device of claim 10, wherein the driver (400) uses a ground-based reference voltage as a supply voltage to remove an effect of a drift in a main supply voltage. [14] The apparatus of claim 10, wherein an output of the demultiplexer (415) is coupled to the integrator circuit (305), and an input of the demultiplexer (415) is coupled to the capacitor (410). [15] The apparatus of claim 10, wherein an output of the demultiplexer (415) is coupled to a current amplifier circuit (300), and an input of the demultiplexer (415) is coupled to the capacitor (410). [16] The device of claim 10, wherein an output of the demultiplexer (415) is coupled to a built-in self-test bus, and an input of the demultiplexer (415) is coupled to the capacitor (410). [17] The apparatus of claim 10, further comprising a current amplifier circuit (300) coupled to the integrator circuit (305) and the compensation circuit (315). [18] The device of claim 10, further comprising a built-in self-test bus coupled to the compensation circuit (315).

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