Control unit for controlled shielding

Abstract

Circuit diagram, including: an analog control unit (102) that can be actuated to replicate a sensor voltage (104) at a capacitive sensor; a digital control unit (103); a shielding control unit (101) coupled to the analog control unit (102) and the digital control unit (103), wherein the shielding control unit (101) can be actuated to: to override the analog control unit (102) and activate the digital control unit (103) during one or more phases of a capacitive measurement of the capacitive sensor in order to control a controlled shield; and during one or more other phases of a capacitive measurement of the capacitive sensor, to override the digital control unit (103) and to activate the analog control unit (102) to drive the driven shield with a driven shield voltage that replicates the sensor voltage (104), wherein. the analog control unit (102) is an analog buffer which contains an input for receiving an output activation signal (105) from the shielding control unit (101).

Description

[0001] The subject of this disclosure relates generally to a control system for a controlled shield.

[0002] A capacitive touchscreen allows a user to interact with an electronic device without using a mouse or trackpad. When an object (such as a user's finger or stylus) touches or comes near the surface of a capacitive touchscreen, a change in capacitance occurs within the touchscreen at the point of contact or proximity. A touch sensor control unit processes this change in capacitance to determine whether an object is touching or near the touch sensor, or to determine the location of the touch or proximity to the touch sensor.

[0003] From US 9,252,769 B2 a capacitive touch sensor with an adjacently arranged guard ring is known, wherein the voltage of the guard ring essentially follows the voltage at the corresponding sensor plate.

[0004] In one embodiment, a circuit comprises: an analog drive unit that, in operation, drives a sensor voltage at a capacitive sensor; a digital drive unit; a shield drive control coupled to the analog drive unit and the digital drive unit, wherein the shield drive control can be operated to: override the analog drive unit and activate the digital drive unit during one or more phases of a capacitive measurement of the capacitive sensor in order to drive the driven shield; and override the digital drive unit and activate the analog drive unit during one or more phases of a capacitive measurement of the capacitive sensor in order to drive a driven shield with a driven shield voltage that replicates the sensor voltage.

[0005] In a further embodiment, a method comprises: providing a sensor voltage to a capacitive sensor; during one or more phases of a capacitive measurement of the capacitive sensor, activating a digital control unit to drive a driven shield; and during one or more other phases of the capacitive measurement, deactivating the digital control unit and activating the analog control unit to drive the driven shield with a driven shield voltage that replicates the sensor voltage.

[0006] In one embodiment, a touch measurement system comprises: a touch sensor; a controlled shield; a detection control circuit coupled to the touch sensor and actuated to generate a sensor voltage on the touch sensor; a detection circuit coupled to the touch sensor and actuated to measure the capacitance at the touch sensor; a control unit comprising: an analog control unit; a digital control unit; a shield control control circuit coupled to the analog control unit and the digital control unit, wherein the control control circuit can be operated such that, during one or more phases of a capacitive measurement of the touch sensor, it activates the digital control unit to control the shield;and during one or more phases of the capacitive measurement of the touch sensor, to override the digital control unit and activate the analog control unit to drive the controlled shield with a controlled shield voltage that replicates the sensor voltage. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a conceptual block diagram illustrating an exemplary hybrid-mode controlled shield for capacitive touch applications according to one embodiment. Fig. Figure 2 is a conceptual block diagram of an exemplary touch measurement system that uses a hybrid-mode controlled shield for capacitive touch applications, according to one embodiment. Fig. 3A and Fig. 3B includes exemplary waveforms representing the operation of a hybrid-mode controlled shield for capacitive touch applications according to one embodiment. Fig. Figure 4 is a flowchart of an exemplary process carried out by a hybrid-mode controlled shield for capacitive touch applications according to one embodiment. DETAILED DESCRIPTION Example system

[0007] In capacitive touch applications, it is often advantageous to have an electrode (“driven shield”) downstream of the touch electrode that is driven to the same potential as the touch electrode using an external or internal amplifier. The driven shield enhances the performance of the touch system in the presence of moisture and also provides noise shielding, improved touch sensitivity, and proximity detection. A driven shield is a device for shielding a sensor (e.g., a touch electrode) from being activated from any direction outside of its intended detection range. In one embodiment, a replica of the sensor signal is applied to an output on the back of the sensor via an analog buffer (e.g., an operational amplifier).This deflects the capacitive field from the back of the sensor to the front, increasing the signal strength and range of the sensor forward while blocking any detection on the back of the sensor. The operational amplifier should have a fast slew rate and rail-to-rail input and output so that the driven shield voltage can accurately replicate the actual sensor signal and provide the desired shielding effect. Operational amplifiers with fast slew rates and rail-to-rail input and output are expensive in terms of silicon area. As described below, a hybrid circuit topology, which uses a digital drive for one or more phases (e.g., a pre-charge phase) and an analog drive to provide a controlled shield voltage that matches the sensor voltage during one or more other phases (e.g.,replicating a capacitive touch measurement (a phase of shared charge), the use of a less expensive operational amplifier to implement the analog drive unit. Example circuit

[0008] Fig. Figure 1 is a conceptual block diagram illustrating an exemplary hybrid-mode controlled shielding circuit 100 for capacitive touch applications according to one embodiment. The circuit 100 comprises a shielding control unit 101, an analog control unit 102 (e.g., an operational amplifier, unity buffer amplifier, voltage follower), and a digital control unit 103 (e.g., a PAD control unit). The analog control unit 102 receives as inputs the sensor voltage 104 and the analog control unit output activation signal 105. The digital control unit 103 receives as inputs the digital control unit output activation signal 106 and the digital control unit output level 107.The shielding control unit 101 comprises a circuit that can be actuated to generate the analog control unit activation signal 105, the digital control unit output activation signal 106, and the digital control unit output level 107. In some embodiments, the shielding control unit 101 includes a circuit arrangement that can be used to decode signals used for sensor measurements in order to generate the output activation signals 105 and 106 for activating and deactivating digital and analog control units 102 and 103.

[0009] During a touch detection phase, the digital drive unit 103 pre-charges the driven shield to a rail voltage (VCC) or ground (GND) to match the pre-charge of the touch electrode. In one embodiment, the digital drive unit 103 can include one or more logic inverters with high current drive capability and an output activation function (e.g., a tristate device). During a charge-sharing phase, after the pre-charge phase, the digital drive unit 103 is deactivated and the analog drive unit 102 is activated, and can be driven to provide a driven shield voltage that replicates the voltage at the touch electrode (e.g., VCC / 2). The analog drive unit 102 can be a low-cost operational amplifier analog buffer or a voltage follower.Accordingly, circuit 100 is an example of a hybrid-mode controlled shielding circuit that uses a less expensive operational amplifier and a digital PAD driver (e.g., a logic inverter) in different phases of a capacitive touch measurement to generate a driven shielding voltage that accurately replicates the sensor voltage.

[0010] Fig. Figure 2 is a schematic diagram of an exemplary touch measurement system that uses a hybrid-mode controlled shield for capacitive touch applications, according to one embodiment. System 200 comprises a finite automaton (FSM) 201, a sensor drive / detection circuit 202, a shield drive / control circuit 101, and a capacitive sensor 203. The FSM 201 generates control signals for controlling the sensor drive / detection circuit 202 and the shield drive / control circuit 101. In one embodiment, the FSM 201 controls the various processes of a touch measurement by means of the sensor drive / detection circuits 202 and the shield drive / control circuit 101. The sensor drive / detection circuit 202 drives the sensor 203 (e.g., a touch electrode) and measures the capacitance of the sensor 203. The shield drive / control circuit 101 generates various output activation and level signals, as described with reference to Fig. 3B is described.

[0011] Fig. 3A and Fig. Figure 3B includes exemplary waveforms representing the operation of a shield controlled in hybrid mode, according to one embodiment. In this example, a touch measurement comprises 6 phases, which are referred to as phases 1 to 6 above. Fig. 3A are marked, with each phase being separated from other phases by vertical dashed lines. Fig. Figure 3A shows the sensor voltage waveform 301 as it goes through phases 1 to 6. Fig. Figure 3B illustrates waveforms 302, 303, and 304 for analog output activation, digital output activation, and digital output level signals, respectively. At the lower end of Fig. 3B contains the symbols "DD" for the digital control unit and "AD" for the analog control unit. These symbols indicate for each phase whether the analog control unit 102 or the digital control unit 103 is activated.

[0012] In Phase 1, the sensor is charged to VCC. Then, in Phase 2, the sensor voltage is reduced to an intermediate level. It should be noted that the intermediate level voltage in Phase 2 is unknown before the capacitive measurement. In Phase 3, the sensor voltage is reduced to VCC / 2. Phases 4 to 6 are the same as Phases 1 to 3, except that the sensor voltage waveform 301 is "inverted" with respect to the center line, which represents VCC / 2. In Phases 2 and 5, the sensor voltage is unknown before the capacitive measurement, so a simplified drive unit approach that drives the controlled shield to a predetermined level, for example, with a programmable resistor-capacitor (RC) slope, cannot be used, and an analog drive unit (e.g., an operational amplifier) ​​is required.Since only the analog drive unit can provide a controlled shield voltage that replicates the analog sensor voltage, the analog drive unit is used in phases 2, 3, 5, and 6. However, the digital drive unit is better suited for use in phases 1 and 4 because it performs better than the analog drive unit when the rails (VCC, GND) are reached. Additionally, dynamic replication of the sensor voltage is less critical in phases 1 and 4, as it will not affect the measurement accuracy (pre-charge phase).

[0013] An operational amplifier capable of generating an output signal that reaches the rails is expensive and consumes more power than one that does not. Furthermore, such expensive operational amplifiers are not as efficient as a digital driver at reaching the rails. The primary goal is to reach VCC or GND at the end of the phases. For phases 2, 3, 5, and 6, it is desirable for the driven shield voltage to dynamically replicate the sensor voltage, ensuring the driven shield voltage is as close as possible to the sensor voltage. The in Fig. The shielding circuit 100 shown, driven in hybrid mode, uses both a digital drive unit and an analog drive unit at different phases of a capacitive measurement to take advantage of the inherent benefits that each drive unit provides.

[0014] With reference to the in Fig. In the output activation and level waveforms shown in Phase 1, the digital output level waveform 304 is high, the digital output activation waveform 303 is high, and the analog output activation waveform 302 is low. This results in the deactivation of the analog control unit 102 and the activation of the digital control unit 103. In Phase 2, the digital output activation waveform 303 is low and the analog output activation waveform 302 is high. It is noted that the digital output level 304 is irrelevant because the digital output activation waveform 303 is low. This leads to the deactivation of the digital control unit 103 and the activation of the analog control unit 102. In phase 3, the digital output level waveform 304 is high, the digital output activation waveform 303 is low, and the analog output activation waveform 302 is high.This results in the analog control unit 102 remaining in effect and the digital control unit 103 remaining out of effect.

[0015] In phase 4, the digital output level waveform 304 is low, the digital output activation waveform 303 is high, and the analog output activation waveform is low. This results in the analog control unit 102 being deactivated and the digital control unit 103 being activated. In phase 5, the digital output level waveform 304 is low, the digital output activation waveform 303 is low, and the analog output activation waveform 302 is high. This results in the digital control unit 103 being deactivated and the analog control unit 102 being activated.

[0016] In phase 6, the digital output level waveform 304 is low, the digital output activation waveform 303 is low, and the analog output activation waveform 302 is high. This results in the analog control unit 102 remaining activated and the digital control unit 103 remaining deactivated. Example process

[0017] Fig.Figure 4 is a flowchart of an exemplary process 400 performed by a hybrid-mode controlled shield for capacitive touch applications according to one embodiment. In one embodiment, the process 400 begins by determining the start of a charge in a pre-charge phase of a capacitive measurement (401). During the pre-charge phase, the analog control unit is disabled (402) and the digital control unit is enabled (403). Disabling the analog control unit may involve disconnecting the analog control unit from the controlled shield. During a charge-sharing phase, the digital control unit is disabled (404) and the analog control unit is enabled (405). Disabling the digital control unit may involve disconnecting the digital control unit from the controlled shield.Activating the digital control unit may involve connecting the digital control unit to the controlled shield.

[0018] Although this document includes many specific application details, these should not be considered limitations on the scope of what could be claimed, but rather descriptions of features that may be specific to certain embodiments. Certain features described in this document in connection with separate embodiments may also be used in combination in a single embodiment. Conversely, various features described in connection with a single embodiment may also be implemented separately in several embodiments or in any suitable subcombination.Although features described above may be in certain combinations and may even be initially claimed as such, in some cases one or more features from a claimed combination may be extracted from the combination and the claimed combination may refer to a subcombination or variation of a subcombination.

Claims

[1] Circuit, comprising: an analog control unit (102) that can be actuated to replicate a sensor voltage (104) at a capacitive sensor; a digital control unit (103); a shielding control unit (101) coupled to the analog control unit (102) and the digital control unit (103), wherein the shielding control unit (101) can be actuated to: to override the analog control unit (102) and activate the digital control unit (103) during one or more phases of a capacitive measurement of the capacitive sensor in order to control a controlled shield; and during one or more other phases of a capacitive measurement of the capacitive sensor, to override the digital control unit (103) and to activate the analog control unit (102) to drive the driven shield with a driven shield voltage that replicates the sensor voltage (104), wherein. the analog control unit (102) is an analog buffer which contains an input for receiving an output activation signal (105) from the shielding control unit (101). [2] Circuit according to claim 1, wherein the activation of the digital control unit (103) or the analog control unit (102) comprises the electrical coupling of the digital control unit (103) or the analog control unit (102) with the controlled shield. [3] Circuit according to claim 1, wherein the shield control unit (101) can be actuated to generate one or more signals for activating and deactivating the digital and analog control units (102, 103) on the basis of one or more signals from a finite automaton (201). [4] Circuit according to claim 1, wherein the shielding control (101) can be actuated to decode one or more signals applicable to capacitive measurements in order to generate one or more output activation signals (105, 106) for activating and deactivating the digital and analog control units (102, 103). [5] Procedure, comprehensive: Providing a sensor voltage (104) for a capacitive sensor; during one or more phases of a capacitive measurement of the capacitive sensor, activation (403) of a digital control unit (103) to control a controlled shield; and during one or more other phases of the capacitive measurement, overriding (404) the digital control unit (103) and activating (405) the analog control unit (102) to drive the driven shield with a driven shield voltage that replicates the sensor voltage (104), wherein the analog control unit (102), which is an analog buffer, has an input for receiving an output activation signal (105) from a shielding control unit (101). [6] Method according to claim 5, wherein the activation of the digital control unit (103) or the analog control unit (102) comprises the electrical coupling of the digital control unit (103) or the analog control unit (102) with the controlled shield. [7] Contact measurement system, comprising: a touch sensor (203); a controlled shield (105); a detection control circuit (202) which is coupled to the touch sensor (203) and can be actuated to generate a sensor voltage on the touch sensor (203); a detection circuit (206) which is coupled to the touch sensor (203) and can be actuated to measure the capacitance at the touch sensor (203); a control unit, comprising: an analog control unit (102); a digital control unit (103); a shielding control circuit (101) coupled to the analog control unit (102) and the digital control unit (103), wherein the shielding control circuit (101) can be actuated to: to activate the digital control unit (103) during one or more phases of a capacitive measurement of the touch sensor (203) in order to control the controlled shield; and during one or more other phases of the capacitive measurement of the touch sensor (203) to override the digital control unit (103) and to activate the analog control unit (102) in order to drive the driven shield with a driven shield voltage that replicates the sensor voltage, wherein the analog control unit (102) is an analog buffer which includes an input for receiving an output activation signal from the shielding control unit (101). [8] System according to claim 7, wherein the activation of the digital control unit (103) or the analog control unit (102) comprises the electrical coupling of the digital control unit (103) or the analog control unit (102) with the controlled shield. [9] System according to claim 7, wherein the shielding control unit (101) can be actuated to generate one or more signals for activating and deactivating the digital and analog control units (103, 102) based on one or more signals from a finite automaton (201). [10] System according to claim 7, wherein the shielding control unit (101) can be actuated to decode one or more signals applicable to capacitive measurements in order to generate one or more output activation signals for activating and deactivating the digital and analog control units (103, 102).

Images