Patent Application
20210191539
The disclosure generally relates to a touch panel, and more specifically, to a touch panel with an analog front-end circuit having a noise cancellation that reduce the influence of environmental noise.
In a touch panel, an analog front-end (AFE) circuit is an interface between the touch sensors disposed on a display and a back-end circuit that processes touch sensing signals generated by the touch sensors for touch detection. However, there are noises from various sources such as static, display panel, power supply, other circuits disposed in the touch panel, other objects near the touch panel, or any other undesired voltage or current. These noises affect the touch sensing and the output dynamic range of the AFE circuit. For example, voltage or current representing electrical noise may be input into the AFE circuit as a touch sensing signal, which may be stored in a capacitor with in the signal path such as a capacitor in the integrator. The energy of the noise would affect the output of the AFE circuit. That is, the output of the AFE circuit would carry the energy representing the electrical noise that is stored in the capacitor and reduce the output dynamic range (a ratio between the largest and smallest outputs the integrator may output) of the integrator of the AFE circuit. In addition, the stored energy of the noise may also be mistakenly processed as a touch event occurred on the touch panel.
In the disclosure, an analog front-end (AFE) circuit is coupled to a touch panel. The AFE circuit includes a first AFE channel and a noise reference circuit. The first AFE channel is coupled to a first terminal connected to the touch panel, and configured to process a first sensing signal received by the first terminal. The first AFE channel includes a first integrator which has an input terminal coupled to the first terminal. The noise reference circuit is coupled between the input terminal of the first integrator in the first AFE channel and a second terminal connected to the touch panel, and configured to reverse a second sensing signal received from the second terminal, and couple the reversed second sensing signal to a common node between the first integrator and the first terminal.
In the disclosure a touch display apparatus includes a touch panel and a touch display driving circuit. The touch panel includes a plurality of electrodes, which are used as common electrodes in display periods and as a plurality of touch sensors in touch periods. The touch display driving circuit includes a touch analog front-end (AFE) circuit, which includes a plurality of AFE channels. Each the plurality of AFE channels receives a input signal through a terminal of the touch display driving circuit coupled to a corresponding touch sensor of the plurality of touch sensors. Each of the plurality of AFE channels includes a first AFE channel and a second AFE channel. The first AFE channel includes a first integrator having an input terminal coupled to the first terminal receiving a first sensing signal. The second AFE channel includes an input amplifier. The second AFE channel is coupled between the input terminal of the first integrator in the first AFE channel and a second terminal connected to the touch panel. The second AFE channel is configured to generate a reversal input signal based on a second sensing signal received by the second terminal and couple the reversal input signal to a common node between the first integrator and the first terminal.
Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
The following disclosure provides many different embodiments, or examples, for implementing different features of the present disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are; of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
In the disclosure, an AFE circuit is designed to cancel environmental noises by utilizing neighboring AFE channels, so as to improve the influence of the noises on the output dynamic range of the AFE circuit. The AFE channels may be coupled to a region of touch sensors, where the touch sensors of that region may be disposed within a proximity or having routing traces that are within proximity. The touch sensor or the routing traces of the touch sensors may be exposed to various sources that emit noises (e.g., power circuitry, static, or other electromagnetic signals). These touch sensors within the proximity would also be exposed to the same noise, and therefore, the noises may be eliminated or reduced by utilizing the neighboring AFE channels that receive signals from the touch sensors disposed in the same vicinity. The embodiments of the disclosure utilize the noise being received (or detected) by the neighboring AFE channels to perform a noise cancellation that eliminate or reduce the influence of the noise.
The touch control circuit 20 includes an AFE circuit 100 and a back-end processing circuit 101. The AFE circuit 100 includes a plurality of AFE channels 110[1]-110[n] and a plurality of sensing terminals T[1]-T[n], and each sensing terminal is coupled to a corresponding AFE channel for receiving an input signal from a sensing line in the touch panel. The back-end processing circuit 101 may include a processor, a memory and any suitable data processing circuitry (a processor, a combination of analog and digital circuits) to perform various operations, such as one or more microprocessors, digital signal processor (DSP) one or more application specific processors (ASICs), or one or more programmable logic devices (PLDs). In some cases, the back-end processing circuit 101 may be implemented by digital circuitry to realize one or more algorithms. In some other cases, the back-end processing circuit 101 may execute programs or instructions (e.g., an operating system or application program) stored on a suitable article of manufacture, such as the local memory and/or the main memory storage device (not shown). In addition to instructions for the processor, the local memory and/or the main memory storage device may also store data to be processed by the back-end processing circuit. For example, the local memory may include random access memory (RAM) and the main memory storage device may include read only memory (ROM), rewritable non-volatile memory such as flash memory, or the like.
The touch screen 10 includes a select circuit 120 and a touch panel 150. The touch panel 150 includes a plurality of sensing lines 153[1]-153[K] (i.e., 153[1, 1] thru 153[m, n]) and a plurality of touch sensors 151 arranged in an array having M columns and N rows, where N and M are positive integers and K equals M by N. Each of touch sensors 151 may be coupled to one of sensing lines 153[1]-153[K]. Since the number of the plurality of AFE channels 110[1]-110[n] are limited, the plurality of sensing lines 153[1]-153[K] are not simultaneously but time-divisionally connected to the touch control circuit 20 through select circuits. With reference to
As mentioned above, the energy of the noise may be stored in a capacitor CF of the integrator 111[k], which affects the output dynamic range of the first AFE channel 110[k]. In the embodiment, with or without the input capacitance Cin generated by the touch object, the configuration of coupling the second AFE channel 110[k+1] to the first AFE channel 110[k] would cancel the noise received at the first terminal T[k]. In other words, the configuration prevents the energy of the noise signal to be stored in the capacitor of the integrator 111[k].
In the embodiments, each of the first and second AFE channels 210[k], 210[k+1] includes an input amplifier 213[k], 213[k+1], current conveyors 215[k], 217[k], 215[k+1], 217[k+1], and an integrator 211[k], 211[k+1] for processing a sensing signal received from the corresponding terminal. The input amplifier 213[k], 213[k+1] may be a differential amplifier having unity gain. Each of the input amplifier 213[k], 213[k+1] includes an inverting input terminal, a non-inverting input terminal, a first output terminal, and a second output terminal. The inverting input terminal is coupled to the corresponding terminal of the AFE circuit to receive a sensing signal received by the corresponding terminal, and the non-inverting input terminal is coupled to a touch driving signal (VTX). The touch driving signal Vtx may be a periodic square wave signal generated by a voltage regulator circuit (not shown) in the touch control circuit 20, or may be generated by switching between a high voltage and a low voltage which define the high level and the lower level of the touch driving signal Vtx. The touch driving signal is provided to the touch sensors to be sensed by the feedback loop of the input amplifier 213. The first output terminal of the input amplifier 213 is configured to output an input signal, while the second output terminal of the input amplifier is configured to output a reversal input signal having the same magnitude but opposite polarity with respect to the input signal. The inverting input terminal of the input amplifier may also be coupled to the first output terminal as a feedback loop. The first output terminal is coupled to a first current conveyor having a first multiplier (denoted by a), or referred to as a first scale factor, that scales the input signal. The second output terminal is coupled to second current conveyor having a second multiplier (denoted by β) that scales the reversal input signal. The first current conveyor then outputs a scaled input signal to the integrator. The second current conveyor outputs the scaled reversal input signal to other AFE channels for noise cancellation in the other AFE channels.
With reference to the first AFE channel 210[k] as illustrated in
In the embodiment, the current conveyors 215[k], 215[k+1], 217[k], 217[k+1] of the first and second AFE channels 210[k], 210[k+1] may be utilized as parameters that enables adjustments on the scaling of the respective input signal. The multiplier (i.e., α, β) of the current conveyors may be configured to fine tune the noise cancellation of each AFE channel. For example, the multiplier β of the second current conveyor that scales the reversal input signal may be configured to scale down the reversal input signal that is to be transmitted to other AFE channels to match the noise component received in the other AFE channels, so that the touch input signal from the touch sensor may be preserved. The multiplier of the current conveyors between the AFE channels may be the same or different. In some embodiments, the multipliers of each AFE channel may be configured respectively to be different. In some other embodiments, the first current conveyor 215 may be omitted in all or some of the AFE channel 210, which pass the first input signal I1 without scaling. The input signal of the AFE channel without the first current conveyor 215 would then be ICH1=I1[k]+βI2[k+1] In the embodiments, the multipliers α, β are positive integers that are designed to remove the noise signal without eliminating the touch sensing signal of the AFE channel. In the embodiments, the multiplier α is greater than the multiplier β. For example, the multipliers α, β may be 2 and 1, respectively. In other words, the first input signal I1[k] propagating on the first AFE channel 210[k] may be scaled by multiplier α, i.e., 2, while the second input signal I2[k+1] propagating on the second AFE channel 210[k+1] may be scaled by multiplier β, i.e., 1. Accordingly, the noise signal N[k+1] may be subtracted from the touch sensing signal I1[k] without eliminating the touch sensing signal received from the terminal T[k]. The 1 to 2 ratio between the multipliers α, β is used as an example. In other embodiments, the multipliers α, β may have any ratios for obtaining an accurate result in detecting the touch sensing signal and removing the noise signals. For example, a ratio of multiplier a to multiplier β may be 3 to 1, 3 to 2, 5 to 1, or any other ratios.
In the embodiment, the third AFE channel 210[k−1] that includes an input amplifier 213[k−1], a first current conveyor 215[k−1], a second current conveyor 217[k−1], and an integrator 211[k−1]. The input amplifier 213 [k−1] receives the noise signal N[k−1] as a third sensing signal. In an occurrence of a touch event, the input amplifier 213[k−1] would also receive a touch input signal regarding to the input capacitance Cin[k−1] in addition to the noise signal N[k−1]. In response to the receipt of the noise signal N[k−1] (or the touch input signal), the input amplifier 213[k−1] outputs a third input signal I1[k−1] to the first current conveyor 215 [k] and a third reversal input signal I2[k−1] having opposite polarity with respect to the third input signal I1[k−1] to the second current conveyor 217[k−1] based on the third sensing signal. The third input signal I1[k−1] would be transmitted to the integrator 211[k−1] through the first current conveyor 215[k−1], where the third input signal I1[k−1] may or may not be scaled by the first current conveyor 215[k−1]. The third reversal input signal I2[k−1] would be coupled to the node C of the first AFE channel 210[k] (i.e., the signal path of the first input signal I1[k]) through the second current conveyor 217[k−1] for noise cancellation on the first AFE channel 210[k]. In other words, the first AFE channel 210[k] would receive two scaled reversal input signals I2[k+1], I2[k−1] for noise cancellation. That is, the channel input signal ICH1 received by the integrator 211[k] of the first AFE channel 210[k] may be obtained as follow:
ICH1=αI1[k]−(β[k+1]I2[k+1]+β[k−1]I2[k−1]).
The multipliers β[k], β[k+1], β[k−1] of the second current conveyors in the first, second and third AFE channels 210[k], 210[k+1], 210[k−1] may be the same or different according to the design requirements. For example, the multipliers β[k+1], β[k−1] of second current conveyor in the second and third AFE channels 210[k+1], 210[k−1] may be predetermined to cancel the noise signal N[k] in the first AFE channel 210[k].
ICH1=αI1[k]−(β1[k+1]I2[k+1]+β2[k−1]I3[k−1]).
ICH2=αI1[k+1]−(β1[k+2]I2[k+2]+β2[k]I3[k]).
ICH3=αI1[k−1]−(β1[k]I2[k]+β2[k−2]I2[k−2]).
Since the touch sensors within a vicinity would experience similar environmental noise, noise cancellation may be effectively performed by utilizing the neighboring AFE channels. Based on the embodiments disclosed above, the input amplifier of the AFE circuit may be configured to output a signal having opposite polarity with respect to the signal received from the touch sensor. The signal having opposite polarity may be coupled to a neighboring AFE channel to perform noise cancellation. In a case of no touch event, the noise received by the AFE channel may be eliminate or reduced by the signal having opposite polarity. In a case where there is a touch event, the signal may be scaled by the predetermined multiplier of the current conveyor in the neighboring channel(s) and used to extract the noise component of the AFE channel. Accordingly, the output dynamic range of the AFE circuit may be improved by eliminating the influence of the noise on the capacitor, and the touch event may be accurately determined without the noise component.
The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the detailed description that follows. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.
This application claims the priority benefit of U.S. provisional application Ser. No. 62/950,893, filed on Dec. 19, 2019. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
| Number | Date | Country | |
|---|---|---|---|
| 62950893 | Dec 2019 | US |
