Patent Application
20190187854
This relates generally to integrated circuits, and more particularly to estimating a touch force applied in a touch system.
A touch system includes interfaces such as touch screens that can include an input device and output device layered on top of an electronic visual display of an information processing system. For example, a user can provide input or control the information processing system through simple or multi-touch gestures by touching the screen with a special stylus and/or one or more fingers. Touch screens are common in devices, such as game consoles, personal computers, tablet computers, electronic voting machines, and smart phones. These interfaces can also be attached to computers or, as terminals, to networks.
To detect user gestures such as touching via the touch system interface, common technologies include resistive touch screens and capacitive touch screens can be employed. An example capacitive touch screen panel consists of an insulator such as glass, coated with a transparent conductor such as indium tin oxide. As the human body is also an electrical conductor, touching the surface of the screen results in a distortion of the screen's electrostatic field, measurable as a change in capacitance. Different technologies may be used to determine the location of the touch. In some touch systems, mutual or self capacitance can be measured by transmitting a signal on a row/column of the touch screen interface and receiving the signal on a respective column/row. When the touch occurs close to a row/column intersection, the received change in signal strength and/or signal phase changes. This change isolates the touch location. In addition to detecting touch location, the amount of touch force applied at a given location may be desired. Strain force resistors are often coupled to the mutual capacitance row/column intersections to determine the force applied. Such added resistors to determine touch force adds significant cost to the system.
In described examples, a system includes a receiver that receives an output signal from a touch system to detect a user's touch. The output signal is received in response to an excitation signal that is applied to a row or column of the touch system. A touch force analyzer determines an indication of a touch force applied to the touch system based on detecting a change in phase of the output signal received from the row or column of the touch system in response to a touch applied to the touch system.
In another example, a system includes a receiver that receives output signals from a touch system to detect a user's touch. The output signals are received in response to at least two out of phase excitation signals applied to at least two rows or columns of the touch system. A touch force analyzer determines an indication of a touch force applied to the touch system based on detecting a change in phase in at least one of the output signals received from the respective rows or columns of the touch system in response to a touch applied to the touch system.
In yet another example, a method includes transmitting an excitation signal to at least one row or column of a touch system. The method includes receiving an output signal from the touch system in response to the excitation signal; the output signal having an amplitude and phase that varies based on application of a touch to the touch system. The method includes comparing the phase of the output signal received from the row or column of the touch system responsive to the application of the touch to a predetermined phase of the output signal to determine a phase change for the output signal. The method includes determining an indication of touch force applied to the touch system based on the determined phase change.
In example embodiments, received signals from a touch system are analyzed with respect to a received signal phase to determine a touch force of a user's touch applied to the rows or columns of the touch system. The touch system includes intersecting wires that make up the rows and columns of the touch system and include capacitive and resistance properties. As touch force is applied to the rows and columns, the resistance of the intersecting wires changes based on the amount of force applied (e.g., via finger or stylus). Such change in resistance can be detected as a change in phase of a received signal that is received in response to an excitation signal (or signals) applied by a transmitter to the touch system. When no touch force is applied to the touch system, a predetermined phase for the received signal can be observed and stored. When differing amounts of touch force are applied to the touch system, the phase changes relative to the predetermined phase. For example, if no touch force is applied, one phase value can be detected and stored. If maximum touch force is applied, a different phase in the received signal can be detected and stored. These two stored phase values can be utilized to detect touch forces between the minimum (no touch force applied) and maximum force applied by interpolating between the phase values of the received signal when an intermediate force is applied to the touch system. In another example, predetermined phase tables can be constructed based on measured forces applied to the touch system. Based on where a received signal phase is with respect to a given phase in the phase table, the amount of touch force can be determined based on a comparison of the received signal phase to the phase table.
In another example, touch location is (e.g., place where finger or stylus touches touch system) determined by analyzing the received amplitude of the received signal from the touch system that has been excited by one or more excitation signals from a transmitter. Based on the touch location (e.g., the row(s) or column(s) where the touch occurred), the respective phase of the receive signal can be determined (e.g., before or after determined location) for the given touch location (or locations). The received signal can be multiplied by a sine and cosine function and then low pass filtered by a digital processing circuit (e.g., digital signal processor). The multiplication and filtering isolates the real and the imaginary alternating current components of the received signal where the arctangent between the real and the imaginary components yield the phase (e.g., phase angle) of the received signal which can then be compared to predetermined phase angles/measurements to determine an indication of force applied. In some examples, touch force can be determined across multiple row and column intersections to determine how force is distributed across the touch system and per a given area of a touch panel of the touch system. Touch forces can be determined by interpolating between maximum and minimum touch force/phase values, comparing to a table of phase/force values, and/or averaging phase measurements over the course of time to determine phase values for the touch forces that are applied over time.
The touch system can be excited by a transmitter that transmits excitation signals that are out of phase with respect to each other (e.g., a sine wave generated as one excitation signal and a cosine wave generated as another excitation signal). At least one of the of excitation signals can be transmitted to at least one row or column of a touch system and at least one other of the excitation signals is concurrently transmitted to at least one other row or column of the touch system. An output signal having a combination of signals from each of the excitation signals can be received by a receiver in response to the excitation signals transmitted to the touch system. Receiver circuits extrapolate the row or column information from the output signal based on the phase of the excitation signals. For example, in a two phase excitation system, at least two receiver circuits include a summing junction to extrapolate signal phases from the output signal to determine which of at least two rows or columns was touched. After the touch location is determined, signal phase analysis as described herein can be utilized to determine the touch force applied to the touch system.
The receiver signal 170 can be analyzed by a touch location analyzer 180 to determine a touch location on the touch system 120 and by a touch force analyzer 184 to determine the touch force applied to the respective location. The touch location analyzer 180 can utilize changes in received signal amplitudes and/or phase in response to the touch to determine touch location as described hereinbelow with respect to
The touch force analyzer 184 then determines an indication of the touch force by interpolating between the minimum and maximum phase change, where determined phases closer to the minimum phase can be associated with less touch force applied and phase changes associated with the maximum phase change can be associated with greater touch forces. A phase change detected about one-half way between the minimum and maximum phase change values can be associated with an intermediate value of maximum touch force applied. The intermediate value and interpolation can be based on linear functions, non-linear functions, or a combination of linear and non-linear functions that are related to the change in resistance of the row/column intersections based on the application of touch force to the touch panel of the touch system.
In one example, the touch force analyzer 184 multiplies the received output signal at 170 by a sine function and a cosine function to determine the real and imaginary phase components of the output signal. For example, the signal at 170 can be multiplied by the sine and cosine of 2πft where f is the frequency of the excitation signal and t is time. The touch force analyzer 184 can apply the real and imaginary phase components of the output signal to a low pass filter to generate filtered real and imaginary phase components of the output signal. This can include determining a phase angle for the output signal by computing the arctangent of the filtered real phase component divided by the imaginary filtered phase component of the output signal. In one example, a phase angle lookup table can be generated that correlates known force values applied to the touch system 120 with determined phase angles by the touch force analyzer 184 to the respective measured force. The touch force analyzer 184 determines an indication of touch force applied to the touch system by comparing the phase angle for the output signal at 170 to the determined phase angles for the output signal to the determined table phase angles, to determine the closest match to the respective force value. A calibration procedure can be conducted to generate the phase table where force instrumentation is applied to the touch system 120 and where phase angles are recorded in the lookup table as differing forces are applied by the instrumentation.
For example, the touch location analyzer 180 utilizes the amplitude and/or phase of the output signal 140 to determine one or more touch locations that touch force is applied to the touch system 120. If multiple touch locations are detected across the touch system 120, the touch force analyzer 184 can analyze touch force across the one or more touch locations with respect to a given area of a touch panel for the touch system 120, which encompasses the one or more touch locations, to quantify the touch force that is distributed across the given area of the touch system and panel. For example, forces can be averaged across two or more locations in a given area of the touch panel of the touch system to determine the force distributed across the given area. As an example, if force is detected between two rows (e.g., adjacent rows) that are known to occupy a given surface area of the touch panel in square millimeters, the force can be average across the given area to determine the distribution of force for the given area.
As noted above, the transmitter 110 can include at least one alternating current (AC) source to generate excitation signals to the touch system. In one example (see, e.g.,
A digital processing circuit (e.g., digital signal processor and associated digital converters) 250 is configured to perform the phase multiplication and filtering operations described herein. The combination of Rs, Cs, and Cf define a transfer function for the system 200 wherein the transmit wave function is defined as 2πft and the circuit transfer function defined as Cs/Cf(1+j2πftRsCs)2πft. The circuit transfer function allows the touch location analyzer to determine changes in phase based on changes in impedance Rs responsive o applying force to the contact surface of the touch system. The changes in phase can be utilized to detect corresponding differences in touch force applied to the touch system. As noted previously, the touch force analyzer can multiply the received output signal by sine and cosine functions to determine the real and imaginary components of the output signal. The real and imaginary components are digitally low pass filtered. Then, an arctangent function can be computed from the quotient of the real and imaginary components to compute the phase angle of the output signal responsive to the applied force. Based on changes in the phase angle due to the change in Rs when touch force is applied, the amount of touch force applied to the touch system can be determined from the phase change.
The transmitter 310 includes at least one alternating current (AC) source 330 to generate the excitation signals 314 to the touch system 320 where each of the excitation signals in one example are transmitted out of phase with respect to each other excitation signal. At least two of the excitation signals 314 can be generated at the same frequency or at different frequencies with respect to each other via the AC source 330. Different frequencies can be employed for the excitation signals 314 so long as they remain in their given phase relationship (e.g., orthogonal) over the integration time, which includes both the time it takes to transmit and receive signals in response to the excitation signals 314.
In one example, at least two of the excitation signals 314 can be transmitted to at least two rows or columns of the touch system 320 where the excitation signals are at least 90 degrees out of phase with respect to each other when transmitted to the respective rows or columns. In other examples, more than two excitation signals 314 can be transmitted to the touch system to further reduce scan time of the touch system. As used herein, the term “scan time” refers to the amount of time it takes to excite all of the rows or columns of the touch system 320. In single phase excitation systems, each row or column had to be excited individually to detect the presence of a touch shown as user input 334. In the multiphase system described herein, multiple rows or columns can be analyzed concurrently to reduce the scan time in half in a two phase excitation system (or reduced more if more than two excitation signals utilized).
As a further example, the touch system 320 can be a mutual capacitance touch system (see e.g.,
By providing multiphase signaling and analysis as described herein to reduce scan time of the touch system, a portion of the touch system 320 can be excited by the transmitter 310 during one scanning sequence and analyzed by the receiver 350 based on the scanning of the portion. At least one other portion of the touch system 320 can be excited by the transmitter 310 during another scanning sequence and analyzed by the receiver based on the scanning of the at least one other portion. In this manner of multiphase signaling and processing, hardware complexity can be reduced because multiple rows or columns can be scanned using fewer connection nodes to the touch system 320 to determine a touch location and touch force to the system. For example, in a two phase excitation system, half of the row or column connections from conventional systems can be reduced.
A touch location analyzer 380 compares an amplitude of the output signals received from different rows or columns of the touch system. A ratio of the output signal amplitudes from the different rows or columns of the touch system can be utilized to determine the location of the user's touch relative to the rows or columns of the touch system. For example, if the amplitude received from one row was at 20% peak and the amplitude received from another row was at 80% peak, touch location can be calculated base on the ratio of 20/80, such that 80 percent of the users touch force is affecting one row and 20% of the user's touch force is affecting the other row. As used herein, peak signal amplitude refers to the maximum signal received when no touch force is applied. If it is known that 10 millimeters separate the rows for example, the touch location is approximately is approximately 8 millimeters away from one row (the 20% peak row) and about two millimeters away from the other row (e.g., 80% peak row).
Based upon determining the touch location, a touch force analyzer 384 can then determine the touch force that has been applied at the respective location (or locations in the case where force is applied across one or more rows or columns). As described previously, the touch force analyzer 384 can determine a touch force applied to the touch system 320 based on computing a change in phase of the output signal 340 received from the row or column of the touch system after a touch is applied to the touch system. The touch force analyzer 384 can determine the change in phase of the output signal by comparing the received phase of the output signal with respect to a predetermined phase of for output signal, such as the phase of the output signal when no touch force or other known amount of force is applied to the touch system 320.
For example, the touch force analyzer 384 multiplies the output signal 340 by a sine function and a cosine function, such as disclosed herein, to determine each of the real and imaginary phase components of the output signal. The touch force analyzer 384 also applies the real and imaginary phase components of the output signal to a low pass filter to generate filtered real and imaginary phase components of the output signal. Responsive to such filtering, the touch force analyzer 384 can determine a phase angle for the output signal 340 by computing the arctangent of the filtered real phase component with respect to the imaginary filtered phase component of the output signal. In one example, a phase angle lookup table is programmed to correlate a range of measured forces applied to the touch system (between minimum and maximum expected forces) with determined respective phase angles at each force measurement. The touch force analyzer 384 determines touch force applied to the touch system by comparing the computed phase angle for the output signal (provided by touch force analyzer 384) to the determined phase angles in the table and outputs a corresponding value indicative of the applied force.
The transmitter 420 can include at least one numerically controlled oscillator (NCO) 450 which drives a digital to analog converter (DAC) 454, which in turn drives an output amplifier 458 to provide the signals 434. The receiver 410 can include an analog front end 459 that includes an input stage or amplifier 460 which drives an analog to digital converter (ADC) 462. Output from the ADC can be multiplied with a signal from an NCO 464 via a multiplier at 466 which is then summed at 468. As described herein with reference to
To reduce the footprint of the touch controller circuit in certain examples of existing single excitation systems, one can reduce the number of receive and/or transmit channels. However, this increases the scan time. The scan time increases by the same factor as the hardware reduction. For example, if the hardware is reduced by a factor of 2, the scan time increases by a factor 2 to obtain the same performance level. However, an increase in scan time decreases the responsiveness of the touch screen controller. In the system and methods described herein, multiphase signaling is provided where two or more rows/columns of the touch panel 520 are excited concurrently effectively reducing the scan time. When the scan time is reduced, hardware complexity can likewise also be reduced.
As shown in the example of
At the receiver circuit 620, the received signal represented as 2Asin(ωn+φ)+2Bcos(ωn+θ) in this example, can be received via analog front end (AFE) 628 and can be match filtered with the transmitted SIN and COS signal in the digital domain via summing junctions 630 and 634, respectively. For example, output from the summing junction 630 can be represented as −Acos(2ωn+φ)+Acos(φ)+Bsin(2ωn+θ)−Bsin(θ), and output from the other summing junction can be represented as Asin(2ωn)+Asin(φ)+Bcos(2ωn+θ)+Bcos(θ). These signals can be filtered via low pas filters 640 and 644, respectively to produce output signals Acos(φ)−Bsin(θ) and Bcos(θ)+Asin(φ), respectively. Output from the filters 650 can be analyzed for amplitude and/or phase differences by a location analyzer 650 to determine touch locations between rows or columns of the touch system.
Because the signals can be maintained in a given phase relationship with respect to each other (e.g., orthogonal), changes in the signal strength of the SIN indicates a touch on row A and the corresponding receiver while any change in COS will give the touch information on rowB and the receiver of interest. Thus, information about two touch locations can be obtained concurrently. This implies that scanning in adjacent row pairs, the touch image can be obtained in half the time. As described hereinabove, more than two adjacent rows can be concurrently scanned using signal having known out-of-phase signals, and respective output signals analyzed. One-half the number of receivers can be employed in an example to facilitate scanning the panel twice (e.g., getting half the entire panel information from the first scan and one half from the second scan). Thus, the total scan time using multiphase stimulation remains substantially the same while the hardware complexity is reduced. In some example, the receive channel can be built with a higher dynamic range to account for interference. Therefore, sending multiphase signals does not impact the individual receiver design. Thus, a factor of two in hardware improvement can be easily obtained using two excitation signals. This can also be easily extended to larger number of concurrent excitations.
In view of the structural and functional features described hereinabove, an example method is described with reference to
In this description, the term “based on” means based at least in part on. Similarly, the term “in response to” means in at least response to. Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.
