Methods and touch devices using multiple sampling frequencies

Techniques for using multiple sampling frequencies to detect the location of touch inputs of a user at a touch panel of a touch device. A determination is made as to which of and second sampling frequencies is provided to a receiver for use in sampling the touch inputs from the touch panel. The user touch inputs are first sampled from the touch panel during first and second successive time frames using first and second different sampling frequencies, respectively.

TECHNICAL FIELD

The present disclosure relates generally to touch devices.

BACKGROUND

Touch sensors or touch panels have become a popular type of user interface and are used in many types of devices, such as mobile phones, personal digital assistants (PDAs), navigation devices, video games, computers, etc., collectively referred to herein as touch devices. Touch devices recognize a touch input of a user and obtain the location of the touch to effect a selected operation.

A touch panel may be positioned in front of a display screen such as a liquid crystal display (LCD), or may be integrated with a display screen. Such configurations, referred to as touch screens, allow the user to intuitively connect a pressure point of the touch panel with a corresponding point on the display screen, thereby creating an active connection with the screen.

SUMMARY

Described herein are methodologies for detecting the location of touch inputs of a user at a touch device. In one embodiment, a determination is made as to which of first and second sampling frequencies is provided to a receiver for use in sampling touch inputs of a user from a touch panel of the touch device. The touch inputs are sampled from the touch panel during first and second successive time frames using first and second different sampling frequencies, respectively.

Another embodiment is directed to a touch device configured to detect the location of touch inputs of a user at a touch panel through the use of multiple sampling frequencies. The touch device may include a touch panel configured to sample a touch input of a user, and a control circuit comprising a driver, a receiver, a sampling frequency generation circuit, and a microcontroller (MCU). The receiver is configured to sample touch inputs from the touch panel and the sampling frequency generation circuit is connected to the receiver and is configured to generate first and second sampling frequencies in first and second successive time frames. The MCU is configured to determine which of the first and second sampling frequencies is provided to the receiver for use in sampling the touch inputs.

DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1is a block diagram of a prior art touch device10comprising a capacitive touch panel15and a control circuit20. Control circuit20may include a driver25, a receiver30, a microcontroller (MCU)35, and a clock40.

Driver25is connected to a plurality of drive signal lines45(1)-45(N), while receiver30is connected to a plurality of sense signal lines50(1)-50(N). As is well known in the art, drive signal lines45(1)-45(N) and sense signal lines50(1)-50(N) are connected to drive and sense electrodes (not shown) in touch panel15to form a matrix of electrode pairs (overlapping drive and sense electrodes) that are used to sense the location (X and Y coordinates) of a user touch input (a user's touch). In operation, driver25provides voltage pulses to the drive electrodes, thereby resulting in an electric field between the drive electrodes and the sense electrodes. The sense electrodes receive or sink the generated electric field via a coupling capacitance, which results in a current signal. Sense signal lines50(1)-50(N) conduct this current signal to receiver30.

If a user touches touch panel15, the coupling between pairs of one or more electrodes will increase at the location of the touch. Receiver30detects this increase in the coupling (via changes in the received current), and MCU35can use this information to determine the X and Y location of the user touch input.

As is known in the art, receiver30is not configured to continuously detect increases in the coupling between all electrode pairs, but rather the receiver30samples the capacitive couplings in a predetermined pattern in accordance with a predetermined sampling frequency. This sampling frequency is controlled by MCU35via clock40which may be, in practice, a voltage controllable oscillator (VCO). In other words, based on one or more control signals55received from MCU35, a sampling frequency60is generated by VCO40for use by receiver30in receiving data representing the coupling between electrode pairs.

In certain circumstances, noise may interfere with the sampling frequency, thereby degrading the ability of touch device10to accurately determine the position of user touch inputs. If noise is detected, control circuit20can be configured to change the sampling frequency generated by VCO40to a different frequency that is not interfered with by the noise. However, during the period of time to effect the sampling frequency change, receiver30may not accurately obtain touch information. This period of time in which user touch inputs are not accurately sampled may make the touch panel feel unresponsive to the user. Moreover, it may take several attempts to obtain a different frequency that is not interfered with by the noise, and each attempt extends the time period during which accurate touch input detection may be degraded.

FIG. 2is a block diagram of a touch device100configured to use multiple sampling frequencies to sample user touch inputs at a touch panel according to a first embodiment of the present disclosure. Touch device100may include a control circuit120and a capacitive touch panel (not shown inFIG. 2). The touch panel of device100may be substantially similar to capacitive touch panel15ofFIG. 1and may be, for example, positioned in front of a display screen such as a liquid crystal display (LCD), or integrated with a display screen. Control circuit120comprises a driver125, a sampling frequency generation circuit128, a receiver130, and a microcontroller (MCU)135. Sampling frequency generation circuit128comprises first and second clocks140(1) and140(2), and a clock switch170. First and second clocks140(1) and140(2) may each be independent voltage controllable oscillators (VCOs).

Similar to the arrangement ofFIG. 1, driver125is connected to a plurality of drive electrodes (not shown inFIG. 2) in the touch panel via drive signal lines145(1)-145(N), while receiver30is connected to a plurality of sense electrodes (also not shown inFIG. 2) in the touch panel via signal lines150(1)-150(N). As noted above, the drive and sense electrodes form a matrix of electrode pairs that are used to sense the location of user touch inputs. In operation, driver125provides voltage pulses to the drive electrodes, thereby resulting in an electric field between the drive electrodes and sense electrodes. The sense electrode sinks the generated electric field via a coupling capacitance, which results in a current signal. Sense signal lines150(1)-150(N) conduct this current signal to receiver130. If a user touches the touch panel, the capacitive coupling between pairs of one or more electrodes will increase at the location of the touch. Receiver130detects this increase in the coupling (via changes in the received current), and MCU135can use this information to determine the X and Y location of the user touch input.

Receiver130is not configured to continuously detect increases in the coupling between all electrode pairs. Rather, in the example ofFIG. 2, the capacitive couplings are sampled in a predetermined pattern using multiple sampling frequencies. A first such sampling frequency (f1) is generated by VCO140(1), while a second sampling frequency (f2) is generated by VCO140(2). Each generated frequency may be used by receiver130to detect user touch inputs at the touch panel. However, in operation, receiver130alternates between the frequencies f1and f2during the sampling process.

More specifically, the sampling process is divided into successive first and second time frames. During the first (odd) time frames (e.g., frames 1, 3, 5, 7, etc.), the first sampling frequency (f1) generated by VCO140(1) is used by receiver130to sample touch inputs at the touch panel, while during the second (even) time frames (e.g., frames 2, 4, 6, 8, etc.), the second sampling frequency (f2) generated by VCO140(2) is used by receiver130to sample touch inputs at the touch panel. Under the control of MCU135, clock switch170controls which sampling frequency (i.e., which VCO output) is used in a given time frame.

FIG. 3is a schematic diagram illustrating the successive first (odd) and second (even) time frames. During the odd time frames, the first sampling frequency f1is used to sample the touch inputs, while during the even time frames, the second sampling frequency f2is used to sample touch inputs. The first and second sampling frequencies f1and f2may be in the range of one to several thousand kHz or one or several hundred MHz. For example, f1may be approximately 50 MHz, while f2may be approximately 100 MHz. It should be appreciated that these values for f1and f2are merely illustrative and that other sampling frequencies may be used.

As shown inFIG. 3, the first and second time frames each have a time length of approximately 10 ms. This provides a frame rate (i.e., the rate at which receiver130alternates between the first and second sampling frequencies to sample touch inputs) of approximately 100 Hz. It should be appreciated that this frame rate is merely illustrative and other time lengths for the first and second time frames may be used.

Returning to the example ofFIG. 2, MCU135controls the frame rate via clock switch170. Clock switch170is electrically connected between receiver130and each of VCO140(1) and VCO140(2). More specifically, MCU135sends one or more control signals175to clock switch170that cause the clock switch to alternatively connect one of VCO140(1) or VCO140(2) to receiver130. When a VCO is connected to receiver130(via clock switch170), the receiver will use the sampling frequency generated by that VCO to sample the touch panel.

FIG. 4Ais a graph schematically illustrating the first (f1) and second (f2) sampling frequencies generated by VCOs140(1) and140(2), respectively. As shown inFIG. 4B, in certain circumstances noise may interfere with, for example, f1, thereby degrading the ability of touch device100to accurately determine the position of user touch inputs received during the first time period.

In the example ofFIG. 2, if it is determined that noise interferes with f1, MCU135will adjust or change f1to a first candidate frequency (f1′) that is not interfered with by the noise. This adjustment is schematically shown inFIG. 4C. More specifically, MCU135may detect noise that interferes with f1by monitoring the signal-to-noise ratio (SNR) of the signals received during the first time frame. If sufficient noise is detected, MCU135provides one or more control signals to VCO140(1) to adjust f1to the new sampling frequency, f1′.

Once the first candidate frequency f1′ is obtained, this sampling frequency is used during the first time period in place of the first sampling frequency. That is, clock switch170continues to alternately connect VCO140(1) and140(2) to receiver130in successive time frames, but, because VCO140(1) is generating the first candidate frequency f1′, this new sampling frequency is used during the first time period (i.e., the period in which VCO140(1) is connected to receiver130via clock switch170).

When MCU135detects noise that interferes with f1and performs the adjustment of f1to f1′, receiver130continues to sample touch inputs, but uses only f2. In one such example, MCU135instructs clock switch170to remain connected between VCO140(2) and receiver130during the adjustment of f1to the first candidate frequency f1′, thereby preventing the use of the VCO140(1) during the frequency adjustment. Because the adjustment may not be instantaneous, f2may be used for multiple time frames, thus effectively temporarily extending the length of the second time frame until the adjustment of f1to the new frequency is completed. In another example, when MCU135detects noise in a first time frame, the MCU is configured to complete the change of f1to the first candidate f1′ during the subsequent second frame. As such, no first time frames are omitted and the frame rate and frame length are not affected.

As noted above, if noise is detected by the prior art touch device, the touch device will be unresponsive to user inputs until a new sampling frequency is set. However, in accordance with the techniques described herein, because sampling of touch inputs continues using f2during the change of f1to f1′, delays resulting from the detection of noise may be eliminated. As such, the touch panel will generally be continually responsive to user inputs, and the noise will not affect operation of the device.

In certain circumstances, when the MCU135changes f1to the first candidate frequency f1′, the MCU is configured to ensure that f1′ is also not affected by any noise. As such, the MCU135may iteratively adjust the first sampling frequency by a predetermined amount (e.g., 100 kHz, 1 MHz, 5 MHz, 10 MHz, etc.) and, at each iteration, determine if noise interferes with the adjusted frequency. This iterative frequency adjustment continues until interference is no longer detected such that the first candidate frequency f1′ can be set.

Additionally, the cause of the noise that interferes with f1may be only temporary. As such, after a period of time, the first candidate frequency f1′ of VCO140(1) may be changed back to f1.

The examples ofFIGS. 2-4have been described with reference to changing f1in response to detected noise. It should be appreciated that noise may be additionally or alternatively detected that interferes with f2used in the second time frame. As such, f2generated by VCO140(2) may be changed in substantially the same manner as described above with reference to f1. That is, f2may be changed to a second candidate frequency f2′ that is not interfered with by the noise.

FIG. 5is a flowchart illustrating a method200implemented by a touch device for sampling touch inputs from a touch panel using multiple sampling frequencies. Method200begins at step205where a determination is made as to which of first and second sampling frequencies is provided to a receiver for use in sampling touch inputs of a user from the touch panel of the touch device. At step210, user touch inputs are sampled from the touch panel during first and second successive time frames using first and second different sampling frequencies, respectively. At step215, the touch device detects noise that interferes with the first sampling frequency used in the first time frame. At step220, while the touch device continues to sample touch inputs from the touch panel using only the second sampling frequency, the first sampling frequency is changed to a first candidate sampling frequency that is not interfered with by the detected noise. At step225, the touch device samples touch inputs from the touch panel in the first and second successive time frames using the first candidate and second sampling frequencies, respectively.

FIG. 6is a flowchart illustrating an operational method230implemented by a touch device, such as device100ofFIG. 2, during sampling operations. More specifically, method230begins at step235where MCU135performs a check to determine if the device is in an odd sampling frame (first time frame) or an even sampling frame (second time frame). If the device is in an odd time frame, the method proceeds to step240where data (touch inputs) are received using the first frequency. However, if the device is in an even time frame, the method proceeds to step245where data (touch inputs) are received using the second frequency. The process remains at step240or step245for the length of the applicable time frame, and then, after the expiration of the time frame, method230ends. This method may be repeated for each successive time frame.

FIG. 7is a flowchart illustrating another operational method250. At step255, noise is detected by MCU135. At step260, a check is performed to determine if the noise is in an even frame (interfering with f2) or is in an odd frame (interfering with f1). If the noise is in an odd time frame, the method proceeds to step265where, while f2is used to receive data, f1is changed to a first candidate frequency f1′ for subsequent use in receiving data. If noise is in an even time frame, the method proceeds to step270where, while f1is used to receive data, f2is changed to a second candidate frequency f2′ for use in receiving data. After f1or f2is changed, method250ends.

Examples have been described above with reference to the use of two sampling frequencies to sample user touch inputs at a touch panel.FIG. 8illustrates an alternative arrangement for touch device100where more than two sampling frequencies (and time frames) may be used. Similar to the example ofFIG. 2, device100comprises a control circuit120and a capacitive touch panel (not shown inFIG. 8). As noted above with reference toFIG. 2, control circuit120comprises a driver125, a sampling frequency generation circuit128, a receiver130, and a microcontroller (MCU)135. Sampling frequency generation circuit128comprises a clock switch170and, in contrast to the example ofFIG. 2in which sampling frequency generation circuit128includes only first and second clocks140(1) and140(2), sampling frequency generation128inFIG. 8comprises one or more additional clocks. More specifically, sampling frequency generation circuit128includes a number (N) of clocks, where N is greater than2.

In operation, each of the clocks140(1)-140(N) generate a sampling frequency for use by receiver130to sample data (user touches) from the touch panel. In this arrangement, the sampling period may be divided into N time frames, with a different frequency used during each time frame. If noise is detected in any of the N time frames, the sampling frequency used therein may be changed as described above.

The above description is intended by way of example only.