Patent Description:
For touch user interface the sensing of touch can be divided into two stages: Firstly, to detect if the interface is touched and secondly recognize the touch event being press, swipe or any type of action made by a user. Such a touch user interface can be realized by using piezoelectric sensor elements each element corresponding to a discrete touch point of the user interface. In the simplest case each piezoelectric sensor element may correspond to a touch switch. In many user interfaces there is a need to plurality of discrete touch switches or touch points, as an example up to <NUM> or more for QWERTY keyboards.

Document <CIT> discloses an input device with several piezoelectric elements and a wake-up trigger monitoring a voltage difference between two different nets.

Now, if the electric signals of many piezoelectric sensor elements are monitored for touch detection in touch user interface, then as one configuration either one monitoring apparatus per piezoelectric sensor element is required, or as alternative configuration many piezoelectric sensor elements are connected to one monitoring apparatus through a multiplexer. In the first configuration the current consumption of such apparatus increases with increasing the amount of piezoelectric sensor elements in the apparatus, since each monitoring sample in the apparatus having multiple piezoelectric sensor elements requires current to operate. In the second configuration each piezoelectric sensor element must continuously be polled by selecting it with the multiplexer to collect monitoring sample. The continuous polling requires current to operate, also in the inactive stage of the apparatus, when the piezoelectric sensor elements are not producing any signal. This is needed for the apparatus to be able to detect when any one of piezoelectric sensor element starts to produce the signal and consequently apparatus can be changed to active stage for touch detection.

In both configurations, of apparatus being equal amount of monitoring apparatus and piezoelectric sensor elements and configuration of multiplexing piezoelectric sensor element signals to single monitoring apparatus, there are constant and significant energy consumption of the apparatus in inactive stage.

Also in both configurations the energy consumption of the apparatus significantly increases with the amount of piezoelectric sensor elements.

In the first configuration of the apparatus mentioned above, the number of wires and the number of connections required to connect electrically each of the piezoelectric sensor elements, increase linearly with the number of piezoelectric sensor elements required to be monitored. As a consequence, apparatus has complex and bulky mechanical and electromechanical structure, which turns into increased manufacturing cost, lower reliability and limited density of the piezoelectric sensor elements in the user interface since large number of circuit elements and wires are required to electrically connect each of the piezoelectric sensor elements.

In the second configuration of the apparatus mentioned above, the multiplexing, or alternatively time interleaved detection of signal originated from each piezoelectric sensor element, there are less wires and components and space required to electrical connections. On the other hand polling of all the piezoelectric sensor elements in the apparatus may turn out to be too time consuming for reliable touch signal detection due to the limitations of polling speed of all piezoelectric sensor elements, especially with the long settling times required for signals in high impedance measurement. Acceleration of the polling speed can be used to improve the signal detection reliability, but it results in increased power consumption of the apparatus and the performance requirements for the touch detection circuitry, for example sampling speed and accuracy required from the analog-to-digital converter in touch detection circuitry.

It is also possible to use commonly known matrix detection method, where there are active signal fed to the matrix of piezoelectric sensor elements consisting of columns and rows, and as the response to the fed signal there is detection of the change in the signal transfer characteristics as a function of touch at one or more of the switches or touch points. In this alternative of the detection apparatus feeding the active signal would require even higher electrical energy compared to the polling in multiplexed signals and the feeding the signal should be in continuous manner regardless is the user interface touched or not. As a result the electrical power consumption of the apparatus is too high for typical requirement of the touch keypad user interfaces.

Piezoelectric sensing based on charge accumulated by deforming the piezoelectric sensor element is proven to be the most energy efficient method for touch sensing (for example patent reference <CIT>). However, there is no reliable and fast enough detection method of touch detection in keypads with plurality of touch switches.

A publication <CIT> discusses information that may be regarded as useful for understanding the background.

It is an object to provide detection of piezoelectric sensor elements. The object is achieved by the features of the independent claims. Further implementation forms are provided in the dependent claims, the description and the figures.

According to a first aspect, a device comprises: a matrix of piezoelectric sensor elements comprising rows of the piezoelectric sensor elements and columns of the piezoelectric sensor elements; measuring circuits configured to detect at least one touch, wherein the measuring circuits are configured to the rows and to the columns; and a wake-up trigger configured to detect the at least one touch and further configured to trigger the matrix to an operation mode when the at least one touch is detected. The device is configured for detecting a press event of a plurality of piezoelectric sensor elements, using, for example only a single activity detecting and touch recognition circuit. Complexity and energy consumption may be reduced.

In a possible implementation of the device, the matrix is configured to a low-power mode, stand-by mode or inactive mode, until the matrix is triggered by the wake-up trigger.

In another possible implementation of the device, the wake-up trigger is configured to maintain an analog comparator to monitor the detection of the at least one touch.

In another possible implementation of the device, the wake-up trigger is configured to maintain an analog to digital converter, ADC, channel to monitor the detection of the at least one touch.

In another possible implementation of the device, further including a controller configured to detect different sensitivity threshold based on the at least one touch or multiple touches in order to recognize different kind of touch events.

In another possible implementation of the device, the controller is configured to detect multiple touches of the matrix at same time.

In another possible implementation of the device, the controller is configured to detect predetermined signal differences on pairs of rows and columns in order to detect the multiple touches.

In another possible implementation of the device, the controller is configured to detect a signal difference between a signal of the at least one touch and any other piezoelectric sensor element originated signal in order to recognize the at least one touch and ignore the other piezoelectric sensor element originated signal.

In another possible implementation of the device, other measuring circuits connected to the rows and columns, where the piezoelectric sensor elements are not touched, detect significantly lower signals in comparison to measuring circuits connected to the rows and columns, where the piezoelectric sensor element is touched.

In another possible implementation of the device, the controller is configured to detect a polarity of a signal of the at least one touch and a polarity of any other signal of the piezoelectric sensor element and compare the signals in order to identify the at least one touch.

In another possible implementation of the device, the wake-up trigger comprises an analogy comparator configured to monitor a voltage difference between isolated common reference nets, and wherein the wake-up trigger further comprises a switch, wherein the comparator is configured to turn the switch on for activating the matrix to the operation mode.

In another possible implementation of the device, the wake-up trigger comprises an analog to digital channel configured to monitor a voltage difference between isolated common reference nets, and wherein the wake-up trigger further comprises a switch, wherein the controller is configured to turn the switch on for activating the matrix to the operation mode.

In another possible implementation of the device, further including a resistor in parallel to the switch.

In another possible implementation of the device, the measuring circuits comprise signal conditioning filters and detection devices.

In another possible implementation of the device, the measuring circuits are configured to only for each row and each column.

In another possible implementation of the device, the measuring circuits further comprise one or more controlled switches configured to multiplex channels of each row and each column.

According to another aspect, a method comprises: detecting, by measuring circuits, at least one touch, wherein the measuring circuits are configured to rows and to columns, and wherein a matrix of piezoelectric sensor elements comprises the rows of the piezoelectric sensor elements and the columns of the piezoelectric sensor elements; and detecting, by a wake-up trigger, the at least one touch; and triggering the matrix to an operation mode when the at least one touch is detected.

According to a third aspect, a computer program is provided, comprising program code configured to perform a method according to the second aspect when the computer program is executed on a computer.

Many of the attendant features will be more readily appreciated as they become better understood by reference to the following detailed description considered in connection with the accompanying drawings.

List of reference numerals may as follows according to an embodiment:.

The detailed description provided below in connection with the appended drawings is intended as a description of the embodiments and is not intended to represent the only forms in which the embodiment may be constructed or utilized. However, the same or equivalent functions and structures may be accomplished by different embodiments.

Accordingly, it may be desirable for a detection circuitry in form of a matrix, having rows and columns in a manner, to reduce the complexity of wiring and energy consumption for reliable touch detection and recognition of the signal produced by piezoelectric sensor element. Furthermore, it may be desirable to be able to keep the detection circuitry in a low power mode in inactive stage of the user interface, while there is no touch detection of individual piezoelectric sensor elements needed, and wake it up when user interface is needed to turn to active stage, in the manner that only the energy accumulated by the piezoelectric sensor element is used to trigger the wake-up. The energy is originated from users applying the pressure while touching to user interface, and converted to electrical charge by bending the piezoelectric sensor element.

According to an embodiment, a device comprises a matrix of piezoelectric sensor elements comprising rows of the piezoelectric sensor elements and columns of the piezoelectric sensor elements. Each piezoelectric sensor element may detect a touch. The device has measuring circuits configured to detect the at least one touch, wherein the measuring circuits are configured to the rows and to the columns. The detection may be based on the rows and the columns and their respective electronics. Furthermore, a wake-up trigger is configured to detect the at least one touch and further configured to trigger the matrix to an operation mode when the at least one touch is detected. The matrix may be resting in a stand-by mode and consume very few power. Consequently, the device is configured for detecting a press event of a plurality of piezoelectric sensor elements, using, for example only a single activity detecting and touch recognition circuit. The device has a matrix with rows and columns of piezoelectric sensor elements and their respective detection electronics in order to reduce complexity and energy consumption of the touch keypads.

The complexity of the electronics between the piezoelectric sensor element matrix <NUM> and the microcontroller <NUM> is reduced as there is no need to have an ADC channel <NUM>, conditioning filter <NUM> and wiring separately for each piezoelectric sensor element <NUM>. Instead, there may be measuring circuits only for each row and each column of the piezoelectric sensor element matrix <NUM>.

When all the rows and columns of the piezoelectric sensor element matrix <NUM> are simultaneously connected to the ADC channels <NUM> of the microcontroller <NUM>, there is no latencies related to otherwise required "select one row, scan all columns, select next row, scan all columns" method, which would take time considering all the settle times of the piezoelectric sensor elements and high impedance filter circuits etc. In addition, after very fast consecutive or parallel collection ("sampling") of signals originating from piezoelectric sensor elements <NUM>, by controller <NUM> using all ADCs <NUM> connected to the piezoelectric sensor matrix <NUM>, it is fast and efficient for the controller <NUM> to check whether any voltage difference between signal values acquired as representations of voltages at rows and columns in piezoelectric sensor matrix <NUM>, exceeded the sensitivity threshold set for the touch event and thus representing for example that the piezoelectric sensor element <NUM> with connections from its terminals to the said row and column signals in the piezoelectric sensor element matrix <NUM>, was touched.

There is no need to feed energy or such signals to the piezoelectric sensor element matrix <NUM>, of which time constants, capacitances or similar characteristic changes would be measured in relation to the fed signals, to correspond with pressure on the piezoelectric sensor elements <NUM>. Any measured changes in the measured signals at ADCs <NUM> by the controller <NUM> in the described circuits are originating from piezoelectric sensor elements <NUM>, by the energy generated in the piezoelectric effect, when the piezoelectric sensor element <NUM> is deformed under pressure produced for example by user's touch to the user interface utilizing the piezoelectric sensor elements <NUM>.

While the following embodiments use <NUM> piezoelectric sensor elements <NUM>, it should be understood that the number of piezoelectric sensor elements <NUM> can be varied, and is not limited to <NUM>. Furthermore, microcontroller <NUM> may, for example be a microcontroller, microprocessor, field programmable gate array, application specific integrated circuit, or any other device capable of running detection algorithm, with software, hardware or their combination, embedded in it.

Referring now to the embodiment of <FIG> there is shown <NUM> piezoelectric sensor elements <NUM> in a matrix <NUM>, with the individual piezoelectric sensor elements 11A-11P, connected to a circuit that is composed of signal conditioning filters 21A-<NUM>, and detection devices 31A-<NUM>: analog-to-digital converters, as many as there are combined number of rows and columns of the matrix <NUM> to be detected. The <NUM> times <NUM> matrix thus requires <NUM> signal input channels at the controller device <NUM>. The number of the ADCs <NUM> can be less, down to one, if the <NUM> channels are multiplexed inside the controller device <NUM>. The number of the signal conditioning filters 21A-<NUM> equals also to the number of rows and columns in the matrix <NUM>. The controller device <NUM> also includes voltage reference circuit <NUM>, VREF, which creates a suitable DC bias voltage for the piezoelectric sensor elements <NUM> in the matrix <NUM>, to be able to have an alternating voltage signal detectable by the ADCs 31A-<NUM>, within a signal range suitable for the ADC(s). An embodiment of the signal conditioning filters 21A-<NUM> is shown in <FIG>, where one possible topology is given for voltage amplitude attenuation of the piezoelectric sensor element <NUM> signal by resistive division by resistors <NUM> and <NUM>, and frequency limitation by low pass filter elements <NUM> and <NUM>. The electrical values of each resistors <NUM> and <NUM> can be selected to provide suitable conditioning effects, anything between zero ohms (no filtering) and high impedances (low frequency cut off). In <FIG>, there is also an example of VREF circuit <NUM>, implemented with a resistive voltage division 36A, 36B between supply voltage <NUM> and ground level <NUM>, and the connection to the piezoelectric sensor element signal conditioning filter <NUM>.

Referring to <FIG>, the energy accumulated by a press of a piezoelectric sensor element <NUM>, may momentarily deviate the voltage value related to the row and column of the piezoelectric sensor element matrix <NUM> connected to the terminals of said (touched) piezoelectric sensor element <NUM>, which can be detected by the ADCs 31A-<NUM>. From these read voltage signals in ADCs <NUM>, the controller device <NUM> can recognize the individual piezoelectric sensor element <NUM> being pressed, touched, or swiped, by processing the analog-to-digital conversion results.

In <FIG>, there is illustrated an embodiment of the piezoelectric sensor element matrix <NUM>, where electrical connections from columns and rows of the piezoelectric sensor element matrix <NUM> to controller <NUM> are multiplexed to save the number of detection devices 31A-31D inside controller <NUM>. The multiplexing is done with a controlled switches 12A-12D for the rows, and 13A-13D for the columns of the piezoelectric sensor element matrix <NUM>. The switches 12A-12D and 13A-13D are controlled by the controlled device <NUM>, via digital signals that are merely for the sake of clarity not explicitly shown in the circuit in <FIG>. The touch detection task in piezoelectric sensor element matrix <NUM> may be performed with significantly lower number of detection devices 31A-31D needed compared to the embodiment illustrated in <FIG>.

In <FIG>, the configuration of <FIG> is equipped with a low power consumption wake-up trigger circuit, which consists of a controllable switch <NUM>, which disconnects and connects the common reference nets <NUM> and <NUM>, according to the control by the controller device <NUM>. When the system is in a low power, stand-by state or inactive stage, not detecting with ADCs 31A-31D, thus not consuming energy for detection function, the common reference nets <NUM> and <NUM> are isolated by a non-conducting state of switch <NUM>. To provide the nets the same DC bias voltage, a high ohmic value resistor <NUM> is connected parallel to the switch <NUM>. An analog comparator <NUM> monitors the voltage difference between the two isolated common reference nets <NUM>, <NUM>. The analog comparator <NUM> may have predefined trigger voltage threshold level, which must be exceeded, to reliably distinguish desired touch detection signals from noise in the circuit. When a voltage difference produced by a piezoelectric sensor element <NUM> being touched is detected between the common reference nets <NUM>, <NUM> by the analog comparator <NUM>, it triggers the controller <NUM> to wake up, to turn the switch <NUM> conductive, and to start monitoring the rows and columns of piezoelectric sensor element matrix <NUM> by activating the detector ADCs 31A-31D. The wake-up sequence can be made in such a short time, that the touch detection and recognition in controller <NUM> from the signal of the same piezoelectric sensor element <NUM>, which produced the signal for the wake-up, can still be reliably performed.

In <FIG> there is illustrated an embodiment for the low power wake-up trigger function, to detect the need to transition from stand-by mode to normal operation mode of the circuit, controlled by the controller <NUM>. In this embodiment, another ADC channel <NUM>, inside the controller <NUM>, is utilized to detect the voltage changes between the common reference nets <NUM> and <NUM>, which are first isolated from each other by disconnected switch <NUM>, but having the same DC bias voltage via high ohmic resistor <NUM>, parallel to the switch. When the ADC <NUM> detects voltage change between the common reference nets <NUM>, <NUM>, the controller device <NUM> activates the ADCs 31A-31D, and connects the common reference nets <NUM>, <NUM> together, making the VREF net common to all detectable channels. In <FIG>, simulated voltage curves shown in time domain represent the signals at the ADC inputs <NUM>, which the detection of the touch and recognition of the touched piezoelectric sensor element <NUM> is based on. The voltage curves are captured from a single touch recognition test, where piezoelectric sensor element 11A of <FIG> is pressed at 50msec, for 20msec period, and piezoelectric sensor element <NUM> of the same <FIG> is pressed at 300msec, for 20msec period. The upper curves indicate the detected signals originated from piezoelectric sensor element 11A at row of piezoelectric sensor element matrix <NUM> which is connected to ADC 31A, and detected signals originated from the same piezoelectric sensor element 11A at column of piezoelectric sensor element matrix <NUM>, which is connected to ADC <NUM> of <FIG>. The lower curves indicate the signals originated from piezoelectric sensor element <NUM> connected to row and column of the matrix <NUM>, as detected at ADC 31B and ADC 31E of <FIG>, respectively.

To detect the row and the column of the touched piezoelectric sensor element <NUM> in the matrix <NUM>, the larger difference of the piezoelectric sensor element <NUM> originated signal amplitudes of a column and a row of the piezoelectric sensor element matrix <NUM> is found at the ADCs <NUM>, in comparison to any other piezoelectric sensor element <NUM> originated signal differences of other columns and rows in the piezoelectric sensor element matrix <NUM>, or to predetermined reference value stored in controller <NUM>. In other words touch detection is made based on large enough signal difference measured by ADC <NUM> from the column and row of the matrix <NUM>, which exceed the signal difference of other columns and rows of the matrix <NUM> measured by ADC <NUM>, and/or a set sensitivity threshold for touch detection stored in controller <NUM>.

The other ADCs <NUM>, connected to rows and columns of the matrix <NUM> where the piezoelectric sensor elements <NUM> are not touched, detect significantly lower signals in comparison to the ADCs <NUM> connected to the rows and columns of the matrix <NUM> where the piezoelectric sensor element <NUM> is touched. This is indicated in <FIG> by signals of ADC 31A and <NUM> at 300msec, upper curves, and ADC 31B and 31E at 50msec, lower curves. There can be several piezoelectric sensor elements <NUM> of the matrix <NUM> of <FIG> touched, pressed, swiped, or otherwise actuated by the user at the same time, providing large enough signal differences on several pairs of rows and columns of the piezoelectric sensor element matrix <NUM>, which can be detected and recognized in microcontroller <NUM> by the same principle. The different and adjustable sensitivity thresholds can be used for recognition of different kind of touch events in the microcontroller <NUM>.

The functionality described herein can be performed, at least in part, by one or more computer program product components such as software components. According to an embodiment, the device comprise a processor, such as the microcontroller <NUM>, configured by the program code when executed to execute the embodiments of the operations and functionality described. For example, and without limitation, illustrative types of hardware logic components that can be used include Field-programmable Gate Arrays (FPGAs), Program-specific Integrated Circuits (ASICs), Program-specific Standard Products (ASSPs), System-on-a-chip systems (SOCs), Complex Programmable Logic Devices (CPLDs), Graphics Processing Units (GPUs).

Also any embodiment may be combined with another embodiment unless explicitly disallowed.

Claim 1:
A device, comprising:
a matrix (<NUM>) of piezoelectric sensor elements (11A - 11P) comprising
rows of the piezoelectric sensor elements and columns of the piezoelectric sensor elements;
measuring circuits (21A-<NUM>, 31A-<NUM>) configured to detect at least one touch, wherein the measuring circuits are configured to the rows and to the columns; and
a wake-up trigger (<NUM>,<NUM>,<NUM>,<NUM>) configured to detect the at least one touch and further configured to trigger the matrix to an operation mode when the at least one touch is detected;
characterized by the wake-up trigger is connected between the common reference net (<NUM>) for the rows of the matrix of piezoelectric sensor elements and the common reference net (<NUM>) for the columns of the matrix of piezoelectric sensor elements (<NUM>) and the wake-up trigger is configured to monitor a voltage difference between the isolated common reference nets, wherein the wake-up trigger further comprises a switch <NUM>) and a high ohmic resistor (<NUM>) permanently coupling the two reference nets, wherein the switch (<NUM>) is an isolation switch, which disconnects the two separate common reference nets (<NUM>, <NUM>), so that the voltage difference between the two common reference nets can be detected and wherein the wake-up trigger is configured to connect and disconnect the isolated reference nets by the switch and accordingly turn the switch on for activating the matrix to the operation mode, wherein the measuring circuits comprise signal conditioning filters (21A-<NUM>) and detection devices (31A-<NUM>), the isolated common reference nets comprise a common reference net for the rows of the matrix of piezoelectric sensor elements and a common reference net for the columns of the matrix of piezoelectric sensor elements, one of the isolated common reference nets is coupled to a signal reference bias voltage, and each row of the matrix of piezoelectric sensor elements is electrically coupled to the common reference net for the rows via a conditioning filter and each column of the matrix of piezoelectric sensor elements is electrically coupled to the common reference net for the columns via a conditioning filter.