Patent Publication Number: US-8970507-B2

Title: Method of waking up and a portable electronic device configured to perform the same

Description:
TECHNICAL FIELD 
     The present disclosure relates to portable electronic devices, including but not limited to portable electronic devices having touch screen displays and their control. 
     BACKGROUND 
     Electronic devices, including portable electronic devices, have gained widespread use and may provide a variety of functions including, for example, telephonic, electronic messaging and other personal information manager (PIM) application functions. Portable electronic devices include, for example, several types of mobile stations such as simple cellular telephones, smart telephones, wireless personal digital assistants (PDAs), and laptop computers with wireless 802.11 or Bluetooth™ capabilities. 
     Portable electronic devices such as PDAs or smart telephones are generally intended for handheld use and ease of portability. Smaller devices are generally desirable for portability. A touch-sensitive display, also known as a touchscreen display, is particularly useful on handheld devices, which are small and have limited space for user input and output. The information displayed on the touch-sensitive displays may be modified depending on the functions and operations being performed. The power consumed by touch-sensitive displays is a relatively large portion of the total power draw for the device. Accordingly, improvements which reduce the power consumption of touch-sensitive displays of portable electronic devices are desirable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified block diagram of components including internal components of a portable electronic device according to one aspect; 
         FIG. 2  is a front view of an example of a portable electronic device in a portrait orientation; 
         FIG. 3A  is a sectional side view of portions of the portable electronic device of  FIG. 2 ; 
         FIG. 3B  is a side view of a portion of the portable electronic device shown in  FIG. 3A ; 
         FIG. 4  is a front view of an example of a portable electronic device in a portrait orientation, showing hidden detail in ghost outline; 
         FIG. 5  is a block diagram of a circuit for controlling the actuators of the portable electronic device in accordance with one example embodiment of the present disclosure; 
         FIG. 6  is a block diagram of a circuit for controlling the force sensors of the portable electronic device in accordance with one example embodiment of the present disclosure; 
         FIG. 7  is schematic diagram of a circuit for controlling the force sensors of the portable electronic device in accordance with one example embodiment of the present disclosure; 
         FIG. 8  is a flowchart illustrating a method of waking up a portable electronic device in accordance with one example embodiment of the present disclosure; 
         FIG. 9  is a flowchart illustrating a method of waking up a portable electronic device in accordance with another example embodiment of the present disclosure; 
         FIG. 10  is a flowchart illustrating a method of waking up a portable electronic device in accordance with a further example embodiment of the present disclosure; and 
         FIG. 11  is a flowchart illustrating a method of waking up a portable electronic device in accordance with another example embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     The present disclosure provides a wakeup detection circuit, and in particular, a low power wakeup detection circuit, and a portable electronic device having such wakeup detection circuits. Portable electronic devices may have several power modes: a “full power” mode (also referred to as an “on mode” or “normal” mode) in which normal full functionality of the device is provided; a sleep mode (also referred to as a “low power” mode or “standby” mode) in which reduced functionality of the device is provided; and an “off mode” in which the device is powered-off and performs no functions or a minimized set of functions. To exit the sleep mode or off mode, portable electronic devices having a touch-sensitive display typically periodically scan the touch-sensitive display to detect a touch event. When a touch event is detected, the device switches from the sleep mode or off mode to the full power mode. Periodic scanning of the touch-sensitive display consumes scarce power. The present disclosure provides a wakeup detection circuit which does not require periodic scanning of the touch-sensitive display. The present disclosure also provides a method of waking a portable electronic device and a portable electronic device configured to perform the same. 
     In accordance with one embodiment, there is provided a method of conserving power on a portable electronic device, the portable electronic device having a device housing which comprises a touch-sensitive display, an accelerometer, and a force sensing transducer, the method comprising: causing the portable electronic device to enter a sleep mode in response to a trigger condition, wherein the touch-sensitive display is deactivated in the sleep mode and the force sensing transducer measures forces applied to the touch-sensitive display at a reduced rate relative to a rate of a full power mode when in the sleep mode; detecting an inertial event using the accelerometer; causing the force sensing transducer to measure forces applied to the touch-sensitive display at the rate of the full power mode in response to detection of an inertial event; detecting forces applied to the touch-sensitive display using the force sensing transducer at the rate of the full power mode; causing the touch-sensitive display to be reactivated in response to detection of a force which is greater than a predetermined wake force threshold; detecting touch events on the touch-sensitive display; and causing the portable electronic device to wake from the sleep mode in response to detection of a touch event within a first predetermined duration of the detection of the force which is greater than a predetermined wake force threshold. 
     In accordance with another embodiment, there is provided a method of conserving power on a portable electronic device, the portable electronic device having a device housing which comprises a touch-sensitive display and a force sensing transducer, the method comprising: causing the portable electronic device to enter a sleep mode in response to a trigger condition, wherein the touch-sensitive display is deactivated in the sleep mode; detecting forces applied to the touch-sensitive display using the force sensing transducer; causing the touch-sensitive display to be reactivated in response to detection of a force which is greater than a predetermined wake force threshold; detecting touch events on the touch-sensitive display; and causing the portable electronic device to wake from the sleep mode in response to detection of a touch event within a first predetermined duration of the detection of the force which is greater than a predetermined wake force threshold. 
     In accordance with a further embodiment, there is provided a method of conserving power on a portable electronic device, the portable electronic device having a device housing which comprises a touch-sensitive display, an accelerometer, and a force sensing transducer, the method comprising: causing the portable electronic device to enter a sleep mode in response to a trigger condition, wherein the touch-sensitive display is deactivated in the sleep mode and the force sensing transducer measures forces applied to the touch-sensitive display at a reduced rate relative to a rate of a full power mode when in the sleep mode; detecting an inertial event using the accelerometer; 
     causing the force sensing transducer to measure forces applied to the touch-sensitive display at the rate of the full power mode in response to detection of an inertial event; detecting forces applied to the touch-sensitive display using the force sensing transducer at the rate of the full power mode; and causing the touch-sensitive display to be reactivated and causing the portable electronic device to wake from the sleep mode in response to detection of a touch event within a first predetermined duration of the detection of the force which is greater than a predetermined wake force threshold. 
     In accordance with a further embodiment, there is provided a method of conserving power on a portable electronic device, the portable electronic device having a device housing which comprises a touch-sensitive display and an accelerometer, the method comprising: causing the portable electronic device to enter a sleep mode in response to a trigger condition, wherein the touch-sensitive display is deactivated in the sleep mode; detecting an inertial event using the accelerometer; causing the touch-sensitive display to be reactivated in response to detection of an inertial event; detecting touch events on the touch-sensitive display; and causing the portable electronic device to wake from the sleep mode in response to detection of a touch event within a first predetermined duration of the detection of inertial event. 
     In some embodiments, the portable electronic device comprises a plurality of piezoelectric elements resiliently biased and located beneath the back side of the touch-sensitive display opposite to the touch-sensitive overlay of the touch-sensitive display, the movement of the touch-sensitive display being caused by modulating the charge of the piezoelectric elements thereby providing haptic feedback which simulates the collapse of a dome-type switch. In some embodiments, the plurality of piezoelectric elements comprise four piezoelectric disks, each piezoelectric disk being located near a respective corner of the touch-sensitive display. 
     In some embodiments in which the portable electronic device comprises a force sensing transducer, the force sensing transducer is located beneath a back side of the touch-sensitive display opposite to a touch-sensitive overlay of the touch-sensitive display, the force sensing transducer measuring forces applied to the touch-sensitive overlay of the touch-sensitive display. In some embodiments, the portable electronic device comprises a plurality of force sensing transducers, wherein a sum of force data measured by the force sensing transducers is used to determine whether an applied force is greater than the predetermined wake force threshold. In some embodiments, the force sensing transducers are force sensing resistors. In some embodiments, the force sensing transducers comprise four force sensing resistors, each force sensing resistor being located near a respective corner of the touch-sensitive display. 
     In accordance with further embodiments, there is provided a portable electronic device having a device housing in which a controller is received and which comprises a touch-sensitive display, and one or both of an accelerometer or force sensing transducer, the controller being configured to perform any one of the methods described herein. 
     In accordance with one example embodiment, there is provided a portable electronic device, comprising: a housing; a processor received within the housing; a touch-sensitive display connected to the processor and exposed by the housing, the touch-sensitive display having a touch-sensitive overlay detecting touch events; an accelerometer received within the housing connected to the controller and measuring inertial events; at least one force sensing transducer located below the touch-sensitive display on an opposite side to the touch-sensitive overlay, the at least one force sensing transducer being connected to the controller and measuring forces applied to the touch-sensitive display; wherein the controller is configured for: causing the portable electronic device to enter a sleep mode in response to a trigger condition, wherein the touch-sensitive display is deactivated in the sleep mode and the force sensing transducer measures forces applied to the touch-sensitive display at a reduced rate relative to a rate of a full power mode when in the sleep mode; detecting an inertial event using the accelerometer; causing the force sensing transducer to measure forces applied to the touch-sensitive display at the rate of the full power mode in response to detection of an inertial event; detecting forces applied to the touch-sensitive display using the force sensing transducer at the rate of the full power mode; causing the touch-sensitive display to be reactivated in response to detection of a force which is greater than a predetermined wake force threshold; detecting touch events on the touch-sensitive display; and causing the portable electronic device to wake from the sleep mode in response to detection of a touch event within a first predetermined duration of the detection of the force which is greater than a predetermined wake force threshold. 
     In accordance with a further embodiment, there is provided a control circuit, comprising: a control circuit, comprising: a controller having a full power duty cycle and a slower sleep mode duty cycle, the full power duty cycle and sleep mode duty cycle each having an active portion in which data is read and an inactive portion in which data is not read; a plurality of force sensing transducers for measuring force data which are connected to the controller; a multi-port switch which sums the force data output of the plurality of force sensing transducers, the multi-port switch having a switch for each of the force sensing transducers, a respective switch for each of the force sensing transducers being closed during an active portion of the sleep duty cycle and the respective switch for each of the force sensing transducers being open during the inactive portion of the sleep duty cycle; and a comparator for comparing the summed force data from the multi-port switch to a wakeup force threshold; wherein the controller is configured to wake from a sleep mode and return to a full power mode when the summed force data is greater than the wakeup force threshold. 
     In accordance with a further embodiment, there is provided a portable electronic device, comprising: a housing; a controller received within the housing; a touch-sensitive display having a touch-sensitive overlay, the touch-sensitive display being mechanically constrained by the housing; at least one force sensing transducer located below the touch-sensitive display on an opposite side to the touch-sensitive overlay, the at least one force sensing transducer being connected to the controller and measuring forces applied to the touch-sensitive display; wherein the controller is configured for: initiating a sleep mode from a full power mode in response to a trigger; when in the sleep mode, reading force data measured by the at least one force sensing transducer at a reduced duty cycle relative to the full power mode, comparing the force data to a wakeup force threshold, and returning to the full power mode from the sleep mode when the force data is greater than the wakeup force threshold. 
     In accordance with a further embodiment, there is provided a control circuit, comprising: a controller having a full power duty cycle and a slower sleep mode duty cycle, the full power duty cycle and sleep mode duty cycle each having an active portion in which data is read and an inactive portion in which data is not read; at least one force sensing transducer for measuring force data which is connected to the controller; a switch connected to the at least one force sensing transducer which is closed during an active portion of the sleep duty cycle and open during the inactive portion of the sleep duty cycle; and a comparator for comparing the force data from the switch to a wakeup force threshold; wherein the controller is configured to wake from a sleep mode and return to a full power mode when the force data is greater than the wakeup force threshold. 
     For simplicity and clarity of illustration, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. Numerous details are set forth to provide an understanding of the embodiments described herein. The embodiments may be practiced without these details. In other instances, well-known methods, procedures, and components have not been described in detail to avoid obscuring the embodiments described. The description is not to be considered as limited to the scope of the embodiments described herein. 
     The disclosure generally relates to an electronic device, which is a portable electronic device in the embodiments described herein. Examples of portable electronic devices include mobile, or handheld, wireless communication devices such as pagers, cellular phones, cellular smart-phones, wireless organizers, personal digital assistants, wirelessly enabled notebook computers, and so forth. The portable electronic device may also be a portable electronic device without wireless communication capabilities, such as a handheld electronic game device, digital photograph album, digital camera, or other device. 
     A block diagram of an example of a portable electronic device  100  is shown in  FIG. 1 . The portable electronic device  100  includes multiple components, such as a processor  102  that controls the overall operation of the portable electronic device  100 . Communication functions, including data and voice communications, are performed through a communication subsystem  104 . Data received by the portable electronic device  100  is decompressed and decrypted by a decoder  106 . The communication subsystem  104  receives messages from and sends messages to a wireless network  150 . The wireless network  150  may be any type of wireless network, including, but not limited to, data wireless networks, voice wireless networks, and networks that support both voice and data communications. A power source  142 , such as one or more rechargeable batteries or a port to an external power supply, powers the portable electronic device  100 . 
     The processor  102  interacts with other components, such as Random Access Memory (RAM)  108 , memory  110 , a display screen  112  (such as a liquid crystal display (LCD)) with a touch-sensitive overlay  114  operably connected to an electronic controller  116  that together comprise a touch-sensitive display  118 , one or more actuators  120 , one or more force sensors  122 , one or more auxiliary input/output (I/O) subsystems  124 , a data port  126 , a speaker  128 , a microphone  130 , short-range communications subsystem  132 , and other device subsystems  134 . It will be appreciated that the electronic controller  116  of the touch-sensitive display  118  need not be physically integrated with the touch-sensitive overlay  114  and display screen  112 . User-interaction with a graphical user interface is performed through the touch-sensitive overlay  114 . The processor  102  interacts with the touch-sensitive overlay  114  via the electronic controller  116 . Information, such as text, characters, symbols, images, icons, and other items that may be displayed or rendered on a portable electronic device, is displayed on the touch-sensitive display  118  via the processor  102 . The processor  102  may interact with an accelerometer  136  that may be utilized to detect direction of gravitational forces or gravity-induced reaction forces. Instead of an accelerometer  136 , another type of inertial sensor could be used in other embodiments. 
     The portable electronic device  100  also includes one or more clocks including a system clock (not shown) and sleep clock (not shown). In other embodiments, a single clock can operate as both system clock and sleep clock. The sleep clock is a lower power, lower frequency clock. By way of example, the system clock may comprise a voltage controlled oscillator operating at a frequency of approximately 700 to 800 megahertz (though the speed of the system clock may vary depending on the mode of the portable electronic device  100 ), whereas the sleep clock may comprise a low power oscillator operating at a frequency in the range of 30 kilohertz to 60 kilohertz. In one example embodiment, the sleep clock operates at 32 kilohertz to reduce the power consumption. 
     The auxiliary I/O subsystems  124  could include other input devices such as one or more control keys, a keyboard or keypad, navigational tool (input device), or both. The navigational tool could be a clickable/depressible trackball or scroll wheel, or touchpad. The other input devices could be included in addition to, or instead of, the touch-sensitive display  118 , depending on the embodiment. 
     To identify a subscriber for network access, the portable electronic device  100  uses a Subscriber Identity Module or a Removable User Identity Module (SIM/RUIM) card  138  for communication with a network, such as the wireless network  150 . Alternatively, user identification information may be programmed into memory  110 . 
     The portable electronic device  100  includes an operating system  146  and software programs or components  148  that are executed by the processor  102  and are typically stored in a persistent, updatable store such as the memory  110 . Additional applications or programs may be loaded onto the portable electronic device  100  through the wireless network  150 , the auxiliary I/O subsystem  124 , the data port  126 , the short-range communications subsystem  132 , or any other suitable subsystem  134 . 
     A received signal such as a text message, an e-mail message, or web page download is processed by the communication subsystem  104  and input to the processor  102 . The processor  102  processes the received signal for output to the display screen  112  and/or to the auxiliary I/O subsystem  124 . A subscriber may generate data items, for example e-mail messages, which may be transmitted over the wireless network  150  through the communication subsystem  104 . For voice communications, the overall operation of the portable electronic device  100  is similar. The speaker  128  outputs audible information converted from electrical signals, and the microphone  130  converts audible information into electrical signals for processing. 
       FIG. 2  shows a front view of an example of a portable electronic device  100  in portrait orientation. The portable electronic device  100  includes a housing  200  that houses internal components including internal components shown in  FIG. 1  and frames the touch-sensitive display  118  such that the touch-sensitive display  118  is exposed for user-interaction therewith when the portable electronic device  100  is in use. It will be appreciated that the touch-sensitive display  118  may include any suitable number of user-selectable features rendered thereon, for example, in the form of virtual buttons for user-selection of, for example, applications, options, or keys of a keyboard for user entry of data during operation of the portable electronic device  100 . 
     The touch-sensitive display  118  may be any suitable touch-sensitive display, such as a capacitive, resistive, infrared, surface acoustic wave (SAW) touch-sensitive display, strain gauge, optical imaging, dispersive signal technology, acoustic pulse recognition, and so forth, as known in the art. A capacitive touch-sensitive display includes a capacitive touch-sensitive overlay  114 . The overlay  114  may be an assembly of multiple layers in a stack including, for example, a substrate, a ground shield layer, a barrier layer, one or more capacitive touch sensor layers separated by a substrate or other barrier, and a cover. The capacitive touch sensor layers may be any suitable material, such as patterned indium tin oxide (ITO). 
     One or more touches, also known as touch contacts or touch events, may be detected by the touch-sensitive display  118 . The processor  102  may determine attributes of the touch, including a location of a touch. Touch location data may include an area of contact or a single point of contact, such as a point at or near a centre of the area of contact. The location of a detected touch may include x and y components, e.g., horizontal and vertical components, respectively, with respect to one&#39;s view of the touch-sensitive display  118 . For example, the x location component may be determined by a signal generated from one touch sensor, and the y location component may be determined by a signal generated from another touch sensor. A signal is provided to the controller  116  in response to detection of a touch. A touch may be detected from any suitable object, such as a finger, thumb, appendage, or other items, for example, a stylus, pen, or other pointer, depending on the nature of the touch-sensitive display  118 . Multiple simultaneous touches may be detected. 
     The actuators  120  comprise one or more piezoelectric devices that provide tactile feedback for the touch-sensitive display  118 . The actuators  120  may be depressed by applying sufficient force to the touch-sensitive display  118  to overcome the actuation force of the actuators  120 . The actuators  120  may be actuated by pressing anywhere on the touch-sensitive display  118 . The actuator  120  may provide input to the processor  102  when actuated. Contraction of the piezoelectric actuators applies a spring-like force, for example, opposing a force externally applied to the touch-sensitive display  118 . Each piezoelectric actuator includes a piezoelectric device, such as a piezoelectric (PZT) ceramic disk adhered to a metal substrate. The metal substrate bends when the PZT disk contracts due to build up of charge at the PZT disk or in response to a force, such as an external force applied to the touch-sensitive display  118 . The charge may be adjusted by varying the applied voltage or current, thereby controlling the force applied by the piezoelectric disks. The charge on the piezoelectric actuator may be removed by a controlled discharge current that causes the PZT disk to expand, releasing the force thereby decreasing the force applied by the piezoelectric disks. The charge may advantageously be removed over a relatively short period of time to provide tactile feedback to the user. Absent an external force and absent a charge on the piezoelectric disk, the piezoelectric disk may be slightly bent due to a mechanical preload. 
     The housing  200  can be any suitable housing for the internal components shown in  FIG. 1 .  FIG. 3A  shows a sectional side view of portions of the portable electronic device  100  and  FIG. 3B  shows a side view of a portion of the actuators  120 . The housing  200  in the present example includes a back  302 , a frame  304 , which frames the touch-sensitive display  118  and sidewalls  306  that extend between and generally perpendicular to the back  302  and the frame  304 . A base  308  is spaced from and is generally parallel to the back  302 . The base  308  can be any suitable base and can include, for example, a printed circuit board or flexible circuit board supported by a stiff support between the base  308  and the back  302 . The back  302  may include a plate (not shown) that is releasably attached for insertion and removal of, for example, the power source  142  and the SIM/RUIM card  138  referred to above. It will be appreciated that the back  302 , the sidewalls  306  and the frame  304  may be injection molded, for example. In the example of the portable electronic device  100  shown in  FIG. 2 , the frame  304  is generally rectangular with rounded corners, although other shapes are possible. 
     The display screen  112  and the touch-sensitive overlay  114  are supported on a support tray  310  of suitable material such as magnesium for providing mechanical support to the display screen  112  and touch-sensitive overlay  114 . A compliant spacer such as a gasket compliant  312  is located around the perimeter of the frame  304 , between an upper portion of the support tray  310  and the frame  304  to provide a gasket for protecting the components housed in the housing  200  of the portable electronic device  100 . A suitable material for the compliant gasket  312  includes, for example, a cellular urethane foam for providing shock absorption, vibration damping and a suitable fatigue life. In some embodiments, a number of compliant spacers may be used to provide the function of the gasket compliant  312 . 
     The actuators  120  includes four piezoelectric disk actuators  314 , as shown in  FIG. 4 , with each piezoelectric disk actuator  314  located near a respective corner of the touch-sensitive display  118 . Referring again to  FIGS. 3A and 3B , each piezoelectric disk actuator  314  is supported on a respective support ring  316  that extends from the base  308  toward the touch-sensitive display  118  for supporting the respective piezoelectric disk actuator  314  while permitting flexing of the piezoelectric disk actuator  314 . Each piezoelectric disk actuator  314  includes a piezoelectric disk  318  such as a PZT ceramic disk adhered to a metal substrate  320  of larger diameter than the piezoelectric disk  318  for bending when the piezoelectric disk  318  contracts as a result of build up of charge at the piezoelectric disk  318 . Each piezoelectric disk actuator  314  is supported on the respective support ring  316  on one side of the base  308 , near respective corners of the metal substrate  320 , base  308  and housing  200 . The support  316  ring is sized such that the edge of the metal substrate  320  contacts the support ring  316  for supporting the piezoelectric disk actuator  314  and permitting flexing of the piezoelectric disk actuator  314 . 
     A shock-absorbing element  322 , which in the present example is in the form of a cylindrical shock-absorber of suitable material such as a hard rubber is located between the piezoelectric disk actuator  314  and the support tray  310 . A respective force sensor  122  is located between each shock-absorbing element  322  and the respective piezoelectric disk actuator  314 . A suitable force sensor  122  includes, for example, a puck-shaped force sensing resistor for measuring applied force (or pressure). It will be appreciated that a force can be determined using a force sensing resistor as an increase in pressure on the force sensing resistor results in a decrease in resistance (or increase in conductance). In the portable electronic device  100 , each piezoelectric disk actuator  314  is located between the base  308  and the support tray  310  and force is applied on each piezoelectric disk actuator  314  by the touch-sensitive display  118 , in the direction of the base  308 , causing bending of the piezoelectric disk actuator  314 . Thus, absent an external force applied by the user, for example by pressing on the touch-sensitive display  118 , and absent a charge on the piezoelectric disk actuator  314 , the piezoelectric disk actuator  314  undergoes slight bending. An external applied force in the form of a user pressing on the touch-sensitive display  118  during a touch event, and prior to actuation of the piezoelectric disk actuator  314 , causes increased bending of the piezoelectric disk actuator  314  and the piezoelectric disk actuator  314  applies a spring force against the touch-sensitive display  118 . When the piezoelectric disk  318  is charged, the piezoelectric disk  318  shrinks and causes the metal substrate  320  and piezoelectric disk  318  to apply a further force, opposing the external applied force, on the touch-sensitive display  118  as the piezoelectric actuator  314  straightens. 
     Each of the piezoelectric disk actuators  314 , shock absorbing elements  322  and force sensors  122  are supported on a respective one of the support rings  316  on one side of the base  308 . The support rings  316  can be part of the base  308  or can be supported on the base  308 . The base  308  can be a printed circuit board while the opposing side of the base  308  provides mechanical support and electrical connection for other components (not shown) of the portable electronic device  100 . Each piezoelectric disk actuator  314  is located between the base  308  and the support tray  310  such that an external applied force on the touch-sensitive display  118  resulting from a user pressing the touch-sensitive display  118  can be measured by the force sensors  122  and such that the charging of the piezoelectric disk actuator  314  causes a force on the touch-sensitive display  118 , away from the base  308 . 
     In the present embodiment each piezoelectric disk actuator  314  is in contact with the support tray  310 . Thus, depression of the touch-sensitive display  118  by user application of a force thereto is determined by a change in resistance at the force sensors  122  and causes further bending of the piezoelectric disk actuators  314  as shown in  FIG. 3A . Further, the charge on the piezoelectric disk actuator  314  can be modulated to control the force applied by the piezoelectric disk actuator  314  on the support tray  310  and the resulting movement of the touch-sensitive display  118 . The charge can be modulated by modulating the applied voltage or current. For example, a current can be applied to increase the charge on the piezoelectric disk actuator  314  to cause the piezoelectric disk  318  to contract and to thereby cause the metal substrate  320  and the piezoelectric disk  318  to straighten as referred to above. This charge therefore results in the force on the touch-sensitive display  118  for opposing the external applied force and movement of the touch-sensitive display  118  away from the base  308 . The charge on the piezoelectric disk actuator  314  can also be removed via a controlled discharge current causing the piezoelectric disk  318  to expand again, releasing the force caused by the electric charge and thereby decreasing the force on the touch-sensitive display  118 , permitting the touch-sensitive display  118  to return to a rest position. 
       FIG. 5  shows a circuit for controlling the actuators  120  of the portable electronic device  100  according to one embodiment. As shown, each of the piezoelectric disks  318  is connected to a controller  500  such as a microprocessor including a piezoelectric driver  502  and an amplifier and analog-to-digital converter (ADC)  504  that is connected to each of the force sensors  122  and to each of the piezoelectric disks  318 . In some embodiments, the ADC  504  could be a 9-channel ADC. The controller  500  is also in communication with the main processor  102  of the portable electronic device  100 . The controller  500  can provide signals to the main processor  102  of the portable electronic device  100 . It will be appreciated that the piezoelectric driver  502  may be embodied in drive circuitry between the controller  500  and the piezoelectric disks  318 . 
     The mechanical work performed by the piezoelectric disk actuator  314  can be controlled to provide generally consistent force and movement of the touch-sensitive display  118  in response to detection of an applied force on the touch-sensitive display  118  in the form of a touch, for example. Fluctuations in mechanical work performed as a result of, for example, temperature, can be reduced by modulating the current to control the charge. 
     The controller  500  controls the piezoelectric driver  502  for controlling the current to the piezoelectric disks  318 , thereby controlling the charge. The charge is increased to increase the force on the touch-sensitive display  118  away from the base  308  and decreased to decrease the force on the touch-sensitive display  118 , facilitating movement of the touch-sensitive display  118  toward the base  308 . In the present example, each of the piezoelectric disk actuators  314  are connected to the controller  500  through the piezoelectric driver  502  and are all controlled equally and concurrently. Alternatively, the piezoelectric disk actuators  314  can be controlled separately. 
     The portable electronic device  100  is controlled generally by monitoring the touch-sensitive display  118  for a touch event thereon, and modulating a force on the touch-sensitive display  118  for causing a first movement of the touch-sensitive display  118  relative to the base  308  of the portable electronic device  100  in response to detection of a touch event. The force is applied by at least one of the piezoelectric disk actuators  314 , in a single direction on the touch-sensitive input surface of the touch-sensitive display  118 . In response to determination of a touch event, the charge at each of the piezoelectric disks  318  is modulated to modulate the force applied by the piezoelectric disk actuators  314  on the touch-sensitive display  118  and to thereby cause movement of the touch-sensitive display  118  for simulating the collapse of a dome-type switch. When the end of the touch event is detected, the charge at each of the piezoelectric disks  318  is modulated to modulate the force applied by the piezoelectric disk actuators  314  to the touch-sensitive display  118  to cause movement of the touch-sensitive display  118  for simulating release of a dome-type switch. 
     The touch-sensitive display  118  is moveable within the housing  200  as the touch-sensitive display  118  can be moved away from the base  308 , thereby compressing the compliant gasket  312 , for example. Further, the touch-sensitive display  118  can be moved toward the base  308 , thereby applying a force to the piezoelectric disk actuators  314 . By this arrangement, the touch-sensitive display  118  is mechanically constrained by the housing  200  and resiliently biased by the compliant gasket compliant  312 . In at least some embodiments, the touch-sensitive display  118  is resiliently biased and moveable between at least a first position and a second position in response to externally applied forces wherein the touch-sensitive display  118  applies a greater force to the force sensors  122  in the second position than in the first position. The movement of the touch-sensitive display  118  in response to externally applied forces is detected by the force sensors  122 . 
     The analog-to-digital converter  504  is connected to the piezoelectric disks  318 . In addition to controlling the charge at the piezoelectric disks  318 , an output, such as a voltage output, from a charge created at each piezoelectric disk  318  may be measured based on signals received at the analog to digital converter  504 . Thus, when a pressure is applied to any one of the piezoelectric disks  318  causing mechanical deformation, a charge is created. A voltage signal, which is proportional to the charge, is measured to determine the extent of the mechanical deformation. Thus, the piezoelectric disks  318  also act as sensors for determining mechanical deformation. 
       FIG. 6  shows a block diagram of a circuit  600  for controlling the force sensors  122  of the portable electronic device  100  according to one embodiment of the present disclosure.  FIG. 7  is schematic diagram of an example circuit according to one embodiment of the present disclosure. The circuit  600  provides a wakeup detection circuit in some modes including, but not limited to (i) a full power mode in which normal, full functionality of the device  100  is provided; (ii) a sleep mode in which reduced functionality of the device  100  is provided; and (iii) an off mode in which the device  100  is powered-off and performs no functions or a minimized set of functions. As described above, the force sensors  122  measure the amount of applied force to the touch-sensitive display  118  (e.g., by the device user&#39;s fingers) and the touch-sensitive display  118  measures the location of touch events. The portable electronic device  100  described above provides a virtual click or “v-click” touchscreen which uses touch data and force data to generate click or unclick inputs and provide tactile feedback in response to click or unclick inputs using the piezoelectric disks  318  to actuate the touch-sensitive display  118 . The touch-sensitive display  118  is actuated (or moved) up and down in response to the expansion and contraction of the piezoelectric disks  318  as described above. For convenience, the touch-sensitive display  118  is sometimes referred to as a touch sensor herein. 
     The circuit  600  consists of both analog and digital sections and provides a means of configuring a programmable response of the force sensors  122  to a user&#39;s press against the touch-sensitive display  118 . In the shown example embodiment, the force sensors  122  comprise a number of force sensing resistors (FSRs)  602  for measuring applied force (or pressure). The resistance of the FSRs  602  change when a force or pressure is applied to them. The change in resistance causes a detectable voltage change. The FSRs  602  are numbered 1 to n where n is the total number of resistors. As described above in connection with  FIG. 3A to 5 , in some embodiments four FSRs  602  are used and located with a piezoelectric disk actuator  314  near a respective corner of the touch-sensitive display  118 . The FSRs  602  may be disk-shaped or puck-shaped and may be located on top of the piezoelectric disks  318  and below the touch-sensitive display  118 . 
     The FSRs  602  are each controlled by a digitally controlled switch. In the shown embodiment, the FSRs  602  are connected to an n-port switch  604  (also known as a multi-port switch) which comprises n single-pole, single-throw (SPST) switches. In embodiments in which four FSRs  602  are used, the n-port switch  604  comprises four SPST switches, one for each FSR  602 . The n-port switch  604  controls which, if any, of the FSRs  602  report force data to host processor  102  (directly or indirectly). The n-port switch  604  and SPST switches are controlled by the controller  500  of  FIG. 5 . 
     The n-port switch  604  generates an output signal which is sent to a signal conditioning circuit or module  606  of the circuit  600 . The signal conditioning module  606  can be used to offset (or bias) the FSRs  602  at various levels under the control of the controller  500 . The signal conditioning module  606  can also be used to vary the sensitivity of the FSR response by varying the gain provided by the signal conditioning module  606 . The controller  500  controls the variable offset and gain of the signal conditioning module  606 . In at least some embodiments, the signal conditioning module  606  comprises digital potentiometers which are controlled by the controller  500  and utilized for adjusting and calibrating the response of the FSRs  602  and an operational amplifier (Op-Amp), while in other embodiments, analog potentiometers could be used. In other embodiments, the signal conditioning module  606  could be omitted depending on the configuration of the FSRs  602  or other force sensor  122  used in the circuit  600 . 
     Typically, the FSRs  602  are pre-loaded with an amount of force as a result of the mechanical forces applied by the housing  200  and touch-sensitive display  118 . The amount of pre-loading may vary between embodiments. The bias and gain of the FSRs  602  can be calibrated to account for the pre-loading and FSR sensitivity differences using the signal conditioning module  606 , for example, using potentiometers. In the shown embodiment, the circuit  600  can be used to calibrate each FSR  602  individually by closing the respective switch in the n-port switch  604 . 
     In other embodiments, rather than summing all of the FSRs  602  via the n-port switch  604  groups of FSRs  602  may be summed and evaluated independently. For example, when four FSRs  602  are used near the respective corners of the touch-sensitive display  108 , the top pair of FSRs  602  and bottom pair of FSRs  602  could be summed and evaluated independently (e.g., groups of two FSRs  602  could be evaluated). These groupings could shift depending on whether the portable electronic device is in a portrait or landscape orientation. Alternatively, the left side and right sight FSRs  602  could be summed and evaluated independently. In yet other embodiments, individual FSRs  602  could be read/scanned and evaluated independently. A force event could be triggered (e.g. for a wakeup event) if all, any group or pair, or any one of the FSRs  602  measured a force which exceeds the predetermined wake force/pressure threshold. In other embodiments, other force sensing transducers comprising a force sensor such as a strain gauge or pressure sensor could be used to detect a force event (e.g. an applied force against the touch-sensitive display which exceeds the predetermined wake force/pressure threshold) instead of FSRs  602 . Alternatively, the piezoelectric disk actuators  314  could be used to detect a force event. 
     The controller  500 , in the shown embodiment of  FIG. 6 , includes a General Purpose Input/Output (GPIO). A GPIO is an interface which can act as input to read digital signals from other parts of the circuit  600  such as the signal conditioning module  606 , or output digital signals to other parts of the circuit. The GPIO may be provided by a GPIO port having a number of individual GPIOs configurable as either input or outputs, and may be configurable to produce interrupts to the host processor  102 . The controller  500  also includes an ADC  504  ( FIG. 5 ) with a corresponding interface as described above. Alternatively, the controller  500  or signal conditioning block  606  could incorporate an analog comparator with a programmable reference for achieving the same. In some example embodiments, the controller  500  could be the electronic controller  116  of the touch-sensitive display  118  or the processor  102 . 
     The portable electronic device  100  has several power modes: (i) a full power mode in which normal, full functionality of the device  100  is provided; (ii) a sleep mode in which reduced functionality of the device  100  is provided; and (iii) an off mode in which the device  100  is powered-off and performs no functions or a minimized set of functions. The sleep mode may be triggered by any one of a number of possible trigger conditions. The portable electronic device  100  monitors for one or more predetermined trigger conditions for entering the sleep mode. The one or more trigger conditions may be include any one or more of a selection of a sleep/standby option or device lock option via corresponding input, user inactivity for a predetermined duration, lack of wireless network coverage for a predetermined duration, a holstering or closing of the portable electronic device  100 , or other suitable trigger condition. In response to detection of a trigger condition, the processor  102  initiates the sleep mode and notifies the controller  500  to initiate a sleep mode for the circuit  600 . The controller  500  then proceeds to read (scan) the FSRs  602  for a wakeup event until either a wakeup force/pressure threshold is met, or the processor  102  signals the controller  500  to cease reading/scanning the FSRs  602 . When the wakeup force threshold is exceeded, the controller  500  can signal an interrupt back to the processor  102  waking it from the sleep mode (or standby state). 
     In some embodiments, when in the sleep mode, power consumption is conserved by powering off the high frequency system clock and switching the controller  500  from the system clock to the sleep clock. This reduces the power consumption of the circuit  600 . In the sleep mode, the sleep clock is used by the controller  500  and the host processor  102  is idle. 
     The controller  500  uses a sleep clock to schedule “on” and “off” time of the circuit  600  accordance with a predetermined duty cycle. The duty cycle is programmable and controls the balance between power consumption and response latency. In some embodiments, the n-port switch  604  is closed and the FSRs  602  are powered “on” for approximately 1 millisecond every 100 milliseconds. During this time, the controller  500  reads the FSRs  602  to detect force events, that is, to determine if a force greater than a predetermined amount of applied force (i.e., a force threshold) is read by one or more of the FSRs  602 . After being powered-on for approximately 1 millisecond during the “on” time, the FSRs  602  are powered-off for 99 milliseconds by re-opening the n-port switch  604  for “off” time or inactive portion of the duty cycle. The FSRs  602  are powered-off for the remainder of the duty cycle. 
     The duration of the duty cycle may be selected to configure the duration of a force applied to the touch-sensitive display  118  (e.g., screen press) required to trigger a force event. For example, in some embodiments the duration of time which the FSRs  602  are read is configured to detect a “push and hold” or “press and hold” action caused by the device user pressing a finger against the touch-sensitive display  118  and holding it against the touch-sensitive display  118  for a predetermined duration such as, for example, approximately 100 milliseconds. The predetermined duration for a press and hold may be programmable/configurable, for example, to tune the wakeup function to the device user&#39;s habits or preferences and to filter out small ambient vibrations from normal movements, such as the device user walking with the device  100 . For example, an inertial event caused by a tap event would occur and be over within a few milliseconds, e.g. approximately 20-25 milliseconds or less. The predetermined duration for a press and hold action is set to be longer than that of a typical tap event such as, for example, approximately 100 milliseconds. However, the predetermined duration could be more or less than 100 milliseconds and would typically be less than one second, and possibly less than 500 milliseconds. This means that any inertial event would have ended when the predetermined duration for detecting a press and hold event is reached. The touch-sensitive display  118  should also detect a tap event of the predetermined duration at the same time. Due to latency issues the forces measured by the force sensors  122  and the touches measures by the touch-sensitive display  118  may not be reported at the same time, however, these events can be synchronized or matched with each other. 
     In the shown example embodiment, the controller  500  configures the n-port switch  604  to sum the measurement of all of the FSRs  602  by closing each of the 4 SPST switches of the n-port switch  604  which are normally open, thereby connecting the FSRs  602  in parallel. The resultant output signal of the n-port switch  604  is then fed as input into the signal conditioning module  606 . The variable offset and gain provided by the signal conditioning module  606  allows for a programmable response from the FSRs  602 , thereby controlling the predetermined amount of applied force (i.e., force threshold) which is needed to trigger a force event. 
     As a result of summing of the readings of the FSRs  602  and a properly set force threshold, it is possible to trigger a force event when a device user presses on the touch-sensitive display  118  at any location. This occurs because a screen press under these conditions causes a force greater than or equal to the predetermined amount of applied force (i.e., the force threshold) to be detected on at least one of the FSRs  602 . The force event will typically be detected by the FSR  602  closest to the location of the applied force on the touch-sensitive display  118  and possibly one or more of the other FSRs  602 . 
     Force events are defined by applied forces greater than the force threshold. Force events can be detected using either analog or digital threshold comparator depending on the embodiment. In some embodiments, the analog signal output by the signal conditioning module  606  can be digitized by an ADC and then evaluated with a digital threshold comparator which can be implemented either in hardware or in software. For example, in some embodiments, force events could be detected by the controller&#39;s internal ADC  504  detecting that the analog signal has exceeded the force threshold. In other embodiments, force events could be detected by an analog comparator circuit (not shown) which triggers an interrupt to the controller  500  when the analog signal output by the signal conditioning module  606  exceeds the force threshold. The analog comparator can detect and signal a high/low output to the processor  102 . When a force event is detected, the controller  500  sends a signal to the host processor  102  of the device  100  that an interrupt event was detected, and brings the portable electronic device  100  out of the sleep mode and into the full power mode. Wakeup events are defined by applied forces greater than a predetermined wakeup force threshold. 
     The described method of wakeup uses a relatively small amount of power while still allowing wakeup events to be detected. This functionality also reproduces the wakeup of a portable electronic device  100  caused by the collapse of a dome-type switch disposed between the touch-sensitive display  118  and housing  200  when the device user presses any where on the touch-sensitive display  118 . 
       FIG. 8  shows a flowchart illustrating a method  800  of providing a sleep mode on the portable electronic device  100  and waking up the device  100  from the sleep mode in accordance with one example embodiment. The steps of  FIG. 8  may be carried out by routines or subroutines of software executed by, for example, the processor  102 . The coding of software for carrying out such steps is well within the scope of a person of ordinary skill in the art given the present disclosure. For example, the sleep mode may be implemented by a sleep process which operates in the background as part of the operating system  146 . 
     In the first step  802 , the processor  102  monitors for one or more predetermined trigger conditions for entering the sleep mode. The one or more trigger conditions may be include any one or more of a selection of a sleep/standby option via corresponding input or possibly a device lock option via corresponding input, user inactivity for a predetermined duration, lack of wireless network coverage for a predetermined duration, a holstering or closing of the portable electronic device  100 , or other suitable trigger condition. 
     When one of the trigger conditions for entering the sleep mode is detected, the processor  102  initiates the sleep mode (step  804 ). The sleep mode may comprise the processor  102  switching from the system clock to the sleep clock and deactivating (e.g., powering off) the touch-sensitive display  118 . When deactivated, the touch-sensitive display  118  does not measure touch data or detect touch events and its backlight is deactivated/disabled. In the sleep mode, the force sensors  122  continue to detect and measure forces applied to the touch-sensitive display  118 . In at least some embodiments, the processor  102  instructs the controller  500  to initiate a sleep mode for the force sensor circuit  600  when one of the trigger conditions for entering the sleep mode is detected. In the sleep mode, the force sensors  122  operate at a reduced duty cycle relative to the full power mode and/or sample at a lower sampling rate relative to the full power mode to consume less power. 
     A locked mode may also be initiated in response to detecting one of the trigger conditions for entering a sleep mode when the sleep mode is itself triggered by a locking process, depending on the configuration of the locking process. In the locked mode, restrictions limiting interaction with the portable electronic device  100  are enforced. The restrictions typically affect at least some of its input interfaces/devices (e.g., overlay  114 , auxiliary I/O  124 , accelerometer  136 ) and at least some of its output interfaces/devices (e.g., display screen  112 , speaker  128 ). 
     To reduce the power and resources consumed by the force sensor circuit  600 , touch-sensitive display  118  and the host processor  102 , the force sensors  122  and touch-sensitive display  118  can be put in a low reporting mode in which data is provided to the processor  102  only when a change in state of the respective sensor occurs. The low reporting mode can be contrasted with a full reporting mode in which the force sensors  122  and touch-sensitive display  118  provide data at regular scanning cycles irrespective of the state of the respective sensor. For the touch sensor  118 , a change in the location of a touch event greater than a predetermined threshold or a change number of touches will trigger a change of state. For the force sensors  122 , a change in state occurs when a force greater than a predetermined force threshold is detected by the force sensor controller  500  on all, any group or pair, or any one of the force sensors  122 . A force greater than the predetermined force threshold is assumed to be a user finger applied to the touch-sensitive display  118 . The predetermined force threshold for trigger a change in state is different from, and less than, the predetermined wake force threshold mentioned above. 
     In some embodiments, the sleep mode comprises changing the sampling of the force sensors  122  from the full reporting mode to the low reporting mode to consume less power. However, in other embodiments, the low reporting mode may be used by the force sensor  122  and possibly the touch-sensitive display  118  in both the full power mode and the sleep mode. 
     Next, in step  806  the force sensor controller  500  reads the force data output by the force sensors  122  and detects any wakeup force. The wakeup force is a force greater than the predetermined wake force threshold. This can be performed using analog or digital means as described above. When a wakeup force is detected, the force sensors  122  (e.g., and the circuit  600 ) wakeup from the sleep mode and return to the normal duty cycle and/or normal sampling rate of the full power mode, and touch-sensitive display  118  is reactivated (powered-up) so that touch data can be read/sampled for a predetermined duration (step  808 ). In other embodiments, the force sensors  122  could be maintained at the lower sampling rate of the sleep mode to consume less power when the touch-sensitive display  118  is reactivated. The force data and touch data are then read and it is determined whether a screen press or “click” has occurred or is in progress. 
     The backlight of the touch-sensitive display  118  may or may not be reactivated during the scanning/reading of the touch-sensitive display  118  which occurs in response to detection of a wakeup force, depending on the embodiment. For example, in some embodiments the backlight of the touch-sensitive display  118  is not activated until the wakeup event is confirmed by touch data read by the touch-sensitive display  118  to conserve power. 
     When the force data read by the forces sensors  122  and the touch data read by the touch-sensitive display  118  indicates a screen press or “click” has occurred or is in progress (step  810 ), the processor  102  wakes up from the sleep mode and returns to full power mode (step  812 ). If the processor  102  was switched from the system clock to the sleep clock during the sleep mode, the processor  102  switches back to the system clock. Other changes made when entering the sleep mode are also reversed. In at least some embodiments, the charge at each of the piezoelectric disks  318  is then be modulated to modulate the force applied by the piezoelectric disk actuators  314  on the touch-sensitive display  118  and to thereby cause movement of the touch-sensitive display  118  for simulating the collapse of a dome-type switch. This provides tactile or haptic feedback to the device user so that they know a screen press or “click” was registered by the device  100 . 
     If a screen press or “click” is not detected, the touch-sensitive display  118  is deactivated again until being reactivated by the detection of another wakeup force, and the force sensors  122  are returned to the lower duty cycle and/or lower sampling rate of the sleep mode. 
     As will be appreciated by persons skilled in the art, sampling forces and touches applied to the touch-sensitive display  118  consumes scarce device power. During normal operation, this sampling occurs at a high rate to keep up with user interaction with the touch-sensitive display  118 . However, when the portable electronic device  100  is idle a high sampling rate needlessly consumes power resulting in a shorter life for the power source  142 . The present disclosure provides a method and portable electronic device  100  which aims to minimize, or at least reduce, the power consumed when the portable electronic device  100  while still clicking in response to forces. 
     To reduce the power and processing resources consumed, the present disclosure provides a sleep mode which deactivates the touch-sensitive display  118  when the device  100  is idle and uses the force sensors  122  to sample force data at a lower sampling rate to detect a potential wakeup when a force greater than the predetermined wakeup force threshold is detected. The sleep mode described in the present disclosure aims to minimize, or at least reduce, the power consumed when the portable electronic device  100  is idle while also registering screen presses or “clicks” in response to applied forces and optionally providing tactile/haptic feedback by modulating the charge at each of the piezoelectric disks  318  to modulate the force applied by the piezoelectric disk actuators  314 . 
     Moreover, the predetermined wakeup force threshold may be set so as to filter out small applied forces such as ambient forces resulting from normal movements of the portable electronic device  100  (such as those applied to the device  100  while in a user&#39;s pocket while walking), while still detecting a finger pressing against touch-sensitive display  118 . This avoids unnecessary wakeup event checks by limiting the applied forces which will be detected as potential wakeup events. 
       FIG. 9  shows a flowchart illustrating a method  900  of providing a sleep mode on the portable electronic device  100  and waking up the device  100  from the sleep mode in accordance with another example embodiment. The steps of  FIG. 9  may be carried out by routines or subroutines of software executed by, for example, the processor  102 . The coding of software for carrying out such steps is well within the scope of a person of ordinary skill in the art given the present disclosure. For example, the sleep mode may be implemented by a sleep process which operates in the background as part of the operating system  146 . 
     In steps  802  and  804 , the processor  102  monitors for one or more trigger conditions for enter a sleep mode, and enters a sleep mode in response to detection of one of the trigger conditions as described above. In the sleep mode of the embodiment shown in  FIG. 9 , the forces sensors  122  are not read by the controller  500 . As a result, the force sensors  122  or the entire circuit  600  may be powered-off to consume less power. In some embodiments, the circuit  600  has a non-power cycled current draw of approximately 80 μA which can be reduced by powering down the forces sensors  122 . In other embodiments, the force sensors  122  could be operated at a reduced/slower duty cycle relative to the full power mode and/or sample at a lower sampling rate relative to the full power mode to consume less power as in the method  800  of  FIG. 8 . 
     Next, in step  902  the accelerometer  136  is used to detect an inertial event. The inertial event could be a tap on the touch-sensitive display  118 , a movement of the device  100  causing a change in acceleration which exceeds a predetermined threshold, or possible a predetermined movement or gesture performed by moving the device  100  in a predetermined manner (this motion being detected by the accelerometer  136 ). 
     A gesture is a predetermined motion performed by moving the device  100  in a predetermined manner such as a predetermined direction or series of directions. Gestures are identified by comparing the accelerations measured by the accelerometer  136  to reference data for the predetermined motions to determine whether the detected motion is characteristic of one of the predetermined motions. This is typically performed by the host processor  102  using acceleration data provided by the accelerometer  136 , but could be performed via a built-in electronic controller of the accelerometer  136 . The predetermined inputs could be a forward movement, backward movement, up movement, down movement, left movement, right movement, tilt left movement, tilt right movement, swing left movement, swing right movement or any other predetermined movement such as a movement which approximate a letter, number of symbol, or a series of such movements. In some embodiments, a horizontal tilt or swing movement (i.e., a left or right horizontal tilt or swing movement) and vertical tilt or swing movement (i.e., an up or down tilt or swing movement). Alternatively, a left tilt or swing movement, right tilt or swing movement, up tilt or swing movement and down tilt or swing movement could each be distinct predetermined inputs. 
     In some example embodiments, the inertial event could be a tap on the touch-sensitive display  118  and the accelerometer  136  is a digital accelerometer having a built-in tap detection function which may be used to detect a tap on the touch-sensitive display  118 . Many commercially available digital accelerometers have a built-in tap detection function. Any digital accelerometer having a built-in tap detection function could be used. The tap detect threshold used by the built-in tap detection function may be programmable/configurable and set so as to filter out small ambient vibrations from normal movements, such as the device user walking with the device  100 . 
     Alternatively, rather than a digital accelerometer an analog accelerometer with an analog comparator circuit (not shown) with a programmable/configurable reference could be used. The programmable reference acts as a predetermined acceleration threshold for an inertial event. The analog comparator circuit sends an interrupt to the controller  500  when the analog output signal of the analog accelerometer exceeds the programmable reference. 
     The accelerometer  136  may also be power-cycled to lower the sampling rate and conserve power when the device  100  is idle, for example, when the acceleration reading has not changed by more than a predetermined amount for a predetermined duration. Power-cycling of the accelerometer  136  may occur automatically as part of entering the sleep mode. When the acceleration exceeds this amount, the accelerometer  136  returns to the higher sampling rate to reduce latency in detection acceleration. In some example embodiments, the accelerometer  136  could have autonomous power cycling that can reduce current consumption to approximately 25 μA or less. 
     When an inertial event is detected, an interrupt is sent from the accelerometer  136  or a comparator circuit for the accelerometer  136  to the controller  500  to wake the force sensors  122  (step  904 ). As noted above, waking the force sensors  122  may comprise powering on the force sensors  122 , increasing from a lower sampling rate of the sleep mode to a higher sampling rate (e.g., normal sampling rate of the full power mode), depending on the configuration of the sleep mode. Alternatively, the interrupt could be sent to the host processor  102 , or to both the controller  500  and processor  102 . 
     Next, in step  806  the force data output by the force sensors  122  is read by the force sensor controller  500  of the circuit  600  which detects any wakeup force. This can be done via analog or digital means as described above. In some embodiments in which sleeping and waking the force sensors  122  comprises powering down and powering up the force sensors, the process of powering up the force sensors  122  and taking a measurement may take approximately 1 millisecond or less depending on the design of the signal conditioning module  606 . This amount of time is sufficiently short that a wakeup force caused by an inertial event should, in at least most circumstances, still be present when the force sensors  122  wake. If no wakeup force is present when the force sensors  122  wake, the inertial event is considered to be erroneous and caused by something other than a screen press or “click”. 
     When a wakeup force is detected, the touch-sensitive display  118  is reactivated/powered-up and the processor  102  wakes up from the sleep mode and returns to full power mode (step  812 ). If the processor  102  was switched from the system clock to the sleep clock during the sleep mode, the processor  102  switches back to the system clock. Other changes made to when entering the sleep mode are also reversed. In at least some embodiments, the charge at each of the piezoelectric disks  318  is modulated to modulate the force applied by the piezoelectric disk actuators  314  on the touch-sensitive display  118  and to thereby cause movement of the touch-sensitive display  118  for simulating the collapse of a dome-type switch. This provides tactile or haptic feedback to the device user so that they know a screen press or “click” was registered by the device  100 . 
     If a wakeup force is not detected, the force sensors  122  are deactivated/powered-off again and returned to the sleep mode until being reactivated by the detection of another inertial event. 
     The method  900  provides a wakeup solution which uses inertial events to trigger a device wakeup and a force event to verify this trigger. The inertial event could be a movement of the device  100  or a tap on the touch-sensitive display  118 . For example, in some embodiments the device could be configured to use a “press and hold” event as a wakeup event. In a press and hold event, the user presses or taps on the touch-sensitive display  118  with a finger to create an inertial event and presses on the touch-sensitive display  118  for a predetermined duration to create a force event. The touch-sensitive display  118  should also detect a tap event of the predetermined duration at the same time. Due to latency issues the forces measured by the force sensors  122  and the touches measures by the touch-sensitive display  118  may not be reported at the same time, however, these events can be synchronized or matched with each other. The inertial event will have ended when the predetermined duration for detecting a press and hold event is reached. The press and hold event will trigger a wakeup as described above. 
     In an alternate embodiment, the force sensors  122  are not affected by the sleep mode. In the sleep mode, the touch-sensitive display  118  and host processor  102  are put to sleep as described above and the accelerometer  136  is used to monitor for inertial events which, when detected, trigger an increase in the duty cycle and/or sampling rate of the force sensors  122  in order to reduce the latency in detecting wakeup events in the form of force events. 
       FIG. 10  shows a flowchart illustrating a method  920  of providing a sleep mode on the portable electronic device  100  and waking up the device  100  from the sleep mode in accordance with a further example embodiment. The steps of  FIG. 10  may be carried out by routines or subroutines of software executed by, for example, the processor  102 . The coding of software for carrying out such steps is well within the scope of a person of ordinary skill in the art given the present disclosure. For example, the sleep mode may be implemented by a sleep process which operates in the background as part of the operating system  146 . 
     The method  920  comprises the steps  802 ,  804 ,  902 ,  904  and  806  described above in connection with the method  900  of  FIG. 9 . However, the force sensors  122  measure force at a reduced rate in the sleep mode as in the method  800  of  FIG. 8 . When a wakeup force is detected, the force sensors  122  (e.g., and the circuit  600 ) wakeup from the sleep mode and return from a reduced duty cycle of the sleep mode to the normal duty cycle and/or normal sampling rate of the full power mode, and touch-sensitive display  118  is reactivated (powered-up) so that touch data can be read/sampled for a predetermined duration (step  808 ). 
     When the force data read by the forces sensors  122  and the touch data read by the touch-sensitive display  118  indicates a screen press or “click” has occurred or is in progress ( 810 ), the processor  102  wakes up from the sleep mode and returns to full power mode (step  812 ). If the processor  102  was switched from the system clock to the sleep clock during the sleep mode, the processor  102  switches back to the system clock. Other changes made when entering the sleep mode are also reversed. In at least some embodiments, the charge at each of the piezoelectric disks  318  is then be modulated to modulate the force applied by the piezoelectric disk actuators  314  on the touch-sensitive display  118  and to thereby cause movement of the touch-sensitive display  118  for simulating the collapse of a dome-type switch. This provides tactile or haptic feedback to the device user so that they know a screen press or “click” was registered by the device  100 . 
     If a screen press or “click” is not detected, the touch-sensitive display  118  is deactivated again until being reactivated by the detection of another wakeup force, and the force sensors  122  are returned to the lower duty cycle and/or lower sampling rate of the sleep mode. 
     The method  920  is similar to the method  800  of  FIG. 8  but adds inertial event detection using the accelerometer  136  from the method  900  of  FIG. 9  to verify potential wakeup events which an aim to reduce the false “wakeups” which may result, for example, from a finger moving across the touch-sensitive display  118 . 
     In an alternate embodiment, the force sensors  122  are not affected by the sleep mode. In the sleep mode, the touch-sensitive display  118  is deactivated and host processor  102  is idled as described above and the accelerometer  136  is used to monitor for inertial events which, when detected, trigger an increase in the duty cycle and/or sampling rate of the force sensors  122  in order to reduce the latency in detecting wakeup events in the form of force events. In another alternate embodiment, detection of the inertial event could wake both the force sensors  122  and touch-sensitive display  118  at the same time. 
     In some embodiments, the detection of an inertial event could cause the duty cycle and/or the sampling rate of the touch-sensitive display  118  to be increased to reduce the latency in wakeup event detection caused by the relatively long scan cycle of the touch-sensitive display  118 . 
       FIG. 11  shows a flowchart illustrating a method  940  of providing a sleep mode on the portable electronic device  100  and waking up the device  100  from the sleep mode in accordance with a further example embodiment. The steps of  FIG. 11  may be carried out by routines or subroutines of software executed by, for example, the processor  102 . The coding of software for carrying out such steps is well within the scope of a person of ordinary skill in the art given the present disclosure. For example, the sleep mode may be implemented by a sleep process which operates in the background as part of the operating system  146 . 
     The method  940  comprises the steps  802 ,  804  and  902  as described above. However, the detection of an inertial event is used to reactivate (power-up) the touch-sensitive display  118  so that touch data can be read/sampled for a predetermined duration (step  808 ) rather than waking up force sensors  122 . The force sensors  122  are not used in the process  940  and could be omitted from a device  100  which implements this method. When the touch data read by the touch-sensitive display  118  indicates a touch event has occurred or is in progress (step  910 ), the processor  102  wakes up from the sleep mode and returns to full power mode (step  812 ). If the processor  102  was switched from the system clock to the sleep clock during the sleep mode, the processor  102  switches back to the system clock. Other changes made when entering the sleep mode are also reversed. The charge of the piezoelectric disks  318  is not modulated and no tactile or haptic feedback is provided to the device user. In such embodiments, the force sensors  122  and actuators  120  (e.g. piezoelectric disk actuators  314 ) could be omitted. 
     If a touch event is not detected (step  810 ), the touch-sensitive display  118  is deactivated again until being reactivated by the detection of another inertial event. 
     The method  940  is similar to the method  900  of  FIG. 9  but does not use the force sensors  122  to detect wakeup events. Instead, the inertial event detection function provided by the accelerometer  136  is used to wake the touch-sensitive display  118 , and the touch data measured by the touch-sensitive display  118  is used verify potential wakeup events which an aim to reduce the false “wakeups” which may result from using only the inertial event detection function as a wakeup event. That is, a touch event must be detected within a predetermined duration of when the touch-sensitive display  118  wakes up. The charge of the piezoelectric disks  318  is not modulated and no tactile or haptic feedback is provided to the device user. 
     The present disclosure teaches a method and portable electronic device which combines measurements from two or more independent sensors to confirm the detection of a wakeup event for a portable electronic device  100 , thereby reducing false-positives. In some embodiments, such as the method  800 , force data provided by force sensors  122  is combined with touch data provided by a touch-sensitive display  118  to verify potential wakeup events with an aim to reduce the false “wakeups”. 
     In some embodiments, such as the method  900  and  920 , inertial event detection provided by the accelerometer  136  is combined with force data provided by the force sensors  122  to verify potential wakeup events which an aim to reduce the false “wakeups” which may result from a finger moving across the touch-sensitive display  118 . The time correlation of the interrupt signal from the threshold crossing event of accelerometer  136  and the interrupt signal from the threshold crossing event of force sensors  122  may be used to reliably detect a device wakeup event at relatively low power and complexity. 
     In some embodiments, such as the method  900  and  920 , the power draw of the sleep mode may be reduced by powering off both the touch-sensitive display  18  and force sensors  122  while powering only the accelerometer  136 . In some embodiments, further power savings may be realized by power cycling the accelerometer  136 . 
     The various embodiments presented above are merely examples and are in no way meant to limit the scope of this disclosure. Variations of the innovations described herein will be apparent to persons of ordinary skill in the art, such variations being within the intended scope of the present application. In particular, features from one or more of the above-described embodiments may be selected to create alternative embodiments comprised of a sub-combination of features which may not be explicitly described above. In addition, features from one or more of the above-described embodiments may be selected and combined to create alternative embodiments comprised of a combination of features which may not be explicitly described above. Features suitable for such combinations and sub-combinations would be readily apparent to persons skilled in the art upon review of the present application as a whole. The subject matter described herein and in the recited claims intends to cover and embrace all suitable changes in technology.