A PORTABLE ELECTRIC APPARATUS HAVING A LIQUID CRYSTAL DISPLAY, AND A POWER PRESERVATION METHOD FOR SUCH AN APPARATUS

Abstract: A portable electric apparatus (1) has a display (6) of the type comprising a liquid crystal layer. The display has an active state for presenting visual information in response to a supply of electric energy to the liquid crystal layer. The display also has an inactive state, in which less electric energy is supplied to the liquid crystal layer and less visual information consequently is presented. The apparatus (1) also has a proximity detector (20) for detecting the presence of an object in proximity with the apparatus and in response causing the display (6) to enter its inactive state.

Description: A PORTABLE ELECTRIC APPARATUS HAVING A LIQUID CRYSTAL DISPLAY, AND A POWER PRESERVATION METHOD FOR SUCH AN APPARATUS Technical Field The present invention relates to a portable electric apparatus having a display of the type comprising a liquid crystal layer, the display having an active state for presenting visual information in response to a supply of electric energy to the liquid crystal layer, the display also having an inactive state, in which less electric energy is supplied to the liquid crystal layer and less visual information consequently is presented. More specifically, the invention is directed at a new and inventive way of preserving electric power in such a portable electric apparatus by bringing the display to its inactive state whenever appropriate. The invention also relates to a method of preserving power for such an apparatus . Prior Art Examples of portable electric apparatuses as set out above are for instance mobile or cellular telephones, wireless telephone handsets, personal communicators, portable digital assistants, palmtop computers, etc. The users thereof are dependent of a fully functional apparatus. More specifically, one of the most common problems in this respect is the limited operational duration between subsequent chargings of a battery used for supplying power to the apparatus. While it has been possible to reach reduced power consumption through the development of low-voltage, high-density integrated circuits, battery capacity is still a major obstacle against full user freedom in terms of virtually unlimited operational duration. Consequently, preservation of electric power is still a very important issue within the field of portable electric apparatuses. For the rest of this document, reference is made to a mobile telephone, which is chosen to represent a portable electric apparatus according to the invention. However, the invention shall in no way be limited to merely a mobile telephone. In a mobile telephone, the liquid crystal display (LCD) is responsible for a significant part of the total power consumption thereof . As is well known, a general liquid crystal display comprises two glass plates with a layer of liquid crystals provided between them. First and second polarizers are placed on either sides of the two glass substrates. A display driver is connected to the liquid crystal display via a plurality of control lines, which normally are arranged in a two-dimensional matrix across the liquid crystal layer. A first set of the parallel control lines is provided in a horizontal direction on the surface of one of the glass plates, facing one side of the liquid crystal layer. Correspondingly, a second set of the parallel control lines is provided in a vertical direction on the surface of the other glass plate, facing the other side of the liquid crystal layer. By supplying electric energy from the display driver through the control lines to the liquid crystal layer, individual elements (crystals or molecules) of the liquid crystal layer may be set to either an on-state, representing an active (e.g. black) pixel in the image presented by the liquid crystal display, or an off-state, representing a blank (e.g. transparent) pixel. In more detail, for a passive-type liquid crystal display, the crystals or molecules of the liquid crystal layer are oriented in parallel with the glass plates in their off-state. Due to the provision of the polarizers, such off-state crystals or molecules will not be visible to a viewer. To make specific crystals or molecules visible (i.e., force them to their on-state), the display driver scans (addresses) the control line matrix and supplies electric energy in the form of a voltage pulse on one specific horizontal control line and one specific vertical control line for each pixel to be set on. At the position where these two specific control lines cross each other, an electric field will be generated and change the orientation of the corresponding crystal or molecule from parallel to orthogonal with respect to the glass plates. Another kind of liquid crystal display is an active- type display, which comprises one transistor at each pixel. Unlike the passive-type liquid crystal display, the active- type display must be fed continuously with electric energy in order to set a pixel to its on-state and maintain the pixel in this state. A previously known active-type liquid crystal display is disclosed in WO-A-9952012 , which is fully incorporated herein by reference. The liquid crystal display may also involve an additional element, such as an electroluminescent film, for providing backlighting to the display. The highest power consumption for a liquid crystal display occurs when an event takes place in the telephone, for instance when a telephone call is generated or ended. In those situations, the visibility of the LCD display is amplified by turning on a back- light illumination of the display. Such back-light illumination consumes too much power than what is acceptable in a long-term perspective. Therefore, back- light illumination is normally restricted to a short time period of a few seconds around the respective event, such as the entering of a telephone number on the keypad, the reception of an incoming call or the termination of an ongoing call (on-hook) . Even if back-light illumination is avoided to a large extent, the display nevertheless consumes electric power also in stand-by mode. The reason for this is that status information has to be presented to the user. Examples of such status information are: current network operator, received signal strength indicator (RSSI) , remaining battery capacity, time of day, etc. Some prior art mobile telephones offer "limited icon mode" during stand-by mode, wherein the display is partially powered off, so that only critical information is displayed. While this approach provides a certain reduction in power consumption, a significant amount of electric power will still be unnecessarily consumed by the display, if the telephone is left in stand-by mode for a long period of time in a bag, a pocket, etc. The document RD-A-332 083, which is available from Derwent Info Ltd under access number 92-022097/199203 in the database commonly known as WPI (World Patent Index) , relates to a portable electric apparatus in the form of a remote control unit. This document observes that the functionality of the remote control unit is only required, when the user focuses attention on it . The remote control unit is provided with a motion or acceleration sensor to detect when the remote control unit is carried in the hand of a user. In the absence of such detection, the remote control unit may determine that the unit is placed on a stable surface and is no longer held by the user, wherein the power- consuming components of the remote control unit may be switched off in order to preserve electric power of the battery. For instance, the display of the remote control unit consumes a substantial amount of electric power from the battery, and by switching off the display in situations other than when the unit is carried by the user, considerable power may be preserved. The solution according to RD-A-332 083 has a drawback in that it requires the use of a motion or acceleration sensor, which is both expensive and bulky. Furthermore, assuming a situation where the user has put the remote control unit in front of him/her on a table, the motion or ac- celeration sensor may be fooled by the apparently stable condition and switch off the unit, even if the user is actually still using the unit, for instance looking at the display thereof. US-A-5 881 377 discloses a radio telephone with a power-saving arrangement, which is adapted to detect the presence of the radio telephone in proximity with an ear of a user and which also is adapted to turn off a display of the radio telephone. Aforesaid arrangement may be of a type capable of detecting heat, or comprise an opto-electric switch. The display of the radio telephone is of a type comprising light emitting diodes (LED) . According to an alternative embodiment of US-A-5 881 377, the display is a liquid crystal display, and a light emitting diode is provided for backlighting the LCD-display. In this embodiment, the backlighting LED, but not the actual liquid crystal display, is switched on and off for saving electric power in response to whether or not the radio telephone is kept near the user's head. US-A-5 729 604 discloses a wireless telephone handset with an arrangement for detecting that the telephone handset is kept in proximity with an ear of a user. This arrangement may for instance operate by detecting infrared radiation and in response turning off a backlighting of a liquid crystal display. Consequently, from the two US publications referred to above it is known to provide a radio telephone or a wireless telephone handset with a proximity detector, the purpose of which is to detect when the telephone is kept in proximity with the user. The main embodiment of US-A-5 881 377 teaches that the output from the proximity detector may be used for turning off an LED display. The alternative embodiment of this US-publication, as well as the disclosure in US-A-5 729 604, teaches that the backlighting of a liquid crystal display (LCD) can be switched on and off de- pending on the output from the proximity detector. The purpose of these inventions is to save electric power when the telephone is kept close to the user (i.e. in proximity with the user's ear in talking position). The liquid crystal display is by far the most commonly used type of display in mobile telephones and other types of portable electric apparatus. Both US publications mention liquid crystal displays, but neither of them teaches or even suggests to use the output from the proximity detector to turn off the actual LCD display. Thus, the US publications only teach to turn off the backlighting of the display. Summary of the Invention The purpose of the present invention is to propose an improved solution to the problem of preserving electric power in a portable electric apparatus having a liquid crystal display. In particular, the invention aims at achieving such power preservation at a lower cost and with improved accuracy, as compared to the prior art solutions. According to the invention, the portable electric apparatus is provided with a proximity detector, which is arranged to detect when an external object is very close to a specific portion of the apparatus (for instance less than 3 cm from the display) . The external object may be the user's ear (when the telephone is held in a normal position for conversation) , or the interior walls of a pocket or bag, in which the telephone has been placed by the user. In all circumstances, the presence of such an external object indicates that the apparatus is not in a position, where it is useful to keep the display turned on, since the user is physically prevented from visual access to the display. Therefore, when the proximity detector has detected the presence of the external object, the display may be powered off or present less visual information. More specifically, the purpose above has been achieved for a portable electric apparatus having a display of the type comprising a liquid crystal layer, wherein the display has an active state for presenting visual information in response to a supply of electric energy to the liquid crystal layer, and wherein the display also has an inactive state, in which less electric energy is supplied to the liquid crystal layer and less visual information consequently is presented, by the provision of a proximity detector for detecting the presence of an object in proximity with the apparatus and in response causing the display to enter its inactive state. The purpose has also been achieved through a method of preserving power for a portable electric apparatus having a display of the type comprising a liquid crystal layer, the display having an active state for presenting visual information in response to a supply of electric energy to the liquid crystal layer, the display also having an inactive state, in which less electric energy is supplied to the liquid crystal layer and less visual information consequently is presented, by the steps of determining whether an object is present in proximity with the apparatus, and, if so, causing the display to enter its inactive state. Other purposes, features and advantages of the present invention will appear from the following detailed disclosure, from the attached drawings as well as from the dependent claims. Brief Description of the Drawings Some embodiments of the invention will now be described in more detail, reference being made to the accompanying drawings , in which FIG 1 is a schematic front view of a portable electric apparatus, exemplified as a mobile telephone, having a liquid crystal display and a proximity detector according to the invention, FIG 2 is a schematic block diagram of the main functional parts of the apparatus shown in FIG 1, and FIG 3 is a flow chart illustrating a proximity sleep mode routine executed by a controller of the apparatus in order to perform the method according to some embodiments of the invention. Detailed Disclosure of Embodiments An example of a portable electric apparatus is given in FIG 1 in the form of a mobile telephone 1 having a housing 10, an antenna 2 mounted on top of the housing, a status indicator LED 3, a speaker 4, volume adjustment controls 5, an LCD display 6 and a keypad 7. The keypad 7 has a plurality of individual keys, such a YES button 12 and a NO button 13, arrow keys 14, 15, a clear key 16, numeric keys 17 (labeled 0 through 9) , a star key 18 and a hash key 19. The liquid crystal display 6 is arranged according to the description in the Prior Art section of this document, i.e. comprises two glass plates with a layer of liquid crystals provided between them, together with a control line matrix placed on either sides of the two glass plates. As previously described, the graphical information presented on the display 6 is controlled by supplying electric energy from the display driver through the control line matrix to the liquid crystal layer. The display 6 is shown in an active state in FIG 1 and comprises graphical symbols or icons for presenting a received signal strength indicator 21, a remaining battery charge indicator 22, information about the active network operator 23 as well as the current date 24. Consequently, the liquid crystal display 6 consumes a certain amount of electric energy, de- pending on the supply of electric energy to the liquid crystal layer. The liquid crystal display 6 also has an inactive state, where less or even no electric energy is supplied to the liquid crystal layer and, thus, less visual information is presented on the display. In contrast to the active state, during which all graphical information (e.g. the icons 21-24) is presented on the display, only parts of this graphical information is shown on the display during its inactive state. For instance, with reference to FIG 1, only the remaining battery charge indicator 22 (but not the icons 21, 22 or 24) is presented on the display 6 during its inactive state. Such an inactive state essentially corresponds to the "limited icon mode", which was described in the Prior Art section of this document. Alternatively, the liquid crystal display 6 may be completely turned off in its inactive state (i.e., no electric energy is supplied to the liquid crystal layer, wherein the power consumption of the display is essentially zero) . A foldable flip 8 is swingably mounted to the apparatus housing 10 by means of a hinge mechanism 11. The flip 8 comprises a sound opening 9, through which vocal sound is received from the user of the telephone and forwarded to an internal microphone (not shown in the drawing) . A proximity detector is provided at the uppermost portion of the front surface of the telephone 1. In the embodiment shown in FIG 1, the proximity detector 20 is located immediately above the display 6 next to the speaker 4. However, the exact location of the proximity detector 20 is not critical but may be varied between many different positions, as long as the functional requirements specified below are satisfied. In one embodiment, the proximity detector 20 is an IR (infrared) detector, which is arranged to emit infrared light from the front surface of the telephone 1 and is ar- ranged to detect infrared light, that has been reflected from an external object located close to the upper portion of front surface of the telephone 1. Hence, as is generally known per se, the proximity detector 20 may measure the intensity of the reflected infrared light and in response determine whether any external object is present in proximity with the detector 20. By establishing a predetermined threshold for the fraction of infrared light reflected back to the proximity detector 20, it is possible to define a predetermined range, within which any external object will be detected by the proximity detector 20. Obviously, such a threshold will depend on i.a. the surface structure and material of the external object in question. However, such an issue is regarded nothing more than a practical parameter, which in an actual application will have to be tested, evaluated and determined by a skilled person. Proximity detectors as such are generally known and are commercially available on the market in large numbers . According to an alternative embodiment, if the mobile telephone is equipped with an IR interface for wireless data communication with external devices (such as a handheld computer) , the IR transmitter thereof may be used also for the purpose of transmitting IR light to be detected by the proximity detector 20. Alternatively, the proximity detector 20 may operate by emitting and detecting visible light, by detecting thermal energy generated by the external object, or by detecting the external object by capacitive means. The main components of the mobile telephone 1 are shown in FIG 2. A controller 30 is operatively connected to the display 6, the keypad 7, the proximity detector 20 and a memory 40. The controller 30 may be any microprocessor, central processing unit (CPU) or other piece of electronic logic circuitry already used in the telephone 1 for performing the various functions thereof (such as telephone call control, keypad control, display control, or execution of utility programs such as a calculator program, electronic game programs, etc) . Alternatively, the controller 30 may be realized by separate electronic logic circuitry, which in itself is generally known, such as a microprocessor, an integrated circuit network, etc. Correspondingly, the memory 40 may be of any type generally known within the field of portable electric apparatuses, such as an EEPROM memory, a RAM memory, a flash memory etc. Together with the proximity detector 20, the controller 30 is arranged to bring the liquid crystal display 6 into its inactive state, whenever an external object is detected in proximity with the portion of the telephone 1, where the display is located. This functionality is referred to as Proximity Sleep Mode in the following. According to one embodiment the man-machine interface of the mobile telephone 1 has an option for allowing the user to disable the Proximity Sleep Mode functionality, so that the display 6 is not turned off, even if an external object is detected by the proximity detector 20. The reason why the user should be given an opportunity to disable this feature is to prevent the display from accidentally being turned off, when the mobile telephone is carried in for instance a protective cover bag. Information regarding whether the Proximity Sleep Mode feature has been disabled by the user is preferably stored as a settings parameter in the memory 40. FIG 3 illustrates a Proximity Sleep Mode routine 100, which according to one embodiment is regularly executed by the controller 30. After the initial step 100 the controller 30 determines, in step 110, whether the Proximity Sleep Mode feature has been disabled by the user. If the answer is in the affirmative, the control is immediately returned to the beginning of routine 100. If, on the other hand, the Proximity Sleep Mode feature has not been disabled by the user, then the output from the proximity detector 20 is read in step 120. In step 130, the value of the output retrieved in step 120 is examined, so as to determine whether any external object is present in proximity with the proximity detector 20 and, consequently, the mobile telephone 1. Preferably, it is required in steps 120 and 130 that the presence of the external object is continuously detected for a certain period of time, before it is ultimately concluded that the display is indeed blocked by an external object. In this way, rapid hand movements, etc., past the display will not accidentally turn off the display. If the answer of step 130 is in the affirmative, the controller 30 forces the liquid crystal display 6 to enter its inactive state in a subsequent step 150. As previously mentioned, the inactive state may either involve displaying only a limited set of icons (such as the remaining battery charge indicator 22), or completely turning off the liquid crystal display 6 by stop supplying electric energy to the liquid crystal layer. The first case is represented by a step 155b in FIG 3, whereas the second case is represented by steps 155a and 157a. Following the last step (i.e., either step 155b or step 157a) the control is transferred back to the beginning of routine 100. If, on the other hand, no external object has been detected in step 130, the controller 30 causes the liquid crystal display 6 to enter its active state, provided that the display 6 is not already active, in a step 140. When step 140 has been completed, the control is transferred back to the beginning of routine 100. In this way, an endless loop is formed by steps 100, 110, 120, 130, 140, 150 and 155b and 155a, 157a, respectively. Consequently, the presence of an external object in proximity with the proximity detector 20 will be continuously monitored, and in response to detecting such an external object, the display 6 will be set to its active state, thereby saving electric power. Furthermore, if the external object disappears from the proximity detector 20, the display 6 is again set to its active state in step 140. Preferably, the endless Proximity Sleep Mode routine 100 may be interrupted by the controller 30 (pre-emptive scheduling) , so that other tasks with higher priority may be executed instead of routine 100. For instance, as soon as the controller 30 has detected that the user has started initiating an outgoing call, the routine 100 is temporarily stopped and the display 6 is activated, thereby avoiding an undesired situation where e.g. the hand or head of the user is accidentally detected by the proximity detector 20, while the telephone number to be called is entered on the keypad 7. Correspondingly, routine 100 may be temporarily aborted upon detection of an incoming telephone call, text message (SMS; Short Messages Services), etc. As an alternative to the endless loop formed by routine 100 in FIG 3, the Proximity Sleep Mode routine may be executed by the controller 30 according to a predetermined time schedule, for instance once every second, without returning to the beginning of routine 100 upon termination of the last step 140, 155b or 157a, respectively. The invention has been described above with reference to a few embodiments. However, the present invention shall in no way be limited by the description above; the scope of the invention is best defined by the appended independent claims. Other embodiments than the particular ones described above are equally possible within the scope of the invention. The invention may also be combined with known power preservation arrangements, such as automatically turning off the display backlighting after certain time, as described in previous sections.

Claims: CLAIMS 1. A portable electric apparatus (1) having a display (6) of the type comprising a liquid crystal, the display having an active state for presenting visual information in response to a supply of electric energy to the liquid crystal layer, the display also having an inactive state, in which less electric energy is supplied to the liquid crystal layer and less visual information consequently is presented, characterized by a proximity detector (20) for detecting the presence of an object in proximity with the apparatus (1) and in response causing the display (6) to enter its inactive state. 2. A portable electric apparatus (1) according to claim 1, wherein the proximity detector (20) operates by detecting infrared (IR) light. 3. A portable electric apparatus (1) according to claim 1, wherein the proximity detector (20) operates by detecting visible light . 4. A portable electric apparatus (1) according to claim 1, wherein the proximity detector (20) operates by detecting thermal energy generated by said object. 5. A portable electric apparatus (1) according to claim 1, wherein the proximity detector (20) operates by detecting said object by capacitive means. 6. A portable electric apparatus (1) according to any preceding claim, the apparatus having a front surface (10) at which the display (6) is located, wherein the proximity detector (20) is located at said front surface. 7. A portable electric apparatus (1) according to any preceding claim, the apparatus being provided with a man- machine interface having an option for allowing a user to disable the operation of the proximity detector (20) or the results of its operation. 8. A portable electric apparatus (1) according to any preceding claim, wherein the display (6) is arranged, in its active state, to present a plurality of graphical symbols or icons and wherein the display (6) , in its inactive state, is arranged to present only some of said plurality of graphical symbols or icons. 9. A portable electric apparatus (1) according to any of claims 1-7, wherein the inactive state of the display (6) is a state, where the display is electrically turned off. 10. A portable electric apparatus (1) according to any preceding claim, wherein the apparatus is a telecommunication device, preferably a mobile telephone (1) . 11. A method of preserving power for a portable electric apparatus (1) having a display (6) of the type comprising a liquid crystal layer, the display having an active state for presenting visual information in response to a supply of electric energy to the liquid crystal layer, the display also having an inactive state, in which less electric energy is supplied to the liquid crystal layer and less visual information consequently is presented, characterized by the steps of determining whether an object is present in proximity with the apparatus (1) , and, if so, causing the display (6) to enter its inactive state. 12. A method according to claim 11, comprising an initial step of determining whether a user of the apparatus has chosen to disable the execution of the steps in claim 11, wherein the steps of claim 12 are only executed, if no such choice has been made by the user.

Inventors: SPARRE ERIK, SPARRE, ERIK
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)
Application year: 2000
Main classification: H04M1
IPC codes: G06F1, H04B1, H04M1