Power saving display

A mobile computing device comprises a power source, a display, a display driver and a control circuit. The power source is configured to provide a power signal. The display comprises a plurality of pixels. The display driver is configured to receive the power signal and to drive the pixels based on the power signal and display data. The control circuit is configured to periodically remove the power signal from at least a portion of the display driver.

BACKGROUND

Low power consumption is a design goal for many electronic devices. This is particularly true for mobile computing devices, and those using color displays. Improvements in display technology have provided bright, colorful displays with many more capabilities than previous displays. Along with the improved display technology, however, has come increased power consumption.

Some display drivers provide a partial display or partial refresh feature. In one example of such a feature, a display driver may switch from providing full display data to a liquid crystal display (LCD) to providing partial display data to the LCD from a dedicated memory. This may allow the display driver to enter a lower power mode and further allow a microprocessor or application-specific integrated circuit providing the display data to the display driver to enter a low power or sleep mode. However, further reductions in power consumption are needed.

Accordingly, what is needed is an improved system and method for reducing power consumption in a display system. Further what is needed is a mobile computing device which has a longer operating time on a single battery charge than in previous devices. Further still what is needed is a system and method for further reducing power consumption in a partial display mode or in a full display mode. Further still, what is needed is a system and method for providing other advantageous features associated with periodically removing a power supply signal from a liquid crystal display.

The teachings herein extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the above-mentioned needs.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Referring first toFIG. 1, a mobile computing device10is shown. Device10is a smart phone, which is a combination mobile telephone and handheld computer having personal digital assistant functionality. The teachings herein can be applied to other mobile computing devices (e.g., a laptop computer, MP3 player, watch, portable gaming system) or other electronic devices (e.g., a desktop personal computer, home or car audio system, etc.). Personal digital assistant functionality can comprise one or more of personal information management, database functions, word processing, spreadsheets, voice memo recording, etc. and is configured to synchronize personal information from one or more applications with a computer (e.g., desktop, laptop, server, etc.). Device10is further configured to receive and operate additional applications provided to device10after manufacture, e.g., via wired or wireless download, SecureDigital card, etc.

Device10comprises a display12(which may be a plurality of displays of different types and sizes) and a user input device14(e.g., a QWERTY keyboard, buttons, touch screen, speech recognition engine, etc.). Device10also comprises an earpiece speaker15. Earpiece speaker15may be a speaker configured to provide audio output with a volume suitable for a user placing earpiece15against or near the ear. Earpiece15may be positioned above display12or in another location on device10. Device10comprises a housing11having a front side13and a back side17(FIG. 2). Earpiece15may be positioned on the front side13along with display12and user input device14, and a loudspeaker16may be positioned on the back side along with a battery compartment19. In alternative embodiments, display12, user input device14, earpiece15and loudspeaker16may each be positioned anywhere on front side13, back side17or the edges therebetween.

Referring now toFIG. 3, device10comprises a processing circuit20comprising a processor22. Processing circuit20can comprise one or more microprocessors, microcontrollers, and other analog and/or digital circuit components configured to perform the functions described herein. Processing circuit20comprises one or more memories (e.g., random access memory, read only memory, flash, etc.) configured to store software applications provided during manufacture or subsequent to manufacture by the user or by a distributor of device10. In one embodiment, processing circuit20can comprise a first, applications microprocessor configured to run a variety of personal information management applications, such as calendar, contacts, etc., and a second, radio processor on a separate chip or as part of a dual-core chip with the application processor. The radio processor is configured to operate telephony functionality. Device10can be configured for cellular radio telephone communication, such as Code Division Multiple Access (CDMA), Global System for Mobile Communications (GSM), Third Generation (3G) systems such as Wide-Band CDMA (WCDMA), or other cellular radio telephone technologies. Device10can further be configured for data communication functionality, for example, via GSM with General Packet Radio Service (GPRS) systems (GSM/GPRS), CDMA/1XRTT systems, Enhanced Data Rates for Global Evolution (EDGE) systems, Evolution Data Only or Evolution Data Optimized (EV-DO), and/or other data communication technologies.

Device10comprises a transceiver24which comprises analog and/or digital electrical components configured to receive and transmit wireless signals via antenna28to provide cellular telephone and/or data communications with a fixed wireless access point, such as a cellular telephone tower, in conjunction with a network carrier, such as, Verizon Wireless, Sprint, etc. Device10can further comprise circuitry to provide communication over a local area network, such as Ethernet or according to an IEEE 802.11x standard or a personal area network, such as a Bluetooth or infrared communication technology.

Device10further comprises a microphone30configured to receive audio signals, such as voice signals, from a user or other person in the vicinity of device10, typically by way of spoken words. Microphone30is configured as an electro-acoustic sense element to provide audio signals from the vicinity of device10and to convert them to an electrical signal to provide to processor22. Processor22can provide a digital memo recorder function, wireless telephone function, etc. with words spoken into microphone30. Processor22may also provide speech recognition and/or voice control of features operable on device10. Display12can comprise a touch screen display in order to provide user input to processor22to control functions, such as to dial a telephone number, enable/disable speakerphone audio, provide user inputs regarding increasing or decreasing the volume of audio provided through earpiece15and/or loudspeaker16, etc. Alternatively or in addition, user input device14can provide similar inputs as those of touch screen display12. Device10can further comprise a stylus31to assist the user in making selections on display12. Processor22can further be configured to provide video conferencing capabilities by displaying on display12video from a remote participant to a video conference, by providing a video camera on device12for providing images to the remote participant, by providing text messaging, two-way audio streaming in full- and/or half-duplex mode, etc.

Referring again toFIG. 3, a power source32is provided to power the electronic components of device10. Power source32comprises circuitry to receive power from a battery and/or external power source and to provide various voltage, current, power regulation, and other power conditioning features for one or more power supply signals as required by the various electronic components of device10. Device10further comprises a switch34configured to selectively remove power to at least a portion of a display driver36, as will be described in more detail below. As illustrated, switch34is controlled by processor22in this exemplary embodiment.

Referring now toFIG. 4, processing circuit20comprises a processor22which can include a microprocessor or microcontroller38and an application-specific integrated circuit (ASIC)40in this exemplary embodiment, though in alternative embodiments other types or combinations of processing or control circuitry may be used. Display12is a liquid crystal display, which may be an active matrix or passive matrix display, and may be a twisted nematic display, a 3LCD display, an in-plane switching (IPS) display, a thin-film transistor (TFT) display, etc. A liquid crystal display (LCD) comprises a plurality of crystals, each pixel comprising a layer of crystal molecules aligned between two transparent electrodes and two polarizing filters, the axis of polarity of which are perpendicular to each other. By applying an electric field, the orientation of liquid crystal molecules changes to selectively allow or disallow the light to pass through the display from a backlight42or reflective light source or other light source. When a voltage or power is removed from the electrodes, a period of time is required for the liquid crystals to align to a non-transmissive or no-display state. The liquid crystal states will be sustained by residual voltages across each liquid crystal cell during this time, thereby providing a “residual image.” While this effect occurs in liquid crystal displays, a similar effect may be found in other displays, and one or more of the embodiments shown herein may be applied to electronic paper, organic light-emitting diodes (OLEDs), cathode ray tube (CRT), electroluminescent (EL) displays or other displays that have persistence, such as displays that use phosphorus materials and electroluminescence.

Referring again toFIG. 4, mobile computing device10comprises a power source32configured to provide a power signal46via a power supply44to a power supply circuit48of display driver36. A battery50(e.g., a lithium-ion battery or other battery type) provides power to power supply44which provides a suitable power supply signal to power supply circuit48. In one example, power supply44is simply a wire providing power from power source32to display driver36. Power source32further comprises a digital voltage power supply52configured to provide a digital voltage power supply signal with a voltage suitable for digital electronics (e.g., 1.8 volts, 3.3 volts, 5 volts, etc.) to a digital circuit portion54of display driver36.

Display driver36is configured to receive power signal46and to drive pixels on display12based on the power signal and based on display data received via a display data signal58from system ASIC40and, more particularly, a display controller portion60(e.g., LCD controller) of system ASIC40. Display driver36is further configured to receive serial display data via a serial display data signal62from a serial interface portion64of system ASIC40for storage in a display driver memory66, for example, for a partial display or partial refresh mode as will be described below. Suitable clock and enable signals68are also provided from display controller60to digital circuit portion54. Other data, control, and power signals may be provided between processing circuit20and display driver36according to various alternative embodiments. In this exemplary embodiment, display driver36may be an FPD95120, FPD95220 or FPD93140 display driver manufactured by National Semiconductor Corporation, but may be other display drivers.

As mentioned, display driver36is configured to receive power signal46and to drive pixels on display12via their corresponding electrodes based on power supply signal46and based on display data58,62received from system ASIC40or replayed from memory66. Processing circuit20is further configured to use a switch70or other mechanism (e.g., a high side switch, a field-effect transistor, such as a P-channel metal-oxide-semiconductor field-effect transistor (MOSFET) designed for high side switching, etc.) to periodically remove power signal46(or in an alternative embodiment power signal32) from at least a portion of display driver36, in this embodiment power supply circuit48. Switch70may have a rating over the max Vbatt, such as 4.2 Volts and a low Rds(on). In an alternative embodiment, switch70is placed between battery50and power supply44. Removing power signal46to disable power supply44from a portion of display driver36also disables the voltage required to turn on or refresh a display pixel of display12. Residual voltages across the pixels will maintain an image being displayed on display12for a period of time. By removing power from power supply circuit48, power consumption may be reduced. The persistence of the liquid crystals may be utilized to allow powering down subsystems of display driver36(and not refreshing display12regularly) while maintaining a consistent image on display12. Power signals46or32may be removed, cycled, pulsed, attenuated, reduced, disconnected, or decreased.

According to one exemplary embodiment, display12and display driver36require a plurality of power signals, one regulated for digital power, such as the digital voltage power supply signal and one which may be unregulated (e.g., Vbatt, such as power signal46) that display driver36may use to generate various display driving voltages (which may include +5V, −5V, etc., depending on the display technology and specifications of display driver36). In this exemplary embodiment, Vbatt, which is the source of display driving voltages, may be removed while maintaining the supply of digital voltage power supply signal to display driver36. As a result, display driver36may continue to function, but it does not have the driving voltage or voltages needed to actively switch on the pixels as it would have in a normal operating mode. By removing Vbatt, in this exemplary embodiment, a high power consuming portion or perhaps the most power consuming portion of display driver36will no longer be consuming power because the power supply signal to that portion has been removed.

A regular or normal refresh rate of display12may be fixed or variable according to software and/or ASIC programming and may, in an exemplary embodiment, provide a display refresh rate of between 50 and 70 Hertz (Hz). The periodic removal or cycling of power signal46may be provided with a variety of frequencies and/or duty cycles. In an exemplary embodiment, power may be removed or the display may be refreshed with a frequency of approximately 0.005 to 10 Hz (corresponding to a period of between approximately greater than 0.1 seconds and/or less than approximately 200 seconds between power cycling). According to another exemplary embodiment, processing circuit20is configured to remove the power signal with a period of less than approximately 20 seconds. The removal of power may happen automatically, without user interaction.

Further, the removal or cycling of power signal46can happen with a rate or frequency or duty cycle which is dynamically adjusted. For example, at least one of a duty cycle and frequency can be adjusted or set based on a criteria, such as a temperature (e.g. an ambient temperature). The settling time of crystals may vary based on temperature, and power savings can be optimized by providing a dynamic control based on this criteria. The removal of power signal46can further be dynamically adjusted based on whether display driver36is operating in a normal display mode or a partial display mode, as will be described below. The removal of power signal46can further be dynamically varied based on the type of display data being provided on display. For example, in a situation when backlight42is on and display12is displaying a static image such as a calendar, a black and white e-mail, etc., power signal46can be cycled to provide power savings. Thus, processing circuit20can be configured to cycle or remove power from power supply circuit48or another portion of display driver36in varying frequencies and duty cycles during a plurality of different modes of operations and/or based on display data, temperature, and/or other criteria.

According to one exemplary embodiment, power can be saved in situations when display data updates less frequently than a normal or regular display mode. Power can be reduced or removed from one or more portions of display driver36and/or display12. In one embodiment, power signal46is removed or reduced. In another embodiment, digital voltage power signal56may also be removed or reduced, along with or independent of power signal46. Further, signals provided to display12from display driver36may also be reduced or removed. A persistence effect of the liquid crystals within display12can be used to increase the period of activating or refreshing the portions of display driver36with little or no user-perceptable effect.

According to one exemplary embodiment, display driver36is operable in a first display mode (e.g., a normal or regular display mode having a conventional refresh rate of between 50 and 70 Hz or other refresh rate) and a second display mode (e.g., a partial display mode). In the second display mode, display driver36is configured to refresh display12with substantially less display data than in the first display mode. For example, partially refreshing display12may comprise reducing a refresh rate, a display size, and/or switching from color to black and white, monochrome or grayscale or a reduced bit-depth color mode. According to one embodiment, memory26is a buffer (e.g., static random access memory (SRAM) or dynamic random access memory (DRAM)) on driver36which can allow refresh of a portion of display data without requiring system ASIC40and display controller60to continuously transmit display data to driver36. According to one example, a full screen or normal image may be provided on display12with 320 by RGB (red, green, blue) by 320 pixels with 16 bits per pixel (bpp), but in a second display mode, memory66provides 320 by RGB by 80 pixels at 3 bpp. In one embodiment, in a partial display mode, every pixel on the screen or on display12is refreshed, wherein pixels not having display data stored in memory66may be refreshed with blank, default or no data. Partial refresh may occur at 30-45 Hz refresh rate or other rates.

The second display mode may also comprise at least one of microprocessor38, system ASIC40, and display driver36or portions thereof, entering a low power mode (e.g., a mode in which power consumption is lower than another, typically normal operating mode). According to another embodiment, a second display mode may comprise a mode in which processing circuit20is configured to dim or turn off backlight42, wherein the partial display data displayed on display12is illuminated by reflected light or another low power light source. According to one exemplary embodiment, in second display mode, display12is configured to show the time of day, battery charge status, date, wireless signal strength, wireless communication type, whether a message has been received in an inbox, etc.

Second display mode can comprise a partial display mode in which the entire display is used (e.g., an image is provided on substantially all of the screen) but only a black and white image is shown or the image is refreshed at a lower rate than a normal refresh mode.

Referring toFIG. 5, device10is shown with an exemplary image72in a partial display or partial refresh mode. Although not necessarily apparent to a user, only the display portion between lines74and76is refreshed with data from memory66. In the second display mode, the icons and other display data shown may be refreshed at a lower refresh rate than a typical 50-70 Hz refresh rate. In this exemplary embodiment, a second display mode is provided when device10is powered off, for example by a user pressing an off switch or by a predetermined timeout timer operated by processing circuit20.

According to one embodiment, in a first display mode, system ASIC40is configured to provide data via display data signal58(e.g., a parallel bus, comprising 16 bits, though serial or other buses may be used) to display driver36. Digital circuit54is configured to provide the display data via control lines78to display12in this first mode. System ASIC40provides a timing signal to shift display data into driver36which latches the data to display12, for example line after line. First display mode may provide a full 16-bit, high-contrast, display and/or other display characteristics associated with a typical normal display mode. In second display mode, memory66can be configured to receive display data on a serial display data signal62via serial interface64of system ASIC40along a serial interface port. Alternatively, memory66can be configured to receive data via parallel ports or other communication ports. In second display mode, memory66provides data through digital circuit54to continually refresh at least a portion of display12. In one exemplary embodiment, prior to entering a sleep or low power mode, processing circuit20shifts into memory66display data sufficient to provide a partial display on display12. Portions of processing circuit20then enter a sleep mode, while a portion or a subsystem of display driver36continues to refresh display12with a sufficient refresh rate to provide a steady image from a user's perspective (e.g., or even to provide a blinking display which dims over time, or even a blinking display separated by a period of no display for several seconds or more). In the first display mode, display refresh rates can be between 50 and 55 Hz, or other display refresh rates. In the second display mode, refresh rates can be 30 Hz or less, or other display refresh rates.

According to another exemplary embodiment, a first display mode can be a display mode in which display12is refreshed at a first refresh rate, for example 50 to 70 Hz. Second display mode may also be a display mode in which substantially all of display12is refreshed, optionally in full color, but in this exemplary second display mode, the refresh frequency is reduced to a lower refresh rate, such as, less than 50 Hz, less than 20 Hz, etc. In this exemplary embodiment, memory66need not be used, and instead, data is continually provided from system ASIC or from a different memory either on driver device36, or off-chip comprising sufficient data for a full screen display. As another alternative, in this embodiment, power may be removed from any portion or portions of display driver36. Alternatively, power can be maintained on display driver36throughout second mode, wherein power savings is realized from a lower refresh rate of display12.

According to one embodiment, power supply48can be an analog power supply for display12, configured to provide a main or primary power to display12via power line80(e.g., power provided to the LCD glass or other electrodes).

According to various alternative embodiments, the components of processing circuit20may be on different chips or on a single chip. For example, display driver36and processor20may be disposed on a single integrated circuit. Microprocessor38and system ASIC40may be disposed on a single integrated circuit. Display driver36and system ASIC40may be disposed on a single integrated circuit. Furthermore, switch control signal82which is configured to remove power via switch70may be provided by system ASIC40or a component thereof, such as LCD controller60, by microprocessor38, by driver36or by another control circuit.

Referring toFIG. 6, an exemplary method is shown for reducing power consumption in mobile computing device10. At step90, power is provided to a display driver. At step92, pixels of display12are driven based on the power signal in display data. At step94, power is periodically removed from at least a portion of the display driver. According to one alternative embodiment, display12may be partially refreshed using any the partial refresh characteristics, such as those described above, while the power signal is periodically removed from the display driver.

While the exemplary embodiments illustrated in the Figs., and described above are presently exemplary, it should be understood that these embodiments are offered by way of example only. For example, other display drivers may allow for removing power from different subsystems or portions of the driver to save power. Further, the features disclosed herein may be applied to other electronic devices, such as laptop computers, handheld navigation devices comprising location determination circuitry, etc. Further still, the backlight can be selectively turned on or off, or even pulsed, in any of the different embodiments or modes of embodiments disclosed herein to provide further power savings. Accordingly, the present invention is not limited to a particular embodiment, but extends to various modifications that nevertheless fall within the scope of the appended claims.