Backlight noise reduction systems and methods for electronic device displays

Aspects of the subject technology relate to control circuitry for light-emitting diodes (LEDs). The control circuitry may include an LED timing controller integrated circuit configured to operate groups of rows of the LEDs with a common randomized row order that mitigates acoustic noise. The LEDs may be implemented in a backlight of a liquid crystal display and the common randomized row order that mitigates acoustic noise may be generated and/or executed to synchronize the LED operation with the operation of the pixels of the liquid crystal display.

TECHNICAL FIELD

The present description relates generally to electronic devices with displays, and more particularly, but not exclusively, to backlight noise reduction systems and methods for electronic device displays.

BACKGROUND

Electronic devices such as computers, media players, cellular telephones, set-top boxes, and other electronic equipment are often provided with displays for displaying visual information. Displays such as organic light-emitting diode (OLED) displays and liquid crystal displays (LCDs) typically include an array of display pixels arranged in pixel rows and pixel columns. Liquid crystal displays commonly include a backlight unit and a liquid crystal display unit with individually controllable liquid crystal display pixels.

The backlight unit commonly includes one or more light-emitting diodes (LEDs) that generate light that exits the backlight toward the liquid crystal display unit. The liquid crystal display pixels are individually operable to control passage of light from the backlight unit through that pixel to display content such as text, images, video, or other content on the display.

SUMMARY OF THE DESCRIPTION

In accordance with various aspects of the subject disclosure, an electronic device is provided that includes a display with a liquid crystal display unit and a backlight unit, the backlight unit including an array of light-emitting diodes arranged in rows and columns, the rows arranged in groups of adjacent rows. The electronic device also includes control circuitry configured to identify a plurality of row orders for operation of the rows of each group of adjacent rows, where each row order synchronizes the operation of the rows of the array with operation of the liquid crystal display unit. The control circuitry is also configured to pseudo-randomly select one of the identified plurality of row orders, and operate, concurrently, the rows of each group using the selected one of the identified plurality of row orders.

In accordance with other aspects of the subject disclosure, an electronic device is provided that includes a display with a liquid crystal display unit and a backlight unit, the backlight unit including an array of light-emitting diodes arranged in rows and columns, the rows arranged in groups of adjacent rows. The electronic device also includes control circuitry configured to identify a backlight scan rate at which to operate the array of light-emitting diodes, the backlight scan rate being an integer multiple of an LCD scan rate for the liquid crystal display unit. The control circuitry is also configured to identify a pseudo-random row order for operation of the rows of each of the groups of adjacent rows, and operate, concurrently, the rows of each group using the pseudo-random row order at the identified backlight scan rate.

In accordance with other aspects of the subject disclosure, a method is provided that includes identifying, for multiple groups of adjacent rows of light-emitting diodes in an array of light-emitting diodes in a backlight of a display of an electronic device, a plurality of row orders for operation of the rows of each group of adjacent rows. Each row order synchronizes the operation of the rows of the array with operation of a liquid crystal display unit of the display. The method also includes pseudo-randomly selecting one of the identified plurality of row orders. The method also includes operating, concurrently, the rows of each group using the selected one of the identified plurality of row orders.

DETAILED DESCRIPTION

The subject disclosure provides electronic devices such as cellular telephones, media players, tablet computers, laptop computers, set-top boxes, smart watches, wireless access points, and other electronic equipment that include light-emitting diode arrays such as in backlight units of displays. Displays are used to present visual information and status data and/or may be used to gather user input data. A display includes an array of display pixels. Each display pixel may include one or more colored subpixels for displaying color images.

Each display pixel may include a layer of liquid crystals disposed between a pair of electrodes operable to control the orientation of the liquid crystals. Controlling the orientation of the liquid crystals controls the polarization of backlight from a backlight unit of the display. This polarization control, in combination with polarizers on opposing sides of the liquid crystal layer, allows light passing into the pixel to be manipulated to selectively block the light or allow the light to pass through the pixel.

The backlight unit includes one or more light-emitting diodes (LEDs) such as one or more strings and/or arrays of light-emitting diodes that generate the backlight for the display. In various configurations, strings of light-emitting diodes may be arranged along one or more edges of a light guide plate that distributes backlight generated by the strings to the LCD unit, or may be arranged to form a two-dimensional array of LEDs.

Although examples discussed herein describe LEDs included in display backlights, it should be appreciated that the LED control circuitry and methods described herein can be applied to LEDs implemented in other devices or portions of a device (e.g., in a backlit keyboard or a flash device).

Backlight (BL) control circuitry for the backlight unit includes backlight row drivers and backlight column drivers that control one or more light-emitting diodes (LEDs) such as an array of LEDs arranged in LED rows and LED columns. In some operational scenarios, during operation of the rows of LEDs, some electronic components of the backlight may be operated at frequencies that are audible to the human ear (e.g., frequencies below 20 kHz).

In accordance with various aspects of the subject disclosure, the order of operation of the rows of LEDs is randomized (e.g., pseudo-randomized) to mitigate acoustic noise by reducing the magnitude and spreading the frequencies of the noise generated by the backlight. The randomized row operations may be performed such that the row operations are synchronized with the operation of the LCD unit of the display.

An illustrative electronic device having light-emitting diodes is shown inFIG. 1. In the example ofFIG. 1, device100has been implemented using a housing that is sufficiently small to be portable and carried by a user (e.g., device100ofFIG. 1may be a handheld electronic device such as a tablet computer or a cellular telephone). As shown inFIG. 1, device100may include a display such as display110mounted on the front of housing106. Display110may be substantially filled with active display pixels or may have an active portion and an inactive portion. Display110may have openings (e.g., openings in the inactive or active portions of display110) such as an opening to accommodate button104and/or other openings such as an opening to accommodate a speaker, a light source, or a camera.

Display110may be a touch screen that incorporates capacitive touch electrodes or other touch sensor components or may be a display that is not touch-sensitive. Display110may include display pixels formed from light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), plasma cells, electrophoretic display elements, electrowetting display elements, liquid crystal display (LCD) components, or other suitable display pixel structures. Arrangements in which display110is formed using LCD pixels and LED backlights are sometimes described herein as an example. This is, however, merely illustrative. In various implementations, any suitable type of display technology may be used in forming display110if desired.

Housing106, which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials.

The configuration of electronic device100ofFIG. 1is merely illustrative. In other implementations, electronic device100may be a computer such as a computer that is integrated into a display such as a computer monitor, a laptop computer, a somewhat smaller portable device such as a wrist-watch device, a pendant device, or other wearable or miniature device, a media player, a gaming device, a navigation device, a computer monitor, a television, or other electronic equipment.

For example, in some implementations, housing106may be formed using a unibody configuration in which some or all of housing106is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). Although housing106ofFIG. 1is shown as a single structure, housing106may have multiple parts. For example, housing106may have upper portion and lower portion coupled to the upper portion using a hinge that allows the upper portion to rotate about a rotational axis relative to the lower portion. A keyboard such as a QWERTY keyboard and a touch pad may be mounted in the lower housing portion, in some implementations. An LED backlight array may also be provided for the keyboard and/or other illuminated portions of device100.

In some implementations, electronic device100may be provided in the form of a computer integrated into a computer monitor. Display110may be mounted on a front surface of housing106and a stand may be provided to support housing (e.g., on a desktop).

FIG. 2is a schematic diagram of display110in which the display is provided with a liquid crystal display unit204and a backlight unit202. As shown inFIG. 2, backlight unit202generates backlight208and emits backlight208in the direction of liquid crystal display unit204. Liquid crystal display unit204selectively allows some or all of the backlight208to pass through the liquid crystal display pixels therein to generate display light210visible to a user. Backlight unit202includes one or more subsections206.

In some implementations, subsections206may be elongated subsections that extend horizontally or vertically across some or all of display110(e.g., in an edge-lit configuration for backlight unit202). In other implementations, subsections206may be square or other rectilinear subsections (e.g., subarrays of a two-dimensional LED array backlight or a two-dimensional array of LED strings). Accordingly, subsections206may be defined by one or more strings and/or arrays of LEDs disposed in that subsection. Subsections206may define operable zones of BLU202that can be controlled individually for local dimming of backlight208.

Although backlight unit202is shown implemented with a liquid crystal display unit, it should be appreciated that a backlight unit such as backlight unit202may be implemented in a backlit keyboard, or to illuminate a flash device or otherwise provide illumination for an electronic device.

FIG. 3shows a schematic diagram of exemplary circuitry for electronic device100including host circuitry and LED circuitry such as backlight circuitry for display110. For example, device circuitry300ofFIG. 3may include a backlight board302that can be implemented in backlight unit202or other LED lighting devices.

In the example ofFIG. 3, device circuitry300includes a main logic board (MLB)301having host circuitry304and includes backlight control circuitry that includes backlight controller (BCON) integrated circuit314, backlight row driver integrated circuits308, backlight column driver integrated circuits310, and backlight LEDs312. As shown, LEDs312are operated by BL row driver ICs308and BL column driver ICs310based on commands/signals from backlight controller IC314. In this example, backlight controller IC314, backlight row driver IC308, backlight column driver IC310, and backlight LEDs312are implemented on a common backlight board302. The backlight controller314, backlight row drivers308, and backlight column drivers310can communicate via a communication protocol (e.g., synchronous serial communication (SPI)). The backlight row drivers308and backlight column drivers310can send interrupt signals to the backlight controller314for specific interrupt conditions. Backlight controller IC314receives control signals from host circuitry304.

In the example ofFIG. 3, a power supply for backlight unit202is provided on MLB301. In this example, the power supply for backlight unit202is implemented as a boost converter306mounted on the same MLB as host circuitry304. However, it should be appreciated that the power supply for backlight unit202may be implemented as any DC/DC converter. The boost converter306provides input power to the backlight controller314and also provides input/LED power to the backlight row drivers308and backlight column drivers310. The arrangement shown inFIG. 3, in which LEDs312are operated by BL row driver ICs308and BL column driver ICs310based on commands from backlight controller IC314, provides various advantages over conventional backlight arrangements including that a single high-speed link is provided between host circuitry304and the backlight control circuitry, analog and digital chips are separated and implemented in different processing nodes, frame memory for the backlight LEDs312is provided in a single chip (e.g., BCON314) for self-refresh of the backlight unit, data transfer bandwidth usage is reduced via dedicated data links for each of BL row driver ICs308and BL column driver ICs310from BCON314, and board-level routing for backlight board302is improved.

Host circuitry304may include one or more different types of storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory), volatile memory (e.g., static or dynamic random-access-memory), magnetic or optical storage, permanent or removable storage and/or other non-transitory storage media configure to store static data, dynamic data, and/or computer readable instructions for processing circuitry in host circuitry304. Processing circuitry in host circuitry304may be used in controlling the operation of device100. Processing circuitry in host circuitry304may sometimes be referred to herein as system circuitry or a system-on-chip (SOC) for device100.

The processing circuitry may be based on a processor such as a microprocessor and other suitable integrated circuits, multi-core processors, one or more application specific integrated circuits (ASICs) or field programmable gate arrays (FPGAs) that execute sequences of instructions or code, as examples. In one suitable arrangement, host circuitry304may be used to run software for device100, such as internet browsing applications, email applications, media playback applications, operating system functions, etc.

As shown inFIG. 3, backlight timing controller integrated circuit314on the backlight substrate302receives backlight data from host circuitry304for the electronic device via a high speed link. Backlight row driver integrated circuits308on the backlight substrate302connect a high voltage power rail to the LEDs312via a plurality of high-side switches. Backlight column driver integrated circuits310are operable by BCON IC314to adjust the amount of current through each LED or string of LEDs312and provide individual PWM dimming for each LED or string of LEDs312. The host circuitry304and backlight timing controller integrated circuit314can communicate via multiple high speed data links (e.g., 2).

In one suitable example, rows of LEDs312are operated in groups by row driver ICs308and column driver ICs310. The grouping or segmentation of the array of LEDs312can increase the duty cycle and reduce peak currents for operation of the LED array.

FIG. 4illustrates how groups406of rows404of LEDs400(e.g., each representing one or more of LEDs312ofFIG. 3) can be operated in a group-based row operation. In the example ofFIG. 4, LED array401includes LEDs400arranged in rows404and columns402. LEDs400may be individual LEDs312or may be strings of series-coupled LEDs (e.g., with four or more individual LEDs coupled in series to a current controller of one of column driver ICs310). As indicated, rows404may be operated in groups406such that one or more rows404in each group406is operated at the same time as the corresponding row(s) in the other groups406. As indicated in the figure, array401may include a number m columns, a number n groups406each having a number k rows, and a total of n*k rows. As indicated in the figure, the first row in each group406is operated at the same time, the second row in each group406is operated at the same time, and so on until the k-th row in each group is operated at the same time, although the first, second, third, etc. rows in each group may be operated non-sequentially and/or pseudo-randomly to mitigate acoustic noise generated by the backlight.

An exemplary layout of traces for coupling the first row404of each group406to a common high-side switch in a row driver IC308is shown inFIG. 5. In the example ofFIG. 5, the first row404in all groups406is shorted together by traces500and coupled to a common high-side switch501in row driver IC308. Each row driver IC308may include a number of high-side switches equal to or greater than the number of rows in groups406. In the example ofFIG. 5, two row driver ICs308, one on each side of array401, are provided to drive array401from both sides. However, it should be appreciated that single-side driving of array401with a single row driver IC308can also be provided. The second row404in all groups406may also be shorted together coupled to a common high-side switch501in row driver IC308, and so forth including the k-th row404in all groups406being shorted together and coupled to a common high-side switch501in row driver IC308.

FIG. 6illustrates an exemplary layout of column driver traces for group-based operation of LEDs400. In the example ofFIG. 6, each group406is operated by a corresponding column driver IC310having a number of channels equal to the number of columns402. As indicated in the figure, m traces600may run between each column driver IC310and m column lines602. In this example, the LEDs400(or strings of LEDs) in the same column402within one group406are shorted together by a column line602and connected to one channel of the corresponding CD IC310.

However, it should be appreciated that the column driver layout described in connection withFIG. 6is merely illustrative and other arrangements are contemplated. For example, in one suitable arrangement, a column intermixing layout is provided in which column driver ICs310are programmed to run as a number of smaller drivers in parallel.

FIG. 7illustrates how, in a column-intermixing layout, groups (subsets)700of p columns, each spanning a portion of a group406of rows404, can be operated by a common column driver integrated circuit310.FIG. 8illustrates an exemplary layout of column driver traces for a column-intermixed group-based operation of LEDs312/400(seeFIGS. 3 and 4). As shown inFIG. 8a number n*p traces800, where n is the number of groups406and p is the number of columns in each subset700, run between each column driver IC310and p column lines802in each of n groups406. In this example, the LEDs400(or strings of LEDs) in the same column402within one group406are shorted together by a column line802and connected to one channel of the corresponding CD IC310.

BCON314(seeFIG. 3) may cooperate with row driver ICs308and column driver ICs310arranged as described herein to operate rows404and columns402of LEDs312/400(seeFIGS. 3 and 4).FIG. 9is a timing diagram900illustrating a sequential operation of k rows in each group406. In the example ofFIG. 9, signal902for each row includes an on pulse904for that row, that sequentially follows the previous (adjacent) row. InFIG. 9, the time corresponding to the operation of each row (1/frow), the time corresponding to a pulse width modulation (PWM) cycle for the LEDs in that row (1/fpwm), and the time corresponding to a backlight scan (1/fBL) are indicated.

However, as indicated inFIG. 10, a sequential operation of backlight rows404in each of several groups406that are operated concurrently, can result in a synchronization error with the operation of LCD unit204. In particular,FIG. 10shows the progression of an LCD scan1002(e.g., sequential operation of rows of LCD pixels in LCD unit204over a display frame) overlaid on the backlight row operation indicators1004in each of several groups (regions)406. Synchronized operation would appear with all backlight row operation indicators1004coinciding with an LCD scan1002. However, as shown, if care is not taken the LCD unit and backlight unit can be out of sync.

In accordance with various aspects of the subject disclosure, synchronization of LCD unit204and backlight unit202can be achieved by, for example, (i) maintaining a scan rate of the array of LEDs312/400(seeFIGS. 3 and 4) above a threshold that is based on the rate of LCD scan1002and a number of the different groups, and/or (ii) operating the rows within each of multiple corresponding groups in a non-sequential order.

FIG. 11shows an example in which the rows of LEDs312/400(seeFIGS. 3 and 4) in each group406are operated in a sequential order, with a backlight scan rate (e.g., 1/(BL Scan) inFIG. 11) of the array of LEDs312/400(seeFIGS. 3 and 4) is maintained above a threshold that is based on the rate (e.g., 1/(LCD Frame inFIG. 11) of LCD scan1002and a number of the different groups. In the example ofFIG. 11, the backlight scan rate is equal to n*RR, where n is the number of groups406and RR is the maximum refresh rate of LCD unit204. As shown, in this arrangement, backlight row operation indicators1004coincide with or progress in accordance with an LCD scan1002, even with concurrent operation of rows in different groups406. More generally, higher backlight scan rates can be applied. For example, for a 120 Hz LCD scan rate, and a backlight with four groups406of rows404of LEDs312/400(seeFIGS. 3 and 4), the backlight scan rate may be maintained at or above 480 Hz.

As noted above, synchronization between LCD unit204and backlight unit202(seeFIG. 2) can also, or alternatively, be achieved by operating the rows within each of multiple corresponding groups406in a non-sequential order.FIG. 12is a table1200illustrative of a row ordering for operation of backlight LED rows404for synchronization with LCD scan1002.

In the example ofFIG. 12, a row of backlight execution times1202(including row execution times X1, X2. . . X8) is aligned with a row of LCD scan times1201and a row of backlight row numbers1204, each corresponding to a row404in a group406. In this example, the first row in each group (row1) is executed first (e.g., illuminated during row execution time X1), the fifth row (row5) in each group is executed second (e.g., illuminated during row execution time X2), the second row (row2) in each group is executed third (e.g., illuminated during row execution time X3), and so forth as indicated in the table. In can be seen in table1200that the backlight row operation is synchronized with the LCD operations in this example.

Execution of rows404of groups406as indicated in table1200is illustrated inFIG. 13. As can be seen inFIG. 13, each LCD scan1002coincides with backlight row operation indicators1300for some rows during a non-sequential operation of the rows in each group406. It should be appreciated that the row ordering indicated in table1200is merely illustrative and other non-sequential row orders can be executed, and more or less than eight rows per group406can result in different non-sequential row orderings for LCD synchronization.

It should also be appreciated that, even with a non-sequential row ordering as indicated inFIGS. 12 and 13, if the same non-sequential order of row operations is repeated, acoustic noise that is audible to the user can occur. For example,FIG. 14shows an example of noise magnitudes1400at various frequencies that can occur when a fixed row ordering is applied in a backlight having twelve rows in each group406.FIG. 15shows, for comparison, the noise magnitudes1500at various frequencies that may occur when randomized row ordering of the rows within each group406, as described hereinafter, is applied. As indicated inFIG. 15, the noise generated by the backlight is reduced and spread evenly over a broader range of frequencies, providing a white noise that is less noticeable than the distinct frequencies indicated inFIG. 14.

FIGS. 16-19illustrate various aspects of examples of randomized row ordering operations that can be performed that mitigate acoustic noise generated by the backlight and preserve the synchronization of the backlight LEDs with the pixels of the LCD unit.

For example,FIG. 16shows a table1600in which the backlight row execution times X1, X2, etc. of table1200are listed vertically and the backlight row numbers (1,2,3, etc.) of table1200are listed horizontally. In table1600, candidate row order indicators1602(each shown as an “x”) are provided for any row-number/row-time entry which is a candidate for execution that synchronizes the backlight row operations with the LCD scan1002. Using the constraint that only one candidate row order indicator1602in each column and each row can be selected (e.g., because each row is only to be executed once per one self-refresh cycle), multiple possible row orders for operation of the rows of each group406can be identified, each of which synchronizes the operation of the rows of the backlight with the operation of LCD unit204. In the example ofFIG. 16, selected row indicators1604(grey-highlighted) indicate one possible row ordering that can be applied to synchronize the operation of the rows of the backlight with the operation of LCD unit204.

The selected row indicators1604in the example ofFIG. 16correspond to the row ordering shown and described above in connection withFIGS. 12 and 13. However, it should be appreciated that, if (for example) the other candidate row order indicators1602in the first column of table1600were selected, a different combination of other selected candidates is possible in which all of the selected candidates still satisfy the constraint that only one candidate row order indicator1602in each column and each row can be selected.

By identifying several row orders for groups406, each of which provides synchronization with the LCD scan, and pseudo-randomly choosing from those identified row orders for different backlight scans, the row ordering within groups406can be randomized to mitigate acoustic noise from the backlight.FIG. 17is a flow chart of illustrative operations that can be performed for randomizing the row ordering within groups406by pseudo-randomly selecting from row orders that preserve synchronization with the LCD scan.

FIG. 17depicts a flow chart of an example process for randomized row operation of backlight LEDs (e.g., to mitigate acoustic noise) in accordance with various aspects of the subject technology. For explanatory purposes, the example process ofFIG. 17is described herein with reference to the components ofFIGS. 1, 2, and 3. Further for explanatory purposes, the blocks of the example process ofFIG. 17are described herein as occurring in series, or linearly. However, multiple blocks of the example process ofFIG. 17may occur in parallel. In addition, the blocks of the example process ofFIG. 17need not be performed in the order shown and/or one or more of the blocks of the example process ofFIG. 17need not be performed.

In the depicted example flow diagram, at block1700, control circuitry such as host circuitry304and/or BCON314(seeFIG. 3) may identify, for multiple groups such as groups406of rows404of light-emitting diodes314/400in an array401of light-emitting diodes in a backlight202(seeFIG. 2) of a display110of an electronic device100(seeFIG. 1), a plurality of row orders for operation of the rows of the group of rows, each row order arranged to synchronize the operation of the rows with operation of a liquid crystal display unit of the display (e.g., as described above in connection withFIG. 16). For example, one of the plurality of row orders may correspond to the row order of table1200ofFIG. 12using selected row indicators1604of table1600ofFIG. 16. Another of the row orders may be generated by initially selecting a different row execution time for row1and selecting other candidate row indicators1602(seeFIG. 16) under the constraint that only one candidate in each column and row is selected. Using this constraint, each of the plurality of row orders synchronizes the operation of the rows with operation of a liquid crystal display unit of the display.

At block1702, the control circuitry pseudo-randomly selects one of the identified plurality of row orders.

At block1704, the control circuitry (e.g., including BCON314, row drivers308and column drivers310ofFIG. 3) operates, concurrently, the rows of each group of rows of light-emitting diodes using the selected one of the identified plurality of row orders (e.g., by operating the rows of each group in the same order as the rows of all other groups, according to the selected one of the identified plurality of row orders).

At block1706, the control circuitry (e.g., including separate LCD control circuitry for LCD unit204ofFIG. 2) operates, while the backlight control circuitry is operating the rows of each group of rows of light-emitting diodes using the selected one of the identified plurality of row orders, a first portion of a pixel array of the liquid crystal display unit to display a portion of a display frame.

At block1708, the control circuitry pseudo-randomly selects another one of the identified plurality of row orders.

At block1710, the control circuitry (e.g., including BCON314, row drivers308and column drivers310ofFIG. 3) operates, concurrently, the rows of each group of rows of light-emitting diodes using the selected other one of the identified plurality of row orders (e.g., by operating the rows of each group in the same order as the rows of all other groups, according to the selected other one of the identified plurality of row orders).

At block1712, the control circuitry (e.g., the separate LCD control circuitry for LCD unit204ofFIG. 2) operates, while the backlight control circuitry is operating the rows of each group of rows of light-emitting diodes using the selected other one of the identified plurality of row orders, a subsequent portion of the pixel array of the liquid crystal display unit to display a subsequent portion of the display frame.

As indicated by arrow1714, the operations of blocks1708,1710, and1712can be repeated. For example, the operations of blocks1708,1710, and1712can be repeated for multiple backlight scans until the display frame (corresponding to one LCD scan such as LCD scan1002ofFIG. 10, 11, or13above orFIG. 19below) is complete. As indicated by arrow1716, when the display frame is complete, the control circuitry may return to block1702to repeat the operations of blocks1702,1704,1706,1708,1710, and1712for a next display frame.

However, it should be appreciated that row orderings that are not pre-selected to preserve synchronization with the LCD scan can also be used without sacrificing synchronization with the LCD scan, as long as the backlight scan rate is maintained at or above an integer multiple (e.g., the number of rows (n*k) in the array) of the LCD scan rate RR as described above.

FIG. 18depicts a flow chart of another example process for randomized row operation of backlight LEDs (e.g., to mitigate acoustic noise) by randomizing the row ordering within groups406by generating pseudo-random row orderings and applying the pseudo-random row orderings at a backlight scan rate that is maintained at or above n*k*RR in accordance with various aspects of the subject technology. For explanatory purposes, the example process ofFIG. 18is described herein with reference to the components ofFIGS. 1, 2, and 3. Further for explanatory purposes, the blocks of the example process ofFIG. 18are described herein as occurring in series, or linearly. However, multiple blocks of the example process ofFIG. 18may occur in parallel. In addition, the blocks of the example process ofFIG. 18need not be performed in the order shown and/or one or more of the blocks of the example process ofFIG. 18need not be performed.

In the depicted example flow diagram, at block1800, control circuitry such as host circuitry304and/or BCON314(seeFIG. 3) identifies, for a backlight202(seeFIG. 2) of a display110of an electronic device100(seeFIG. 1), a backlight scan rate at which to operate an array401(seeFIG. 4) of light-emitting diodes312/400(seeFIGS. 3 and 4) of the backlight, the backlight scan rate being an integer multiple of an LCD scan rate for a liquid crystal display unit204(seeFIG. 2) of the display. The integer multiple may be, for example, the number of rows of LEDs in the array of LEDs.

At block1802, the control circuitry identifies, for a group406of rows of light-emitting diodes in the array of light-emitting diodes in the backlight, a pseudo-random row order for operation of the rows of the group of rows. In contrast to the plurality of row orders identified at block1700ofFIG. 17, the pseudo-random row order may be identified without ensuring that the pseudo-random row order synchronizes the backlight LEDs with the LCD scan rate (e.g., at low backlight frame rates). Instead, in this example, the synchronization of the LCD pixels with the backlight LEDs operating in the pseudo-random row order is preserved using the identified backlight scan rate (e.g., n*k*RR).

At block1804, the control circuitry (e.g., including BCON314, row drivers308and column drivers310ofFIG. 3) operates the rows of the group406(seeFIG. 4) of rows of light-emitting diodes and the rows of one or more additional groups406of the rows of light-emitting diodes concurrently using the pseudo-random row order at the identified backlight scan rate.

At block1806, the control circuitry (e.g., including separate LCD control circuitry for LCD unit204ofFIG. 2) operates, while the backlight control circuitry is operating the rows of the group406and the rows of the one or more additional groups406(seeFIG. 4) using the pseudo-random row order at the identified backlight scan rate, a first portion of a pixel array of the liquid crystal display unit to display a portion of a display frame.

At block1808, the control circuitry identifies another pseudo-random row order for operation of the rows of the group of rows.

At block1810, the control circuitry (e.g., including BCON314, row drivers308and column drivers310ofFIG. 3) operates the rows of the group406(seeFIG. 4) of rows of light-emitting diodes and the rows of one or more additional groups406of the rows of light-emitting diodes concurrently using the other pseudo-random row order at the identified backlight scan rate.

At block1812, the control circuitry (e.g., including separate LCD control circuitry for LCD unit204ofFIG. 2) operates, while the backlight control circuitry is operating the rows of the group406and the rows of the one or more additional groups406using the other pseudo-random row order at the identified backlight scan rate, a subsequent portion of the pixel array of the liquid crystal display unit to display a subsequent portion of the display frame.

As indicated by arrow1814, the operations of blocks1808,1810, and1812can be repeated. For example, the operations of blocks1808,1810, and1812can be repeated for multiple backlight frames until the display frame (corresponding to one LCD scan such as LCD scan1002ofFIG. 10, 11, or13above orFIG. 19below) is complete. As indicated by arrow1816, when the display frame is complete, the control circuitry may return to block1802to repeat the operations of blocks1802,1804,1806,1808,1810, and1812for a next display frame.

FIG. 19illustrates a space-time diagram in which a randomized row ordering (e.g., generated using the operations described above in connection withFIG. 18) is applied concurrently within each group406(seeFIG. 4) of rows of LEDs and in which the randomized row ordering is synchronized with LCD scan1002. As shown, in this arrangement, all of backlight row operation indicators1300coincide with or progress in accordance with an LCD scan1002, even with the randomized and concurrent operation of rows in different groups406.

In accordance with various aspects of the subject disclosure, an electronic device is provided that includes a display with a liquid crystal display unit and a backlight unit, the backlight unit including an array of light-emitting diodes arranged in rows and columns, the rows arranged in groups of adjacent rows. The electronic device also includes control circuitry configured to identify a plurality of row orders for operation of the rows of each group of adjacent rows, where each row order synchronizes the operation of the rows of the array with operation of the liquid crystal display unit. The control circuitry is also configured to pseudo-randomly select one of the identified plurality of row orders, and operate, concurrently, the rows of each group using the selected one of the identified plurality of row orders.

In accordance with other aspects of the subject disclosure, an electronic device is provided that includes a display with a liquid crystal display unit and a backlight unit, the backlight unit including an array of light-emitting diodes arranged in rows and columns, the rows arranged in groups of adjacent rows. The electronic device also includes control circuitry configured to identify a backlight scan rate at which to operate the array of light-emitting diodes, the backlight scan rate being an integer multiple of an LCD scan rate for the liquid crystal display unit. The control circuitry is also configured to identify a pseudo-random row order for operation of the rows of each of the groups of adjacent rows, and operate, concurrently, the rows of each group using the pseudo-random row order at the identified backlight scan rate.

In accordance with other aspects of the subject disclosure, a method is provided that includes identifying, for multiple groups of adjacent rows of light-emitting diodes in an array of light-emitting diodes in a backlight of a display of an electronic device, a plurality of row orders for operation of the rows of each group of adjacent rows. Each row order synchronizes the operation of the rows of the array with operation of a liquid crystal display unit of the display. The method also includes pseudo-randomly selecting one of the identified plurality of row orders. The method also includes operating, concurrently, the rows of each group using the selected one of the identified plurality of row orders.