Display driver circuitry with selectively enabled clock distribution

This application claims the benefit of provisional patent application No. 62/146,127 filed on Apr. 10, 2015, which is hereby incorporated by reference herein in its entirety.

This relates generally to electronic devices, and, more particularly, to electronic devices with displays.

Electronic devices such as cellular telephones, computers, and other electronic equipment often contain displays. A display includes an array of pixels for displaying images to a user. Display driver circuitry such as source line driver circuitry may supply data signals to the array of pixels. Gate line driver circuitry in the display driver circuitry can be used to assert a gate line signal on each row of pixels in the display in sequence to load data into the pixels.

Clock signals are distributed to registers in the gate line driver circuitry using clock signal distribution lines. Power is consumed when driving clock signals onto the clock signal distribution line. Excess power consumption can lead to undesired effects such as reduced battery life.

It would therefore be desirable to be able to reduce the amount of power consumed when distributing clock signals in the gate driver circuitry of a display.

A display may have an array of pixels controlled by display driver circuitry. The display driver circuitry may supply data to columns of the pixels over data lines. The display driver circuitry may include gate driver circuitry that supplies gate line signals to rows of the pixels over gate lines.

The gate driver circuitry may include gate driver integrated circuits. Each gate driver integrated circuit may have a shift register that supplies the gate line signals to the rows of pixels. The display driver circuitry may supply a clock signal to the gate driver integrated circuits. Each gate driver integrated circuit may have one or more clock trees that distribute the clock signal to one or more respective shift registers.

The gate drive integrated circuits may contain control circuitry that controls the distribution of the clock signal to the clock trees. This allows the clock signal to be distributed to a subset of the clock trees to save power. Clock trees that are coupled to active shift register circuitry may receive the clock signal. Clock trees that are coupled to inactive shift register circuitry can be temporarily disabled.

Each gate driver integrated circuit may have a controller and a buffer that is controlled by a control signal from the controller. The buffer may be adjusted so as to supply or so as not to supply the clock signal to an associated clock tree in that gate driver integrated circuit.

FIG. 1 is a schematic diagram of an illustrative electronic device having a display in accordance with an embodiment.

FIG. 2 is a top view of an illustrative display in an electronic device in accordance with an embodiment.

FIG. 3 is a circuit diagram of gate driver circuitry in a display in accordance with an embodiment.

FIG. 4 is a state diagram showing the operation of internal clock gating logic in gate driver circuitry in accordance with an embodiment.

FIG. 5A is a timing diagram showing how the gate driver circuitry of FIG. 3 may operate in a 1 H gate pulse scheme in accordance with an embodiment.

FIG. 5B is a timing diagram showing how the gate driver circuitry of FIG. 3 may operate in a 4 H gate pulse scheme in accordance with an embodiment.

FIG. 6 is a circuit diagram showing how multiple clock trees can be selectively controlled within a gate driver integrated circuit that has been partitioned into sections each of which is clocked using a separate clock tree in accordance with an embodiment.

An illustrative electronic device of the type that may be provided with a display is shown in FIG. 1 . As shown in FIG. 1 , electronic device 10 may have control circuitry 16 . Control circuitry 16 may include storage and processing circuitry for supporting the operation of device 10 . The storage and processing circuitry may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in control circuitry 16 may be used to control the operation of device 10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application specific integrated circuits, etc.

Input-output circuitry in device 10 such as input-output devices 12 may be used to allow data to be supplied to device 10 and to allow data to be provided from device 10 to external devices. Input-output devices 12 may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device 10 by supplying commands through input-output devices 12 and may receive status information and other output from device 10 using the output resources of input-output devices 12 .

Input-output devices 12 may include one or more displays such as display 14 . Display 14 may be a touch screen display that includes a touch sensor for gathering touch input from a user or display 14 may be insensitive to touch. A touch sensor for display 14 may be based on an array of capacitive touch sensor electrodes, acoustic touch sensor structures, resistive touch components, force-based touch sensor structures, a light-based touch sensor, or other suitable touch sensor arrangements.

Control circuitry 16 may be used to run software on device 10 such as operating system code and applications. During operation of device 10 , the software running on control circuitry 16 may display images on display 14 using an array of pixels in display 14 .

Device 10 may be a tablet computer, laptop computer, a desktop computer, a display, a cellular telephone, a media player, a wristwatch device or other wearable electronic equipment, or other suitable electronic device.

Display 14 may be an organic light-emitting diode display, a liquid crystal display, or a display based on other types of display technology. Configurations in which display 14 is a liquid crystal display may sometimes be described herein as an example.

Display 14 may have a rectangular shape (i.e., display 14 may have a rectangular footprint and a rectangular peripheral edge that runs around the rectangular footprint) or may have other suitable shapes. Display 14 may be planar or may have a curved profile.

A top view of a portion of display 14 is shown in FIG. 2 . As shown in FIG. 2 , display 14 may have an array of pixels 22 formed from substrate structures such as substrate 36 . Substrates such as substrate 36 may be formed from glass, metal, plastic, ceramic, or other substrate materials. Pixels 22 may receive data signals over signal paths such as data lines D and may receive one or more control signals over control signal paths such as horizontal control lines G (sometimes referred to as gate lines, scan lines, emission control lines, etc.). There may be any suitable number of rows and columns of pixels 22 in display 14 (e.g., tens or more, hundreds or more, or thousands or more). In organic light-emitting diode displays, pixels 22 contain respective light-emitting diodes and pixel circuits that control the application of current to the light-emitting diodes. In liquid crystal displays, pixels 22 contain pixel circuits that control the application of signals to pixel electrodes that are used for applying controlled amounts of electric field to pixel-sized portions of a liquid crystal layer. The pixel circuits in pixels 22 may contain transistors having gates that are controlled by gate line signals on gate lines G.

Display driver circuitry 20 may be used to control the operation of pixels 22 . Display driver circuitry 20 may be formed from integrated circuits, thin-film transistor circuits, or other suitable circuitry. Thin-film transistor circuitry may be formed from polysilicon thin-film transistors, semiconducting-oxide thin-film transistors such as indium gallium zinc oxide transistors, or thin-film transistors formed from other semiconductors. Pixels 22 may have color filter elements of different colors (e.g., red, green, and blue) to provide display 14 with the ability to display color images.

Display driver circuitry 20 may include display driver circuits such as display driver circuit 20 A and gate driver circuitry 20 B. Display driver circuit 20 A may be formed from one or more integrated circuits and/or thin-film transistor circuitry. Gate driver circuitry 20 B may be formed from integrated circuits or may be thin-film “gate-on-array” circuitry. Display driver circuit 20 A of FIG. 2 may contain communications circuitry for communicating with system control circuitry such as control circuitry 16 of FIG. 1 over path 32 . Path 32 may be formed from traces on a flexible printed circuit or other conductive lines. During operation, the control circuitry (e.g., control circuitry 16 of FIG. 1 ) may supply circuit 20 A with information on images to be displayed on display 14 .

To display the images on display pixels 22 , display driver circuitry 20 A may supply image data to data lines D while issuing clock signals and other control signals such as a gate start pulse GSP and clock signal CLK to supporting display driver circuitry such as gate driver circuitry 20 B over path 38 . Circuitry 20 A may supply clock signals and other control signals to gate driver circuitry 20 B on one or both edges of display 14 (see, e.g., path 38 ′ and gate driver circuitry 20 B′ on the right-hand side of display 14 in the example of FIG. 2 ).

Gate driver circuitry 20 B (sometimes referred to as horizontal control line control circuitry) may control horizontal control lines (gate lines) G (e.g., G( 1 ), G( 2 ), G( 3 ) . . . ). Gate lines G in display 14 may each carry a gate line signal for controlling the pixels 22 of a respective row (e.g., to turn on transistors in pixels 22 when loading data from the data lines into pixel storage capacitors in those pixels from data lines D). During operation, frames of image data may be displayed by asserting a gate signal on each gate line G in the display in sequence. Shift register circuitry (e.g., a chain of registers) in gate driver circuitry 20 B may be used in controlling the gate line signals.

Multiple integrated circuits such as illustrative gate driver integrated circuits 40 - 1 . . . 40 -N of FIG. 2 may be used in supplying gate signals G. The registers in each gate driver integrated circuit may be connected in a chain to form a shift register for that gate driver integrated circuit. The output of the last register in the shift register of each gate driver integrated circuit may be coupled to the input of the next gate driver integrated circuit in circuitry 20 B to form a shift register that spans all of the gate lines in display 14 . The registers may each receive a clock signal CLK from circuitry 20 A. Clock trees may be used to distribute clock signal CLK within the gate driver integrated circuits. To conserve power, clock trees that are not being used may be disabled.

A circuit diagram of illustrative gate driver circuitry 20 B with clock tree control circuitry that allows inactive clock trees to be temporarily disabled is shown in FIG. 3 . As shown in FIG. 3 , gate driver circuitry 20 B has multiple gate driver integrated circuits such as integrated circuits 40 - 1 , 40 - 2 , etc. Each gate driver integrated circuit has a chain of registers that form a shift register. For example, integrated circuit 40 - 1 has a shift register formed from registers R 1 , R 2 , . . . RX for asserting gate line signals G( 1 ), G( 2 ) . . . G(X) in sequence. The output OUT of each register is provided to the next register in the chain of registers to serve as a triggering input for that register.

The first register (R 1 ) in circuit 40 - 1 is not coupled to the output of any preceding registers. Instead, circuit 20 A generates a gate start pulse GSP to serve as the trigger signal for register R 1 . Gate start pulse GSP is distributed to register R 1 by control logic 44 (sometimes referred to as internal clock gating logic, clock tree controller circuitry, or controller) as internal gate start pulse signal iGSP.

Gate driver integrated circuits 40 - 1 , 40 - 2 . . . 40 -N are coupled together by providing the output signal of the last register in each integrated circuit to the input IN of the first register in the next gate driver integrated circuit (see, e.g., output signal LASTX from last register RX of integrated circuit 40 - 1 , which serves as the trigger input for the first register in integrated circuit 40 - 2 ).

Clock signal CLK is distributed to all gate driver integrated circuits in circuitry 20 B. Within each gate driver integrated circuit, one or more clock trees such as clock tree 46 may be used to distribute clock signal CLK to the shift register circuitry of that gate driver integrated circuit. The clock signal distribution control circuitry of each gate driver integrated circuit includes controller 44 and buffer 48 . Controller 44 receives signals such as gate start pulse signal GSP (the trigger signal for first register R 1 ), signal HSEL (to select between operating modes such as a 1 H mode, 2 H mode, 3 H mode, 4 H mode, and, if desired additional operating modes such as an 8 H mode, etc.), and clock signal CLK.

Clock distribution buffer 48 can be enabled and disabled by controller 44 using control signal iCLKg. Controller 44 supplies control signal iCLKg to buffer 48 using path 50 . When signal iCLKg has one value (e.g., a low value), buffer 48 is enabled and clock signal CLK is passed from input 52 to output 54 so that clock tree 46 can distribute clock CLK to the shift register that is coupled to clock tree 46 . When signal iCLKg has another value (e.g., a high value), buffer 48 is disabled. When buffer 52 is disabled, clock signal CLK is not driven into clock tree 46 , which conserves power for gate driver circuitry 20 B. At any given time during the operation of display 14 , only about 1-8 registers are generally active and supplying gate line output signals. It is therefore not necessary for the registers of all gate lines G in display 14 (which may number in the hundreds or thousands) to be active at the same time. By disabling clock trees 46 that are not being actively used (e.g., by using controllers 44 in gate driver integrated circuits that are not actively producing gate line signals to disable the clock trees in those gate driver integrated circuits), unwanted power consumption that would otherwise arise from driving clock signals into these clock trees can be avoided.

Each controller 44 can determine when to activate its corresponding clock tree 46 by operating in accordance with a state diagram of the type shown in FIG. 4 . The illustrative state diagram of FIG. 4 supports 1 H operation, 2 H operation 3 H operation, and 4 H operation for its gate line signals (each having a different respective pulse duration ranging from one clock cycle for 1 H to four clock cycles for 4 H). Other modes of operation may be supported if desired. The example of FIG. 4 is merely illustrative.

In state A, controller 44 does not assert internal gate start pulse iGSP (i.e., iGSP is zero) and controller 44 holds clock distribution control signal iCLKg high to disable buffer 48 and thereby prevent clock signals from being driven into clock tree 46 . While in state A, controller 44 awaits assertion of gate start pulse GSP by display driver circuitry 20 A (or, for subsequent gate driver integrated circuits, controller 44 awaits assertion of the output LASTX from the last register in the shift register of the preceding gate driver integrated circuit, which serves as a trigger pulse).

When GSP is asserted (i.e., when controller 44 detects that GSP is high), controller 44 can conclude that the shift register circuitry of the gate driver integrated circuit containing controller 44 is being activated, so controller 44 may transition to state B. In state B, controller 44 takes signal iCLKg low to enable buffer 48 and thereby distribute clock signal CLK to clock tree 46 and the shift register circuitry. Because GSP is high, controller 44 takes internal gate start pulse iGSP high upon the first transition of clock signal CLK, thereby triggering operation of register R 1 (and thereby starting the shift register of circuit 40 - 1 ).

The length of time that signal iGSP is asserted (which controls the length of each gate line output pulse) depends on the mode of operation of display 14 (e.g., 1 H, 2 H, 3 H, or 4 H in the present example). If circuit 40 - 1 is being operated in 1 H mode, signal HSEL will be equal to 1 H and iGSP will be deasserted after one clock cycle (at which point controller 44 will transition to state F from state B), as shown in the illustrative 1 H timing diagram of FIG. 5A . If circuit 40 - 1 is being operated in 2 H mode, signal HSEL will be equal to 2 H and iGSP will be deasserted after 2 clock cycles (i.e., operation of controller 44 will transition to state C for one clock cycle before transitioning to state EF). Operation in modes 3 H and 4 H is similar. If circuit 40 - 1 is being operated in 3 H mode, signal HSEL will be equal to 3H and iGSP will be deasserted after 3 clock cycles (i.e., operation of controller 44 will transition from state C to state D for one additional clock cycle before transitioning to state F). If circuit 40 - 1 is being operated in 4 H mode, signal HSEL will be equal to 4H and iGSP will be deasserted after 4 clock cycles (i.e., operation of controller 44 will transition from state D to state E for one additional clock cycle before transitioning to state F).

During state F, shift register operation continues (and gate lines G are asserted in succession) until the last gate line signal in the shift register is asserted (i.e., LASTX=1). When LASTX is asserted, controller 44 transitions to state A (i.e., clock tree 46 is disabled and controller 44 is idle and awaiting its next trigger pulse). As shown by states G, H, and I, 1, 2, or 3 additional clock cycles may be imposed before returning to state A from state F, depending on whether controller 44 is operating in 2 H, 3 H, or 4 H mode. FIG. 5B is a timing diagram showing how the signals of FIG. 3 transition during 4 H operation.

If desired, the gate driver circuits of circuitry 20 B may be partitioned internally. This type of arrangement is shown in FIG. 6 . In the example of FIG. 6 , the shift register of circuit 40 - 1 has been partitioned into two parts—a first part that receives clock signals from clock tree 46 - 1 and a second part that is coupled in series with the first part and that receives clock signals from clock tree 46 - 2 . Multiple controllers may be used to individually control each of the clock trees in circuit 40 - 1 . For example, controller 44 - 1 may control buffer 48 - 1 to control when clock signal CLK is distributed to the first portion of the shift register using clock tree 46 - 1 and controller 44 - 2 may control buffer 48 - 2 to control when clock signal CLK is distributed to the second portion of the shift register using clock tree 46 - 2 . In circuits with three or more clock trees, three (or more) respective controllers may be provided.

The use of multiple controllers within a single gate driver integrated circuit allows portions of the clock tree circuitry of the gate driver integrated circuit to be enabled when needed to produce gate line output signals while remaining portions of the clock tree circuitry of the same gate driver integrated circuit may be disabled to save power. The clock tree circuitry of other gate driver integrated circuits with inactive shift registers may be disabled using the controllers in those gate driver integrated circuits.

The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.