Patent Application
20200082760
This application claims priority to Japanese Patent Application No. 2018-168834, filed on Sep. 10, 2018, and Japanese Patent Application No. 2019-029883, filed on Feb. 21, 2019, the disclosures of which are incorporated herein by reference in their entireties.
This disclosure relates to a technology for driving a display panel.
Example display panels include a liquid crystal display (LCD) panel and an organic light emitting diode (OLED) display panel. The brightness level of an image displayed on a self-luminous display panel, such as an OLED display panel, can be controlled by adjusting the ratio of light producing pixels to total pixels at each moment. Further, the brightness level of the displayed image increases as the ratio of the light producing pixels increases, and vice versa.
In one or more embodiments, a semiconductor device comprises circuitry configured to generate an emission control signal that controls light emission of pixels of a display panel such that a first vertical sync period comprises a plurality of control cycles for the light emission of the pixels. The semiconductor device further comprises a timing generator configured to, when a length of the first vertical sync period is changed, start a next vertical sync period following the first vertical sync period at timing based on a length of the control cycles.
In one or more embodiments, a semiconductor device comprises circuitry configured to generate an emission control signal that controls light emission of pixels of a display panel such that a first vertical sync period of a plurality of vertical sync periods comprises a plurality of control cycles for the light emission of the pixels. The semiconductor device further comprises a data interface configured to transmit an image data transmission request to a host in the first vertical sync period. Further, the semiconductor device comprises a timing generator configured to generate a vertical sync signal defining the plurality of vertical sync periods and, when the data interface does not start receiving image data within a predetermined period after the transmission of the image data transmission request, delay timing at which the vertical sync signal is next asserted, based on a length of the control cycles.
In one or more embodiments, a display panel driving method comprises supplying to a display panel an emission control signal controlling light emission of pixels of the display panel to dispose a plurality of control cycles of the light emission of the pixels are disposed in a first vertical sync period, and when a length of the first vertical sync period is changed, starting a next vertical sync period following the first vertical sync period at timing based on a length of the control cycles.
So that the manner in which the above recited features of the present disclosure may be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only some embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.
In one or more embodiments, as illustrated in
In one or more embodiments, the display panel 1 comprises pixels 4 arrayed in a matrix, scan lines S[-1] to S[m], emission lines EM[1] to EM[m], data lines D[1] to D[n], and scan driver circuitry 5. In one or more embodiments, each pixel 4 is configured to emit light with a brightness level corresponding to a specified grayscale value.
In one or more embodiments, as illustrated in
In one or more embodiments, when a write operation is performed to program a drive voltage corresponding to a grayscale value into the pixel 4, the emission line EM[i] is deasserted, and the scan lines S[i-2], S[i-1] and S[i] are operated in a predetermined sequence with the data line D[j] supplied with the drive voltage, to write the drive voltage into the hold capacitor Cst. In one or more embodiments, the hold capacitor Cst is configured to hold a hold voltage corresponding to the drive voltage written into the pixel 4. In one or more embodiments, when the emission line EM[i] is deasserted, the PMOS transistors M1 and M6 are turned off and the light emitting element 6 stops emitting light. In one or more embodiments, when the emission line EM[i] is asserted after the write operation is completed, the PMOS transistors M1 and M6 are turned on and the light emitting element 6 emits light with the brightness level corresponding to the hold voltage held across the hold capacitor Cst. The pixels 4 may adopt various configurations other than that illustrated in
Referring back to
In one or more embodiments, the scan driver circuitry 5 is further configured to control light emission from rows of pixels 4 for which a write operation is not being performed, based on an emission control signal received from the display driver 2. In one or more embodiments, the emission control signal controls light emission of pixels 4. In one or more embodiments, an emission clock is supplied from the display driver 2 to the scan driver circuitry 5, and permission and prohibition of light emission from pixels 4 of each row are controlled in synchronization with the emission clock. In one or more embodiment, the emission line EM corresponding to the row of pixels 4 for which the write operation is being performed is deasserted to prohibit light emission of pixels 4 of this row.
In one or more embodiments, the display driver 2 is configured as a semiconductor device which comprises a data interface 11, a display memory 12, data driver circuitry 13, a graphic engine 14, register circuitry 15, a timing generator 16, and a panel interface 17.
In one or more embodiments, the data interface 11 is configured to communicate with the host 3 to exchange with the host 3 various data used for control of the display driver 2. In one or more embodiments, the data interface 11 is configured to receive image data and control data. In one or more embodiments, the image data comprise commands for controlling the operation of the graphic engine 14 and/or grayscale data to be written into the display memory 12, the grayscale data describing grayscale values of the respective pixels 4. In one or more embodiments, the control data is used for control of the operation of the display driver 2. In one or more embodiments, the data interface 11 is further configured to interpret commands included in the image data and control data and forward the commands to desired destinations, including the graphic engine 14 and the register circuitry 15. In one or more embodiments, the data interface 11 is further configured to transmit control packets to the host 3 under the control of the timing generator 16. In one or more embodiments, the data interface 11 is configured to transmit to the host 3 a tearing effect (TE) packet which requests transmission of image data, under the control of the timing generator 16.
In one or more embodiments, the display memory 12 is configured to store grayscale data specifying grayscale values of the respective pixels 4.
In one or more embodiments, the data driver circuitry 13 is configured to generate drive voltages corresponding to the grayscale values specified in the grayscale data received from the display memory 12 and write the drive voltages into the respective pixels 4 via the data lines D[1] to D[n].
In one or more embodiments, the graphic engine 14 is configured to receive commands included in the image data received from the host 3 and update the grayscale data stored in the display memory 12 based on the commands.
In one or more embodiments, the register circuitry 15 is configured to store various register values used for the control of the operation of the display driver 2. When a control data transmitted from the host 3 to the display driver 2 comprises a register value, the register value may be stored in the register circuitry 15, in one or more embodiments.
In one or more embodiments, the timing generator 16 is configured to perform timing control of the display driver 2. In one or more embodiments, the timing generator 16 is configured to generate an internal vertical sync signal VSYNC used in the display driver 2. In one or more embodiments, vertical sync periods in the display driver 2 are defined by the internal vertical sync signal VSYNC, and various timing controls in the display driver 2 are performed using the internal vertical sync signal VSYNC as a timing reference.
In one or more embodiments, the panel interface 17 is configured to generate scan control signals to control the scan driver circuitry 5. In one or more embodiments, the scan control signals include the above-described emission control signal, and the scan driver circuitry 5 is configured to control light emission of the pixels 4 based on the emission control signal. In one or more embodiments, the scan control signals include the above-described emission control signal and emission clock, and the scan driver circuitry 5 is configured to control light emission of the pixels 4 based on the emission control signal and the emission clock.
In one or more embodiments, as illustrated in
In one or more embodiments, control of light emission of the pixels 4 is performed with a constant periodicity. In one or more embodiments, the emission control signal is used for permission and prohibition of light emission of the pixels 4 of the respective rows. In one or more embodiments, the emission control signal is asserted and deasserted with a constant periodicity. In the following, the cycle to control the light emission of the pixels 4 may be referred to as “control cycle”. In one or more embodiments, the control cycle may be a cycle to assert and deassert the emission control signal. In one or more embodiments, the length of the control cycles is constant and equal to the periodicity of the emission control signal. In one or more embodiments, as illustrated in
In one or more embodiments, a non-light emitting area 7 in which pixels 4 do not emit light is inserted at an edge of the display panel 1 based on the emission control signal. In one or more embodiments, a non-light emitting area 7 is inserted at the edge of the display panel 1 while the emission control signal is deasserted. In
In one or more embodiments, non-light emitting areas 7 are moved in the direction along the data lines D[1] to D[n] in synchronization with the emission clock. In one or more embodiments, the non-light emitting areas 7 are moved by shifting the deasserted emission lines EM in the direction along the data lines D[1] to D[n] in synchronization with the emission clock.
In one or more embodiments, when the period of time in which the emission control signal is deasserted is prolonged, the period of time in which a non-light emitting area 7 is inserted is also prolonged, and this enlarges the width of the inserted non-light emitting area 7 in the direction along the data lines D[1] to D[n].
In one or more embodiments, the display brightness level of the display panel 1, that is, the brightness level of the entire image displayed on the display panel 1 is controlled by controlling the width of the non-light emitting areas 7 in the direction along the data lines D[1] to D[n]. In one or more embodiments, the display brightness level of the display panel 1 decreases when the ratio of the non-light emitting areas 7 to the entire display area of the display panel 1 increases, wherein the display area is the area in which the pixels 4 are arrayed. In one or more embodiments, when the width of the non-light emitting areas 7 is maximized, none of the pixels 4 emit light and the display brightness level of the display panel 1 becomes the lowest brightness level. In one or more embodiments, the display brightness level of the display panel 1 increases as the ratio of the non-light emitting areas 7 decreases. In one or more embodiments, when the width of the non-light emitting areas 7 is minimized, the display brightness level of the display panel 1 becomes the highest brightest level.
In one or more embodiments, the display brightness level of the display panel 1 is controlled by controlling the ratio of the period during which the emission control signal is asserted to the entire period of each control cycle. In one or more embodiments, when the ratio of the period during which the emission control signal is deasserted is increased in each control cycle, the widths of the non-light emitting areas 7 increase and the display brightness level decreases. In one or more embodiments, when the ratio of the period during which the emission control signal is asserted is increased in each control cycle, the widths of the non-light emitting areas 7 decrease and the display brightness level increases.
In one or more embodiments, the display device 100 operates as illustrated in
In one or more embodiments, the display driver 2 transmits a request for image data transmission to the host 3 once the display driver 2 is ready to receive image data. The request may be a TE packet. Once the host receives the request, the host 3 may start transmitting image data #1, and the data interface 11 of the display driver 2 may start receiving image data #1.
In one or more embodiments, the timing generator 16 asserts the internal vertical sync signal VSYNC upon the start of the reception of image data #1. In one or more embodiments, the assertion of the internal vertical sync signal VSYNC initiates vertical sync period #1 in the display driver 2. In one or more embodiments, image data #1 transmitted from the host 3 to the display driver 2 may contain a predetermined command. In this case, the data interface 11 of the display driver 2 may detect the start of the reception of image data #1 from the host 3 based on the predetermined command. The predetermined command may be disposed at the head of the image data #1.
In one or more embodiments, vertical sync period #1 comprises a back porch period, a display period following the back porch period, and a front porch period following the display period. In one or more embodiments, preparation for writing drive voltages into the respective pixels 4 during the display period is performed in the back porch period. In one or more embodiments, the drive voltages are written into the respective pixels 4 during the display period. In one or more embodiments, the scan driver circuitry 5 sequentially selects the rows of the pixels 4 during the display period, and the data driver circuitry 13 writes the drive voltages into the pixels 4 of the selected row via the data lines D[1] to D[n], the drive voltages corresponding to the grayscale values specified for the pixels 4 of the selected row. In one or more embodiments, preparation of the operation for in the next vertical sync period #2 is performed in the front porch period.
In one or more embodiments, light emission of the pixels 4 of the display panel 1 is controlled on the emission control signal. In one or more embodiments, assertion and deassertion of the emission lines EM[1] to EM[m] are controlled based on the emission control signal and the emission clock. In one or more embodiments, rows of pixels 4, for which the write operation is not performed, emit light when the corresponding emission lines EM are asserted and do not emit light when the corresponding emission lines EM are deasserted. Illustrated in
In one or more embodiments, as illustrated in
In one or more embodiments, the host 3 performs image processing to generate image data #2 corresponding to an image to be displayed in vertical sync period #2 in the meantime.
In one or more embodiments, when the display driver 2 is ready to receive image #2 from the host 3 after a predetermined period of time has elapsed after the start of vertical sync period #1, the display driver 2 transmits a TE packet to the host 3. In one or more embodiments, the host 3 starts transmitting image data #2 when receiving the TE packet. In one or more embodiments, this results in that the display driver 2 starts receiving image data #2.
In one or more embodiments, the timing generator 16 asserts the internal vertical sync signal VSYNC once the display driver 2 starts to receive image data #2. This initiates vertical sync period #2 in the display driver 2.
In one or more embodiments, vertical sync period #2 comprises: a back porch period for the preparation of writing drive voltages into the respective pixels; a display period for writing the drive voltages into the respective pixels 4; and a front porch period for the preparation of the operation for the next vertical sync period #3, similarly to vertical sync period #1. In one or more embodiments, light emission of the pixels 4 of the display panel 1 is controlled by the emission control signal during vertical sync period #2.
In one or more embodiments, during the display driver 2 is in vertical sync period #2, the host 3 generates image data #3 corresponding to an image to be displayed during vertical sync period #3. When the generation of image data #3 takes longer time than vertical sync period #2 and cannot be completed before receiving a next request or TE packet from the display driver 2, vertical sync period #2 may be extended.
In one or more embodiments, when the display driver 2 does not detect the start of reception of image data #3 until a predetermined period of time has elapsed after the transmission of the TE packet to the host 3, the display driver 2 changes or extends the length of vertical sync period #2 by extending the front porch period and waits for the host 3 to start transmitting image data #3. In The extended part of the front porch period is indicated as “extended FP” in
In one or more embodiments, once the generation of image data #3 is complete, the host 3 starts transmitting image data #3 to the display driver 2. At the start of the reception of image data #3, the timing generator 16 asserts the internal vertical sync signal VSYNC to initiate vertical sync period #3.
In one or more embodiments, the timing generator 16 adjusts the timing to initiate vertical sync period #3, that is, the timing at which the timing generator 16 asserts the internal vertical sync signal VSYNC, based on the length of the control cycles. In one or more embodiments, information indicative of the length of the control cycles may be stored in the register circuitry 15. For example, such information may be a register value that specifies the periodicity of the emission control signal. The timing at which vertical sync period #3 is initiated may be determined based on the stored register value.
In one or more embodiments, the timing generator 16 may synchronize the timing at which vertical sync period #3 is initiated, that is, the timing at which the internal vertical sync signal VSYNC is asserted, with the timing at which the final control cycle is completed. In some embodiments, such synchronization may be performed by making the timing of the initiation of vertical sync period #3 match or coincide with the timing of the completion of the final control cycle. In other embodiments, the timing generator 16 controls the timing of the vertical sync period #3 initiation so that the length of vertical sync period #2 becomes an integer multiple of the length of the control cycles or an integer multiple of the periodicity of the emission control signal.
If the final control cycle of vertical sync period #2 does not match or coincide with the timing of the vertical sync period #3 initiation, the final control cycle of vertical sync period #2 is not fully completed. For example, the period during which the emission control signal is being deasserted is prolonged to bridge vertical sync periods #2 and #3. This may make the user observe an instantaneous brightness decrease in the image displayed on the display panel 1. Through the operation as described above in connection with
In one or more embodiments, as illustrated in
In one or more embodiments, the vertical sync signal generator circuitry 21 comprises: VSYNC timing control circuitry 23 configured to determine the timing at which the internal vertical sync signal VSYNC is asserted; and a vertical sync signal output stage 24 configured to output the internal vertical sync signal VSYNC and assert the internal vertical sync signal VSYNC at timing determined by the VSYNC timing control circuitry 23.
In one or more embodiments, the VSYNC timing control circuitry 23 is configured to control the timing of the assertion of the internal vertical sync signal VSYNC, based on a back porch register value 31, a display line register value 32, a front porch register value 33, and a memory write start signal, where the back porch register value 31, the display line register value 32, and the front porch register value 33 are stored in the register circuitry 15. In one or more embodiments, the back porch register value 31 specifies the length of the back porch periods and the display line register value 32 specifies the length of the display periods. In one or more embodiments, the front porch register value 33 specifies the length of the front porch periods. In one or more embodiments, the memory write start signal is asserted when the data interface 11 receives a memory write start command from the host 3. In one or more embodiments, image data transmitted from the host 3 comprises a memory write start command and this allows the VSYNC timing control circuitry 23 to detect start of reception of image data by the display driver 2 based on the memory write start signal.
In one or more embodiments, the emission control signal generator circuitry 22 comprises a pulse generator 25 configured to generate the emission control signal based on emission control signal setting parameters stored in the register circuitry 15. In one or more embodiments, the emission control signal setting parameters specify the waveform of the emission control signal, including the length of the period during which the emission control signal is asserted in each control cycle and the length of the period during which the emission control signal is deasserted in each control cycle. The emission control signal setting parameters may directly describe the length of the period during which the emission control signal is asserted and the length of the period during which the emission control signal is deasserted, or may comprise parameters from which these lengths can be calculated. In one or more embodiments, the internal vertical sync signal VSYNC is supplied to the pulse generator 25 and the operation of the pulse generator 25 is reset when the internal vertical sync signal VSYNC is asserted.
In one or more embodiments, the VSYNC timing control circuitry 23 may determine the timing of the assertion of the internal vertical sync signal VSYNC once each vertical sync period is initiated through an operation illustrated in
In one or more embodiments, at step S01, the VSYNC timing control circuitry 23 calculates a parameter value SET_VSYNC that specifies the default length of the vertical sync period by adding up the back porch register value 31, the display line register value 32, and the front porch register value 33.
In one or more embodiments, at step S02, the VSYNC timing control circuitry 23 monitors the memory write start signal. In one or more embodiments, when the memory write start signal is not asserted within a predetermined period of time after a TE packet is transmitted to the host 3 in the front porch period, the VSYNC timing control circuitry 23 extends the front porch period by a predetermined extension amount #1 at step S03. In one or more embodiments, the operation to extend the front porch period by the predetermined extension amount #1 is repeated until the assertion of the memory write start signal is detected.
In one or more embodiments, when the memory write start signal is asserted, the VSYNC timing control circuitry 23 determines at step S04 whether the current vertical sync period length is appropriately determined with reference to the emission control signal setting parameters. In one or more embodiments, the length of the control cycles can be obtained from the emission control signal setting parameters, and the timing of the completion of the current vertical sync period, that is, the timing of the initiation of the next vertical sync period is adjusted based on the length of the control cycles.
In one or more embodiments, when the current vertical sync period length is determined as being appropriate, the internal vertical sync signal VSYNC is asserted upon the completion of the front porch period to initiate the next vertical sync period. In one or more embodiments, when the current vertical sync period length is determined as being an integer multiple of the length of the control cycles as a result of the extension of the front porch period at step S03, the internal vertical sync signal VSYNC is asserted at step S06 when the front porch period is completed.
In one or more embodiments, when the current vertical sync period length is not determined as being appropriate, the front porch period is further extended by an extension amount #2 at step S05. In one or more embodiments, the extension amount #2 is determined to match the length of control cycles based on the emission control signal setting parameters. In one or more embodiments, the extension amount #2 may be determined so that the current vertical sync period length becomes an integer multiple of the length of the control cycles. In one or more embodiments, the internal vertical sync signal VSYNC is asserted when the extended front porch period is completed.
In one or more embodiments, as illustrated in
In one or more embodiments, the timing of the initiation of vertical sync period #3 is synchronized with the timing of the completion of the final control cycle of vertical sync period #2. In one or more embodiments, the timing of the initiation of vertical sync period #3 is made coincident with the timing of the completion of the final control cycle of vertical sync period #2, as illustrated in
In one or more embodiments, such synchronization or coincidence is achieved by setting the lengths of vertical sync periods #1 and #2 to integer multiples of the length of the control cycles or by setting the length of the control cycles so that the lengths of vertical sync periods #1 and #2 are both integer multiples of the length of the control cycles. In one or more embodiments, the frame rate is 90 Hz during vertical sync period #1 and vertical sync period #1 comprises four control cycles. In such embodiments, the length of vertical sync period #1 is four times of the length of the control cycles, and the emission control signal comprises four emission pulses in vertical sync period #1. In one or more embodiments, the frame rate is switched to 60 Hz in vertical sync period #2. In such embodiments, the lengths of vertical sync period #2 and the following vertical sync periods are extended to six times of the length of the control cycles. In one or more embodiments, the timing of the completion of the final control cycle of vertical sync period #2 is made coincident with the timing of the initiation of vertical sync period #3.
In one or more embodiments, the switching of the frame rate by extending the lengths of vertical sync periods may be accompanied by variations in the display brightness level. In one or more embodiments, the variations in the display brightness level may result from leakage currents form the pixels 4. In one or more embodiments, the hold voltages held in the pixels 4 may gradually decrease after the writing of the drive voltages. Illustrated in
In one or more embodiments, as illustrated in
In one or more embodiments, vertical sync period #2, disposed between vertical sync periods #1 and #3, is used for dimming of the display brightness level; the length of vertical sync period #2 is set to be longer than that of vertical sync period #1 and shorter than that of vertical sync period #3. In such embodiments, the display brightness level during vertical sync period #2 becomes between the display brightness levels during vertical sync periods #1 and #3, reducing the change rate of the display brightness level. In one or more embodiments, the display brightness level is 450 nit during vertical sync period #1, 440 nit during vertical sync period #3, and 445 nit during vertical sync period #2. In one or more embodiments, occurrence of flicker is suppressed by reducing the change rate of the display brightness level.
In one or more embodiments, the timing of the initiation of vertical sync period #3 is synchronized with the timing of the completion of the final control cycle of vertical sync period #2, and the timing of the initiation of the vertical sync period following vertical sync period #3 is synchronized with the timing of the completion of the final control cycle of vertical sync period #3. In one or more embodiments, as illustrated in
In one or more embodiments, such synchronization or coincidence may be achieved by setting the lengths of vertical sync periods #1 to #3 to integer multiples of the length of the control cycles or by setting the length of the control cycles so that the lengths of vertical sync periods #1 to #3 are integer multiples of the length of the control cycles. In one or more embodiments, the frame rate is 90 Hz during vertical sync period #1 and 60 Hz during vertical sync period #3 and the following vertical sync periods. In one or more embodiments, the length of vertical sync period #1 is four times of the length of the control cycles, the length of vertical sync period #3 and the following vertical sync periods is six times of the length of the control cycles, and the length of vertical sync period #2 is five times of the length of the control cycles. In one or more embodiments, this operation can be achieved by appropriately determining the length of the control cycles.
In one or more embodiments, as illustrated in
In one or more embodiments, as illustrated in
In one or more embodiments, as illustrated in
In one or more embodiments, the switching of the frame rate through the reduction in the vertical sync period length may be accompanied by a change in the display brightness level, similarly to the case where the vertical sync period length is extended. To reduce the change rate of the display brightness level, in one or more embodiments, dimming is performed in switching the frame rate and the vertical sync period length is gradually shortened.
In one or more embodiments, vertical sync period #2, disposed between vertical sync periods #1 and #3, is used for dimming of the display brightness level; the length of vertical sync period #2 is set to be shorter than the length of vertical sync period #1 and longer than the length of vertical sync period #3. In such embodiments, the display brightness level during vertical sync period #2 becomes between the display brightness levels during vertical sync periods #1 and 3, and this reduces the change rate of the display brightness level. In one or more embodiments, the reduction in the change rate of the display brightness level effectively suppresses occurrence of flicker.
In one or more embodiments, the timing of the initiation of vertical sync period #3 is synchronized with the timing of the completion of the final control cycle of vertical sync period #2, and the timing of the initiation of the vertical sync period following vertical sync period #3 is synchronized with the timing of the completion of the final control cycle of vertical sync period #3. In the operation illustrated in
In one or more embodiments, such synchronization or coincidence is achieved by setting the lengths of vertical sync periods #1 to #3 to integer multiples of the length of the control cycles. In one or more embodiments, the frame rate is 60 Hz during vertical sync period #1 and 90 Hz during vertical sync period #3 and the following vertical sync periods. In one or more embodiments, the length of vertical sync period #1 is six times of the length of the control cycles, the length of vertical sync period #3 and the following vertical sync periods is four times of the length of the control cycles, and the length of vertical sync period #2 is five times of the length of the control cycles.
In one or more embodiments, as illustrated in
In one or more embodiments, as illustrated in
Although various embodiments of this disclosure have been specifically described, the person skilled in the art would appreciate that the technologies disclosed herein may be implemented with various modifications.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-168834 | Sep 2018 | JP | national |
| 2019-029883 | Feb 2019 | JP | national |
