CN115206223A

CN115206223A - Method for preventing tearing effect

Info

Publication number: CN115206223A
Application number: CN202210852341.6A
Authority: CN
Inventors: 姜圣显; 吴水兵
Original assignee: Shenghe Microelectronics Zhaoqing Co ltd
Current assignee: Shenghe Microelectronics Zhaoqing Co ltd
Priority date: 2022-07-19
Filing date: 2022-07-19
Publication date: 2022-10-18

Abstract

A method for preventing a tearing effect is applied to a display driving chip, the display driving chip comprises a frame memory, a display channel and a synchronous signal generator for providing synchronous signals for the frame memory and the display channel, and the method for preventing the tearing effect comprises the following steps: when a power-on time sequence is detected, adding a WAIT state in a synchronous signal generated by the synchronous signal generator, wherein the WAIT state starts from the end of the VACTIVE state and is ended when VSYNC from an external application processor is received, and the power-on time sequence is a power-on time sequence for internally adjusting the power state for displaying when a sleep command from the external application processor is received. The method can eliminate the tearing effect generated when the display driving chip with the built-in frame memory is used in the video mode.

Description

Method for preventing tearing effect

Technical Field

The invention relates to the field of display driving chips, in particular to a method for preventing Tearing Effect (TE).

Background

In the conventional display system, the display driving chip is divided into: a display driver chip that operates in a video mode without a built-in frame memory, and a display driver chip that operates in a command mode with a built-in frame memory.

However, in reality where the display condition function is required to be more complicated and diversified, even in a display driver chip operating in a command mode, there is a case where a video mode operation is required in a specific system, and in a system operating in a video mode, there is a case where a display is required to be performed using a frame memory incorporated in the display driver chip.

For example, in a system operating in the video mode, the display driver chip needs to use an internal up-scaler, or in the video mode, in order to reduce the power consumption of the entire system, the Application Processor (AP) transmits an image at a low frame rate when the image is not changed, and the display driver chip needs to store the image in an internal memory and then display the image at a higher frame rate than the frame rate transmitted by the application processor.

In a system operating in the video mode, if the display driver chip needs to use the built-in frame memory for displaying, a tearing effect occurs because there is no TE pin required for synchronization between the application processor and the display driver chip.

In order to eliminate the tearing effect occurring in a system operating in video mode, it is necessary to implement a function of synchronizing with an image sent by an application processor inside a display driver chip.

In view of the above-mentioned studies, the present invention has been made.

Disclosure of Invention

The invention aims to provide a method for preventing tearing effect, which keeps the time difference d between a synchronous signal from an application processor and a synchronous signal generated inside a display driving chip constant by adding a WAIT state, thereby avoiding the tearing effect.

The technical scheme adopted by the invention is as follows:

a method for preventing a tearing effect is applied to a display driving chip, the display driving chip comprises a frame memory, a display channel and a synchronous signal generator for providing synchronous signals for the frame memory and the display channel, and the method for preventing the tearing effect comprises the following steps: when a power-on time sequence is detected, adding a WAIT state in a synchronous signal generated by the synchronous signal generator, wherein the WAIT state starts from the end of the VACTIVE state and stops when VSYNC (Vertical Synchronization) from an external application processor is received, and the power-on time sequence is the power-on time sequence for internally adjusting the power state for displaying when a sleep command from the external application processor is received.

Alternatively, the WAIT state is added only in the first frame after the power-up sequence.

Alternatively, the WAIT state is added only within a frame that is performed at power-up timing.

There is also a scheme in which the WAIT state is added every frame after the power-on timing.

Preferably, the method of preventing a tearing effect further includes transmitting image data for generating a black image to the display panel in the WAIT state.

Compared with the prior art, the invention at least has the following beneficial effects:

capable of eliminating tearing effect generated when using display driving chip with built-in frame memory in video mode

Drawings

FIG. 1 shows an external interface and an internal frame synchronization signal when a display driver chip with a built-in frame memory is used in a system using a video mode operation;

FIG. 2 illustrates the conventional operation of the video mode interface and the internal synchronization signals of the display driver chip;

fig. 3 shows a timing relationship between a frame synchronization signal generated in the display driver chip after the sleep and a frame synchronization signal input through an MIPI (Mobile Industry Processor Interface);

fig. 4 shows a timing diagram included in the proposed functionality for preventing the tearing effect.

Detailed Description

The invention is further described below with reference to the following figures and examples.

Fig. 1 shows how frame synchronization is configured and operated when a display driver chip uses a built-in frame memory in a system operating in a video mode. In general, since a video mode motion system does not use a frame memory, a frame synchronization signal entered through an external interface is directly used.

However, when the frame memory is required to be used inside the display driver chip for some special reasons, the display driver chip needs to generate a frame synchronization signal inside the display driver chip for use in the display operation. In the figure 101, MIPI video mode interface signals are shown, including PCLK, VSYNC (Vertical Synchronization), HSYNC (horizontal Synchronization), DE (active DATA strobe), and RGB _ DATA, where VSYNC, HSYNC, and DE are frame Synchronization signals. Reference numeral 102 denotes a frame synchronization signal for display, which is internally generated in the display driver chip and includes VSYNC, HSYNC, and DE.

Fig. 2 shows the timing of the operation of a conventional synchronization signal to transfer display data.

The timing from VSYNC to the time before the actual display image data is transferred is denoted by VBP (Vertical Back Porch).

202 denotes the ACTIVE interval, denoted by ACTIVE, where image data is transferred between each HYSNC. The DE signal is active at the timing of actual image data transfer.

The timing between the transfer of image data and the next VSYNC is denoted by VFP (Vertical Front Porch) 203.

Fig. 3 shows a timing difference between a VSYNC signal 305 input through the MIPI and a VSYNC signal 304 internally generated in the display driving chip after the application processor transmits a sleep command SLPOUT 301 to the display driving chip.

Since there is no signal to synchronize its time between the VSYNC signal 305 input through the MIPI and the VSYNC signal 304 generated inside the display driving chip, the time difference 306 between the two signals is random, thereby generating a tearing effect.

If the application processor sends a sleep command to the display driving chip, the display driving chip internally performs various power-on timing sequences for adjusting the power state for display. 302 represents the power-up sequence state at this time, after which the substantive display is run in the subsequent SLEEP _ OUT state 303.

Fig. 4 shows a method of preventing the tearing effect according to the present embodiment.

In the figure, 401 indicates a frame period transmitted by the application processor through the video mode interface MIPI, and 402 indicates a frame period inside the display driver chip.

Since the frame rate inside the display driver chip can be adjusted by a plurality of parameter values, it can be set to be the same as the frame rate of the application processor, and thus, they are all represented by the same p. Fig. 4 assumes that the frame rate inside the display driver chip is the same as the frame rate sent by the application processor. However, since the tearing effect cannot be prevented only by matching the frame rates, the present embodiment proposes a method of preventing the tearing effect as follows.

As shown in 403, after the display driver chip enters the sleep state, the display driver chip enters the WAIT state instead of entering the VFP state after the start of the first frame. The WAIT state WAITs until receiving VSYNC coming in from the MIPI, that is, terminates when receiving VSYNC from an external application processor, and thus the duration of the WAIT state is not fixed but variable.

In WAIT state, VFP state is entered if VSYNC is received from MIPI, as shown in 404.

As shown at 405, this is so that the frame period is not p, but p + WAIT, which is longer than the other frames.

By using the method, a certain time difference can be kept between the frame synchronization signal input by the MIPI and the frame synchronization signal generated in the display driving chip.

The application processor is also the same as the display driver chip, since the VBP-v active-VFP state is repeated and data is transferred through the MIPI, as shown in 406, in the MIPI interface, the VBP state enters the v active state after passing, image data is input, and at this time, the input data starts to be stored in the frame memory inside the display driver chip.

Since the display driver chip reads data from the frame memory for display in the active state of the internal synchronization signal, the time difference d represents a difference between the time when the frame memory starts writing data and the time when the frame memory starts reading data, as shown by 407.

The parameter value of the frame rate is adjusted inside the display driving chip, the difference d between the MIPI frame synchronization value and the internal frame synchronization value is determined, the d value of each frame is kept unchanged all the time, and the tearing effect can be avoided.

Although the above-described tearing effect can be prevented, the period of the other frames is p, the period of the frame for increasing the WAIT state is p + WAIT, and since the increased period may affect the operation of the panel, it is preferable to add a function of transmitting image data for generating a black image to the display panel in the WAIT state to make the panel display the black image instead of inputting the image of the frame in MIPI.

In the above embodiment, it is the best solution to start with the end of the power on timing and add the WAIT state only in the first frame after the power on timing.

As a sub-optimal scheme, a WAIT state is added in a frame performed at a power-on timing sequence, and a d value of each frame can be kept unchanged all the time, so that a tearing effect can be avoided.

As an expansion scheme, a WAIT state can be added in each frame after the power-on time sequence, and the d value of each frame is kept constant all the time by adding the WAIT state in each frame, so that the tearing effect can be avoided.

It should be understood that, in the above embodiments, the MIPI interface is used as the video mode interface only as a specific example, and the method is also applicable to a general RGB interface system other than the MIPI interface.

The present invention has been described in detail with reference to the specific embodiments, and the detailed description is only for the purpose of helping those skilled in the art understand the present invention, and is not to be construed as limiting the scope of the present invention. Various modifications, equivalent changes, etc. made by those skilled in the art under the spirit of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preventing tearing effect is applied to a display driving chip, the display driving chip comprises a frame memory, a display channel and a synchronous signal generator for providing synchronous signals for the frame memory and the display channel, and the method for preventing tearing effect comprises the following steps: when a power-on time sequence is detected, adding a WAIT state in a synchronous signal generated by the synchronous signal generator, wherein the WAIT state starts from the end of the VACTIVE state and is terminated when VSYNC from an external application processor is received, and the power-on time sequence is a power-on time sequence for internally adjusting the power state for displaying when a sleep command from the external application processor is received by the power-on time sequence.

2. The method of claim 1, wherein the WAIT state is added only in a first frame after a power-up sequence.

3. The method of claim 1, wherein the WAIT state is added only within a frame that is performed at a power-up timing.

4. The method of claim 1, wherein the WAIT state is added every frame after a power-up sequence.

5. The method of claim 1, further comprising sending image data for generating a black image to the display panel in the WAIT state.