What are Display Timing Parameters?
Display timing parameters are crucial for driving Midas LCD TFT Displays with LVDS (Low Voltage Differential Signaling), RGB, MIPI (Mobile Industry Processor Interface), and eDP (Embedded DisplayPort) interfaces because they ensure proper synchronisation and accurate data transfer between the display driver and the panel. These parameters govern how the display interface communicates pixel data and control signals. Here’s a few reasons why they are important:
- Correct Image Display: Incorrect timing parameters can lead to distorted images, flickering, or no display at all.
- Synchronisation: Proper timing ensures that the display controller and the display panel are synchronised, preventing data loss or corruption.
- Power Efficiency: Optimised timing parameters can help reduce power consumption.
- Compatibility: Different display technologies have different timing requirements, so it’s important to use the correct parameters for the specific display.
How to Obtain Display Timing Parameters?
- Display Datasheet: The most reliable source of timing parameters is the display’s datasheet. It will provide detailed information on the required timing signals and their specifications.
- Display Controller Documentation: The documentation for the display controller will often provide information on supported display modes and their corresponding timing parameters. Hence a note about using the display controller datasheet must be used with the display datasheet as shown below.
Display Timing Parameters Diagram
Display Parameters Relationships
Vertical Blanking Period = Vertical Sync Width + Vertical Back Porch + Vertical Front Porch
Horizontal Blanking Period = Horizontal Sync Width + Horizontal Back Porch + Horizontal Front Porch
Vertical Total Size = Vertical Blanking Period + Active Area Height
Horizontal Total Size = Horizontal Blanking Period + Active Area Width
Horizontal Scan Rate = Vertical Total Size × Vertical Frame Rate
Line Frequency = Frame Rate x Vertical Total Size
Pixel Clock = Line Frequency x Horizontal Total Size
= Frame Rate x Vertical Total Size x Horizontal Total Size
Definitions
Video Data
Video data consists of a succession of frames. Each frame is made of lines and each line is made of pixels. The term Frame Rate is the frequency of frames appearing on the display.
Frame Components
Each frame consists of:
- Active area
- Vertical Blanking Period/Interval (contains Vertical Sync/Pulse Width, Vertical Front Porch, Vertical Back Porch)
- Horizontal Blanking Period/Interval (contains Horizontal Sync/Pulse Width, Horizontal Front Porch, Vertical Front Porch)
Interlaced Video
In case of interlaced formats, the frame is divided into 2 fields: odd lines and even lines.
Display Enable (DE) Mode and Sync Mode
Both Video modes are essential for ensuring that video data is displayed correctly and without artifacts. If you’re working with video processing or display technologies, understanding these modes can help you troubleshoot and optimize video performance.
DE Mode is used to indicate the active video data period. It helps in defining the portion of the video signal that contains only the active area without blanking intervals. In this mode the LCD panel itself generates Horizontal and Vertical Pulse/Sync Width signals. So, the Pulse Width signals from the source isn’t required.
Sync Mode involves synchronization signals that ensure the proper timing of video data. These signals include Horizontal sync (HSYNC) and Vertical sync (VSYNC). In this mode the video source (MCU/SBC) generates the Horizontal and Vertical Pulse/Sync Width signals. Hence, they must be specified and configured accordingly.
These sync signals are crucial for aligning the video data correctly on the display, so screen tearing is likely to occur.
Active Area
Active area is the visible part of the display (what the user can see).
Blanking Period
Blanking Period is the phase between each line (horizontal blanking) and each frame (vertical blanking). This was originally intended to give CRT monitors the chance to move the electron guns. However, LCD displays don’t need as much time, so the blanking area can be reduced.
Horizontal Front Porch (HFP)
Numbers of pixel clock pulses (pixels) between the last valid pixel data (end of Active Area) in the line and the next Horizontal Sync pulse. It is also known as sync offset, is basically the number of pixel clock before the sync pulse
Horizontal Back Porch (HBP)
Numbers of pixel clock pulses (pixels) between the Horizontal Sync signal and the first valid pixel data in the line (Active Area). It can also be known as the number of pixel clocks after the sync pulse, before the start of the active pixels.
Horizontal Sync Width
Sometimes this can also be referred to as Horizontal Sync Pulse. Number of pixel clock pulses when a Horizontal Sync signal is active. It is the duration of the horizontal sync pulse. The sync pulse marks the start of the next line or the start of a new line of video data.
Horizontal Sync Polarity
Value of Horizontal Sync to indicate the start of a new line (active LOW or HIGH).
Vertical Front Porch (VFP)
Number of lines (Horizontal Sync Pulses) between the last valid line of the frame (end of Active Area) and the next Vertical Sync Pulse. It is also known as sync offset, is basically the number of lines before the Vertical Sync Pulse.
Vertical Back Porch (VBP)
Number of lines (Horizontal Sync Pulses) from a Vertical Sync signal to the first valid line (first line of Active Area). It is also known the number of lines after the sync pulse, before the start of the active lines.
Vertical Sync Width
Sometimes this is referred to as Vertical Sync Pulse. Number of H-SYNC pulses when a VSYNC signal is active. It is the duration of the vertical sync pulse. The sync pulse marks the start of the next frame.
Vertical Sync Polarity
Value of Vertical-Sync to indicate the start of a new frame (active LOW or HIGH).
Active frame width
Horizontal resolution of the display.
Active frame height
Vertical resolution of the display.
Screen Width
Number of Pixel clocks between the last Horizontal Sync and the new Horizontal Sync.
Screen height
Number of lines between Vertical Sync Pulses.
Refresh rate (Vertical frame rate)
The number of screen refreshes per second.
Horizontal scan rate
The total number of horizontal lines per second including blanking.