Screen panel interface RGB_TTL、LVDS、MIPI Study

Screen panel interface RGB_TTL、LVDS、MIPI Study

The LCD screen has RGB TTL, LVDS, and MIPI DSI interfaces. These interfaces are different from the type (type) of the signal, and also different from the signal content. RGB TTL interface signal type is TTL power, the content of the signal is RGB666 or RGB888 and line and field synchronization and clock; The signal type of LVDS interface is LVDS signal (low voltage differential pair), and the content of the signal is RGB data, line and field synchronization, and clock; The signal type of MIPI DSI interface is LVDS signal, and the content of the signal is video stream data and control instructions.

• RGB_TTL
• LVDS
• MIPI

RGB TTL

TTL interface, the data transmission rate is not high, the transmission distance is short, and the anti-electromagnetic interference (EMI) ability is also relatively poor, which will have a certain impact on RGB data; in addition, TTL multi-channel data signals are transmitted by means of cables. The number of the entire cable is dozens of lines, which is not only inconvenient to connect, but also not suitable for the trend of ultra-thinning. The wiring is as follows:

• Data signal: refers to RGB data signal, such as R0~R5, G0~G5, B0~B5
• Clock signal: pixel clock signal (DCLK), which is the reference for transmitting data and reading data signals
• Control signals: including data valid signal (DE), a line synchronization signal (HSYNC), a field synchronization signal (VSYNC)

LVDS

LVDS (Low Voltage Differential Signaling) is a low-voltage differential signal transmission, which is a new technology that meets today’s high-performance data transmission applications. It is also future-proof as it enables system supply voltages as low as 2V.

The LVDS output interface utilizes low-voltage differential signal transmission. Using its output interface, the signal can be transmitted on the differential PCB line or balanced cable. Due to the low voltage and low current driving mode, low noise and low power consumption are realized. LVDS output interface LCD display.

This type of LCD is currently widely used in mid-to-high-end flat panels and notebooks. Now there is a relatively new specification in the industry – eDP, which will be widely used in the notebook industry to replace LVDS and support the ultra-high resolution (>1080P)

MIPI

MIPI (Mobile Industry Processor Interface) is an alliance established by ARM, Nokia, ST, TI, and other companies in 2003. complexity and increased design flexibility.

MIPI signals are transmitted in pairs, mainly to reduce interference. MIPI signals are routed in pairs, and the two lines are in anti-phase from the waveform, so if there is external interference, it will be offset by a large part. Mainly used on tablets and mobile phones.

MIPI interface LCD includes 1 pair of the differential clock (CLKP, CLKN), 4 pairs of data differential lines (D0P, D0N; D1P, D1N; D2P, D2N; D3P, D3N), each pair has a GND line, 4 pairs of data differential lines It is not necessary to use all the wires, and many screens only need 2 pairs; RESET (reset pin), STBYB (high level active), VGL, VGH (the on-off voltage of the switch tube on the pixel point, added to the switch tube On the gate of VGH, VGH high level turns on to charge the pixel capacitor, VGL negative voltage turns off the switch tube), VCOM (the common electrode of the storage capacitor of the liquid crystal pixel), VLED- (backlight negative pole), VLED+ (backlight positive pole), power supply There are 1.8V and 3.3V.

In the power supply of the TFT LCD drive circuit, the VGH voltage and the VGL voltage are responsible for turning on the TFT (thin film field effect transistor) to charge the capacitor (correcting the voltage across the capacitor) and turning off the TFT to maintain the capacitor voltage (one field cycle time). . Because the circuits of VGH and VGL are complex and difficult to adjust, the basic screens are already built-in.

The main difference between LVDS and MIPI:

1. The LVDS interface is only used to transmit video data, while MIPI DSI can not only transmit video data, but also transmit control commands;

2. The LVDS interface mainly converts RGB TTL signals into LVDS signals according to the SPWG/JEIDA format for transmission, while the MIPI DSI interface transmits video data and control data required for screen control according to specific handshaking sequences and command rules.

Supplementary explanation: LCD interface type description: DSI, DPI (RGB interface), DBI (MCU interface, commonly known as 80 system interface)

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