LCD common interface principle

LCD common interface principle

1. TTL

TTL (Transistor Transistor Logic), and TTL level signals are generated by TTL devices. TTL devices are a major category of digital integrated circuits. They are manufactured using bipolar technology and have the characteristics of high speed, low power consumption, and variety. The TTL interface is an interface for data transmission in parallel. When using this interface, it is not necessary to use a dedicated interface circuit on the driver board side and the LCD panel side of the liquid crystal display, but the TTL data signal output by the main control chip of the driver board through the cable Directly transmitted to the input interface of the LCD panel. Due to the high signal voltage of the TTL interface, many connections, and long transmission cables, the circuit's anti-interference ability is relatively poor and it is prone to electromagnetic interference (EMI). In practical applications, TTL interface circuits are mostly used to drive small size (below 15in) or low resolution LCD panels. The highest TTL pixel clock is only 28MHz. TTL is the only signal that TFT-LCD can recognize when the signal is in. The early digital processing chips are all TTL, that is, RGB is directly output to TFT-LCD.

2. Signal type of TTL interface

The TTL output interface of the driver board generally contains three types of signals: RGB data signals, clock signals and control signals.

(1) RGB data signal

Single-channel 6bit TTL output interface-----For 6bit single-channel TTL output interface, there are 18 RGB data lines, which are 6 data of R0～R5 red primary color, 6 data of G0～G5 green primary color, and B0～B5 blue There are 6 primary color data, 3*6=18 in total. Since the primary color RGB data is 18bit, it is also called 18bit or 18bitTTL interface.

Single-channel 8bit TTL output interface-----For 8-bit single-channel TTI, the output interface has 24 RGB data lines, which are 8 red primary color data R0～R7, 8 green primary color data B0～B7, and BO～B7 There are 8 blue primary data, 3*8=24 in total. Since the primary color RGB data is 24bit, it is also called 24-bit or 24bitTTL interface.

(2) Dual-channel TTL-----Dual-channel, that is, two sets of RGB data, divided into odd and even channels, some of the clocks are also divided into OCLK/ECLK, and some share one

Dual channel 6bit TTL output interface-----For 6bit dual TTL output interface, there are 36 RGB data lines, 18 odd RGB data lines, 18 even RGB data lines, 3*6*3 =36. Since the primary color ROB data is 36bit, it is also called 36bit or 36bitTTL interface.

Dual-channel 8bit TTL output interface-----For 8bit dual-channel TTL output interface, there are 48 RGB data lines, 24 odd RGB data lines, 24 even RGB data lines, 3*8*2= 48 articles. Since the primary color RGB data is 48bit, it is also called 48bit or 48bitTTL interface.

(3) Clock signal-----refers to the pixel clock signal, which is the reference for transmitting data and reading the data signal. When using odd/even pixel dual-channel transmission of RGB data, different output interfaces use pixel clock methods differently. Some output interfaces for odd/even pixel dual data share a pixel clock signal, and some output interfaces for odd/even two channels respectively set odd pixel data clock and even pixel clock signals to meet the needs of different LCD panels.

(4) Control signal ----- The control signal includes data enable signal (or effective display data strobe signal) DE, line synchronization signal HS, and field synchronization signal VS.

3. LVDS interface overview

LVDS, or Low Voltage Differential Signaling, is a low voltage differential signal technology interface. A digital video signal transmission method developed to overcome the shortcomings of high power consumption and large EMI electromagnetic interference when transmitting broadband high bit rate data in TTL level mode. The LVDS output interface uses a very low voltage swing (about 350mV) to transmit data via differential on two PCB traces or a pair of balanced cables, that is, low-voltage differential signal transmission. Adopting LVDS output interface, can make the signal transmit at the speed of several hundred Mbit/s on the differential PCB line or balanced cable, because of adopting the low voltage and low current driving mode, therefore, realize low noise and low power consumption.