Detailed LVDS interface

Detailed LVDS interface

1: Overview of LVDS output interface

In addition to the RGB digital signals, the digital signals output by the LCD driver board also include line sync, field sync, pixel clock and other signals. The highest frequency of the pixel clock signal can exceed 28MHZ. The TTL interface is adopted, and the data transmission rate is not high. , The transmission distance is short, and the electromagnetic anti-interference ability is poor, which will have a certain impact on the RGB data. In addition, the TTL multi-channel data signal is transmitted by the method of flat cable. The number of the entire flat cable reaches dozens of channels, not only the connection is not Convenient, and not suitable for the trend of ultra-thinness, the use of LVDS output interface to transmit data can solve these problems, and achieve high-speed, low-noise, long-distance, and high-accuracy data transmission. The LVDS output interface uses very low voltage swing (about 350mV) to transmit data through differential on two PCB traces or a pair of balanced cables, that is, low-voltage differential signal output. The LVDS output interface enables signals to be transmitted on differential PCB lines or balanced cables at a rate of several hundred Mbit/s. Due to the low-voltage and low-current drive mode, low noise and low power consumption are realized.

2: The composition of LVDS interface circuit

In the liquid crystal display, the LVDS interface circuit includes two parts, namely, the LVDS output drive circuit (LVDS transmitter) on the driver board side, and the LVDS input interface circuit (LVDS receiver) on the liquid crystal panel side. The LVDS transmitter converts the 17L level parallel RGB data signal and control signal output by the main control chip of the driver board into a low-voltage serial LVDS signal, and then transmits the signal to the liquid crystal through a flexible cable (line) between the driver board and the LCD panel The LVDS receiver on the panel side converts the serial signal into a TTL level parallel signal and sends it to the LVDS receiver on the LCD panel side. The LVDS receiver then converts the serial signal to a TTL level parallel signal. , Sent to the LCD screen timing control and row and column drive circuit

In the process of data transmission, a clock signal must also be involved. The LVDS interface uses differential signal pairs for both data transmission and transmission clock transmission. The so-called signal pair is just each data transmission channel or clock transmission in the LVDS interface circuit. The output of the channel is two signals (positive output and negative output). It should be noted that different LCD displays have different LVDS transmitters on the driver board. Some LVDS transmitters are one or two independent The chip (if DS90C383), some are integrated in the main control chip.

LVDS sends the input signal of the chip

The input signal of the LVDS sending chip comes from the main control chip, and the input signal includes three types: RGB data signal, clock signal and control signal.