LCD interface

1. LVDS (Low Voltage Differential Signaling)

LVDS is low voltage differential signal transmission, which is a new technology that meets today's high-performance data transmission applications.

It is 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. Because it can make the system power supply voltage as low as 2V, it also Can meet the needs of future applications. The LVDS output interface uses low-voltage differential signal transmission. With its output interface, signals can be transmitted on differential PCB lines or balanced cables. Due to the low-voltage and low-current drive mode, low noise and low power consumption are realized.

Same as TTL output interface, LVDS output interface is also divided into the following four types:

(1) Single-channel 6-bit LVDS output interface

In this interface circuit, single-channel transmission is adopted, and each primary color signal uses 6-bit data, a total of 18-bit RGB data, so it is also called 18-bit or 18-bit LVDS interface.

(2) Dual 6-bit LVDS output interface

In this interface circuit, the dual-channel transmission is adopted, and each primary color signal uses 6-bit data, of which the odd-channel data is 18-bit, and the even-channel data is 18-bit. A total of 36-bit RGB data is therefore also called 36-bit or 36-bit. LVDS interface.

(3) Single 8-bit LVDS output interface

In this kind of interface circuit, single-channel transmission is adopted, and each primary color signal uses 8 bits of data, a total of 24 bits of RGB data, so it is also called a 24-bit or 24-bit LVDS interface.

(4) Dual 8-bit LVDS output interface

In this interface circuit, the dual-channel transmission is adopted, and each primary color signal adopts 8-bit data, of which the odd-channel data is 24 bits, and the even-channel data is 24 bits, a total of 48 bits of RGB data, so it is also called 48-bit or 48-bit LVDS interface.

2. eDP

The eDP interface is a fully digital interface based on the DisplayPort architecture and protocol. It can use a simpler connector and fewer pins to transmit high-resolution signals, and can achieve simultaneous transmission of multiple data, so the transmission rate is much higher In LVDS. The eDP interface features a micro-packet structure, which enables simultaneous transmission of multiple data. No LVDS conversion circuit is required, and the circuit is simple. Smaller EMI (electromagnetic interference), and has a strong copyright protection function. Take a 1920x1200, 24-bit color LCD screen as an example. If the LVDS interface is used, 20 pairs of data transmission lines are required; if the eDP interface is used, only 4 pairs of lines are required. This shows that the advantages of the eDP interface are quite obvious, especially in high-definition screens. In recent years, in order to increase the data transmission speed between the panel and the processor, a large number of eDP interfaces have been adopted in industrial computers and industrial tablet computers, and the eDP interface is rapidly becoming the mainstream interface.

The DisplayPort standard connector includes four pairs of differential signal lines, or four main channels, which use the main channels to transmit image data, and can choose to use one, two or four lanes to transmit data according to the amount of display data. In addition, DisplayPort defines three different transmission rates, and each channel can choose to use 1.62Gbit/s, 2.7Gbit/s or 5.4Gbit/s transmission. Since DisplayPort uses 8b/10b encoding method, some more data bits will be added after encoding, so the highest data transmission rate that can actually be supported is: (4 channels) x (5.4Gbit/s per channel) x (8/10 Coding) Overhead)=17.28Gbit/s. The DisplayPort connector also contains an independent two-way transmission auxiliary channel, called AUX channel or AUX for short. It also uses two differential signal lines, and the single direction rate is only about 1Mbit/s, which is used to transmit settings and control commands.