Tag: TTL LVDS TDMS DisplayPort
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The panel industry is rapidly advancing toward higher resolutions and more digits per color. Only by increasing the data rate from the host to the panel as a whole, the resolution and color can be broken. Therefore, the task of surpassing this limitation is directly shouldered by the panel display interface.
Panel display interface standard
In order to best look to the future, the progress of revisiting panel display interface standards is just right. From transistor-transistor logic gate (TTL) to today's DisplayPort digital display interface, the following is an overview of panel display interfaces from the early 1960s to 2007, and prospects for future panel interface technologies. .
Transistor-transistor logic gate
When the display panel was first introduced, the classic TTL digital interface was chosen as the standard. At that time, the panel size was less than 10 inches, its VGA resolution was 6 bits per color, and the bandwidth requirement was 300 Mbps. TTL integrated circuits represent small-scale to large-scale integration, compared to hundreds of millions of transistors today, when each chip has a capacity of only a few hundred transistors.
The popularity of TTL is based on Texas Instruments' (TI) 7400 series chips. After the TI series quickly became the industry standard, Motorola, Signetics, SGS-Thomson, National Semiconductor and other companies joined the TI standard. Compared to analog solutions, TTL represents a low-cost chip that makes digital technology more economically viable.
The panel size increased to 15 inches in the second half of the 1990s, requiring an XGA resolution format and bandwidth requirements jumped to 850 Mbps. The challenges include power consumption and electromagnetic interference (EMI), which makes the slow TTL interface a bottleneck for display panels.
LVDS display interface
The Low Voltage Differential Signaling (LVDS) Display Interface (LDI) is a differential signaling system that transmits two different voltages over a twisted pair copper cable. Compared to TTL, the tight coupling between small amplitude signals and twisted pairs reduces the power and EMI inherent in TTL.
LVDS describes an electrical signal method for high speed signals running on less expensive copper conductors. With two different voltages running at the receiving end, LVDS encodes the information using a voltage difference (typically 350 mV). The acceptance detection determines the voltage polarity of the logic level. EMI is reduced due to the very small signal amplitude and the tight electromagnetic field coupling between the wires. The average voltage on the wire is 1.25 volts. This form of interface was adopted in the late 1990s.
LVDS obviously chose a serial data transmission instead of parallel transmission. LVDS combines high-speed and intra-channel synchronization to deliver more data with fewer wires.
Based on LVDS technology, National Semiconductor released its open LDI specification in 1999, reducing the total number of wires from 22 to 8 on the TTL interface. Therefore, the number of connectors and cables is also reduced. More importantly, LDI broke the TTL bottleneck and increased bandwidth to about 2.8 Gbps. As an open standard, LDI does not require absolute authority, which allows it to grow rapidly into panel display interface standards.
Second, the bottleneck problem began to show up gradually. As panel makers continue to increase panel size and increase color richness, 40-inch to 50-inch 1080p panels have become mainstream. The 8-bit color of the panel requires approximately 3 Gbps of bandwidth, which greatly exceeds the capabilities of four pairs of LVDS interfaces. Currently, even larger digital panels with 4096x2160 resolution and 10-bit and 12-bit colors that display darker colors are on the agenda. To meet the bandwidth requirements of digital cinema resolution, a bus width of up to eight connections and 40 pairs (808 wires) is used.
However, new problems have arisen at this level, such as complex connectors, wire connections and crosstalk noise, data misalignment and other problems. Currently, LDI is the bottleneck of the panel display interface, and another interface revolution is gaining momentum.
Minimize the transmission of differential signals
In the late 1990s, Silicon Image began to promote its proprietary standards to the display industry in the form of panel connectivity, digital visual interface (DVI) and high-definition multimedia interface (HDMI) to minimize the transmission of differential signaling (TMDS). In this case, the transmitting end mixes a higher-level encoding algorithm with reduced EMI characteristics on the copper wire, so that the receiving end has robust clock recovery performance.
The 8-bit/10-bit code is a second-order process that converts an 8-bit input signal into a 10-bit code. Similar to LVDS, it uses differential signals to reduce EMI and improve accurate signal transmission rates. Also similar to LVDS is that it is a serial transmission design.
DVI technology has been successfully applied in the PC field, and HDMI technology has also successfully pushed to the consumer electronics market. However, TMDS has not become a widely used panel interface standard. In contrast, LVDS without patent fees has been widely used. In addition, current DVI versions are not updated and have physical, functional, and cost limitations.
DisplayPort
Currently, DisplayPort has entered a new historical arena as a digital display interface standard released by the Video Electronics Standards Association (VESA). The standard was first released in May 2006 and the V1.1 version was released on April 2, 2007. The standard is promoted between computers and monitors or between computers and home theater systems.
DisplayPort consists of a one-way primary connector that carries audio and video streams and a half-duplex bidirectional auxiliary channel (AUX CH) that can be used for hot swapping. The main connector and AUX CH consist of an AC-coupled differential pair. The main connector has 1 pair, 2 pairs, 4 pairs of wires or channels. The AUX CH has only 1 pair of wires and does not require a clock to be connected. This result maximizes the use of differential pairs.
For example, a panel with a resolution of 1680x1050 might be supported by a single primary connection channel. Currently, the DisplayPort specification can support up to 10.8 Gbps of bandwidth and provide WQXGA (2560x1600) resolution over 15 meters of cable.
Free license, free ownership
DisplayPort is a free, proprietary, free digital audio and video interconnect technology that details the connection between the computer and the display. It is supported by AMD/ATI, Dell, IDT, Genesis, HP, Intel, Lenovo, Quantum Data, Molex, NVIDIA, and these companies also support the continued promotion of the standard. DisplayPort is also recognized by panel manufacturers as a panel display interface standard, and products using this technology are also in the ascendant.
Advantages of DisplayPort include: more available LCD display capabilities, a wide range of requirements and application performance enhancements, from entry level to high performance display. DisplayPort also supports future technological innovations through its miniature packaging structure. Currently, it is being used in the computer display market.
Table 1 shows the difference between DisplayPort and other previous standards. By browsing through these standards one by one, you can clearly recognize that DisplayPort has many advantages.
in conclusion
Despite the advancement of panel display technology, current display interface standards have reached their bandwidth limits and become a bottleneck. In the past decade, the LVDS interface used has been abandoned. This technology is limited to the rapid changes in the PC and notebook display, LCD TV field. With better performance and industrial support, DisplayPort-based products are on the stage as next-generation technologies to better drive the display interface market.
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