Samsung Helps 8K to Move to 120Hz
A sometimes neglected topic in the 8K technology supply chain is the challenge of getting the large number of pixels from the timing controller in the panel to the driver chips at the edge of the frame. Having higher vertical and horizontal resolution means that the pixels have to be driven at very high speed as each pixel and line occupies less time. As an example, an 8K 120Hz display needs a bandwidth of 6Gb/s. Further, 8K sets are usually bigger so the cable lengths are longer, meaning more losses and potential for errors.
LVDS is Traditional for Panels
Typical in-panel interfaces are usually delivered using Low Voltage Differential Signalling (LVDS) concepts (although 8K also uses technologies such as V-by-one from THine of Japan). LVDS interfaces were used for external interfaces in the past (e.g. Firewire) but were superseded by others such as HDMI (which used TMDS) and DisplayPort. They persist still in displays.
Digital interface techniques send the stream of values for each pixel, line and frame, but the receiver needs to be able to accurately identify the beginning and the end of each bit and byte to ensure that the stream is correctly interpreted. To be sure that the two ends of the interface are in sync, a clock signal is embedded in the signal. If you simply send the data as it is over the cable, the DC balance would not be correct and there might not be enough bits to accurately keep the clock synchronized. To avoid this problem, the data is encoded so that, for example, long runs of zeros are avoided.
A well known example of this encoding is 8b/10b encoding where an 8 bit data word is encoded into a 10 bit ‘symbol’ which is then converted back to data. Unfortunately, extra bits means an ‘overhead’ to the encoding scheme. A more economical (in bit terms) encoding scheme for 8K panels was described in an SID Poster paper at Display Week 2021 from AUO that described the use of 8b/9b encoding. That scheme can get up to 5.4Gbp/s but still has an overhead of 11.11%.
In a paper presented in the Journal of the SID (A clock embedded intra-panel interface with 1.96% data overhead for beyond 8K displays Yong-Yun Park et al.) a team of researchers from Samsung Electronics described a novel channel encoding scheme that reduces the overhead from 11.11% in the case of the AUO 8b/9b scheme to just 1.96%, allowing more data to be transmitted in the same time.
The AUO interface used an adaptive equalizer system to ensure the quality of the signal at the receiver and a suitable ‘eye’ in the transmission. This is needed to improve the stability and robustness of the transmission over the distance from the TCon to the driver chips.
The Samsung design uses an on-chip eye margin tester (EMT) that can measure the internal timing margin of the receiver using just 1% of the area of the received signal. As a result it can achieve 6Gb/s over a 25-dB loss channel with a data overhead of 1.96%. The signal is encoded using an advanced channel coding system that uses a concept of linked lists. The paper gives a detailed description of the protocol but shows that just a single 10 bit header is required for 510 bits of transmission – giving the overhead of just 1.96%.
Why is this important for 8K?
Because of the challenges of making 8K OLEDs, going into the future, the majority of 8K TVs will be made using LCD panels, as they are today. The economics of the LCD business mean that the cost of a panel is very much related to the materials used in manufacturing. That’s good for 8K because the amount of material is not radically different between 4K and 8K (same glass, polarisers, LC material etc). However, the cost of the electronics and connectors does go up, so improvements in the efficiency and performance of internal interfaces can really help to reduce the cost differential between 4K and 8K panels.
(Regular readers will know that we have also been featuring a completely ‘sampled analog’ way of running the internal interfaces by Hyphy, an 8K Association member – we spoke to them at Display Week 2023. There is an article about their technology here.