Product How-to: Addressing timing challenges in 6G-SDI applications
Digital video transmission rates have steadily increased since the introduction of high-definition video. The latest trend in the industry for high-resolution video is the market adoption of 6G-SDI to support 4K digital cinema and ultra-high definition (UHD) television. Digital video data delivery at higher speeds required by 6G-SDI poses new challenges in designing broadcast video production and transmission equipment.
In particular, high frequency, low-jitter clocking solutions are a critical element to maintain proper signal integrity through the various components and interconnecting cables that constitute the high-definition video network. In addition, these timing solutions must be flexible enough to accommodate the multiple frequencies required by legacy video standards.
Higher Speed Video Standards on the Horizon
The Society of Motion Picture and Television Engineers (SMPTE) was founded in 1916 to standardize video content distribution. Video equipment manufacturers have since adhered to these standards. In 1997, the SMPTE established the SD-SDI 259M standard, which was the first ratified definition of a serial digital interface (SDI) to send and receive uncompressed digital video over 75-ohm coaxial cable within a studio environment. SDI supports transmission rates ranging from 270 Mbps to 360 Mbps.
Due to the fact that digitized video signals accumulate jitter across video components and interconnecting cables, SMPTE established limits on the allowable jitter content of SDI signals. As high-definition digital video advanced to 720p and 1080i, SMPTE defined the HD-SDI 292M standard to support higher bandwidth video transmission at 1.485 Gb/s.
In 2005, the SMPTE introduced 3G-SDI to enable the transmission of 1080p video at 2.97 Gbps over existing 75-ohm coaxial cable. To support these higher video transmission speeds, the SMPTE has set increasingly stringent jitter requirements. Table 1 summarizes the timing requirements for the SMPTE-ratified SDI standards.
Table 1. SMPTE SDI Timing Requirements
In recent years, continued technological innovation in digital video has pushed the boundaries of video resolution from 1080p (2K resolution) to 4K. Transmitting a larger number of pixels on the same infrastructure implies having to deliver the video payload at 5.97 Gb/s. The goal of the standards published by the SMPTE has been to guide the increasing data transmission rates to ensure that existing video production facility infrastructure can support and broadcast higher resolution video. Although the SMPTE body has yet to ratify a standard for 6G-SDI, video equipment suppliers are already meeting the demand for 4K by introducing solutions to support the faster data rates.