HD Transition and Standards

Transcription

1 Electronic Product Design, September 2006 HD Transition and Standards By Adam Eades and Palani Subbiah, Cypress Semiconductor Corp. The switch over from analog to digital television transmissions started in 2001 with the Digital Television Project. Today 70% of UK homes have DTVs (Digital Televisions) and broadcasters have already started digital broadcasts. High-definition entertainment arrived at the beginning of the World Cup, Wimbledon, and the introduction of Sky HD. Currently 2% of UK homes own HD-ready televisions, but a million more HD ready televisions are predicted to be sold in the UK in Even though the analog transmission cutoff seems almost complete in the UK and US broadcasters still must support analog consumers until the end of the digital transition starting around Meanwhile, broadcasters need to (1) transmit both analog and digital transmissions for the same channel simultaneously (called simul-casting) and to (2) switch from analog to digital transmissions individually. The switch to digital broadcasting has also provided broadcasters the freedom to either transmit one HD channel (during primetime) or multiple SD (Standard Definition) channels (during nonprimetime) in the same bandwidth. The challenge was given to video equipment manufacturers to introduce multi-rate and multi-format systems to include variable video protocols from SMPTE (Society of Motion Picture and Television Engineers) to DVB- ASI (Digital Broadcast-Asynchronous Serial Interface) that will support both HD and SD formats simultaneously. Moving away from the studio into the consumer premises, sales of HD peripherals, HD DVD players, HD game consoles and so on are growing worldwide. Manufacturers and broadcasters are protecting their HD content through HDCP (High- Bandwidth Digital Content Protection) using HDMI (High Definition Multimedia Interface), a spin off of DVI (Digital Interface). HDMI has already expanded into most HD-DVDs and is the HD interface of choice for HD set-top boxes. In fact HDMI or DVI is required in all HD set-top boxes in Europe and the US. HDMI is also required to support both SD and HD resolutions to aid the transition from analog to digital formats at the consumer end. Broadcast Studio Impact Professional video equipment manufacturers need to transform all of their equipment (video production switchers, editing platforms, or storage servers) that store, process, or distribute DTV to accept and deliver either SD or HD streams. As shown in Figure 1, different components of a professional broadcast studio need to carry uncompressed digital video serially from one piece of equipment to another. The two specifications transporting serial digital video within the studio for the SD format are SMPTE259M, which allows 480 or 576 interlaced lines per frame, and the HD format SMPTE292M, which allows transport of 720 progressive, and 1080 interlaced lines per frame. The higher resolution of the HD format is one of the major selling points for consumers in their transition. The benefit for broadcasters is the move to digital, which

2 allows them to multi-cast multiple channels of SD or fewer channels of HD. At the edge of the broadcast studio, both SD and HD streams need to be compressed and transmitted using an MPEG2 transport stream via a serial interface protocol called DVB-ASI. This requires MPEG2 ENDECs that can handle both SD and HD streams. Cable Box & Viewers Studio Monitors Non-Linear Editor Storage Server Cable Headend Digital Cameras Production Switcher Router Satellite Transport Camera Control Unit Logo Generator Master Playout Controller MPEG2 Encoding/Decoding Figure 1. Components of Professional Broadcast studio The implementation of a multi-rate video system for the delivery of video data from studios to broadcast stations has many issues. Most of the professional video systems prefer serial rather than parallel connections between the delivery and acceptance systems. Serial connections are usually necessary because parallel connections are not feasible for distances greater than 50m for SD and 20m for HD, due to the technical issues involved in delivering multiple bits of data at high speeds with a common clock over a single bus. As a result the parallel data needs to be converted to a single serial stream before delivery and the serial data needs to be converted to a parallel bus after receipt. A serializer/deserializer (PHY) is an important part of the SDI (Serial Digital Interface), present at any point where serial data is converted to 10-bit video data or 10- bit video data is converted to serial digital data. The parallel component video for SD consists of 10-bit data transmitted at 27MHz resulting in a serial data rate of 270Mb/s. The HD-SDI parallel component video consists of two 10-bit data-streams, a 10-bit luminance channel and a 10-bit color-difference channel transmitted at MHz resulting in a serial data rate of Gb/s. SDI is used as the standard serial communication interface within broadcast studios for professional video cameras, video format converters, SD-to-HD up and down converters, production switches, broadcast routers, and non-linear editors.

3 The block diagrams of an SDI receiver and transmitter are shown in Figures 2 and 3, respectively. RefCLK Training Clock SEL sel Signal from Cable Equalizer Equalizer HOTLink TM II Deseralizer CDR Deserializer 8B/10B Encoding (Optional) Auto. Rate Detection Descrambler Format Detection TRS Framer Digital Component YCbCr Processing EDH or CRC Detection FPGA IP Figure 2. Block Diagram of an SDI receiver VCXO External Input Clock for Jitter Clean Up RefCLK Crystal Osc HOTLink TM II Seralizer Signal to Cable Cable Driver Cable Driver Serializer Tx PLL 8B/10B Encoding (Optional) 10 Scrambler EDH or CRC Insertion YCbCr Digital Component Processing Figure 3. Block Diagram of an SDI transmitter FPGA IP Provided by Cypress There are many different types of video PHYs. Some can be just serializers (transmitters), deserializers (receivers), or a complete SERDES (transceiver). Also many PHYs have multiple channels enabling the PHY to integrate the serializationdeserialization function across multiple SDI inputs and outputs. An independent multichannel PHY will have the ability to handle different video signals that operate at very different data rates simultaneously on the same IC (e.g., SD-SDI in one channel and HD- SDI in another channel). Designers of serializers and deserializers have the most difficulty designing the transmit and receive PLLs and their associated VCOs. Current solutions are also capable of integrating high-speed components like voltage-controlled oscillators and loop filters into the same package. There are also SERDES devices that can handle DVB-ASI on the same device that handles SD- and HD-SDI. This allows the same port to be used for transporting uncompressed SDI video or compressed DVB-ASI video.

4 When the video data is serialized and ready to be transmitted over the SDI from the PHY a separate cable driver IC is used. The purpose of the cable driver is to drive the signal over a coaxial cable with a set output voltage swing with minimized reflections and to be able to operate at both SD and HD data rates. This guarantees that the output signal will abide by the SMPTE and DVB-ASI specifications. The cable driver usually will be a differential output. This enables broadcasters who use the SMPTE standard (which is polarity free) to have two redundant outputs per channel, enabling the video signal to be broadcast to more than one location, which is required in many professional studio environments. However for incumbent DVB-ASI solutions only the positive end of the differential output can be used for transmission. Recently, some semiconductor companies have introduced cable drivers that have two positive serial outputs to allow redundant DVB-ASI outputs. The maximum-allowable cable length is different for SD and HD and is limited by capabilities of the SDI receiver. For SD, the length of the cable can be 350m (using Belden 1694A), and for HD the length of the cable can be 140m (using Belden 1694A). For such long cable lengths the actual signal can have large amounts of jitter and be severely attenuated. An equalizer is used on the receivers (deserializer) as a filter that corrects the amplitude and removes the jitter. The equalizer must be able to equalize either format of the incoming signal, whether HD or SD. From a distance standpoint, the higher data rate needed for HD reduces the transmission distance. There is a need in the broadcast market to increase the transmission distance for HD and bring it closer to the SD transmission distance. This will allow broadcasters to use existing SD cable infrastructure with minimal alteration to support HD. Current equalizer solutions allow cable lengths of up to 200m for HD and 400m for SD. A recent specification standard that is in progress roughly named 2xHD, SMPTE424M, has begun to enter the market. Not yet being used by broadcasters, the standard runs 1080 progressive lines per field (1080p), mandating a serial data rate of roughly 3 Gb/s. 1080p has recently gotten the recommendation from the EBU (European Broadcasting Union) as the forward-looking video broadcast standard due to its higher resolution. The product and IC support for this standard is still in its infancy; one of the concerns for some broadcasters in Europe, North America, and Asia is the future implementation and product investment support for a new HD format. Consumer Impact For the end user, HD is becoming widely available. The BBC already aired HD broadcasts of Bleak House, Planet Earth, and the World Cup. HD peripherals such as HD DVD players and HD game consoles like Playstation 3 are all showing the consumer the benefits of HD. As HD content become more abundant many manufacturers and broadcasters are hoping to use HDCP to control piracy. HDCP, a controlled mathematical algorithm, verifies that the receiver is authorized to receive HD content. This will hinder splitters or multiple connectors from sending HD content to multiple receivers (i.e., a TV and an HD DVD-Recorder). Manufacturers such as Sony, Panasonic, Samsung, Pioneer, etc., are using HDMI, the only HDCP authorized interface, to implement HD protection. Unlike composite, S-, or component interfaces, HDMI was designed to handle the high-resolution 720p, 1080i, and even 1080p of HD content.

5 HDMI is increasingly being added to DTVs, set-top boxes, and DVD players. HDMI will grow from 61.2 million active ports in 2006 to upwards of million active ports in HDMI is similar to DVI where all video is passed using one cable through four differential signals using TMDS (Transition Minimized Differential Signaling) at 1.65 Gb/s. (The new HDMI 1.3 specification allows signals to run at 3.4 Gb/s). HDMI contains all of the audio data from the video source as well as the ability to receive manufacturing data and display resolution data from the receiver and transmitter through two I 2 C type interfaces. Similar to professional video multi-rate benefits, HDMI is able to take the display resolution data from the video source to detect if the source is outputting SD and HD content. Currently DTVs are limited in the amount of HDMI receiver ports due to their processors abilities to handle only one input. This causes problems for consumers that have HD set-top boxes, HD DVD players, and game consoles using HDMI when there is only one input on their DTV. However many semiconductor companies are developing HDMI switches or multiplexers that have the ability to handle two to three inputs while outputting one HDMI output to the DTV processor. This allows DTV manufacturers the ability to increase the amount of HDMI ports with short design times. To support PiP (picture in picture) or PaP (picture and picture) some switches have two outputs with multiple inputs, anticipating when DTV processors will expand their HDMI receive ports. Other semiconductor companies have developed independent HDMI receivers similar to the PHYs developed in professional video systems. Also similar to professional broadcast equipment, HDMI receivers are limited to the length and quality of the cable. To ensure the consumer is satisfied with their DTV, manufacturers are using HDMI equalizers, or switches and receivers with built-in equalization to extend the length of cable or PCB that can be used to route the signal from the multi-media source to the monitor. This allows the consumer to purchase the cheapest or longest HDMI cable available and still receive their HD content. This also allows the consumers to hide their multi-media sources at a remote cabinet with long hidden cables routed to the flat panel display. Equalization for HDMI switches/receivers again comes in handy in situations where TV manufacturers have to design their HDMI interface in one corner of the PCB inside the TV, especially with PCB lengths of up to 50 cm in today s large television sets. The overall future of HDMI will be the consumer s decision. Manufacturers implementations of the interface into HD home theatre peripherals such as HD DVD players and A/V amplifiers will entice the consumer to adopt HDMI. Semiconductor vendors like Cypress Semiconductor are coming up with high-speed interconnect solutions that solve the issues involved in taking high-speed digital serial video from point-to-point over long distances of cable for both the broadcast world and consumer world. About the authors: Adam Eades: Adam Eades works as an Associate Product Manager at Cypress Semiconductor Corporation. He focuses on project business development of Cypress Broadcast and Professional and consumer video portfolio. He has a Bachelor s of

6 Engineering Degree in Electrical Engineering from Purdue University. He can be contacted at Palani Subbiah: Palani Subbiah works as a Senior Staff Applications Engineer at Cypress Semiconductor Corporation. His expertise includes High Speed Physical Layer Devices (HOTLink Family), Broadcast and Professional Products and High Speed PCB Design and Characterization. He has a Bachelor s of Engineering Degree in Electronics and Communication Engineering from Sri Venkateswara College of Engineering, Tamilnadu, India. He also has a Masters degree in Electrical Engineering from the University of Missouri Rolla, USA. He can be contacted at pds@cypress.com. Bibliography Building a Serial Digital Interface for a Multi-format System, AnalogZone, April 2004, Digital Television. 12 th of July, Department for Culture, Media and Sport. 12 th of July, < HDTV UK. 13 th of July, Shiny Media. 13 th of July, < HDTV format wars. 26 th of January, European Broadcasting Union. 12 th of Jul, < Trademarked Terms HDMI HDCP Playstation