CCD or CMOS sensors and image processing components play an important role to ensure both long-distance transmission and high image quality which are rendered in HD-SDI. Asides from sensors, we will examine other components.
CCD or CMOS sensors and image processing components play an important role to ensure both long-distance transmission and high image quality which are rendered in HD-SDI. Asides from sensors, we will examine other components.
Sensor Overview
Once the signals are captured by CCD or CMOS sensors, uncompressed HD video streams can be transported in analog or digital approaches. Analog signal transmission usually adopts YPbPr color separation, and one channel of HD-SDI video signals requires three coaxial cables to deliver the transmission simultaneously.
Digital signal transmission uses digital visual interface (DVI), High-Definition Multimedia Interface (HDMI), or HD-SDI for transmission. Among them, DVI or HDMI support only several meters of transmission distances, which can be increased to dozens of meters with video signal amplifiers, so both of them are not suitable for transmitting video data for longer distances. By contrast, HD-SDI signals can reach 100 meters over CVBS coaxial cables with BNC connectors. Therefore, this approach is usually adopted for on-site video capturing and transmitting to the management equipment connected in 100 meters.
Most leading HD-SDI camera manufacturers are providing CCD or CMOS cameras. CMOS has an advantage over CCD, that CMOS needs lower cost and power consumption, and can be integrated with video signal processing circuits on one chipset. Whether it is for professional video, home video or video surveillance equipments, the trend is to adopt CMOS sensors than to use CCD sensors in HD applications.
Even though Analog Front End (AFE) components can work with CCD sensors to digitalize CCD video signals and produces CCD sequences, CMOS sensors are able to deliver digital signal outputs. This feature makes AFE components unnecessary in CMOS solutions.
Camera Component Overview
HD-SDI surveillance solutions are becoming more popular in European or American markets. There are increasingly more vendors who prefer to deploy higher pixels and more dynamic front end SDI cameras. As a result of HD, data volumes generated are larger, hence requiring stronger CPU processing capabilities. While analog cameras adopting DSP/ASIC/ASSP architecture have problems meeting the volume demands, components supporting field-programmable gate arrays (FPGAs) are the right choices with parallel and programmable flexibility.
Therefore, when designing an HD-SDI camera, manufacturers have to consider high volumes and CPU performance. They can adopt FPGA components for parallel data processing capability and cost-efficiency reasons (cost of FPGA has reduced to compete with ASICs).
Receiver Component Overview
HD-SDI receivers are used in products embedded with SDI slots such as HD encoding cards and HD-SDI DVRs. Both adopt the same SDI receiver solutions. When adaptive cable equalizers have higher data transmission rates, it is harder to maintain consistent signal integrity. The transmission distances of SDI signals are determined by the cable equalizers of receivers. Take LM0394 equalizer of National Semiconductor Corporation (part of TI) for example, this chipset guarantees low power and long distance performance available in the industry in any transmission rates: it supports up to 200m cables for 3Gbps(3G), 220m cables for HDTV, and 400m cables for SDTV.
A clock and data recovery circuit receives signals, it filters out the high-frequency jittered signals, and delivers noise-free clock and data signals, or drive the signals in sequence to another side of the coax. Designing a system with more than two channels of SDI outputs requires a clock and data recovery circuit.
Adopting FPGA architecture needs a Serializer/Deserializer (SerDes) module. 1st solution is to take Altera's Cyclone IV GX FPGA Development Kit, which supports 3G transmission with four SerDes modules. High-end FPGA chipsets with on-board SerDes receivers are usually made with sophisticated CMOS technologies, but they produce internal noise and jitters as well. Designing SDI cameras requires the incorporation of high quality stabilizers, clock and data reference circuits, isolated layers of power supplies and grounding, plus overheat protection circuits to improve above limitations. However, this complicates the wiring design and takes longer time. The 2nd solution: the SerDes solution used with low-cost FPGA chipsets and fewer add-in components; this was introduced by National Semiconductor (part of TI) and Gennum (part of Semtech) corporations.
The 1st option with stabilizers and other circuits are compatibility-sensitive. For this reason, National Semiconductor (part of TI) and Gennum (part of Semtech) corporations deliver various equalizers of different speeds with standard pins and backward compatibility support. For example, in order to support 3G and HD-SDI speeds, simply replace the related equalizers without the need to modify hardware design and PCBs. It is an easier and cheaper way to meet the demands of product customization.
The 2nd option, although it seems cost-efficient, the front end receivers, cable equalizers, and SerDes circuits could increase the cost of FPGA front end components.
When deciding which receivers to adopt, manufacturers need to consider thoroughly whether to select ease of maintenance and product customization or take advantage of hardware chipsets to handle the SDI signal converting and processing. It ensures shorter time to market so manufacturers can launch products faster.
What to Expect
National Semiconductor (part of TI) and Gennum (part of Semtech) corporations provide various SDI chipsets for broadcast-grade applications, but their high prices make them less acceptable in the security industry. Security sectors have bigger shipping volumes and are cost-oriented, where dedicated regulations and solutions for specified applications are required in order to successfully promote SDI standards.
HD-SDI systems feature digital methods of transporting HD video data without packetizing it, ensuring continuous latency-free and uncompressed streams without loss. Therefore, immediacy and integrity of signals are better guaranteed. Both HD-SDI and IP HD solutions have their unique advantages in security and surveillance applications. Users can select solutions according to their on-site requirements. HD-SDI solutions are developed to solve the challenges when many cannot afford a major disruption to their existing analog systems or the cost of building an entirely new infrastructure.
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