High-speed video: unlocking fast and reliable connectivityStory
February 20, 2023
Today’s video applications, particularly in the defense arena, are challenged by more complex video-signal processing from an increasing number of video sources with higher bandwidth and higher resolutions. Critical to defense applications: minimizing latency between video capture and display.
Defense-related video applications increasingly require high-resolution sensors for image accuracy. Sensor data rates are increasing with capability for 4K and higher video streams. Systems are processing video data as close to the sensor as possible for lower latency and reduced cabling complexity. These trends are driving new video architectures and the use of higher-speed protocols in video-signal transmission for capture, compression, processing, artificial intelligence (AI) inference, and encoding/decoding.
Higher-bandwidth video protocols such as ARINC 818 [avionics digital video bus], SDI [serial digital interface], and CoaXPress (CXP) support industry demands for speed and are driving new interconnect requirements for video-signal transmission between the sensor and processing platforms and displays. These standards include protocols with data rates as fast as 12 Gb/sec and higher.
Traditional connectors for video applications
Traditionally video signals have been transmitted on 75-ohm coax cable with standard coax connectors: 75-ohm BNC connectors, F-Type connectors (commonly used in CATV applications), MIL-C-39029 coax contacts for 75-ohm cable, or even 50-ohm coax connectors terminated to 75-ohm cable where the impedance mismatch didn’t adversely affect the signal because of the lower frequencies.
MIL-C-39029 coax contacts (populated in MIL-DTL-38999 circular connectors) were defined in the 1970s; some designations terminate to 75-ohm cable, but do not have 75-ohm impedance-matched interfaces and construction. As a result, performance is typically limited to frequencies of 3 GHz or lower.
To transmit video signals with higher-speed protocols over coax, newer 75-ohm impedance matched coaxial cables and connectors are required for both box-to-box connectivity and within a chassis.
Emerging interconnect solutions: inside the box
Sensor platforms using OpenVPX architecture can leverage 75-ohm NanoRF connector modules for the interface between the plug-in modules and the backplane. New VPX slot profiles proposed for the next revision of VITA 65.1 feature connector modules with the high-density, high-frequency 75-ohm NanoRF coaxial interface with optical MT terminations to support high-speed video.
The 75-ohm NanoRF connectors leverage the rugged design of the original 50-ohm NanoRF interface already standardized for OpenVPX and SOSA aligned solutions. The NanoRF technology features contacts with a tapered pin and floating inserts that enable fine alignment of the array of coaxial contacts and optical MT [mechanical transfer] ferrules before they begin to mate. The 75-ohm NanoRF connector module configurations now undergoing standardization include a half-size VPX connector module with six 75-ohm NanoRF contacts and an MT, and a full-size module with two of the same inserts (twelve coax contacts and two MTs). Other coax and/or optical configurations using the same interconnect technology are possible. (Figure 1.)
[Figure 1 | Shown are VITA 67.3 connector modules with 75-ohm NanoRF and optical MT.]
Integrating coax and optics into a common connector module adds versatility, especially in applications where – for example – video signals are received from multiple sensor devices over coax, then processed and transmitted over fiber using ARINC 818 for high-bandwidth, low-latency, digital video transmission.
The VITA 67.3 standard is under revision to add 75-ohm coaxial interfaces for VPX plug-in modules and backplanes, including 75-ohm NanoRF and 75-ohm SMPM (miniature push-on connectors), a variant of the 50-ohm SMPM interface specified in the standard today. These contact interfaces and designs optimize return loss and isolation in 75-ohm transmission lines and will support next-generation video-signal requirements.
New applications are increasingly specifying 75-ohm coaxial cables with lower loss and attenuation; these are applications where traditional 75-ohm cables such as RG-179 may not have the shielding or size needed for higher-density, higher-frequency defense applications. In such applications, 75-ohm conformable cables with shielding of both foil tape and tinned braid reduce the attenuation versus traditional braided cables. They also fit in tight packaging for high-density multicontact solutions by omitting an external jacket, effectively reducing the outer diameter and bend radius. Being conformable, these cables can be easily shaped and routed in tight spaces, for example within a VPX plug-in module (Figure 2).
[Figure 2 | Shown: An example of a VPX plug-in module with VITA 67 coax cables routed. Image courtesy of Annapolis Micro Systems.]
Emerging interconnect solutions: box-to-box
For box-to-box connectivity (for example, between a sensor turret and a compute chassis), both 75-ohm coax and optical solutions need to be supported.
For coax, 75-ohm impedance matched variants of size 12 SMPM contacts are designed for MIL-DTL-38999 circular connectors, using standard size-12 cavity inserts for high density. These feature the same 75-ohm SMPM interface being proposed for addition to the VITA 67.3 standard at the backplane interface but packaged for use in MIL-DTL-38999 connectors at the chassis interface.
Similarly, high-density optical circular connectors standardized by VITA 87 and specified in the SOSA standard can provide the bandwidth for ARINC 818 video signals. These MIL-STD-38999-based connectors have inserts for one, two, or four MTs; MTs designated for ARINC 818 can be populated in the same connector with MTs supporting Ethernet or other protocols. (Figure 3.)
[Figure 3 | VITA 87 high-density optical connectors can handle the bandwidth for ARINC 818 video signals.]
Outside of VPX architecture, small-form-factor (SFF) systems are being developed and standardized with requirements for video signal transmission. These same interconnect technologies – whether optical or coax – can be adopted for SFF platforms.
Demands for higher-bandwidth and higher-speed video-signal processing are growing, whether the application is a high-definition camera pod on an uncrewed aerial system (UAS), a sensor turret of a ground vehicle, or livestreaming video over an onboard spacecraft network. (Figure 4.)
[Figure 4 | A high-definition camera pod is shown mounted on an uncrewed aerial system (UAS). Stock image.]
Recent developments in high-speed interconnect will support the next-generation systems for video capture, processing, and display. The need to support higher-speed protocols running at data rates of 6 Gb/sec, 12 Gb/sec, and higher has driven new connector solutions and new interconnect packaging for both coaxial and optical signal transmission. In newer systems, 75-ohm coaxial cables and interconnects designed for improved signal integrity and higher density will replace traditional alternatives. Additionally, optics will play a larger role with the emergence of the ARINC 818 ecosystem in avionics and the advantages of fiber: high-density bandwidth, light weight, and immunity to EMI [electromagnetic interference].
Standards bodies such as the VITA Standards Organization (VSO) and the SOSA (Sensor Open Systems Architecture) Consortium are addressing the next-generation video signal requirements with open-architecture solutions that will meet the technical challenges and create an ecosystem for interoperability in the future.
Michael Walmsley has more than 35 years of experience with TE Connectivity (TE), and formerly AMP Inc., primarily in engineering and product management with an emphasis on new-product development. His areas of expertise include interconnect solutions for embedded computing, rugged high-speed board level, and RF connectors. He serves on the board of directors of the VITA Standards Organization, which drives technology and standards for the bus and board industry. Mike earned his MBA from Penn State University Harrisburg and a bachelor’s degree in mechanical engineering from the University of Rochester (New York).
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