Camera Link (CL) standardizes the hardware connection between cameras and frame grabbers. It includes specifications for data transfer, camera timing, serial communication, and real-time signaling. Camera Link variants include base, medium, full, deca, high speed (CLHS), PoCL (power over Camera Link), and PoCL Lite.
Camera Link is a serial communication protocol standard maintained and administered by the Automated Imaging Association (AIA). It’s offered in a wide array of configurations. AIA, the European Machine Vision Association (EMVA), and the Japan Industrial Imaging Association (JIIA) have a cooperation agreement for global standardization of CL.
Base
The base CL configuration uses a single 26-conductor mini delta ribbon (MDR) or shrunk delta ribbon (SDR) connector and cable optimized for low-voltage differential signaling (LVDS) with CL. At the maximum operating frequency of 85 MHz, the base CL configuration supports a video data throughput of 2.04 Gigabits per second (Gbit/s).
Medium
Medium CL adds a second cable to double the data transfer to 4.08 Gbps.
Full
Full CL adds another 16 bits to the medium configuration, producing a 64-bit data path and a 5.44 Gbps data rate.
Deca
Deca CL, also called 80-bit CL, uses 8 unused bits and reassigns the 8 redundant framing/enable bits from Full CL to extend the data path to 80 bits over two cable assemblies with a combined bandwidth of 6.8 Gbps (Figure 1).
Pictures and power
PoCL can deliver up to 4 W (400 mA at 10 V or 333 mA at 12 V) per CL cable to power the camera. The specification assumes a supply voltage of 11 V and a cable loss of 1V. Base CL has a single cable limited to 4 W; medium, full, and deca CL configurations can deliver up to 8 W, 4 W per cable.
PoCL can be carried over some standard CL cables and use different connectors than the standard versions. It can use a 6-pin PCIe auxiliary power connector. PoCL-Lite is also available and can deliver equivalent power levels in a smaller configuration. Typical cables for PoCL-Lite include SDR-14, HDR-14, and SDR-26.
Camera Link HS
CLHS is not a direct extension of the previous CL protocols. It’s a separate high-speed interface standard for machine vision and imaging applications. Like CL, CLHS supports scalable bandwidths. It offers designers a choice of copper or fiber cabling. CLHS can use Small Form-factor Pluggable (SFP) and SFF-8470 connectors (Infiniband or CX4).
Key features of CLHS include low latency, low jitter, and support for real-time signaling between the camera and frame grabber. CLHS supports high bandwidth, long-distance, and low-cost connectivity but can’t deliver power (Table 1). CLHS implements its protocol in two physical layer encodings:
CLHS M Protocol IP Core: 8bit/10bit line encoding with single-bit error immunity for use in lower-cost, lower-power FPGAs. It supports copper (C2) cabling hardware with CX4 connections up to 15 m and 2.1 GBps in the CLHS cable. Typical data rates are up to 5 Gbps per lane. An active plug-on fiber cable can be added to reach up to 100 m.
CLHS X Protocol IP Core: 64bit/66bit line encoding with forward error correction (FEC). The X protocol is designed for 10 Gbps and higher. It supports connector type F2 (SFP+) and F3 (quad small-form-factor pluggable (QSFP+) and multifiber push-on (MPO) fiber connections at rates up to 25.7 Gbps per lane.
References
Camera Link, Wikipedia
Camera Link HS: The Path to 50 Gbps and Beyond, Vision Systems Design
Camera Link HS Standard, Association for Advancing Automation
Camera Link Standard, Association for Advancing Automation
Digital camera interfaces, Opto Engineering
Primer: Camera Link HS, Teledyne Vision Solutions
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