LVDS line scan camera to frame grabber: match the signaling first

A line scan camera whose data sheet says only LVDS output is usually a parallel-digital design from before Camera Link, and the wording invites an expensive mistake: Camera Link frame grabbers also run LVDS over similar-looking pairs. The two still do not talk. This article sets out what raw LVDS output carries, why the serialized LVDS inside Camera Link is a different protocol, which checks decide compatibility, and the three fixes when a camera turns out to be raw LVDS. A worked example shows that data rate is almost never the constraint; the documented interface match is.

What raw LVDS output means on a camera

Cameras of that generation move pixels off the sensor as a parallel digital bus. An 8-bit camera drives eight data pairs, one per bit, plus a bit clock and control pairs such as LVAL and FVAL for line valid and frame valid. Every pair is LVDS, the electrical layer defined by ANSI/TIA/EIA-644: a low-swing differential driver and receiver with a nominal swing near 350 mV. That low swing keeps edges fast and runs clean over metres of cable at tens of megahertz.

A 512-pixel single-tap camera therefore leaves its connector on roughly a dozen pairs: eight data, one clock, two or three control, plus trigger lines. A dual-tap part doubles the data pairs. What this bus never standardizes is the mapping — which pair carries which bit, how taps split a line, what the clock range is. That mapping is camera-specific, so the only frame grabber that reads it is one whose documentation names this camera, or a parallel-digital grabber set up for the same pair count, clock and tap layout.

Camera Link is also LVDS — serialized, and that is the whole difference

Camera Link sits in the same electrical family: its channels run over low-swing differential pairs of the same class. The difference is a serializer. A Channel Link device at the camera takes 28 bits — up to 24 data bits plus the frame-valid, line-valid and data-valid flags and a spare — and transmits them over four LVDS data pairs and one LVDS clock pair, each data pair carrying seven bits per input clock. The receiver deserializes the streams back to 28 bits and a clock; the channel structure is summarized on Wikipedia's Camera Link page.

So a Camera Link receiver expects data at seven times its input clock, in a fixed bit order. A raw parallel camera delivers one bit per pair at the pixel clock itself, on pairs that mean something else. Nothing in the grabber can lock to that: the frame buffer stays empty or fills with noise. The connectors may mate and the levels may match, and the link still fails.

The checks that decide compatibility

Put five facts from the camera's documentation next to the grabber's before anything is ordered.

1. Interface standard. The camera page must name the interface — Camera Link with base, medium or full configuration, or another named standard. If it says only LVDS output with a pair count and a clock range, the output is raw parallel and no Camera Link grabber applies.
2. Tap configuration. How the sensor splits the line across outputs: one tap of 512 pixels, or two taps of 256. Frame grabber documentation lists the tap configurations each device accepts, and the device must accept the camera's tap configuration, not just its connector.
3. Pixel clock and line rate. Compare the camera's clock with the grabber's stated maximum. Under Camera Link 2.0 a base channel accepts up to 85 MHz, which the next section turns into data rates.
4. Control and trigger lines. Camera Link defines four camera-control lines, CC1 to CC4, plus serial links in both directions. Count what the camera needs for exposure and rate control, and confirm the grabber exposes them. Raw-LVDS cameras carry their control lines as dedicated pairs with camera-specific timing — another mapping a generic grabber does not know.
5. Camera file or GenICam descriptor. The grabber needs timing support for this camera model. Without it, integration means hand-mapping the timing from vendor tables, which is realistic only when those tables are published in full.

The same configuration logic, applied to line scan cameras specifically, is set out in Camera Link frame grabber compatibility for line scan.

Base, medium, full: the configuration check in numbers

Camera Link support splits by configuration, and the split decides which camera a grabber can take:

The rates are the standard's published maxima: 24 data bits × 85 MHz ÷ 8 = 255 MB/s for base, doubled for medium, and 64 data bits for full. A base-only grabber cannot take a medium or full camera — the extra channel sets have nowhere to land — so the configuration name belongs on the order line next to the model number. Once the pair is chosen, acquisition-side bring-up is covered in frame grabber image acquisition for Camera Link and CoaXPress.

Worked example: bandwidth is never the constraint

Bandwidth is the number people check first, so put it on record with the arithmetic. Take a hypothetical 512-pixel, 8-bit, dual-tap TDI camera running at 30,000 lines/s — typical proportions for the raw-LVDS generation. If the line rate is not fixed yet, how to set the line rate of a line scan camera derives it from web speed and pixel size, and the calculator below does the conversion.

• Bits per line: 512 px × 8 bit = 4,096 bit
• One tap at 30,000 lines/s: 4,096 bit × 30,000 lines/s = 122,880,000 bit/s = 15.36 MB/s
• Two taps together: 2 × 15.36 MB/s = 30.72 MB/s

A single base channel moves 255 MB/s, so this stream uses 30.72 ÷ 255 ≈ 12% of one channel. Even a four-tap, 16-bit variant stays under one-fifth of base. The conclusion is the decision: capacity does not decide this compatibility question, the documented interface does — and a grabber that passes the bandwidth check while failing the signaling check delivers zero images.

The three fixes for a raw-LVDS camera

Once the output is confirmed raw parallel LVDS, three paths exist, in the order we would take them.

Vendor Camera Link conversion first. Some camera families of that era shipped a factory Camera Link variant or listed a converter for specific models. Look for a conversion the camera vendor publishes for your exact model; it keeps the sensor and swaps only the signaling, leaving a standard Camera Link camera that pairs with any current grabber.

Camera replacement second. Current line scan cameras deliver the same jobs on standard interfaces. For any new or upgraded station this is the decision, and for most legacy lines it is too — the reasoning matches the walkthrough on replacing a legacy line scan camera when an old output has no modern match.

Legacy parallel-digital grabber last. Boards that terminate raw LVDS pairs exist as legacy hardware, largely out of current production and without long-term driver support. Reserve one for keeping an installed line alive while a replacement camera is qualified — not for a new build.

Stated plainly: new or upgraded station, replace the camera. Installed line that must keep running, vendor Camera Link conversion first; a legacy parallel-digital board only as a stopgap.

Modern TDI cameras: the same job, standard interfaces

TDI is a sensor technique, not an interface: staged rows integrate the same moving feature for a longer effective exposure, which is why TDI parts suit fast webs and short exposures. Nothing about TDI requires raw LVDS — current TDI cameras ship with GigE, Camera Link, CoaXPress or XoFLink outputs.

The range here shows both ends. The LS-LCM-0016 is a 2K GigE camera with TDI, 7 μm pixels, a 58 kHz line rate and an M42 mount. Pair it with the LS-FGB-0004, a PCIe x4 card with four PoE Gigabit ports, and camera plus host form one documented chain, with trigger handling in the camera's GenICam line settings — the setup side is in hardware trigger source not detected: check GenICam line settings.

At the high end, the MV-CL166-91F2C reads 16K at 5 μm with RGB/4TDI over XoFLink on two SFP+ ports, and the MV-GS1104F-DF is a four-port XoF frame grabber with SFP+ slots supporting 40G total bandwidth. The bandwidth arithmetic from the worked example applies unchanged, with far more headroom.

If a Camera Link camera stays in the plan, the MV-GC1102IOL is a Camera Link frame grabber — order it with the camera's configuration and tap count on the same line.

At a 58 kHz line rate the light budget, not the link, becomes the next constraint; line scan light: how much power a fast line really needs sizes it.

When the usual answer is wrong

• The camera says LVDS and the grabber says LVDS. The word names the electrical layer, ANSI/TIA/EIA-644, not the protocol. Raw LVDS and Camera Link LVDS share the low swing and nothing else.
• A medium camera will work on a base grabber over a smaller region of interest. It will not: medium and full cameras use extra channel sets that a base-only grabber has no inputs or logic for.
• The bandwidth check passes, so the link will work. Capacity and compatibility are different checks; the camera in the worked example uses about 12% of one base channel and still sends zero frames to a Camera Link grabber.
• Trigger wiring can wait until commissioning. On a raw-LVDS camera the control pairs follow camera-specific timing; on a modern camera the trigger path lives in GenICam line settings. Count and assign the trigger lines before the order.

Before you order: a short checklist

Camera side:

• Interface standard named exactly: raw parallel LVDS, or Camera Link base, medium or full.
• Tap configuration written down: taps and pixels per tap.
• Pixel clock range and maximum line rate.
• Control and trigger pairs or lines listed, with a purpose for each.

Grabber side:

• Support for the camera's configuration and tap configuration, as printed in the grabber's own documentation.
• Pixel-clock maximum above the camera's clock, with margin.
• Enough CC lines or configurable I/O for the camera's control needs.
• A camera file or GenICam descriptor for the model, or vendor timing tables you can map yourself.

Link side:

• A cable rated for the interface, its configuration and the run length.
• The trigger source agreed before wiring — for web inspection that is usually an encoder, and encoder-triggered line scan capture: wiring quadrature inputs covers the wiring.

The decision

Match the interface standard, not the connector. A camera that names Camera Link needs a grabber chosen by configuration and tap configuration; a camera with raw parallel LVDS needs the vendor's Camera Link conversion or a replacement — and for a new station, replacement is the answer.

Start from the frame grabbers category for current Camera Link, CoaXPress, XoFLink and GigE host devices, or the line scan cameras range for TDI parts on standard interfaces. The frame grabber finder filters by interface and ports, and the system configurator starts from the camera and proposes the host side. If the question is a legacy camera with an undocumented output, contact the applications team with the model and the interface line from its data sheet — that one line decides the path. The systems topic page collects the rest of the integration guides.