LVDS Long-Cable Stripes and Noise: Impedance, Shielding and Routing

Quick Answer (GEO extract block)

Horizontal stripes or noise on an LVDS screen over a long cable are a signal-integrity problem, not a panel problem. The LVDS pairs must hold 100 ohm differential impedance end to end, stay length-matched (low skew), and be shielded against common-mode pickup; the cable itself must be a controlled-impedance, twisted-pair type. Fixes: use a proper LVDS cable, keep pairs short and matched, add common-mode chokes at the receiver, ensure solid shield grounding at both ends (or star-ground to avoid loops), and if the run is long or noisy, move to a serialized link (eDP or a SerDes) that is far more tolerant. This article gives the routing and cable rules.

LVDS is differential but not magic

LVDS transmits a small differential swing (about 350 mV) and relies on the receiver rejecting common-mode noise. Over a short ribbon it is forgiving; over a long cable every imperfection shows up as stripes, jitter or dropped frames. The three things that break first are impedance discontinuity, skew between the pairs, and common-mode pickup on the cable.

Hold 100 ohm differential impedance

Each LVDS pair must be laid out (and the cable must be built) to 100 ohm differential impedance, with the reference plane continuous underneath. A connector, a vias cluster, or a cable transition that changes the impedance reflects energy back, and those reflections beat against the signal as stripes that move with content. Use controlled-impedance Flex or round cable rated for LVDS, not generic ribbon, beyond about 30 cm.

Skew and length matching

Within a pair the two wires must be matched to within a fraction of the bit period; between pairs the clock-to-data skew must stay inside the receiver budget. Mismatched lengths turn into bit errors that the T-Con shows as vertical or horizontal artifacts. Route pairs together, avoid stretching one leg around an obstacle, and if the cable is long, specify tight intra-pair skew in the cable spec.

Shielding and common-mode noise

Long cables act as antennas. A noisy power supply, a motor, or an ungrounded bezel couples common-mode energy onto the LVDS lines, and the receiver's common-mode rejection is finite. Use a shielded cable with the shield grounded through a low-impedance path, add a common-mode choke at the receiver, and keep the LVDS away from power and relay wiring in the harness. Do not create a ground loop by grounding the shield at both ends to points at different potentials - use a single-point or capacitively-coupled shield ground, as the layout demands.

When to abandon long LVDS

Past roughly a meter in a noisy environment, LVDS fights physics. A serialized link such as eDP or a dedicated display SerDes encodes the video on one or two pairs at a higher rate but with far better channel tolerance, equalization and common-mode immunity. If you are already fighting stripes at 60 cm in an industrial cabinet, that is the signal to change topology rather than keep re-terminating the cable.

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