How two wires work together to silence electrical noise
In short: High-speed data transmission faces a constant enemy: electromagnetic interference. Low-voltage differential signaling (LVDS) solves this by sending information as the difference between two wires. By balancing currents perfectly, it creates opposing fields that cancel out noise, allowing for lightning-fast speeds over simple copper cables.
Introduced in 1994 by National Semiconductor, LVDS became a cornerstone of modern electronics because it balances power efficiency with high performance. Unlike single-ended signaling, where a voltage level is measured against a common ground, LVDS transmits data as the difference between two wires. A steady 3.5 mA flow is supplied by a transmitter into these conductors during standard configurations. When this current hits a termination resistor—usually between 100 and 120 ohms—it creates a voltage difference of about 350 mV. The receiver simply senses the polarity of this difference to determine the digital logic level.
The brilliance of LVDS lies in its noise immunity. Because the two wires carry equal and opposite currents, they generate electromagnetic fields that tend to cancel each other out. Furthermore, any external interference typically affects both wires equally (common-mode noise). Since the receiver only cares about the difference between the wires, this shared noise is effectively ignored. This mechanism also prevents 'ground bounce,' a common issue in single-ended lines where switching currents cause fluctuations in power and ground lines.
While LVDS was famously used to shrink notebook computer video interfaces—reducing a 21-bit wide interface down to just four differential pairs (8 wires)—it remains a versatile physical layer. It supports both parallel and serial data transmission, often using techniques like 8b/10b encoding to embed clock signals and maintain DC balance. Despite being superseded by newer standards like eDP in some consumer niches, LVDS persists as a low-cost, high-speed standard for industrial cameras, machine vision, and various computer buses.
The technology has evolved into specialized variants to meet different power needs. For instance, sub-LVDS (introduced by Nokia in 2004) uses a typical common-mode voltage of 0.9 V, while SLVS-400 allows for power supplies as low as 800 mV with a common-mode voltage of about 400 mV.
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