Noise_margin

In electrical engineering, noise margin is the amount by which a signal exceeds the minimum amount for proper operation. It is commonly used in at least two contexts:

• In communications system engineering, noise margin is the ratio by which the signal exceeds the minimum acceptable amount. It is normally measured in decibels.
• In a digital circuit, the noise margin is the amount by which the signal exceeds the threshold for a proper \'0\' or \'1\'. For example, a digital circuit might be designed to swing between 0.0 and 1.2 volts, with anything below 0.2 volts considered a \'0\', and anything above 1.0 volts considered a \'1\'. Then the noise margin for a \'0\' would be the amount that a signal is below 0.2 volts, and the noise margin for a \'1\' would be the amount by which a signal exceeds 1.0 volt. In this case noise margins are measured as an absolute voltage, not a ratio.

Noise margins are generally defined so that positive values ensure proper operation, and negative margins result in compromised operation, or perhaps outright failure.

See also

• Digital circuit
• Signal integrity
• Substrate coupling
• ITU G.992.1
• signal-to-noise ratio

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