In electrical engineering

Electrical engineering

Electrical engineering is a field of engineering that generally deals with the study and application of electricity, electronics and electromagnetism. The field first became an identifiable occupation in the late nineteenth century after commercialization of the electric telegraph and electrical...

, noise margin is the amount by which a signal

Signal (electrical engineering)

In the fields of communications, signal processing, and in electrical engineering more generally, a signal is any time-varying or spatial-varying quantity....

 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 decibel
  Decibel
  The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
  
  s.
• In a digital circuit
  Digital circuit
  Digital electronics represent signals by discrete bands of analog levels, rather than by a continuous range. All levels within a band represent the same signal state...
  
  , 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 volt
  Volt
  The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
  
  s, 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 for CMOS chips is usually much greater than TTL because the V_{OH min} is closer to the power supply voltage and V_{OL max} is closer to zero.

In simple words, Noise margin(in circuits) is the amount of noise that a circuit can withstand.
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
  Digital circuit
  Digital electronics represent signals by discrete bands of analog levels, rather than by a continuous range. All levels within a band represent the same signal state...
  
  
• Signal integrity
  Signal integrity
  Signal integrity or SI is a set of measures of the quality of an electrical signal. In digital electronics, a stream of binary values is represented by a voltage waveform. However, digital signals are fundamentally analog in nature, and all signals are subject to effects such as noise,...
  
  
• Substrate coupling
  Substrate coupling
  In an integrated circuit, a signal can couple from one node to another via the substrate. This phenomenon is referred to as substrate coupling or substrate noise coupling....
  
  
• ITU G.992.1
  ITU G.992.1
  In telecommunications, ITU G.992.1 is an ITU standard for ADSL using discrete multitone modulation. G.DMT full-rate ADSL expands the usable bandwidth of existing copper telephone lines, delivering high-speed data communications at rates up to 8 Mbit/s downstream and 1.3 Mbit/s upstream.DMT...
  
  
• signal-to-noise ratio
  Signal-to-noise ratio
  Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
  
  

External links

• DMT, a DSL monitoring and downstream noise margin tweaking program.