NOISE

DIKSHA PRAKASHBTech-ECE140020204002

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What is NOISE?

• In electrical terms, noise maybe defined as unwanted form of energy which tend to interfere with proper reception and reproduction of the transmitted signals.

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Various Daily-life Examples:

• In radio receivers, noise may produce hiss type of a sound in the output of the loudspeaker.

• In TV receivers, noise may produce ‘snow’.

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FIGURE : Snow produced in TV channels due to noise

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Classification of Noise

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• ATMOSPHERIC NOISE/ STATIC NOISEProduced by lightening discharges in thunderstorm and other natural electrical disturbances.

• EXTRA TERRESTRIAL NOISE/ SOLAR NOISE

SOLAR NOISESun, being at very high temperature, radiates electrical energy in the form of noise. It happens at the peak of eleven year cycle.

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COSMIC NOISENoise received from distant stars, our galaxy and various other galaxies.

• INDUSTRIAL NOISEMan-made noise due to sources like automobiles, aircraft ignition, electric motors etc.

• SHOT NOISEArises in active devices due to random behaviour of charge carriers.“ Fluctuating/shot noise current”

• PARTITION NOISENoise generated when current has to divide between two or more paths in a circuit.

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• FLICKER NOISE/ LOW FREQUENCY NOISE/ PINK NOISEFlow of current at low frequencies produces this particular type of noise.

• TRANSIT TIME NOISE/ HIGH FREQUENCY NOISEIncrease in conductance with increase in frequency causes this type of noise.

• THERMAL NOISE/ JHONSON NOISEThe noise produced in resistor with increase in absolute temperature.

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Signal to Noise Ratio

Signal to noise ratio is defined as ratio of signal to noise power at the same point in the system.

• A ratio higher than 1:1 (greater than 0 dB) indicates more signal than noise.

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Mathematical Interpretation

• The reciprocal of the coefficient of variation, i.e., the ratio of mean to standard deviation of a signal or measurement

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Application (contd.)

• This definition holds true for the situation where the values are non negative. Thus, it is used in image processing.

• The ’Rose criterion’ (named after Albert

Rose) states that an SNR of at least 5 is needed to be able to distinguish image features at 100% certainty.

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FIGURE: High SNR vs. Low SNR (REFERENCE: www.jeffgeerling.com )

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Learning SNR with MATLABrng defaultTpulse = 20e-3;Fs = 10e3;t = -1:1/Fs:1;x = rectpuls(t,Tpulse);y = 0.00001*randn(size(x));s = x + y;pulseSNR = snr(x,s-x)

OUTPUT:

pulseSNR =  80.0818

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NOISE FIGURE

Indicates how much the signal to noise ratio deteriorates as a signal passes through a circuit or series of circuits.

The noise figure for an ideal receiver is 1 whereas that for a practical receiver can be expressed as an actual ratio or in decibels (dBs).

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REFERENCES

• www.electronicdesign.com • www.en.wikibooks.org• www.gatebooks.blogspot.in• www.wikipedia.com• www.jntubook.com• www.inmathworks.com

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