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Noise

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noise in various forms and their effects
noise factor and noise figure

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Noise

  1. 1. Noise and its variousNoise and its various effectseffects Prepared by:Prepared by: Kushagra Ganeriwal (130010111009)Kushagra Ganeriwal (130010111009) Kamlesh Desai (130010111006)Kamlesh Desai (130010111006) Sweetu Ratnani (130010111048)Sweetu Ratnani (130010111048) Guided by:Guided by: Prof. Mehul Thakkar (EC Dept.)Prof. Mehul Thakkar (EC Dept.)
  2. 2. NoiseNoise  Any unwanted input is termed as noise.Any unwanted input is termed as noise.  Limits systems ability to process weak signalsLimits systems ability to process weak signals  Sources:Sources: 1.1. Random noise in resistors and transistorsRandom noise in resistors and transistors 2.2. Mixer noiseMixer noise 3.3. Undesired cross-coupling noiseUndesired cross-coupling noise 4.4. Power supply noisePower supply noise  capability of detecting weak signals in presence of large-amplitudecapability of detecting weak signals in presence of large-amplitude signalssignals  ““noisiness” of the signal measure = signal-to-noise ratio (frequency-noisiness” of the signal measure = signal-to-noise ratio (frequency- dependant)dependant)
  3. 3. powernoiseaverage powersignalaverage fN fS SNR −− −− == )( )(  Random noiseRandom noise  ExternalExternal • AtmosphericAtmospheric • InterstellarInterstellar  Receiver internalReceiver internal • ThermalThermal • Flicker noise (low frequency)Flicker noise (low frequency) • Shot noiseShot noise
  4. 4. Noise factorNoise factor  ““The noise factor, at a specified input frequency, is defined as theThe noise factor, at a specified input frequency, is defined as the ratio of (1) the total noise power per unit bandwidth available atratio of (1) the total noise power per unit bandwidth available at the output port when noise temperature of the input termination isthe output port when noise temperature of the input termination is standard (290 K) to (2) that portion of (1) engendered at the inputstandard (290 K) to (2) that portion of (1) engendered at the input frequency by the input termination.”frequency by the input termination.” sourcetoduenoiseoutputavailable powernoiseoutputavailable F −−−−− −−− =
  5. 5.  It is a measure of the degradation of SNR due to the noise added.It is a measure of the degradation of SNR due to the noise added. SNR gets worse as we process the signalSNR gets worse as we process the signal  Spot noise factor, Quantitative measure of receiver performance wrtSpot noise factor, Quantitative measure of receiver performance wrt noise for a given bandwidthnoise for a given bandwidth  Noise figureNoise figure  Quantitative measure of receiver performance wrt noise for a givenQuantitative measure of receiver performance wrt noise for a given bandwidthbandwidth  Noise figureNoise figure  Typically 8-10 db for modern receiversTypically 8-10 db for modern receivers
  6. 6. Amplifier input noise in terms of noise figureAmplifier input noise in terms of noise figure  Noise Factor (linear not dB) of a  receiver is the ratio of the SNR at its input to the ratio of the SNRat its output.  NoiseFactor  F(linear)= SNR_input[linear]/SNR_output[linear]  Noise Factor_F[dB]= SNR_input[dB] - SNR_output[dB]  NoiseFigure_NF[dB]= 10*LOG (NoiseFactor_F(linear))  SNR at the output will always be smaller than the SNR at the input, due to the fact that circuits always add to the noise in a system.  The Noise Factor, at a specified input frequency, is defined as the ratio of the total Noise Power per unit bandwidth available at the output port when noise temperature of the input termination is standard (290K) to that portion of engendered at the input frequency by the input termination.
  7. 7. Noise factor in cascaded amplifiers
  8. 8.  Vs is the source voltage, Zs=Rs+jXs is the source impedance,Vts is the thermal noise voltage generated by the source, and Vn and In are the noise sources representing the noise generated by the amplifier. The output voltage is given by Where A is the voltage gain and Zi is the input impedance. The equivalent noise input voltage Vni is defined as the voltage in series with Vs that generates the same noise voltage at the output as all noise sources in the circuit. Noise factor and equivalent input noise generators
  9. 9. noise factor of a lossy networknoise factor of a lossy network Input Noise Factor would be given as Fi = Si/Ni and Output Noise Factor would be given as Fo = So/No. Therefore F = Fi/Fo.
  10. 10. Noise temperatureNoise temperature  The noise temperature is a means for specifying noise in terms ofThe noise temperature is a means for specifying noise in terms of an equivalent temperature. The noise power is directly proportionalan equivalent temperature. The noise power is directly proportional to temperature in degrees Kelvin and that noise power collapses toto temperature in degrees Kelvin and that noise power collapses to zero at absolute zero (0°K).zero at absolute zero (0°K).  the equivalent noise temperaturethe equivalent noise temperature TTee is not the physical temperatureis not the physical temperature of the amplifier, but rather a theoretical construct that is anof the amplifier, but rather a theoretical construct that is an equivalentequivalent temperature that produces that amount of noise power.temperature that produces that amount of noise power. The noise temperature is related to the noise factor by:The noise temperature is related to the noise factor by: TTee = (F= (Fnn - 1) T- 1) Too and to noise figure by:and to noise figure by:
  11. 11.  noise temperature Tnoise temperature Tee, we can also define noise factor and noise, we can also define noise factor and noise figure in terms of noise temperature:figure in terms of noise temperature:  The total noise in any amplifier or network is the sum of internallyThe total noise in any amplifier or network is the sum of internally and externally generated noise. In terms of noise temperature:and externally generated noise. In terms of noise temperature: PPn(total)n(total) = GKB(T= GKB(Too + T+ Tee)) wherewhere PPn(total)n(total) is the total noise poweris the total noise power
  12. 12. Behavior of Analog systems inBehavior of Analog systems in presence of Noisepresence of Noise

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