CHAPTER 6 NOISE
INTRODUCTION <ul><li>Noise is random energy that interfere with the information signal. </li></ul><ul><li>Noise may be def...
NOISE <ul><li>Electrical noise – any undesirable that falls within the passband of the signal. </li></ul><ul><li>Figure 4 ...
Classification of Uncorrelated Noise NOISE EXTERNAL INTERNAL ATMOSPHERIC  NOISE EXTRATERRESTRIAL NOISE INDUSTRIAL  NOISE T...
ATMOSPHERIC NOISE <ul><li>Caused by lightning discharges in thunderstorms and other natural electric disturbances occurrin...
EXTRATERRESTRIAL NOISE <ul><li>SOLAR NOISE: </li></ul><ul><ul><li>Normal condition, there is a constant noise radiation fr...
INDUSTRIAL NOISE <ul><li>Between 1 to 600 MHz, the intensity noise made by humans easily outstrips that created by any oth...
SHOT NOISE <ul><li>Caused by the random arrival of carriers at the output element of an electronic device. </li></ul><ul><...
THERMAL NOISE <ul><li>Is associated with the rapid and random movement of electrons within a conductor due to thermal agit...
<ul><li>Thermal noise power is proportional to the product of bandwidth and temperature. </li></ul><ul><li>Mathematically,...
NOISE   VOLTAGE <ul><li>Figure 4.2 shows the equivalent circuit for a thermal noise source. </li></ul><ul><li>Internal res...
Example 1 <ul><li>Convert the following temperatures to kelvin: </li></ul><ul><li>a) 100°C </li></ul><ul><li>b) 0°C </li><...
Example 2 <ul><li>Calculate the thermal noise power available from any resistor at room temperature (290K) for a bandwidth...
Example 3 <ul><li>For an electronic device operating at a temperature of 17 o C with a  bandwidth of 10 kHz, determine  </...
Example 4 <ul><li>Two resistor of 20k    and 50 k   are at room temperature (290K). For a bandwidth of 100kHz, calculate...
Correlated Noise <ul><li>Form of internal noise that is correlated to the signal and cannot be present in a circuit unless...
Intermodulation Distortion <ul><li>Generation of unwanted sum and difference frequencies produced when two or more signals...
Cont.. <ul><li>Cross products = mf 1 ±nf 2 . </li></ul><ul><li>F1 and f2 are fundamental frequency. </li></ul><ul><li>F1>f...
Correlated Noise-Intermodulation Distortion f1 f2 V1 V2 f1 f2 f1-f2 f1+f2 V1 V2 V difference V sum Input frequency spectru...
Example 6 <ul><li>For a nonlinear amplifier with 2 input frequencies, 3kHz and 8kHz, determine: </li></ul><ul><li>First 3 ...
Interference <ul><li>Form of external noise. </li></ul><ul><li>Means to disturb or detract from. </li></ul><ul><li>Electri...
Review Notes <ul><li>Gain </li></ul><ul><li>Attenuation </li></ul><ul><ul><li>Both has the ratio output to the input. </li...
Gain <ul><li>Ratio output to the input. </li></ul><ul><li>Output has greater amplitude than the input </li></ul><ul><li>Mo...
Attenuation <ul><li>Refers to loss introduced by a circuit. </li></ul><ul><li>Output is less than input. </li></ul><ul><li...
<ul><li>Attenuation can be offset by introducing gain. </li></ul>Figure 6.8 Total attenuation in cascaded network Figure 6...
Figure 6.10 Total gain is the product of the individual stage gains and attenuation
<ul><li>Example 7 </li></ul><ul><li>What is the gain of an amplifier that produces an output of 750 mV for 30   V input? ...
Signal to Noise Ratio (SNR) <ul><li>Ratio of the signal power level to the noise power level. </li></ul><ul><li>Express in...
Example 10 <ul><li>For an amplifier with an output signal power of 10W and an output noise power of 0.01W, determine the S...
Noise Factor (F) and Noise Figure (NF) <ul><li>Figures of merit used to indicate how much the SNR deteriorates as a signal...
Cont.. <ul><li>NF is noise factor stated in dB. </li></ul><ul><li>Used to indicate the quality of a receiver. </li></ul>
Ideal Noiseless Amplifier Ideal Noiseless Amplifier Ap=power gain Figure 6.11
Non ideal amplifier Nonideal amplifier Ap=power gain Nd=internally generated noise Figure 6.12
Example 11 <ul><li>For a nonlinear amplifier and the following parameter, determine: </li></ul><ul><li>a) Input SNR(dB) </...
Noise Figure of Cascaded Amplifier Ap1 NF1 Ap2 NF2 Ap3 NF3 Input Output Figure 6.13
Cont.. <ul><li>Total noise factor is the accumulation of the individual noise factor. </li></ul><ul><li>Friiss’s formula i...
Example 12 <ul><li>For 3 cascaded amplifier stages, each with noise figure of 3 dB  and power gain of 10 dB, determine the...
Equivalent Noise Temperature (T e ) <ul><li>Hypothetical value that cannot be directly measured. </li></ul><ul><li>To indi...
Example 13 <ul><li>Determine: </li></ul><ul><li>Noise Figure for an equivalent noise temperature of 75K. </li></ul><ul><li...
Example 14 <ul><li>A voltage divider shown in  Figure 6.9  has values of R 1  = 10k   and R 2  = 47k  . </li></ul><ul><u...
Example 15 <ul><li>An amplifier has gain of 45,000, which is too much for the amplification. With an input voltage of 20  ...
Example 16 <ul><li>A RF sine wave generator whose output impedance is 50    is connected to a 50    load using 50    co...
Example 17 <ul><li>The input signal to a telecommunications receiver consists of 100  W of signal power and 1  W of nois...
Upcoming SlideShare
Loading in …5
×

Communication Engineering - Chapter 6 - Noise

20,898 views

Published on

Published in: Education, Business, Technology
3 Comments
23 Likes
Statistics
Notes
  • hey? wheres the solution for the examples?
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
  • where is the solutions of the examples?
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
  • The firri's formula at slide no.36 is not correct,in the last term it is A(N-1) INSTEAD OF A(N)KINDLY CORRECT IT THANKS
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
No Downloads
Views
Total views
20,898
On SlideShare
0
From Embeds
0
Number of Embeds
13
Actions
Shares
0
Downloads
1,154
Comments
3
Likes
23
Embeds 0
No embeds

No notes for slide
  • Audio recording – any unwanted signal that fall within audio frequency band of 0Hz to 15kHz will interfere with the music
  • Communication Engineering - Chapter 6 - Noise

    1. 1. CHAPTER 6 NOISE
    2. 2. INTRODUCTION <ul><li>Noise is random energy that interfere with the information signal. </li></ul><ul><li>Noise may be defined as any unwanted introduction of energy tending to interfere with the proper reception and reproduction of transmitted signal. </li></ul><ul><li>In radio receiver, noise may produce hiss in the loudspeaker output. </li></ul><ul><li>Noise can limit the range of systems. </li></ul><ul><li>It affects the sensitivity of the receiver. </li></ul>
    3. 3. NOISE <ul><li>Electrical noise – any undesirable that falls within the passband of the signal. </li></ul><ul><li>Figure 4 show the effect of noise on electrical noise. </li></ul><ul><li>2 general categories </li></ul><ul><ul><li>Correlated noise – implies relationship between the signal and the noise, exist only when signal is present. </li></ul></ul><ul><ul><li>Uncorrelated noise – present at all time, whether there is signal or not. </li></ul></ul>
    4. 4. Classification of Uncorrelated Noise NOISE EXTERNAL INTERNAL ATMOSPHERIC NOISE EXTRATERRESTRIAL NOISE INDUSTRIAL NOISE THERMAL NOISE SHOT NOISE Figure 6.1
    5. 5. ATMOSPHERIC NOISE <ul><li>Caused by lightning discharges in thunderstorms and other natural electric disturbances occurring in the atmosphere. </li></ul><ul><li>Consist of spurious radio signal with components distributed over a wide range of frequencies. </li></ul><ul><li>It propagates over the earth in the same way as ordinary radio waves of the same frequencies. </li></ul><ul><li>Become less severe at frequencies above 30MHz because: </li></ul><ul><ul><li>The higher frequencies are limited to line-of-sight propagation. </li></ul></ul><ul><ul><li>Nature of the mechanism generating this noise is such that very little of it is created in the VHF range and above. </li></ul></ul>
    6. 6. EXTRATERRESTRIAL NOISE <ul><li>SOLAR NOISE: </li></ul><ul><ul><li>Normal condition, there is a constant noise radiation from the sun, simply because large body at a very high frequency. </li></ul></ul><ul><ul><li>Radiates over a very broad frequency spectrum. </li></ul></ul><ul><li>COSMIC NOISE: </li></ul><ul><ul><li>Stars radiate RF noise in the same manner of sun. </li></ul></ul><ul><ul><li>The noise received is called thermal noise and distributed fairly uniformly over the entire sky. </li></ul></ul>
    7. 7. INDUSTRIAL NOISE <ul><li>Between 1 to 600 MHz, the intensity noise made by humans easily outstrips that created by any other source to the receiver. </li></ul><ul><li>Sources such as: automobile, aircraft, electric motors and other heavy machine. </li></ul><ul><li>The nature of industrial noise is so variable that it is difficult to analyze. </li></ul>
    8. 8. SHOT NOISE <ul><li>Caused by the random arrival of carriers at the output element of an electronic device. </li></ul><ul><li>First observed in the anode current of a vacuum-tube amplifier. </li></ul><ul><li>The current carriers are not moving in continuous steady flow. </li></ul><ul><li>Randomly varying and superimposed onto any signal present. </li></ul><ul><li>Sometimes called transistor noise. </li></ul>
    9. 9. THERMAL NOISE <ul><li>Is associated with the rapid and random movement of electrons within a conductor due to thermal agitation. </li></ul><ul><li>Present in all electronic component and communications systems. </li></ul><ul><li>Referred as white noise. </li></ul><ul><li>Is a form of additive noise, cannot be eliminated. </li></ul><ul><li>It increases in intensity with the number of devices in a circuit. </li></ul>
    10. 10. <ul><li>Thermal noise power is proportional to the product of bandwidth and temperature. </li></ul><ul><li>Mathematically, noise power is </li></ul><ul><li>N=KTB </li></ul><ul><li>N = noise power, </li></ul><ul><li>K=Boltzmann’s constant ( 1.38x10 -23 J/K ) </li></ul><ul><li>B = bandwidth, </li></ul><ul><li>T = absolute temperature (Kelvin)( 17 o C or 290K ) </li></ul>
    11. 11. NOISE VOLTAGE <ul><li>Figure 4.2 shows the equivalent circuit for a thermal noise source. </li></ul><ul><li>Internal resistance R I in series with the rms noise voltage V N . </li></ul><ul><li>For the worst condition, the load resistance R = R I , noise voltage dropped across R = half the noise source ( V R =V N / 2 ) and </li></ul><ul><li>From the final equation The noise power P N , developed across the load resistor = KTB </li></ul>The mathematical expression : Figure 6.2 : Noise source equivalent circuit
    12. 12. Example 1 <ul><li>Convert the following temperatures to kelvin: </li></ul><ul><li>a) 100°C </li></ul><ul><li>b) 0°C </li></ul><ul><li>c) -10°C </li></ul><ul><li>T=a°C+273°C </li></ul>
    13. 13. Example 2 <ul><li>Calculate the thermal noise power available from any resistor at room temperature (290K) for a bandwidth of 1 MHz. Calculate also the corresponding noise voltage, given that R = 50  . </li></ul>
    14. 14. Example 3 <ul><li>For an electronic device operating at a temperature of 17 o C with a bandwidth of 10 kHz, determine </li></ul><ul><ul><li>Thermal noise power in watts and dBm </li></ul></ul><ul><ul><li>rms noise noise voltage for a 100  internal resistance and 100  load resistance. </li></ul></ul>
    15. 15. Example 4 <ul><li>Two resistor of 20k  and 50 k  are at room temperature (290K). For a bandwidth of 100kHz, calculate the thermal noise voltage generated by </li></ul><ul><li>each resistor </li></ul><ul><li>the two resistor in series </li></ul><ul><li>the two resistor in parallel </li></ul>
    16. 16. Correlated Noise <ul><li>Form of internal noise that is correlated to the signal and cannot be present in a circuit unless there is a signal. </li></ul><ul><li>Produced by nonlinear amplification. </li></ul><ul><li>All circuits are nonlinear therefore, they all produce nonlinear distortion . </li></ul><ul><li>Nonlinear distortion creates unwanted frequencies that interfere with the signal and degrade performance. </li></ul>
    17. 17. Intermodulation Distortion <ul><li>Generation of unwanted sum and difference frequencies produced when two or more signals mix in a nonlinear device. </li></ul><ul><li>The sum and difference frequencies are called cross products. </li></ul><ul><li>Unwanted cross products can interfere with the information signal. </li></ul><ul><li>Cross products are produced when harmonics as well as fundamental frequency mix in a nonlinear device. </li></ul>
    18. 18. Cont.. <ul><li>Cross products = mf 1 ±nf 2 . </li></ul><ul><li>F1 and f2 are fundamental frequency. </li></ul><ul><li>F1>f2 </li></ul><ul><li>M and n are positive integer. </li></ul>
    19. 19. Correlated Noise-Intermodulation Distortion f1 f2 V1 V2 f1 f2 f1-f2 f1+f2 V1 V2 V difference V sum Input frequency spectrum Output frequency spectrum Figure 6.4
    20. 20. Example 6 <ul><li>For a nonlinear amplifier with 2 input frequencies, 3kHz and 8kHz, determine: </li></ul><ul><li>First 3 harmonics present in the output for each input frequency. </li></ul><ul><li>Cross-product frequencies produced for values of m and n of 1 and 2. </li></ul>
    21. 21. Interference <ul><li>Form of external noise. </li></ul><ul><li>Means to disturb or detract from. </li></ul><ul><li>Electrical interference is when information signals from one source produce frequencies that fall outside their allocated bandwidth and interfere with information signals form another source. </li></ul><ul><li>Most interference occur when harmonics frequencies from one source fall into the passband of a neighboring channel. </li></ul>
    22. 22. Review Notes <ul><li>Gain </li></ul><ul><li>Attenuation </li></ul><ul><ul><li>Both has the ratio output to the input. </li></ul></ul>Figure 6.5
    23. 23. Gain <ul><li>Ratio output to the input. </li></ul><ul><li>Output has greater amplitude than the input </li></ul><ul><li>Most amplifiers are power amplifier, the same procedure can be used to calculate power gain, A p . </li></ul><ul><li>A p = P out /P in </li></ul>Figure 6.6
    24. 24. Attenuation <ul><li>Refers to loss introduced by a circuit. </li></ul><ul><li>Output is less than input. </li></ul><ul><li>For cascade circuit, total attenuation is, A T =A 1 x A 2 x A 3 ….. </li></ul><ul><li>Voltage divider network may introduce attenuation. </li></ul>Figure 4.7 Voltage divider introduces attenuation
    25. 25. <ul><li>Attenuation can be offset by introducing gain. </li></ul>Figure 6.8 Total attenuation in cascaded network Figure 6.9 Gain offsets the attenuation
    26. 26. Figure 6.10 Total gain is the product of the individual stage gains and attenuation
    27. 27. <ul><li>Example 7 </li></ul><ul><li>What is the gain of an amplifier that produces an output of 750 mV for 30  V input? </li></ul><ul><li>Example 8 </li></ul><ul><li>The power output of an amplifier is 6 W. The power gain is 80. What is the input power? </li></ul><ul><li>Example 9 </li></ul><ul><li>Three cascade amplifier have power gains of 5,2, and 17. The input power is 40 mW. What is the output power? </li></ul>
    28. 28. Signal to Noise Ratio (SNR) <ul><li>Ratio of the signal power level to the noise power level. </li></ul><ul><li>Express in logarithmic function: </li></ul>
    29. 29. Example 10 <ul><li>For an amplifier with an output signal power of 10W and an output noise power of 0.01W, determine the SNR. </li></ul><ul><li>For an amplifier with an output signal voltage of 4V, an output noise voltage of 0.005V and an input and output resistance of 50 Ω , determine the SNR. </li></ul>
    30. 30. Noise Factor (F) and Noise Figure (NF) <ul><li>Figures of merit used to indicate how much the SNR deteriorates as a signal passes through a circuit. </li></ul><ul><li>Noise factor is simply a ratio of input SNR to output SNR. </li></ul>
    31. 31. Cont.. <ul><li>NF is noise factor stated in dB. </li></ul><ul><li>Used to indicate the quality of a receiver. </li></ul>
    32. 32. Ideal Noiseless Amplifier Ideal Noiseless Amplifier Ap=power gain Figure 6.11
    33. 33. Non ideal amplifier Nonideal amplifier Ap=power gain Nd=internally generated noise Figure 6.12
    34. 34. Example 11 <ul><li>For a nonlinear amplifier and the following parameter, determine: </li></ul><ul><li>a) Input SNR(dB) </li></ul><ul><li>b) Output SNR(dB) </li></ul><ul><li>c) Noise Factor and Noise Figure </li></ul><ul><li>Input signal power=2x10 -10 W </li></ul><ul><li>Input Noise power=2x10 -18 W </li></ul><ul><li>Power gain=1,000,000 </li></ul><ul><li>Internal noise (Nd)=6x10 -12 W </li></ul>
    35. 35. Noise Figure of Cascaded Amplifier Ap1 NF1 Ap2 NF2 Ap3 NF3 Input Output Figure 6.13
    36. 36. Cont.. <ul><li>Total noise factor is the accumulation of the individual noise factor. </li></ul><ul><li>Friiss’s formula is used to calculate the total noise factor of several cascaded amplifiers. </li></ul>
    37. 37. Example 12 <ul><li>For 3 cascaded amplifier stages, each with noise figure of 3 dB and power gain of 10 dB, determine the total noise figure. </li></ul>
    38. 38. Equivalent Noise Temperature (T e ) <ul><li>Hypothetical value that cannot be directly measured. </li></ul><ul><li>To indicates the reduction in the SNR a signal undergoes as it propagates through a receiver. </li></ul><ul><li>The lower Te is the better quality of a receiver. </li></ul>
    39. 39. Example 13 <ul><li>Determine: </li></ul><ul><li>Noise Figure for an equivalent noise temperature of 75K. </li></ul><ul><li>Equivalent noise temperature for a noise figure of 6dB. </li></ul>
    40. 40. Example 14 <ul><li>A voltage divider shown in Figure 6.9 has values of R 1 = 10k  and R 2 = 47k  . </li></ul><ul><ul><li>What is the attenuation? </li></ul></ul><ul><ul><li>What amplifier gain would you need to offset the loss for an overall gain of 1? </li></ul></ul>
    41. 41. Example 15 <ul><li>An amplifier has gain of 45,000, which is too much for the amplification. With an input voltage of 20  V, what attenuation factor is needed to keep the output voltage from exceeding 100mV?. Let A 1 = amplifier gain = 45,000; A 2 = attenuation factor; A T = total gain. </li></ul>
    42. 42. Example 16 <ul><li>A RF sine wave generator whose output impedance is 50  is connected to a 50  load using 50  coaxial cable. The generator’s output amplitude level is set to + 3 dBm. An rms voltmeter is used to measure the effective voltage, and an oscilloscope is used to display the sine wave. Compute the following: </li></ul><ul><ul><li>The rms voltage measure by the rms voltmeter </li></ul></ul><ul><ul><li>The peak voltage, V p of the sine wave that should be displayed on the oscilloscope. </li></ul></ul><ul><ul><li>The peak-to-peak voltage, V p-p of the sine wave that should be displayed on the oscilloscope </li></ul></ul>
    43. 43. Example 17 <ul><li>The input signal to a telecommunications receiver consists of 100  W of signal power and 1  W of noise power. The receiver contributes an additional 80  W of noise, N D , and has a power gain of 20 dB. Compute the input SNR, the output SNR and the receiver’s noise figure. </li></ul>

    ×