dB - Noise

dB OPERATIONS and NOISEdB OPERATIONS and NOISE

ENGR. CARLO ROMEROENGR. CARLO ROMERO

DECIBEL

A means of expressing change in

power level

Comparison of two powers and

does not express a fixed value unless it

refers to dB above or below some specific

reference point

dB CALCULATIONSdB CALCULATIONS

Change in POWER expressed in Decibels

PdB = 10 log (Pout/Pin)

Change in VOLTAGE expressed in Decibels

VdB = 20 log Vout/Vin ;

(if R2=R1)

Change in CURRENT expressed in Decibels

IdB = 20 log Iout/Iin ;

(if R2=R1)

dB CALCULATIONSdB CALCULATIONS

dBk = 10 log (Plevel/1x103 W)

dBw = 10 log (Plevel/1 W)

dBm = 10 log (Plevel/1x10-3 W)

dBu = 10 log (Plevel/1x10-6 W)

dBn = 10 log (Plevel/1x10-9 W)

dBp = 10 log (Plevel/1x10-12 W)

dBf = 10 log (Plevel/1x10-15 W)

POWER with RESPECT to SPECIFIC POWER with RESPECT to SPECIFIC REFERENCE POWER LEVELREFERENCE POWER LEVEL

1. How much in decibels is 125 W larger than 45 W?a. 2. 78 dBb. 4.44 dBc. 27.8 dBd. 44.4 dB

SAMPLE QUESTIONSSAMPLE QUESTIONS

2. Determine the attenuation in decibels for the attenuator having an input power of 100mW and an output power of 3.5 mW.a. 0.035 dBb. -1.46 dBc. 14.6 dBd. -14.6 dB

3. Express 38 dB as a voltage ratio.a. 6309b. 79.43c. 158.87d. 63.09


4. Express 425 mW as dBm.a. 2.63 dBm

b. 26.3 dBm

c. -2.63 dBm

d. -26.3 dBm

dB1 + dB2 = dBT

dB + dBm = dBm

dB + dBu = dBu

dB + dBk = dBk

dBm1 + dBm2

dBw1 + dBw2

dBk + dBw

dB OPERATIONSdB OPERATIONS

Invalid operation

Note: convert power levels into watts and

perform the operation

1. What is the power output of a 3-stage amplifier having gains equalto 25 dB, -35 dB and 50 dB respectively, if the input power is 10 mW?a. 100 Wb. 100 mWc. 10 Wd. 10 mW


2. The input to a three-stage system is -12 dBm. The power gain of the first stage is 40 dB, for the second stage a loss of 35 dB, and for the third stage, a gain of 25 dB. What is the power output in dBm?a. -18 dBm

b. 18 dBm

c. 36 dBm

d. -36 dBm

3. What is the difference between -18 and 22 dBm?a. 40 dBb. 40 dBm

c. 4 dBd. 4 dBm


Power can also be defined in terms of the natural

logarithm to the base e=2.718281828.

PNeper = ½ ln (Pout/Pin)

1 Neper = 8.686 dB ; 1 dB = 0.1151 Neper

POWER EXPRESSED in POWER EXPRESSED in NEPERSNEPERS

When defined as the natural logarithm, the unit is

Neper.

1. The correct symbol for decibel?a. DBb. dBc. dbd. Db

REVIEW QUESTIONSREVIEW QUESTIONS

2. A voltage change that is equal to twice its original value corresponds to a change ofa. 3 dBb. 6 dBc. 9 dBd. 30 dB


3. Which of the following is not an actual amount of power?a. dBb. dBm

c. dBw

d. dBk

4. What does a power difference of – 3 dB mean?a. a loss of one third of the powerb. a loss of one-half of the powerc. a loss of 3 watts of powerd. a noise figure value of 3

5. A gain of 60 dB is the same as a gain ofa. 10 volts/voltb. 100 volts/voltc. 1000 v/vd. 10000 v/v


6. A network has a loss of 20 dB. What power ratio corresponds to this loss?a. 0.01b. 0.1c. 10d. 100


7. The input current of a network is 190 uA and the output is 1.3 uA. The loss in dB isa. 20.2b. 21.6c. 28.6d. 43.3

8. What is the gain in dB if the output to input ratio is 1000.a. 20b. 30c. 40d. 10

9. What is the equivalent output of a circuit in dBm if it has an output of 10 watts?a. 10 dBm

b. 30 dBm

c. 20 dBm

d. 40 dBm


10. If four networks connected in series have gains of -0.5 dB, -0.3 dB, -2 dB and 6.8 dB, the overall gain isa. 2 dBb. – 2 dBc. 4 dBd. – 4 dB


11. Determine the attenuation in dB for the attenuator having an input power of 100 mW and an output power of 3.5 mW.a. 0.035 dBb. – 1.46 dBc. 14.56 dBd. – 14.56 dB

12. If you have available number of power amplifiers with a gain of 100 each, how many such amplifiers do you need to cascade to give an overall gain of 60 dB?a. 20b. 3c. 4d. 5


13. A network has an input of 75 dB and an output of 35 dB. The loss of the network isa. – 40 dBb. 40 dBc. 40 dBm

d. – 40 dBm

14. The input is 0.1 W and the network gain is 13 dB, the output isa. 2 Wb. 2.5 Wc. 1.5 Wd. 1.8 W

15. The input is 1 W and the network loss is 27 dB, the output isa. 1 nWb. 3 mWc. 2 mWd. 4 mW


16. A combiner has two inputs of +30 dBm each, what is the resultant output?a. 36 dBm

b. 30 dBm

c. 60 dBm

d. 33 dBm

17. The input power to a loss free cable is 5 W. If the reflected power is 7 dB down on the incident power, the output power to the load isa. 4 Wb. 5 Wc. 6 Wd. 7 W


18. If an electronic network has an input of 40 W and an output of 40 W, the gain isa. 0 dBb. 1 dBc. 6 dBd. 12 dB

19. A filter has a voltage gain of -12 dB. If the input voltage is 48 volts, the output voltage isa. 8 voltsb. 10 voltsc. 12 voltsd. 24 volts


20. A theoretical antenna has a gain of 1 dB. It’s gain in nepers isa. 8.686b. 0.1151c. 6.868d. 0.5111

NOISENOISE

Any unwanted form of electrical energy, usually random or aperiodic in character,

which tends to interfere with the proper and easy reception and reproduction of

transmitted signals.

DISTORTION and DISTORTION and INTERFERENCEINTERFERENCE

Any waveform perturbation or

deviation caused by the

imperfect response of the system to the desired signal

Contamination by extraneous or

external signals from human

sources, other transmitters, power

lines, machinery, switching circuits,

and related sources

DISTORTION INTERFERENCE

RESULTS OF NOISERESULTS OF NOISE

hiss - loudspeakers

snow or confetti – TV CRT

bit error – digital transmission

GENERAL CATEGORIES GENERAL CATEGORIES of NOISEof NOISE

CORRELATED NOISE

unwanted electrical energy that is

present as a direct result of a signal, such as harmonic

and intermodulation distortion.

noise present regardless of

whether there is a signal or none.

UNCORRELATED NOISE

CORRELATED NOISECORRELATED NOISE

unwanted multiples of a

single frequency created when

amplified in non-linear device

% THD = Vhigher/Vfundamental

HARMONIC DISTORTION

unwanted cross-product (sum and

difference) frequencies

created when two or more signals are amplified in a non-

linear device.

INTERMODULATION DISTORTION

UNCORRELATED UNCORRELATED NOISENOISE

noise created outside the receiver and

allowed to enter the circuit

noise created within the receiver or the device.

EXTERNAL

INTERNAL

EXTERNAL NOISEEXTERNAL NOISE

caused by lightning discharges in thunderstorms

and other natural electric disturbances occurring in the

atmosphere.

ATMOSPHERIC NOISE (STATIC)

less severe at frequencies above 30 MHz


Severe at 10 MHz – 1.45 GHz

EXTRATERRESTRIAL NOISE (SPACE NOISE)

Constant noise radiation from the sun (6000°C). Due to

electrical disturbances due to solar cycle activities that

repeat every 11 years and supercycles every 99 years

SOLAR NOISE

EXTRATERRESTRIAL EXTRATERRESTRIAL NOISENOISE

EXTRATERRESTRIAL EXTRATERRESTRIAL NOISENOISE

Noise radiated from distant stars and

other heavenly bodies

COSMIC NOISE (THERMAL, BLACKBODY, GALACTIC)


Noise coming from automobile and aircraft ignition, electric

motors and switching equipment, fluorescents, leakage from high voltage lines and a multitude of other heavy electric machines.

INDUSTRIAL NOISE (MAN MADE NOISE)

Severe at 15 – 160 MHz

INTERNAL NOISEINTERNAL NOISE

White, Gaussian, Johnson Noise

THERMAL AGITATION NOISE

Due to the rapid and random motion of the molecules, atoms and electrons of which

any component (resistor) made of.


Noise Power Pn=kTB

Noise Voltage Vn=√4kTBR

R

Vn


RIn

Noise Current In=√4kTBG


Noise Bandwidth and Noise Voltage of RC Network

Bn = 1/4RC fc=1/2piRC

Vn = √(kT/C)

R

Vn

C

1. An amplifier operating over a 4 MHz BW has a 100 ohm input resistance and is operating at 300 deg K. Determine the noise power generated.a. 1.656 x 10 exp -13 Wb. 16.56 fWc. 1656 nWd. 1.656 pW


2. An amplifier with an input resistance of 1000 Ω is operating over a 4 MHz bandwidth. Calculate the rms noise voltage if the amplifier is operating at 27 C.a. 8.14 nVb. 8.14 uVc. 6.6 nVd. 6.6. uV

3. Determine the equivalent noise bandwidth for a single RC low pass filter if R = 20 kΩ and C = 0.1uF.a. 125 Hzb. 250 Hzc. 125 MHzd. 250 MHz



Random variations in the arrival of electrons (or holes) at the

output electrode of an amplifying device

SHOT NOISE

When amplified, it is supposed to sound as though a shower of lead

shot were falling on a metal sheet.

in=√(2eipB)

1. Determine the noise current for a diode with a forward bias of 3.5 mA over a 100 kHz BW.a.10.58 nAb. 0.335 nAc. 21.2 nAd. 5.6 nA


2. Determine the open circuit noise current in 1 Hz of bandwidth at 290 K for a diode biased at 1mA.a. 1.78 pAb. 17.88 pAc. 1.78 nAd. 17.88 nA


High frequency noise resulting from delayed travel of electrons from emitter-collector of

a vacuum tube or transistor

TRANSIT TIME NOISE

a. FLICKER NOISE (MODULATION NOISE, PINK NOISE)

MISCELLANEOUS MISCELLANEOUS NOISENOISE

Low frequency noise from carrier density fluctuations. It is

proportional to emitter current and junction temperature, inversely proportional to

frequency (negligible above 500 Hz)

b. RESISTANCE NOISE

Due to the base (greatest contributor), emitter and

collector internal resistance


c. NOISE in MIXERS

Low transconductance of mixers compared to amplifiers and inadequate image frequency

rejection.

d. CROSSTALK

Interference signal from one channel to another


e. AVALANCHE NOISE

Large noise spikes due to collision that result in

avalanching action

f. BURST NOISE (POP-CORN)

Low frequency noise observed in BJT which appears as a series of burst of

two or more levels.

g. PARTITION NOISE

Random fluctuations in the division of current in two or more electrodes.



h. IMPULSE NOISE

Non-continuous, consisting of irregular pulses or noise spikes of

short duration and of relatively high amplitude. The spikes are

called HITS.

NOISE ANALYSIS and NOISE ANALYSIS and CALCULATIONSCALCULATIONS

ADDITION of NOISE due to SEVERAL SOURCES:

Vn total = √4kTBRt

RESISTORS IN SERIES:

Rt = R1 + R2 + R3 + . . .

RESISTORS IN PARALLEL:

Rt = 1/(1/R1 + 1/R2 + 1/R3 + . . .)


ADDITION of NOISE due to

SEVERAL AMPLIFIERS in CASCADE:

R1Vn1

R2

Vn2

R3

Vn3

A1 A2

When a noise resistance is transferred from the output of a stage to its input, it must be divided by the square of the voltage gain of that particular stage.


ADDITION of NOISE due to SEVERAL AMPLIFIERS in CASCADE:

Vn total = √4kTBReq

Req = equivalent noise resistance as referred to the input

Req = R1 + R2/A12 + R3/A1

2 A22

1. Two resistors, 20 KΩ and 50 kΩ at ambient temperature. Calculate, for a bandwidth equal to 100 kHz, the thermal noise voltage for the two resistors connected in parallel.a. 0.4782 uVb. 4278 uVc. 4.78 uVd. 47.8 uV


2. Calculate the noise voltage at the input of a TV RF amplifier using a device that has a 200-Ω equivalent noise resistance and a 300-Ω input resistor. The bandwidth of the amplifier is 6 MHz and the temperature is 17 C.a. 6.93 nAb. 6.93 uAc. 69.3 nAd. 69.3 uA

3. The resistor R1 and R2 are connected in series at 300 degrees K and 400 degrees K temperature respectively. If R1 is 200 ohms and R2 is 300 ohms, find the power produced at the load (Rl = 500 ohms) over a bandwidth of 100 KHz.a. 0.496 pico Watts b. 0.816 femto Wattsc. 620 Wattsd. 914 Watts


3. Two resistors in series (R1= 50 ohms T1 = 350 Kelvin and R2= 100 ohms T2= 450 K) Determine the total noise voltage, over a bandwidth of 120 KHz

a.643.4 nvb.123.5 nvc.173.6 nvd.785.5 nv


4. A mixer with input resistance of 300 ohms has equivalent noise resistance of 100 ohms. What is the noise voltage at the input when the effective noise bandwidth is 25 KHz, the source voltage is 2 micro volts and with internal resistance of 20 ohms?

a.0.218 micro voltsb.0.318 micro voltsc.0.418 micro voltsd.0.518 micro volts


SIGNAL-to-NOISE RATIO (S/N)

S/N = (signal voltage/noise voltage)2

= (Vs/Vn)2 ; voltage ratio

S/N = (signal power/noise power)

= (Ps/Pn) ; power ratio

Relative strength of the signal power to the noise power at the same point


NOISE FACTOR (F) and NOISE FIGURE (NF)

The figure of merit that indicates the degradation in the signal-to-noise ratio

as the signal propagates through an amplifier or a communications system.


a. NOISE FACTOR from SIGNAL to NOISE RATIO

F = (input S/N) / (output S/N)

NFdB = 10 log F


b. NOISE FACTOR from EQUIVALENT NOISE RESISTANCE


Ra

Vn

RtVi Rt Vo

Av

Amplifier (receiver)Generator (antenna)

F = 1 + (Req’/Ra) Req’ = Req - Rt

c. Noise Factor in Terms of Equivalent Noise Temperature

F = 1 + (Teq/T0)

Teq = T0 (F – 1)


1. The signal in a channel is measured to be 23 dB while noise in the same channel is measured to be 9 dB. The signal to noise ratio isa. 9/23b. 23/9c. 32 dBd. 14 dB


2. What is the S/N at the output of an amplifier whose F = 10 dB and the input S/N = 25 dB?a. 35 dBb. 15 dBc. 25 dBd. 10 dB

3. The equivalent noise temperature of the amplifier is 25 K. What is the noise figure?a. 10.86b. 1.086c. 0.1086d. 1.86


4. A receiver is connected to an antenna whose resistance is 60 Ω has an equivalent noise resistance of 40 Ω. Calculate the receiver’s noise figure in decibel and its equivalent noise temperature.a. 1.67 and 194 Kb. 2.23 and 194 Kc. 1.67 and 174 Kd. 2.23 and 174 K

CARRIER to NOISE RATIO (C/N)

Is the ratio of the wideband carrier to the wideband noise power

The signal-to-noise ratio measured before the signal is demodulated, that

is, while it still has a carrier.


Curve showing the relative interfering effects of sinusoidal tones compared to a

reference frequency

Weighting Curve

Usual reference 1000 Hz at 1 mW applied at a point of 0 relative level

A pure signal at a signal frequency and power level

Test tone

NOISE UNITS and NOISE UNITS and LEVELSLEVELS

The difference between the power of a signal at one point and its power a

reference point

Relative Level

Equalizer which attenuates frequencies in the same manner as would be done by the

average ear with the specific listening apparatus to which the weighting refers.

Weighting Network


1. dBrn (144 Weighting Curve,

Western Electric 144 Handset)

dB above reference noise

Reference level: -90 dBm at 1 kHz (pure

tone)

2. dBa (F1A Weighting Curve, F1A

Handset)dB above reference

noise adjusted


tone)

-82 dBm at 3 kHz (random, white noise)


3. dBrnC (C-Message Weighting Curve, 500 type handset)

dB above reference noise


tone)

4. pWp (pW psophometrically

weighted)

Psophometrically weighted picowatt

Reference level: -90 dBm at 800 Hz

-88 dBm at 3 kHz (random, white

noise)


5. dBaO

dBa adjusted at 0 dBm level point

6. dBrnCO

dBrnC at 0 dBm level point


1. At what power level does a 1 kHz tone cause zero interference, 144 weighted?a. – 90 dBb. – 90 dBm

c. 90 dBm

d. 90 dB


2. What is the reference noise level?a. 10 pWb. 0 dBm

c. 1 mWd. – 90 dBm


3. What is the reference frequency of CCITT psophometric noise measurement?a. 800 Hzb. 1500 Hzc. 3400 Hzd. 1000 Hz

4. A decibel notation relative to a reference noise level.a. dBab. dBpc. dBfd. dBr n

5. 15 dBa F1A weighteda. – 90 dBm

b. – 82 dBm

c. – 85 dBm

d. – 70 dBm


6. The extent of noise referred to a test tone of zero dBm.a. dBab. dBm

c. dBa0d. dbr n C


7. How many dBmV units correspond to a 1 mV signal level?a. 0b. 1c. 3d. 6

1. Any unwanted form of energy that tends to interfere with the wanted signal is calleda. noiseb. spectrumc. radiationd. Absorption


2. The following are characteristics of noise excepta. unwanted energyb. present in the channelc. predictable in characterd. due to any cause

3. The noise created outside the receivera. internalb. externalc. shotd. industrial


4. Noise that is produced by the active components within the receivera. thermalb. externalc. internald. White

5. Noise created by man.a. solarb. industrialc. extra-terrestriald. Galactic


6. The most prevalent noise found in urban areas, and is normally caused by arc discharge from automobile or aircraft ignition systems, induction motors, switching gears, high voltage lines and the like.a. industrialb. Johnsonc. Flickerd. Mixer

7. Noise from distant planets, stars, galaxies, and other celestial objectsa. extra-terrestrialb. atmosphericc. transit timed. thermal


8. Which of the following is not a source of space noise?a. sunb. starsc. lightningd. black body


9. Noise caused by random variations in the arrival of electrons at the output electrode of an amplifying devicea. shotb. randomc. impulsed. transit time

10. Noise that is due to the random and rapid motion of the charge carriers inside a resistive component.a. Johnsonb. Thermalc. Mixerd. Transit time

11. Atmospheric noise is less severe at frequencies abovea. 10 GHzb. 30 MHzc. 1 GHzd. Audio level


12. Indicate the noise whose source is in a category different from that of the other three.a. solarb. cosmicc. atmosphericd. Galactic

13. Which of the following types of noise becomes of great importance at high frequencies?a. shotb. randomc. impulsed. transit time


14. Indicate which of the following does not occur in transistorsa. shotb. partitionc. flickerd. resistance

15. The value of a resistor creating thermal agitation noise is doubled. The noise power generated is thereforea. halvedb. quadrupledc. doubledd. unchanged


16. The noise power generated by a resistor is proportional toa. temperatureb. bandwidthc. a and bd. none of these

17. If bandwidth is doubled, the signal power isa. unchangedb. quadrupledc. tripledd. Doubled


18. In noise analysis, the reference temperature isa. 75 Kb. 250 Kc. 290 Kd. 300 K

20. Which noise figure represents the lowest noise?a. 1.5 dBb. 2 dBmc. 3.7 dBd. 4.1 dB


19. Noise figure for an amplifier with noise is alwaysa. 0 dBb. Infinityc. Less than 1d. Greater than 1


21. The noise figure of a totally noiseless device.a. unityb. infinityc. zerod. 100

Engr. Romero, Engr. Romero,

PROUD TO BE PROUD TO BE KAPUSO.KAPUSO.

dB - Noise

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