Electronics Noise Analysis
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Questions and Answers

What does Johnson's Formula calculate?

  • Average noise power
  • Voltage drop across a resistor
  • Rms noise voltage (correct)
  • Thermal resistance

    • Which of the following is NOT a variable in Johnson's Formula?

  • Boltzman's Constant
  • Resistance
  • Bandwidth
  • Temperature in Celsius (correct)

    • What is the value of Boltzman's Constant used in noise calculations?

  • 1.38 x 10^-23 Kelvin (correct)
  • 2.88 x 10^-23 Joule
  • 1.60 x 10^-23 Joule
  • 1.28 x 10^-23 Kelvin

    • How can you convert Celsius to Kelvin?

    <p>T_K = T_C + 273</p> Signup and view all the answers

    Which formula expresses the relationship for averaging noise power?

    <p>P_n = kTB</p> Signup and view all the answers

    Shot noise is directly proportional to which of the following?

    <p>Amount of DC bias</p> Signup and view all the answers

    What does the formula for the rms noise current 𝑰𝒏 represent?

    <p>The relationship between charge, current, and bandwidth</p> Signup and view all the answers

    Which of these temperature scales can directly impact noise calculations?

    <p>All of the above</p> Signup and view all the answers

    What type of noise is characterized by its strength at lower frequencies, generally below a few kHz?

    <p>Flicker Noise</p> Signup and view all the answers

    What characteristic is true about shot noise?

    <p>Contains all frequencies and amplitudes</p> Signup and view all the answers

    In calculating the Signal-to-Noise Ratio (SNR), which of the following ratios may be used?

    <p>$ rac{P_s}{P_n}$</p> Signup and view all the answers

    What does Noise Figure (NF) express in terms of Noise Ratio (NR)?

    <p>The ratio of input SNR Power to output SNR Power in decibels</p> Signup and view all the answers

    Which factor is crucial for cascaded stages of amplifiers according to Friis' formula?

    <p>Individual noise ratios of each amplifier stage</p> Signup and view all the answers

    What does a higher Signal-to-Noise Ratio (SNR) indicate about a communication system?

    <p>The system has a better quality signal relative to noise</p> Signup and view all the answers

    In the formula for overall noise performance 𝑵𝑹𝑻, what do the denominators represent?

    <p>Gain values of the amplifiers</p> Signup and view all the answers

    Which component is NOT included in the calculation of the rms noise current 𝑰𝒏?

    <p>Temperature</p> Signup and view all the answers

    What type of noise is classified as produced by sources in space?

    <p>Extraterrestrial Noise</p> Signup and view all the answers

    Which of the following options is an example of industrial noise?

    <p>Turned on electric motors creating transients</p> Signup and view all the answers

    Thermal noise is often referred to as what?

    <p>White noise</p> Signup and view all the answers

    What is the primary source of extraterrestrial noise?

    <p>Radiation from the sun</p> Signup and view all the answers

    Which type of noise comes from electrical disturbances in the earth's atmosphere?

    <p>Atmospheric Noise</p> Signup and view all the answers

    What condition must be satisfied for proper amplitude modulation to occur?

    <p>The amplitude of the modulating signal must be less than that of the carrier signal.</p> Signup and view all the answers

    What represents the instantaneous value of the information signal in amplitude modulation?

    <p>$v_m$</p> Signup and view all the answers

    What is the relationship between the carrier frequency and the modulating frequency in amplitude modulation?

    <p>The carrier frequency is always greater than the modulating frequencies.</p> Signup and view all the answers

    What occurs if the amplitude of the modulating signal exceeds that of the carrier signal?

    <p>Distortion will occur.</p> Signup and view all the answers

    In the equation $v_m = V_m ext{sin}(2 ext{pi} f_m t)$, what does $f_m$ represent?

    <p>Frequency of the modulating signal.</p> Signup and view all the answers

    What expression defines the instantaneous value of the carrier sine wave voltage?

    <p>$v_c = V_c ext{sin}(2 ext{pi} f_c t)$</p> Signup and view all the answers

    Which parameter is NOT a part of the amplitude modulation process?

    <p>Phase modulation index.</p> Signup and view all the answers

    What is a modulation technique that varies the amplitude of a carrier signal called?

    <p>Amplitude Modulation</p> Signup and view all the answers

    What does the modulation index (m) represent when computed from Vmax and Vmin?

    <p>The amplitude variation in an amplitude-modulated signal</p> Signup and view all the answers

    Which formula correctly computes the upper sideband frequency (fUSB)?

    <p>fUSB = fc + fm</p> Signup and view all the answers

    How are sidebands related to the carrier frequency?

    <p>They are generated at frequencies that are deviations from the carrier frequency</p> Signup and view all the answers

    What characteristic is essential for avoiding interference between signals using modulation?

    <p>Translating signals to new frequencies</p> Signup and view all the answers

    Which statement accurately describes sidebands in the frequency domain?

    <p>They lie directly above and directly below the carrier frequency</p> Signup and view all the answers

    What does the vertical axis of a frequency domain representation indicate?

    <p>Magnitude of the signals, often in voltage or power amplitude</p> Signup and view all the answers

    Which of the following frequencies represents the lower sideband (fLSB)?

    <p>fLSB = fc - fm</p> Signup and view all the answers

    What is the peak value of the modulating signal (Vm) used in calculating the modulation index?

    <p>The difference between Vmax and Vmin</p> Signup and view all the answers

    Study Notes

    Johnson's Formula for Noise Voltage

    • Open-circuit noise voltage across a resistor calculated by Johnson's Formula: 𝑽𝒏 = √𝟒𝒌𝑻𝑩𝑹.
    • Parameters:
      • 𝑽𝒏 = rms noise voltage
      • 𝑘 = Boltzmann’s Constant (1.38 x 10⁻²³ K)
      • 𝑻 = temperature in Kelvin (ᵒC + 273)
      • 𝑩 = bandwidth in Hertz
      • 𝑹 = resistance in ohms (Ω).

    Thermal Noise Power Calculation

    • Thermal noise power given by: 𝑷𝒏 = 𝒌𝑻𝑩.
    • Average noise power (𝑷𝒏) is essential for assessing thermal noise in circuits.

    Temperature Conversion Formulas

    • Common temperature scales: Fahrenheit (ᵒF), Celsius (ᵒC), Kelvin (K).
    • Conversion formulas:
      • Celsius from Fahrenheit: 𝑻𝒄 = 5(𝑻𝑭 - 32) / 9.
      • Fahrenheit from Celsius: 𝑻𝑭 = (9𝑻𝒄 / 5) + 32.
      • Kelvin from Celsius: 𝑻𝑲 = 𝑻𝒄 + 273.

    Shot Noise Characteristics

    • Shot noise is a type of white noise containing a wide range of frequencies.
    • Proportional to the DC bias flowing in a device, leading to maximum output power and voltage with minimal distortion.

    Modulation Index in AM Signals

    • Modulation index (m) computed using AM signal values:
      • 𝑚 = (𝑉𝑚𝑎𝑥 - 𝑉𝑚𝑖𝑛) / (𝑉𝑚𝑎𝑥 + 𝑉𝑚𝑖𝑛).

    Sidebands and Modulation

    • Sidebands are frequencies generated when a carrier is modulated, occurring above and below the carrier frequency.
    • Upper sideband frequency: 𝒇𝑼𝑺𝑩 = 𝒇𝑐 + 𝒇𝒎; Lower sideband frequency: 𝒇𝑳𝑺𝑩 = 𝒇𝑐 − 𝒇𝒎.
    • Modulation enables frequency translation, preventing signal interference.

    rms Noise Current Calculation

    • rms noise current (𝑰𝒏) calculated as: 𝑰𝒏 = √𝟐𝒒𝑰𝑩.
    • 𝑞 = charge on an electron (1.6 x 10⁻¹⁹ C), 𝑰 = direct current in Amperes, 𝑩 = bandwidth in Hertz.

    Types of Noise

    • Transmit-time Noise: Delay of current carriers from input to output.
    • Flicker Noise: Dominates at low frequencies (below a few kHz), increases spectral density as frequency decreases.

    Signal-to-Noise Ratio (SNR)

    • Measures the strength of signal in comparison to noise in communication systems.
    • Computed using voltage or power values:
      • 𝑆𝑁𝑅 = 𝑉𝑠 / 𝑉𝑛 or 𝑆𝑁𝑅 = 𝑃𝑠 / 𝑃𝑛.

    Noise Factor and Noise Figure

    • Noise Factor (NR): 𝑁𝑅 = 𝑆𝑁𝑅 𝑖𝑛𝑝𝑢𝑡 / 𝑆𝑁𝑅 𝑜𝑢𝑡𝑝𝑢𝑡.
    • Noise Figure (NF): Expressed in dB as: 𝑁𝐹 = 10 log(𝑁𝑅).
    • Overall Noise Performance for cascaded stages computed using Friis’ formula.

    Amplitude Modulation Concepts

    • Modulation is key for effective information transmission.
    • Modulating signal represented as: 𝑣𝑚 = 𝑉𝑚 sin(2𝜋𝑓𝑚𝑡).
    • Carrier frequency expressed as: 𝑣𝑐 = 𝑉𝑐 sin(2𝜋𝑓𝑐𝑡).
    • Amplitude of the modulating signal must be less than the carrier amplitude to avoid distortion (𝑉𝑚 < 𝑉𝑐).

    External Noise Sources

    • External noise classifications: industrial, atmospheric, and extraterrestrial noise.
    • Industrial noise emits from equipment like motors and generators.
    • Atmospheric noise often results from environmental phenomena like lightning.
    • Extraterrestrial noise encompasses signals from solar and cosmic sources.

    Internal Noise Characteristics

    • Generated by electronic components, such as resistors and transistors.
    • Thermal noise arises from random motion of electrons due to heat, often referred to as white noise.

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    Description

    Explore Johnson's Formula for calculating noise voltage across a resistor. This quiz will test your understanding of the relationship between temperature, bandwidth, and noise in electronic circuits. Perfect for students of electrical engineering and physics.

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