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?

T_K = T_C + 273 Signup and view all the answers

Which formula expresses the relationship for averaging noise power?

P_n = kTB Signup and view all the answers

Shot noise is directly proportional to which of the following?

Amount of DC bias Signup and view all the answers

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

The relationship between charge, current, and bandwidth Signup and view all the answers

Which of these temperature scales can directly impact noise calculations?

All of the above Signup and view all the answers

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

Flicker Noise Signup and view all the answers

What characteristic is true about shot noise?

Contains all frequencies and amplitudes Signup and view all the answers

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

$rac{P_s}{P_n}$ Signup and view all the answers

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

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

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

Individual noise ratios of each amplifier stage Signup and view all the answers

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

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

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

Gain values of the amplifiers Signup and view all the answers

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

Temperature Signup and view all the answers

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

Extraterrestrial Noise Signup and view all the answers

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

Turned on electric motors creating transients Signup and view all the answers

Thermal noise is often referred to as what?

White noise Signup and view all the answers

What is the primary source of extraterrestrial noise?

Radiation from the sun Signup and view all the answers

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

Atmospheric Noise Signup and view all the answers

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

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

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

$v_m$ Signup and view all the answers

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

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

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

Distortion will occur. 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?

Frequency of the modulating signal. Signup and view all the answers

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

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

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

Phase modulation index. Signup and view all the answers

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

Amplitude Modulation Signup and view all the answers

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

The amplitude variation in an amplitude-modulated signal Signup and view all the answers

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

fUSB = fc + fm Signup and view all the answers

How are sidebands related to the carrier frequency?

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

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

Translating signals to new frequencies Signup and view all the answers

Which statement accurately describes sidebands in the frequency domain?

They lie directly above and directly below the carrier frequency Signup and view all the answers

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

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

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

fLSB = fc - fm Signup and view all the answers

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

The difference between Vmax and Vmin 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.