What is called a thermal noise
Thermal noise, also known as Johnson-Nyquist noise, is a type of noise that arises from the random thermal motion of electrons inside an electrical conductor. It is a fundamental form of noise in electronic systems and circuits, and it occurs across a wide range of frequencies.
Key Characteristics of Thermal Noise:
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Origin: Thermal noise is caused by the random thermal motion of charge carriers (electrons) in conductors, such as wires, resistors, and other electronic components. These charge carriers move randomly due to thermal energy, creating fluctuating electrical signals.
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Frequency Dependence: The power spectral density of thermal noise is approximately flat across a wide range of frequencies, meaning it has equal power per unit bandwidth. This characteristic makes it a significant consideration in both low-frequency and high-frequency electronic systems.
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Amplitude and Power: The amplitude of thermal noise increases with temperature and bandwidth. It is quantified by its root mean square (RMS) voltage or current, which depends on the resistance and temperature of the conductor.
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Impact on Systems: Thermal noise affects the performance of electronic devices and systems in several ways:
- In communication systems, it sets a lower limit on the smallest signals that can be reliably detected.
- In analog circuits, it can degrade the signal-to-noise ratio (SNR) and limit the accuracy of measurements.
- In digital systems, it can affect the reliability of data transmission and reception, especially at low signal levels.
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Mitigation: Engineers employ various techniques to mitigate the effects of thermal noise, such as using low-noise components, cooling circuits to reduce temperature, and employing signal processing techniques to filter or suppress noise.
Example:
In an electrical circuit, a resistor at room temperature generates thermal noise. The noise voltage VnV_nVn? across the resistor can be approximated by:
Vn=4kBTRΔfV_n = \sqrt{4 k_B T R \Delta f}Vn?=4kB?TRΔf?
where:
- kBk_BkB? is the Boltzmann constant,
- TTT is the absolute temperature in Kelvin,
- RRR is the resistance of the resistor,
- Δf\Delta fΔf is the bandwidth over which the noise is measured.
Thermal noise is an unavoidable phenomenon in electronic systems and plays a critical role in their design and performance, particularly in sensitive applications where low noise levels are essential.
