12.20 Noise in Oscillators

12.20.1 Thermal Noise

There are different kinds of electrical noise: thermal noise, shot noise, flicker noise (c12-math-1272 noise), burst noise, and avalanche noise. A shot noise is caused by random fluctuations of charge carriers in semiconductor devices. A metallic resistor c12-math-1273 is a source of thermal noise. Figure 12.90 shows two equivalent sources of thermal noise: a voltage source and current source. The spectrum of thermal noise is uniform, called white noise, as illustrated in Fig. 12.91. At ambient temperature c12-math-1274K, resistors contain free electrons, which move randomly in different directions with different velocities and experience collisions. Thermal noise (also called Johnson noise [2], Nyquist noise [3], or Johnson–Nyquist noise) is caused by the random motion of charge carriers in a resistor due to thermal agitation, with a kinetic energy that is proportional to the temperature c12-math-1275. These motions are called Brownian motions of free electrons. Random statistical fluctuations of electrons cause the existence of transient differences in electron densities at the two terminals ...

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