RF Power Amplifier, 2nd Edition

12.20 Noise in Oscillators

12.20.1 Thermal Noise

There are different kinds of electrical noise: thermal noise, shot noise, flicker noise ( noise), burst noise, and avalanche noise. A shot noise is caused by random fluctuations of charge carriers in semiconductor devices. A metallic resistor 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 K, 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 . 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 ...