ABSTRACT
Noise is an important problem in science and engineering because it degrades the accuracy of any measurement and the quality of electronically processed signals. To understand and minimize these effects, one must measure this noise simply and accurately. Perhaps the two most commonly encountered types of noise are thermal noise and shot noise. Thermal noise arises from the random velocity fluctuations of the charge carriers (electrons and/or holes) in a resistive material. The mechanism is sometimes said to be Brownian motion of the charge carriers due to the thermal energy in the material. Thermal noise is present when the resistive element is in thermal equilibrium with its surroundings, and it is often referred to as Johnson noise (or Nyquist noise) in recognition of two early investigators of this phenomenon (1, 2). Thermal noise is usually represented by the equation
where k is Boltzmann’s constant (1.38×10−23J/K), R is the resistance of the conductor, T is the absolute temperature, and Sv is the voltage noise power spectral density.
