ABSTRACT
One of the most frequent causes of noise in a conductor is the random movement of electrons due to their finite temperature, resulting in a certain noise power. This chapter discusses the noise behaviour of the bipolar transistor, the unipolar or the field effect transistor (FET) and the diode. Flicker noise is roughly inversely proportional to frequency and starts to be of importance at 1 kHz in both junction FETs and bipolar transistors. As can be seen from the following equation the equivalent noise voltage increases as frequency is decreased. The characteristics show the equivalent voltage noise and the equivalent current noise behaviour versus frequency. As said already, these noise measurements can be performed by measuring the output of the amplifier’s stage with the input terminals short circuited, giving the noise voltage, or ‘open circuited’, giving the noise current, and dividing both measured quantities by the gain of the amplifier.
