5.3 Electronic Noise Analysis in Basic Circuits

In this section we will switch our attention back from components to circuits and systems. Circuit analysis of circuits that contain noise sources differs fundamentally from the usual one due to the specific nature of the noise sources. Namely, what we know is the noise power generated within the components, while for circuit analysis we need voltages and currents. To that end we use square roots of power supposed to be developed on a resistor of unity resistance. These sources (roots of power) may get both signs mathematically speaking. Since that is not possible in the circuit representation, we use multiple analyses each one for every single noise source. The very procedure is simplified by use of the superposition theorem in a specific way. Ultimately, the obtained representation of the noise sources at the output is first converted into powers and then added. It seems rather complicated which is why, in this chapter, we will elaborate the method on a set of simple circuits gathering knowledge at the same time on the noise properties of these circuits. When considering BJT and JFET noise, in the previous chapter we already established the general properties of the basic CE and CS amplifiers, respectively, from the noise point of view. Here we will discuss the situation of a CS amplifier withDegenerated emitter degenerated sourceDegenerated source and a CE amplifier with degenerated emitter. Then we will go for the CC, CD, CB, CG, and the bipolar differential amplifier. Special attention will be paid to the noise analysis of the current mirror. Models of monolithic amplifiers seen as a single component will be introduced, and their implementation to the simplest amplifiers with feedback based on the monolithic circuits will be elaborated.