Before going further, let's answer the following question:
For many electronic engineers, it is the nightmare branch of electronics...
For others it is what they like, at work and often at home too...
Often, definitions of analog electronics is very personal, very affective.
For the author, and for the sake of clarity:
Analog electronics is the branch of electronics in which electrical signals representing data can have an a priori unlimited number of significant values.
In contrast digital electronics is the branch of electronics in which electrical signals representing data have a limited number of significant values.
In electronic circuits, electrical signals interact with components and generate other electrical signals. Let's simplify a bit and consider a simple circuit with just one input and one output. The output signal characteristics depend on:
The circuit characteristics divide in two groups:
It is then very difficult and sometimes impossible for an analog circuit to know whether a change in the output signal results from a change in the input signal or from a change in the circuit characteristics.
If an analog circuit is properly designed and implemented, the output signal depends mainly on the input signal, the circuit itself introduces limited signal distortions and adds minor parasitic.
The circuit must then be designed and implemented in such a way that changes in circuit parameters have a minor impact on the output signal and that noise and parasitic signals are kept to an acceptable level.
As a consequence, the influence of circuit parameters on the output signal must be analyzed carefully and circuit must be optimized until the target specification is met whatever the parameters inside their specified tolerances and whatever the environment conditions within specifications.