What is Analog Logic?

You may have heard of digital logic and 1s and 0s, but have you heard of analog logic?

Unfortunately, it is not a well-known nor well-defined concept. If you search for the term analog circuit logic, you will find a page describing the differences between digital circuit logic and analog circuit logic and differences between analog signals and digital signals. However, the term analog circuit logic is not explicitly defined which is why I am writing this blog post.

I have come up with a definition for analog circuit logic from my experience of learning about analog circuits in university and reading books on it, as well as designing completely analog circuits.

Analog circuit logic is the reasoning and development of manipulation of continuous signals based on the electrical properties of electronic circuit components.

Why is this definition for analog circuit logic valid?

This definition is valid because the words in the definition were chosen to accurately describe what goes on in developing an analog circuit for a purpose.

reasoning, This word was put in the definition because logic includes making inferences and conclusions and proving it with facts and observation.

development, Development was included because a circuit must be produced to justify claims of what the circuit does. Also designing analog circuits involves growth and building upon fundamental circuit blocks.

manipulation, Manipulation was placed in the definition because in analog circuits, signals are controlled, changed, and used for a purpose.

continuous signal, This combination of words was included in the definition because analog circuits process a signal that is not broken in parts unlike digital. These words are included to exclude digital circuit logic and digital circuit components.

electrical properties of electronic circuit components, This is what is used to change the signal. For example, the electrical properties of a transistor make it so that a connection between 2 terminals(points in circuit) is not made unless a sufficient amount of current or voltage is present at input. The signal can be amplified or switched on or off with this property.

Example of analog circuit logic.

In the video above, a challenge from the Jim Williams Analog IQ test is worked through. From 0:30 to 3:00 the analog circuit is explained simply and the explanation fits the definition for analog circuit logic. The explanation included reasoning, development of circuit blocks and components to make a useful item, manipulation of a continuous signal, and the signal manipulation was done based on electrical properties of electronic circuit components such as charging a capacitor to a certain voltage level, and comparing the voltage level of the capacitor with an op-amp.

Unfortunately, analog circuit logic practice is lacking in electronics circuits courses. Typically an application circuit is shown and its parameters are memorized and changed. A challenge to analyze or design a circuit based on known circuit component functions or circuit block functions isn’t given which would really be good practice for real world design work. For example, being challenged to analyze how a voltage to frequency converter circuit works would show the student how each component in its arrangement and component properties works to make something useful.

However, education is one’s own responsibility. Also an analog circuit designer is like a composer, for both it takes practice, experience, hard-work, and theory to make a good composition.