Circuit Idea/Philosophy

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Philosophy behind the Book

Imagination is more important than knowledge...
Albert Einstein

The idea behind an AC transistor amplifier revealed by heuristic means.

The classical approach

Nobody shows us how to transform imperfect passive circuits into almost ideal active ones.

As a rule, classic electronics courses follow a traditional "scenario": first, authors present electronic circuits in their complete, final and perfect form; then, authors analyze accurately circuits by using abstract formal methods. This classical teaching approach predominates in electronics education. Just look around and you will see that it is everywhere: in books, magazines and web sites authors present ready-made circuit solutions; in lecture halls teachers try to explain qualitative circuit phenomena by using quantitative tools; in educational laboratories, students carry out "ascertaining" experiments that only confirm the rightness of predominating circuit ideas.

Ultimately, there is no place for revealing basic circuit ideas. Nobody shows what we, human beings, actually need - what basic circuit ideas are, where new circuit ideas come from and how they have been evolving through years, in order to be able not only to understand but even to invent new circuits. In this way, relying mainly on logical reasoning, education suppresses the most human capability that we possess owing to our imagination - to create and even invent things, which do not exist in nature. Thus education does not induce creativity in student minds.

For example, nobody shows us the relation between the passive and active versions of same circuits. First, they present passive electric circuits (e.g., the passive RC integrator in the upper figure on the right) as ready-made circuit solutions and persuade us how imperfect they are. Then, they give us active electronic circuits (e.g., the op-amp inverting RC integrator in the lower figure) and persuade us now how perfect they are. Only, although they present passive and active versions separately, we guess that they are related. So, nobody shows us what we actually need - how to transform imperfect passive circuits into almost ideal active electronic circuits. If we only know how, we will be able to understand and even invent more new electronic circuits!

A need of human-friendly circuit philosophy

In the well-known circuit of an op-amp inverting amplifier we might discern the simpler V-to-I converter and I-to-V converter.

Only, we are not robots or computers but ordinary human beings; no cold engine oil but warm human blood flows in our veins. When еxamining complicated mixtures of electronic components we try to discern desperately simpler circuit building blocks and to associate the abstract circuit idea with well-known everyday situations. For example, we might think that the popular circuit of an op-amp inverting amplifier is composed of two simpler converters: a passive voltage-to-current converter and an active current-to-voltage converter unified by the famous virtual ground phenomenon.

We human beings, do not think in terms of formal analysis when understanding, explaining and inventing circuits. We need first to understand qualitative things by qualitative means; then, to compute quantitative things by quantitative means. In electronics, that means first to understand, build and invent circuits by using human intuition, imagination and emotions; then, to define exactly the circuit parameters and to analyze thoroughly the circuit operation by using formal methods.

We need not only concrete technical explanations and calculations. First of all, we, human beings, need a human-friendly circuit philosophy.

Philosophy foundations

In this wikibook, we establish a novel circuit philosophy as an alternative to the classical formal approach. The new philosophy relies more on human imagination than on logical reasoning. It considers analog circuitry more as art than science and the creation of electronic circuits as a result of human fantasy, imagination and enthusiasm.

A heuristic approach

Reinventing electronic circuits

The best way of understanding and presenting unfamiliar circuits is to "invent" them again (reinvent). So, instead of presenting circuits as finished cut-and-dried solutions we may reinvent them including the very students in this "game". In this way, reproducing the inventing process, we can show the evolution of circuit ideas. This helps students to master a set of circuit design techniques and tricks, which enables them later to construct and... why not to invent new circuits?

Levels of implementation

In this book, we evolve the heuristic idea at three levels:

• At a book level, we reveal circuit ideas generally by moving in a sequence passive > active > negative feedback circuits (see the main subtitles of the content's section Revealing circuit ideas).
  • At a page level, we expound the subject step-by-step by moving from simple to complex - imperfect to perfect, passive to active, transistor to op-amp circuits (see, for example, current-to-voltage converter)
    • At every step inside a story, we first reveal the basic circuit idea; then we show the concrete circuit solution.

A reinventing scenario

When we reinvent a circuit, we move from the beginning to end. Here is such a typical top-down scenario:

1. Posing the problem to be solved (improving a passive circuit, solving a circuit contradiction, etc.)
2. Revealing the basic idea in the non-electrical domain (looking for analogies, deriving a block-diagram and operation algorithm).
3. Applying the general idea in the electricity domain (building an equivalent and "man-controlled" electrical circuit).
4. Showing the passive circuit applications (building standalone and composite passive devices).
5. Revealing the passive circuit imperfections (revealing and evaluating inherent circuit deficiencies).
6. Improving the imperfect passive circuit and creating a perfect active version (converting the passive circuit into an active one).
7. Applying the idea in the electronics domain (building various active devices based on the same idea).

Typical examples of this top-down reinventing approach are the stories about passive and active voltage-to-current converter that we have derived from the elementary Ohm's electric circuit.

A building approach

Circuit idea is based on the belief that the truth about circuit phenomena is hidden rather in the movement from simple to complex circuits than in the final perfect circuit solutions. That is why, we do not present here circuits as ready-made solutions to be analyzed in their complete, final and perfect form. Instead, we build circuits step-by-step using more elementary building blocks that are already "invented". We connect these "bricks" according to the basic ideas that we have derived from real life.

We can build a parallel voltage summer by a few V-to-I converters, a current summer and an I-to-V converter.

Following this building approach, in the present book we present every new more complex circuit as based on the previous simpler one. First, we derive the most elementary passive building blocks from the basic electric circuits of Ohm, Kirchoff, Thevenin and Norton. Then, we use these "cubes" to build more complicated compound passive circuits. Further, adding active elements in accordance with suitable basic ideas, we build various transistor circuits. Finally, applying powerful negative feedback principle in all its variety, we metamorphose these circuits into almost ideal op-amp ones.

An example of this bottom-up building approach is the story about parallel voltage summer that evolves as follows. In the initial stories, we derive the elementary voltage-to-current converter, current-to-voltage converter and current summer. In the next story, we use them to build a compound passive voltage summer. Finally, we add an op-amp to this passive circuit thus converting it into an active parallel voltage summer.

Using associations

We begin learning from the day we are born. In this way, in the early years of our childhood, we accumulate a knowledge of life for visible (mechanical, hydraulic, pneumatic, social, etc.) phenomena of our world. But this world is arranged so interesting that apparently different phenomena obey the same laws; they are analogous.

A hydraulic analogy of an op-amp inverting integrator.

Then, why do not we use associations as educational mainstays that convey the common knowledge about visible worldly phenomena to invisible abstract electric phenomena? Thus they will look familiar, elementary and accessible. This is so because we, human beings, begin understanding new unfamiliar things when we begin discerning something familiar inside them. We just consider new complex things as composed by a few simpler well-known components. Here are some examples of applying analogies.

When we "reinvent" the elementary electric circuits (voltage-to-current converter, current-to-voltage converter, etc.) and more complex electronic circuits (e.g., the op-amp inverting integrator on the right, Deboo integrator, etc.) we use various fluid analogies (pneumatic, hydraulic, thermal, diffusion, etc.) When we try to figure out what blocking capacitors really do in an AC transistor amplifying circuit, we will think of them as an electrical "shock-absorbers", which move the voltage "movements" (see the welcome circuit diagram at the top). Later, we will derive the simplest block diagram of a negative feedback system by using various driver, teacher, weight, economic, social, etc. analogies.

Visualization

A voltage distribution along the resistive film inside a linear potentiometer.

According to the old proverb "A picture is worth a thousand words", we have to place as much as possible images in this book. When this is not possible, we will use an imaginative, figurative and colorful language to plot pictures in reader's mind.

Also, we can visualize the invisible electrical attributes voltage and current by analogous geometrical attributes bars and loops that are based on the famous water tower and fish tank hydraulic analogies. In this geometrical presentation, the height of the voltage bars is proportional to the corresponding voltages and the thickness of the current loop is proportional to the magnitude of the current.

Finally, we can present the circuit operation by a voltage diagram that represents the voltage distribution along a resistive film. In this attractive geometrical presentation, local bars with corresponding height represent the local voltage drops. For simplicity, we usually draw only the envelope of the voltage diagram.

Relying on causality

Revealing causality. Classical electronics courses do not reveal cause and effect relations in electronic circuits. For example, who cares if there is a causality and what causes what (what quantity is an input and what an output) in Ohm's law? Authors just suppose that voltage and current change simultaneously; they do not mind how the famous rule is written (I = V/R, V = I.R or R = V/I).

Voltage causes current

Current causes voltage

Only, we human beings consider every change in this world as a result of some cause (in electronics that means the output quantity is a result of the input one). We cannot imagine that the input and output quantities can change simultaneously. We know that always the input is first and the output is second; so, the output always follows (delays) the input.

Introducing causality. In the case when apparently there is no causality in electronic circuits, we can introduce it. Let's for concreteness consider the example above of Ohm's law. There, we first assume that voltage causes current (I = V/R) in a voltage supplied Ohm's circuit; thus we "invent" the simplest voltage-to-current converter.

Changing causality. But we know that this cause and effect relation is an arbitrary choice; so, we can change (reverse) it. This means we can assume with the same success that current causes voltage (V = I.R) in a current supplied Ohm's circuit; thus we "invent" the reverse current-to-voltage converter.

Evolving this powerful idea we will (re)invent a lot of useful and original circuits by using any accessible circuit points (including circuit outputs, supply terminals, etc.) and component parameters as an input. For example, varying with resistance as an input quantity we will obtain a resistance-to-current converter (in the case of a voltage supplied Ohm's circuit) and a resistance-to-voltage converter (in the case of a current supplied Ohm's circuit). Then, applying an input voltage to the output of an emitter follower we will "invent" the odd common-base transistor amplifying stage. Later, changing causality, we will transmute a digital-to-analog converter into a digital controlled amplifier.

Applying sensomotor activities

In order to "feel" how electronic circuits operate, we have to interact with them: first, to stimulate them and then, to perceive their reactions. Of course, the best way of doing that are real and simulated laboratory experiments. In this book, we will also carry out mental experiments to establish sensomotor notions into readers.

For example, when we explore the popular common-emitter transistor amplifying stage, we "raise" and "lower" mentally the base voltage. Then, when we "experiment" with the odd common-base stage, we apply an input voltage to the emitter and then "wiggle" it. Similarly, when we explore the classic differential transistor amplifier, we "move" (in the same and in the contrary directions) the both input voltages to observe the differential and common-mode operation.

A more sophisticated example is the ECL gate visualized by voltage bars and current loops:

A functional consideration

We may consider electronic components at various levels of abstraction. For example, we might explain how a transistor works at "micro level" presenting it in terms of semiconductor theory. Only that is not sufficient to explain how a particular electronic circuit works. In order to understand transistor circuits, we need to know not so much what the internal transistor structure is but how a transistor behaves in the circuit.

At this "macro level", we present the transistor operation by the well-known basic concepts of electricity (current source, non-linear resistor, current-to-current converter, rheostat, etc.). Thinking "functionally", we imagine where currents (not particular electrons or holes) flow, what voltages and resistances across the component terminals are, etc.

Evolving this functional approach, we will implement electronic circuits at various component levels. For example, we will present a voltage amplifier at these levels: single transistor amplifier, discrete transistor amplifier (built by a few transistors), integrated circuit amplifier (e.g., a single op-amp), negative feedback amplifier (here the op-amp is only a component of a system), an electronic device (now the negative feedback amplifier is only a component), etc.

Putting emotions to work

As you can see, in this book circuitry manifests more as an art than a science. Figuratively speaking, the book is a peculiar "theatre" where the particular circuit stories are "scenes", on which electronic circuits "play" our "scenarios":)

Emotions lie at the root of the art. We are human beings that possess emotions; we can feel, excite, love, hate, embarrass, suffer, envy, imagine, dream... but we cannot function blindly as a Turing machine when analyze circuits!

So, in this book, we will love our circuits... will get excited before their "premieres"... will suffer when they fail... and will triumph when a new circuit idea conceives in our minds!

External web resources

Build to understand circuits is the intro of a web based multimedia tutorial (Flash player needed) designed for Poptronics in 2003 (see also a paper).
Web-based building course on analog electronics - a teacher's story about implementing the philosophy.
Op-amp inverting summer is an animated tutorial (Flash player needed) that shows another implementation of the philosophy.

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