Circuit Idea/How to Derive Basic Circuit Principles

The Idea

Once we have accumulated ideas about many specific electronic circuits and built up a "philosophy" about them, it is not difficult to notice that the seemingly large variety of electronic circuits and devices is actually built on a small number of clear and ingeniously simple fundamental ideas. Thus, the idea of making a hierarchical classification of universal principles on which the specific circuits are built, along the lines of Altshuler's 40 principles, developed by him in the field of mechanical engineering, naturally arose in us. The formulation of such universal circuit principles and their arrangement in a hierarchical system would allow us not only to deeply analyze the operation of electronic circuits, revealing their mutual connection but also to create, synthesize, pseudo-invent and even truly invent new devices.

Tools

We can extract these "pearls" of human thought with the help of various creative thinking techniques as follows:

Transferring intuitive ideas from our life experience to abstract electronic circuits
Looking for associations and analogies between different at first glance devices
Functionally representing the phenomena in the studied circuits
Revealing the circuit contradictions in the operation of electronic devices
Clarifying the cause-and-effect relationships in the studied phenomena
Building sensor-motor models
Thinking figuratively, etc.

Classification

The idea of this story is to share our experience in systematizing circuit principles, "tricks" and effects in the field of analog circuitry but this can be done in any field of electrical and electronic engineering. The classification consists of four main parts. In the first, we can include universal principles of inventive creativity that can be found in all areas of analog circuitry. In the remaining three parts, we can reveal the principles for building passive analog devices, devices without negative feedback, and devices with negative feedback. We can illustrate the principles both with specific devices from the field of analog circuit engineering and with "non-electrical" examples from life.

General principles

Turning loss into gain
Pre-deliberate deterioration with the idea of future improvement
Annihilating a harmful quantity with a useful "anti-quantity"
Splitting the functions of a device into multiple functions and assigning them to different devices

Principles for Building Passive Analog Devices

We can divide them into two large groups concerning resistive and reactive analog devices.

The principles by which resistor analog devices are built are derived from the basic laws of Electrical engineering. So, for example, from Ohm's basic electrical circuit we get six operations for converting electrical quantities: voltage-to-current, resistance-to-current, current-to-voltage, resistance-to-voltage, divide voltage/current, multiply current x resistance. Thevenin and Norton's real electrical circuits give us the idea of five more operations: voltage-to-voltage conversion, resistance-to-voltage, resistance-to-voltage ratio, current-to-current, multiplication of voltage by ratio of resistances. From the branched Kirchhoff circuits we naturally obtain the other operations: series summing, subtraction and comparison of voltages, parallel summing, subtraction and comparison of currents and voltages.

The principles for building reactive analog devices are based primarily on intuitive notions and associations with life phenomena. These are passive voltage copying, dynamic "moving" of voltage changes (coupling of one voltage to another), dynamic "hardening" of "soft" voltage, fast charging - slow discharging and vice versa, reversal of voltage polarity, etc.

Principles for Building Electronic Analog Devices without Negative Feedback

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Principles for Building Electronic Analog Devices with Negative Feedback

We can derive them primarily by generalizing analogies from human everyday life and transferring them to electronic devices.

We can present the fundamental idea of negative feedback sequentially in three logically related principles. The first of these, called figurative active copying, uses Kirchhoff's laws to implement serial and parallel active followers.

We can summarize the property of negative feedback systems to suppress disturbing effects in the principle of disturbed active copying, which finds application in precision diode rectifiers (to eliminate the diode forward voltage VF), emitter followers included in the op-amp negative feedback network (elimination of the transistors threshold voltage VBE), voltage stabilizers with a three-wire connection to the load, etc.

The principle of intentionally disturbed active copying turns negative feedback followers into amplifiers. So for example, through multiplicative constant disturbance we can invent common emitter stage with negative feedback, op-amp inverting and non-inverting amplifier, etc. Similarly, when we attack a follower system at its output, it reacts to this intentional disturbance by becoming an amplifier - this "trick" is based, for example, on the operation of a common-base stage. If we further develop this idea by connecting two follower systems with their outputs to each other, we cause a conflict between them and force them to amplify - this is how the differential amplifier (conflict between voltage sources) and the transistor stage with a dynamic load (conflict between current sources) work.

Apart from the conflict principle, the relations between two follower systems can also be built on the principle of mutual assistance. For example, if we apply common-mode signals to the inputs of a differential amplifier, we will observe a current source assisting a voltage source. This phenomenon also exists in some cascode circuits, where a voltage source assists a current source.

When we vary the disturbance at a constant input, the output signal of the system becomes a function of the disturbance. This principle tells us how to create various resistance-to-voltage converters (thermo-, photo- and other resistive sensors, digital-to-analog converters with R-2R ladder), threshold voltage meters of light-, zener and other types of diodes included in the negative feedback loop.

If we analyze our behavior in a number of life situations and transfer the obtained ideas about the observed phenomena to electronic circuits, we can formulate a group of universal principles for converting passive analog devices into active ones. The first of these we can call active copying with removing the original or removing the disturbance by anti-disturbance. It resolves a contradiction typical of passive circuits - if a current is consumed in an electric circuit, a voltage drop occurs on the consumer, which is harmful to the source but useful to the consumer. We can destroy the "harmful" voltage on the "disturbing" element by adding an "anti-voltage" equal in value and opposite in sign to it. Thus, we can invent "ideal" measuring devices (ammeter, ohmmeter) and circuits for charging batteries, driving LEDs, DC motors and other current consumers. We can improve this principle by using the value of the "anti-disturbance" to judge the degree of the disturbance and thus obtain more extremely valuable "ideal" devices - current-to-voltage converter, op-amp ammeter and ohmmeter, summers, integrators, differentiators, etc.

In some cases, however, the disturbing influence is not harmful but even beneficial to us, and therefore we should not destroy it. This is the principle of active copying without destroying the original on which the devices are built: an "ideal" ohmmeter made with an ideal current source and a real voltmeter; non-inverting resistive voltage summer; "ideal" current integrator, exponential generator, etc.

In negative feedback circuits, we can find another interesting principle - reversal of the causal relationship (swapping the input and output of electronic devices). It allows us to make "inverted" devices (inverting and non-inverting voltage dividers, integrators, differentiators, etc.).

Conclusion

The presented classification is an open, hierarchically constructed system that is constantly expanding with new circuit principles, "tricks" and effects from the field of analog circuit engineering. The tendency is to cover other related fields of electronic technology.

Web resources

Circuit Principles is a collection of basic circuit ideas derived from the specific circuit solutions