# Circuit Idea/Circuit Principles
## Prerequisites

The seemingly large variety of electronic circuits and devices is actually based on a small number of clear and ingeniously simple fundamental ideas. The formulation of universal circuit principles (like Altshuller's 40 principles in the field of mechanical engineering) on which specific circuits are built and their arrangement in a hierarchical system would allow us not only to analyze in depth the operation of electronic circuits revealing their mutual relationship but also to create, synthesize, pseudo-invent, and even truly invent new devices.

## Contents

The classification consists of four main parts. In the first part, universal principles of inventive creativity that can be found in all areas of analog circuitry are included. In the remaining three parts, principles for building passive analog devices, devices without negative feedback, and devices with negative feedback are considered.

### General principles

* Turning loss into gain
** The "harmful" hysteresis becomes useful
*** Eliminating the influence of interference superimposed on the useful signal
*** Debouncing mechanical contacts
*** Getting memory
**** Converting a Schmitt trigger to an RS-latch
**** Converting a reed contact from a "button" to a "switch"
** The "harmful" threshold voltage VF becomes useful
*** "Zener Diode" with low threshold voltage
*** Artificially raising the threshold voltage of an LED so that it can be "turned off" by another LED
** The "harmful" temperature dependence of the threshold voltage VF u VBE becomes useful
*** Diodes and transistors acting as semiconductor temperature sensors
** The "harmful" nonlinearity of the characteristic becomes useful
*** Obtaining logarithmic and anti-logarithmic function by a semiconductor diode
* Pre-deliberate deterioration with the idea of future improvement
* Annihilating a harmful quantity with a useful "anti-quantity"
** Passive destruction (in circuits without negative feedback)
** Active destruction (in circuits with negative feedback)
* Splitting the functions of a device into multiple functions and assigning them to different devices (only one of them is active at a given time)
** Push-pull stage (emitter follower with bipolar output)
** Bridge circuits

### Principles for Building Passive Analog Devices with Resistors

* Principles derived from Ohm's law
** Principles applied to an electrical circuit driven by an ideal voltage source
*** Converting voltage to current
**** Building a current source using a voltage source
**** Building a voltmeter using an ammeter
**** Base resistor in a transistor switch (CB stage)
**** Integrating circuit
**** Logarithmic circuit
*** Converting resistance to current
**** Building an ohmmeter using an ammeter
**** Resistive sensors with current output
*** Dividing voltage by resistance
**** Multiplying digital-to-analog converter (R-2R ladder) with current output
** Principles applied to an electrical circuit driven by an ideal current source
*** Converting current to voltage
**** Current-to-voltage converter
**** Building a voltage source using a current source
**** Building an ammeter using a voltmeter
**** Differentiating circuit
**** Antilogarithmic circuit
*** Converting resistance to voltage
**** Building an ohmmeter using a voltmeter
**** Resistive sensors with voltage output
*** Multiplication of current by resistance
**** Multiplying digital-to-analog converter (R-2R ladder) with voltage output
* Principles derived from the equivalent circuits of real electrical sources
** Applied to an electrical circuit driven by a real voltage source (after Thevenin)
*** Converting voltage to voltage
**** Voltage divider
*** Converting resistance to voltage
**** Series regulation of electrical energy: transistor amplifier, series regulator
**** Resistive sensors with "voltage" output: thermo-, photo-, tenso-, etc. (linear output only within small limits)
*** Converting the ratio of resistances to voltages
**** Potentiometric resistive sensors with "voltage" output (linear output)
**** Potentiometric voltage regulation
*** Multiplying voltage by resistance ratio
**** Analog multiplier
** Applied to an electrical circuit driven by a real current source (after Norton)
*** Converting current to current
**** Current divider
**** Shunt (in ammeters)
* Principles derived from Kirchhoff's laws
** Principles derived from KCL
*** Parallel summing, subtracting and comparing currents
**** Parallel summing currents
***** Current summer
***** Circuits with parallel positive feedback
**** Parallel subtracting currents
***** Current subtractor
***** Parallel comparing currents
***** Current comparator
***** Circuits with parallel negative feedback
*** Parallel summing, subtracting and comparing voltages by intermediate converting to currents
**** Parallel summing voltages
***** Voltage summer
***** Converting an ADC with a unipolar positive input to a bipolar one
***** Circuits with parallel positive feedback
**** Parallel subtracting voltages
***** Voltage subtractor
***** Converting a DAC with a unipolar positive output to a bipolar one
**** Parallel comparing voltages
***** "Virtual ground" principle
****** Parallel voltage comparator (electrical "scale")
***** Principle of the "immovable virtual ground" (simultaneous opposite change of both input voltages)
****** Circuits with parallel negative feedback
***** Principle of the "movable virtual ground"
****** Principle of "scissors" (changing one voltage)
****** Principle of "guillotine" (simultaneous unidirectional change of both voltages)
** Principles derived from KVL
*** Series summing, subtracting and comparing currents
**** Series summing voltages
***** Voltage summer
***** Circuits with series positive feedback
**** Series subtracting voltages
***** Voltage subtractor
**** Series comparing voltages
***** Voltage comparator
***** Circuits with series negative feedback

### Principles for Building Passive Analog Devices with Reactive Elements

* Passive voltage copying
** Initial charging of the decoupling capacitors in RC-coupled AC amplifiers
** "Sample & hold" circuit in sample mode
* Dynamic "shifting" voltage variations ("coupling" a voltage to another voltage)
** Decoupling capacitors in AC amplifiers (converting a bipolar to unipolar voltage and vice versa)
** Circuits with artificial increasing resistance ("bootstrapping")
** Positive feedback capacitor in a Hartley oscillator
* Dynamic "hardening" of "soft" voltage
** Filtering capacitor
** Converting a real to an "ideal" voltage source
** Potentiometer shunted by a capacitor
** Average detector
* "Fast charging - slow discharging"
** Peak and amplitude rectifier
* Increasing the speed by forcing the current (overcoming stray capacitances)
* "Slow charge - fast discharge"
** Relaxation oscillators
** Photo flash
** Impulse magnetization of permanent magnets
** Charge dosing
** Capacitive ADC
* Reversing voltage polarity
** Symmetrical multivibrator
** Power supplies
* Current forcing
** Transistor switch with accelerating capacitor
* Generating linearly changing voltage
** Sweep circuits in CRT
** ADC implemented by comparing the input voltage with a linearly varying voltage
* Generating step changing voltage
* Rising the voltage across a coil
** DC-DC converter

### Principles for Building Electronic Analog Devices without Negative Feedback

* Principle of dynamic resistance
** RV-type dynamic resistance
*** Diodes (ordinary, zener, LED, etc.)
** RI-type dynamic resistance
*** Transistors
** Negative resistance
*** Tunnel diode amplifier
*** Circuits with artificially created negative resistance
* Regulating (generating, amplifying) voltage through a voltage divider composed of series-connected resistors
** by changing the resistance of one resistor while keeping the resistance of the other constant (ohmic resistor)
*** "Floating" regulating element
**** "Common emitter" circuit with a positive supply and a PNP transistor
*** Grounded regulating element
**** "Common emitter" circuit with a positive supply and a NPN transistor
** by changing the resistance of one resistor while the other resistor "helps" it in trying to change the output voltage (RI-type non-linear resistor)
*** where both elements are RI-type nonlinear resistors
**** Amplifier with dynamic load
** by changing (simultaneously and oppositely) the resistance of both resistors (resistance redistribution)
*** Complementary (push-pull) stage
**** Where both elements are RI-type nonlinear resistors
* Regulating current through a current divider composed of resistors connected in parallel
** by changing the resistance of one resistor while keeping the resistance of the other constant (ohmic resistor)
** by changing the resistance of one resistor while the other resistor "helps" it in trying to change the output voltage (RV-type nonlinear resistor)
*** where only one element is RV-type nonlinear resistor
**** Zener diode voltage stabilizer
*** where both elements are RV-type nonlinear resistors
**** "Turning off" LEDs with different threshold voltages
**** Zero voltage LED indicator
**** Switching zener diodes (the diode with the lower threshold voltage "turns off" the diode with the highest voltage)
** by changing (simultaneously and oppositely) the resistance of both resistors (resistance redistribution)
*** Differential amplifier
* Static "movement" of voltage changes
** through a current source creating a constant voltage drop across a resistor
*** Output stages of operational amplifiers
** through a nonlinear element with V-type IV curve
*** Compensating the base-emitter voltage VBE in the bias circuits in the output amplifier stages (class AB)
* Passive compensation of harmful quantities by "anti-quantities"
** Compensating vision defects (myopia, farsightedness, astigmatism) with glasses
** Compensating the forward voltage drop VF in a diode rectifier (detector, limiter) by a reverse voltage created on a second diode
** Compensating for nonlinear distortions in a push-pull stage, class AB
** Compensating the influence of the input bias currents of an operational amplifier by inserting the same resistors in both inputs
** Temperature compensation
*** in bias circuits of amplifier stages
**** through thermistors
**** through diodes
*** in circuits producing reference voltage
**** in constant current sources

### Principles for Building Electronic Analog Devices with Negative Feedback

* "Active copying" principle
** "Active copying" with serial comparing
*** Emitter follower
*** Op-amp voltage follower
** "Active copying" with parallel comparing
*** Op-amp voltage inverter
* Principle of "disturbed active copying" (suppression of disturbances in a negative feedback system)
*** Suppressing additive disturbances
**** Eliminating the diode threshold voltage VF in a precision diode rectifier (detector, limiter)
**** Eliminating the transistor threshold voltage VBE in an emitter follower put in the op-amp negative feedback loop
**** Compensating the voltage drop along a long supply wire by a negative feedback voltage stabilizer (the idea of the three-wire connection)
**** Compensating the voltage drop across the op amp output resistance
*** Suppressing multiplicative disturbances
**** Compensating for attenuation in the Rout-RL divider of an op-amp voltage follower and voltage inverter
* Principle of "intentional disturbed active copying" (intentional disturbing voltage follower with negative feedback)
** Converting a follower system into an amplifier system by deliberate constant disturbing
*** Transistor amplifier stages
**** "Common-emitter stage with negative feedback ("emitter degeneration")
**** Phase splitter
*** Op-amp amplifiers with negative feedback
**** Inverting amplifier
**** Non-inverting amplifier
** Deliberately varying disturbance of a follower system with negative feedback (the output signal becomes a function of the disturbance)
*** Multiplicative disturbance
**** Resistance-to-voltage converter (putting thermal, photo, etc. resistive sensors in the negative feedback network)
***** "R1-V"
***** "R2-V"
***** "P-V"
**** Digital-to-analog converter with R-2R ladder
*** Additive disturbance
**** Measuring the voltage VF of diodes and LEDs, batteries, etc.
** Deliberately disturbing a follower system with negative feedback by "attacking" its output (there is a conflict; the system reacts to attempts to change its output signal)
*** "Attacking" a voltage source
**** Common-base stage
**** Emitter-coupled circuits
*** "Attacking" a current source
**** Transistor stage with dynamic load
** Mutual disturbing follower systems connected by their outputs to each other (there is a conflict; systems react to attempts to change their output signals)
*** Conflict between two voltage sources
**** Differential amplifier (mutual disturbing of two follower systems)
*** Conflict between two current sources
**** Transistor stages with controlled dynamic load
** Principle of mutual "helping" between various follower systems with negative feedback
*** voltage sources
*** current sources
*** voltage source and current source
**** Differential amplifier with a current source included in the transistor emitters at common-mode
**** Cascode circuits - a current source driving a voltage source through its output
** Reversing cause-and-effect relationships in analog devices through the principle of active copying (swapping their input and output)
*** Reversed non-inverting voltage divider of the type 1/(1 +R1/R2) - we change the "output" voltage of the divider so that the voltage across the resistor R2 is equal to the input voltage
*** Reversed R2/R1 type inverting voltage divider - we change the "output" voltage across resistor R2 so that the voltage across resistor R1 is equal to the input voltage (we change the total voltage applied across the two series-connected resistors so that the voltage across resistor R1 to be equal to the input voltage)
*** Integrator > differentiator - we change the "output" voltage of an integrating circuit so that the voltage across the capacitor is equal to the input voltage
*** Differentiator > integrator - we change the "output" voltage of a differentiating circuit so that the voltage across the resistor is equal to the "input" voltage
*** Reversed frequency divider - we change the "output" frequency so that after division it is equal to the input (PLL circuits)
** Principles of converting passive analog devices to active
*** Active copying with destroing the original (removing of disturbance by anti-disturbance)
**** without using the copy (we only destroy the harmful disturbance, providing ideal conditions for the circuit to work)
***** Maintaining a constant current by destroying the harmful voltage drop across the "disturbing" element
****** Charging rechargeable battery
****** Driving LEDs, DC motors, electromagnets
****** "Ideal" ammeter and ohmmeter
****** Voltage/resistance divider
***** Maintaining a constant voltage by eliminating the harmful current leakage through the "disturbing" element
**** using the copy (we judge the degree of disturbance according to the "anti-disturbance")
***** "Ideal" current-to-voltage converter
****** "Ideal" ammeter made with a real voltmeter
***** "Ideal" resistance-to-voltage converter
****** "Ideal" ohmmeter made with a real voltmeter
****** "Ideal" resistive sensors with output voltage
****** "Ideal" current x resistance multiplier
****** "Ideal" parallel summer
****** "Ideal" integrator and differentiator
****** "Ideal" logarithmic and anti-logarithmic device
****** Measuring the diode forward voltage VF
*** Active copying without destroying the original
**** A current meter in a circuit supplied by an ideal current source
**** "Ideal" ohmmeter made with an ideal current source and a real voltmeter
**** Non-inverting resistor voltage adder
**** "Ideal" current integrator
* Principles for inventing analog devices by simultaneous operation of the two op-amp inputs
** Follower with controlled gain sigh (+1 or -1)
** Op-amp differential amplifier
* Principles for inventing analog devices by applying both negative and positive feedback
** Current source with grounded load (Howland current pump)
** Circuits with negative resistance
* Artificial dynamic change of electrical circuit parameters
** Dynamically increasing resistance by "active copying" (following negative feedback, bootsrapping)
*** Increasing the input resistance of systems with series negative feedback (voltage follower)
*** Eliminating the shunting effect of the biasing divider in a transistor amplifier
*** Artificial increasing Rc in output transistor stages
*** Eliminating the influence of on-board leakage acting between the op-amp inputs and power rails
** Dynamically decreasing capacitance through "active copy"
*** Suppressing parasitic input capacitances in an op-amp circuit with series negative feedback
*** Suppressing the capacitance of a shielded cable through which it feeds the input signal to an operational amplifier (following shield)
** Dynamically decreasing resistance by "inverting active copy" (parallel negative feedback)
*** Low input resistance of systems with parallel negative feedback (negative effect)
** Dynamically increasing capacitance through "inverting active copy" (parallel negative feedback)
*** Miller effect (undesirable) in common-emitter amplifier stage
*** Active integrator (desired Miller effect)
** Obtaining "negative" resistance by "overdosing" dynamic resistance

## See also

How to Derive Basic Circuit Principles provides insight into the tools with which to derive general principles from specific electronic circuits