home - list of papers - dramatic conflict principle (the second story)
Cyril Svetoslavov Mechkov
Department of Computer Systems, Technical University of Sofia,
e-mail: firstname.lastname@example.org, site: http://www.circuit-fantasia.com
Abstract : In this paper, first a general heuristic principle “conflict causes amplification” is revealed. For this purpose, a few analogies of the conflict phenomenon are generalized into a block scheme of a negative feedback follower disturbed from the output. Then the conflict principle is used as a tool for analysing various electronic circuits with dynamic load - common-base stage, emitter-coupled circuits (e.g. ECL), op-amp inverting amplifiers, transistor stages with collector dynamic load, op-amp internal structures etc. Finally, a universal procedure for building all kinds of electronic circuits with dynamic load is established.
Keywords: dynamic load, negative feedback circuits, emitter-coupled logic.
1. INTRODUCTION. We may find out a lot of interesting phenomena in the operation of electronic circuits with dynamic load (common-base transistor amplifier, emitter coupled circuits, transistor stages with collector dynamic load, op-amp internal structures etc.). Unfortunately, they are explained by formal means, which do not reveal the nature of the phenomena. In order to fill up this deficiency, the following goals are posed in this work:
to reveal the basic idea behind dynamic load by using a set of heuristic means,
to apply the obtained results in order to analyse and to present the existing electronic circuits with dynamic load,
to establish a universal procedure for building various electronic circuits based on dynamic load.
2. DERIVING THE UNIVERSAL CONFLICT PRINCIPLE. When we analyse the operation of the negative feedback systems by heuristic means [1, 2] we may find the interesting phenomenon “conflict causes amplification”. This unique, absurd but yet useful phenomenon enables us to present in an impressive way the operation of a whole class of legendary electronic circuits [3, 4].
Let's consider the block diagram of a classic negative feedback follower – fig. 1, in order to reveal the essence of the phenomenon. What we are doing there? Changing the input X1 of the system we in fact control indirectly its output value Y1. For instance, what are we doing when we do not like the actions of a person? Of course, we try to convince him to change his behaviour himself.
But what happens if we try to change not so delicately but directly the output signal Y1? This means to attack with power the system output by another input value X keeping constant X1 – fig. 2. In the example above this means to change forcibly the actions of the person. Obviously, a conflict arises here – the person reacts to our intervention trying to keep the old situation.
There is a conflict on fig. 2 because the basic task of the negative feedback follower (stabilizer) is to keep steady output value Y1. Doing that, it reacts to any attempt to change its output signal thus transmuting itself into an amplifier.
Now, the disturbing influence X at the output of the old system-follower plays the role of an input signal of the new system-amplifier; the system reaction acts as an output signal Y.
3. INVESTIGATING CONFLICTS IN ELECTRONIC CIRCUITS. We may apply the universal conflict principle in order to understand so odd electronic circuits with dynamic load. There, we may encounter two kinds of conflicts - between voltage sources (in stages with voltage dynamic load) and
between current sources (in stages with current dynamic load). In the first case, the reaction of the disturbed system is a current one; in the second case, the reaction is a voltage one.
3.1. Circuits with voltage dynamic load. By perceiving conflicts between voltage sources we may realize profoundly a set of classic electronic circuits - common-base stage, emitter coupled circuits, op-amp inverting circuits etc.
3.1.1. Common-base transistor stage. Following the general conflict idea we may present classic common-base stage - fig. 3, as a deliberately output disturbed common-collector stage (emitter follower). Here the transistor T, playing the role of a regulating element, has copied the steady input voltage VREF into its emitter as a “hard” voltage VE = VREF. If we attempt to change it by applying an input voltage VIN (another “hard” voltage) to the emitter, a conflict between two voltage sources arises. The transistor reacts to our intervention by changing its current resistance RCE and current IOUT thus trying to keep the voltage VE = VREF. The resistor RC converts the current reaction IOUT into a voltage one VOUT, which appears to be an output of the new circuit .
A geometrical interpretation of the phenomenon is showed on fig. 4. When we change the input voltage VIN its IV-characteristic moves horizontally remaining parallel to itself; the working point A slides vertically over static IV-characteristic of the second voltage source VE = VREF. As the two characteristics are almost in parallel, small variations of the input voltage cause significant variations of the output current. We may think of this interpretation as a geometrical “amplifier” (we might see also a similar geometrical phenomenon in a one-sided guillotine).
3.1.2. Emitter-coupled circuits. Only, attacking the transistor at the output we are forced to bear its reaction. Note that the two voltage sources on fig. 3 are in a different position – only the small base current IB of the transistor T flows through the reference voltage source VREF of the common-base circuit while the whole output current IOUT passes through the input voltage source VIN. Then a new idea arises – to buffer the input voltage source VIN with another identical follower. Thus we obtain a double symmetrical structure – fig. 5.
It is composed of two identical negative feedback systems, which following outputs are connected together to a common load L. As the one system keeps up the common output value Y1 steady while the other system strives to change it, a conflict arises in the common node.
In our concrete example (fig. 6), that means to connect together the emitters of the transistors T1 and T2 to the common resistor RE. Then we have to change the input voltageVIN1 keeping steady VIN2 = VREF. As a result the follower transmutes into an amplifier and classical emitter-coupled circuit is derived. In this circuit the transistors fight each other (T1 strives to change the voltage drop across the emitter resistor while T2 strives to keep it). The voltage drops across the collector resistors RC1 (RC2) and their complements VOUT1 (VOUT2) are proportional to the degree of the conflict; they play the role of the output signal of the circuit.
3.2. Circuits with current dynamic load. Similarly, in a classic amplifying stage with dynamic load a conflict between two current sources arises – fig. 7. In this circuit, the transistors T1 and T2 function as current sources fighting each other. The transistor T2 strives to set the current I = IIN by changing its current resistance (voltage VCE). In the same time, the transistor T1 strives to keep the current I = IREF. This conflict causes a significant change of the output voltage VOUT determining the high amplification of the circuit .
In the geometrical interpretation - fig. 8, IV-characteristic of the input current source moves vertically remaining parallel to itself; the working point A slides horizontally over static IV-characteristic of the second current source IREF. As the two characteristics are almost in parallel, small variations of the input current cause significant variations of the output voltage (think of this picture as a horizontal guillotine).
4. BUILDING ELECTRONIC CIRCUITS BY USING THE CONFLICT PRINCIPLE. Once we have revealed the basic idea behind electronic circuits with dynamic load, we may build them in the process of teaching. Furthermore, we may build any even completely new circuits with dynamic load applying the universal 4-step building procedure below:
1. Get an electronic circuit with negative feedback (voltage follower).
2. Set a steady quantity at the circuit input (voltage or current).
3. Apply the real varying input quantity at the circuit output.
4. Get the circuit reaction (current or voltage) as an output quantity.
5. CONCLUSIONS. Applying the heuristic approach in this paper, we have managed to process a large class of electronic circuits with dynamic load (common-base stage, emitter-coupled circuits, transistor stages with collector dynamic load, op-amp internal structures etc. ) following the order below:
deriving a universal principle “conflict causes amplification“ from our routine,
investigating existing circuits with dynamic load by using the conflict principle,
building new circuits with dynamic load by applying a universal procedure based on the conflict principle.
The obtained results may be used for the purposes of teaching and circuit design.
 Mechkov, C. (1997) “Heuristic course on analog electronics”. XXXII Scientific session CECS , Technical university, Sofia.
 Mechkov C. (1997) “ Heuristic presentation of negative feedback principle. Proceedings of The Sixth Int. Conference ELECTRONICS'97 , Sozopol.
 Mechkov, C. (1998) “Looking for an idea – Obtaining amplification by a conflict”. Engineering Review (1311-0470) 9, p. 12.
 Mechkov C., "Invention" of basic transistor gain stages trough negative feedback methode, The 7th Int. Conference ELECTRONICS'97, 1998.
 Mechkov, C. (1999) “Looking for an idea – Voltage conflicts in common-base stage”. Engineering Review (1311-0470) 1, p. 16.
 Mechkov, C. (1999) “Looking for an idea – Current conflicts in amplifiers with dynamic load”. Engineering Review (1311-0470) 3, p. 18.
6.2. Links. Here are additional internal links related to the conflict principle:
My great circuit penetrations is a collection of circuit concepts I have realized.
Opposing systems with negative feedback shows that like people in society negative feedback systems may interact i.e. opposing each other.
List of circuit conflicts is a weekly updated column about conflict circuit phenomenon.
Transistor Circuits with Negative Feedback shows the content of Class 7 from the course on Analog electronics.
How to invent electronic circuits is a series of 17 papers that I prepared for Popular Electronics magazine in 1999 (3 MB pdf, BG version only). Three of them are dedicated to the conflict principle:
Paper 10. Amplification by a conflict between voltage sources,
Paper 11. Dramatic voltage conflict,
Paper 12. Conflicts between current sources.
Common-base stage is a scanned draft of my Lecture 5 (BG version only).
Differential amplifiers is a scanned draft of my Lecture 6 (BG version only).
home - list of papers - dramatic conflict principle (another story)
Last updated, September 21, 2005