User:Circuit-fantasist

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1 My Teaching Philosophy
2 How to evade NOR (The King is naked!)

[edit] My Teaching Philosophy

My name is Cyril Mechkov. For the last 20 years I have been teaching analog circuitry at the Technical University of Sofia. My teaching philosophy (see my last paper to know more about it) is simple:

1. Electronic circuits are based on clear and simple basic ideas, which may be derived from our routine.

2. In order to really understand electronic circuits, we human beings have first to reveal these basic ideas.

3. In order to successfully present circuits to students, we teachers have to build them according to the basic ideas revealed.

4. In order to make students think creatively, we teachers have to (re)invent circuits according to the basic ideas behind them.

I just believe that we - human beings - can really understand the abstract electronic circuits by using human, non-electrical means. Basic ideas behind circuits are "non-electrical". So, they do not depend on the specific implementation (tube, transistor, op-amp etc.); they are eternal.

[edit] How to evade NOR (The King is naked!)

Hi to all members of Wikipedia society in this area of electronics! I realize that I have disturbed to some extent your calmness:); so, maybe I have to say some words about me, my reasons and my intentions. Simply speaking, I have to say what I (will) do on talk and article pages of Wikipedia.

[edit] Yes, I do original research!

Honestly, I realize that I actually do an original research on talk pages of Wikipedia contrary to NOR. According to its definitions, I do "research that consists of collecting and organizing information from existing primary or secondary sources (generalization, analysis, synthesis, interpretation, or evaluation of information or data)..." What is more, my explanations on talk pages are based on my "self-published resources" available to readers from my web site of circuit-fantasia.com. In addition, I do all the "bad" things listed in What is excluded? As far as I know, there is nothing wrong with it, if I stay at talk pages. But what have I to do, in order to join the article pages abiding by NOR? Below, I share some tips about how to evade Wikipedia NOR barrier.

[edit] But yet, how do we evade NOR? (a tip for creatively thinking Wikipedians)

My idea is extremely simple - to explain circuits so simply, clearly and evidently that there is no any need to verify these explanations (NOR stipulates such a possibility - to use sources "the accuracy of which is easily verifiable by any reasonable adult without specialist knowledge..."). For this purpose, I present circuits relying only on human (web visitor's) experience, imagination and intuition. I implement this approach by using a 3-step "scenario" (see my teaching philosophy). First, I extract the basic idea from many everyday situations formulating it verbally and in a form of block-diagram, then I show the possibly simplest equivalent electrical circuit diagram and finally I draw the specific electronic circuit solution.

You probably guess why I can't cite "verifiable sources", which reveal circuit phenomena - just because there are not such sources! I have been looking for them on the web from years but I have not found yet. I don't know why but it is true that the existing "verifiable sources" are dull and formal. Maybe, their authors pursue other goals (for example, to climb up the scientific ladder); that is why they make the simple complex while I try to make the complex simple, the simple - simpler and the simpler - simplest.... Figuratively speaking, I am just the boy from Andersen's story who says "The King is naked!":)

I have refused a long time ago to publish my ideas in the so-called "verifiable sources" since they consider this human-friendly approach as a non-scientific (in the bad sense of the word). Note - they do not reveal the ideas behind circuits but if you do that, they will probably shout, "This is non-scientific"! I can't stop showing some example of this paradox; here is such a story about it.

[edit] An example of this approach

[edit] Bob Pease's viewpoint at transimpedance amplifier

Electronic design magazine is an extremely reputable source and Bob Pease is an extremely reputable author. Well, let's then try to understand what the op-amp actually does in the circuit of a transimpedance amplifier following the link from the bottom of this Wiki page pointing to Bob's reputable article What's All This Transimpedance Amplifier Stuff, Anyhow?. I have formatted his text in bold italic and inserted my comments into the original text between his thoughts.

"One of the first things you learn about operational amplifiers (op amps) is that the op amp's gain is very high", Mr. Pease begins his story. Only, the gain is the most insignificant op-amp's feature, if we try to understand what the op-amp does in the circuit discussed. What is the problem to be solved?

"Now, let's connect a feedback resistor across it, from the output to the −input (Fig. 1)." I ask, "Why?" Is there any reasonable need to do that? Because we, human beings, do something, only if there is some reason to do that.

"When you put some input current into the −input..." Again, I ask, "Why?" What is the need to put the current just into there?

"...(also known as the summing point),..." Is the −input a summing point here? If yes, what does it sum here (recall that the op-amp has extremely high input impedance)? As far as I know, we need at least two inputs and one output, in order to sum something.

"...the gain is so high that all of the current must go through the feedback resistor." Can you see any direct connection between the very high gain and the behavior of the current? Has the current any other alternative to flow? No, as the op-amp has extremely high input impedance.

"So, the output will be VOUT = −(IIN × RF). That's neat." Again, "Why?" Can you see any connection between this speculation and the previous one from above? It is only evident (according to Ohm's law) that the voltage drop across the resistor R is VR = IIN × RF; however, I wonder why "the output will be VOUT = −(IIN × RF)"? I would like to know why.

"While we used to call this a "current-to-voltage converter," which it is indeed, it's also sometimes referred to as a "transimpedance amplifier," where the "gain" or "transimpedance" is equal to RF", concludes Mr. Pease at the end.

Now, answer honestly to my questions. What have you understood from this reputable source? Have you known what the problem actually is? Have you realized how the problem was solved? Have you made sense of connecting an op-amp? Do you understand what it actually does in this circuit? Simply speaking, what is the basic idea behind the circuit? Can you elaborate it, in order to get circuits that are more complex (for example, circuits with negative resistance)? Can you simplify it, in order to get circuits that are simpler (for example, op-amp ammeter)?

Try to find ahswers to these questions yourself. As for me, I will prepare a human-friendly story about this legendary circuit and will place a link to this "non-verifiable" source on transimpedance amplifier page. This circuit deserves attention. --Circuit-fantasist 07:59, 16 July 2006 (UTC)

[edit] My viewpoint at transimpedance amplifier

As I can see, there aren't any suggestions; as usual, I have first to expose my viewpoint. If I have to express briefly the main idea, I will say:

In transimpedance amplifier, the op-amp compensates the voltage drop across the resistor adding as much voltage as it loses; the compensating voltage serves as an output voltage.

If I have to express in details the main idea, I will build the circuit in three successive logically connected steps. In the beginning, imagine we have to measure a current flowing through a circuit. However, we have a voltmeter instead an ammeter; so, we decide to convert the current into voltage. For this purpose, we break the circuit and connect a resistor R acting as a simple current-to-voltage converter.

What does the op-amp actually do in the circuit of transimpedance amplifier?


Step 1: Passive current-to-voltage converter	Step 2: Active current-to-voltage converter	Step 3: Op-amp current-to-voltage converter

Step 1: The problem. Only, a problem appears here: from one side, the voltage drop V_R = R.I across the resistor (the output voltage) is useful for us; from the other side, this voltage is harmful as it enervates the excitation voltage (not shown on the picture). As a result, the current I_IN decreases. What do we do to solve this contradiction?

Step 2: The remedy. Obviously, we have to compensate the voltage losses across the resistor R. For this purpose, we connect an additional voltage source V_H and adjust its voltage so that V_H = V_R. As a result, the "harmful" voltage V_R and the resistance R disappears; the point A becomes a virtual ground (V_A = 0). Actually, the additional voltage source V_H "helps" the excitation voltage in its efforts to create the current I_IN. Note that the two voltage sources are connected in series, in one and the same direction (- +, - +) so that their voltages are added. Then we take the compensating voltage V_H = -V_R = -R.I as a "mirror" output. The advantage: the load consumes energy from the "helping" voltage source instead from the excitation voltage source.

Step 3: The implementation. Finally, we make an op-amp do this donkeywork. Now, it "observes" the virtual ground and adjusts its output voltage V_H = -V_R = -R.I.

User:Circuit-fantasist

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