Photolitics

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Photons Hit Electrons

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Recent Pole-Zero Pairs

▨ Not deserted - temporarily stranded

▨ Analog-style digital design observations

▨ The semiconductor industry in Bulgaria Vol. 2

▨ Small-signal and large-signal MOSFET channel resistance

▨ Bricks and mortar of the internet

▨ Harvesting gamma radiation

▨ Dominant gate capacitance of a MOSFET

▨ Mr. Sievert, a fictional character

▨ "This could be a very strong paper"

▨ Major milestone: Oxford thesis submission

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Deep N-Well

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Teaching analog design in an esoteric fashion.

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Occasionally I browse through the pages of some of the Bulgarian academic and research centres focusing in the field of IC design. This week, I have been enjoying the pages of Cyril Mechkov, a teacher in analog circuit theory in the Technical University of Sofia. I am more than impressed by his methods of explaining circuits, avoiding derivation of complex transfer functions and formulas, but instead guiding the students with intuitive explanations and examples related to everyday life.

Apart from Mechkov's circuit-fantasia website, he has also uploaded all his work in wikibooks, a book called Circuit Idea. A great fantasy has struck him - trying to involve students taking his courses to actively participate in the book development and have this as a micro assignment. I feel this great work needs somehow more attention and this is partly why I am writing about him. Here is a simple illustrative example on his thoughts and ways of explaining things:

As simple phenomenon as voltage drop over a resistor is explained by Mechkov in the following way. Imagine a large water tank that is connected to smaller vessels of the same height. The water tank is full and the end of the tap is closed. Mechkov's hand-drawn diagram:

The local pressures along a tapped pipe are equal to the input pressure, source: Cyril Mechkov, Circuit Idea

Now if one opens the far end of the pipe water will start flowing accordingly, therefore the pressures would decrease gradually according to basic hydraulic principles.

The local pressures along a tapped pipe decrease gradually, source: Cyril Mechkov, Circuit Idea

A very simple analogy could be made with a resistor and the voltage drop over it. Two analogies with voltage drop follow:

No voltage drop if no current flows, source: Cyril Mechkov, Circuit Idea

And the other way around:

If current is drawn, then the voltage drops linearly, source: Cyril Mechkov, Circuit Idea

The wikibook is enriched with figures following the same intuitive fashion accompanied with solid explanations and finally mathematical formulae (offtopic: oh this fancy way of writing such a simple word) covering the basic circuits in-depth.

Come to think of it, I did not find in his records an explanation of the Miller effect. Well, this is my trial for drawing an intuitive figure about the Miller effect:

My trial to explain the Miller effect with manikins pulling a rope through a system of reels. Poor phone camera picture plus an attempt to apply color threshold filtering.

At first sight this looks a rather funny way of explaining it. Our poor single manikin pulling down, whilst a bunch of other strong guys are counteracting to our single boy. So, the higher the gain (A), or transconductance (gm) in the case here, the stronger the guys would be, thus the miller cap - . Well, one should represent Cgd in another way to get a better picture, but still.

Ah well, if not for educational purposes, this might make out a good nerdy t-shirt:

The t-shirt fashion trends next year.

Happy last six hours of the weekend :)

Date:Sun May 11 18:05:00 CEST 2014

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