Quotes

"No one believes an analysis – except the person who did it.

Everyone believes a test – except the person who did it."

- ???

‘‘The best way to predict the future is to invent it.’’

 - Alan Kay

"... true knowledge can only be acquired piecemeal, by the patient interrogation of nature."

- Edmund Whittaker, A History of the Theories of Aether and Electricity

“Successful engineering is all about understanding how things break or fail.”

- Henry Petroski

"All science is either physics or stamp collecting."

- Ernest Rutherford

"The first time you go through the subject, you do not understand it at all. The second time, you think you understand it, except for one or two small points. The third time, you know that you do not understand it, but you are so used to the subject that it does not bother you anymore."

- Arnold Sommerfeld, about thermodynamics

"those who can, do; those who can't, teach."

George Bernard Shaw, Man and Superman

"engineering ... is the art of doing that well with one dollar, which any bungler can do with two after a fashion."

- Arthur M. Wellingtony, The Economic Theory of the Location of Railways

"Engineer - the man who can do for a reasonable cost what another would expend a fortune on"

- Rutherford Aris, Vector, Tensors and the Basic Equations of Fluid Mechanics 

“In God we trust. All others bring data.”

- Bo Lojek, History of Semiconductor Engineering

"Research is when you don't know what you're doing."

- ??? 

The cheapest, fastest, and most reliable components are those that aren’t there.

- C. Gordon Bell

"When you test you find something is wrong."

- Donald Trump (May 14, 2020)

I would rather have a general who was lucky than one who was good.

- Napoleon Bonaparte

"Perfect is the Enemy of Good Enough"

- Eric Johns (October 1988), U.S. Naval Institute Proceedings: 37

“If an expert says something can be done he is probably correct, but if he says it is impossible then consider getting another opinion.”

- Richard Hamming, The Art of Doing Science and Engineering 

People who are really serious about software should make their own hardware.

- Alan Kay

The management question, therefore, is not whether to build a pilot system and throw it away. You will do that. […] Hence plan to throw one away; you will, anyhow.

- Brooks, The Mythical Man Month (Page 116)

Brooks's Law: 

Adding manpower to a late software project makes it later.

 - Brooks, The Mythical Man Month

... this was going to be one of these Onion Syndrome deals - you peel off a couple layers, and cry; then you peel off a couple more layers, and cry some more.

- Bob Pease, What's All This Ground Noise Stuff, Anyhow?

Thinking is recommended. Heck, thinking is required.

- Bob Pease, Troubleshooting Analog Circuits

... a little known tenet of precision op amp circuits: Williams's Rule.  Williams's Rule is simple: always invert (except when you can't).

- Jim Williams, Analog Circuit Design: Art, Science, and Personalities

"Any idiot can count to ONE ..."

- Quoted by Samuel Wilensky in Analog Circuit Design: Art, Science, and Personalities

(maybe attributed to Bob Wildar)

Anyone can build a bridge that stands up, but only an engineer can build a bridge that just barely stands up.

- ????

In real estate, it is location, location, location.  In mathematics, it is notation, notation, notation.

- ????

In software, debugging is harder than writing code.  If you write the code as clever as you can, then you are not smart enough to debug it.

- ????

... where there is no confusion there is no prestige.

-Linderholm, Mathematics Made Difficult

All problems in computer science can be solved by another level of indirection, except for the problem of too many layers of indirection.

-????

... practicing what was called "the mushroom theory of management." ... defined it as follows: "Put 'em in the dark, feed 'em shit, and watch 'em grow."

- Tracy Kidder, The Soul of A New Machine

Hardware eventually fails. Software eventually works.

-Michael Hartung

Common Emitter Frequency Response using EET

Even the simple common emitter circuit can result in some pretty complicated expression for the frequency response. The inclusion of a single element, the base-collector capacitance, introduces much complexity.  This circuit is analyzed in detail by most of the textbooks, including Gray & Meyer's.  None of them makes use the EET.  We give a derivation using Middlebrook's EET to see if the analysis is simplified.

 We work out the factor involving Cf,

This is a little bit less work than the more direct method,

The two methods produce the same expression, so using EET does not give more insight.  

The base-collector capacitor results in an additional pole and a right-hand side zero and shifts the dominant pole.  The dominant pole can be approximated from the input capacitance and the Miller capacitance.

Useful Circuits with Two Transistors

The preeminent circuit designer Barrie Gilbert asks "How many distinctly different and really useful circuits can be made with two transistors, anyway?"  and his answer "about twenty-four" (Williams, Analog Circuit Design, p179).  Let's see what they might be.  It is perhaps subjective to tell what is useful or different.  Also what type transistors, BJT, JFET, MOSFET?  Same circuit configuration with different type of transistors should not be considered distinct. What about other circuit elements?  Assume the passives, resistors, capacitors, inductors, are OK, but what about diodes? And what about a multi-emitter/collector transistor or a dual-gate MOSFET?  Is it considered one transistor or multiple transistors?

A single transistor has three basic amplifier configurations; it can also be configured as a diode, and the emitter-base junction also makes a somewhat usable Zener diode.  A JFET makes a good current source (current regulating diode).

Input Impedance of a Bipolar Transistor Bias with Feedback

AoE shows a bipolar transistor bias circuit using feedback from the collector.  AoE2 and AoE3 show the identical circuit, but they differ in the values of the input impedance: AoE2 states 300 Ohms and AoE3 200 Ohms.  We would like to analyze the circuit to see why the value has changed.  Here the base bias is established by a resistor from the collector, which has the effect of negative feedback: a high bias lowers the collector voltage that reduces the base voltage.  

Here we estimate the collector current to be about 1mA.  The input impedance is about 200 Ohms for a beta of 100; it does not exceed 225 Ohms as the beta goes to infinity.  So it seems justified that AoE3 makes the correction.   Even when the temperature varies, the input resistance stays relative constant.  For example, if T = 100C, VT = kT/q = 32mV, but because Vbe decreases with increasing temperature, the emitter current also goes up, Vbe = 0.4V, Ie = 1.34mA, gm is still around 1/25 A/V.

N Light Switches

AoE2 has an exercise asking readers to wire up N switches that any one of the switches can turn on or off a light bulb.   It comments that every electrician knows how to do this, but few electronic circuit designers do.  Given the hint that it requires 2 SPDT and N-2 DPDT switches, it is not hard to do.

This exercise is retained in AoE3.

A Current Source Circuit from AoE-X

H&H show a clever current source circuit and challenge readers to prove the circuit works especially without using two of the constraints.

It is a circuit of an opamp driving a bipolar transistor.  The base current of the bipolar transistor would normally cause an error.  Here the error is compensated.  The base current is sensed with the base resistor kR1; the emitter voltage is Vin with the differential voltage added using a circuit configuration resembling a difference amplifier.

The derivation makes no use of the constraints on the resistors.  The base current compensation is strictly accurate (assuming ideal opamp).

Home Lab On the Cheap

Computer: Raspberry Pi 4B ($50), Atomic Pi ($35), OrangePi Prime ($35)

Atomic Pi only has 2GB RAM, which limits its use; but it is PC compatible.  It is usable with a decent USB drive.  Raspberry Pi 4B is usable.  They all can run KiCad for PCB design.  Atomic Pi can run LTSpice.

Multimeters: ANENG AN8008 DMM ($20), ST213 Clamp meter ($20),  Cen-Tech/HaborFreight multimeter ($5), LCR-T4 ($6)
AN8008 gives pretty good voltage and resistor measurement but the current measurement is not reliable at high range. Cen-Tech's current measurement is good enough.  And ST213 is for high current.  LCR-T4 is also good for verifying component values and the firmware is open source.

Soldering Station: TS100 solder iron ($40 with coupon), Chandler Tools heat gun HG603D ($24), PCB Holder fixture ($4)
TS100 is pretty decent.  There is an open-source version of the firmware. It is portable with a battery pack.   I also got 3 more soldering iron tips for about $4 each: TS-KU, TS-JL02, TS-C1 in addition to TS-D24.  The 320W heat gun with two speeds works well.  The PCB holder works for small boards.  A Harbor Freight "Helping Hand" with two alligator chips and a magnifier is somewhat usable after I secured the base with a plate. 

Caliper: iGaging EZCal digital caliper ($29)
It has a nice large display and works except for the battery life.  It is relatively a little pricey.

Scale: Digital Jewelry Scale ($4)

200g range, 0.01g resolution.  It seems accurate.  Good for weighing small components.

Rotary Tools:  HarborFreight Chicago rotary tool set ($5)
This is a cheap tool, barely usable.  I power it with a variable voltage power adapter to make it somewhat usable.

Lights: Desk lamp with magnifier
It had a fluorescent lamp, but burnt out.  I installed 10 1W LEDs.  It works very well.

Hand Tools: Set of pliers, wire strippers, set of small screw drivers, nibbler, diagonal wire cutter, tweezers, 6" ruler in SAE and metric ($3 for 2), Dental picks and mirror ($6)
A Harbor Freight 16 in 1 electronic repair kit was inexpensive ($5) and usable.  A small diagonal wire cutter is very nice to have.