volume40-number3(1).pdf

A forum for the exchange of circuits, systems, and software for real-world signal processing

In This Issue

Editors’ Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

D-Day [ The Wit and Wisdom of Dr. Leif—4 ] . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Fast, Versatile Blackfin Processors Handle Advanced RFID

Reader Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Precision Signal-Processing and Data Conversion ICs for PLCs

Now Have More Performance at Less Power, Size, and Cost . . . . . . . . . . . 11

Wideband A/D Converter Front-End Design Considerations . . . . . . . . . . . . . 19

Product Introductions and Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

www.analog.com/analogdialogue

Editors’ Notes

SPINNING THE WEB ARCHIVES

You may have noticed that the time span of

our Web archive has been growing. As these

words are being penned (all right, keyed !) the

list of complete back issues in PDF goes back

to Volume 11 (1977). By the end of the current

year (2006), our 40 th consecutive year in print,

the roll call will be complete, starting with

Volume 1, Number 1 (1967), and our weary

scanner (and its wearier operator) can rest.

What does it all mean? First of all, the world will have available a

journalistic history of products, technologies, and applications Analog

Devices has been involved in, including our many successes—and yes,

the few egregious failures otherwise lost in the mists of history.

Second, you will meet many of the (by now, several generations of)

engineers who were part of this stream, including (perhaps too much

of) ourselves—and so will get a lavor of the times.

A few cautions are necessary: These pages are reproduced without

further editing, and may contain inaccuracies, especially in light

of the passage of time. Since many (perhaps most ) of the products

mentioned, especially in the earliest days, are obsolete and perhaps

long forgotten, even by us, the words you read in our pages may be

the only surviving record of their existence. Your expectations of

obtaining further information from us should properly be low.

Looking back at sampled pages, we’re again impressed at their

readability, but we also note that, even with the high-resolution

scanning, the detail in some of the illustrations is inevitably lost.

The interested reader may have to tap one’s own creativity to guess

at the details. Finally, because the scanning technique does not

recognize characters, suficient information has not been available

to conveniently assemble a helpful index the easy way.

So with these caveats, we invite the historically interested reader to

plunge into this literary stream and sample our global low of signal

processing products, technologies, and applications, as viewed from

Norwood, Massachusetts.

“Frederic has been a key leader of the RF and Wireless business

unit’s system-on-a-chip efforts and champion for SOC design at ADI.

His technical leadership and design innovations in digital ICs have

contributed to ADI’s accomplishments in wireless; and our analog

design teams received a greater exposure to system IC techniques

through his work.”

Prior to joining ADI, Boutaud was an IC design engineer at Texas

Instruments, where he worked with a wide range of technologies,

including CPU design, oversampling converters, graphic and video

processing, and low-power DSP core design. Born in Meudon

(France), he graduated from École Centrale de Lyon in 1978 with

an MSEE degree. He lives in Waltham, Massachusetts, and his

spare-time activities include music, yoga, and biking.

Dan Sheingold [dan.sheingold@analog.com]

FEEDBACK

We love hearing from you, our faithful readers,

and invite your comments on anything from

the quality of our articles to the layout of our

publications to the content of these editorials.

Those of you who read Analog Dialogue online

may already have noticed the new feedback

box at the end of each recent article. In each

box, you will ind a link to Analog Diablog

( h t t p : / / a n a l o g d i a b l o g . b l o g s p o t .c o m ) ,

where we encourage you to open a dialogue with the authors and

your fellow readers. Or, as always, please feel free to send email

directly to the authors, or to us, your attentive editors. As a token

of our appreciation, we’ll send a limited-edition 40 th -anniversary

pint glass to those readers who send the best suggestions for

improving the Dialogue .

RFID

While reading about Blackin processors in RFID readers, many of

you may have realized that this is the same technology that you use

every day to open doors with your company ID badge, buy groceries

with your MasterCard PayPass, or pay at the pump with your Mobil

Speedpass. In the age of identity theft, many of you may be concerned

about the conidentiality of your personal information. Smart cards

contain the same information that is encoded on the magnetic strip

of a conventional credit card, but they are much more secure. Unlike

magnetic strips, which can be cloned with a $20 reader—following

easy-to-ind instructions—smart cards allow different pieces of

data to be kept distinct, where they can only be accessed by relevant

applications. They use various levels of encryption and authentication,

and can be combined with biometrics or keypads for additional

security. The card never leaves your possession, providing additional

safety and speed. More information on contactless smart-card

technology, payment options, and privacy concerns can be found at

http://www.ieprox.com/epayment_white_papers_payment.asp .

Scott Wayne [scott.wayne@analog.com]

NEW FELLOW NAMED

Frederic Boutaud , an ADI Senior Engineer, has

been named to the distinguished position of

Fellow during the Company’s 2006 General

Technical Conference (GTC), which attracted

more than 1500 engineers from our design

sites worldwide.

The Fellows honor is bestowed on a select group

of engineers whose innovation, leadership,

entrepreneurialism, and consultative skills

have contributed signiicantly to ADI’s business success. In addition,

“an ADI Fellow must be a Company ambassador, bridging across

organizations and demonstrating an unparalleled ability to teach and

mentor others within the Company,” noted Sam Fuller, Vice President

of Research and Development.

With his induction, Boutaud, who has amassed an impressive 46

patents in the CPU and wireless processing ields, brings to 31 the

number of Fellows at the top of the technical ladder among the

Company’s 3000 or so engineers worldwide.

A 25-year veteran in the ield of digital IC design and architecture,

Boutaud joined ADI in 1996 and assumed project lead responsibility

for the digital baseband IC team, which designed the SoftFone ®

architecture for GSM baseband processors, “one of ADI’s largest

and most complex system-on-a-chip designs at the time,” said

Fuller. “Frederic was the IC leader, as part of the core team—from

system engineering, algorithm engineering, and IC engineering

disciplines—who drove architecture- and product innovation to

realize this highly innovative, scalable wireless architecture.”

www.analog.com/analogdialogue dialogue.editor@analog.com

Analog Dialogue is the free technical magazine of Analog Devices, Inc., published

continuously for 40 years—starting in 1967. It discusses products, applications,

technology, and techniques for analog, digital, and mixed-signal processing. It is

currently published in two editions— online , monthly at the above URL, and quarterly

in print , as periodic retrospective collections of articles that have appeared online. In

addition to technical articles, the online edition has timely announcements, linking to

data sheets of newly released and pre-release products, and “Potpourri”—a universe

of links to important and rapidly proliferating sources of relevant information

and activity on the Analog Devices website and elsewhere. The Analog Dialogue

site is, in effect, a “high-pass-filtered” point of entry to the www.analog.com

site—the virtual world of Analog Devices . In addition to all its current information,

the Analog Dialogue site has archives with all recent editions, starting from Volume

11, Number 1 (1977), plus three special anniversary issues, containing useful articles

extracted from earlier editions, going all the way back to Volume 1, Number 1.

If you wish to subscribe to—or receive copies of—the print edition, please go to

www.analog.com/analogdialogue and click on <subscribe> . Your comments

are always welcome; please send messages to dialogue.editor@analog.com

or to these individuals: Dan Sheingold , Editor [dan.sheingold@analog.com]

or Scott Wayne , Managing Editor and Publisher [scott.wayne@analog.com].

ISSN 0161-3626 ©Analog Devices, Inc. 2006

D-Day

[The Wit and Wisdom of Dr. Leif—4]

which minimize solution time; 32 Tactical Units For Technical

Explication (TUFTE) optimize how each type of simulation result

is presented to maximize insight content; its Multilingual Speech

Engine , MUSE, can accept verbal inputs from users and generate

a same-language or translated response (or requested data), using

its Ubiquitous Text Transformer (UTTER) ...” and so on.

At the bottom of a GE8E cabinet, with the comms agents, iber-optic

ports, silent power-management modules, and other riffraff, is a dusty

nest of totally unimaginative binary CPUs. While tiny, fabricated in

16 nm, their lust for line power, so much more than all the rest of a

GE8E combined, and so hugely out of proportion to their contribution

to its function, can only be called distasteful.

Dr. Leif’s breezy preamble began right on time. “Good morning,

fellow travelers! Today, it’s my distinct pleasure to introduce

Dr. Niku Yeng, who will be describing her work concerning how

an RF oscillator starts up from cold. You may perhaps be thinking

this is a very simple topic, but Niku will remind us how complex the

behavior of a small analog circuit can be when it is examined closely,

and more thoroughly than found in most textbooks. As you know,

at ADI we place a strong emphasis on the learning experience . It’s as

much a ‘product’ as the silicon we sell.

“I must also tell you that Niku undertook this work without any

prompting. Great advances have never come from one who must be

asked . More than a century ago, in his book The Art of Living , Wilfred

A. Peterson said ‘[A] Decision is the courageous facing of issues knowing

that if they are not faced problems will remain forever unanswered. [It] is the

spark that ignites Action. Until it is made, nothing happens.’ Today, our

best products, and those going right back to our novel ICs of the 1970s,

have come from those who independently selected some challenge and

immersed themselves in it. They know no other way to pursue their

craft than by tracking trends and anticipating the future . Then, ignoring

all naysayers and using whatever subterfuges may be required, they

bring into existence a product providing a new function , perhaps years

ahead of any market demand. It is this , not mere Invention (which

is invariably a leeting moment ) that alone may be called Innovation,

the arduous process of turning thinking into things.

“I recall how reluctant were our valiant marketing folks to accept

such a fait accompli ! But those Pied Piper products often created

whole new families , even new businesses . Many of mine are still alive,

after decades of proitability. So please—don’t hold back! Have the

courage of your deepest convictions! You may make a few mistakes

at irst, but you must always follow your instincts— and seek ways to

convert your clever ideas into tangible realities. Alright, well, that’s

quite enough from me! I’m sure you’ll enjoy this talk, and beneit

from Niku’s exemplary work ethic and her unusual way of thinking.

So now, young Yeng, it’s your turn!”

Feeling more poised than she had expected, perhaps because her

faithful companion Micha was right behind her, ready to assist with

the presentation, Niku began with an icebreaker.

“Thank you, Dr. Leif, and good morning, everyone! First, in case

you are wondering about my mixed-up name, let me explain. My

Chinese father was on business in Bangalore the day I was born in

Oulu, Finland, and my Iranian mother chose my Persian name. We

moved to Solna when I was about six. I must have spent my childhood

in a perpetual state of perplexity because, ever since, I have always

been attracted to anything enigmatic or anomalous.

“Although I’m a relative newcomer to ADI, I already consider myself

fortunate in being able to tap into the wisdom of Dr. Leif, who taught

me about the Four Dees . Let’s see: Analog circuits are Durable,

Diverse, and ... oh yes, Dimensional. However, he left me to ind out

for myself that this domain of design is at times deceptively Dificult,

and demands Determination, Drive, and Dedication to deal with

dozens of dastardly devious and daunting Details!”

The smiles of acknowledgement rustling around the audience assured

her that she’d overcome the irst barrier to acceptance.

“Oscar, as I call my oscillator, is a basic LC-tuned, differential

topology using a simple BJT negative-impedance cell—an NIC.

The small-signal behavior of the CMOS version will be similar;

but differences appear as the oscillator approaches its eventual

cyclostationary end-state, particularly for large overdrives. The

fundamentals of the BJT make analysis far easier for this state.

By Barrie Gilbert [ barrie.gilbert@analog.com]

For Niku Yeng, August 29, 2025 came far too quickly; but for Dr. Leif,

it was just another of his Daedalus Day events. He had started this

series—always convened on the last Friday of each month, with the

objective of providing a forum for the youngest Originators to present

their unique perspectives—shortly after the founding, in 2018, of this

Analog Devices campus, in Solna, a suburb of Stockholm. Why Solna?

Some believe it was ADI’s decision, being quite close to customers

in northern Europe and Russia. Others think it was simply Leif’s

hometown, and if he wished to establish a new design center there,

that was good enough for the Company. It wasn’t the irst time.

Presentations such as D-Days are instantly available at all ADI sites

worldwide and are automatically archived. It is understood that

information contained in every technical presentation and review (like

the ruthlessly probing Design Scrutiny) represents the lifeblood of

any company at the fringes of nanotronics. To allow it to be quickly

forgotten would be as irresponsible as the old practice of incinerating

‘waste’ materials or burying them in landills. Recycling philosophy

today is radically different from the short-minded practices pervasive

at the turn of the century. Nowadays, a subscriber to the Global

Used Materials Registry can readily locate over 85% of the world’s

recycled materials.

Usually convened in the Michael Faraday auditorium, D-Days are

always well attended by the local audience; but this morning many

late arrivals had to stand at the back, or on the side steps. Curiosity

to watch how a ‘new guy’ might fare always ran high. Today it was

a ‘new gal,’ so an extra dash of excitement stirred among the male

contingent, roughly two-thirds of the total. All these auditoriums were

equipped with imaginative technology for enabling and enhancing

effective presentations. In planning the campus, Leif proposed that

their neuromorphic simulators, impressive and inspiring showpieces

as well as active partners, be located in full view at the front of the

largest auditoriums.

This choice was partly dictated by their size: a General Electro-optical

Emulator (GE8E) was bulky, due to the space required for the dense 3D

webs of opto-connection ibers for the concurrent information paths.

Unlike the old digital machines, a GE8E is not a mindless number

cruncher. Rather, the processes active within it are an inseparable , organic

aspect of its structure. Each is a GE8E, having a unique personality and

its own repertoire of individually learned problem-solving tricks and

philosophies. However, these are unobtrusive—users see a uniform

I/O image, at least on most days ... So it is appropriate that the little

ID plate, discreetly attached to the fascia by Neuromorphix Inc. shows

the simulator’s personal name , not that of the manufacturer. Here, it is

the MF-GE8E, informally Michaday, more cozily Micha: one of the

smaller GE8Es on campus, having some 3 million hacks. Few today

can remember how this term arose. It is a hybrid analog computing

kernel , a neuromorphic emulator ASIC, with 8192 intraconnected

analog array processors, comparable to a 1-mm 2 patch of human

cortex but quite incapable of autonomous ‘thought’ (as is the patch

of cortex—although that begs the question). In circuit-simulation

studies, each hack assumes the behavioral characteristics of an

individual element, such as a transistor, in the user’s circuit.

The GE8E designers weren’t lacking a sense of humor, some of which

leaked into each unique—and playful—platform, as well as into

the Manual. On p. 72 we read: “Hacks are organized into groups,

each representing a user’s network to be simulated, by a Matrix

Attach Designator and Description Organizer , MAD D O G , while the

actual interconnections are set up by St.VITZ, the State Variable

Intertwining Zoner . Details of the IC processes, stimuli, and all other

essential data are loaded into the job-speciic hacks by Feed Units

for Parameters (FedUPS). The fast analog results are optionally

delivered to a Pre-Output Unit Processor (POP UP ) for numerical

puriication and sanitization, using conventional matrix methods.”

(Puriication? Sanitization!?)

“The GE8E dynamically selects heuristics and accelerators from

its personally-acquired repertoire. Every job can access over

250 HURRYUPs ( Handler Unit for Redeploying Unused Paths )

Analog Dialogue Volume 40 Number 3

(a)

(b)

1MV

100kV

10kV

I CRIT �

2.0681008663033986mA

CT/2

CT CT

1kV

100kV

RESONANCE �

2.500002364296GHz

(FREQUENCY SWEPT

FROM 2.500GHz +

2.36429 TO 2.36430kHz,

BY 0.1 � Hz)

100V

10V

10kV

100mV

1kV

10mV

LT = 4.05nH

CT = 1pF

RL = 50 �

Slide 1. Two forms of the basic Oscar.

“Micha, irst slide, please. Thank you. As you see, there are two forms

of the basic Oscar. Both are innocent looking, aren’t they? Almost all

basic analog cells have deceptively simple topologies. But, as you know,

their behavior is complex and the explanations found in textbooks

are frequently incorrect or, at best, supericial and inadequate for any

serious design work. I must admit that, at the start of my studies, I

had no idea of how many winding lanes and back alleys Oscar would

lead me down. But, in the process, I have gained many rewarding

and unexpected personal insights.

“Initially, the question was simply this: does Oscar start because of an

external disturbance —a ‘supply glitch’? Or rather, is this process driven

by internal noise ? Any oscillator that’s expected to provide a spectrally

clean output can’t afford to be susceptible to supply hash; this is the

irst reason for using fully symmetrical circuits. The second reason is to

minimize even-order harmonics. In an ideal, perfectly balanced cell,

the start-up process can only be driven by noise ampliication . But all

practical circuits have mismatches so bias sensitivities are inevitable;

even a minuscule mismatch could be the dominant destabilizing

factor. Therefore, both noise and circuit mismatches can drive this

process. So the question becomes: How do these two inluences

compare in their power to shake Oscar from his slumbers?

“Noise is analytic and can readily be quantiied, with or without the

help of Micha;” (Niku thought she detected a tolerant sigh behind

her) “whereas the impact of device mismatches can only be assessed

by making assumptions , about their types and their magnitudes, for

a small subset of possibilities. So my objective took another turn:

Could I demonstrate that noise is invariably the dominant driving

force behind startup, even in the presence of signiicant mismatches?

That is clearly the desired outcome, because it provides a reasonable

assurance that, if nothing else, our choice of circuit topology is probably

as good as it gets.

“In these cells, the only power source is the tail current, I T , thus

avoiding questions of supply sequencing. We can experiment in a

number of ways: I T can appear abruptly, that is, in a time much less

than the tank’s period—400 ps with the values shown—or slightly to

much longer, and with or without mismatches added.

“Putting aside the ‘glitch postulate’ for the moment, let’s try to

understand whether noise alone could be the culprit, by ramping I T

very slowly. It makes only a little difference which form of Oscar we

use—and even, in moderation, whether we include any mismatches.

We must examine the voltage noise spectral density and total integrated

noise at the output A, B right at the resonant frequency , since it has a

hyperine width of only microhertz, as this current reaches its critical

value. So, Micha, please run some examples of this for us, up to and

beyond I CRIT . By the way, what is I CRIT , and the resonant frequency,

at this current?”

“Roughly stated, the resonance at 300 K, with R L = 50 V, is at

2.500002364296 GHz for an I CRIT of 2.0681008663033986 mA,”

piped up Micha, “and I’ve also found that the line width at 50%

power level is about 19.22157 mHz, and that numerically the VSND

and rms cross over at roughly 11 (V/Hz or V rms).”

2kV

1mV

100 � V

TOTAL RMS NOISE (V)

CURRENT-DEPENDENT

INTEGRATED OVER

TANK BANDWIDTH

10 � V

1kV

1 � V

100nV

TAIL CURRENT

10nV

TANK VOLTAGE NOISE

SPECTRAL DENSITY V/ Hz

I T (mA)

1nV

2.500002364292

2.500002364296

1.74

1.90

2.06

2.22

2.38

FREQUENCY (GHz)

Micha 1. VNSD and rms noise (a) vs. frequency, at I T = I CRIT

and (b) vs. I T for values just above and below I CRIT .

“Well, thank you, Micha, for those, um ... observations. What we

should especially note here is that the basic noise sources in this

circuit, which I will later identify and quantify, are ampliied to

extremely high values of voltage noise spectral density , across the nodes

A-B; likewise, the total rms noise, integrated over the actual, very

narrow resonance bandwidth, attains an improbably high value. But

this is simply the inevitable consequence of the closed-loop gain briely

reaching ininity. The plot on the right shows how the VSND and

rms noise vary, as the tail current is varied slightly below or above

I CRIT —where they again decline.”

“The apparently high noise levels just indicate that the negative-

impedance converter comprising Q1, Q2, and their current tail, in

conjunction with the resistive component of its load, R L = 50 V,

exhibits an open-loop gain that rises to unity at I CRIT . Thus, the

closed-loop gain briely becomes ininite . But, even at this value,

an oscillation can’t build up in amplitude, since if it tried to, the

nonlinearity of the incremental r e of each transistor, kT/q(I T /2) at

balance, quickly raises their sum , kT/qI C 1 + kT/qI C 2 , to above the

permissible maximum, 4kT/qI CRIT , during each cycle.

“Perhaps now it’s apparent why the critical current is 2.086 mA. Do

you see? It’s because the total incremental emitter resistance

is 4 3 25.85 mV/2.086 mA, which is 50 V, the load resistance

at 300 K, while at resonance the parallel-tuned tank behaves like

an open circuit. So now, Micha, show us the tank voltage in the time

domain at precisely I CRIT , following its appearance with an onset time

of, say, 1 ns. First, switch off your stochastic noise sources, and then

repeat the experiment with them active.”

Micha demurred. “Well, there’ll be nothing much to show either

way because, with no noise, the fully balanced circuit will never

start; and even with my stochonoise sources switched on, it will take

over 14 hours to show signiicant signs of life, because the resonance

bandwidth is only ~19 mHz. Do you have that long?”

“Ah, Micha! You’re good at many things, but not talented when

it comes to thinking things through! That hyperine resonance is

present only when the tail current is exactly I CRIT . In rising from

zero, the loop gain gradually increases; but, as it passes through

lower currents, the resonance bandwidth is much higher and the

loop response is proportionally faster. Alright? So now Micha, please

run my time-domain experiment, but let’s take the tail current just

a little bit past I CRIT , say, to 2.1 mA.”

Analog Dialogue Volume 40 Number 3

auditorium clock had no doubts: lashing orange at the ingertip of

its minute hand, it informed Niku that she had spent ifteen minutes

saying little of substance. Then, standing four-square in front of her

coworker, Michaday, Leif’s zealous young protégé did something

that amazed even him.

“I knew that I was going to have a hard time including in a one-hour

talk even a small selection of all the issues comprising my recent

studies, so I have asked Micha to pick up my presentation here. He

will talk at normalratetimestwo, so pay close attention!”

Clever kid ! thought Leif. What a liberty ! thought the audience.

“Thank you, Nicky,” began Michaday, speaking in single-time.

( Oh-ho! so it’s ‘Nicky’ now , gasped the stunned audience, some

thinking: He never calls me by my nickname! ). “In picking up this

presentation, I will repeat it just as Dr. Yeng delivered it to me, last

night, except for the time-compression factor.” Then, switching

to zeropitchshiftnormalratetimestwo, Michaday said, “Let’s now

examine the effect of element mismatches.”

Absorbing technical material in double-time was no novelty to the

audience; many were quite used to triple-time . But Niku’s artful

subversion had left several people feeling that this was cheating.

They had come to watch the Niku girl coping with her irst D-Day

presentation, not listen to a clever box of wires. As the smoldering

dissent spread, it grew exponentially, like Oscar’s noise, and soon

became palpable enough to cut with a knife.

“This next study will show some re-re-re-re-re-re ...”

Leif had sensed the audience’s unease and, using his privileged veto

over “ improper use of facilities ,” he interrupted Michaday’s gleeful

takeover with one transponder click. Before standing, he thought for

a moment how best to handle this delicate impasse, not wishing to

sound critical, or undermine Niku’s clever ruse.

“Dr. Yeng, I’m conident that Michaday will be faithful to your

material, and won’t pull a HAL on you.” Those aware of the old

movie grinned broadly at so delightful a prospect. “But we came to

hear you, and I suggest we can afford the time, this morning, to take

in your material at Niku_in_single_time.”

Everyone laughed, relieved to see that the respected guru was still

fully in charge. Blushing like an Arizona sunset, Niku said, “I’m really

very sorry, Dr. Leif. To tell the truth, I was hoping to capitalize on

my discovery of how extraordinarily accomplished our GE8Es are,

and to allow my good companion Micha to be in the limelight for a

while. But I see that this was presumptuous of me, and I apologize

to you—and everyone.”

With that, she picked up where Micha was left in mid-sentence.

(a)

(b)

2.25

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

TAIL CURRENT I T RISING TO 8mA

TAIL CURRENT I T = 2.1mA

1.20

COLLECTOR CURRENT OF Q1, Q2

1.00

COLLECTOR CURRENT OF Q1 AND

Q2 (EACH EXACTLY HALF OF I T )

0.80

0.60

0.40

0.20

1.00

300

TANK VOLTAGE RISES TO ±0.25V p-p

0.75

200

0.50

0.25

TANK VOLTAGE–FRACTIONAL FEMTOVOLT,

EVEN OUT TO 1 SECOND

100

–0.25

–0.50

–100

–200

–0.75

–1.00

–300

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

TIME ( � s)

TIME (ns)

Micha 2. The time-domain response of the full-balanced

Oscar, (a) with stochastic noise processes excluded and

(b) included.

“As you see, a huge ‘glitch’—in fact, the full onset of the tail current—

fails to wake up a perfectly balanced Oscar, while the internal noise,

amounting to rms values that readily reach many volts, and included

here by Micha’s complete modeling of noise as a process in time ,

evidently cause a very rapid startup. But we’ve a lot more to study,

before reaching our inal position.”

A voice was raised from the back of the hall, “Why do you rely so

much on simulation, when a more satisfying answer ought to come

from an algebraic analysis?” asked the speaker.

“That’s a fair question, although I’m not sure what constitutes a

satisfying answer. I’ve learned from Dr. Leif to simulate irst , then

address the analytical issues later. This is not indicative of laziness, or

weak-headedness, as was once so widely believed—vehemently—by

a few analog diehards decades ago. In my own experience, and

everyone’s I expect, much precious time can be saved in trying to

develop a general theory, by irst spending a few minutes studying a

number of special cases by simulation. This time helps us to realize

both the scope of possibilities and the circuit’s limitations ; and we are

led forward, not always to the analytical solution we may have been

seeking, but to deeper insights than typically come out of many tedious

pages of error-prone algebra. Further, the mathematics is frequently

intractable in highly nonlinear circuits, even though very simple,

like Oscar.

“On the other hand, in pursuing this approach (which some still

adamantly call ‘tinkering’) it’s inadmissible to accept Micha’s answers

without veriication,” (another sigh from behind) “and without any

personal understanding of what the answers mean , that is, without asking

Why? , or without extending one’s special case to the more general case.

Bursts of insight can transport you into wild new realms of invention ;

but you must assimilate these insights, and organize them, if you wish

to become their master!”

Dr. Leif was beaming, not at all surprised that Niku’s intensity was

so unashamedly visible. But the audience wasn’t sure what to make of

this impassioned outpouring; she was “preaching to the choir.” The

[ For the conclusion of Niku’s talk about Oscar, and all of Micha’s

slides, please visit http://www.analog.com/library/analogdialogue/

leif1.html].

Barrie Gilbert , the irst-appointed ADI

Fellow, has “spent a lifetime in pursuit

of analog excellence.” Barrie was born

i n Bou r nemout h, Eng la nd, i n 1937.

Before joining ADI, he worked with irst-

generation transistors at SRDE in 1954. At

Mullard, Ltd., in the late ’50s, he pioneered

transistorized sampling oscilloscopes, and

in 1964 became a leading ’scope designer

at Tektronix. He spent two years as a group

leader at Plessey Research Labs before

joining Analog Devices in 1972, where he

is now director of the Northwest Labs in Beaverton, Oregon. Barrie is

a Life Fellow of the IEEE and has received numerous service awards.

He has about 70 issued patents, has authored some 50 papers, is

a reviewer for several professional journals, and is a co-author or

co-editor of ive books. In 1997, he was awarded an honorary doctorate

of engineering from Oregon State University.

Analog Dialogue Volume 40 Number 3

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