Editors' Notes—Volume 41, Number 3, 2007


In This Issue

Modern op amps and in-amps provide great benefits to the designer, and a great many clever, useful, and tempting circuit applications have been published. But all too often, in one’s haste to assemble a circuit, some very basic issues are overlooked, leading to the circuit not functioning as expected—or perhaps at all. The article on page 3, destined to be a classic, will discuss a few of the most common application problems and suggest practical solutions.

Medical ultrasound systems, among the more complex signal processing devices in use today, are used for real-time detection of health problems and general diagnostic procedures. Slower than radar and faster than sonar, ultrasound systems have become increasingly portable, evolving from cart-based systems into palm-sized devices. The article on page 10 discusses some of the necessary ingredients of compactness.

As electret microphones become smaller, their element capacitance decreases. JFET preamps no longer suffice, as their relatively large input capacitance attenuates the signal from the microphone. Much can be gained by replacing JFET amplifiers with CMOS analog and digital circuitry, including easier gain setting, multiple functional modes, direct digital outputs, enhanced sound quality, and higher noise immunity (see page 13).



The centerfold of this issue depicts the cover of 40 Years of Analog Dialogue, our 40th anniversary CD. Sure to become a valuable collector’s item, the CD contains a complete set of PDF reproductions of (every page of) every issue published in print during its first 40 years, from Volume 1, Number 1, in 1967, through Volume 40, Number 4, in 2006. Articles can be accessed by issue or by author. In addition, Editors’ Notes, articles in the “Ask The Applications Engineer” series, and Barrie Gilbert’s “The Wit and Wisdom of Dr. Leif” can be accessed directly.

If you’re on our North American print distribution list, you should have received a copy with this magazine. If you’re on our European print distribution list, you should be receiving a copy soon. For all other readers in North America who want a copy, please contact your local sales office, or send your name and mailing address, along with a check or money order for $50.00, made out to Analog Devices, Inc., to this address:

Analog Dialogue 40th Anniversary CD

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Norwood, MA 02062



In the Analog Dialogue Volume 41, Number 2 Editors’ Notes, you wrote:

“The second problem is that the GPS loses its signal when I travel through Boston’s Big Dig tunnels, making it unable to maintain its bearings or to provide instructions for lane splits and exits. Too bad it doesn’t include an ADI accelerometer, whose inertial navigation capabilities could provide positional information during these temporary signal losses.”

Now, extend that problem to coal mines, where GPS is useless “ALL” of the time. How do you tell a miner’s location “after” an anomalous event like an earthquake, when the mine is literally a different place? Way points might be damaged, so they can’t be relied on. Coal absorbs most radio frequencies, so like GPS, RF is nearly useless.

The physical environment also presents several challenges: dust so thick that you cannot see through it; irreplaceable batteries that must be capable of lasting through a 12-hour work shift; intrinsic safety, which requires that the total available energy must not be capable of igniting a methane gas atmosphere; and the need for a small, lightweight device that can be carried for 12 hours.

Some possible areas for research include underground and underwater radio antennas, RFID-radar, black hole antennas, and NIST WWVB radio broadcasts. More information can be found at the Location Challenge (http://www.wearablesmartsensors.com/location_challenge.html).

Do any of your readers have an idea that no one has yet thought of?

Bob Paddock [bpaddock@designer-iii.com]

Dan Chimes In

A productive place to start may be with locating tunnels used by escaping convicts, terrorists, and smugglers of dope, other contraband, and people. As a medium for R&D, there are many more of them to be found, and if we can solve that problem, it may be a big step toward locating the (less frequently) lost miners. A solution to this problem could perhaps even allow us to follow miners (and terrorists) around in real time. The answer is (im?)possibly through gravitational waves, but I don’t know of any likely technologies for exploiting them.



In June 1952, George A. Philbrick Researches, Inc., a company soon to become the originator of a new product category, the (octal-socket plugin) differential operational amplifier, published Volume 1, Number 1, of The Lightning Empiricist, “A Journal for devotees of high-speed analog computation, those enthusiasts for the new doctrine of Lightning Empiricism, publishable aperiodically and distributed without charge … and offering items of interest and value on such computational topics as applications, techniques, and new or improved components.”

Its first editor was George A. Philbrick himself; later, from 1957 through 1966 (the year that Philbrick was acquired by Teledyne, Inc.) it was edited by Dan Sheingold—who also wrote much of the foreword to the first Teledyne/Philbrick issue, that would be published in March 1969, after his departure to become editor of Analog Dialogue. You can find quite a few issues of The Lightning Empiricist at www.philbrickarchive.org.

Dan’s favorite issue was one published in 1964, featuring an article containing many good ideas with the lengthy title: “IMPEDANCE AND ADMITTANCE TRANSFORMS Using Operational Amplifiers—Transadmittance, Transimpedance, Positive and Negative Self-Impedance through Active Circuits, including references to Photomultiplier and ion-current amplifiers; Current sources and generators; and Negative resistors and capacitors for dynamic compensation with Single-Ended, Differential, and Inverted Amplifiers.” Even after more than 40 years, one may find a few fresh ideas in it at www.philbrickarchive.org/1964-1_v12_no1_the_lightning_empiricist.htm.


Dan Sheingold [ dan.sheingold@analog.com]

Scott Wayne [ scott.wayne@analog.com]


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