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Electronic Design


Which Filter Can Get The Job Done?
I've just read the "Simple AC Stop, DC Pass Circuit" by Ankur Bal and Abha Jain in the Sept. 7, 1999 issue of ED (p. 112). I'm not sure if the authors realise what they've done. Although they claim that the function "...can't be performed by conventional low-pass filters," this is exactly what they've got. Simple math on the circuit indicates that the output voltage is related to the input by the equation:

Vout = Vin / (1 + sR1C1)

which is the function that could be performed by a low-pass filter comprising R1 and C1 alone. Add a couple of unity-gain buffers, and they'd have saved the other six resistors and two op amps.

Matching considerations also disappear. I'd be interested if anyone else has noticed this. Meanwhile, thanks for an excellent mag.
Peter F. Vaughan
Chief Engineer
Aero Stanrew Ltd.

The Real Cost Of Communications
I just read \[Cheryl Ajluni's\] column in Electronic Design, Oct. 18, 1999 (p. 18). It's very thought-provoking. My thought is, "With friends like MIT, who needs the Borg?" With every advance in consumer electronics, the assimilation becomes more complete.

Communication is wonderful and I think we need more of it. But on what level and why should we communicate? What is communication technology doing to enhance our lives on a social and spiritual level? Technology is already at the point where we can communicate with thousands, globally, and yet never see them or experience them as fellow humans. E-mail is a very poor conveyor of emotions. Cell phones and pagers have superseded manners in social situations. Why is it OK for a gadget to interrupt when a person would not be allowed to do so?

Internet advertisers say seeing a picture is just as good as being there in person. Some scientists think we should embrace bionic implants—not because we can't live without them, but because they might make us better. Why do I need to see ultraviolet on a daily basis? Others suggest immortality comes by turning your brain waves into a computer program. As long as there are no power glitches, you can live in virtual bliss forever. I can't wait! Put my brain in a jar and plug me in!

Current technology makes it possible to live most of your adult life without physically contacting another human. Television, video games, and now the Internet have replaced flexible, caring mothers. If a computer said it, it's gospel. It's now possible to electronically steal a person's identity.

Why? Because we deal with numbers and not people. Who needs social interaction when we have machines? Let the computer match my clothes and make-up. Let the computer find my soulmate. Let the faceless Internet doctor tell me why I feel bad.

Sometimes I think it would be good if all the computers really died from the Y2K bug. Maybe we could take some time and get back to being human.Why do we need to talk to our kitchen? Just because we can do something doesn't mean we should. Simple is not bad, just different.
CAD caveman #1
Keith Morgan, C.I.D.
Hardware Engineer/CAD
Applied Innovation Inc.

Lonely In Taiwan
I am a long-time reader of Electronic Design magazine. I am particularly intrigued by your editorial on the "analog world" (Oct. 28, 1999, p. 16). Our company is the only so-called "IDM" analog company located in Taiwan. In the midst of the local DRAM and foundry boom, we are lonely and having a hard time recruiting new graduates to join.

Your article and the reference cited from The New York Times should be very convincing for non-analog people. Thank you very much.
James S. Ni
Analog Technology Inc.

Those Ever-Elusive Toaster Jokes
Read your editorial and laughed at the snippits of the "Diary Of A Digital Toaster" (Nov. 8, 1999, p. 16). You mentioned that you were going to post it to your web site. However, I was not able to find it. Can you send me the URL?
Ralph Bellofatto
Principal Engineer
Voyetra Turtle Beach Inc.

The toaster humor got a little lost in the shuffle as we switched to a new server. You can now find it on our web site. Starting at our home page,, go under the current issue into "Community" and then "Comedy Club."—Ed.

A Safety Warning Is Never Enough
Articles such as the Analog Outlook feature in the Nov. 22, 1999 issue pop up in magazines from time to time ("Shed Some Pounds With This AC/DC Transformerless Power Supply," p. 109). Audio enthusiasts are sometimes tempted to propose high-power stereo amplifiers with transformerless power supplies. Your article has a safety warning included. But from my view in the power industry, this is insufficient.

Articles of this type should be presented (if at all) only as a theoretical solution, but they should really never be used in practice. Besides the liability issues, people really can be killed. If the author has a target market in mind, then his company's applications engineers should work directly with potential customers, not publish it for general consumption.

I suppose we could propose building a lighter-weight lawnmower by replacing the metal housing with just supports for the wheels, and telling everybody to stay away from the blades. But we all know what trouble that would create.

If there are people involved, you must assume the worst.
Jim Booth
Sr. Staff Engineer
Motorola Inc.

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