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August 28, 2008
[Pease Porridge]
What's All This Output Impedance Stuff, Anyhow? (Part 2)
When I present seminars, I often ask the members of the audience to hold up their hands if they think bipolar op amps have better gain and linearity than CMOS. I get a good majority of hands. But neither is bad! The good-old LM301A (well over 30 years old) has a good gain of 260,000 at no load, with just 75 µV p-p of gain error while its output is swinging 20 V p-p (Fig. 1). What happens ...
August 14, 2008
[Pease Porridge]
What's All This Output Impedance Stuff, Anyhow? (Part 1)
A few engineers were having a debate. According to all the books, some of them said, op amps are supposed to have zero output impedance, or very low. That means the output voltage wonâ??t change, just in case the output current changes. Some older op amps had an output impedance of 600 ? or 50 ?. So, the gain of the amplifier wonâ??t change just because the load changes. That must be good. But a couple of other engineers pointed out that many modern op...
July 24, 2008
[Pease Porridge]
Bob's Mailbox
HI BOB, I am trying to build a test circuit that will produce a pulse current from a capacitor. My target is around 200 A at 100 ms. Is this possible? We have an instrument called a PVI that does the same only at lower current and at shorter duration, but I don’t know how it is being controlled. I hope you can give me advice or a basic control circuit that I can start working on. –ROMMEL C. VILLON HELLO, MR. VILLON, You...
July 10, 2008
[Pease Porridge]
What's All This Sudoku Stuff, Anyhow?
I suspect most of you have seen these “logical” puzzles in many newspapers (not to mention little books). They consist of putting numbers into squares so each big square of nine squares has every number, one through nine. Likewise, so does every row and every column. The easy ones are too easy, and the hard ones are substantially impossible. But the moderate ones are fairly challenging and satisfying. Sudoku is a big time-waster, and I won’t recommend anybody...
June 30, 2008
[Pease Porridge]
Bob's Mailbox
Analog and power guru Bob Pease corresponds with readers about the latest proposals for electric cars in this exclusive online edition of his popular mailbag.
June 26, 2008
[Pease Porridge]
Bob's Mailbox
HI BOB, I have been collecting some new but mostly museum-grade test instruments. Along with purchases from various instrument rental houses, flea markets, and so on, for a while I bid on items in government liquidation auctions. Occasionally, I won. The starting bid was always $50, and some I got at that price. Some went way higher but seldom approached the original list price, and I gave up way before that. Often, the shipping costs to a pickup and forward...
June 12, 2008
[Pease Porridge]
What's All This Current-Source Stuff, Anyhow?
Recently, a guy asked me how to draw a constant 1.00 mA from a node of a circuit. Of course, he did not tell me what volts, ohms, or frequency. But, he admitted, he basically did not know how to design a current source. So I’m sorry to waste the time of all you guys who do know how to design a current-source. But maybe this lecture can help and save you some time so you don’t have to teach all the young kids. If you need a current source, and you don’t know ...
May 27, 2008
[Pease Porridge]
Bob's Mailbox
Check out these additional letters to and answers from electronics guru Bob Pease.
May 22, 2008
[Pease Porridge]
Bob's Mailbox
HI BOB, Any big trips to exotic spots planed this year? We’re headed for Newfoundland and Prince Edward Island for a change of pace. (I may go to Scotland in September. /rap) My question: Do you have some circuitry I could use for an electronic bagpipe simulator? It would need nine notes selected by removing fingers from some form of contact that would reasonably simulate a finger hole. I don’t need too many...
May 8, 2008
[Pease Porridge]
What's All This One-Transistor Op-Amp Stuff, Anyhow?
One day, back about 1966, I was going up the elevator at 285 Columbus Avenue in Boston to look at some production problems on Philbrick’s fifth floor. And who was in the elevator, but George Philbrick’s friend Jim Pastoriza. Jim was going up to show George his new analog computer demonstrator—portable and battery-powered. In fact, it was running, and he gave me a demo right on the elevator as we ascended. And, this modular analog computer ran on a couple of...
April 24, 2008
[Pease Porridge]
Bob's Mailbox
HELLO BOB, A note concerning electric cars and plugin hybrids: Consider that politics has little to do with engineering and/or science. It only pays lip service at those altars. So, somebody has to do serious planning for the immediate future. I’ve been working on some serious battery-charger designs. One of our planners (an engineer) did some research in good old California. We learned that your utility companies have ...
April 10, 2008
[Pease Porridge]
What's All This AMT Stuff, Anyhow? (Part 2)
I’ve often heard that if you’re going to owe the Alternative Minimum Tax, there’s nothing you can do about it. And that makes me scream! Most of these officious statements say you can postpone some income and defer the AMT, but you’ll just pay them next year. “There’s nothing you can do to avoid the AMT.” It’s a lie! I was absent-mindedly reading some of the boilerplate on some of my other investments. “You might like to buy some AMT-free bonds,” Dreyfus...
March 27, 2008
[Pease Porridge]
Bob's Mailbox
HI BOB: I would like to ask about designing a sinewave amplitude attenuator with programmable attenuation. Preferably, it will just contain basic components (op amps, transistor, resistors, caps, etc.). Input: 1-V p-p sine wave (1 kHz frequency), symmetric at 0-V level. Desired output: still at 1 kHz, but the amplitude varies from 0 to 1000 mV. –JOERICH SUNICO HELLO,...
March 13, 2008
[Pease Porridge]
What's All This LED Power Stuff, Anyhow?
Recently, NSC put on a webcast with Howard Johnson, NSC’s Chris Richardson, and some guys from Philips and Future. As they had set it all up and presented it at the last minute, I didn’t know what points they were going to make. When they made their pitch, it all made perfect sense—but I wasn’t prepared to contribute very much. I sat there like a “fifth wheel,” not making many comments. But I did set up one experiment, which wasn’t shown on the webcast. I...
February 28, 2008
[Pease Porridge]
Bob's Mailbox
DEAR RAP: You answered one question for me last year (“Why are FETs so expensive in India?”), and I now have another. How does a bipolar op-amp-based non-inverting dc amplifier amplify dc signals that are below a 0.6-V bipolar threshold (e.g., an LM358- based non-inverting dc amplifier)? (Okay, you want a gain of +1.5 or 2 or 3 for a small signal that is barely above ground, such as +0.1 or +0.2 V? And the LM358 uses a small...
February 14, 2008
[Pease Porridge]
What's All This Oscillator Stuff, Anyhow?
Anybody can make an oscillator these days at almost any imaginable frequency. But how do you make a good one at low power? A couple of people recently asked me why I add so much complexity by using an op-amp oscillator in my Cold Toe Detector. (That general-purpose slow oscillator is in the LH upper corner of www.national.com/rap/coldtoes.html.) "What kind of analog freak are you?" they asked. "Why don’t you just use a CD4060, which has a built-in oscillator?" I responded that everybody...
January 31, 2008
[Pease Porridge]
Bob's Mailbox
DEAR EDITOR: At first I thought I picked up an April Fool issue, but no, you have Al Gore in the Tech Year in Review section honoring him for imploring engineers to turn green (Dec. 1, 2007, p. 45; ED Online 17958). What crap. Please cancel my subscription. –"RAY" Hello, Ray: There are several reasons to “turn green,” and Al Gore’s bleating about warming theories is only one of those reasons. Energy is expensive. Or haven’t you...
January 17, 2008
[Pease Porridge]
What's All This Layout Stuff, Anyhow?
December 13, 2007
[Pease Porridge]
Bob's Mailbox
Bob: While my full-time job is writing for Electronic Design, I still teach part-time and work on an NSF grant that is attempting to update the electronics curricula in community colleges. From my observations in my own college and across the country, most curricula are out of date with what is going on in the industry. (True, but not disastrously bad. We canâ??t ask that education for techs or for EEs be really up to date. That has almost always...
December 3, 2007
[Pease Porridge]
What's All This "Best Trick Circuit" Stuff, Anyhow?
Once upon a time, op amps didn’t swing very close to the positive or negative rails. Even a couple volts away from the rails—that was okay in the old days of transistor-ized op amps. Hey, that was a lot better than with vacuum-tube op amps that wouldn’t swing within 200 V of the rail. Some op amps could do a little better, but customers never asked us for better 35 years ago. The LM324 can swing pretty close to ground (–VS) if you have a...
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Bob Pease obtained a BSEE from MIT in 1961 and is staff scientist at National Semiconductor Corp., Santa Clara, Calif.
