Electronic Design

Bob's Mailbox

BOB,
You said, “I don’t recall if I’ve ever seen this circuit in print” (“What’s All This PNP Stuff, Anyhow?” Sept. 11, 2008, p. 80; www.electronicdesign.com, ED Online 19605), regarding Figure 2. See:
1. P.J. Baxandall, E.W. Swallow, “Constant Current Source With Unusually High Internal Resistance And Good Temperature Stability,” Electronic Letters, Sept. 1966, Vol. 2, No. 9, p. 351-352.
2. Thomas M. Frederiksen, “A Monolithic High-Power Series Voltage Regulator,” IEEE Journal of Solid-State Circuits, Dec. 1968, Vol. 7, #12, p. 380-387. –WALT JUNG

HI BOB,
You said, “I don’t recall if I’ve ever seen this circuit in print.” I came up with the dash-circled NPN-PNP combination during a coffee bet with Tom Frederiksen when he was at Motorola. You might ask Tom when exactly that was, but it had to be the early 1960s. It’s in the MC1494 (multiplier with level shift). It’s also written up in several ICE (Integrated Circuit Engineering, Glen Madland/Howard Dicken) tutorials that I wrote during the 1960s.

–JAMES E. THOMPSON, PE

HELLO, JIM:
I might have seen some of the ICEs, but it does not ring a bell if I first saw the circuit there. Even if I did re-invent it independently, which I doubt, I sure doubt I did it first. Hey, why didn’t you patent it? Why was Motorola so foolish? Thanks for explaining where it came from. I’m glad to see you get the credit. I’m also going to mail your e-mail to Tom. I was just on the phone with him. He does have some recollections of the days when this circuit was invented. As I mentioned to Walt Jung, I don’t recall where I saw this circuit. I didn’t really think I invented it independently. But on the other hand, I didn’t see either of those magazines Walt mentioned. And I don’t think it has been in print very often since 1968.

–RAP

HI BOB,
A couple of decades ago, I was experimenting with some complementary JFET circuits, including the lambda diode configuration. I was amazed. Here was a configuration that allowed me to construct a sine-wave oscillator using only four components (two JFETs, a capacitor, and an inductor). I was able to construct a very simple 455-kHz BFO for my homebuilt short-wave receiver when the exigencies of family and career took precedence. Since then, I’ve had no real need to return to researching this device. So I was wondering if there were any modern-day applications for the lambda diode or if this device is now just as much a laboratory curiosity as a standard tunnel diode or tetrode valve.

–MARK BARNER

HI, MARK,
Tetrodes are consistent and reproducible. FETs have such a wide range of VP and IDSS that if you made a good circuit with some FETs, you would never be sure you could make a good circuit again! I’d much rather design with tetrodes. I can’t think of anything I would design with JFETs. It is true that monolithic op amps made with adjacent (well matched) FETs can be pretty good. Almost nobody designs with tunnel diodes anymore. Almost nobody makes them. They, too, are far out and not easy to characterize. Hard to select for the characteristics you might want. Almost anything you could make with FETs or lambda diodes, I could make better with bipolars. Or an op amp. I do like JFETs for analog switches.

–RAP

BOB,
I haven’t seen you comment on either the DTV transition or HD radio. We keep hearing about how DTV will make us happier because it’s “better.” But I don’t see the video or audio being noticeably better than a good analog signal. And now we’re hearing from the Wilmington, Va., test that DTV doesn’t work at all in the fringe areas (as expected). DTV even with a converter box won’t let me program my VCR to record more than one channel. And it won’t work with my portable TV. HD radio has been available for several years, but I still don’t hear much talk about it. Analog FM with a good signal is quite good enough for me. Why do I need FM HD, unless I want the extra channels that a few stations might offer? FM HD has such low power that it has much less range. AM HD is useless. At least in Chicago, there is hardly any music on AM. So why do I need better fidelity for news and talk? In fact, AM HD has degraded analog AM. It wipes out the adjacent channels and raises the on-channel noise floor. Very annoying. The radio stations don’t promote it much, and I don’t know anyone who has an HD radio.

–KENNETH LUNDGREN

HI, KEN:
I’m not an RF man. Like many “digital” things, it sounds like the hype and the reality are far apart. What’s new?

–RAP

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