Page 91 - Analog Circuit Design Art, Science, and Personalities

The Story of the P2

fier (four stages, remember) and was patched back to the other PC board, it would
be able to regeneratively amplify even more than the honest gain of the RF ampli-
fier. That was why the demodulator wouldn’t work right unless a certain constant
minimum amount of 5 Mcps signal was always flowing through the amplifier. That
was why the gain would “pop into mode” (and when it wouldn’t “pop into mode,”
that explained why not). That was why the engineer down at Burr Brown couldn’t
figure out how to get it working right-the gain depended on the two PC boards
being spaced just the right distance apart! That was the trick that Bob Malter had
accidentally built into the P2, and that he had figured out how to take advantage of.
To this day, I am not sure if Bob Malter knew exactly what a tiger he had by the tail.
But I would never dare to underestimate Malter’s tough and pragmatic brilliance, so
I guess he probably did know and understand it. (I never did have the brass to ask
him exactly how he thought it worked. I bet if I had had the brass to ask him, he
would have told me.) I must say, if any engineer was bright enough to grasp and
take advantage of a strange interaction like this, well, Bob Malter was that sharp guy.
Now, since my P2A was designed on a single board, with the demodulator far
away from the inputs and oscillator, we wouldn’t have any “mode” to help us. But
that was okay-now that I understood the “mode” business, I could engineer the
rest of it okay without any “mode,” and I did. But that explained why none of our
competitors ever second-sourced the P2. And the P2A and SP2A remained profitable
and popular even when the new FET-input amplifiers came along at much lower
prices. It was years before these costly and complex parametric amplifiers were
truly and finally made obsolete by the inexpensive monolithic BIFETTM (a trademark
of National Semiconductor Corporation) amplifiers from National Semiconductor
and other IC makers. Even then, the FET amplifiers could not compete when your
instrument called for an op amp with a common-mode range of 50 or 200 V.
A friend pointed out that in 1966, Analog Devices came out with a “Model 301,”
which had a varactor input stage. It did work over a wider temperature range, but it
did not use the same package or the same pin-out as the P2.
Still, it is an amazing piece of history, that the old P2 amplifier did so many things
right-it manufactured its gain out of thin air, when just throwing more transistors
at it would probably have done more harm than good. And it had low noise and
extremely good input current errors-traits that made it a lot of friends. The profits
from that P2 were big enough to buy us a whole new building down in Dedham,
Massachusetts, where Teledyne Philbrick is located to this day. The popularity of
the P2 made a lot of friends. who (after they had paid the steep price) were amazed
and delighted with the performance of the P2. And the men of Philbrick continued
to sell those high-priced operational amplifiers and popularize the whole concept of
the op amp as a versatile building block. Then, when good low-cost amplifiers like
the ~A741 and LM301A came along, they were accepted by most engineers. Their
popularity swept right along the path that had been paved by those expensive
amplifiers from Philbrick. If George Philbrick and Bob Malter and Dan Sheingold
and Henry Paynter and Bruce Seddon hadn’t written all those applications notes
and all those books and stories, heck, Bob Widlar might not have been able to give
away his kA709s and LM301 s! And the P2-the little junk-box made up virtually
of parts left over from making cheap transistor radios-that was the profit-engine
that enabled and drove and powered the whole operational-amplifier industry.
Since George Philbrick passed away about 1974, and Bob Malter had died earlier,
1 figured I had an obligation to tell this story as there was nobody else left to tell it.
Even though 1 was not in on the design of the P7 or the P2. I understood their designs
better than just about anybody else. So, I just have to express my appreciation to
Jim Williams for leading and editing this book. I know he will want to read about
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