Iremember the day it arrived. All of our
design engineers gathered around the lab
bench waiting for our technician to unpack
the box. As it was slowly lifted from the
protective cardboard packing and set on
the bench, we all looked on in amazement—
5 Mbytes in a single hard drive that
could fit in your hand! It was a Control
Data Corporation ST-506-compatible hard-disk drive
that weighed 4.5 lb and consumed around 40 W.
Just about everyone made some statement that was
the equivalent of “Who could ever use that much
storage?” The drive didn’t even have an onboard disk
controller. It also needed a circuit card loaded with
electronics to allow a computer to store and retrieve
the data! This was 1983, and 64 kbytes of RAM in
your computer was a bunch.
In those days, we all did our designs on vellum
paper with a mechanical pencil. It was not uncommon
for me to have 15 to 20 “E” size pages of
schematics all hand-drawn that were copied (using an
ammonia process) onto blueprint paper for our peer
design reviews.
I was a 23-year-old engineer then, and I remember
being hacked to death by my older colleagues.
I would get questions like, “Why did you use this
octal latch here?” or “Is this extra NAND gate really
necessary?” These were the days when an octal buffer
would cost you $0.80 (about $1.72 today) in
volume, so every transistor, gate, buffer, and latch
was questioned.
My old boss and mentor always told me, “I can
hire anyone off the street that can design something
that will work in the lab… I pay you an engineer’s
salary because I expect you to design something that
we can mass-produce. We are going to build thousands
of them and I expect all of them to work!”
I never forgot those words. It was a very interesting
time. If you wanted to learn how to build a charge
pump from transistors, a precision instrumentation
amplifier from discrete JFETs, and op amps or a
digital pipeline graphics engine from ROMs, latches,
and gates, it was the time to be alive.
Sticks and Stones? Almost...
It was the day of the PAL or programmable array
logic, which was the predecessor to the modern
complex programmable logic device (CPLD). These
little devices allowed us to build state machines
and consolidate logic, even though they were quite
expensive at the time.
We used primitive tools like PALASM (PAL
Assembler) and other simple PC-based tools to construct
the fuse maps. The maps were loaded into programmers
that would literally blow out a titaniumtungsten
fuse inside the PAL device. (You only got
one shot.) In the early days, it was not uncommon for
these “fuses” to actually grow back due to incomplete
programming and high signal currents. That would
always keep me guessing if I designed my logic correctly.
Oh, those were the days!
All of this hardware required power, and at that
time, the LM7800 (also known as the LM340) family
was our standard component for power-supply
design. We would use a transformer to step-down the
ac line voltage to approximately 8 V, rectify it with a
full bridge, and then use a linear regulator to produce
the 5 V needed for the logic. We also needed ±12 V
as well as –5 V, which were generated off split windings
of the transformer.
These voltages were also controlled by linear regulators
(both positive and negative versions). The –5
and +12 V in addition to the +5 V were required for
the ultraviolet (UV) erasable EPROMs that were used
for state machines or held processor code (see the figure).
Such power supplies were extremely inefficient.
Switching regulators existed, but for most engineers,
they were far too complex to use in a design.
Most engineers would wonder why we needed
extreme voltages for a digital IC. Remember, this was
the early 1980s and state-of-the-art NMOS processes
used to manufacture the 2708 and 2716 EPROMs had
geometries on the order of 2 µm (no, not 0.2 µm, 2
µm). That would represent more than 40 times larger
gate geometries than a modern 45-nm process.
Today, we have problems keeping charge carriers
out of the conduction channel (keeping the transistors
off). But back then, you had to help them out by
biasing the channel near conduction. These PROMs
contained a quartz window for erasing the programming
with UV light. If you accidentally plugged one
into a socket backwards, you created a light-emitting
PROM (LEP), which glowed orange through the
window for about a second while the gold bond wires
were incinerated—really fun times!
By the mid 1980s, Daisy Systems and Mentor
Graphics workstations started to appear—at an amazing
cost by today’s standards. Only very large corporations
could afford these tools, and the PCs of the
time were really underpowered to handle large schematic
capture or printed-circuit-board (PCB) layout
tasks. Many were still done by hand. I watched technicians
cut Rubilyth film with a razor knife to create
the patterns used to fabricate PCBs way before CAD
tools were used to do the same. That’s a lost art.
As the 1980s and 1990s progressed, we saw
advances in computers and computer tools. In 1993,
I remember my close friend calling me up to boast
about his brand-new, 33-MHz Intel 80386-based
computer and its 320-Mbyte hard drive. (I think he hocked his car to buy it.) I couldn’t wait to play
with the system. It was so much more powerful
than the 80286-based machine that I was using
at the time. His new 386 machine had real
memory management and a companion 80387
floating point unit (FPU), and it could run some
serious software. I was extremely jealous!
So the digital devices and tools were getting
better, but what about the rest of the analog
system components? Remember the LM780x/
LM340 linear regulators I mentioned earlier?
Well, they were still around (and still are), but
they had company. A new breed of powersupply
components was finding its way into
engineers’ hands. These were the integrated
switching regulators such as the LM2575.
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