Analog: back to the future, part one

Kludge boxes
According to Maida, the company also used color keys to compare one layer with another (Figure 2). The color keys were printed on Mylar sheets representing one of the physical layers, and each layer was assigned a color, such as red for the base or green for the collector. When the designers stacked the two colors over a light source, they produced a third color. This approach provided an efficient way to check whether a part of the geometry was missing or incorrectly drawn. The designers also developed so-called kludge boxes to verify the performance of the design and sometimes for use in production-test equipment (Figure 3).

“Kludge boxes were a necessity in that test equipment did not exist that could measure the performance of the IC,” says Moraveji. “These boxes often used some clever measurement tricks, which would also find their way into the data sheet.” According to Moraveji, the designers used transistor-kit parts in breadboarding a new design idea or to prototype a chip. They performed comprehensive measurements on a breadboard to ensure the validity of a design idea. “Breadboarding was fun, as well as challenging,” he says. “During the process, if a component went bad, it was extremely painful to debug and get it to work again. Technicians, who used to do a neat breadboard, were valuable parts of our team in the development phase.”


Designers used to be able to get into the transistor-level details and even modify the transistor design to create ICs. Today’s designers instead receive standard cells with which to design; they cannot modify them because manufacturing does not support modified designs. In the early days, time to market was less critical than it is now. A 50-transistor circuit—including breadboard design; layout; debugging, which often took place on a probe station; and, typically, some mask changes—would take 18 to 24 months to complete. Now, a period of eight to 10 months is the norm for several-thousand-transistor designs (Figure 4).


The designers used simulation tools for validation but first had to perform manual calculations, and developing breadboards was a standard practice until the mid-’80s. Sometimes, they had to use slide rules to make the paper design work before building the breadboard. They also couldn’t use many library textbooks because they were developing new designs, especially in CMOS. According to Archer, researching articles in various IEEE journals was often more insightful and useful than using textbooks. And, according to Monticelli, recent engineering-school graduates would try to find a good mentor who used blackboards because there were no whiteboards in those days. You learned by reading the latest published papers and meeting other engineers at the watering holes in Silicon Valley. “In many cases, we had to take a multitude of measurements and then use the data to create an explanation [about] the operation of the circuit,” says Dietz.

Moving to plastic-mold compounds caused stress effects that changed low-offset voltages in a chip after the application of the mold. “Sometimes, we would not offer the premium A-grade specs in the plastic package,” explains Maida. “The same part often had two or three electrical grades and two or three temperature grades: commercial, industrial, and military.” He adds that designers always tested military-temperature-range parts over temperature but almost never tested commercial parts in the same way.

According to Dietz, the op amp served as the canary in the coal mine for uncovering any process problems. The sensitive nature of the tight specs in an analog IC provided warnings when the process started going awry. Designers back then had never heard of the phrase “guaranteed by design.” Instead, they “tested the daylights” out of the IC during development. However, Maida claims that this testing was not true for production testing. “Good managers knew what could be put in as a design limit,” he says. “The test-everything mentality came in later, toward the late ’80s, as [part-per-million] quality levels became important.” However, Maida adds, they had to characterize the parts on the bench, which always involved manual measurements and, sometimes, kludge boxes for the tricky measurements, such as settling time, sample-and-hold acquisition time, and linearity.

Fast-forward 40 years, and the customer has hundreds if not thousands of op amps and multiple suppliers to choose from, says Dietz. Once engineers get comfortable with an op amp, they tend to use it over and over again. If they need a little better performance, then the chances are that they can find a product that fits the bill. “It is rare that someone comes to us today and asks for a new op amp,” he says.