TTL and CMOS logic integrated circuits: the building blocks of a revolution

When we start a new electronics project today, one of the first things we tend to do is choose the integrated circuits that are the heart of the design. It could range from a microcontroller and various controller ICs to a pinch of MOSFETs, op-amps, and possibly 7400 or 4000 series logic ICs to tie things together. Yet, it wasn’t too long ago that this high level of integration and miniaturization was firmly in the realm of science fiction, even NORBIT mods seemed futuristic.

Beginning with the construction of the first point contact transistor in 1947 and the bipolar junction transistor (BJT) in 1948 at Bell Labs, the world of electronics would soon see the start of its greatest transformation at this point. Yet, due to the interesting geopolitical circumstances of the 20th century, it has led to a fascinating situation of parallel development, blatant copying of designs, and one of the most fascinating stories in the history of technology on both sides of the curtain. of iron.

An assortment of new technologies

Dual 3 input NOR gate implemented in RTL as used in the Apollo guidance computer. (Credit: NASA)

After the invention of the transistor, of course, it wasn’t just about sticking transistors onto a silicon chip to create logic gates, putting them in a plastic (or ceramic) case, and taking over the world of digital electronics.

The first viable approach to creating logic gates with transistors in the early 1960s was resistance-to-transistor (RTL) logic, which limited the number of transistors needed. At the time, resistors were cheaper and transistors were still difficult to manufacture. This approach was used with the Apollo guidance computer, which was built using discrete 3-input, RTL-based NOR gates.

Competitive diode transistor logic circuit (DTL) technology had the advantage of using less power and allowing much more fan-in (the number of inputs supported in a circuit), as well as more ” relatively easily increase the fan-out (number of outputs) by using additional diodes and transistors. A disadvantage of DTL was that the propagation delay through a circuit is relatively long due to the charge stored in the base region of the transistors.

This has led to a number of attempts to control this saturation problem, including an additional capacitor, a Baker clamp, and the Schottky transistor. The early 1960s saw the release of DTL-based logic chips, with Signetics’ SE100 series, followed by Fairchild with the DTμL (micrologic) series of the 930 series. DTL was followed by transistor-transistor logic (TTL ), which is quite similar to DTL, but as the name suggests, only uses transistors.

The first commercially produced TTL microchips were the Sylvania Universal High Logic Level (SUHL) and its successor SUHL II series. Texas Instruments (TI) will introduce the 5400 TTL series for military applications in 1964, with two years later the 7400 series introduced for general applications.

Somewhat in parallel, Emitter Coupled Logic (ECL) also saw continued success in the 1980s. The main advantage of ECL over approaches such as RTL and DTL as well as TTL is that ECL is very fast due to its emitter tracking nature, using a single overloaded bipolar junction transistor (BJT). The design is such that none of the transistors used are ever saturated, with small voltage variations between high and low (0.8V) levels that allow relatively fast switching times.

Although ECL has the disadvantage of requiring relatively complicated power supplies with low noise and constant current, its high switching speeds made it an obvious choice in mainframes and other applications where speed was the most important factor. important. This included the Cray-1 supercomputer, as well as a line of IBM and VAX mainframes.

This contrasts with the development of the MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor), which saw its basic operating principles already proposed in 1926, but took much longer to be ready for commercialization than the BJT. , although MOSFETs offer significant advantages in terms of size and scale over them. Yet when MOS technology became ready for mass production in the late 1960s, it sparked a small revolution that enabled not only the still common 4000 series CMOS logic chips (introduced by RCA in 1968), but also to the microprocessors that would power the home computer revolution of the 1970s.

Inquire with the CIA

The average reader probably doesn’t know much about the previous story, but where things get interesting is with the development of these technologies in the Soviet Union and allied countries. As this part of the world had an unfriendly relationship with the United States and its allies since the 1940s, it was largely excluded from the great semiconductor revolution that was unfolding mainly in the United States.

Essentially, this meant that the manufacturing equipment and know-how for making transistors and MOSFETs were under strict embargo, with first world countries prohibited from exporting such items to the USSR and allied territories. When looking at a top secret 1976 CIA document (declassified in 1999) titled The USSR seeks to build an advanced semiconductor industry with Western machinery under embargo, we can get a good impression of the state of affairs at that time.

Even as the United States, Europe and Japan developed their respective semiconductor industries, the USSR lagged behind. Although the leaders of the USSR recognized the enormous tactical advantage that modern semiconductor technology would give them, it was not one that they could easily overcome. This led to a large-scale effort by the USSR to illegally import Western machines for advanced semiconductor manufacturing and copy any technology they could get their hands on.

The joys of standards

Four TTL integrated circuits: Czechoslovakian MH74S00, Texas Instruments SN74S251N, East German DL004D (74LS04), Soviet K155LA13 (7438).
Four TTL integrated circuits: Czechoslovakian MH74S00, Texas Instruments SN74S251N, East German DL004D (74LS04), Soviet K155LA13 (7438).

Part of the result of this can be found in the many logic integrated circuits compatible with the TTL 7400 series logic integrated circuits. While European manufacturers would follow the Pro Electron naming scheme (e.g. FJH101 for the 8-input 7403 NAND gate), Soviet and to some extent Eastern Bloc manufacturers used the Soviet designation scheme for integrated circuits. It started with the NP0.034.000 standard in 1968 which saw its first update in 1973 with GOST 18682—73.

Logic IC chips produced for the Soviet market use metric pin spacing (2.5mm and 1.2mm) rather than imperial (2.54mm and 1.27mm). In Eastern Bloc countries like Czechoslovakia, Poland and East Germany, various IC designation schemes have been used, many of them corresponding to the Western equivalent. In East Germany, for example, there were three compatible 7400 – 6400, 7400 and 8400 series – each targeting a different market with different temperature ranges and other properties.

Eastern European 7400 series prefixes.
Prefixes of the 7400 series logic chips from Eastern Europe.

Even more confusing, logic chips designated for export would sometimes be branded using the American-style 7400 designation. Using Cyrillic letters instead of Latin characters can also be very confusing, especially when a Cyrillic and Latin character look the same. The continued production of these series of logic integrated circuits after the dissolution of the Soviet Union in 1991 at semiconductor factories that may not offer Cyrillic type printing – forcing the use of Romanized characters – confused the denomination even more here.

Turn iron into silicon

Stained glass window with logo of the Czechoslovak company Tesla Radio in Pasáž Světozor, Vodičkova ulice, Praha.  Author: František Hudeček.
Stained glass window with logo of the Czechoslovak company Tesla Radio in Pasáž Světozor, Vodičkova ulice, Praha. (Credit: František Hudeček)

For people who lived in the USSR or one of its satellite countries, much of the technological revolution from the 1960s to the 1980s went largely unnoticed. Due to the lack of semiconductor manufacturing capacity in the USSR, the integrated circuits that were produced mostly ended up in military and related equipment, leaving inferior and obsolete integrated circuits for the average citizen, which also made it possible to valve technology to survive in the USSR for decades thereafter. much of the West.

However, with the fall of the Soviet Union, everything changed. With embargoes against the USSR no longer in place, consumer goods filled with Western integrated circuits flooded the markets of Eastern Europe and Russia, prompting the rapid demise of companies like Czechoslovakian Tesla, which made pretty much all the electronics for the local market there. .

Military contracts and other long-term contracts ensured that the naming scheme of Soviet integrated circuits and special integrated circuits survived to this day, but the exciting days of Cold War espionage versus espionage are over, leaving behind them a strangely divided story that will not be in doubt. confuse a lot for decades to come.