A Brief History of Chips - Next Steps in Integration
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Limited fan-in capability was a key limitation of RTL technology that was solved by the introduction of DTL technology into integrated circuitry by Signetics in 1962. DTL technology still had a relatively slow propagation delay due to the time it took for the base charge to leak out through the diode for the transistor to stop conducting. This problem was solved by TTL (Transistor-Transistor Logic) integrated circuit technology which quickly superseded DTL.
The most familiar example (though not the first) of TTL integrated circuit technology is the extensive 7400 series (and the Milspec counterpart 5400 series) originally introduced by Texas Instruments in 1964. It was widely copied by other integrated circuit manufacturers and became quickly a de facto industry standard. Also while the military mostly purchased the integrated circuits in flat-pack packages, commercial applications primarily use dual inline packages (DIP) which were initially ceramic, but later used lower-cost plastic.
Other bipolar integrated circuit technologies include ECL (Emitter Coupled Logic) and IIL (Integrated Injection Logic). ECL was somewhat faster than TTL, but consumed significantly more power and dissipated more heat. IIL was developed late for the SSI marketplace but later found a niche in VLSI (Very Large Scale Integration) because it had a performance comparable to TTL with power consumption almost as low as the FET transistor-based CMOS (Complementary Metal Oxide Semiconductor) technology.
In 1968 RCA introduced the 4000 series logic family based on CMOS technology logic. It mimicked the functionality and pin out of most of the existing 7400 series TTL parts, but operated at a much lower power and over a much wider (3V - 15V) voltage range at the expense of lower performance and higher part cost. Soon after its introduction, I actually used this 4000 series logic while working as a summer intern at Harry Diamond Laboratories, Department of the Army. For all I know, the details may still be classified; I can say that a piezoelectric crystal can be vibrated to produce enough electrical energy to act as the sole power source for a small digital circuit built from these devices, and when the vibrations are properly modulated, they can transmit a digital signal to this circuit as well.
While the 7400 series TTL started out as SSI with typically tens of transistors per integrated circuit, by the late 1960s improvements in chip processing technology allow a family of MSI (Medium Scale Integration) components with typically hundreds of transistors, each to be added to the series. The next generation in the 7400 family with more than a thousand logic gates per chip was then dubbed LSI (Large Scale Integration).
In my very first project at IBM in 1975, I built a couple of wire-wrapped prototype circuit boards out of the SSI and MSI 7400 series integrated circuits. For "mass production," these wire wrap boards were replaced with "printed circuit" boards where the wires were etched from copper-cladding on the circuit boards. There were still a few "overflow" wires on the printed circuit boards made from my prototype wire wrap boards which had to be soldered onto the printed circuit boards by hand. One time in manufacturing, a wire-wrap board got mixed into a batch of printed circuit boards and manufacturing dutifully soldered the components and overflow wires onto that board without ever noticing the difference. I kept that non-functional board as a reminder that sometimes engineers can do everything right, and someone else can still screw up the project.
By the 1970s, the term VLSI (Very Large Scale Integration) was invented to describe chips with tens of thousands of logic gates, but for VLSI, TTL technology consumed too much static power and dissipated too much heat. So for VLSI and subsequent generations, a migration was made from Bipolar to Field Effect transistors, and eventually to CMOS for the lowest static power dissipation. Over time, as microprocessor chip sets, solid state memory, and ASICs (Application Specific Integrated Circuits) became dominant, the venerable 7400 series was relegated to a lesser role primarily as signal buffers/drivers and as "glue" logic connecting the larger integrated circuits to each other.
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