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Transistor-Transistor Logic

TTL, or transistor-transistor logic, is a digital circuit that uses multiple transistors to derive its output.^[1] It was first created in 1965.

Overview

The first family of transistors, Sylvania Universal High-level Logic (SUHL), was produced in 1963. TTL is most often used with integrated circuitry. TTL first became popular with designers after Texas Instruments released the 5400 series which had a military grade temperature range, allowing the integrated circuits to work in hot or cold climates. ^[2] In transistor-transistor logic, transistors can both amplify the output and isolate the inputs; a step up from the previous resistor-transistor logic and diode-transistor logic. TTL is bipolar logic, meaning it contains at least one BJT, or a bipolar junction transistor, which contributes to the amplifying power of transistor-transistor logic. TTL circuits also include diodes and resistors. TTL circuits are often used to send a low or high signal using a 5V power supply, a low signal being between 0V and .8V and a high signal being between 2V and 5V.

TTL devices were packaged in through-hole, dual in-line packages. Through-hole meaning devices that have pins that are inserted through holes in circuit boards and are then soldered on the other side and dual in-line meaning the device has a rectangular housing with parallel pins on both sides that are pointed downward allowing for through hole soldering to a circuit board.

TTL was also a big step up from DTL which required to much space on an integrated circuit. With the invention of TTL it only required one input diode because a specific type of transistor called an NPN transistor replaced the inverter. A DTL NAND gate, DTL meaning diode-transistor logic, below was replaced with a TTL inverter below that, which does the same job as the DTL NAND gate but takes up less precious space on an integrated circuit chip. ^[3]

Also, with the new configuration above it is possible to add more emitters without taking up much more space. This means that a multiple input gate can be constructed in about as much space as an inverter. With space being a commodity on an integrated circuit, this was a great invention.^[4]

Significance

The low cost of transistors made digital techniques using transistor-transistor logic more economically practical. Also, previously analog tasks switched to digital. The decreased space of a TTL inverter saves significant costs during manufacturing which reduces the cost for the consumer as well. This makes TTL a cheap alternative, making it more popular. TTL revolutionized integrated circuit chips.