History of Computers - TTL
Page created by Kelsey Duncombe-Smith
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 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.
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.
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.
References
Links
http://en.wikipedia.org/wiki/Transistor–transistor_logic
http://www.computerhistory.org/semiconductor/timeline/1963-TTL.html
http://www.globalspec.com/reference/3360/Transistor-Transistor-Logic-TTL
http://www.play-hookey.com/digital/electronics/ttl_gates.html