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Transistor Transistor Logic

The name refers to the fact that both input and output of a TTL circuit will have connection to a transistor.
This not true for RTL (Resistor - Transistor - Logic).

The TTL technology declared "dead" years ago, but you might still find a few around. During the 60ies was a TTL family of logic known as the 74-family developed.

In the 70ies came a new CMOS based family known as the 4000-family - The 74-family and the 4000 are not compatible in any way (pin or voltage).

A Modern alternative to the 74-family can be found in the 74HC and the 74HCT families.
The HC accept CMOS levels as input, whereas HCT accept TTL levels as input.

Last updated: 27-01-09

Basic logic function (gates)


Standard TTL Data Book from the 60ies


Inside a 7400 TTL - NAND


The BJT or Bipolar Junction Transistors was invented in the late 1940ies and started the age of electronic.

You may look at a BJT as a:  Current generator controlled by a current - meaning the current which lead into the base will result in a larger collector current.   Ic = hFE * Ib


Drag mouse for answerYES - It will cost you at least one more transistor in order to turn a NAND gate into a AND gate. This fact was important to have in mind before the IC became common. All digital circuits was built with discrete components

 Why where NAND gates so popular in the 60ies ?

Drag mouse for answerYour able to build all digital logic with only NAND gates - Hence can a NAND gate be an inverter and the classic AND-OR network can be replaced by a NAND-NAND.


TTL demands current to keep a state 0/1








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