- TTL Logic Definition: Transistor Transistor Logic (TTL) is a digital logic circuit made using NPN transistors, PN junction diodes, and resistors.
- Standard TTL: Standard TTL uses NAND gates as the basic building block, featuring quad two-input circuits with NPN transistors.
- Low Power TTL: This subfamily reduces power consumption by using higher resistance values, though it operates at a slightly slower speed.
- High Power TTL: High power TTL focuses on high-speed operation with higher power dissipation, using additional transistors and resistors.
- Schottky TTL: Schottky TTL doubles the speed of high power TTL without extra power use, employing Schottky diodes for faster switching.
The full form of TTL is Transistor Transistor Logic. This is a logic family which is mainly build up of NPN transistors, PN junction diodes and diffused resistors. The basic building block of this logic family is NAND gate and there are various subfamilies of this logic gate those are standard TTL, advanced Schottky TTL, schottky TTL, low power TTL, high power TTL, fast TTL etc. now to know about this family in a more descriptive way we will discuss the internal structure and characteristic parameters of some of its subfamilies.
Standard TTL
The figure shows the internal structure of a standard TTL NAND gate, which is a quad two-input type. It has four circuits of 5400/740. The circuit operates with a Q1, a two-emitter NPN transistor.
This type is NAND gate is analogous to two transistors whose base and emitter terminals are joined together. The diodes named as D2 and D3 are used to limit the input voltages which are negative in nature.
Low Power TTL
Low Power TTL is a subfamily designed for lower power consumption and dissipation, though it operates a bit slower. The figure shows a low power TTL using AND gates. It uses a 74L00 or 54L00 quad two-input NAND gate. The construction is similar to standard TTL but with higher resistance values, reducing power dissipation.
High Power TTL
Unlike the low power TTL the High power TTL is the high speed edition of the standard TTL. The speed of operation of this type of TTL is more than the previously discussed. The power dissipation for this higher than other previously discussed TTLs. The above diagram is of a high power TTL NAND gate. The NAND gate is a quad two input of type 74H00 or 54H00. The above drawn figure is very similar to that of a standard TTL except Q3 transistor and D1 diode combination, which has been replaced by an arrangement of Q3, Q5 and R5. The speed of operation is higher and the power dissipation is also higher for this type of TTLs.
Schottky TTL
Schottky TTL is another subfamily designed for faster operation, offering twice the speed of high power TTL without extra power consumption. The figure shows a basic Schottky TTL NAND diagram, similar to high power TTL but without the Q transistor. Schottky TTL uses a bipolar transistor with a schottky diode connecting the base and collector. It has variants like low power Schottky and advanced Schottky.
