TTL stands for Transistor-transistor logic (transistor-transistor logic), is a class of digital circuits built from bipolar junction transistors (BJT) and resistors. It is called transistor-transistor logic because both the logic propagation function and amplifying function are performed by transistors. The TTL is derived from the DTL (Diode transistor logic) and differentiates the use of CMOS transistors of base (bipolar) instead of MOSFETs, and FETs.
Transistor multiemissor
Bipolar transistors are used in TTL circuits have several transmitters , called multiemissor , (pictured above ) this technology reduces the number of transistors used to make a particular gate , another feature is that the TTL circuits work with 5 Volt voltage . The TTL integrated circuits are notable for having a wide range of uses in many applications such as control circuits , computers , instrumentation , consumer electronics products , etc. . The TTL integrated circuits offer a wide variety of logic gates , inverters , flip- flops , counters , driver , decoder , memory, adder , comparator , recorder , multiplier , and other circuits .
What is TTL
The TTL designation is sometimes used to denote TTL compatible logic levels (0 and 1-0 Volts and 5 Volts ) , even when not associated directly with TTL integrated circuits , for example, as the input or output of electronic instruments . The TTL was invented in 1961 by James L. Buie of TRW , and was originally called coupled transistor-transistor logic ( TCTL ) . The first commercial TTL integrated circuits were manufactured by Sylvania in 1963 , and called family Sylvania Universal High-Level Logic ( SUHL ) .
CI SG52A Silvanya TTL GATE AND-OR-INVERT
A flat-pack 14-pin dated 1966
These TTL integrated circuits Sylvania were used in the control of Phoenix missiles because they function as primary military use. But became popular after Texas Instruments introduced the 5400 series of ICs, with military temperature range in 1964, and later the 7400 series, specified in a narrower range, and low cost plastic package in 1966.'s Family 7400 integrated circuit from Texas Instruments has become a standard TTL industry worldwide. Equivalent components were made by Motorola, Fairchild, Intersil, AMD, Signetics, SGS-Thomson, National and other companies.
Subfamilies of Integrated Circuits TTL 74xx line : L , M , S , LS , F , AS, ALS
74Lxx - (obsolete ) are integrated circuits for low power , and has the characteristic of low speed and low power dissipation . Its switching speed is 33 ns with a power consumption of 1 mW . (Replaced by CMOS logic)
74Hxx - (obsolete ) are high-speed integrated circuits , is characterized by an increase in speed compared to 74L series, has the side effect of an increase in consumption . Its switching speed is 6ns with a power consumption of 22 mW .
74Sxx - Schottky , has this name because it reduces the delay storage using Schottky diodes . Works with twice the speed 74H , consuming roughly the same. Its switching speed is 3rd with a power consumption of 19 mW .
74LSxx - integrated circuits are Low Power Schottky , compared with previous versions it has a lower power but with speed also slightly lower . These features made the TTL LS 7400 family commonly used . Its switching speed is 8ns with a power consumption of 2 mW .
74Fxx - integrated circuits are fast ( F ) , one of the variants manufactured by Fairchild 74LS .
74ASxx - are integrated circuits Advanced Schottky TTL is the number of higher speed , and a speed / power ratio than the earlier series. There are other subfamilies of the line 7400 , but were not shown here for various reasons , are often used or obsolete .
Variations of the line 74xx
Several unique variations of bipolar TTL were developed by different manufacturers , and circuits with higher speed , lower power dissipation , less ports , etc. . This all to allow optimization of new electronic designs . There are also some with CMOS components such 74HCT74 to High Speed CMOS inputs compatible with standard TTL are functionally similar to its counterpart TTL .
There are some Cis line 74xx TLL low voltage , called LV- TTL , for power supply of 3.3 volts . Most manufacturers offer commercial and extended temperature ranges : for example the Texas Instruments 7400 is the line that runs from 0 to 70 ° C , and the line 5400 running from -55 to +125 ° C. These lines have stronger specifications military , their levels of quality are special high reliability and are available for military and aerospace applications .
What is the logic of Truth Table Table or TTL
TTL logic table (IBM)
The truth table is a mathematical table used in logic, specifically in relation to Boolean functions and Boolean algebra to compute the functional values of logical expressions on each of their functional arguments, that is, on each combination of values taken by their variables logical
Practically a truth table consists of one column for each variable (input) input (e.g., A and B, C, D) and a final column for all possible results of the logic operation output or output. Each row of the truth table contains one possible configuration of input variables (eg, A and B = true or false), and the result of the operation of such values. See the examples below in Figure 1.
We take into account that each table is made of a form, then:
H = HIGH = 1 high = 5 Volts
L = LOW = 0 = 0 = Low Volts
Using the truth table
Let's take the example of the integrated circuit 7408 (Figure 2) which is a C TTL four two-input AND gates, we have the truth table in Figure 1, A and B are the inputs and the output is AB. Have with the pins 1,4,9 and 12 pin B are 2, 5, 10 and 13 pin 2 AB 3, 6, 8 and 11.
Figure 1 - Table 2 INPUTS AND logic
We will use the truth table (truth table) above, we can define that connect an LED and a resistor on pin 3 AB output it will behave as follows:
If we have to Pin 1 (A) 0 Volts, pin 2 (B) = 0 Volts Pin 3 (AB) 0 Volts ==> LED OFF
If we have to Pin 1 (A) 0 Volts, pin 2 (B) = 5 Volts Pin 3 (AB) 0 Volts ==> LED OFF
If we have to Pin 1 (A) 5 Volts, pin 2 (B) = 0 Volts Pin 3 (AB) 0 Volts ==> LED OFF
If we have to Pin 1 (A) 5 Volts, pin 2 (B) = 5 Volts Pin 3 (AB) 0 Volts ==> LED ON
We then noted that only when the two ports are H or 1 is that the LED lights.
Figure 2-7408
In the figure below we can see an AND gate made of transistors or diodes.
Method of making a gate transistors or diodes.
Theory of TTL Gates
AND gate
An AND gate is the physical realization of the logical multiplication operation . It is an electronic circuit that generates an output of 1 only if all input signals are 1 .
OR gate
The OR gate is the physical realization of the logical addition operation . It is an electronic circuit that generates an output signal of 1 if any of the input signal is 1 .
NOT gate
The NOT gate is the physical realization of the operation of complementation . It is an electronic circuit that generates an output signal which is the inverse of the input signal . a NOT gate is also known as an inverter, because it inverts the input.
NAND gate
The NAND gate is an AND gate complemented . The output of the NAND gate is '0 ' if all input signals are '1' and will be '1 'if any of the input signals are '0'.
NOR gate
A NOR gate is an OR gate complemented . The output of NOR gate is '1 'if all inputs are '0' and will be '0 ' if any of the input signals is '1' .
EX -OR gate
It is similar to the OR gate but excluding the combination of both A and B are equal to one. XOR is a function which gives an output signal '0 ' when the two input signals are equal to or '0' or '1 ' .
Advantages and disadvantages of TTL integrated circuits
In comparison with other digital technologies and logic families TLL has advantages and disadvantages , see below major .
Advantages
fastest switching ;
greater noise immunity ;
Disadvantages
high cost of manufacture;
low input impedance ;
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