why does the ttl family use a totem pole circuit on the output

Some TTL chips are now also made in surface-mount technology packages. TTL devices were originally made in ceramic and plastic dual in-line package(s) and in flat-pack form. Variations of the original TTL circuit design offered higher speed or lower power dissipation to allow design optimization. TTL manufacturers offered a wide range of logic gates, flip-flops, counters, and other circuits. The 7400 series by Texas Instruments became particularly popular. Īfter their introduction in integrated circuit form in 1963 by Sylvania Electric Products, TTL integrated circuits were manufactured by several semiconductor companies.

The operation is the same as the 2-input TTL NAND gate.TTL integrated circuits (ICs) were widely used in applications such as computers, industrial controls, test equipment and instrumentation, consumer electronics, and synthesizers. It is the same as that we discussed in the 2-input TTL NAND gate circuit, except that here, the input transistor Q 1 has three emitters instead of two. The following figure shows the circuit of the standard 3-input TTL NAND gate. Circuit of standard 3-input TTL NAND Gate

With Q 2 turned ON, transistor Q 4 will also be turned ON.īoth the transistors at the output side will conduct and so the output at terminal will have LOW value, which is considered as logic 0. The diode D C at the collector-base junction is forward biased. When both the inputs A and B are high, both the diodes at the emitter-base junction will be reverse biased. The same operation will take place as explained above.

When any one input, either A or B is low, the diode with low input will be forward biased. Since Q 3 is an emitter follower, the output at the terminal will also be HIGH, which is at logic 1. With Q 2 open, the transistor Q 4 will also cut off. The supply voltage gets dropped in the resistor R 1 and it will not be sufficient to turn ON the transistor Q 2. So the current due to the supply voltage +V CC = 5 V will go to the ground through R 1 and the two diodes D A and D B. When both inputs A and B are low, both the diodes are forward biased. Diode D C represents the collector-base junction of transistor Q 2. In the figure, diodes, D A and D B represent the 2-input emitter junction of transistor Q 1.

Why does the ttl family use a totem pole circuit on the output