totem pole output for ttl logic families

The operation is the same as the 2-input TTL NAND gate. 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 The non-saturated bipolar logic families are. 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. logic functions have been fabricated using a specific circuit configuration. 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 output consists of a push-pull driver with a resistor and a diode added. The same operation will take place as explained above. This is the schematic of a TTL logic component (here an 7404 inverter), with the typical totem-pole output. 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. In some cases (e.g., when the output of a TTL logic gate needs to be used for driving the input of a CMOS gate), the voltage level of the totem-pole output.

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. The fan-out in TTL totem-pole circuit is limited by the amount of current that the output transistor can sink in LOW state or can source in HIGH state. In the figure, diodes, D A and D B represent the 2-input emitter junction of transistor Q 1.

Totem pole output for ttl logic families