![]() ![]() Mostly used NAND gate IC number is the 7400 series which is shown below. Both symmetric diagrams are provided below. NAND gate IC comes in Dual in-line and QUAD line packages. However, if any transistor out of two is “OFF” then the output is “HIGH” NAND GATE IC If both transistors are in the state of “ON” the output is “LOW” as output taken to ground potential. To implement both transistors are connected in series and output is taken above them. Up until this point, our analysis of transistor logic circuits has been limited to the TTL design paradigm, whereby bipolar transistors are used, and the general strategy of floating inputs being equivalent to high (connected to V cc) inputsand correspondingly, the allowance of open-collector output stagesis maintained. Draw transistor circuit of NAND Gate? NAND Gate using Transistor Circuit Using the same method, we can implement a 4 or more inputs logic AND gates. The truth table is similar to the one shown above, where switches are used. We can find that if all inputs are “HIGH” the output “LED” is not glowing whereas if any input is “LOW” the output is “HIGH” hence LED is glowing. We can build a 3-input AND gate from 2-input AND gates in cascade, as shown in the diagram below. The above simulation example shows the implementation of a 6-input NAND gate using only 2-input NAND gates. How to design Multi- input NAND gate circuit?Ĭommercially NAND gate ICs are available with 2,3, and 4-input NAND gates but to implement more than 4-input NAND gates we should cascade lower-input NAND gates. How to design a 4-input NAND gate circuit using 2-input NAND Gate? ![]() In the same way, if more than 2,3 or 4 input NAND gate circuit is required then we should implement it with cascading of lower input gates as explained below. In the above 3-Input NAND gate simulation, if all the input bits are “HIGH” then the output is “LOW” hence LED is not glowing in that situation. We should observe in the simulation that if any input is “LOW” then the output “LED” is glowing. The truth table can be verified using the above simulation. The Boolean expression of NAND gate is given below Boolean expression of NAND gate 2-Input NAND Gate Simulation and Truth Table A (Input) The output of this circuit is logic 1 when either one input is logic. The bubble shows inverted output from gate. Therefore the transistor is switched Fully-OFF. In a simplified mode, we use NAND gate symbol as represented in the second figure. Cut-off Region Here the operating conditions of the transistor are zero input base current ( IB ), zero output collector current ( IC ) and maximum collector voltage ( VCE ) which results in a large depletion layer and no current flowing through the device. The first figure shows the NAND gate is a combination of the AND and NOT gates. In other words, it gives a complement or inverted output of AND gate.
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