Universal Gates: Complete Guide on Universal Gates

Universal Gates
Universal Gates

 

Universal Gates: Complete Guide on Universal Gates

Universal Gates, in electronics field, we start our study with basic gates like AND, OR, NOT. But there are two logic gates viz. NAND & NOR from which we can derive basic logic gates or Boolean expression. Such logic gates are called as Universal Logic Gates.

Truth table of NAND GATE-

 

INPUT INPUT OUTPUT
A B Y
0 0 1
0 1 1
1 0 1
1 1 0

Y = (AB)

Truth table of NOR GATE-

INPUT INPUT OUTPUT
A B Y
0 0 1
0 1 0
1 0 0
1 1 0

 Y= (A+B)

NAND and NOR gates are economical and easier to fabricate and are the basic gates used in all IC digital logic families. So, first we will see NAND gate as universal gate that is we will construct all logic gates using only NAND gate.

Universal Gates: AND GATE USING NAND GATE

and gate using nand gate
And gate using Nand gate

Here, we are using IC7400 two inputs NAND GATE. For AND GATE, if one of the inputs is zero and if all are zero, output is zero. Here, we have inputs 0 and 1, for which output is zero. The first NAND gate will give output as 1 according to truth table and then second NAND will toggle this input and the output will be zero.

Universal Gates: OR GATE USING NAND GATE

or gate using nand gate
or gate using nand gate

As we know NOT gate is nothing but an inverter. It simply inverts the input. If input is 1, output is 0 and vice versa. The inputs of the NAND gates are shorted together and connected to Vcc. AS NAND gate is inputted with 1, 1 then output is zero. So, output is zero which is according to truth table of NOT gate.

Universal Gates: NOR GATE USING NAND GATE-

NOR using NAND
NOR using NAND

Here, we are making NOR gate using NAND gates. It’s circuit is similar to OR gate only but only thing is that at last, we have added one NAND gate which will toggle the OR output and we will get NOR  output at the end of the circuit.

Universal Gates: EX-OR GATE USING NAND GATE-

EXOR GATE USING NAND GATE
EXOR GATE USING NAND GATE

As you can see here, when we apply 1 and 0 at the input, we are getting 1 output that is 5 volts. This is nothing but an EX-OR gate. 5 NAND gates are used here. The first two NAND gates will toggle the input (A and B) and then applied to next two NAND gates and these gates get another input from our original inputs which are A and B and then the outputs are applied to last NAND gate which gives the output which is according to truth table of EX-OR gate.

Universal Gates: EX-NOR GATE USING NAND GATE-

EXNOR GATE USING NAND GATE
EXNOR GATE USING NAND GATE

As you can see, this circuit is similar to EX-OR using NAND but only one NAND gate is added at last. This last NAND gate is there to toggle the output EX-OR gate because it is connected in such a manner to toggle the EX-OR output. At last, we get EX-NOR output according truth table.

Now, we will see all these above gates using NOR gate. So, we have used 7402 two inputs NOR gate.

Universal Gates: AND GATE  USING NOR GATE-

And gate using nor gate
And gate using nor gate

For connecting AND gate using NOR gate, above circuit diagram is used. As we know if we apply one input as 1 and another as 0, we will get output as 0.So, here we have used 3 gates, first two NOR gate will toggle and then applied to third one which gives output according truth table of AND gate.

Universal Gates: OR GATE  USING NOR GATE-

OR GATE USING NOR GATE
OR GATE USING NOR GATE

This arrangement gives the output of OR gate. First NOR  gate will take inputs and give output as NOR gate which will be applied to another NOR gate which toggles the input and we get output according to truth table of OR gate.

Universal Gates: NOT GATE USING NOR GATE

NOT GATE USING NOR GATE
NOT GATE USING NOR GATE

For connecting, NOR gate as NOT gate, we should short the inputs of NOR gate and apply the input because NOT gate requires only one input. This arrangement will toggle the input as shown in figure that is we have applied 5 volts and we are getting 0 volt as output.

Universal Gates: NAND GATE  USING NOR GATE-

NAND GATE USING NOR GATE
NAND GATE USING NOR GATE

For connecting NOR gate as NAND gate we will implement the circuit of AND gate using NOR gate and then we will apply the output of this circuit that is AND gate to another NOR gate which will toggle the output of NAND gate and we will get output according truth table NAND gate.

Universal Gates: EX-OR GATE USING NOR GATE:

EX-OR GATE USING NOR GATE
EX-OR GATE USING NOR GATE

For this circuit we have used 6 NOR gates. First two NOR gates take inputs which are 1 and 0 and toggle them that is they act like NOT gate. Another two NOR gates take inputs from previous gates and another input from original inputs (1 and 0) and then these outputs are applied to further gates and at last we get output as 5 volts which is logic 1. This is according to truth table of EX-OR gate.

Universal Gates: EXNOR GATE USING NOR GATE

EX-NOR GATE USING NOR GATE
EX-NOR GATE USING NOR GATE

This circuit is similar to EX-OR using NOR gate only last gate is omitted and total 5 gates are used. We have applied 1 and 0 and our output is 0 which is according to truth table of EX-NOR gate.

 

Article by:

Guest Blogger: Tanvi Shivgan

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