## LOGIC GATES

Table of Contents

**“Gate is electric circuit in which any signal gone or stopped itself its called Logic Gates.”**

LOGIC GATES are three types-

1. AND GATE

2. OR GATE

3. NOR GATE

### 1. AND GATE :-

**“An AND GATE has two or more inputs and only one output.”**

Where the output Y is in logic 1 State, when both input A and B are in logic state.(logic gates)

#### BOOLEAN OPERATION:-

Y = a.b

#### LOGIC SYMBOL :-

#### SWITCHING CIRCUIT :-

#### WORKING :-

1. If A = 0 and B = 0 then no any current flow in electric circuit so bulb will not burn.

Y = 0.

2. If A = 1 and B = 0 then no any current flow in electric circuit so bulb will not burn.

Y = 0.

3. If A= 0 and B = 1 then no any current flow in electric circuit so bulb will not burn.

Y = 0.

4. If A = 1 and B = 1 then slow current in electric circuit A and B so bulb will burn.

hence Y = 1.

#### TRUTH TABLE :-

#### AND GATE FIND BY USING DIODE :-

1ST CONDITION :-

If A and B both are connected to earth E ( A = 0 , B = 0 ) , Then diode D1 and D2 both are being forward bias, hence both diode will worked.

But in this condition used ideal diode in which diode point do not first potential loss,

so output

Y = 0.

2ND CONDITION :-

If A connect to S and B connect to Earth (B = 0) , Then diode D2 will forward bias and D1 will reverse bias so D2 will work ,

But D2 is ideal diode

so Y = 0 .

3RD CONDITION :-

If A connect to earth and B connect to S then in the same way output of second condition.

Y = 0.

4TH CONDITION :-

If A and B both are connect to S then diode A and B both are reverse bias, so both diode will not working .

But battery Vcc to found the potential difference 5V , 5C

Y = 0 .

#### AND GATE FIND BY USING TRANSISTOR :-

As mentioned earlier, we can also simulated the AND Gate operation by using resistors and transistor.

This is known as resistor transistor logic or RTL.

1. A = 0 , B = 0 transistor Q1 and Q2 will not conduct making Ic = 0 voltage at P i.e Vc equal Vcc base of Q3 gets necessary forward bias.

Hence Y = 0 .

2. A = 0 , B = 0 or B = 0 , A = 0. in both the cases Q1 and Q2 cannot conduct.

Hence Y = 0.

3. A = 0 , B = 0 . in this case Q1 and Q2 conduct voltage at P which is Vc , therefore goes down and becomes 0.2v .

Due to this Q3 does not get necessary forward bias.

Hence Q3 does not conduct naturally its collector voltage Vcc = 5V becomes

Y = 0 .

### 2. OR GATE :-

**“An OR GATE has two or more inputs and only one output.”**

The OR GATE is an electronic circuit , in which the output (Y) is in logic 1 state.(logic gates)

#### When any one or both the inputs are in logic 1 state otherwise output find in logic state 0 .

#### BOOLEAN EQUATION :-

Y = a + b

#### LOGIC SYMBOL :-

#### SWITCHING CIRCUIT :-

#### WORKING :-

1. If A= = 0 and B = 0 then no any current flow in electric circuit so Lamp L will not born.

Y = 0.

2. If A= 0 and B = 1 then flow current in electric circuit B so lamp L will Burn.

Y = 1 .

3. If A = 1 and B = 0 , then flow current in electric circuit A so lamp L will Barn.

Y = 1

4. If A = 1 and B = 1 , then flow current in electric circuit A and B so lamp will Burn.

Y = 0

#### TRUTH TABLE :-

#### OR GATE FIND P-N JUNCTION DIODE :-

Above the diagram show the diode electronic circuit OR gate. In the OR gate are two input signal so two diodes D1 and D2 set in parallel combination Y is output signal.

1ST CONDITION :-

If A and B both are connect to E then both diode become reverse bias , so both diode A and B not working.

Therefore 5K-ohm load in find no any potential difference .

Then Y = 0.

2ND CONDITION :-

If A connect to S and B connect E ( means A=1 , B = 1) then diode D1 will forward bias and diode D2 will reverse bias .

So D1 will work, therefore find potential difference between two point of load 5K-ohm, so

Y = 0.

3RD CONDITION :-

If A connect to E and B connect to S (means A = 0 , B = 1 ) then diode D2 will forward bias and diode D1 reverse bias ,

then D2 will working therefore find potential difference between two point of load 5k-ohm.

Hence Y= 0.

4TH CONDITION :-

If A and B both are connect to S then D1 and D2 both are forward bias so find output.

Y = 1.

#### OR GATE FIND BY USING TRANSISTOR :-

### 3. NOT GATE :-

**“A NOT GATE has only one Input and one output.”**

its counterpart in Boolean Algebra is known as not operation.

The NOT GATE is also called as an inverter, because it only inverts the input.

#### BOOLEAN EQUATION :-

Y = A

#### LOGIC SYMBOL :-

#### SWITCHING CIRCUIT :-

#### WORKING :-

1. If A=1 , then in the circuit flow current so bulb not burn.

Y= 0.

2. If A = 0 , then the circuit flow current so bulb will burn.

Y = 0.

#### TRUTH TABLE :-

#### NOT GET BY USING A TRANSISTOR IN CE MODE :-

1ST CONDITION :-

When A = 0 connect to E (A= 0 ) , then the transistor in Reverse bias and will not conduct.

Therefore Vc = Ccc =+5V.

Y = 1.

2ND CONDITION :-

Similarly when (A = 1) connect to S the transistor will get necessary forward bias and will conduct having .

Hence Vc = 0.2 V which mean

Y = 0.