A Logic AND Gate is a type of digital logic gate that has an output which is normally at logic level “0” and only goes “HIGH” to a logic level “1” when ALL of its inputs are at logic level “1”.
The output state of a “Logic AND Gate” only returns “LOW” again when ANY of its inputs are at a logic level “0”. In other words for a logic AND gate, any LOW input will give a LOW output.
The logic or Boolean expression given for a digital logic AND gate is that for Logical Multiplication which is denoted by a single dot or full stop symbol, ( . ) giving us the Boolean expression of: A.B = Q.
Then we can define the operation of a 2input logic AND gate as being:
“If both A and B are true, then Q is true”
A simple 2input logic AND gate can be constructed using RTL Resistortransistor switches connected together as shown below with the inputs connected directly to the transistor bases. Both transistors must be saturated “ON” for an output at Q.
Logic AND Gates are available using digital circuits to produce the desired logical function and is given a symbol whose shape represents the logical operation of the AND gate.
Symbol  Truth Table  
2input AND Gate

B  A  Q 
0  0  0  
0  1  0  
1  0  0  
1  1  1  
Boolean Expression Q = A.B  Read as A AND B gives Q 
Symbol  Truth Table  
3input AND Gate

C  B  A  Q 
0  0  0  0  
0  0  1  0  
0  1  0  0  
0  1  1  0  
1  0  0  0  
1  0  1  0  
1  1  0  0  
1  1  1  1  
Boolean Expression Q = A.B.C  Read as A AND B AND C gives Q 
Because the Boolean expression for the logic AND function is defined as (.), which is a binary operation, AND gates can be cascaded together to form any number of individual inputs. However, commercial available AND gate IC’s are only available in standard 2, 3, or 4input packages. If additional inputs are required, then standard AND gates will need to be cascaded together to obtain the required input value, for example.
The Boolean Expression for this 6input AND gate will therefore be: Q = (A.B).(C.D).(E.F)
If the number of inputs required is an odd number of inputs any “unused” inputs can be held HIGH by connecting them directly to the power supply using suitable “Pullup” resistors.
Commonly available digital logic AND gate IC’s include:
In the next tutorial about Digital Logic Gates, we will look at the digital logic OR Gate function as used in both TTL and CMOS logic circuits as well as its Boolean Algebra definition and truth tables.
It is very usefull and easyly understand .
i need to design the register ckt block diagram using logic componet . if posible please help me ? thank you
3input AND gate, this is a combination switch with on, off, but with 8 combination of possible solutions. The reset button makes it a 0 on reset again, but high on a second “on” recount. And it continuous. So there are 8 possible outcomes, with 7 upon the first count. Make sense.
This was helpful. I have of a picture of a transceiver. It is a control module of a firing system. Such as a module of shells to be fired on a new year’s eve countdown celebration. It now make sense. Circuitry.
What is Boolean ?
Boolean Algebra
Who is Boolean?
In 1854, George Boole performed an investigation into the “laws of thought” which were based around a simplified version of the “group” or “set” theory, and from this Boolean Algebra was developed.
please someone can tell me the transistor code for 2 input and gate!!!
sir …….tell me how to i download logic gates pdf format file ……….please given me that link
plz anyone can tell me single 4 input AND gate ic number not dual 4 input AND gate ic? plzzzzzzzzzzzzzzz reply me as soon as possible at my email address..thanks for consideration
There is no single 4input digital AND gate IC. Only 7421 or 4082 Dual 4input AND
but in my own experiment, when B is 1, then Q is 1