The Logic AND Gate is a type of digital logic circuit, that implements logical conjunction (∧) from mathematical logic – AND gate behaves according to the truth table. The output state of a digital logic AND gate only returns ‘LOW’ again when any of its inputs are at a logic level of ‘0’. In other words for a logic AND gate, any LOW input will give a LOW output.
The AND gate with inputs A and B and output C implements the logical expression C=A.B
Digital AND Gate Types
The 2-input Logic AND Gate
The AND gate with inputs A and B and output C implements the logical expression C=A.B
The 3-input Logic AND Gate
The AND gate with inputs A and B and output C implements the logical expression Z=W.X.Y.
Because the Boolean expression for the AND function is defined as (.), which is a binary operation, AND gates can be cascaded together to form any number of individual inputs. However, commercially available AND gate ICs are only available in standard 2, 3, or 4-input packages. If additional inputs are required, then standard AND gates will need to be cascaded together to obtain the required input value, for example.
Multi-input AND Gate
The Best Example of a Multi-input AND Gate is 7408 Quad 2-input AND Gate.
The Boolean Expression for this 6-input AND gate will therefore be:
Q = (A.B).(C.D).(E.F)
2-input Transistor AND Gate
A simple 2-input AND gate can be constructed using RTL Resistor-transistor switches connected together as shown below with the inputs connected directly to the transistor bases. Both transistors must be saturated “ON” for output at Q.
Application Of AND Gate
- Used in Digital Measuring Devices
- Used in Alarm Circuits