74LS08 Quad 2 Input AND Gate: Datasheet, Pinout and Uses
Время обновления: 2023-11-29 14:07:51
The 74LS08 is a Quadruple 8-bit Two Input AND IC. An AND gate is a fundamental digital circuit employed for logical state conversion. It operates by using two logic state signals: HIGH, denoted as 3-5 Volts, and LOW, represented as 0-2.6 Volts.
A single AND gate comprises two input pins and one output pin. The output state can be either HIGH or LOW, but it will only be HIGH when both input states are HIGH simultaneously. Creating a single AND gate can be achieved by using transistors along with resistors or diodes. In this guide, you will learn what the 74LS08 IC does and how to hook it up in a circuit.
What is 74LS08 IC?
The 74LS08 IC belongs to the 74XXYY IC series. Within this chip, you'll find four AND gates, each equipped with two inputs. This configuration is why it's referred to as a "QUADRUPLE 2-INPUT AND GATE." Notably, the gates in this IC are crafted using SCHOTTKY TRANSISTORS, ensuring swift and efficient logic operations.
74LS08 Pin Diagram
Pin No. Description
AND GATE 1
1 A1-INPUT1 of GATE 1 2 B1-INPUT2 of GATE 1 3 Y1-OUTPUT of GATE1
AND GATE 2
4 A2-INPUT1 of GATE 2 5 B2-INPUT2 of GATE 2 6 Y2-OUTPUT of GATE2
AND GATE 3
9 A3-INPUT1 of GATE 3 10 B3-INPUT2 of GATE 3 8 Y3-OUTPUT of GATE3
AND GATE 4
12 A4-INPUT1 of GATE 4 13 B4-INPUT2 of GATE 4 11 Y4-OUTPUT of GATE4
7 GND- Connected to ground 14 VCC-Connected to positive voltage to provide power to all four gates
74LS08 Features and Specifications
Operating Voltage Range: +4.75V to +5.25V
Recommended Operating Voltage: +5V
Maximum Supply Voltage: 7V
Maximum Current Allowed Through Each Gate Output: 8mA
Low Power Consumption
Typical Rise Time: 18ns
Typical Fall Time: 18ns
Operating Temperature: 0°C to 70°C
Storage Temperature: -65°C to 150°C
Low Power Consumption
High Operating Speed
Multiple Package Options: SOIC, PDIP, and SOP
Cost-Effective and User-Friendly
Independent Gate Operation: Using a single AND gate does not affect others.
Single Power Supply Control: One power supply suffices for all four gates.
What does the 74LS08 do?
The 74LS08 IC provides four separate AND gates, each capable of independent operation. An AND gate, a fundamental logic gate, generates an output of 1 (HIGH) exclusively when all of its inputs are set to 1 (HIGH). Refer to the truth table below for a clear representation of the output corresponding to various input conditions:
Truth table for the AND gate
Where to Use 74LS08 IC?
IC 74LS08 finds numerous applications, some of which are outlined below:
AND Logic Operations: This chip is primarily employed in scenarios that require AND logic operations. With four AND gates integrated into
the chip, users can utilize one or multiple gates simultaneously.
High-Speed AND Operations: In systems demanding high-speed AND operations, the 74LS08 chip excels. Its gate design, incorporating
SCHOTTKY TRANSISTORS, minimizes switching delays, rendering it ideal for swift AND operations.
Cost-Effective Solution: 74LS08 stands out as one of the most economical ICs available for AND logic operations. Its cost-effectiveness
contributes to its widespread popularity and ready availability in the market.
TTL Outputs: The chip offers TTL outputs, which are indispensable in certain systems.
How to Use 74LS08 IC
The internal connectivity of the four AND gates within the chip is illustrated in the diagram below.
Each AND gate conducts an AND operation on two logic inputs. For example, Gate 1 performs the AND operation between inputs A1 and B1, yielding an output at terminal Y1.
The truth table of AND gate is as follows:
Input1 Input2 AND Output LOW LOW LOW HIGH LOW LOW LOW HIGH LOW HIGH HIGH HIGH
To implement the truth table described above, consider a straightforward AND gate application circuit shown below.
To better understand its internal operation, let's consider a simplified internal circuit of the AND gate, as depicted below.
In this circuit, two transistors are connected in series to create an AND gate. The inputs of the AND gate are derived from the bases of these two transistors. Buttons are used to modify the logic of these inputs. The AND gate's output is represented by the voltage across resistor R1. This output is connected to an LED, D1, through a current-limiting resistor, R2, to indicate the output state.
The circuit's operation can be explained in the following stages:
Stage 1: When both buttons are unpressed, no current flows through the bases of the transistors, causing both Q1 and Q2 to be OFF. The total supply voltage, VCC, appears across transistors Q1 and Q2. As a result, the voltage drop across resistor R1 is zero. Since the output is determined by the voltage across resistor R1, it remains LOW. Therefore, when INPUTS = LOW, OUTPUT = LOW.
Stage 2: When either of the buttons is pressed, the corresponding transistor turns ON, while the other remains OFF. The ON transistor effectively creates a short circuit, with the OFF transistor acting as an open circuit and bearing the full VCC across it. Consequently, the voltage drop across resistor R1 is zero. As in Stage 1, the output remains LOW. So, when one INPUT = LOW, OUTPUT = LOW.
Stage 3: When both buttons are pressed, both transistors become ON, and the voltage across each of them drops to zero. In this scenario, the total VCC appears across resistor R1, resulting in a HIGH output. Thus, when both INPUT = HIGH, OUTPUT = HIGH.
By examining these three states, it becomes evident that the truth table is satisfied. The logic equation for the AND gate can be expressed as Y = A.B or A + B, as indicated by the truth table.
Each gate within the chip can be employed based on specific requirements.
74LS08 Circuit Example
Here's a straightforward project that can be assembled using a single AND gate within the 74×08 integrated circuit.
To maintain the inputs at a LOW state when the buttons are not pressed, pull-down resistors are employed. When any of the buttons are pressed, it will result in the input pin being set to a HIGH state. The AND gate's output will activate only when both inputs are in a HIGH state, subsequently illuminating the Light-Emitting Diode (LED).
It's worth noting that the LED will illuminate exclusively when both buttons are pressed simultaneously.
To construct this circuit, you will require the following components:
1 x 74HC08
1 x Light-Emitting Diode (LED)
2 x 10 kΩ resistor (R1-R2)
1 x 1 kΩ resistor (R3)
2 x pushbutton
In addition, here are other alternatives:
74×09 – Quad 2-input AND gates (with open-collector outputs).
74×7001 – Quad 2-input AND gates (with Schmitt-trigger inputs).
CD4081 – Quad 2-input AND gates.
General-purpose AND logic operations
Utilized in measuring instruments
Integral to digital electronics
Commonly employed in servers
A component in Arithmetic Logic Units (ALUs)
Found in memory units
Used in networking applications
Essential for various digital systems
Measurements in (Inches/millimeters)
The 74LS08 Quad 2 Input AND Gate is a valuable component in the realm of digital electronics. Its high-speed operation, low power consumption, and quad configuration make it a versatile choice for various applications, from simple logic operations to complex control systems.
For detailed information, always refer to the datasheet and pinout of the specific 74LS08 component you are using, as these may vary slightly between manufacturers.
- What is the function of 74LS08?
The 74LS08 IC is used to transform one logic state into another specific logic state.
- How many gates does 74LS08 have?
The 74LS08 IC comprises four individual gates, and each one is capable of executing the logical AND operation.
- What is the delay time for 74LS08?
The propagation delay times for a 74LS08 AND gate are as follows: tPLH = 15 ns and tPHL = 20 ns. For a 7402 NOR gate, the delay times are tPLU = 22 ns and tPHL = 15 ns.
- What is the maximum supply voltage for a 74LS08?
- What is the difference between 74LS08 and 74HC08?
A key distinction between the HC and LS variants of this chip lies in their voltage specifications. The 74HC08 is compatible with a voltage range of 2V to 6V, whereas the 74LS08 is limited to a 5V operating range.
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