QS74FCT251

series introduction

# QS74FCT251 Product Series Introduction

## 1. Overview
The QS74FCT251 product series is a high - performance family of integrated circuits designed to meet the demanding requirements of modern digital systems. These devices are part of the FCT (Fast CMOS Technology) logic family, which combines the speed advantages of bipolar technology with the low power consumption and high noise immunity of CMOS technology. The QS74FCT251 series is specifically engineered for applications where fast data selection and multiplexing are crucial.

## 2. Key Features

### 2.1 High - Speed Operation
One of the most prominent features of the QS74FCT251 series is its high - speed performance. With propagation delays in the range of a few nanoseconds, these devices can handle high - frequency data signals efficiently. This makes them ideal for use in high - speed data communication systems, such as Ethernet networks, where rapid data transfer is essential.

### 2.2 Low Power Consumption
Despite their high - speed operation, the QS74FCT251 devices consume relatively low power. This is achieved through the use of advanced CMOS manufacturing processes, which minimize static and dynamic power dissipation. Low power consumption not only reduces the overall energy requirements of the system but also helps in heat management, leading to increased reliability and longer device lifespan.

### 2.3 Wide Operating Voltage Range
The QS74FCT251 series supports a wide operating voltage range, typically from 4.5V to 5.5V. This flexibility allows the devices to be used in a variety of power supply environments, making them suitable for both legacy and modern systems. It also provides some tolerance to power supply fluctuations, enhancing the stability of the overall system.

### 2.4 High Noise Immunity
CMOS technology inherently offers high noise immunity, and the QS74FCT251 series is no exception. These devices can withstand significant levels of electrical noise without experiencing false triggering or data errors. This is particularly important in noisy industrial environments or in systems with multiple high - speed components that may generate electromagnetic interference.

### 2.5 3 - State Outputs
The QS74FCT251 devices feature 3 - state outputs, which can be placed in a high - impedance state. This allows multiple devices to be connected to a common bus without causing signal conflicts. The 3 - state outputs are controlled by an enable input, providing a convenient way to manage data flow on the bus.

## 3. Functional Description

### 3.1 Multiplexing Function
The primary function of the QS74FCT251 series is multiplexing. Each device has multiple data inputs (usually 8 inputs), a select input, and an output. The select input determines which of the data inputs is routed to the output. This makes it possible to select one of several data sources based on the control signal, enabling efficient data routing in digital systems.

### 3.2 Enable Control
In addition to the select input, the QS74FCT251 devices have an enable input. When the enable input is active, the device functions normally, and the selected data input is passed to the output. When the enable input is inactive, the output is placed in a high - impedance state, effectively disconnecting the device from the bus.

## 4. Applications

### 4.1 Data Communication Systems
In data communication systems, such as routers, switches, and modems, the QS74FCT251 series can be used for data selection and multiplexing. For example, in a router, it can be used to select the appropriate data stream from multiple input ports and route it to the output port, ensuring efficient data transfer between

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