SN74HCT14D

SN74HCT14D Application Field and Working Principle

The SN74HCT14D is a hex-inverting Schmitt trigger from Texas Instruments. It\'s part of the 74HCT family of TTL compatible logic chips and has six independent inverter circuits. Each of these circuits contains a Schmitt trigger which has hysteresis, making the SN74HCT14D useful for signal/level translation. This article will discuss the application field, general characteristics and working principle of the SN74HCT14D.

Application Field

The SN74HCT14D has a variety of applications, primarily in level translation, voltage level translation and signal conditioning. The Schmitt trigger action enable it to provide good noise immunity and speed. Therefore it is particularly suitable for use in the following application fields:

• Communication systems
• Computers and peripherals
• Computing instruments
• Embedded systems
• Mobile phone charging systems
• Power supplies
• Test and measurement equipment

General Characteristics

The SN74HCT14D is a six inverter logic IC. It has a 14-pin DIP package and operates from a single supply voltage of 3.6V – 10V. It consumes less than 10uA when operating from a 5V supply and has a low input current of 1uA. It has an output current of 2.6mA and a propagation delay of 8ns which makes it particularly suitable for high speed applications.

Working Principle

The six inverters in the SN74HCT14D are Schmitt triggers which have hysteresis. This means that they have two different thresholds, one for each direction of the input signal. When the input signal crosses one of the thresholds, the output will toggle. The amount by which the input signal needs to cross the threshold is the amount of hysteresis. This can be controlled by adjusting the amount of positive feedback of the inverter.

The Schmitt triggers are constructed using transistors and capacitors. The input signal is applied to the base of the transistor which is then amplified and the amplified signal is then fed to the comparator which has two different reference voltages set by two resistors connected to it. The output of the comparator then drives the output of the inverter.

The amount of hysteresis can be controlled by adjusting either the amount of positive feedback or by adjusting the resistance of the two resistors connected to the comparator. The amount of positive feedback will affect the amount of hysteresis, whilst the resistance of the two resistors will adjust the voltage levels of the two thresholds.

Conclusion

The SN74HCT14D is a hex-inverting Schmitt trigger from Texas Instruments which is suitable for level/signal translation and low power applications. It has a 14-pin DIP package and an operating range of 3.6V – 10V. The Schmitt triggers in the SN74HCT14D have hysteresis which can be controlled by adjusting either the amount of positive feedback or the resistance of the two resistors connected to the comparator.