Logic Level Shifting

A Guide To Logic Level Shifting

Logic level shifting is changing the logic level of a digital signal from one voltage to another. Logic level shifting is a technique that allows a device to change the voltage of a signal. This is done by shifting the logic level from one voltage to another.

The voltage difference between those two levels can be as low as 0.2 V, achievable with CMOS logic circuits. The input and output voltages are not required to be identical, but they must be within the range of the input and output logic levels.

What Is Logic Level Shifter

A logic level shifter is a device that can convert voltage levels between different systems. A logic level converter is a device used to convert the output of one logic family into the input of another logic family. Logic families are defined by the voltage levels they use, for example, CMOS (0.5 V) and TTL (0.8 V).

Logic level shifter
Logic Level Shifter

Types Of Level Shifting

There are four main types of level shifting available based on their working principle: 

  • Uni-directional
  • Bi-directional with Dedicated ports
  • Bi-directional with external direction indicator
  • Bi-directional, auto-sensing

How is Logic Level Shifting Works?

Logic level shifting is a technique in which the voltage levels are changed to match the logic state for a specific device. Logic level shifting is achieved by changing the voltage levels of the signal rather than its logic state. Logic level shifters use three or more voltage levels to represent one logic state.

When We Use Logic Level Shifter

Logic level shifting is used in many different applications, including:

  • Changing an input signal from TTL to CMOS
  • Converting the logic levels of an I/O signal to match with the logic levels of the system
  • Converting between different voltage standards (5 V and 3.3 V).


The term “logic level shifting” is used to describe a process where the voltage levels of digital signals are changed from one logic level to another.

This is a common technique for interfacing between digital circuits operating at different voltage levels, such as TTL and CMOS. This method also allows for interfacing between different types of logic families, such as DTL and RTL.


About the Author: BDElectricity Staff

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