A level shifter in digital electronics, also called a logic-level shifter, is a circuit used to translate signals from one logic level or voltage domain to another, allowing compatibility between ICs with different voltage requirements, such as TTL and CMOS. Many modern full featured systems use level shifters to bridge domains between low-power application processors running at 1.8 V and other system functions like sensors or other analog intensive applications running at 3.3 or 5V.
Uni-directional – All input pins are dedicated to one voltage domain, all output pins are dedicated to the other.
Bi-directional with Dedicated Ports – Each voltage domain has both input and output pins, but the data direction of a pin does not change.
Bi-directional with External direction indicator – When an external signal is changed, inputs become outputs and vice versa.
Bi-directional, auto-sensing – A pair of I/O spanning voltage domains can act as either inputs or outputs depending on external stimulus without the need for a dedicated direction control pin.
Fixed Function Level Shifter ICs – these ICs provide several different types of level shift in fixed function devices. Often lumped into 2-bit, 4-bit, or 8-bit level shift configurations offered with various VDD and VDD2 ranges, these devices translate logic levels without any additional integrated logic or timing adjustment.
Configurable Mixed-signal ICs (CMICs) – Level shifter circuitry can also be implemented in a CMIC. The no-code programmable nature of CMICs allows designers to implement fully customizable level shifters with the added option to integrate configurable logic or timing adjustments in the same device.
Since level shifters are used to resolve the voltage incompatibility between various parts of a system, they have a wide range of applications as well. Level shifters are widely used in interfacing legacy devices and also in SD cards, SIM cards, CF cards, Audio codecs and UARTs.