level shifter

A level shifter is a special cell placed wherever a signal crosses from one voltage domain to another, translating a logic level that means '1' on one side into a logic level that means '1' on the other. Picture two countries with different mains voltages: you can't just plug a 110 V appliance into a 230 V socket — you need an adapter. The level shifter is that adapter for on-chip signals.

Why is it needed? If a block running at 0.6 V drives a gate expecting 1.0 V, the '0.6 V high' may sit in the receiver's grey zone, leaving its input transistors half-on and bleeding short-circuit current forever. A level shifter cleanly restores the signal to the receiver's rails. There are two flavours: low-to-high shifters need a dual-rail design (they must reach up to the higher voltage), while high-to-low shifters are simpler. UPF lets you specify exactly which crossings require shifters, and the tool inserts them automatically along every offending net.