Present technologies for integrated circuit with clearances of 0.5 µm and less, limit the maximum supply voltage
and consequently the logic levels for the digital I/O signals. To interface these lower voltage circuits with
existing 5 Volt devices a level shifter is needed. For bi-directional bus systems as e.g. the I2
C-bus, such a level
shifter must be bi-directional, without the need of a direction control signal. With only one appropriate MOS-FET
for each bus line the desired level shifting with automatic direction control can be done. The levels may have a
vast range, depending on the used MOS-FET, e.g. down to 2 Volt at the “Lower voltage” side and up to 10
Volt or more at the “Higher voltage” side of the level shifter.