On this page, the two versions of this gyro/accelerometer IC have two different Logic Supply Voltages.
What is the VDD voltage?
Why would one version of the chip also have an option to make the voltage 1.8V?
http://invensense.com/mems/gyro/mpu6000.html
note: not intended to be a dupe of
What is the difference between \$V_{CC}\$, \$V_{DD}\$, \$V_{EE}\$, \$V_{SS}\$.
Best Answer
\$V_{DD}\$ is the supply voltage (i.e. the main voltage "in" to power the IC).
Quote from 1st the link you posted:
As for why there's the 1.8V VLOGIC version? I suppose it's for those that want to interface with a 1.8V \$I^2C\$ bus (as opposed to, say, 3.3V SPI or \$I^2C\$ as you'd likely use with the non-1.8V version).