If we have an H-bridge made of 4 N-MOSFETs, the gate voltage applied to each pair must be different because in an active circuit the sources will have different voltages. How much?

• The difference will be approximately that of the value of the DC supply feeding the bridge. – Andy aka Apr 7 at 13:23
• For large supply voltages, grossly exceeding typical $V_{GS}$ of MOSFETs, high-side driver ICs take care that the high-side MOSFET gates are driven with respect to the local Source Voltage – tobalt Apr 7 at 13:31