depletion and enhancement mosfet + difference
As mentioned in former replies to your question, Depletion and Enhancement Mosfet's differ in the channel formation.
Enhancements Mosfet's have a channel already between the Drain and Source, so adding a gate voltage of either positive or negative polarity, controls its conductivity. This allows us to use a signal of both polarities without having to worry about the MOSFET cutting off
While in Depletiong MOSFET the channel needs to be created, and that is done by adding a DC voltage to the Gate, untill the condition of "Inversion" is reached and the channel is formed. This restricts us to use only signals of one polarity to maintain the MOSFET operating and avoid the cut-off condition.