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I'm implementing mosfet switching circuitry using the P channel enchancement mode mosfet DMP2305U.Where Vs = 3V and Vg is using as control voltage and toggleing between 0 and 3V . When Vg is zero volts , I'm getting output at Vd as high , when Vg is 3Volts I'm getting output at Vd as low as desired functionality, but i'm not getting the sufficient current through the mosfet . It seems like Vth of this mosfet is -0.9V and as a ground rule , Vgs should be greater than Vth to supply the max current , but here in my case Vgs is -3V (When the mosfet is on Vg=0v and Vs=3) .Here, do we need to consider the signs ?(negative , positive) of Vgs and Vth ?

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Drain current is dependent on load. What load do you have on the drain to 0 volts? Note that R1 is not connected in the right place to act as a load. \$\endgroup\$ – Andy aka Dec 12 '18 at 10:24
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when Vg is 3Volts I'm getting output at Vd as low as desired functionality, but i'm not getting the sufficient current through the mosfet .

When you pull the gate to 3 V, you are putting the MOSFET in cut-off mode. You should expect approximately 0 current between source and drain. Figure 10 in the datasheet shows the typical leakage current in cut-off, and it is measured in nanoamps.

It seems like Vth of this mosfet is -0.9V and as a ground rule , Vgs should be greater than Vth to supply the max current ,

For a p-channel MOSFET like this one, \$V_{gs}\$ should be less than \$V_{th}\$ to enter triode or saturation operation, not greater than \$V_{th}\$.

do we need to consider the signs ?(negative , positive) of Vgs and Vth ?

Yes, you need \$V_{gs} < V_{th}\$ to form a channel, and \$V_{th}\$ will be less than 0 for an enhancement mode p-channel MOSFET.

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