sharas said:
Hi, Is forcing a specific current between the source and the drain and measuring the voltage at the gate terminal - yield the same result as forcing Vds and sweeping the Gate terminal untill the same current is measured at the drain terminal?
No, this is not the case.
If you force a current through the source and drain terminal while leaving the gate floating, there is no way to accumulate charge on the gate terminal and it will remain fixed at its initial value. This is surely not what you want.
Remember that when you hold Vds constant and sweep Vgs, you are sweeping the transistor through its three regions of operation. In a simplified ideal transistor model, if Vgs < Vt, you have cutoff. If Vt < Vgs < Vds + Vt, you are in the saturation region. Finally, if Vgs > Vds + Vt, you are in the triode, or linear, region.
Most of the time, we want our transistors to operate in the saturation region. To determine the gate voltage required for a specific current to pass through, we can diode-connect the transitor. That is, connect the gate and drain terminals while passing the current through. This will force the transistor to operate in saturation mode and the gate voltage will be a well-defined function of the drain current.
jayc