Basic FET operation

Normally on type

From the simplified diagram shown in Fig 13.1 we have

Resistance of channel

L=length

Z=width

and

Channel acts like a constant resistor

Now if increases-voltage distribution over channel changes as V(x) and the with of the depletion region becomes

Therefore,

when source is grounded

Along the length of the channel the Resistance changes and the overall resistance of the channel now i

However as V D increases, after a certain voltage, I D saturates at

Where V P is called the pinch-off voltage as shown in Fig 13.2

When the additional voltage appears across the depletion region, so the depletion region widens, this is shown in Fig 13.3

.