Question

A circuit designer intending to operate a n-MOSFET in saturation is considering the effect of changing the device dimensions and operating voltages on the drain current ID.

(a) Specifically, by what factor will ID change in each of the following situation?
I. The channel length is doubled
II. The channel width is doubled
III. The overdrive voltage is doubled
IV. The drain-to-source voltage is doubled
V. Changes (I), (II), (III), and (IV) are made simultaneously.
(b) From above 5 cases, which of these cases might cause the n-MOSFET to leave the saturation region? And how?

Answer 1

(a) Let's analyze each situation separately to determine the factor by which the drain current (ID) will change.

I. Doubling the channel length:

When the channel length (L) is doubled, the drain current (ID) will decrease. The drain current is inversely proportional to the channel length, so doubling the channel length will result in halving the drain current. Therefore, the drain current (ID) will change by a factor of 1/2.

II. Doubling the channel width:

Doubling the channel width (W) will increase the drain current (ID). The drain current is directly proportional to the channel width, so doubling the channel width will result in doubling the drain current. Therefore, the drain current (ID) will change by a factor of 2.

III. Doubling the overdrive voltage (Vov):

Doubling the overdrive voltage (Vov) will also double the drain current (ID). The drain current is directly proportional to the square of the overdrive voltage, so doubling the overdrive voltage will result in four times the drain current. Therefore, the drain current (ID) will change by a factor of 4.

IV. Doubling the drain-to-source voltage (VDS):

Doubling the drain-to-source voltage (VDS) will not significantly change the drain current (ID) in the saturation region. The drain current is relatively independent of the drain-to-source voltage in saturation mode. Therefore, the drain current (ID) will change by a factor close to 1 (no significant change).

V. Simultaneous changes of (I), (II), (III), and (IV):

If all the changes are made simultaneously, we need to consider the combined effect of these changes on the drain current (ID). The drain current will change based on the individual factors calculated above. For example, if we consider doubling the channel width (factor of 2) and doubling the overdrive voltage (factor of 4), the combined effect will be the product of these factors: 2 * 4 = 8. So, the drain current (ID) will change by a factor of 8 when all the changes are made simultaneously.

(b) The case that might cause the n-MOSFET to leave the saturation region would be when the drain-to-source voltage (VDS) is doubled. If the drain-to-source voltage exceeds a certain threshold voltage (Vth) known as the pinch-off voltage, the MOSFET will enter the triode or linear region instead of remaining in the saturation region. In the triode region, the drain current (ID) is no longer proportional to the square of the overdrive voltage (Vov), and the device behaves differently. Therefore, doubling the drain-to-source voltage (VDS) could cause the MOSFET to leave the saturation region and enter the triode region.





Sorry for it being so long, it's a very complex question :l but yw for the answer lol

Step-by-step explanation: