Operating Regions Of An Enhancement Mode NMOS Transistor
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Operating Regions Of An Enhancement Mode NMOS Transistor

Figure 123.2 illustrates an enhancement-mode NMOS. The threshhold voltage, VT = 2 V, The source terminal of the nmos is grounded and a voltage source VGG = 3 V DC is connected to the gate.

Determine the operating state of the transistor for each of the following values of vD:
(a) vD = 0.5 V
(b) vD = 1 V
(c) vD = 5 V

The strings: S7P5A51 (Physical Change).

The math:
Pj Problem of Interest is of type change (physical change). Transistors are primarily used for signal amplification and switching. Both are change problems.

(a)The NMOS has three terminals: gate (G), the drain (D), and the source (S).
It has a p-material substrate (or bulk) electrically connected to the source. So the substrate does not appear as a separate terminal in circuit diagram.
The gate consists of a metal film separated from the p-substrate by a thin oxide layer (hence called metal oxide semiconductor).
both drain and source are made of n+ material.

(a)vGS = 3 V
vGD = vGS + vSD = vGS - vDS = vGS - vD = 3 - 0.5 = 2.5 V.
Where vGS = gate-source voltage
vGD = gate-drain voltage
vDS = drain-source voltage
vSD = source-drain voltage
So, vGS > VT and vGD > VT
So, NMOS is operating in the Triode or Ohmic Region.

(b) vGS = 3 V
vGD = vGS + vSD = vGS - vDS = vGS - vD = 3 - 1 = 2 V.
So, vGS > VT and vGD = VT
So, NMOS is operating in the Triode or Ohmic Region; or Saturation Region.

(c) vGS = 3 V
vGD = vGS + vSD = vGS - vDS = vGS - vD = 3 - 5 = -2 V.
So, vGS > VT and vGD < VT
So, NMOS is operating in the Saturation Region.

Blessed are they that have not seen, and yet have believed. John 20:29