Analog circuits Test 1

Result

Analog circuits Test 1

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Question 1
2 / -0.33

The drain of an n-channel MOSFET is directly connected to gate so that V_DS = V_GS. The threshold voltage of it is 3V, if the drain current is 3 mA when V_GS = 4 V then for V_GS = 5V the value of I_D is____ mA

A
12-12

B
124-121

C
127-126

D
129-122

Solution

Concept:
For VDS ≥ VGS - VTN, the MOSFET operates in the saturation region, with the saturation current given by:
ID(sat) = Kn (VGS - VTN)2
\({K_n} = \frac{{W{\mu _n}{C_{ox}}}}{{2L}}\)
Application:
Since V_GS= V_DS for the given MOSFET, we observe that V_DS will always be greater than V_GS - V_TH. Hence the MOSFET is operating in saturation.
Given for V_GS = 4 V and V_TH = 3 V, the current is 3 mA, we can write:L
I_D = K [4 – 3]²
\(\frac{3m}{1} = K\)
K = 3 mA/V²
∴ For V_GS = 5 V, the drain current will be:
I_D = 3 [5 - 3]² = 12 mA