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nmos_example

# nmos_example - V ds = V dd − V rd = 5 − 0.1 20 = 3 V...

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[NMOS Transistor Example]: Calculate the drain current and drain-to-source voltage V ds , of the following circuit. It is given that R 1 = 30 kOhms, R 2 = 20 kOhms, R d = 20 kOhms, V dd = 5 V, V th = 1 V, and K = 0.1 mA/V 2 . Solution: Step 1: Assume a mode, or region, of operation. For this problem, let's assume the NMOS transistor operates in the saturation region. Step 2: Choosing the saturation region of operation implies, i d = K V gs V th 2 = 0.1 V gs 1 2 mA (1) Step 3: Solve for V gs and any other variables to determine i d , V ds , and any other useful variables in the circuit using circuit analysis techniques. By applying voltage divider at node V g , V g = V gs = R 2 R 1 R 2 V dd = 2 5 5 = 2 V (2) Then from equations (1) and (2), i d = 0.1 2 1 2 mA = 0.1 mA and V ds can be found by applying KVL between V dd and ground, V dd V rd V ds =

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Unformatted text preview: V ds = V dd − V rd = 5 − 0.1 20 = 3 V Step 4: Check that the inequalities are satisfied for the mode of operation chosen in Step 1. If the inequalities are not satisfied, then make another guess on the region. For the saturation region, the following conditions must be upheld: V gs V th and V ds V gs − V th . Since both conditions are satisfied for the calculations for id and V ds above, then the initial guess is correct, and the problem is solved. Therefore, i d = 0.1 mA and V ds = 3 V. [Exercise 1]: For the above example, try guessing the triode region, then show that the triode region would be an incorrect guess. [Exercise 2]: Try the same example with a PMOS transistor....
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