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Analog & Digital Electronics > MOSFET > Flashcards

MOSFET Flashcards

1
Q

What are the three parts of the MOSFET

A

Gate, Source, and Drain

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2
Q

What happens when there’s zero gate voltage?

A

Two back to back diodes prevent a current conduction from the drain to the source when a voltage V(DS) is applied

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3
Q

What happened when a voltage is applied to the gate and the source is grounded?

A

A voltage V(GS) is created allowing for a channel to form between the source and drain which creates a current when V(DS) is applied

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4
Q

Does the gate receive a current?

A

No because of the oxide insulator

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5
Q

What is threshold voltage V(TN)?

A

The value of V(GS) at which a sufficient number of mobile electrons accumulate in the channel region to form a conducting channel

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6
Q

What is enhancement mode?

A

When V(GS) is greater than V(TN)

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7
Q

What is the relationship between drain current I(D) and Drain-Source Voltage V(DS) in saturation mode?

A

I(D) is independent of V(DS)

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8
Q

What is the equation for I(D) in saturation mode?

A

I(D) = K * [V(GS)-V(TN)]^2

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9
Q

When is a MOSFET in saturation mode?

What is the saturation voltage V(DS)sat?

A

V(DS) >= V(GS) - V(TN)

V(DS)sat = V(GS) - V(TN)

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10
Q

What a MOSFET is not in Saturation mode what is the mode called?
What is the effect of each mode?

A

Linear mode the MOSFET is a voltage-controlled resistor.

Saturation mode the MOSFET is used as an amplifier.

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11
Q

What is the output resistance r(o) equation?

A

r(o) = V(A) / I(D)Q

V(A) = Early Voltage
I(D)Q = Drain current at Q point
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12
Q

What is the first step for solving for Q point of a MOSFET (DC Analysis)?

A
  1. Use the Gate-Source loop to develop an equation as a function of V(GS) and I(D)
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13
Q

What is the second step for solving for the Q point of a MOSFET (DC Analysis)

A
  1. Assume the MOSFET is in saturation mode and use the I(D) equation
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14
Q

What is the third step for solving for the Q point of a MOSFET (DC Analysis)?

A
  1. Apply the equation in step 2 to find V(GS) and I(D)
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15
Q

What is the fourth step in finding the Q point of a MOSFET (DC Analysis)?

A
  1. Use Drain-Source loop to find the value of V(DS)
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16
Q

What is the fifth step for finding the Q point for a MOSFET (DC Analysis)?

A
  1. If V(DS) >= V(GS) - V(TN) then I(D) is valid. Otherwise the assumption of I(D) is invalid and use the Linear Mode equation to find for I(D) and V(DS)
17
Q

What is the sixth step for finding the Q point for a MOSFET (DC Analysis)?

A
  1. Draw the DC load line by expressing I(D) as a function of V(DS) from the Drain-Source loop equation
18
Q

What is the equation for I(D) in Linear mode?

A

I(D) = K * [2 * [V(GS)-V(TN)] * V(DS) - V(DS)^2]

19
Q

What are the three types of MOSFET amplifiers?

A

Common-Source, Common-Drain, Common-Gate

20
Q

What are the characteristics of a Common-Source amplifier?

A

Input to the Gate, output from the Drain, source is grounded in the AC equivalent circuit

21
Q

What is the equation for transconductance g(m)?

A

g(m) = 2 * sqrt(K * I(D)Q)

22
Q

What is the small signal equivalent circuit for a Common-Source amplifier?

A

———oG D———————
+ | |
V(GS) ♦️g(m)V(GS) } r(o)
- | |
————o—————————-
S

23
Q

How do you find the small signal equivalent circuit for a Basic CS Amplifier (no R(s) Resistor)?

A

Short capacitors and short bias voltage sources and obtain r(g) = r1 || r2. Place R(D) drain resistance and R(L) load resistance in parallel after r(o)

24
Q

How do you find the voltage gain Av in general and for a Basic Common-Source amplifier

A

General Av = Vo/V(GS) * V(GS)/Vsig
BCSA Av = -g(m) * [r(o) || R(D) || R(L)] *
[R(G) / [R(S)+R(G)]]

25
Q

What is the input resistance R(i) in the small signal model?

A

Anything before the gate and after the signal resistance Rsig

26
Q

What is the output resistance R(o) in the small signal model?

A

The resistance connected to the Drain in parallel with every resistance before the load resistance R(L)

27
Q

How do you draw the AC load line for a basic CS amplifier?

A

Find R(AC) = r(o)||R(D)||R(L)

Use the Q point to find b in
i(D) = -V(DS)/R(AC) + b

Plot the points at V(DS) = 0 and at I(D) = 0 and at the Q point found in DC analysis.

28
Q

How do you find the maximum allowable input signal such that the output is not distorted for a basic CE amplifier?

A

Look at the AC load line and do V(DS)Q - [V(GS)-V(TN)] and divide that by the voltage gain

Analog & Digital Electronics (4 decks)

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