1)
If a transistor is biased so that gm = 75 millimhos and rπ = 2 KΩ, what is the value of β?
(a) 50
2)
(d) 150
(e) 250
(b) 1.0 KΩ
(c) 1.5 KΩ
(d) 2.0 KΩ
(e) 4.0 KΩ
A transistor has β = 50 and VA = 50 V and is to have an ro of 100 KΩ, what is gm in
millimhos?
(a) 19
4)
(c) 100
What is the new value of rπ for the transistor in Problem 1 if the collector current is
doubled?
(a) 0.5 KΩ
3)
(b) 75
(b) 38
(c) 57
(d) 76
(e) 100
For the circuit shown below, β = 200; what is the small signal voltage gain?
(a) +0.97
(b) +110
(c) -110
2
(d) +60
(e) –60
5)
For the circuit shown below, RE is chosen so that IE = 0.5 mA. The transistor is biased in
the active region, β = 100, and RC = RL = 5 KΩ. What is the input impedance seen by the
source (i.e. remove the source and its series resistance, RS)?
(a) 5 KΩ
6)
(c) 12 Ω
(d) 55 KΩ
(e) not enough info given
For the circuit shown in Problem 5, what happens if the capacitor, CE, is removed?
(a)
(b)
(c)
(d)
(e)
7)
(b) 2.5 KΩ
the small signal voltage gain is reduced
the small signal voltage gain is increased
the input impedance decreases
the dc bias current is lowered
no change
For the circuit shown below, assume that Vbias is set so that IC = 1.0 mA. The transistors have
β = 100 and VA = 100 V. What is the small signal voltage gain, Vo/Vs?
(a) -4
(b) -7
(c) -110
3
(d) -3800
(e) -1900
8)
The circuit shown below is biased so that ID = 1.0 mA, what is the value of the small signal
gain? Assume kn = 1mA/V2 and VTh = 2 V. Circuit parameters include: VDD = 12 V, RS = 4
KΩ, RD = RL = 6 KΩ, and R1 = 500 KΩ.
(a) –11
9)
(c) +6
(d) –0.7
(e) +0.7
For the circuit in Problem 8, what is the input impedance?
(a) 200 KΩ
10)
(b) –6
(b) 300 KΩ
(c) 120 KΩ
(d) 1 MΩ
(e) 100 Ω
Select RS in the circuit below so that IS = 1 mA. The transistor parameters are VTh = –1 V and
kn = 4 mA/V2. The circuit parameters are VDD = 10 V and RD = RL = 4 KΩ. The appropriate
value of RS is
(a) 0.25 KΩ
(b) 0.5 KΩ
(c) 1.0 KΩ
4
(d) 1.5 KΩ
(e) 2.0 KΩ
11)
What is the output resistance of the circuit shown below?
(a) RE
(b) RE + rπ
(c) RE || (β+1)rπ
(d) RE || [rπ/(β+1)]
(e) RE || [(rπ + R1||R2)/(β+1)]
12)
What is the input impedance of the circuit shown below? Assume ICC = 1.0 mA and β = 200.
(a) 1 KΩ
13)
(b) 200 Ω
(c) 50 Ω
(d) 25 Ω
(e) 10 Ω
What is the small signal voltage gain of the amplifier shown in Problem 12?
5
(a) +393
14)
(c) +39
(d) +19
(e) +13
What is the best description of the expected input impedance, output impedance, and gain of
the circuit shown below?
(a)
(b)
(c)
(d)
(e)
15)
(b) –126
low Ris
low Ris
low Ris,
high Ris
high Ris
low Ro
low Ro
moderate Ro
low Ro
low Ro
low AV
high AV
moderate AV
low AV
moderate AV
What is the input impedance of the circuit below?
(a) R1||R2
(b) (R1||R2) || (rπ1 + rπ2)
(c) (R1||R2) || [rπ1 + (β+1)rπ2]
(d) (R1||R2) || [rπ1 + (β+1)(rπ2+RE2)]
(e) (R1||R2) || [rπ1 + rπ2/(β+1)]
6
16)
For the circuit shown below, assume that ID1 = ID2 ; the best estimate for the gain of the first
stage is:
(a) +0.1
(b) +0.5
(c) +1.0
7
(d) +5.5
(e) +7.3
Problem 17: Partial Credit (20 points total)
For the circuit below, VCC = 12 V, R1 = 250 Ω, R4 = 1 kΩ, R5 = 2 kΩ, RL = 1 kΩ, C1 = C2 = C3 =
100 µF. The transistor has |VBE(on)| = 0.6 V, |VCE(sat)| = 0.3 V, β = 100 and VA = 200 V.
(6 pts)
(a) Draw the mid-frequency small-signal model for the circuit above. Identify the input
and output currents (is and io) and the output voltage (vo).
(6 pts)
(b) Derive an equation for the current gain, Ai = io i s in terms of the small-signal circuit
elements and transistor properties
(2 pts)
(c) Select an appropriate DC operating point: ICQ = ________
(6 pts)
(d) Compute values for R2 and R3 such that Ai = 10. [Hint: Use KVL to determine the
voltage at the base, and then use your equation for Ai to determine (R2 || R3)]
8
VCEQ = ________