ECEN3714 Exam
#2 6 April 2006
1) The circuit shown contains an ideal Op Amp (Zin = infinity, H(ω) =
constant, |Iout_max| = infinity).
1a) [5] Compute the voltage gain of the circuit at ω
= 0.
[Answer: H(0) = 5]
1b) [5] Compute the voltage gain of the circuit as ω approaches
infinity. [H(infinity) =
-0.2]
1c) [15] If vin(t) = 10sin0.2t, what is the steady state vout(t)?
[5.358sin(0.2t + 117.5 degrees)]
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2) The circuit shown contains an non-ideal Op Amp (Zin = infinity, H(ω)
= constant, |Iout_max| = ?? amp).
2a) [15] If a unit step voltage is input, compute vout(t)
assuming the op amp can provide a sufficient amount of current. [vout(t) = -5u(t) + 4.8e-t/50]
2b) [10] After the transient has subsided, how much current must the op
amp be capable of sourcing (or sinking) in order to generate the output
calculated in part 2a? [Must
be able to sink 1 amp.]
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Mini Design Project
3a) [15] Design a passive band reject filter with a 3dB reject
bandwidth of 5 Hz that will completely eliminate any 60 Hz
interference, i.e. want H(f = 60 Hz) = 0. [From chapter 14.5, one option is a
series RLC circuit with R = 10 K ohms, L = 318.3 H, and C = 22.10
nF. The input voltage would be dropped across all three elements,
and the output voltage dropped across the resistor and capacitor.]
3b) [10] Practically speaking, would you be able to physically build a
passive circuit that would meet the specs above? Explain. [Probably not with the values
chosen. Would require a hard to find inductor. However, the
values could be adjusted to more commonly found sizes, such as R = 10
ohms, L = 318.3 mH, and C = 22.1 microF. Might be difficult to
get precisely the correct values needed. However a tunable
capacitor and resistor might be found such that a circuit very close to
the desired value might be constructed.]
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4) The switch has been in the position shown for a long time. At
time t = 0, the switch is connected to ground.
[25] Find i(t). [-5e-0.1t amps]
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