This set of Electronic Devices and Circuits online quiz focuses on “Large Signal Operations on operational Amplifiers”.
1. Slew rate of an amplifier is defined as
a) Minimum rate of change of the output possible in a real operational amplifier
b) Maximum rate of change of the output possible in a real operational amplifier
c) Average rate of change of the output possible in a real operational amplifier
d) Ratio of the maximum and the average rate of change of the output in a real amplifier
Explanation: By definition slew rate is the maximum rate of change of the output possible in a real operational amplifier.
2. Determine the slew rate of the amplifier having full power bandwidth f0 and the rated output voltage as V0. Given that the input signal is of sinusoidal nature.
a) 2πf0 V0
b) V0 / 2πf0
c) V0 / f0
d) f0 V0
Explanation: v = V0sin wt
dv/dt = wV0 sin wt
max value of dv/dt = wV0
max value of w = w0 = 2πf0
w0 V0 = Slew Rate = 2πf0 V0.
3. The units of the full power bandwidth is
Explanation: It has the units of frequency.
4. The full-power bandwidth, fM, is the maximum frequency at which
a) an output sinusoid with an amplitude equal to the op-amp rated output voltage (Vo max) can be produced without distortion
b) it is the range of the frequencies in which the amplitude of output signal is equal to or greater than half of the op-amp rated output voltage
c) it is the range of the frequencies in which the amplitude of output signal is equal to or less than half of the op-amp rated output voltage
d) It is the range of the frequencies in which the power gain is half or more than half of the maximum rated power gain of the op-amp
Explanation: This is the only statement that satisfies the definition of the full-power bandwidth.
5. Which of the following is not limitation of the operational amplifier
a) Output voltage saturation
b) Output current limits
c) Slew rate
d) None of the mentioned
Explanation: None of the mentioned are the limitations of the operational amplifier.
6. A particular op amp using ±15-V supplies operates linearly for outputs in the range −12 V to +12 V. If used in an inverting amplifier configuration of gain –100, what is the rms value of the largest possible sine wave that can be applied at the input without output clipping?
a) 120 mV
b) 60 mV
c) 84.85 mV
d) 42.42 mV
Explanation: Peak value of input wave = 12/100 or 120 mV. Hence the rms value is 120/√2 or 84.85 mV.
7. For operation with 10-V output pulses with the requirement that the sum of the rise and fall times represent only 20% of the pulse width (at half amplitude), what is the slew-rate requirement for an op amp to handle pulses 2 µs wide? (Note: The rise and fall times of a pulse signal are usually measured between the 10%- and 90%-height points.)
a) 10 V/µs
b) 20 V/µs
c) 40 V/µs
d) 80 V/µs
8. An op amp having a slew rate of 20 V/µs is to be used in the unity-gain follower configuration, with input pulses that rise from 0 to 3 V. What is the shortest pulse that can be used while ensuring full-amplitude output?
a) 0.10 µs
b) 0.15 µs
c) 0.20 µs
d) 0.30 µs
Explanation: Time taken to reach 3V from 0V with slew rate of 20V/µs is 3/20 µs or 0.15 µs.
(Q.9-Q.10) In designing with op amps one has to check the limitations on the voltage and frequency ranges of operation of the closed-loop amplifier, imposed by the op-amp finite bandwidth (ft), slew rate (SR), and output saturation (Vo max). Consider the use of an op amp with ftt = 2 MHz, SR = 1 V/µs, and V0 max = 10 V in the design of a non-inverting amplifier with a nominal gain of 10. Assume a sine-wave input with peak amplitude Vi.
9. If Vi = 0.5 V, what is the maximum frequency before the output distorts?
a) 31.8 kHz
b) 318 kHz
c) 3.18 kHz
d) 3.18 MHz
Explanation: Vi = 0.5v, V0 = 0.5 X 10 = 5V
2πf V0 = SR or f = 31.8 kHz.
10. If f = 20 kHz, what is the maximum value of Vi before the output distorts?
a) 0.397 V
b) 0.795 V
c) 1.192 V
d) 1.590 V
2πf V0 = SR = 20πf Vi, here f is 20 kHz, SR is 1 V/µs. Hence the value of Vi is 0.795 V.
Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.
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