Opamp Circuits

11. Differential amplifiers are used in

1. Instrumentation amplifiers
2. Voltage followers
3. Voltage regulators
4. Buffers

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12. For an ideal op-amp, which of the following is true?

1. The differential voltage across the input terminals is zero
2. The current into the input terminals is zero
3. The current from output terminal is zero
4. The output resistance is zero

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13. For an op-amp having differential gain Av and common-mode gain Ac the CMRR is given by

1. Av + Ac
2. Av / Ac
3. 1 + Av / Ac)
4. Ac / Av

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14. How many op-amps are required to implement this equation Vo = V1

1. 4
2. 3
3. 2
4. 1

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15. Hysteresis is desirable in Schmitt-trigger, because

1. Energy is to be stored/discharged in parasitic capacitances.
2. Effects of temperature would be compensated.
3. Devices in the circuit should be allowed time for saturation and desaturation.
4. It would prevent noise from causing false triggering.

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16. If ground is applied to the (+) terminal of an inverting op-amp, the (–) terminal will

1. Not need an input resistor
2. Be virtual ground
3. Have high reverse current
4. Not invert the signal

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17. In the above circuit the current ix is

1. 0.6A
2. 0.5A
3. 0.2A
4. 1/12A

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18. In the differential voltage gain & the common mode voltage gain of a differential amplifier are 48db & 2db respectively, then its common mode rejection ratio is

1. 23dB
2. 25dB
3. 46dB
4. 50dB

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19. The approximate input impedance of the opamp circuit which has Ri=10k, Rf=100k, RL=10k

1. ∞
2. 120k
3. 110k
4. 10k

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20. The closed-loop voltage gain of an inverting amplifier equal to

1. The ratio of the input resistance to feedback resistance
2. The open-loop voltage gain
3. The feedback resistance divided by the input resistance
4. The input resistance

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