1. An inverting amplifier that amplifies dc input level is called
A. DC and AC amplifier
B. AC amplifier
C. DC amplifier
D. None of the mentioned
Answer: C
In a DC amplifier, the output signal changes in response to changes in its dc input level. A DC amplifier can be inverting, non-inverting or differential.
2. Why DC amplifier uses offset null circuitry?
A. To reduce the distortion in the output
B. To improve the accuracy of the amplifier
C. To get a large output gain
D. All of the mentioned
Answer: B
A DC amplifier uses offset null circuitry to reduce the output offset voltage to zero, that is, to improve the accuracy of the DC amplifier.
3. Why are coupling capacitors used in audio receiver systems?
A. All of the mentioned
B. Thermal drift
C. Component tolerance
D. Variation in signal
Answer: A
An audio receiver system consists of a number of stages because of thermal drift, components tolerance, and variation, which introduces a dc level. To prevent the amplification of such dc level, the coupling capacitors are used.
4. Determine the bandwidth of the AC inverting amplifier for a high cut-off frequency of 15 Hz?
A. 4.321Hz
B. 8.356Hz
C. 7.056Hz
D. 2.334Hz
Answer: B
Input resistance RIF=R1=100Ω (for ideal inverting amplifier).
=> The source resistance RIN=RO=5kΩ.
Therefore, Low frequency cut-off,
fL=1/2πCi(RIF+RO) = 1/ [2π×4.7µF×(5kΩ+100Ω)]
= 6.64Hz. and the bandwidth is calculated as,
BW= fH-fL
= 15 Hz –6.64 Hz = 8.356 Hz.
5. When does the offset voltage compensating network must be used in inverting configuration?
A. When the input is AC voltage
B. When the input is DC voltage
C. When the input is either AC or DC voltage
D. None of the mentioned
Answer: B
To reduce the output offset voltage to zero, the offset minimizing resistor is used to minimize the effect of input bias currents on the output offset voltage. However, when the inputs are DC voltages, the offset compensating network must be used.
6. State the application in which summing, scaling, or averaging amplifiers are used?
A. Multiplexers
B. Counters
C. Audio mixers
D. All of the mentioned
Answer: C
Summing, scaling, or averaging amplifiers are commonly used in audio mixers, in which several inputs are added up to produce the desired output.
7. How an AC amplifier can be powered by a single supply voltage and produces voltage swing?
A. By inserting a voltage divider at the inverting input
B. By inserting a voltage divider at the non-inverting input
C. By inserting a voltage divider at the output
D. By inserting a voltage divider at the feedback circuit
Answer: B
A positive dc level is intentionally inserted using a voltage-divider network at the non-inverting input terminal so that output can swing both positively as well as negatively.
8. Find the maximum output voltage swing of an AC inverting amplifier using op-amp 741C?
A. +15Vpp
B. ±15Vpp
C. ±13Vpp
D. +13Vpp
Answer: A
The value of power supply for 741 op-amp=±15v. Therefore, the ideal maximum output voltage swing for an AC amplifier with a single power supply = +Vcc = +15v.
6. Determine the lower cut-off frequency of the circuit.
A. 21.3Hz
B. 12.15Hz
C. 1.35Hz
D. None of the mentioned
Answer: D
The input resistance of the amplifier is RIF =(R2 ||R3) || [ri×(1+AB.] –> equ 1
As [ri×(1+AB.] >> R2
=> Therefore, equ 1 becomes
RIF ≅ R2 || R3 = 100kΩ || 100kΩ
= (100×100)/(100+100) = 50kΩ.
=> Rin = Ro = 150Ω.
∴ Lower cut off frequency
fL= 1/[2πCi×(RIF+Ro)]
= 1/[2π×0.47µF×(50kΩ+150Ω)] = 6.75Hz.
9. In differential op-amp configuration a subtractor is called as
A. Summing amplifier
B. Difference amplifier
C. Scaling amplifier
D. All of the mentioned
Answer: C
In a subtractor, input signals can be scaled to the desired values by selecting appropriate values for the external resistors. Therefore, this circuit is referred to as a scaling amplifier
10. How the peaking response is obtained?
A. Using a series LC network with op-amp
B. Using a series RC network with op-amp
C. Using a parallel LC network with op-amp
D. Using a parallel RC network with op-amp
Answer: C
The peaking response is the frequency response that peaks at a certain frequency. This can be obtained by using a parallel LC network with the op-amp.
