Signals and Amplifiers topics include: The basics of signals, amplifiers, sinusoidal steady state analysis, amplifier circuit models and frequency response. A signal amplifier is a circuit that uses electrical power to increase the amplitude of an incoming signal voltage or current signal. The output terminals of the signal amplifier output the higher amplitude version.  Here are some types of amplifiers: Small signal amplifiers: Also called voltage amplifiers, these amplifiers amplify an input voltage to a higher output voltage. However, the output may not have enough power to drive loads... Show more

Signals and Amplifiers topics include: The basics of signals, amplifiers, sinusoidal steady state analysis, amplifier circuit models and frequency response.

A signal amplifier is a circuit that uses electrical power to increase the amplitude of an incoming signal voltage or current signal. The output terminals of the signal amplifier output the higher amplitude version. 

Here are some types of amplifiers:
Small signal amplifiers: Also called voltage amplifiers, these amplifiers amplify an input voltage to a higher output voltage. However, the output may not have enough power to drive loads like motors and loudspeakers.
Power amplifiers: This subtype of amplifier raises the power of a signal. They are used in modern consumer electronic devices such as smartphones and tablets.
RF amplifiers: These tuned amplifiers convert the input signal into an output signal that provides the required response at a given frequency.
Differential amplifiers: These amplifiers amplify the difference of the two signals applied to its input. They are subtractor circuits that subtract the two applied input and then produce amplified output.
Current amplifiers: These amplifiers increase the current of an input signal. They are often used in power electronic systems, such as in power supplies or motor controllers.
Transistor amplifiers: These amplifiers are fully reliant on transistors. They can use a current, voltage, or power signal as the input signal. The signal is amplified without affecting its properties, and the output is a modified version of the original signal. 

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Electronic Devices and Circuits Practice Test: Signals and Amplifiers

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25 Questions

1. Q = 2000 VAR, pf = 0.9 (leading). The power in complex form is

4129.8 j2000 VA2000 j41.29.8 VA2000 j4129.8 VA

2. i(t) = ?

2.48 cos(300t – 68.2) A20 cos(300t – 68.2) A20 cos (300t + 68.2) A2.48 cos(300t + 68.2) A

3. A transconductance amplifier with Ri = 2 kΩ, Gm = 40 mA/V, and Ro = 20 kΩ is fed with a voltage source having a source resistance of 2 kΩ and is loaded with a 1-kΩ resistance. Find the voltage gain realized.

18.05 V/V21.05V/V20.05 V/V19.05 V/V

4. Vc(t) = ?

2.25 cos (5t – 140.71) V2.25 cos (5t + 140.71) V2.25 cos (5t – 150) V2.25 cos (5t + 150) V

5. Consider the DAC (digital to Analog Converter) shown below. Where b₁, b₂….b_n can be either 0 or 1. Which is the Most Significant Bit and Least Significant Bit in this case?

MSB: b1, LSB: bNMSB: bN, LSB: bNMSB: bN, LSB: b1MSB: b1, LSB: b1

6. The output voltage of a voltage amplifier has been found to decrease by 20% when a load resistance of 1 kΩ is connected. What is the value of the amplifier output resistance?

350Ω50Ω250Ω200Ω

7. What is the binary representation of 57?

0011 10010011 11010111 10010101 1001

8. Which of the following is true?

Monolithic IC amplifiers are directly coupled or dc amplifiersAudio amplifiers have coupling capacitor amplifierTelevisions and radios use tuned amplifiersAll of the mentioned

9. If A_v, A_i and A_p represents the voltage gain, current gain and power gain ratio of an amplifier which of the below is not the correct expression for the corresponding values in decibel?

Power gain: 10 log ApCurrent gain: 20 log Ai dbVoltage gain: 20 log Av dbPower gain: 20 log Ap db

10. The signal to be amplified is current signal and the output desired is a voltage signal. Which of the following amplifier can perform this task?

Current amplifierTransconductance amplifierVoltage amplifierTransresistance amplifier

11. Consider a voltage amplifier having a frequency response of the low-pass STC type with a dc gain of 60 dB and a 3-dB frequency of 1000 Hz. Then the gain db at

f = 100 kHz is 25 dbf = 10 Hz is 55 dbf = 1Mhz is 0 dbf = 10 kHz is 45 db

12. You are given two amplifiers, A and B, to connect in cascade between a 10-mV, 100-kΩ source (S) and a 100-Ω load (L). The amplifiers have voltage gain, input resistance, and output resistance as follows: for A, 100 V/V, 10 kΩ, 10 kΩ, respectively; for B, 1 V/V, 100 kΩ, 100 Ω, respectively. Your problem is to decide how the amplifiers should be connected so that the voltage gain is maximum.

SBALBoth have the same voltage gainNone as neither combination is able to amplify the input signalSABL

13. The ratio of the open circuit voltage of a voltage amplifier (A_V) to the short circuit transconductance of a (G_m) of a transconductance amplifier, given that both have the same value of the internal resistance (R_i) and the output resistance (R₀), is

1/RiR01/R0Ri

14. An amplifier operating from ±3V provide a 2.2V peak sine wave across a 100 ohm load when provided with a 0.2V peak sine wave as an input from which 1.0mA current is drawn. The average current in each supply is measured to be 20mA. What is the amplifier efficiency?

25.2%35.2%30.2%20.2%

15. Statement 1: Voltage gain of -5 means that the output voltage has been attenuated.
Statement 2: Voltage gain of -5db means that the output voltage has been attenuated.

Statement 1 and Statement 2 are falseOnly Statement 1 is trueStatement 1 and Statement 2 are trueOnly Statement 2 is true

16. i2(t) = ?

2.04 sin (4t 2.13) A2.04 cos (4t 2.13) A2.04 cos (4t 92.13) A2.04 sin (4t 92.13) A

17. What is meant by stability of the an amplified signal?

The amplified signal must have a finite amplitudeThe input and the output signal must be proportionalThe ratio of the input and the output signal must be finiteThe amplified signal should not have self oscillation

18. The ratio of the short circuit current gain of a current amplifier (A_i) to the open circuit voltage gain of a voltage amplifier (A_V), given that both amplifiers have the same value of the input resistance (R_i) and output resistance (R₀), is

Ro / RiRiRoRi / R0

19. Consider the DAC (digital to Analog Converter) shown below. Where b₁, b₂….b_n can be either 0 or 1. For v_ref = 10V, n = 6, and R= 5000 ohm, which of the following is true?

The change in the output current is the MSB is change from 0 to 1 is 0.5 mANone of theseThe maximum value of the output current is 1.9375 mAThe change in the output current if the LSB is changed from 0 to 1 is 0.03125 mA

20. When a circuit is called compensated attenuator?

Transfer function is independent of the frequencyNatural log of the transfer function is proportional to the frequencyTransfer function is inversely proportional to the frequencyTransfer function is directly proportional to the frequency

21. Which of the following isn’t true?

Both transformer and amplifier can provide current gainBoth transformer and amplifier can provide voltage gainNone of theseBoth transformer and amplifier can provide power gain

22. i1(t) = ?

2.36 cos (4t 41.07) A1.37 cos (4t 41.07) A

23. An amplifier has a voltage gain of 100 V/V and a current gain of 1000A/A. the value of the power gain decibel is

40 db60 db30 db50 db

24. In compact disc (CD) audio technology, the signal is sampled at 44kHz. Each sample is represented by 16bits. What is the speed of the system in bits/second?

1,441,792,000 bits/second704,000 bits/second1.34 bits/second2,750 bits/second

25. An electrical signal can be represented in either Thevenin form or Norton From. However, Norton representation is preferred when

Both of the cases mentioned are the preferred caseThe load resistance is very large as compared to the source resistanceThere is no preferred caseThe load resistance is very low as compared to the source resistance