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Answer: The sine wave shifted downward by 3V. The new peak values are 2.5V and -8.5V

The instantaneous value of a complex voltage wave is denoted as

vA = VB + vc

Sketch the output waveform, vA if VB is a DC voltage of -3 V and vc is equivalent to 5.5 sin ωt.

Label the peak values of the output waveform

2 of 13

 

 

3 of 13

A sinusoidal voltage signal, sin (ωt) with a magnitude of 2V is superimposed on a 5V DC voltage.

    • Write down the total instantaneous value of AC and DC.
    • Sketch the output sinusoidal voltage with correct peak values.

Answer: �i) vO = 5 + 2 sin (ωt)

The sine wave shifted upward by 5V. The new peak values are 7 V and 3 V

4 of 13

A current amplifier is shown below. Its input resistance is 200 Ω and its output resistance is 50 kΩ. The short circuit current gain is 100. Calculate the current gain, (io /is)

Answer = 33.3

5 of 13

Calculate the open circuit voltage gain, Av given that the open circuit current gain, Ai = 84.5

Ri = 450 Ω

RO = 2.5 kΩ

+

​

vi

​

​

-

Answer = 469.4

6 of 13

Determine the open circuit voltage gain of the amplifier when the load resistance of RL = 350 Ω is connected to the output of a voltage amplifier as shown below. The output voltage across the load resistance is 10 V when the amplifier input is 100 mV. Assume that the output resistance of the amplifier is 15 Ω.

Answer = 104.3

7 of 13

The open circuit voltage of a voltage amplifier is 12 V when its input is connected to a signal source. The voltage of the signal source is 1.5 V and its resistance is 5 kΩ. The input and output resistances of the amplifier are 1.0 kΩ and 150 Ω respectively.

    • Draw the schematic of the amplifier circuit.
    • Determine the output current and output voltage of the amplifier when a 30 Ω load resistor is connected at the output. 

Answers:

io = 66.67 mA

vo = 2 V

8 of 13

For a voltage amplifier model shown below, answer the questions below:

 

Answers

  1. RI = 0.353 kΩ
  2. New voltage gain = 5
  3. vo = 75 sin (ωt) V and io = 0.75 sin (ωt) mA

9 of 13

Consider the voltage-amplifier circuit model shown below in which 𝐴𝑣 = 20, 𝑅𝑖 = 60 kΩ 𝑅0 = 1kΩ 𝑅𝑆 = 40kΩ and 𝑅𝐿 = 1.5kΩ. When source 𝑣S = 1𝑉:

  1. Find the load voltage 𝑣0 and the current 𝑖0
  2. Calculate the voltage gain 𝐴𝑣𝑠 = 𝑣0 / 𝑣S considering 𝑅0 = 0

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Answers

  1. vo = 7.2 V and io = 4.8 mA
  2. 𝑣0 / 𝑣S = 12

10 of 13

 

Answer

Vo = 12.86 V

11 of 13

An equivalent circuit of a current amplifier is shown below. The input and output resistance of the amplifier are 10 kΩ and 2.5 kΩ respectively. The amplifier is connected to a signal current source, is = 1.5 mA with a resistance of 5 kΩ. Calculate the short circuit current gain, Ai given that RL = 500 Ω and the voltage across it is 6 V

Answer: Ai = 19.2

12 of 13

Answers

  1. vi = 0.625 vs
  2. vo = 67 vs
  3. Av = 67

 

13 of 13

A current amplifier equivalent circuit is shown below. The short circuit current gain of the amplifier is 25. The output resistance is 2.5 kΩ. A 450 Ω load is then connected to the output, determine the output voltage across the load. Assume that the input current is 2 mA.

Answer

Vo = 19.07 V