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Oscillator Circuits
49 questions By Tony R. Kuphaldt
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Question 19 of 49
Identify the type of oscillator circuit shown in this schematic diagram, and explain the purpose of the tank circuit (L1, C1, and C2):
Also, write the equation describing the operating frequency of this type of oscillator circuit.
Reveal answerThis is a Colpitts oscillator circuit, and the tank circuit establishes its frequency of operation.
$$f = \frac{1}{2{\pi}\sqrt{L_1 \frac{C_1 C_2}{C_1+C_2}}}$$
Follow-up question: calculate the operating frequency of this oscillator circuit if L1 = 270 mH, C1 = 0.047 μF, and C2 = 0.047 μF.
Notes:Ask your students to describe the amount of phase shift the tank circuit provides to the feedback signal. Also, ask them to explain how the oscillator circuit’s natural frequency may be altered.
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Question 20 of 49
Describe the purpose and operation of a crystal in an oscillator circuit. What physical principle does the crystal exploit, and what other components could be substituted in place of a crystal in an oscillator circuit?
Reveal answerA “crystal” is a chip of piezoelectric material that acts as an electromechanical tank circuit.
Notes:Ask your students to describe the phenomenon of piezoelectricity, and how this principle works inside an oscillator crystal. Also, ask them why crystals are used instead of tank circuits in so many precision oscillator circuits.
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Question 21 of 49
Identify the type of oscillator circuit shown in this schematic diagram, and explain the purpose of the crystal:
Challenge question: this type of oscillator circuit is usually limited to lower power outputs than either Hartley or Colpitts designs. Explain why.
Reveal answerThis is a Pierce oscillator circuit, and the crystal plays the same role that a tank circuit would in a Hartley or Colpitts oscillator.
Notes:Ask your students to explain how the oscillator circuit’s natural frequency may be altered. How does this differ from frequency control in either the Hartley or Colpitts designs?
