Which oscillator configuration uses a tapped coil in parallel with a capacitor to determine the oscillation frequency?

Which oscillator configuration uses a tapped coil in parallel with a capacitor to determine the oscillation frequency?

• A. Crystal-controlled Oscillator
• B. Hartley Oscillator
• C. LC Tank Oscillator
• D. Tuning Circuit

Answer: (B)

The main idea is that a Hartley oscillator uses a tapped inductor as part of its LC tank to set the frequency and provide feedback. The capacitor is across the coil, and the coil’s tap splits the inductance into two portions. Since those portions are effectively in series for the tank, the resonant frequency depends on the total inductance, which is L1 + L2, together with the capacitance: f = 1/(2π√((L1+L2)C)). The tap feeds a portion of the output back to the active device to sustain oscillation, with the exact feedback level set by the ratio of the two inductances. This configuration—tapped coil in parallel with a capacitor forming the resonant tank and providing feedback—fits the Hartley oscillator. Crystal-controlled uses a crystal, which fixes frequency differently; a generic LC tank could be arranged without a tap; a tuning circuit isn’t an oscillator by itself.

The main idea is that a Hartley oscillator uses a tapped inductor as part of its LC tank to set the frequency and provide feedback. The capacitor is across the coil, and the coil’s tap splits the inductance into two portions. Since those portions are effectively in series for the tank, the resonant frequency depends on the total inductance, which is L1 + L2, together with the capacitance: f = 1/(2π√((L1+L2)C)). The tap feeds a portion of the output back to the active device to sustain oscillation, with the exact feedback level set by the ratio of the two inductances. This configuration—tapped coil in parallel with a capacitor forming the resonant tank and providing feedback—fits the Hartley oscillator. Crystal-controlled uses a crystal, which fixes frequency differently; a generic LC tank could be arranged without a tap; a tuning circuit isn’t an oscillator by itself.