How is positive feedback supplied in a colpitts oscillator?
The Correct Answer and Explanation is:
Correct Answer:
Positive feedback in a Colpitts oscillator is supplied through a capacitive voltage divider.
Explanation:
A Colpitts oscillator is an electronic oscillator that uses an LC circuit (inductor-capacitor combination) to generate high-frequency oscillations. Its working principle is based on providing positive feedback to sustain oscillations. Positive feedback ensures that a portion of the output signal is fed back to the input in phase with the original signal, thus reinforcing it.
The distinctive feature of the Colpitts oscillator is its capacitive voltage divider, which consists of two capacitors connected in series (typically denoted as (C_1) and (C_2)). These capacitors are part of the LC tank circuit, which also includes an inductor ((L)). The tank circuit determines the oscillator’s resonant frequency, given by the formula:
[
f = \frac{1}{2 \pi \sqrt{L \cdot \left( \frac{C_1 \cdot C_2}{C_1 + C_2} \right)}}
]
In this configuration:
- The capacitors (C_1) and (C_2) divide the voltage across them based on their values.
- The junction of (C_1) and (C_2) provides the feedback signal, which is taken back to the active device (e.g., transistor or operational amplifier).
The active device amplifies the feedback signal, and the capacitive divider ensures that the feedback signal has the correct amplitude and phase for positive feedback.
Positive feedback occurs because the signal at the base or gate of the active device (derived from the capacitive divider) is in phase with the output signal. This phase alignment sustains oscillations.
The capacitive divider’s role is critical because it stabilizes the oscillator and controls the feedback level, preventing overloading or distortion. This design simplicity and frequency stability make the Colpitts oscillator widely used in communication systems and signal generation circuits.