For a circuit to function as an oscillator and produce sustained sinusoidal output, the feedback applied must be:
Positive feedback with proper phase
To determine the correct type of feedback required for an oscillator circuit to produce a sustained sinusoidal output, we need to understand the role of feedback in oscillators.
An oscillator is an electronic circuit that generates a continuous, periodic waveform without an input signal. For an oscillator to function correctly, it must satisfy the Barkhausen criterion, which states that:
- The total loop gain of the system should be equal to one, implying A\beta = 1, where A is the amplifier gain and \beta is the feedback factor.
- The phase shift around the loop must be 0^\circ or an integer multiple of 360^\circ.
Considering this background, let's analyze the given options:
- Zero feedback to avoid distortion: Zero feedback would mean no signal is fed back into the oscillator circuit, which isn't helpful for generating oscillation. Thus, this option is incorrect.
- Random feedback depending on input signal: Random feedback could lead to instability or failure to sustain oscillation, as it does not provide the consistent positive feedback required. This option is incorrect.
- Negative feedback to stabilize gain: Negative feedback is useful in amplifiers to stabilize the gain but is not typically used in oscillator circuits for generating sustained oscillations. Thus, this option is incorrect for oscillators.
- Positive feedback with proper phase: This option is correct because positive feedback helps the circuit to sustain oscillations by reinforcing the signal, and proper phase alignment ensures that the Barkhausen criterion is satisfied.
Therefore, the correct answer is: Positive feedback with proper phase.
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