Discussion
An oscillator always needs an amplifier with :
Answer: D
An oscillator always needs an amplifier with positive feedback.
An oscillator produces an output with no input signal. By the Barkhausen criterion, this needs a loop gain \(A\beta = 1\) with a total phase shift of 0° or 360° around the loop, so that the fed-back signal reinforces itself. That is positive (regenerative) feedback.
An LC tank or an RC network sets the frequency only in particular types of oscillator, so neither is always needed; crystal and relaxation oscillators use neither in that role. Negative feedback is used to stabilise amplifiers and would kill the oscillation.
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