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Why the o/p of starting oscillators is sinusoidal ?

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sreejith

sreejith

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starting of oscillators

when the oscillators pick up a noise and start working ,
why the o/p of them are always sinusoidal ?(for LC and RC sin osc.)
 

Re: starting of oscillators

A sinusoidal oscillator generates this kind of waveform because the feedback loop contains a tuned circuit (the LC or RC) that is a filter that attenuates all other frequency signals, so the remaining signal is unique in frequency and "pure" (without harmonics).
 

    sreejith

    sreejith

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Re: starting of oscillators

Well about your questions:

when the oscillators pick up a noise and start working ,
why the o/p of them are always sinusoidal ?(for LC and RC sin osc.)

Noise contaminate the signal in every stage, because it is in the enviroment, but the critical part is the amplifier stage where noise will amplified then pass to the feedback and returns to the input of the amplifier again and continues to increase his amplitud.

For your second question, there are two kinds of oscillators: sinusoidals and relaxation. LC and RC are of the first kind.
 

    sreejith

    sreejith

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Re: starting of oscillators

When the supply is switched on,this action can be modelled as a unit step.unit step contains all frequency components.Now the transfer functionof LC oscillator is such that all the freequencies are attenuated except the one frequency which is given by (1 +Aβ)=0.
 

    sreejith

    sreejith

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starting of oscillators

for sinusoidal oscillation, noise the reason
but for non sinusoidal oscillator, i think cannot play its " dubious " role.moreover,they will be always built with two matched elements .at a single time any one will be in "ON " and other will be "OFF" condition..
for ur first query,the connecting element between capacitance and inductance is like a resistance.Further it is vital to remember that resistance will generate "thermal noise".This locally generated noise will follow between 'C' and 'L' which is a continous process.this leads to sinusoidal wave generation
 

    sreejith

    sreejith

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starting of oscillators

I think sinusoidal signal is the only signal that remains unchanged when passed through a linear system.So even if the oscillator picks up noise which may be thought of as composed of several different random signals,only sinusoidal signal will persist in steady state and is mantained due to the tank cicuit.
 

    sreejith

    sreejith

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Re: starting of oscillators

hi

when u plot the impedance curve for the LC pair of the oscillator... the impedance due to the capacitor attains minimum at 1/(2*pi*f*c) and the impedance of the inductor is minimum at 1/(2*pi*f*L) these two curves combine to form a resonant curve where the impedance droops till f = 1/(2 * pi * √ (L * C)) and then it increases. so this is the only frequency passed through the LC pair. so a single frequency component is always sinusoidal...(remember fourier series)
 

    sreejith

    sreejith

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