oscillator basic

Apr 05, 2006 3 Replies
E

Can anyone give help. here.. I have an elementry question on oscillator theory. The oscillation criterion from a TI journal says the phase shift feedback from the output to the input is 180 but whereas many books tell the total phase shift of the whole circuit should be 0 deg or n360..



i got confused on the subject



The TI journal (talks about Ab = 1 /_ -180deg)

formatting link



Books talks about total phase shift is 360 deg Robert J. Matthys, CRYSTAL OSCILLATOR CIRCUITS, Krieger publishing company, malabar florida



Confused. Em7



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A

"The 180 degree phase shift criterion applies to negative feedback systems, and 0 (or 360) degree phase shift applies to positive feedback systems."

The inversion at the -ve summer input supplies the other 180 degrees.

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P

hi when you give a phase shift of 180 the circuit behaves as a amplifier and a 360 gives a oscillator

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E

thanks, but why peoples say when ABeta = -180, gives you the divider is

0 and the circuit becomes ocsillate ( unstable)
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