oscillator basic

[E Minor 7]

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)
http://www.ti.com/sc/docs/apps/msp/journal/aug2000/aug_07.pdf

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

Confused.
Em7

 

[Andrew Holme]

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)
http://www.ti.com/sc/docs/apps/msp/journal/aug2000/aug_07.pdf

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

Confused.
Em7

"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.

 

[prad]

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

 

[E Minor 7]

thanks, but why peoples say when ABeta = -180, gives you the divider is
0 and the circuit becomes ocsillate ( unstable)