this is the output after 2 RC stages designed to give 55° phase difference.but further adding of more stages does not effect the output phase(yellow).the output is already 180° out of phase as it is the output of an Common emitter amplifier.i want to add 180° more phase with 3 RC stages.but no phase addition takes place after adding 3rd RC stage.what might be the potential problem?

first image is of output from transistor

http://postimg.org/image/ikm2n0uab/

second image is after two RC stages

http://postimg.org/image/u5lv9ienz/

 

Please post the schematic. The details matter.

ak

 

Oscillation will occur at whatever frequency results in positive feedback. Adding more delay in the loop will only reduce the operating frequency, not add more phase shift at the same oscillation frequency.