# Can oscillations happen even if negative feedback is present?

By OPAMP book says that virtual short is applicable in OPAMP only if negative feedback is present an output is not oscillating.I don't get how oscillations can occur at output if the feedback is negative

• If the phase shift of the feedback is 180 degrees, it is no longer negative – crj11 Mar 2 at 4:42
• Each and every negative feedback (defined for DC and low frequencies) will turn into positive feedback for rising frequencies - however, this will not cause severe stability problems as long as the loop gain is smaller than unity for the critical frequency with an overall phase shift within the loop of 360 deg (equal to 0 deg). – LvW Mar 2 at 9:24
• Suppose, at high frequencies, the OPAMP has only 50X gain in the openloop. Just how "Zero" will that virtual short be? – analogsystemsrf Mar 2 at 13:44

• @Buzzbee Do a Bode plot for some amplifier schematic. It's not hard to find a case where the voltage gain remains above 1 while the phase transitions to values larger than $180^\circ$. – jonk Mar 2 at 10:13