Excitable behavior of an operational amplifier

We find excitable behavior in an operational amplifier (OPA27). When an output terminal is connected to an inverting input terminal through a resistor and a positive input terminal is connected to the ground, the simple electronic circuit exhibits a transition from a steady state to a relaxation oscillation state through quasi-harmonic and excitable pulsation states as the positive and the negative power supply voltages are varied. The observed distribution of the excitable pulsation intervals shows that the pulsations are phase-locked with the internal quasi-harmonic oscillation.