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A new strategy for on-chip test of an operational amplifier as a part of complex analog and mixed-signal systems is described. During test mode, the operational amplifier is disconnected from the rest of the circuit and transformed to an oscillator. To evaluate the circuit, its oscillation frequency is then compared to a frequency given by a Schmitt trigger oscillator, used as the on-chip reference to compensate technology variations. This method might bring a possibility to implement the Oscillation-based Built-In Self-Test (OBIST) for operational amplifiers as a part of complex systems.