Due to the increasing complexity of analog circuits, finding out whether an analog circuit meets the required specification is a difficult and time consuming task. We propose a complete Build- In Self-Test and Fault-Diangosis circuit based on the frequency domain specifications for analog circuits in order to reduce the time and effort for testing. This built-in circuit supports an automated yes or no testing when used in production test. Furthermore, the ability to access internal blocks inside an analog circuit provides a fault diagnosis ability when an engineer wants to find out the cause of faulty circuits. Coupled with extra multiplexers, this circuit can be used to detect faults in analog parts in a mixed signal circuit.