Design for testability of integrated operational amplifiers using oscillation-test strategy

This paper treats the problem of testing integrated operational amplifiers. The efficiency of a new low-cost vector-less test solution, known as oscillation-test, is investigated. During the test mode, the op-amps are converted to a circuit that oscillates. The oscillation frequency is evaluated to monitor faults. The tolerance band of the oscillation frequency is determined using a Monte Carlo analysis taking into account the nominal tolerance of all important technology and design parameters. Faults in the op-amps under test which cause the oscillation frequency to exit the tolerance band can therefore be detected. Some design for testability (DFT) rules to rearrange op-amps to form oscillators are presented and the related practical problems and limitations are discussed. The oscillation frequency can be easily and precisely evaluated using pure digital circuitry. The simulation and practical implementation results confirm that the presented method assures a high fault coverage with a low area overhead.