Design for two-pattern testability of controller-data path circuits

This paper introduces a design for testability, (DFT) scheme for delay faults of a controller-data path circuit. The scheme makes use of both scan and non-scan techniques. Firstly, the data path is transformed into a hierarchically two-pattern testable (HTPT) data path based on a non-scan approach. Then an enhanced scan (ES) chain is inserted on the control lines and the status lines. The ES chain is extended via the state register of the controller. If necessary, the data path is further modified. Then a test controller is designed and integrated into the circuit. Our approach is mostly based on a path delay fault model. However, the multiplexer (MUX) select lines and register load lines are tested as register transfer level (RTL) segments. For a given circuit, the area overhead incurred by our scheme decreases proportionally with increase in bit-width of the data path of the circuit. The proposed scheme supports hierarchical test generation and can achieve fault coverage similar to that of the ES approach.