| 摘要 |
A logic circuit on a substrate is switchable between a test mode and an operational mode. First and second NOR gates are cross-coupled and may be switched between an operational mode and a test mode by the application of a control signal to first and second transfer gates coupled to the inputs of the NOR gates. The first NOR gate includes a p-type region and an n-type region formed in said substrate and traversed with first and second conductive layers insulated from the p and n-type regions. Thus, the first NOR gate includes two p-channel transistors and two n-channel transistors. The second NOR gate is also formed by a p-type region and an n-type region traversed with third and fourth conductive layers. Thus, the second NOR gate also includes two p-channel transistors and two n-channel transistors. The transfer gates are located on the substrate between the first and second NOR gates. Both transfer gates include an n-type region formed in the substrate with a conductive layer disposed over the n-type region. In the operational mode, the cross-coupled NOR gates may perform as a flip-flop. In the test mode, each NOR gate essentially becomes an inverter.
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