| 摘要 |
PROBLEM TO BE SOLVED: To avoid the illegal circuit copy by mixedly providing an apparent layout pattern of an actual chip incorporating normally on- and normally off- type transistors and dummy circuits different in logic operation. SOLUTION: N1, N2, P1, P2 are n- and p-type transistors usually forming a circuit constituting an NAND gate having inputs A, B and output C, the threshold voltages of N1, P1 are set lower than usual, N1 is set to a normally on-type and P1 is set to a normally off-type to thereby obtain an inverted value of the input B from the output C, irrespective of the value of the input A. The apparent layout pattern of an actual chip provides an NAND gate with inputs A, B and output C but actually a dummy circuit operating as an inverter with inputs A, B and output C can be constituted. It is possible that a circuit analyzed by connecting adequate signals causing a malfunction to the input A of the dummy circuit cannot normally operate.
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