BUILT-IN SELF TEST FOR DETECTING STUCK-AT-FAULTS IN CMOS COMBINATIONAL LOGIC ICS

Stuck-at-faults may occur at input and output gates inside CMOS combinational logic ICs. The faults may be caused by an imperfect manufacturing process. Moreover, they may generate a function of the ICs becomes errors. There are two types of the faults, namely stuck-at-1 and stuck-at-0. The stuck-at-1 and the stuck-at-0 may affect logic values of the gates become 1 and 0, respectively. Thus, they should be detected early. In this paper, a built-in self test circuit is proposed to detect them. The test circuit consists of a linear feedback shift register and multiplexers. The shift register is made by D-flip flops and an XOR gate and is used to generate test vectors. The multiplexers are used as test selectors to select the ICs either in a normal mode or a test mode. Analysis results show that the stuck-at-faults at the combinational logic IC of xx855 can be detected by the test circuit.