4366 Chapter7.ppt - Chapter 7 Testing of a digital circuit...

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Chapter 7. Testing of a digital circuit
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Failure : any departure of a system or module from its specified correct operation. A failure is a malfunction. Fault : a condition existing in a hardware or software module that may lead to the failure of the module Hardware fault : external disturbances, manufacturing defects. Software fault : design mistake. Error : an incorrect response from a hardware or software module. An error is the manifestation of a fault. The occurrence of an error indicates that a fault is present in the module. Testing : fault detection/ fault location. Test pattern source Circuit under test (C.U.T) Compare Good/bad Reference value
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Fault model stuck-at fault bridging fault o stuck at fault • open collector or open base Z is stuck at logic value 1 regardless of x (Z s-a-1 or x s-a-0) • short between collector and emitter Z is stuck at 0 regardless of x (Z s-a-0) o bridging fault Most case: assume single stuck-at fault o Test generation x z = x’ Vpp Z C E B x x 1 x 2 x 1 x 2 bridging x 1 x 2 A B C D E F Z x 1 x 2 x n Z exhausting test 2 n (n+1) test
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1 1 1 1 1 1 0 1 0 0 0 1 1 0 1 1 A/1 B/0 ••• ••• ••• too much A/0 Z x 1 x 2 Test vector (1,0) Test generation 1. Algebraic algorithm: Boolean difference difficult to make computer program 2. Standard algorithm: D-algorithm o Boolean difference: to determine the complete set of test to detect a stuck-at fault. The Boolean difference of F(x) with respect to the input x i ) 1 ( ) 0 ( ) , , , 1 , , , , ( ) , , , 0 , , , , ( ) ( 1 1 2 1 1 1 2 1 i i n i i n i i i F F x x x x x F x x x x x F dx x dF , let be the fault where the input x i is s-a-0 ) 0 ( ) , , , 0 , , , , ( ) , , , ( 1 1 2 1 2 1 i n i i n F x x x x x F x x x F The test pattern that detects the fault (x i s-a-0) 1 ) 0 ( ) ( F x F Fault free value
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Using Shannon’s expression theorem ) 0 ( ) 1 ( ) 0 ( ' ) 0 ( )) 1 ( ) 0 ( ' ( i i i i i i i i i i F F x F x F F x F x ) 0 ( ) 0 ( ' ) 1 ( ) 0 ( ' ) 0 ( ) ' ( ) 1 ( ) 0 ( ' i i i i i i i i i i i i i i i F x F x F x F x F x x F x F x 1 ) ( ) 0 ( ) 1 ( ( i i i i i dx x dF x F F x The test pattern to detect x i s-a-0 The test pattern to detect x i s-a-1 1 ) ( ' i i dx x dF x If F(x) is dependent on x i (i.e. the fault on x i is detectable). F i (0) will be different from F i (1) i i i dx x dF F F ) ( 1 ) 1 ( ) 0 ( The test pattern that detects the fault x i s-a-0 1 ) ( 1 ) ( 1 i i i i dx x dF x dx x dF And x The test pattern that detects the fault x i s-a-1 1 ) ( ' 1 ) ( 0 i i i i dx x dF x dx x dF And x
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Test set for x 1 s-a-0 F=x 1 x 2 +x 2 ’x 3 ' ) ( ' ) ( ' , ' ) ( ) ( i i i i dx x dF dx x dF dx x dF dx x dF x 1 x 2 x 3 G 1 G 2 F s-a-0 1 ) ( i i dx x dF x 2 3 2 2 3 2 3 2 2 3 2 3 2 2 3 2 1 1 1 ) ' ( )' ' ( )' ' )( ' ( ) ' ( ) ' ( ) 1 ( ) 0 ( ) ( x x x x x x x x x x x x x x x x F F dx x dF 1 ) ( 2 1 1 1 x x dx x dF x Test vector x 1 , x 2 , and x 3 for x 1 s-a-0 is (1,1,0) or (1,1,1) x 1 x 2 x 3 G 1 G 2 F s-a-0 h Test set for h s-a-0 F=x 1 x 2 +h 1 ) ( dh x dF h 1 ' ' ' ' ) ' ' ( ) ' ( ) ( ' ' )' ( 1 ) 1 ( ) 0 ( ) ( 3 2 3 2 3 2 1 2 1 3 2 2 1 2 1 2 1 1 1
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  • Fall '15
  • prasad

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