System and apparatus for scanning integrated circuits with numerically controlled delay lines
View Patent ↗A system and method for scan testing an NCDL and latches controlled by the NCDL is presented. The NCDL is controlled by control logic, a switch is used to control the latches by a clock signal that is not controlled by the control logic. A controllability circuit provides test vectors to, and controls, the NCDL. The outputs of the NCDL are observed by an observability circuit that captures the outputs of the NCDL.
1. A circuit for scan testing, said circuit comprising:
a signal line for providing a signal;
an NCDL for providing a delayed signal; and
a switch for providing the signal to a group of latches during scan testing, and otherwise providing the delayed signal to the group of latches;
wherein the NCDL receives the signal line providing the signal and wherein the delayed signal is offset from the signal a certain period of time.
2. The circuit of claim 1 , further comprising:
delay control logic for controlling the certain period of time.
3. The circuit of claim 1 , further comprising:
a bypass loop for providing the signal to the switch, said bypass loop bypassing the NCDL.
4. The circuit of claim 1 , further comprising:
a scan mode signal for controlling the switch.
5. A circuit for scan testing, the circuit comprising:
a signal line for providing a signal;
a controllability circuit for providing a test vector;
a first switch for providing the test vector to an NCDL during scan testing and for otherwise providing the signal to the NCDL; and
an observability circuit for capturing an output from the NCDL.
6. The circuit of claim 5 , further comprising:
a scan mode signal for controlling the first switch.
7. The circuit of claim 5 , wherein the controllability circuit further comprises:
a test vector line for providing the test vector;
a second switch for selecting the test vector during a shift phase of scan testing; and
a flip-flop for providing the registered output of the second switch to the first switch.
8. The circuit of claim 7 , wherein the controllability circuit further comprises:
a scan enable signal for controlling the second switch.
9. The circuit of claim 5 , wherein the observability circuit further comprises:
a third switch for selecting the output of the NCDL a capture phase of the scan test; and
a flip-flop for storing the selection of the third switch.
10. The circuit of claim 9 , wherein the third switch is controlled by the scan enable line.
11. The circuit of claim 5 , further comprising:
a fourth switch for providing the signal to a group of delayed latches during scan testing, and otherwise providing the output of the NCDL to a group of latches.
12. A device for scan testing, said device comprising:
a signal line for providing a signal;
a circuit for providing a test vector;
a first switch for providing the test vector to an NCDL during scan testing and for otherwise providing the signal to the NCDL; and
wherein the circuit captures an output from the NCDL.
13. The circuit of claim 12 , further comprising:
a scan mode signal for controlling the first switch.
14. The circuit of claim 12 , wherein the circuit further comprises:
a test vector line for providing the test vector;
a second switch for selecting the test vector during a shift phase of scan testing and for selecting the output of the NCDL during a capture phase of scan testing; and
a flip-flop for providing the test vector to the first switch.
15. The circuit of claim 14 , wherein the controllability circuit further comprises:
a scan enable signal for controlling the second switch.
16. The circuit of claim 12 , further comprising:
a third switch for providing the signal to a group of delayed latches during scan testing, and otherwise providing the output of the NCDL to a group of latches.
17. A circuit for scan testing, said circuit comprising:
a signal line providing a signal;
an NCDL connected to the signal line; and
a switch connected to the NCDL and the signal line, wherein the switch connects the signal line to a group of latches during scan testing, and otherwise connects the NCDL to the group of latches; and
wherein the signal line is connected to the NCDL and wherein the NCDL provides a delayed signal that is offset from the signal by a certain period of time.
18. The circuit of claim 17 , further comprising:
control logic connected to the NCDL.
19. The circuit of claim 17 , further comprising:
a bypass loop connecting the signal line to the switch, said bypass loop bypassing the NCDL.
20. The circuit of claim 17 , further comprising:
a scan mode signal connected to the switch.
21. A circuit for scan testing, the circuit comprising:
a signal line;
a controllability circuit;
a first switch connected to the signal line and the controllability circuit, wherein the first switch connects the controllability circuit to the NCDL during scan testing and otherwise connects the signal line to the NCDL; and
an observability circuit connected to an output from the NCDL.
22. The circuit of claim 21 , further comprising:
a scan mode signal connected to the first switch.
23. The circuit of claim 21 , wherein the controllability circuit further comprises:
a test vector line;
a flip-flop connected to the first switch; and
a second switch connected to the test vector line, wherein the second switch connects the test vector line to the flip-flop during a shift phase of scan testing.
24. The circuit of claim 23 , wherein the controllability circuit further comprises:
a scan enable signal connected to the second switch.
25. The circuit of claim 21 , wherein the observability circuit further comprises:
a flip-flop; and
a third switch connected to the output of the NCDL, and wherein the third switch connects the output of the NCDL to the flip-flop during a capture phase of the scan test.
26. The circuit of claim 25 , wherein the observability circuit further comprises a scan enable line connected to the third switch.
27. The circuit of claim 21 , further comprising:
a fourth switch connected to the signal and the output of the NCDL, wherein the fourth switch connects the signal to a group of delayed latches during scan testing, and otherwise connects the output of the NCDL to the group of delayed latches.
28. A circuit for scan testing, said circuit comprising:
a signal line;
a circuit providing a test vector;
a first switch connected to the circuit and the signal line, wherein the first switch connects the circuit to an NCDL during scan testing and otherwise connects the signal line to the NCDL; and
wherein the circuit is connected to the output of the NCDL.
29. The circuit of claim 28 , further comprising:
a scan mode signal connected to the first switch.
30. The circuit of claim 28 , wherein the circuit further comprises:
a test vector line providing the test vector;
a flip flop connected to the first switch;
a second switch connected to the test vector line and the output of the NCDL, wherein the second switch connects the test vector line to the flip-flop during a shift phase of scan testing and connects the output of the NCDL to the flip-flop during a capture phase of scan testing.
31. The circuit of claim 30 , wherein the controllability circuit further comprises:
a scan enable signal connected to the second switch.