Automation of tie cell insertion, optimization and replacement by scan flip-flops to increase fault coverage
A method for designing an integrated circuit is disclosed. The method generally comprises the steps of (A) splitting a design layout of the integrated circuit into a plurality of tiles, (B) adding a plurality of tie-to cells to the design layout, wherein at least one of the tie-to cells generating a tie-to signal at a particular logical level is added into each of the tiles having at least one gate with an input fixed to the particular logical level and (C) routing the tie-to signal to each of the inputs within each of the tiles.
1. A method of designing an integrated circuit, comprising the steps of:
(A) generating a design layout of said integrated circuit in a computer, said design layout including (i) a scan chain and (ii) at least one logic gate having a) a first logic input fixed to a particular logic level and not connected to said scan chain and (b) a second logic input connected to a data output of a particular scan cell of said scan chain;
(B) adding at least one new scan cell to said scan chain proximate said logic gate; and
(C) rerouting said first logic input of said logic gate to a data output of said new scan cell.
2. The method according to claim 1 , wherein said particular scan cell of said scan chain has a data input connected to a data path, the method further comprising the step of:
rerouting said data input of said particular scan cell from said data path to said data output of said new scan cell.
3. The method according to claim 2 , further comprising the step of:
rerouting said data path from said data input of said particular scan cell to said data input of said new scan cell.
4. The method according to claim 1 , further comprising the step of:
routing a control signal to said new scan cell, wherein said new scan cell drives said first logic input of said logic gate to said particular logic level in response to an assertion of said control signal.
5. The method according to claim 4 , wherein (i) said control signal comprises a reset signal and (ii) said new scan cell drives said first logic input of said logic gate to a logical low level in response to said assertion of said reset signal.
6. The method according to claim 4 , wherein (i) said control signal comprises a set signal and (ii) said new scan cell drives said first logic input of said logic gate to a logical high level in response to said assertion of said set signal.
7. The method according to claim 1 , further comprising the step of:
routing an enable signal to a test-enable input of said new scan cell, said new scan cell selectively operating in one of (i) a test mode and (ii) a feed-through mode in response to said enable signal.
8. The method according to claim 7 , wherein said first logic input of said logic gate is held constant while said new scan cell is in said feed-through mode.
9. The method according to claim 7 , wherein said first logic input of said logic gate is controlled by an input signal received at a data input of said new scan cell while said new scan cell is in said test mode.
10. The method according to claim 7 , wherein a data input of said new scan cell is not utilized while said new scan cell is in said feed-through mode.
11. The method according to claim 1 , wherein the steps are preformed by processor executable instructions contained within a non-transitory computer readable medium.
12. The method according to claim 1 , wherein (i) said at least one logic gate comprises at least two of said logic gates, each having said first logic input fixed to said particular logic level, and (ii) each of said first logic inputs of said at least two logic gates are rerouted to said data output of said new scan cell.
13. A non-transitory computer readable medium containing processor executable instructions configured to perform the steps of:
(A) generating a design layout of an integrated circuit, said design layout including (i) a scan chain and (ii) at least one logic gate having a) a first logic input fixed to a particular logic level and not connected to said scan chain and (b) a second logic input connected to a data output of a particular scan cell of said scan chain;
(B) adding at least one new scan cell to said scan chain proximate said logic gate; and
(C) rerouting said first logic input of said logic gate to a data output of said new scan cell.
14. The non-transitory computer readable medium according to claim 13 , wherein said particular scan cell of said scan chain has a data input connected to a data path, further comprising the step of:
rerouting said data input of said particular scan cell from said data path to said data output of said new scan cell.
15. The non-transitory computer readable medium according to claim 14 , further comprising the step of:
rerouting said data path from said data input of said particular scan cell to said data input of said new scan cell.
16. The non-transitory computer readable medium according to claim 13 , further comprising the step of:
routing a control signal to said new scan cell, wherein said new scan cell drives said first logic input of said logic gate to said particular logic level in response to an assertion of said control signal.
17. The non-transitory computer readable medium according to claim 16 , wherein (i) said control signal comprises a reset signal and (ii) said new scan cell drives said first logic input of said logic gate to a logical low level in response to said assertion of said reset signal.
18. The non-transitory computer readable medium according to claim 16 , wherein (i) said control signal comprises a set signal and (ii) said new scan cell drives said first logic input of said logic gate to a logical high level in response to said assertion of said set signal.
19. The non-transitory computer readable medium according to claim 13 , further comprising the step of:
routing an enable signal to a test-enable input of said new scan cell, said new scan cell selectively operating in one of (i) a test mode and (ii) a feed-through mode in response to said enable signal.
20. The non-transitory computer readable medium according to claim 19 , wherein said first logic input of said logic gate is held constant while said new scan cell is in said feed-through mode.