Static Timing Analysis Facts PDF

Static Timing Analysis Facts 1. Static Timing Analysis is a technique of analysing timing paths in a digital logic by adding up delays along a timing path (gates and interconnect) and comparing it with constraints (like clock period) to check whether the path meets the constraint. 2. Static Timing Analysis is popular because it is simple to use and only needs commonly available inputs like technology library, netlist, constraints, and parasitics(R and C). 3. Static Timing Analysis tend to be comprehensive and provides a very high level of timing coverage. Static Timing also honours timing exception to exclude the paths that are either not true path are not exercised in an actual design. A good static timing tool corelates well with timing in silicon. 4. A digital logic can be broken down into a number of timing paths. A timing path can be any of the following: i. a path between the clock pin of register/latch to the d-pin of another register/latch. ii. a path between primary input to the d-pin of a register or latch. iii. a path between clock-pin of a register to a primary output. iv. a path between input pin and output pin of a block. 5. Static Timing Analysis is used to check the following: i. Setup Timing ii. Hold timing iii. max/min timing between two points on a segment of timing path. iv. Latch Time Borrowing v. Removal and Recovery Timing on resets vi. clock gating checks vii. clock pulse width requirments viii. min max transition times ix. min/max fanout x. max capacitance 6. Capture edge time of a setup path = launch clock edge time + 1 period 7. Max Timing Equation Launch time clock edge + clock network delay + clock-q delay + path delay (cell + internconnect) =< (capture edge time of setup path) + clock network delay - clock uncertainty - setup time - output external delay (only for paths to output ports) 7. Min Timing Equation Launch clock edge + clock network delay + input external delay + clock-q delay + path delay (cell + internconnect delays) >= (Capture edge time of the corresponding setup path - 1 clock period) + clock network delay + clock uncertainty + library hold time - output external delays (only for paths to output port) 8. Capture edge time of a setup path = launch clock edge time + 1 period 9. Multicycle paths are paths that are allowed to take more than one clock period to complete. Multicycle paths make setup easy but hold difficult unless corrected. 10. Recovery time is like setup time on a reset pin. 11. Removal time is like hold time on a reset pin.

12. clock gates also have setup hold requirements 13. Clock Domain Crossing issues are not detected by Static Timing Analysis.

RETURN TO ASIC INTERVIEW QUESTIONS INDEX