Method for determining load capacitance
View Patent ↗A method for optimal driver selection uses a cost function that is based on the non-linear delay characteristics and the stage gain of the candidate drivers. The cost function operates to select an optimal driver for driving the predetermined capacitive load which. simultaneously minimizes the delay and the amount of input capacitance introduced. In one embodiment, a method for selecting a driver for driving a load capacitance from a group of drivers includes: computing for each driver a cost based on a cost function associated with the driver, and selecting the driver having the smallest cost. The cost function is directly proportional to a delay of the driver and inversely proportional to the logarithm of a stage gain of the driver. In another embodiment, the stage gain is an output capacitance driven by the driver (the load capacitance) divided by an input capacitance of the driver.
1. A method for determining a first load capacitance to be driven by a driver, said method comprising:
providing a set of cost values as a function of load capacitance based on a cost function for said driver, said cost function being directly proportional to a delay of said driver and inversely proportional to the logarithm of a stage gain of said driver; and
selecting said load capacitance associated with the smallest cost value as said first load capacitance.
2. The method of claim 1 , wherein said driver comprises a buffer or an inverter.
3. The method of claim 1 , wherein said driver comprises a NAND gate or a NOR gate.
4. The method of claim 1 , wherein said providing a set of cost values as a function of load capacitance comprises computing said set of cost values over a range of load capacitance values using said cost function, and storing said set of cost values in a precomputed table, said precomputed table being associated with said driver in a cell library.
5. The method of claim 1 , wherein said providing a set of cost values as a function of load capacitance comprises providing a set of cost values as a function of stage gain, said stage gain being an output capacitance driven by said driver divided by an input capacitance of said driver.
6. The method of claim 5 , wherein said providing a set of cost values as a function of stage gain comprises computing said set of cost values over a range of stage gain values using said cost function, and storing said set of cost values in a precomputed table, said precomputed table being associated with said driver in a cell library.
7. The method of claim 1 , wherein said cost function is given as
C
=
StageDelay
ln
(
Cout
Cin
)
,
where C is said cost, said stage delay is said delay of said driver, C OUT is an output capacitance driven by said driver and C in is an input capacitance of said driver, said output capacitance being said load capacitance.