Library Timing characteristics

For delay calculation, this timing characteristics part is used which is in the form of lookup tables

Timing characteristics is defined in the multiple lookup tables for each type of delay that are

• Rise delay
• Rise transition 
• Fall delay

Following is the example of timing characteristics

- lookup table contain two variables and the full  N x N lookup tabel is displayed, where N is positive integer

Example:

                    pin(Y) {

                    direction: output;

                    capacitance: 0.0;

                    function: "(A B)";

                    internal_power() {

                               related_pin: "A";

                               cell_rise(delay_template_7x7) {

                                            index_1 ("0.04, 0.07, 0.1, 0.2, 0.5, 1.0, 2");

                                            index_2 ("0.006, 0.030, 0.078, 0.174, 0.366, 0.749,1.523");

                                            values ( \

                                           "0.07, 0.09, 0.13, 0.20, 0.35, 0.64, 1.23", \

                                           "0.08, 0.10, 0.13, 0.21, 0.35, 0.65, 1.24", \

                                           "0.09, 0.11, 0.15, 0.22, 0.37, 0.66, 1.25", \

                                           "0.11, 0.13, 0.17, 0.25, 0.39, 0.68, 1.28", \

                                           "0.14, 0.17, 0.20, 0.28, 0.42, 0.72, 1.31", \

                                           "0.18, 0.21, 0.25, 0.33, 0.47, 0.76, 1.35", \

                                           "0.23, 0.26, 0.31, 0.39, 0.54, 0.83, 1.42");

                               }

( To understand the format of the lookup table, study the template of timing characteristics template in library)

Here,

index_1 represents input net transition and

index_2 represents total output net capacitance

depending on the various values for these indexes, corresponding delay values are looked up from the table

here, table can be any size 3 x 3, 7 x 7 etc depending upon the library vendor.

Now, how it work lets understand with the following example

here, 

- 7 x 7 indicates the size of the lookup table to be 7 rows and 7 columns

- index_1 indicates the factor for row indices 

- index_2 indicates the factor for column indices

what would the cell_rise time be if the input_net_transition is 0.1 and the total_ouptut net capacitance is 0.030?

answer : from the table, we get the value to be 0.11ps