Syn -19

x4 Drive Strength for Critical Path Cells

gate count               1515
number of cells           521
number of library cells   128
number of used cells       41
max fanin                  17
max input capacitance     189
max internal fanout        34
critical path  0fF       2320
critical path  6fF       2793

An x4 drive strength is added according to the following criteria:

Applies to cells with 2 or 3 inputs plus the 4-AND gate.
Does not apply to XOR and XNOR gates.
Keep cell size below 20 tracks or 160 lambda.
If cell size is above 160λ then set the drive strength to x3 instead.

The aim is to improve the critical path by allowing the use of higher drive cells. The critical path consists of x2 drive strength cells plus higher drive inverters, and looks maxed out in drive strength.

The higher drive strengths that are selected are:

an2v0x4     1
cgi2v0x3    8
cgi2abv0x3  4
nr2v0x4     2
nr2av0x4    2
oai21v0x4  11

These are well used on the critical path below and give a significant speed improvement of 7%. The gate count increases though by 5.3%. The conclusion is that high drive gates are useful, provided that they do not become excessively large.

    x 1          17                  189
 1  aoi22v0x2     1  b2->z     298   109
 2  oai21v0x4     4  a2->z     402   104
 3  xnr3v1x1      1  c->z      601   199
 4  cgi2v0x3      3  c->z      699    98
 5  xnr3v1x2      1  b->z      909   210
 6  nr2av0x4      3  b->z     1058   149
 7  oai21v0x4     1  a2->z    1126    68
 8  oai31v0x2     2  b->z     1210    84
 9  iv1v0x4       1  a->z     1265    55
10  cgi2abv0x3    2  c->z     1359    94
11  iv1v0x4       1  a->z     1413    54
12  cgi2v0x3      2  c->z     1498    85
13  iv1v0x4       1  a->z     1553    55
14  cgi2abv0x3    2  c->z     1649    96
15  iv1v0x4       1  a->z     1698    49
16  cgi2abv0x2    2  c->z     1847   149
17  iv1v0x6       1  a->z     1905    58
18  cgi2v0x3      2  a->z     2024   119
19  iv1v0x8       1  a->z     2077    53
20  cgi2v0x3      2  a->z     2177   100
21  iv1v0x4       1  a->z     2232    55
22  cgi2abv0x3    2  c->z     2367   135
23  an2v0x4       2  b->z     2481   114
24  nr2av0x4      2  a->z     2622   141
25  xaon21v0x2    0  a1->z    2793   171

Table of synthesis results
	critical path (ps)	gate count	cell count	library cells	used cells
synthesis 1	5328	1761	994	9	8
synthesis 2	5158	1690	896	15	11
synthesis 3	5537	1594	792	19	15
synthesis 4	5537	1594	792	20	15
synthesis 5	4024	1342	666	21	15
synthesis 6	3955	1349	666	28	18
synthesis 7	3133	1458	651	68	25
synthesis 8	3121	1466	651	68	27
synthesis 9	3072	1489	651	68	29
synthesis 10	3043	1474	651	74	32
synthesis 11	3043	1474	651	77	32
CyHP synthesis	4311	1494	799	18	16
synthesis 12	3037	1490	651	77	32
synthesis 13	3033	1491	651	77	32
synthesis 14	3025	1481	649	89	31
synthesis 15	3013	1492	649	92	34
synthesis 16	3013	1525	643	93	35
synthesis 17	3010	1474	608	99	39
synthesis 18	3000	1439	521	111	37
synthesis 19	2793	1515	521	128	41