LVS mismatch on parallel devices and issue on ambiguity resolution

[klayoutmatthias]

Issue 1: mismatch on parallel devices

This may when device with different parameters are connected in parallel. The device comparison may report mismatching devices because the parallel ones are not associated correctly.

Here are two netlists that reproduce the problem:

.SUBCKT LVS_TEST 1 2
M1I38 1 2 1 1 PCH_18_MAC L=0.225U W=10653U AS=0P AD=0P PS=0U PD=0U
M1I39A 1 2 1 1 PCH_18_MAC L=0.135U W=1809U AS=0P AD=0P PS=0U PD=0U
.ENDS LVS_TEST

and

.SUBCKT lvs_test 1 2
M$1 1 2 1 1 PCH_18_MAC L=0.135U W=1809U
M$150 1 2 1 1 PCH_18_MAC L=0.225U W=10653U
.ENDS lvs_test

Issue 2: ambiguity resolution problem

This is the schematic of three inverter chains (2x5 inverters, 1x6 inverters):

.SUBCKT inv_chain 20 21
M$1 20 1 2 20 NCH_SVT_MAC L=0.016U W=3U 
M$2 20 2 3 20 NCH_SVT_MAC L=0.016U W=3U 
M$3 20 3 4 20 NCH_SVT_MAC L=0.016U W=3U 
M$4 20 4 5 20 NCH_SVT_MAC L=0.016U W=3U 
M$5 20 5 6 20 NCH_SVT_MAC L=0.016U W=3U 
M$6 20 6 7 20 NCH_SVT_MAC L=0.016U W=3U 
M$7 20 8 9 20 NCH_SVT_MAC L=0.016U W=3U 
M$8 20 9 10 20 NCH_SVT_MAC L=0.016U W=3U 
M$9 20 10 11 20 NCH_SVT_MAC L=0.016U W=3U 
M$10 20 11 12 20 NCH_SVT_MAC L=0.016U W=3U 
M$11 20 12 13 20 NCH_SVT_MAC L=0.016U W=3U 
M$12 20 14 15 20 NCH_SVT_MAC L=0.016U W=3U 
M$13 20 15 16 20 NCH_SVT_MAC L=0.016U W=3U 
M$14 20 16 17 20 NCH_SVT_MAC L=0.016U W=3U 
M$15 20 17 18 20 NCH_SVT_MAC L=0.016U W=3U 
M$16 20 18 19 20 NCH_SVT_MAC L=0.016U W=3U 
M$17 21 1 2 21 PCH_SVT_MAC L=0.016U W=3U 
M$18 21 2 3 21 PCH_SVT_MAC L=0.016U W=3U 
M$19 21 3 4 21 PCH_SVT_MAC L=0.016U W=3U 
M$20 21 4 5 21 PCH_SVT_MAC L=0.016U W=3U 
M$21 21 5 6 21 PCH_SVT_MAC L=0.016U W=3U 
M$22 21 6 7 21 PCH_SVT_MAC L=0.016U W=3U 
M$23 21 8 9 21 PCH_SVT_MAC L=0.016U W=3U 
M$24 21 9 10 21 PCH_SVT_MAC L=0.016U W=3U 
M$25 21 10 11 21 PCH_SVT_MAC L=0.016U W=3U 
M$26 21 11 12 21 PCH_SVT_MAC L=0.016U W=3U 
M$27 21 12 13 21 PCH_SVT_MAC L=0.016U W=3U 
M$28 21 14 15 21 PCH_SVT_MAC L=0.016U W=3U 
M$29 21 15 16 21 PCH_SVT_MAC L=0.016U W=3U 
M$30 21 16 17 21 PCH_SVT_MAC L=0.016U W=3U 
M$31 21 17 18 21 PCH_SVT_MAC L=0.016U W=3U 
M$32 21 18 19 21 PCH_SVT_MAC L=0.016U W=3U 
.ENDS inv_chain

Comparing such a netlist suffers from manyfold ambiguities and in the current version fails because the algorithm picks nodes that do not match. This is because currently ambiguity resolution is shortcut when the nodes lead to other nodes from the same ambiguity group. In this case the nodes between the inverters which form 13 topologically ambiguous nodes.