Back Annotate PDF
Back Annotate PDF
Back Annotate PDF
Version IC6.1.7ISR5
IC6.1.7ISR5 VLS XL Back Annotation
Workshop
July 2016
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Action 1: cd BackAnnotate
Action 5: In the Library Manager form, select library vxlwrkshp, cell halfcell, and
schematic. Double click on the schematic view to open it.
Action 7: In the Startup Option form, click on Create New, Automatic and OK the form.
Use the picture below as a guide.
Action 10: Click on the Generate Selected From Source icon or Connectivity->Generate-
>Selected From Source..
Action 11: In the Schematic select instance M3 which is the far left member of the
Diff pair, use the picture below a guide. You can also select instance M3
from navigator of schematic or layout.
Action 13: Select Instance M2 in the schematic which is to the right of M3 or you can select instance M2
from the Navigator.
Action 14: Place the abutted M2 chain in the layout to the right of M3 as shown in the picture below.
Place one of the M1’s to the left of the M3 chain. When you place the transistor make
sure to overlap the metal1 regions so that M1 will abut to the M3 chain. Place the other
one to the right side of the M2 chain. Your final result should look like the picture below.
One of the challenges in designing at smaller nodes is you do not know how many
dummy devices you need until you create the layout. In addition, those dummies can
become active, by active it means that at least one of the terminals is connected to a
signal. This addition usually ends up in a layout that is not XL complaint. Today in
VLS XL, you can add dummies with a few clicks and they can be ignored or back
annotated into the schematic.
Action 1: Click on instance M1.1 and M1.2 as pointed to in the picture below.
Action 2: RMB select Create Dummy With Net->VSS. You are prompted to “Point at
the reference point for the copy”. Click on instance M1.1
Action 4 Click on one of the dummy’s you just created and copy it. Place it as shown in
the picture below.
Note: You can use the regular copy command for these dummy devices and they will
remain XL complaint and have connectivity.
Action 6: In the Property Editor Assistant, Change Number of Fingers from 1 to 4. Use
the picture below as a guide.
Note: When a dummy device is created in VLS XL, ignore and lvsIgnore properties are
automatically set to true as you can see in the Property Editor Assistant. It means VLS XL
will not attempt to bind it to anything. Connectivity and other properties are set so it
makes it easy to search for dummy devices in your layout.
Action 8: Create a chain by abutting the dummies created in the previous step to either
side of the M2 and M3 chains using move command as shown in the picture below.
Final result
Action 9: In the layout, click on the “Back Annotate All Dummy Instances” icon pointed
to in the picture below or use Connectivity->Back Annotate -> All Dummy
Instances.
In the schematic zoom into the upper left hand corner as shown in the picture below.
Notice how in the schematic only one dummy was back annotated and the reason is
because if a dummy has all terminals assigned to power and ground then that
dummy is considered real and should be ignored, not back annotated. If the
dummy is abutted to a signal then it can no longer be ignored and the dummy
becomes an active device and is back annotated. The device that got back
annotated has source and drain attached to net a and the gate and bulk node are on
net VSS.
IC6.1.7ISR5 VLS XL Back Annotation 13
Action 10: If you again click on Back Annotate all Dummy Instances icon then you will get message in
CIW as shown in picture below
Action 11: In the schematic delete the device that was back annotated.
Action 12: In the layout click on the Back Annotate All Dummy Instances icon again. Ok the LayoutXL
info window that comes up.
Notice that this time all 3 dummy instances were back annotated to the schematic and this
is because you do have a choice to back annotate all types or just the active ones.
Action 13: Delete the three dummy devices that were back annotated into the schematic.
Action 15: Bring the schematic forward and notice that only the selected dummy device
Dummy_I1 was back annotated.
Generate Chained Devices lets you chain devices interactively while you are editing a
layout. You can also chain dummy instances but you have to take a few things into
consideration. If in the Generate Chained Devices form, you select the use Device Order
check box, the dummies are treated as regular devices during the chaining operation and can
support abutment on one side or both sides depending on the state of the
chaindummyFlexBothEndNets environment variable. As a result, irrespective of their order,
the dummies are placed at the end of the chain and their initial connectivity is retained.
Action 1: Deselect all in the layout, bindkey control d. Then either in the Navigator or the
layout canvas select all three dummy instances Dummy_I0, Dummy_I1 and I2.
Action 2: Move the selected set above the other transistors as shown in the picture below.
Action 5: In the Generate Chained Devices form, Make sure all checked boxes are
deselected as shown in the picture below and click Apply.
Action 6: Click to place the new chain. Notice that you do not get a totally abutted chain
and in the next few steps that situation will be corrected.
Action 8: In the Generate Chained Devices form click on the Use Device Order check box.
Then click Apply.
Action 9: Click to place the new chain and notice that all instances are abutted including
center dummy device. The reason the center dummy instance is also abutted because the
environment variable chainDummyFlexBothEndNets is set to t (default) which means both
IC6.1.7ISR5 VLS XL Back Annotation 18
sides of dummy device can change nets.
Note: If this environment variable is set to nil then only one side of the dummy device can
change nets and thus center dummy device will not be able to abut as shown in the picture
below
This concludes our examination of back annotation. We hope you found the workshop to
be informative. If you have any questions, talk with the Cadence applications engineer
who is staffing this workshop or contact your Cadence account team.