NovelPanda
Junior Member level 3
Dear All:
I am now running PEX after dummy fill and evaluate its impact. I use TSMC 40nm RF process with automatic dummy fill script provided by foundry. During the test of VCO, I use dummy blocker to enclose the varactor and interconnects, leaving other space automatically filled by dummy (the VCO core, subsequent buffer are all using RF NMOS with "RFDMY" layer enclosed), but KVCO did not change. The PEX is set to C+CC with gate level extraction, and all RF devices have been included in xcell. Post-layout simulation indicates that the VCO frequency drops 600MHz from 29GHz (post layout result without any dummy fill). The same frequency drops for all VCO bands. It seems that the dummy actually have large impact by adding parastics, and the layer "RFDMY" seems little help on reducing such a effect. I may want to know if I can enclose all sensitive RF NMOS by dummy blocker, and what will be the bad consequence if I inform the foundry to waive some density error if I have to. In addition, when I simulate the whole chip with dummy fill, the charge pump outputs zero current.
Thanks in advanced!
I am now running PEX after dummy fill and evaluate its impact. I use TSMC 40nm RF process with automatic dummy fill script provided by foundry. During the test of VCO, I use dummy blocker to enclose the varactor and interconnects, leaving other space automatically filled by dummy (the VCO core, subsequent buffer are all using RF NMOS with "RFDMY" layer enclosed), but KVCO did not change. The PEX is set to C+CC with gate level extraction, and all RF devices have been included in xcell. Post-layout simulation indicates that the VCO frequency drops 600MHz from 29GHz (post layout result without any dummy fill). The same frequency drops for all VCO bands. It seems that the dummy actually have large impact by adding parastics, and the layer "RFDMY" seems little help on reducing such a effect. I may want to know if I can enclose all sensitive RF NMOS by dummy blocker, and what will be the bad consequence if I inform the foundry to waive some density error if I have to. In addition, when I simulate the whole chip with dummy fill, the charge pump outputs zero current.
Thanks in advanced!