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<H1 CLASS="Heading1">
<A NAME="pgfId=17235">
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17.4 <A NAME="11650">
</A>
Circuit Extraction and DRC</H1>
<P CLASS="BodyAfterHead">
<A NAME="pgfId=17236">
</A>
After detailed routing is complete, the exact length and position of each interconnect for every net is known. Now the parasitic capacitance and resistance associated with each interconnect, via, and contact can be calculated. This data is generated by a <SPAN CLASS="Definition">
circuit-extraction</SPAN>
<A NAME="marker=24875">
</A>
tool in one of the formats described next. It is important to extract the parasitic values that will be on the silicon wafer. The mask data or CIF widths and dimensions that are drawn in the logic cells are not necessarily the same as the final silicon dimensions. Normally mask dimensions are altered from drawn values to allow for process bias or other effects that occur during the transfer of the pattern from mask to silicon. Since this is a problem that is dealt with by the ASIC vendor and not the design software vendor, ASIC designers normally have to ask very carefully about the details of this problem. </P>
<P CLASS="Body">
<A NAME="pgfId=64116">
</A>
<A HREF="CH17.4.htm#19399" CLASS="XRef">
Table 17.2</A>
shows values for the parasitic capacitances for a typical 1 <SPAN CLASS="Symbol">
m</SPAN>
m CMOS process. Notice that the fringing capacitance is greater than the parallel-plate (area) capacitance for all layers except poly. Next, we shall describe how the parasitic information is passed between tools. </P>
<DIV>
<H2 CLASS="Heading2">
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</A>
17.4.1 <A NAME="11985">
</A>
SPF, RSPF, and DSPF</H2>
<P CLASS="BodyAfterHead">
<A NAME="pgfId=17258">
</A>
The <SPAN CLASS="Definition">
standard parasitic format</SPAN>
<A NAME="marker=17256">
</A>
(<SPAN CLASS="Definition">
SPF</SPAN>
<A NAME="marker=17257">
</A>
<A NAME="marker=39137">
</A>
) (developed by Cadence [<A NAME="Cadence90">
</A>
1990], now in the hands of OVI) describes interconnect delay and loading due to parasitic resistance and capacitance. There are three different forms of SPF: two of them (<SPAN CLASS="Definition">
regular SPF</SPAN>
<A NAME="marker=70735">
</A>
and <SPAN CLASS="Definition">
reduced SPF</SPAN>
<A NAME="marker=70734">
</A>
) contain the same information, but in different formats, and model the behavior of interconnect; the third form of SPF (<SPAN CLASS="Definition">
detailed SPF</SPAN>
<A NAME="marker=70736">
</A>
) describes the actual parasitic resistance and capacitance components of a net. <A HREF="CH17.4.htm#23689" CLASS="XRef">
Figure 17.22</A>
shows the different types of simplified models that regular and reduced SPF support. The load at the output of gate A is represented by one of three models: lumped-C, lumped-RC, or PI segment. The pin-to-pin delays are modeled by RC delays. You can represent the pin-to-pin interconnect delay by an ideal voltage source, V(A_1) in this case, driving an RC network attached to each input pin. The actual pin-to-pin delays may not be calculated this way, however.</P>
<TABLE>
<TR>
<TD ROWSPAN="1" COLSPAN="3">
<P CLASS="TableTitle">
<A NAME="pgfId=76949">
</A>
TABLE 17.2 <A NAME="19399">
</A>
Parasitic capacitances for a typical 1 <SPAN CLASS="Symbol">
m</SPAN>
m (<SPAN CLASS="Symbol">
l</SPAN>
= 0.5 <SPAN CLASS="Symbol">
m</SPAN>
m) three-level metal CMOS process.<A HREF="#pgfId=76953" CLASS="footnote">
1</A>
</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=76959">
</A>
<SPAN CLASS="TableHeads">
Element</SPAN>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableFirst">
<A NAME="pgfId=76961">
</A>
Area / fF<SPAN CLASS="Symbol">
m</SPAN>
m<SUP CLASS="Superscript">
–2</SUP>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableFirst">
<A NAME="pgfId=76963">
</A>
Fringing / fF<SPAN CLASS="Symbol">
m</SPAN>
m<SUP CLASS="Superscript">
–1</SUP>
</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=76965">
</A>
poly (over gate oxide) to substrate</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=76967">
</A>
1.73</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=76972">
</A>
NA<A HREF="#pgfId=76971" CLASS="footnote">
2</A>
</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=76974">
</A>
poly (over field oxide) to substrate </P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=76976">
</A>
0.058</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=76978">
</A>
0.043</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=76980">
</A>
m1 to diffusion or poly</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=76982">
</A>
0.055</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=76984">
</A>
0.049</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=76986">
</A>
m1 to substrate</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=76988">
</A>
0.031</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=76990">
</A>
0.044</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=76992">
</A>
m2 to diffusion</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=76994">
</A>
0.019</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=76996">
</A>
0.038</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=76998">
</A>
m2 to substrate</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77000">
</A>
0.015</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77002">
</A>
0.035</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=77004">
</A>
m2 to poly</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77006">
</A>
0.022</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77008">
</A>
0.040</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=77010">
</A>
m2 to m1</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77012">
</A>
0.035</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77014">
</A>
0.046</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=77016">
</A>
m3 to diffusion</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77018">
</A>
0.011</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77020">
</A>
0.034</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=77022">
</A>
m3 to substrate</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77024">
</A>
0.010</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77026">
</A>
0.033</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=77028">
</A>
m3 to poly</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77030">
</A>
0.012</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77032">
</A>
0.034</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=77034">
</A>
m3 to m1</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77036">
</A>
0.016</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77038">
</A>
0.039</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=77040">
</A>
m3 to m2</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77042">
</A>
0.035</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77044">
</A>
0.049</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=77046">
</A>
n+ junction (at 0V bias)</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77048">
</A>
0.36</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77050">
</A>
NA</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=77052">
</A>
p+ junction (at 0V bias)</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77054">
</A>
0.46</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=77056">
</A>
NA</P>
</TD>
</TR>
</TABLE>
<TABLE>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableFigure">
<A NAME="pgfId=17270">
</A>
<IMG SRC="CH17-22.gif" ALIGN="BASELINE">
</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
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