ch15.4.htm

介绍asci设计的一本书

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&nbsp;</P>
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PLCC = plastic leaded chip carrier</P>
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&nbsp;</P>
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&nbsp;</P>
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We shall need to add (0.175/0.5) <SPAN CLASS="Symbol">
&#165;</SPAN>
 2 <SPAN CLASS="Symbol">
&#165;</SPAN>
 (15 to 20) = 10.5 to 21 mil (per side) for the pad heights (we included the effects of scaling in this calculation). With a pad pitch of 5 mil and roughly 166/4 = 42 I/Os per side (not counting any power pads), we need a die at least 5 <SPAN CLASS="Symbol">
&#165;</SPAN>
 42 = 210 mil on a side for the I/Os. Thus the die size must be at least 210 <SPAN CLASS="Symbol">
&#165;</SPAN>
 210 = 4.4<SPAN CLASS="Symbol">
  &#165;</SPAN>
 10<SUP CLASS="Superscript">
4</SUP>
 mil<SUP CLASS="Superscript">
2</SUP>
 to fit 166 I/Os. Of this die area only 1.19 <SPAN CLASS="Symbol">
&#165;</SPAN>
 10<SUP CLASS="Superscript">
4</SUP>
/(4.4 <SPAN CLASS="Symbol">
&#165;</SPAN>
 10<SUP CLASS="Superscript">
4</SUP>
 ) = 27 % (at most) is used by the core logic. This is a severely pad-limited design and we need to rethink the partitioning of this system.</P>
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<A HREF="CH15.4.htm#39404" CLASS="XRef">
Table&nbsp;15.4</A>
 shows some typical areas for <A NAME="marker=99523">
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datapath elements. You would use many of these datapath elements in <A NAME="marker=192373">
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floating-point arithmetic (these elements are large&#8212;you should not use floating-point arithmetic unless you have to):</P>
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<A NAME="pgfId=84089">
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A <A NAME="marker=99524">
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leading-one detector with <A NAME="marker=99525">
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barrel shifter normalizes a <A NAME="marker=192371">
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mantissa.</LI>
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<A NAME="pgfId=83826">
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A <A NAME="marker=99526">
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priority encoder corrects <A NAME="marker=192372">
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exponents due to mantissa normalization.</LI>
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A <A NAME="marker=99527">
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denormalizing barrel shifter aligns mantissas.</LI>
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<A NAME="pgfId=84060">
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A <A NAME="marker=99528">
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normalizing barrel shifter with a leading-one detector normalizes mantissa subtraction. </LI>
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TABLE&nbsp;15.3&nbsp;<A NAME="30274">
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Some useful numbers for ASIC estimates, normalized to a 1 <SPAN CLASS="Symbol">
m</SPAN>
m technology unless noted.</P>
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Parameter</SPAN>
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Typical value </SPAN>
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<A NAME="pgfId=195288">
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<SPAN CLASS="TableHeads">
Comment</SPAN>
<A HREF="#pgfId=195287" CLASS="footnote">
1</A>
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<SPAN CLASS="TableHeads">
Scaling</SPAN>
</P>
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<A NAME="marker=195292">
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Lambda, <SPAN CLASS="Symbol">
l</SPAN>
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<A NAME="pgfId=195295">
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0.5  <SPAN CLASS="Symbol">
m</SPAN>
m = 0.5 (minimum feature size)</P>
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In a 1 <SPAN CLASS="Symbol">
m</SPAN>
m technology, <SPAN CLASS="Symbol">
l</SPAN>
 <SPAN CLASS="Symbol">
&#170;</SPAN>
 0.5 <SPAN CLASS="Symbol">
m</SPAN>
m.</P>
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<A NAME="pgfId=195299">
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NA</P>
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CAD pitch</P>
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1 micron  =  10<SUP CLASS="Superscript">
&#8211;6</SUP>
 m  =  1<SPAN CLASS="Symbol">
  m</SPAN>
m</P>
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<A NAME="pgfId=195305">
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=  minimum feature size</P>
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Not to be confused with minimum CAD grid size (which is usually less than 0.01 <SPAN CLASS="Symbol">
m</SPAN>
m).</P>
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<A NAME="pgfId=195309">
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<SPAN CLASS="Symbol">
l</SPAN>
</P>
</TD>
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<P CLASS="TableLeft">
<A NAME="pgfId=195312">
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Effective gate length</P>
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<A NAME="pgfId=195314">
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0.25 to 1.0 <SPAN CLASS="Symbol">
m</SPAN>
m</P>
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Less than drawn gate length, usually by about 10 percent.</P>
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<A NAME="pgfId=195318">
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<SPAN CLASS="Symbol">
l</SPAN>
</P>
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<A NAME="pgfId=195321">
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I/O-pad width (pitch)</P>
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5 to 10 mil </P>
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<A NAME="pgfId=195324">
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= 125 to  250 <SPAN CLASS="Symbol">
m</SPAN>
m</P>
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For a 1 <SPAN CLASS="Symbol">
m</SPAN>
m technology, 2LM (<SPAN CLASS="Symbol">
l</SPAN>
 = 0.5  <SPAN CLASS="Symbol">
m</SPAN>
m). Scales less than linearly with <SPAN CLASS="Symbol">
l</SPAN>
.</P>
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<A NAME="pgfId=195328">
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<SPAN CLASS="Symbol">
l</SPAN>
</P>
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<A NAME="pgfId=195331">
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I/O-pad height</P>
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15 to 20 mil </P>
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<A NAME="pgfId=195334">
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= 375 to  500 <SPAN CLASS="Symbol">
m</SPAN>
m</P>
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<A NAME="pgfId=195336">
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For a 1 <SPAN CLASS="Symbol">
m</SPAN>
m technology, 2LM (<SPAN CLASS="Symbol">
l</SPAN>
 = 0.5 <SPAN CLASS="Symbol">
m</SPAN>
m). Scales approximately linearly with <SPAN CLASS="Symbol">
l</SPAN>
.</P>
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<TD ROWSPAN="1" COLSPAN="1">
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<A NAME="pgfId=195338">
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<SPAN CLASS="Symbol">
l</SPAN>
</P>
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Large die</P>
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1000 mil/side, 10<SUP CLASS="Superscript">
6</SUP>
 mil<SUP CLASS="Superscript">
2</SUP>
</P>
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Approximately constant</P>
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1</P>
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Small die</P>
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<A NAME="pgfId=195350">
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100 mil/side, 10<SUP CLASS="Superscript">
4</SUP>
 mil<SUP CLASS="Superscript">
2</SUP>
</P>
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Approximately constant</P>
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<A NAME="pgfId=195354">
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1</P>
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Standard-cell density</P>
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1.5 <SPAN CLASS="Symbol">
&#165;</SPAN>
 10<SUP CLASS="Superscript">
&#8211;3</SUP>
 gate/<SPAN CLASS="Symbol">
m</SPAN>
m<SUP CLASS="Superscript">
2</SUP>
</P>
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<A NAME="pgfId=195359">
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= 1.0 gate/mil<SUP CLASS="Superscript">
2</SUP>
</P>
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<A NAME="pgfId=195361">
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For 1<SPAN CLASS="Symbol">
m</SPAN>
m, 2LM, library </P>
<P CLASS="TableLeft">
<A NAME="pgfId=195362">
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=  4 <SPAN CLASS="Symbol">
&#165;</SPAN>
 10<SUP CLASS="Superscript">
&#8211;4</SUP>
 gate<SPAN CLASS="Symbol">
/l</SPAN>
<SUP CLASS="Superscript">
2</SUP>
 (independent of scaling).</P>
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<A NAME="pgfId=195364">
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1/<SPAN CLASS="Symbol">
l</SPAN>
<SUP CLASS="Superscript">
2</SUP>
</P>
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<P CLASS="TableLeft">
<A NAME="pgfId=195366">
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Standard-cell density</P>
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<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=195368">
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 8 <SPAN CLASS="Symbol">
&#165;</SPAN>
 10<SUP CLASS="Superscript">
&#8211;3</SUP>
  gate/<SPAN CLASS="Symbol">
m</SPAN>
m<SUP CLASS="Superscript">
2</SUP>
</P>
<P CLASS="TableLeft">
<A NAME="pgfId=195369">
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=  5.0 gate/mil<SUP CLASS="Superscript">
2</SUP>
</P>
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<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=195371">
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For 0.5 <SPAN CLASS="Symbol">
m</SPAN>
m, 3LM, library</P>
<P CLASS="TableLeft">
<A NAME="pgfId=195372">
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=  5 <SPAN CLASS="Symbol">
&#165;</SPAN>
 10<SUP CLASS="Superscript">
&#8211;4</SUP>
  gate/<SPAN CLASS="Symbol">
l</SPAN>
<SUP CLASS="Superscript">
2</SUP>
 (independent of scaling).</P>
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<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=195374">
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1/<SPAN CLASS="Symbol">
l</SPAN>
<SUP CLASS="Superscript">
2</SUP>
</P>
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<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
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Gate-array utilization</P>
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<P CLASS="TableLeft">
<A NAME="pgfId=195378">
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60 to 80 %</P>
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<TD ROWSPAN="1" COLSPAN="1">
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<A NAME="pgfId=195380">
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For 2LM, approximately constant</P>
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<TD ROWSPAN="1" COLSPAN="1">
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<A NAME="pgfId=195382">
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1</P>
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&nbsp;</P>
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<A NAME="pgfId=195386">
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80 to 90 %</P>
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<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=195388">
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For 3LM, approximately constant</P>
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<TD ROWSPAN="1" COLSPAN="1">
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<A NAME="pgfId=195390">
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1</P>
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<P CLASS="TableLeft">
<A NAME="pgfId=195392">
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Gate-array density</P>
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<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=195394">
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(0.8 to 0.9) <SPAN CLASS="Symbol">
&#165;</SPAN>
 standard cell density</P>
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<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=195396">
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For the same process as standard cells</P>
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<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=195398">
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1</P>
</TD>
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<P CLASS="TableLeft">
<A NAME="pgfId=195401">
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Standard-cell<A NAME="marker=195400">
 </A>
 routing factor = (cell area + route area)/cell area</P>
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<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=195403">
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1.5 to 2.5 (2LM)</P>
<P CLASS="TableLeft">
<A NAME="pgfId=195404">
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1.0 to 2.0 (3LM)</P>
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<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=195406">
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Approximately constant</P>
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<TD ROWSPAN="1" COLSPAN="1">
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<A NAME="pgfId=195408">
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1</P>
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<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=195411">
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