ch03.3.htm
来自「介绍asci设计的一本书」· HTM 代码 · 共 2,812 行 · 第 1/5 页
HTM
2,812 行
.</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnNumber">
<A NAME="pgfId=295773">
</A>
<A NAME="22086">
</A>
(3.27)</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=295775">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=295777">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=295779">
</A>
<SPAN CLASS="EquationVariables">
C</SPAN>
<SUB CLASS="Subscript">
in</SUB>
<SPAN CLASS="EquationVariables">
</SPAN>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=295781">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=295830">
</A>
2<SPAN CLASS="EquationVariables">
g</SPAN>
C<SUB CLASS="Subscript">
inv</SUB>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=295832">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=295834">
</A>
(2)·(0.036 pF)</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnLeft">
<A NAME="pgfId=296290">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=295783">
</A>
</P>
</TD>
</TR>
</TABLE>
<P CLASS="BodyAfterHead">
<A NAME="pgfId=88054">
</A>
(Notice that <SPAN CLASS="EquationVariables">
g</SPAN>
cancels out in this equation, we shall discuss this in the next section.) </P>
<P CLASS="Body">
<A NAME="pgfId=180327">
</A>
The delay of the NOR logic cell, in units of <SPAN CLASS="Symbol">
t</SPAN>
, is thus </P>
<TABLE>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=297107">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=297109">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=297111">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=297113">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=297115">
</A>
0.3 <SPAN CLASS="Symbol">
¥</SPAN>
10<SUP CLASS="Superscript">
–12</SUP>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnLeft">
<A NAME="pgfId=297117">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=297119">
</A>
</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=297121">
</A>
<SPAN CLASS="EquationVariables">
d</SPAN>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=297123">
</A>
=</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=297125">
</A>
<SPAN CLASS="EquationVariables">
gh</SPAN>
+ <SPAN CLASS="EquationVariables">
p</SPAN>
+ <SPAN CLASS="EquationVariables">
q</SPAN>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=297127">
</A>
=</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=297129">
</A>
––––––––––––––––––––</P>
</TD>
<TD ROWSPAN="1" COLSPAN="2">
<P CLASS="TableEqnLeft">
<A NAME="pgfId=297131">
</A>
+ (3)·(1) + (3)·(1.7)</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=297135">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=297137">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=297139">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=297141">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=297143">
</A>
(2)·(0.036 <SPAN CLASS="Symbol">
¥</SPAN>
10<SUP CLASS="Superscript">
–12</SUP>
)</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnLeft">
<A NAME="pgfId=297145">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=297147">
</A>
</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=297149">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=297151">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=297153">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=297155">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=297157">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnLeft">
<A NAME="pgfId=297159">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=297161">
</A>
</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=297163">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=297165">
</A>
=</P>
</TD>
<TD ROWSPAN="1" COLSPAN="4">
<P CLASS="TableEqn">
<A NAME="pgfId=297167">
</A>
4.1666667 + 3 + 5.1</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=297175">
</A>
</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=297177">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=297179">
</A>
=</P>
</TD>
<TD ROWSPAN="1" COLSPAN="4">
<P CLASS="TableEqn">
<A NAME="pgfId=297181">
</A>
12.266667 <SPAN CLASS="Symbol">
t .</SPAN>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnNumber">
<A NAME="pgfId=297189">
</A>
<A NAME="14951">
</A>
(3.28)</P>
</TD>
</TR>
</TABLE>
<P CLASS="BodyAfterHead">
<A NAME="pgfId=88059">
</A>
equivalent to an absolute delay, <SPAN CLASS="EquationVariables">
t</SPAN>
<SUB CLASS="SubscriptVariable">
PD</SUB>
<SPAN CLASS="Symbol">
ª </SPAN>
12.3<SPAN CLASS="Symbol">
¥ </SPAN>
0.06<SPAN CLASS="Symbol">
</SPAN>
ns<SPAN CLASS="Symbol">
</SPAN>
=<SPAN CLASS="Symbol">
</SPAN>
0.74<SPAN CLASS="Symbol">
</SPAN>
ns.</P>
<P CLASS="Body">
<A NAME="pgfId=88060">
</A>
The delay for a 2X drive, three-input NOR logic cell in the C5 library is </P>
<TABLE>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=222685">
</A>
<SPAN CLASS="EquationVariables">
t</SPAN>
<SUB CLASS="SubscriptVariable">
PD </SUB>
= (0.03 + 0.72<SPAN CLASS="EquationVariables">
C</SPAN>
<SUB CLASS="Subscript">
out</SUB>
+ 0.60) ns .</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnNumber">
<A NAME="pgfId=222687">
</A>
(3.29)</P>
</TD>
</TR>
</TABLE>
<P CLASS="Body">
<A NAME="pgfId=88065">
</A>
With <SPAN CLASS="EquationVariables">
C</SPAN>
<SUB CLASS="Subscript">
out</SUB>
<SPAN CLASS="Symbol">
</SPAN>
=<SPAN CLASS="Symbol">
</SPAN>
0.3<SPAN CLASS="Symbol">
</SPAN>
pF, </P>
<TABLE>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=222700">
</A>
<SPAN CLASS="EquationVariables">
t</SPAN>
<SUB CLASS="SubscriptVariable">
PD</SUB>
= 0.03 + (0.72)·(0.3) + 0.60 = 0.846 ns .</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnNumber">
<A NAME="pgfId=222702">
</A>
(3.30)</P>
</TD>
</TR>
</TABLE>
<P CLASS="BodyAfterHead">
<A NAME="pgfId=88070">
</A>
compared to our prediction of 0.74<SPAN CLASS="Symbol">
</SPAN>
ns. Almost all of the error here comes from the inaccuracy in predicting the nonideal delay. Logical effort gives us a method to examine relative delays and not accurately calculate absolute delays. More important is that logical effort gives us an insight into why logic has the delay it does.</P>
</DIV>
<DIV>
<H3 CLASS="Heading2">
<A NAME="pgfId=109865">
</A>
3.3.2 Logical Area and Logical Efficiency</H3>
<P CLASS="BodyAfterHead">
<A NAME="pgfId=109869">
</A>
Figure <A HREF="#42525" CLASS="XRef">
3.9</A>
shows a single-stage OR-AND-INVERT cell that has different logical efforts at each input. The logical effort for the OAI221 is the <SPAN CLASS="Definition">
logical-effort vector</SPAN>
<A NAME="marker=109870">
</A>
<SPAN CLASS="EquationVariables">
g</SPAN>
<SPAN CLASS="Symbol">
</SPAN>
=<SPAN CLASS="Symbol">
</SPAN>
(7/3, 7/3, 5/3). For example, the first element of this vector, 7/3, is the logical effort of inputs A and B in Figure <A HREF="#42525" CLASS="XRef">
3.9</A>
.</P>
<TABLE>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableFigTitleSide">
<A NAME="pgfId=109877">
</A>
FIGURE 3.9 <A NAME="42525">
</A>
An OAI221 logic cell with different logical efforts at each input. In this case <SPAN CLASS="EquationVariables">
g</SPAN>
<SPAN CLASS="Symbol">
</SPAN>
=<SPAN CLASS="Symbol">
</SPAN>
(7/3, 7/3, 5/3). The logical effort for inputs A and B is 7/3, the logical effort for inputs C and D is also 7/3, and for input E the logical effort is 5/3. The logical area is the sum of the transistor areas, 33 logical squares.</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableFigure">
<A NAME="pgfId=109882">
</A>
</P>
<DIV>
<IMG SRC="CH03-19.gif">
</DIV>
</TD>
</TR>
</TABLE>
<P CLASS="Body">
<A NAME="pgfId=109884">
</A>
We can calculate the area of the transistors in a logic cell (ignoring the routing area, drain area, and source area) in units of a minimum-size <SPAN CLASS="EmphasisPrefix">
n</SPAN>
-channel transistor—we call these units <SPAN CLASS="Definition">
logical squares</SPAN>
<A NAME="marker=158627">
</A>
. We call the transistor area the <SPAN CLASS="Definition">
logical area</SPAN>
<A NAME="marker=109883">
</A>
. For example, the logical area of a 1X drive cell, OAI221X1, is calculated as follows:</P>
<UL>
<LI CLASS="BulletFirst">
<A NAME="pgfId=109886">
</A>
<SPAN CLASS="EmphasisPrefix">
n</SPAN>
-channel transistor sizes: 3/1<SPAN CLASS="Symbol">
</SPAN>
+<SPAN CLASS="Symbol">
</SPAN>
4<SPAN CLASS="Symbol">
¥ </SPAN>
(3/1)</LI>
<LI CLASS="BulletList">
<A NAME="pgfId=109887">
</A>
<SPAN CLASS="EmphasisPrefix">
p</SPAN>
-channel transistor sizes: 2/1<SPAN CLASS="Symbol">
</SPAN>
+<SPAN CLASS="Symbol">
</SPAN>
4<SPAN CLASS="Symbol">
¥ </SPAN>
(4/1)</LI>
<LI CLASS="BulletLast">
<A NAME="pgfId=109888">
</A>
total logical area<SPAN CLASS="Symbol">
</SPAN>
=<SPAN CLASS="Symbol">
</SPAN>
2<SPAN CLASS="Symbol">
</SPAN>
+<SPAN CLASS="Symbol">
</SPAN>
(4<SPAN CLASS="Symbol">
¥ </SPAN>
4)<SPAN CLASS="Symbol">
</SPAN>
+<SPAN CLASS="Symbol">
</SPAN>
(5<SPAN CLASS="Symbol">
¥ </SPAN>
3)<SPAN CLASS="Symbol">
</SPAN>
=<SPAN CLASS="Symbol">
</SPAN>
33<SPAN CLASS="Symbol">
</SPAN>
logical squares</LI>
</UL>
<P CLASS="Body">
<A NAME="pgfId=109892">
</A>
Figure <A HREF="#38892" CLASS="XRef">
3.10</A>
shows a single-stage AOI221 cell, with <SPAN CLASS="EquationVariables">
g</SPAN>
<SPAN CLASS="Symbol">
</SPAN>
=<SPAN CLASS="Symbol">
</SPAN>
(8/3, 8/3, 6/3). The calculation of the logical area (for a AOI221X1) is as follows:</P>
<UL>
<LI CLASS="BulletFirst">
<A NAME="pgfId=109893">
</A>
<SPAN CLASS="EmphasisPrefix">
n</SPAN>
-channel transistor sizes: 1/1<SPAN CLASS="Symbol">
</SPAN>
+<SPAN CLASS="Symbol">
</SPAN>
4<SPAN CLASS="Symbol">
¥ </SPAN>
⌨️ 快捷键说明
复制代码Ctrl + C
搜索代码Ctrl + F
全屏模式F11
增大字号Ctrl + =
减小字号Ctrl + -
显示快捷键?