mirror of https://github.com/VLSIDA/OpenRAM.git
116 lines
5.5 KiB
TeX
116 lines
5.5 KiB
TeX
\section{Results}
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\label{sec:results}
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Figure~\ref{fig:layout} shows several different SRAM layouts
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generated by OpenRAM in FreePDK45. OpenRAM can generate single
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bank and multi-bank SRAM arrays. Banks are
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symmetrically placed to have the same delay for data and address
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while sharing peripheral blocks such as decoders.
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\begin{figure}[tb]
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\centering
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\includegraphics[scale=.4]{./figs/layout.pdf}
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\caption{Single bank and multi-bank SRAMs (not to scale) use
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symmetrical bank placement to share peripheral circuitry and
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equalize signal delays.}
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\label{fig:layout}
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\end{figure}
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Figure~\ref{fig:density_figure} shows the memory area of different
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total size and data word width memories in both FreePDK45 and
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SCMOS. As expected, the smaller process technology (45nm) has lower
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total area overall but the trends are similar in both technologies.
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Figure~\ref{fig:density_figure} also shows the access time of
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different size and data word width in FreePDK45 and SCMOS. Increasing
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the memory size generally increases the access time; long bit-lines
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and word-lines increase the access time by adding more parasitic
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capacitance and resistance. Since OpenRAM uses multiple banks and
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column muxing, it is possible to have a smaller access time for larger
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memory designs, but this will sacrifice density.
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\begin{figure}[tb]
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\begin{center}
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\centering
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%\includegraphics[width=8.5cm]{./figs/Results.pdf}
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\includegraphics[width=7.5cm , height=14cm]{./figs/Results2.pdf}
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% \subfigure[FreePDK45 memory area \label{fig:freepdk_area}]{
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% \includegraphics[scale=1]{./figs/Freepdk_Area.pdf}}
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% \subfigure[SCMOS memory area \label{fig:scn3me_area}]{
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% \includegraphics[scale=.5]{./figs/Scn3me_Area.pdf}}
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\caption{OpenRAM provides high-density memories in multiple
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technologies and sizes with corresponding characterized
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delays. \label{fig:density_figure}}
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\vspace{-0.5cm}
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\end{center}
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\end{figure}
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%Table~\ref{table:bit-density-comparison} shows a comparison between bit
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%density of OpenRAM's generated memory designs and other publications
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%which are close in technology node with FreePDK45 and SCMOS. As shown
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%in this table, OpenRAM provides very dense SRAM arrays in both technologies.
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\begin{table}[t]
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\centering
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\caption{OpenRAM has high density compared to other published memories in
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similar technologies.}
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\begin{tabular}{|c|c|c|c|l|l|l|l|l|} \hline
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\texttt{Ref.} & \texttt{Feature} & \texttt{Tech.} & \texttt{Density} \\
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& \texttt{Size} & & [Mb/$mm^2$] \\
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\hline \hline
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$~\cite{4585946}$ & $65$ nm & CMOS & $0.7700$ \\ \hline
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$~\cite{Bit_Density_3}$ & $45$ nm & CMOS & $0.3300$ \\ \hline
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$~\cite{Bit_Density_2}$ & $40$ nm & CMOS & $0.9400$ \\ \hline
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\verb+OpenRAM+ & $45$ nm & FreePDK45 & $0.8260$ \\ \hline \hline
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$~\cite{127339}$ & $0.5$ um & CMOS & $0.0036$ \\ \hline
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$~\cite{Bit_Density_6}$ & $0.5$ um & BiCMOS & $0.0020$ \\ \hline
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$~\cite{Bit_Density_5}$ & $0.5$ um & CMOS & $0.0050$ \\ \hline
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\verb+OpenRAM+ & $0.5$ um & SCMOS & $0.0050$ \\ \hline
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\end{tabular}
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\label{table:bit-density-comparison}
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\end{table}
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%\begin{table*}
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%\centering
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%\caption{OpenRAM has high density, fast access time and low power consumption compared to other published memories in similar technologies.}
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%\begin{tabular}{|c|l|l|l|l|l|l|l|l|} \hline
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%\texttt{Reference} & \texttt{Technology} & \texttt{Density (Mb/$mm^2$)}& \texttt{Access time (ns)}& \texttt{Power consumption} \\ \hline \hline
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%$~\cite{Bit_Density_1}$ & $65 nm CMOS$ & $0.77$ & $28$ & $22$ $uW/MHz$ \\ \hline
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%$~\cite{Bit_Density_2}$ & $40 nm CMOS$ & $0.94$ & $45$ & $13.8$ $pJ/access/Mbit$ \\ \hline
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%$OpenRAM$ & $45 nm FreePDK45$ & $0.826$ & $9.86$ & $13.14$ $mW$ \\ \hline \hline
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%$~\cite{Bit_Density_4}$ & $0.5 um CMOS$ & $0.0036$ & $1.5$ & $6$ $W$ \\ \hline
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%$~\cite{Bit_Density_6}$ & $0.5 um BiCMOS$ & $0.002$ & $1.5$ & $35$ $W$ \\ \hline
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%$~\cite{Bit_Density_5}$ & $0.5 um CMOS$ & $0.005$ & $75$ & $3.9$ $mW$ \\ \hline
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%$OpenRAM$ & $0.5 um SCMOS$ & $0.005$ & $44.9$ & $115$ $mW$ \\ \hline
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%\end{tabular}
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%\label{table:bit-density-comparison}
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%\end{table*}
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Comparison of power consumption and read access time of different
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memories is a bit more complicated to make a conclusion, because there
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are many trade-offs. Power and performance are highly dependent on
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circuit style (CMOS, ECL, etc.), memory organization (more banks is
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faster but sacrifices density), and the optimization goal: low-power
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or high-performance. In general, OpenRAM has reasonable trade-off
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between the two and can be customized by using an alternate sense
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amplifiers, decoders, or overall dimensional organization.
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Table~\ref{table:bit-density-comparison} compares the bit-density of
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OpenRAM against published designs using similar technology nodes. The
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results show the benefit of technology scaling and that OpenRAM has
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very good density in both technologies. As a comparison, a 76ns SRAM
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consumes 3.9mW~\cite{Bit_Density_5} while OpenRAM is much faster at
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44.9ns but consumes 115mW for the same size.
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%Table~\ref{table:bit-density-comparison} shows a comparison between bit density, access
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%time and power consumption of OpenRAM’s generated mem-
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%ory designs and other publications which are close in tech-
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%nology node with FreePDK45 and SCMOS. As shown in this
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%table, OpenRAM provides very dense SRAM arrays in both
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%technologies. There is no easy comparison on power con-
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%sumption and read access time as these values vary with the
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%array size and configuration. Therefore, we only try to com-
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%pare the features of each work from a more general point of
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%view.
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