
MEMORY COMPILERS
OVERVIEW
SEC ASIC
5-1
STD80/STDM80
OVERVIEW
This chapter contains information for memory compilers available in STD80/STDM80 cell library. These are
complete compilers that consist of various generators to satisfy the requirements of the circuit at hand. Each
of the final building block, the physical layout, will be implemented as a stand-alone, densely packed,
pitch-matched array. Using this complex layout generator and adopting state-of-the-art logic and circuit
design technique, these memory cells can realize extreme density and performance. In each layout
generator, we added an option which makes the aspect ratio of the physical layout selectable so that the
ASIC designers can choose the aspect ratio according to the convenience of the chip level layout.
In the STD80/STDM80 cell library, there are 4 groups of memory compilers — ROMs; Static RAMs;
Register File; FIFO.
Generators
Each memory compiler is a set of various, parameterized generators. The generators are:
Layout Generator
: generates an array of custom, pitch-matched leaf cells.
Schematic Generator & Netlister
: extracts a netlist which can be used for both LVS check and functional verification.
Function & Timing Model Generators
: for gate level simulation, dynamic/static timing analysis and synthesis
Symbol Generator
: for schematic capture
Critical Path Generator & ETC
: there are many special purpose generators such as critical path generator used for both
circuit design and AC timing characterization.
Advanced Design Technique
All of 0.5
μ
m CMOS standard cell memory compilers adopt very advanced design technique to obtain
extremely high performance in terms of both speed and power consumption. Below are major techniques.
For reducing power consumption
Minimized bit-line precharge/discharge voltage swing
Zero static current consuming sense amplifier
Automatic power down after an access
For optimizing and minimizing the read access time
Size sensitive self-timer delay
Extremely simple tri-state output circuit
Flexible Aspect Ratio
The size of a memory cell is defined by its number of words (WORDS) and number of bits per word (BPW).
But, this size is only a logical size. The physical size of a memory is defined by the number of rows (ROWS)
and the number of columns (COLS) of its bit cell array. Usually, we can't make the bit cell array with WORDS
and BPW because the range of WORDS is much larger than the range of BPW. If we make the bit cell array
with WORDS and BPW, most of memory layouts will have too tall and too thin aspect ratio. Therefore,
column decoder and y-mux circuit are included in most of memory cells to adjust the aspect ratio.