Hi all; Re those 32-bit wide DRAMs, a long, winding post...
I designed 32-bit wide SDRAMs into a product so long ago,
that the parts are now verging on obsolescence. About 6
manufacturers made them, and they were priced just a few
percent higher than x16 SDRAMs. We are not talking about
some future technology, this is old stuff. The only thing
confusing to the uninitiated about them is that they are
referred to as SGRAM rather than SDRAM. An SDRAM
controller will also control SGRAM, provided it can handle
the different address topology, but that is no more than
the usual difference between different width DRAMs (i.e. x4
vs x8 vs x16). In addition, SGRAMs provide some additional
actions besides reading and writing that are not available
in SDRAM. These don't take up a lot of die size, and if
you don't need them, you pretty much ignore them. (To use
them as an SDRAM, just tie the DSF pins low. If you look
through the data sheets, you will find that this action
will not prevent any SDRAM actions, but will eliminate all
the graphics actions. The part then fully imitates a x32
DRAM or SDRAM interface.)
Micron shows the following x32 SDRAMs/SGRAMs:
Type Config Part Cycle Samples Production
SGRAM 512Kx32 MT45V512K32 6ns DDR NOW 3Q99
SDRAM 2Mx32 MT48LC2M32B2 6ns SDR NOW 3Q99
SDRAM 2Mx32 MT46V2M32 6ns DDR 4Q99 1Q00
Here's 5 different x32 SDRAMs (SGRAMs) from Samsung. Note that the ones
marked "End of Life" have already been sampled, in production, used in
products, and are now obsoleted by the newer models. This sort of proves
that x32 DRAM is possible:
SGRAM 256Kx32 KM4232W259AQ 12ns EDO (End of Life) Window RAM...
SGRAM 256Kx32 KM4132G271BQ 7ns SDR (End of Life)
SGRAM 512Kx32 KM4132G512 5ns SDR
SGRAM 1Mx32 KM4132G112 4.5ns SDR
SGRAM 512Kx32 KM432D5131 7ns DDR
SDRAM 2Mx32 KM432S2030CT 5.5ns SDR
usa.samsungsemi.com
usa.samsungsemi.com
usa.samsungsemi.com
usa.samsungsemi.com
Also note that the same Samsung web page that advertises RDRAM, also
advertises 32M DDR SGRAM. Look just under the "DRAM" sign:
usa.samsungsemi.com
Some NEC part numbers:
SGRAM 512Kx32 uPD4811650 Phase Out
SGRAM 256Kx32 uPD481850 Phase Out
SDRAM 2Mx32 uPD4564323 8ns SDR Current
necel.com
I got diverted during a search of the Fujitsu web site, but they
have a fascinating newsletter that they send out to their sales team.
It talks a lot about various memory types. Here are some direct
quotes:
Here's what you can do to help your customers:
1. Urge them to migrate to 16M PC100 as soon as possible.
2. Offer teh 64M (2Mx32) SDRAM for wide bandwidth applications.
3. For high-performance systems, expose your customers to our new
FCRAM and DDR.
...
Get Ready to Sell 64M (2Mx32) SDRAM B-die
Our development status for the new 64M (x32) SDRAM B-die and the A-
die (in production) includes sampling and production dates, part numbers,
and applications.
Sales Strategy
Work with the A-die until the B-die is ready. If necessary, we can screen
the A-die to 125MHz to address near term "high speed" opportunities. Get
the A-die designed in now, and then show the customer a cost-reduction
path using the B-die.
Applications
The 64M (x32) is ideal for applications where extremely large memory and
bandwidth are needed, yet a simple interface is required. Workstations,
networks, personal computers, laser printers, set-top boxes, and high-
performance resolution graphics adapters/accelerator cards are examples.
The B-die's super low power (SLP) version is especially useful in mobile
applications like PDAs, still cameras, and VCR cameras.
64M (x32) A-Die in Full Production
The A-die (0.36um), available in normal or standard power (NP) and low
power (LP), is now in full production. It comes in the JEDEC-standard
86-pin TSOP-II package.
64M (x32) B-Die Product Development Schedule
Two voltages for Vcc are supported by the B-die (0.24um): 3.3V and 2.5V.
The 3.3V version is compatible with the A-die. The 2.5V version is an
evolutionary voltage for the next-generation SDRAM. Both devices will be
available in normal power, low power and super-low power. The self-refresh
current of the super-low power version has decreased so much that at
45oC, ICC6 (self-refresh current) is only 0.1mA. Portable applications
customers will love the fact that this is one fifth of the low power version
and one tenth of the normal power version!
Below is a detailed development schedule for the B-die.
Table: <<< Engineering samples April-September 1999, Production
Q399-Q100, depending on voltage and power, each at 143 to 100MHz >>>
They then go on to discuss FCRAM, which I take to be their version of VCRAM.
They are talking 200MHz, DDR parts, x32, for a total of 1.6GB/sec, the same
as an RDRAM, but probably at a lot lower power consumption and cost, somewhat
easier to design with, and with much, much better latency.
A fascinating newsletter, it ends with the answer to the previous newsletter's
crossword puzzle, and an announcement of the winners.
-- Carl |
