DRAM-CMOS and BiCMOS - Electrical Engineering Video Lecture - Electrical Engineering (EE)

ha ha ha ha they just feed all of us
really
you
so we have been discussing memories and
the last few classes we discussed the
static Ram so today's class we shall
take up the other form of memory which
is the dynamic Ram which as you know is
very popular nowadays the reason being
that you can get very large capacity of
memories in a single chip okay so we
shall take up what is dynamic Ram how do
you actually realize it and what are the
properties of such a memory
so the DRAM the dynamic Ram the basic
cell of a dynamic Ram as it is nowadays
is just what you have is you have a
simple pass transistor okay followed by
a capacitance okay so this is the cell
all right now the memory or the storage
you know the memory you basically have a
storage okay the storage is done in the
capacitor okay that is the charge is
stored in the capacitor and depending on
whether the capacitance is charged or
not you I have stored either a one or a
zero alright so if the capacitance is
charged you say you have stored a 1 if
the capacitance is in the discharged
condition can say as 0 is stored in the
memory cell so basically you can see
that it is a very simple structure okay
compared to a static Ram where you had
six transistors per cell or four
transistors per cell okay here you just
have one single transistor so the area
occupied by the cell should be much
smaller okay with the result that you
can have a larger capacity of memory of
course there is a capacitor here one has
to remember that and you we know that
actually in integrated circuit or in the
integrated circuit
okay the capacitor usually takes up a
lot of area okay so that is the problem
now but nowadays with the development of
technology you know that you have what
is called change capacitors okay that is
basically you dig a change in the
semiconductor like this okay and then
you grow a thin oxide all right
a thin oxide all right and then you fill
it up with again some different
materials a poly silicon okay all right
so this oxide here okay this capacitance
here the oxide is the insulator okay and
on two sides you have silicon so
basically this forms our capacitance and
here the surface area taken up by the
capacitance is not large although you
have a large area because of the very
nature of the capacitance which is in
the form of a trench okay so you are
actually not taking up without AF area
in fact in modern IC technology you have
the transistor this single transistor
and the capacitance integrated in the
sense that the capacitance actually sits
on the top of the the transistor
actually sits on the top of the
capacitor okay so basically the area
requirement is there is quite smaller
okay so what did what you do is
basically here you have a select line
okay so this is the word select okay you
can say and this is the data line
alright so when you select this word
okay that when this capacitance when
this word select line goes high this
transistor which is nothing but a pass
transistor this turns on and the
capacitance is connected to the data
line okay and the capacitance and
whatever if it is it is basically
connected to the data line and on the
data line you have the information
corresponding to the voltage across the
capacitance alright so that is how you
read that capacitance okay that is you
of course you will have a large number
of such cells and again just in the same
way as we have already discussed for
other memories that you have an array
okay and so on this particular line okay
you will have different selves located
okay so once you energize this word
select okay all the all the cells all
the cells on this word line is going to
be selected and then you again you have
so many columns and then you have to
again select one of these all these
columns okay and that is how you
particularly zero in on one cell in the
particular array okay now but so this is
how you actually use a dynamic Ram now
why is it called a dynamic Ram it is
called a dynamic Ram because the
mechanism of store charge here is
mechanism of information storage here is
charge stored across the capacitance and
when charge is stored across the
capacitance there will always be some
leakage paths okay for example here you
have an MOS transistor here so you have
the the junction here that is the source
to the substrate junction of this Mo's
transistor okay so this can be a leakage
path alright and you also have other
leakage paths okay which will result in
the what will happen is slowly that
information stored in across the
capacitance is going to degrade with
time okay and with the result that if if
you wait for a long time okay after you
have written into it to read from the
cell okay
the information may have leaked away so
that is if you have charged this
capacitance so slowly this charge will
will leak off okay and if after a long
time okay
this you have lost enough charge so that
what is going to happen is you may read
a zero instead of the one which was
stored here so that is the dynamic
nature so basically what you have to do
is if you have stored a one you have to
refresh the memory from time to time
that is one drawback of a dynamic Ram
compared to a static Ram
that because of the dynamic nature of
the storage okay you have to refresh the
memory from time to time all right so
that is one the other problem is the
because we want this cell to be small it
must take up a small area okay
this capacitance again must necessarily
be of a small value you cannot have a
very large capacitance although you are
making a change capacitance okay you
cannot have a very large value of
capacitance okay whereas this data line
capacitance is going to be a very large
capacitance okay because you have on
this sitting on this data line a large
number of such cells okay
so this data line capacitance is going
to be very large okay so what do you do
is basically if you think of the
mechanism that what you are doing is
suppose you initially charge the data
line to some value say VD VD is the
initial data line voltage wave okay and
then what do you do is you select a
particular cell okay so now suppose we
say that this data line voltage is equal
to VDD by 2 say all right that is if you
are operating on a 5 volts power supply
this is 2.5 volts and then when this
capacitance is charged it was 5 volts
say the voltage across the capacitance
is 5 volts if it is discharged with zero
volts so when it is connected to the
data line if it is fully charged it is
going to increase the data line voltage
and if it was zero volts it is going to
pull down the data line voltage okay now
let us just do a small calculation and
see what is going to be the change in
the data line voltage now this VD we can
say is equal to QD by CD okay where QD
is the total charge data line charge we
can say and CD is the data line
capacitance okay similarly if
say that VC is the initial cell voltage
or that is basically the capacitance
voltage okay so that is equal to Q C by
CC okay that is the total charge across
the in the across the capacitance okay
and CC is their the cell capacitance
okay that is basically the capacitance
here alright now so what is going to be
the final voltage when you when you
connect the two when the cell is
selected it is going to be the total
charge by the total capacitance okay so
if you just do and so this is the final
capacitance a final voltage okay that is
basically when you connect them you will
have a common voltage across the
capacitance and the data line because
this is basically if you connect a
consider this transistor to be a short
okay there will be a common voltage
across the capacitance and the data line
so this is the final voltage the common
voltage so the Delta VD or the change in
the data line voltage is equal to okay
we can say is equal to VD minus VF okay
this is equal to what is VD QD by C D
minus QD plus QC by C D plus
all right so this we can simplify like
this okay we can write is equal to just
QD into if you see D plus CC minus C D
QD plus Q C divided by C D into C D plus
C okay now if you do further analysis
okay
if you for example if you divide by C D
then you get is equal to I'm writing it
here QD into 1 plus CC plus DD minus u D
by QC CD plus CC okay now QD + QD will
cancel here okay and what you are left
with is QD by CD okay into CC okay QD by
CD is VD alright and this is QC okay
which is nothing but CC into VC okay so
you can take CC common here okay so you
get QD by CD is VD - and here you get
this
GD plus cz okay so what you get is VD is
the initial data line voltage so this is
the difference the change in the data
line voltage after you have connected
after the data line after the cell is
connected to the data line okay
so VD + VC VD minus VC is the difference
initial difference between the data line
voltage and the cell voltage okay into
this CC by CD + CC all right now the
cell capacitance is usually much smaller
compared to the data line capacitance
okay some typical value would be for
example CC would be CC would be of the
order of say 40 femto farad whereas CD
would be of the order of say 1 Pico
farad alright so if you take that values
okay so and this VD minus VC okay
suppose you have initially charged the
data line to say 2.5 volts alright and
say
so basically BD minus VC so if VC is say
5 volts or zero volts the difference VD
minus VC is 2.5 volts so basically what
you have is CC by CD + CC CC is much
smaller than C D so this is 40 by 1 PF
is around 120 v okay so this Delta VD
under such situation will be almost
about 100 milli volts okay so what is
the situation initially what you have
done is you have charged this to 2.5
volt V DD by 2 okay and then you have
connected this cell okay irrespective of
whether the 0 is stored here or a 1 is
stored here okay the cell the data line
voltage is going to be VDD by 2 plus
minus 100 millivolts okay if this was a
zero is stored here it becomes VDD by 2
that is 2.5 it changes to 2 point 4
volts if
five it was charged to five volts it
would just go up to two point six volts
okay so you have to detect that very
small difference all right so it is very
difficult and the other thing is since
you are this cell is connected to this
data line okay
the cell voltage also becomes the same
okay so whatever is stored in the cell
is lost
okay initially whatever you are stored
okay whether a zero are stored or one
was stored now after you have read from
the cell it is it is no longer there
because if the voltage is become the
same as the data line voltage so
irrespective as zero or one does now
become very close to 2.5 volts so these
are the problems okay that is the data
line voltage change is very small and
number two while reading the memory the
contents of the memory is lost
okay all right so how do you overcome
these two problems so any reading
mechanism must be able to overcome these
problems okay so the way to do it is
basically again when you are reading
from the memory okay you have to have a
again mechanism like you are you are
detecting not the absolute value of the
voltage but a differential voltage okay
that is whether it goes for whether it
is increasing above 2.5 or going below
2.5 okay so at a mechanism of that sort
okay a differential voltage and also you
have to ensure that while you are
reading you also refresh the memory or
you basically of this call is you
rewrite into the memory okay that it is
also that is also necessary because the
reading mechanism must not spoil the
whatever is contained in the memory okay
so we shall just take up a daram circuit
which will do this
okay so basically you can consider it
like this you have what is the
pre-charge organism and then you have
memory cells large number of memory
cells like this okay this is these are
connected to the word lines what I am
drawing is just a column in the memory
okay so you have a sense amplifier okay
the sense amplifier is nothing but again
what you have is the back-to-back
inverters okay
in the flip-flop convict configurations
okay that is the output of one inverter
feeding as the input to the other
inverter okay so that is the this is
basically the sense amplifier okay then
you have sensing input here so this is
VDD say okay then you have control to
connect the data line to this sense
amplifier okay call this F F okay if it
stands for flip-flop and then again you
have another set of such cells
okay alright so this is say and these
are the another set of word line okay so
this is another pre-charged
voltage VP and this is the pre-charge
signal so the pre-charge signal okay and
then what you have is you have this is
the sense input here and then you will
have a sort of column this is column
select signal okay
I just put CS here okay here also
so this point is to be connected to the
there is a column line here okay this is
the so this point is connected to this
line and this is the another column
select ok ok now so basically what you
have is I just explained again so this
is one column of the memory ok this is
one column of the memory ok and this
these are the word lines so suppose you
have a 128 cells in a column okay so you
will have what you are doing is you are
dividing the column into two parts
okay so 64 cells on top and 64 cells at
the bottom okay so you have two halves
64 cells and 64 cells and this cell
which you see is just like the cell
which we have already seen okay now what
happens is first is you pre-charge these
data lines so you have two halves of the
data line now the one is the bottom half
and the other is the top half so you
first pre-charge this data line say to
VDD by 2 okay that is done through this
so this is the peachoid voltage okay
then the pre-charge signal comes both
the data lines are pre charged to VDD by
2 okay then what happens is this sense
of all these other signals okay the
sense is off initially and all this FF
is also off and the CS that is a column
select is also off okay all right now
what happens is one of the cell so
either you are selecting a cell in the
upper half or in the bottom half okay
only one word line can go high so if you
are selecting a cell in the upper half
that means all the cells in the bottom
half are not selected okay so say
suppose you have charged to 2.5 volts
this data line voltage at the bottom
half is going to remain at 2.5 volts now
if you are
but in the upper half if a one is stored
in that memory cell okay
this upper half data line voltage is
going to go up by say 100 millivolts as
we have seen okay so it is going to go
up to two point six volts okay so the
upper line data line upper half data
line voltage and the lower half data
line voltage there is going to be a
difference okay if a zero was stored
this may go down by 100 millivolts to
two point four volts okay now then what
you do is you energize this flip-flop
okay now these two pass transistors
there are two pass transistors here okay
they connect the data lines to this
sense amplifier okay these these are
pass transistors okay so what you do is
first you select the cell let the
differential voltage develop okay and
then you connect the the data line to
the sense amplifier as well as you
energize the sense amplifier by making
this transistor go high okay as long as
this sends input is low okay there is no
current flowing so this sense amplifier
is not it is not operational it is in a
you know there is no current flowing all
right so only when this transistor turns
on okay then the sense amplifier is
activated and then depending on the
difference in voltage look at these two
points okay
this sense amplifier is going to what
happened what is going to happen this
sense this the sense amplifier output is
going to go to one of the two stable
states okay so if the upper half voltage
is higher okay the upper line is going
to be pulled up all the way to five
volts and the lower voltage is going to
go down all the way to zero volts okay
because in that part of the
characteristics okay it is an inverter
because the gain is very high and they
are connected in which with positive
feedback okay so it is going to
and pull up one side to vdd and the
other side is going to be pulled down to
zero okay so and in the same process
what you are doing is since say suppose
you had selected one cell in the upper
half okay it had gone by up the upper
line voltage had gone up by 100
millivolts okay
now this line is going up to five volts
and basically what you are doing is you
are rewriting into that particular cell
so that cell itself is being written
back in two to five volts okay now if
this side had gone down by 100
millivolts or 2.4 volts what is going to
happen is this half the lower half is
going to go up to five volts the upper
half is going to go to zero so basically
you are writing back into that cell you
are writing a zero back into the that
particular cell the lower half no cell
is selected so it is not going to affect
the contents of any cell in the lower
half alright so what you are doing is
basically you are by the sense amplifier
it is doing two functions okay
one is it is that it is magnifying that
small difference in voltage so it is you
are going to have five volts on one side
and zero volt on the other side okay it
is amplifying the difference and also it
is rewriting okay into that particular
cell okay which was the which the
voltage of which was affected during the
reading mechanism alright
and then do you do the next thing okay
once you have developed that five volts
the zero volt difference okay there are
two transistors here so this is one
column line this line the two lines here
okay so you have a number of columns
situated like this and all the so this
is one particular column okay you have
so many similar columns okay with each
with a sense amplifier alright and then
what you do is this is a column select
okay so all of this columns will have
the input here okay so basically you are
selecting again you have a decoder the
output of the decoder is going to go to
this column select so basically you
select
one of the so many columns okay and only
one column is going to be output is
going to be connected to this output
line okay so this is the pass transistor
again so what this does is it connects
the output of the flip-flop okay or the
sense amplifier to the column line okay
so then once you have developed that
extra that large voltage difference you
connect it to the view you choose one
particular column okay through the Y
decoder and then that is connected to
the output lines okay so basically one
has to be careful in that there has to
be a proper sequencing of all this okay
first you select the particular cell in
a column okay let the difference small
difference develop okay then only you
energize the sense amplifier you should
not do that before because if you
energize the sense amplifier before what
is going to happen is it is going to go
to one of the two stable states okay and
then once it goes to one of the two
stable states okay a small voltage
difference of 100 millivolts is not
going to affect that stable state okay
so it is the first you have to develop
that small difference okay all right and
then you have to energize the sense
amplifier okay and then once you have
that you have energize the sense
amplifier the two voltage levels are
developed that is 5 volts and 0 volts
then only you do choose the particular
column okay but you don't choose the
column beforehand because if the column
capacitance if you choose it beforehand
the column is connected to the data line
and also the column capacitance will
come into picture all right okay which
is again going to affect the
differential voltage okay so once you
developed that 5 volts okay - zero volt
then only you connect that
particular column to this but to this
output line because this line also has a
large capacitance because all the
columns are sitting on that line okay so
that actually because you require
definite sequencing of operations it
makes the dynamic Ram comparatively
slower compared to the static Ram okay
so this is how you operate a dynamic Ram
okay as we said the dynamic Ram the
problem is you require to refresh the
memory from time to time okay so
obviously if you read from a particular
row so suppose you have energized this
particular first row zero zero okay
what is happening is you are in all the
columns okay the road zero is energized
okay and the row zero value is actually
read by the sense amplifier okay in all
the columns okay and and the sense
amplifier actually refreshes that memory
location okay but it may happen that you
know that when you are reading okay you
may not have read a particular row for a
long time okay so that cells okay all
the cells in that particular row if it
was charged to five volts if that
charges may go down okay and so you
actually have lost that whatever was
stored in that memory so you what you
have to do is deliberately you have to
refresh the memory location so how do
you do that you the way to refresh your
memory is by reading that memory okay
once you read a particular cell you
actually refresh that particular cell so
what you have to do is you have to
deliberately read every cell okay after
some interval of time okay and in that
process you basically refresh that
particular memory cell okay so in fact
what you do is once you say you read
that means you have to energize
sequentially all the rows one
to another okay once you do that okay
once you energize say row zero you on
all the columns you are actually
refreshing that particular cell
corresponding to row zero you know each
of the columns so if you have a square
array of n bits say okay so you have
root n times number of cells in each
column and you have root n times root n
number of columns so basically you
require root n refresh cycles to refresh
all the memory locations all right so
basically you have to read each row ok
energize each row ok so all the cells
are refreshed ok so that is how you
refresh the memory just by reading
McKenna alright so this is the
configuration for a dynamic Ram ok
normal MOS type dynamic Ram we shall now
just take up another example of a
dynamic Ram where which uses the BI CMOS
concept ok that is using a bipolar
transistors okay now obviously the
reason to use bipolar transistors is to
speed up operation okay I shall just
give a reference and we shall take up
the structure they have used ok let's
just see how it actually improves the
operation so it lets get zhukava and
others ok I Triple E again the same
journal Journal of solid state circuits
volume 25 number 5
Sage's 1100 to 211 11 October 1990 okay
alright so Keith soukara and others I
Triple E Journal of solid state circuits
volume 25 number five pages eleven
thousand eleven hundred and two to 1111
October 1990 so that is the reference I
will just this is a different way of
sensing I just give you how they do it
okay so what they have is again the cell
is quite similar okay do you have a
transistor and a capacitance okay and
then so this is the cell okay one
particular cell so again I'll draw the
column although it is a column no you
are drawing it like this okay so what
you have is each column will have a
sense amplifier again the sense
amplifier is the same sense amplifier
you have the CMOS sensor amplifier that
is to CMOS and inverters okay the output
of one going in as input to the other
okay and this outputs are connected here
alright so this is the sense amplifier
then so this is called the CMOS or sense
amplifier as well as the rewrite
amplifier okay basically it does two
functions it senses what is the voltage
in the cell and at the same time
rewrites back into the particular cell
then you have a pre-charge circuit okay
so
okay so this is the pre-charge circuit
so pre-charge circuit the function is to
pre charge the the two lines the bit
lines okay so this is the pre charge
voltage pypy okay
so these are two mas transistors okay so
when Phi P is high these two transistors
turn on okay and whatever is VP is
passed on to these two lines there is
another transistor which is basically
again connected across the lines and
when this is on it is there at the extra
transistor is there to equalize the
voltages between the two lines
okay just as acting as a sort of
connection between the two lines so that
it ensures that the two line voltages
are the same then you have the mechanism
for reading okay you have two
transistors here okay
all right so
these two lines carry the output of each
column okay so this is the y select line
y select okay then you have two more
lines this is for the writing mechanism
so you have two transistors sitting here
one is connected here that is connected
here so this is energized only when you
want to write into this cell so this is
right okay so this is the and function
of this and this okay
all right then you have the amplifier
which is used to amplify the signals
right signals so you have the basic
structure is like this you have two
bipolar transistors
okay this is a constant base voltage
here and then these two lines are
connected to the emitters of the two
transistors okay this is VDD so these
two go to the main amplifier okay now
this is the circuit I will explain okay
so this is as I said this is a
particular column okay this is a
particular column so you have so many
number columns all sitting on this set
of lines okay so you have all this
columns connected to this set of lines
and in each column okay on this column
you have a number of such cells okay I
have just shown one cell but you are
going to have a number of such shell as
such cells okay all right so what you do
is so this is the word line which
selects a particular cell suppose you
select this particular cell okay so what
happens is if you select this cell this
particular voltage on this line is going
to get affected okay this part of the
bit line so previously again just like
the previous circuit which we have
discussed we the line voltages are pre
charged to a particular value with this
help of this pre-charge circuit so this
pre-charge circuit okay using these
three transistors the pre charges the
two bit lines okay to a common voltage
say VDD by 2 okay now you select a
particular cell on this column okay and
what is going to happen this upper line
on this column is going to get voltage
is going to get affected so again as we
have seen this the voltage
friends is going to be pretty small okay
small voltage difference so this line
voltage may go up by 100 millivolts or
go down by 100 millivolts but it creates
a difference between the two between the
two bit lines then what you have to do
is you have to energize this sense
amplifier so basically you have the two
signals here is and Phi s Prime okay
connect it to this sense amplifier
obviously if Phi s is high and Phi s
prime is low okay then only the sense
amplifier is going to get activated if
it is the other way round okay then it
is not going to get activated okay it is
not operational okay so once it gets
activated okay so after you after this
creates a differential voltage small
differential voltage the sense amplifier
is activated which creates a large
difference in voltage between the two
lines okay and then what happens is so
this line voltages I am different now we
come to this part here okay so this what
is the structure here is the you have
two transistors here okay the gate of
these two transistors are connected to
the bit lines so what is going to happen
is on one of the transistors the gate
voltage is going to be very small less
than the threshold voltage the other
transistors the gate voltage is going to
be very high okay then you have these
two transistors these two transistors
act nothing and just like pass
transistors okay why is connected here
so it basically selects a particular
column so this is a column okay sitting
on these two lines okay so you have
different number of columns so only one
of the columns is connected to this
particular line okay suppose this column
is selected what is going to happen is
one of the one of since one of the
transistors is selected okay so what is
going to happen is see a current is
going to flow in one of these two lines
okay sorry that so it is a drain current
so it is going to flow the other way
okay so here so these are current
sources these are very small current
sources the 50 micro ampere current
sources
okay now the emitter current of this
transistor okay is what is it equal to
it is equal to this 50 micro ampere plus
the current flowing on that line so you
have two transistors here okay who has a
which has a common base voltage the base
voltage is the same VB okay which means
that the emitter voltage is almost
constant you see for a bipolar
transistor even with large change in
current okay the base to emitter voltage
difference is very small okay so what is
going to happen is suppose one of these
lines is going to is going to carry
current okay so one of that for one of
the bipolar transistors the current is
going to be 50 micro amperes for the
other bipolar transistors it is going to
be 50 micro ampere plus the current
which is drawn by the mass transistor
which is as may be as large as about 1
milli ampere okay so it is 50 micro
ampere and 1 milli ampere so that is the
emitter current of this bipolar
transistor so the emitter current is
almost equal to the collector current
there is a resistance here okay so the
one of these the drop across one of the
resistances is going to be very large
the other drop is going to be very small
so you get a differential voltage here
okay and this differential voltage is
fed to a main amplifier which is at
another you know bipolar and the
differential amplifier which is similar
to the structure which we have seen in
the case of static Ram okay so this is
how you detect this voltages now what is
the advantage of using a bipolar
transistor here the advantage here is
that although you get a large voltage
difference at the output you see the on
this on this line which
across which all that all the columns
are connected okay the voltage is going
to change by a very small amount okay
see this capacitance of this line okay
it's going to be very large because so
many columns are sitting on these lines
okay it is going to be very large
capacitance okay in fact for this
particular circuit goes about a Pico
farad capacitance
okay now this capacitance if you have to
charge it through a large voltage it
would take some time okay but here since
the emitter voltage of the bipolar
transistor is held almost constant okay
what you are sensing is basically a
current okay and so this line voltage
the voltage across this line is almost a
constant it is not changing okay all
right so the delay is going to be much
less okay if it was if it was a voltage
which you are sensing okay then what
would have happened is that voltage had
to go all the way you have to change
from 0 to 5 volts say then it would take
a long time because the line capacitance
had to be charged through that voltage
okay so here although you get a large
change in voltage at the output you see
across this line the voltage change is
minimal okay it is the VB whatever is
the VB of this voltage which is take of
this transistor it is changing that is
very small so the the because of that
okay it is going to be a much faster
mechanism all right
so by this way you can sense the what is
stored in that memory cell so that is
how you incorporate a bipolar transistor
okay to improve the speed of the dynamic
Ram also here this part of the circuit
is of course to write into that cell so
if you select Y and you select W that is
right okay whatever is on this lines
okay goes into the data line okay and
you can write into that memory cell so
this is the circuit for a dynamic Ram
okay so with a bipolar transistors
idea is still this almost the same again
you have to use a differential voltage
you cannot sense the actual voltage in
the dynamic Ram directly because once
you connect it to the bit line okay
creates a very marginal change in the
bit line voltages so you have to compare
it with another voltage the difference
in the two voltages are sensed you
require a sense amplifier to sense that
difference in voltage okay at the same
time to rewrite into the particular cell
okay and here the difference is just the
difference in mechanic in the reading
mechanism okay here you use a bipolar
transistor to sense the the the bit line
voltages once you have created that big
difference in the two bit line voltages
the bipolar transistor advantages with a
small you can have a large difference in
current okay having even in that case
the vbe difference is going to be
minimal okay so this you can actually
sense the current rather than the
voltage okay and the line voltage
changes by a very small amount on this
line okay which is may going to make it
much faster okay so that is how you can
with a help of a bipolar transistor you
can improve the speed of operation on a
dynamic Ram okay so with that we
conclude this discussion on dynamic Rams
you
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