1、Ramaxel Technology LimitedRamaxel Technology LimitedConfidentialDRAMDRAM工作原理工作原理Ramaxel Technology LimitedRamaxel Technology LimitedConfidential Dynamic Random Access Memory Each cell is a capacitor+a transistor Very small size SRAM uses six transistors per cell Divided into banks,rows&columns Each
2、bank can be independently controlledDRAMRamaxel Technology LimitedRamaxel Technology LimitedConfidentialMain MemoryEverything that happens in the computer is resident in main memoryCapacity:around 100 Mbyte to 100 Gbyte Random access Typical access time is 10-100 nanosecondsWhy DRAM for Main Memory?
3、Cost effective(small chip area than SRAM)High Speed(than HDD,flash)High Density(Gbyte)Mass Production Main memoryRamaxel Technology LimitedRamaxel Technology LimitedConfidentialNotation:K,M,G In standard scientific nomenclature,the metricmodifiers K,M,and G to refer to factors of 1,000,1,000,000 and
4、 1,000,000,000 respectively.Computer engineers have adopted K as thesymbol for a factor of 1,024(210)K:1,024(210)M:1,048,576(220)G:1,073,741,824(230)DRAM density 256M-bit 512M-bitRamaxel Technology LimitedRamaxel Technology LimitedConfidentialDRAM DensityRamaxel Technology LimitedRamaxel Technology
5、LimitedConfidentialWhat is a DRAM?DRAM stands for Dynamic Random Access Memory.Random access refers to the ability to access any of the information within the DRAM in random order.Dynamic refers to temporary or transient data storage.Data stored in dynamic memories naturally decays over time.Therefo
6、re,DRAM need periodic refresh operation to prevent data loss.Ramaxel Technology LimitedRamaxel Technology LimitedConfidentialMemory:DRAM position Semiconductor memory device ROM:Non volatile Mask ROM EPROM EEPROM Flash NAND:low speed,high density NOR:high speed,low density RAM:Volatile DRAM:Dynamic
7、Random Access Memory SRAM:Static Random Access Memory Pseudo SRAMRamaxel Technology LimitedRamaxel Technology LimitedConfidentialDRAM Trend:Future High Speed-DDR(333MHz500MHz),DDR2(533800Mbps),DDR3(8001600Mbps)-Skew-delay minimized circuit/logic:post-charge logic,wave-pipelining-New Architecture:mul
8、ti-bank structure,high speed Interface Low Power-5.5V=3.3V(sdr)=2.5V(ddr)=1.8V(ddr2)=1.5v(ddr3)=1.2v?-Small voltage swing I/O interface:LVTTL to SSTL,open drain-Low Power DRAM(PASR,TCSR,DPD)High Density-Memory density:32MB=64MB=.1GB=2GB=4GB-application expansion:mobile,memory DB for shock(than HDD)-
9、Process shrink:145nm(03)=120nm(04)=100nm=90nm=80nm Other Trends-Cost Effectiveness,Technical Compatibility,Stability,Environment.ReliabilityRamaxel Technology LimitedRamaxel Technology LimitedConfidentialStatic RAM SRAM Basic storage element is a 4 or 6 transistor circuit which will hold a 1 or 0 as
10、 long as the system continues to receive power No need for a periodic refreshing signal or a clock Used in system cache Fastest memory,but expensiveSRAM ElementEnable Line/Bit LineBit LineRamaxel Technology LimitedRamaxel Technology LimitedConfidentialDynamic RAM DRAM Denser type of memory Made up o
11、f one-transistor(1-T)memory cell which consists of a single access transistor and a capacitor Cheaper than SRAM Used in main memory More complicated addressing schemeDRAM CellWord LineBit LineRamaxel Technology LimitedRamaxel Technology LimitedConfidentialRefresh in DRAMsCapacitor leaks over time,th
12、e DRAM must be“REFRESHED”.DRAM CellWord LineBit LineCapacitance LeakageRamaxel Technology LimitedRamaxel Technology LimitedConfidentialSRAM vs.DRAMRamaxel Technology LimitedRamaxel Technology LimitedConfidentialRamaxel Technology LimitedRamaxel Technology LimitedConfidentialDRAM Lead Frame and Wire
13、bondingRamaxel Technology LimitedRamaxel Technology LimitedConfidentialDRAM ArchitectureRamaxel Technology LimitedRamaxel Technology LimitedConfidential SDRAM has the multi bank architecture.Conventional DRAM was product that have single bank architecture.The bank is independent active.memory array
14、have independent internal data bus that have same width as external data bus.Every bank can be activating with interleaving manner.Another bank can be activated while 1st bank being accessed.(Burst read or write)Multi Bank ArchitectureRamaxel Technology LimitedRamaxel Technology LimitedConfidentialD
15、RAM Multi Bank ArchitectureRamaxel Technology LimitedRamaxel Technology LimitedConfidentialDRAM Single Bank ArchitectureRamaxel Technology LimitedRamaxel Technology LimitedConfidentialRamaxel Technology LimitedRamaxel Technology LimitedConfidentialDRAM Block Diagram(1)Ramaxel Technology LimitedRamax
16、el Technology LimitedConfidentialDRAM Block Diagram(2)Ramaxel Technology LimitedRamaxel Technology LimitedConfidentialDRAM Core ArchitectureRamaxel Technology LimitedRamaxel Technology LimitedConfidentialDRAM AddressRamaxel Technology LimitedRamaxel Technology LimitedConfidentialDRAM Core Architectu
17、reRamaxel Technology LimitedRamaxel Technology LimitedConfidential16bit DRAM CoreRamaxel Technology LimitedRamaxel Technology LimitedConfidentialDRAM Data PathRamaxel Technology LimitedRamaxel Technology LimitedConfidentialDRAM 1T-1C structureRamaxel Technology LimitedRamaxel Technology LimitedConfi
18、dentialuRAS:row address strobeuCAS:column address strobeuWE:write enableuAddress:code to select memory cell locationuDQ(I/O):bidirectional channel to transfer and receive datauDRAM cell:storage element to store binary data bituRefresh:the action to keep data from leakageuActive:sense data from DRAM
19、celluPre charge:standby stateDRAM Key wordRamaxel Technology LimitedRamaxel Technology LimitedConfidentialDRAM cell array consist of so many cells.One transistor&One capacitorSmall sense amplifierLow input gain from charge sharingCS:Small storage capacitor:25fFCBL:Large parasitic capacitor:over 100f
20、FVc:Storage voltageVCP:half Vc for plate biasVBLP:half Vc for BL pre charge bias(initial bias)DRAM CellRamaxel Technology LimitedRamaxel Technology LimitedConfidentialDRAM Array Overview Simplified ExampleBITLINE 0BITLINE 0#BITLINE 1BITLINE 1#BITLINE 2BITLINE 2#BITLINE 3BITLINE 3#ROW DECODERSELECTS
21、A SINGLE WORDLINECOLUMN MULTIPLEXER CONNECTS A SINGLE BITLINECOLUMNADDRESSROWADDRPRECHARGE CONTROL LINEWORDLINE 0WORDLINE 1WORDLINE 2WORDLINE 3DATA BITRamaxel Technology LimitedRamaxel Technology LimitedConfidentialActivating a Row Activating a Row Must be done before a read or write Just latch the
22、row address and turn on a single wordlineBITLINE 0BITLINE 0#BITLINE 1BITLINE 1#BITLINE 2BITLINE 2#BITLINE 3BITLINE 3#ROW DECODERSELECTS A SINGLE WORDLINECOLUMN MULTIPLEXER CONNECTS A SINGLE BITLINECOLUMNADDRESSROWADDRPRECHARGE CONTROL LINEWORDLINE 0WORDLINE 1WORDLINE 2WORDLINE 3DATA BITRamaxel Techn
23、ology LimitedRamaxel Technology LimitedConfidentialWriting Writing A row must be active Select the column address Drive the data through the column mux Stores the charge on a single capacitorBITLINE 0BITLINE 0#BITLINE 1BITLINE 1#BITLINE 2BITLINE 2#BITLINE 3BITLINE 3#ROW DECODERSELECTS A SINGLE WORDL
24、INECOLUMN MULTIPLEXER CONNECTS A SINGLE BITLINECOLUMNADDRESSROWADDRPRECHARGE CONTROL LINEWORDLINE 0WORDLINE 1WORDLINE 2WORDLINE 3DATA BITZEROONERamaxel Technology LimitedRamaxel Technology LimitedConfidentialReading Reading A row must be active Select the column address The value in the sense-amplif
25、ier is driven back outBITLINE 0BITLINE 0#BITLINE 1BITLINE 1#BITLINE 2BITLINE 2#BITLINE 3BITLINE 3#ROW DECODERSELECTS A SINGLE WORDLINECOLUMN MULTIPLEXER CONNECTS A SINGLE BITLINECOLUMNADDRESSROWADDRPRECHARGE CONTROL LINEWORDLINE 0WORDLINE 1WORDLINE 2WORDLINE 3DATA BITZEROONERamaxel Technology Limite
26、dRamaxel Technology LimitedConfidentialThe Sense-Amplifier Sense-Amplifier A pair of cross-coupled inverters Basically an SRAM element Weaker than the column mux Write data will“outmuscle”the sense-amplifier Keeps the data at full levelBITLINEBITLINE#WORDLINEPRECHARGE CONTROL LINERamaxel Technology
27、LimitedRamaxel Technology LimitedConfidentialPrechargePrecharge Inactive state(no wordlines active)Precharge control line high Ties the two sides of the sense-amp together This makes the bitlines stay at VDD/2 Only stable as long as the precharge control line is highotherwise this is unstable!No cap
28、acitors connectedBITLINEBITLINE#WORDLINEPRECHARGE CONTROL LINERamaxel Technology LimitedRamaxel Technology LimitedConfidentialActivation RevisitedActivation Turn off the precharge control line Makes the sense-amp unstableit wants to go to either 0 or 1 instead of staying at VDD/2 A very very very sh
29、ort time later,turn on the wordline of the row to be activated.Couples the capacitor onto the bitlines This“tips”the bitlines to hold the stored value.The sense-amp amplifies the capacitor back to full value.(hence the name!)BITLINEBITLINE#WORDLINEPRECHARGE CONTROL LINERamaxel Technology LimitedRama
30、xel Technology LimitedConfidentialDRAM Refresh Because the stored memory value is stored on a capacitor(that has resistive leakage),the memory is constantly“forgetting”its contents.Eventually,the charge on the capacitor wont be enough to tip the sense-amp in the right direction.But,activating a row
31、restores the cells on that row to their full value.There is an explicit refresh command that just activates and immediately deactivates a row.The DRAM has an internal counter that contains the next row to be refreshed and increments every time a refresh command is issued.Ramaxel Technology LimitedRa
32、maxel Technology LimitedConfidentialDRAM Refresh Data Retention Time DRAM Cell consists of capacitance which has leakage as time Retention time is period for maintaining its data especially 1 data Usually,DRAM Cell refresh period is 64ms Refresh Timing tREF:Real cell retention time(Device characteri
33、stic),ex)90ms(Hot)tRFC:Refresh command operating time,ex)75ns Refresh Spec.Burst Refresh:64ms Distribute refresh-128Mb device(12 Row address):64ms/4K=15.6us-256Mb device(13 Row address):64ms/8K=7.8usRamaxel Technology LimitedRamaxel Technology LimitedConfidentialAUTO Refresh When this command is inp
34、ut from the IDLE state,the synchronous DRAM starts autorefresh operation.During the auto-refresh operation,refresh address and bank select address are generated inside the Synchronous DRAM.For every auto-refresh cycle,the internal address counter is updated.Accordingly,8192times are required to refr
35、esh the entire memory.Before executing the auto-refresh command,all the bank must be IDLE state.In addition,since the Precharge for all bank is automatically performed after auto-refresh,no Precharge command is required after auto-refresh.Ramaxel Technology LimitedRamaxel Technology LimitedConfident
36、ialSelf Refresh Self-Refresh EntrySELF:When this command is input during the IDLE state,the Synchronous DRAM starts self-refresh operation.After the execution of this command,selfrefresh continues while CKE is Low.Since self-refresh is performed internally and automatically,external refresh operatio
37、ns are unnecessary.Self-Refresh ExitSELFX:When this command is executed during self-refresh mode,the Sync DRAM can exit from self-refresh mode.After exiting from self-refresh mode,the Sync DRAM enters the IDLE state.,no Precharge command is required after auto-refresh.Ramaxel Technology LimitedRamax
38、el Technology LimitedConfidentialMode Register Special command to initialize the DRAM Burst length Interleaving CAS Latency(read command to read data in clocks)For DDR,DLL reset is also hereRamaxel Technology LimitedRamaxel Technology LimitedConfidentialMRS Block DiagramRamaxel Technology LimitedRam
39、axel Technology LimitedConfidentialMode Register Because the stored memory value is stored on aRamaxel Technology LimitedRamaxel Technology LimitedConfidentialExtended Mode Register Special command to initialize DDR DRAM DDR onlydont use for SDR DLL Enable Drive StrengthRamaxel Technology LimitedRam
40、axel Technology LimitedConfidentialDRAM Interface Command Signals CAS#,RAS#,WE#,CS#CS#+CAS#=Read CS#+WE#+CAS#=Write CS#+RAS#+CAS#=Refresh CS#+RAS#=Activate CS#+WE#=Burst Stop CS#+WE#+RAS#=Precharge CS#+WE#+CAS#+RAS#=MRS or EMRS All others:NOP Other signals:CLK,DATA,DQSRamaxel Technology LimitedRamax
41、el Technology LimitedConfidentialDRAM Interface All signals go from the host to the memory except DQS and data which are bi-directional.Ramaxel Technology LimitedRamaxel Technology LimitedConfidentialRead Cycle Typical Read Cycle Burst Length 4 CAS Latency=3Setup TimeHold TimeCAS LatencyCLKCAS#DQSDA
42、TADQS delayed to simulate what the NV controller does.Ramaxel Technology LimitedRamaxel Technology LimitedConfidentialWrite Cycle Typical Write Cycle Burst Length 4 Write latency is always zeroSetup TimeHold TimeCLKCAS#DQSDATARamaxel Technology LimitedRamaxel Technology LimitedConfidentialData Clock
43、ing CLK is always driven by the host DQS is driven by whoever is driving the data NV chip drives on write cycles Memory chip drives on read cycles This scheme is called“source-synchronous clocking”Eliminates a lot of the timing headaches from SDR Adds marginRamaxel Technology LimitedRamaxel Technolo
44、gy LimitedConfidentialLatencies All kinds Activate to Precharge Last write data to precharge Activate to Read Activate to Write Refresh cycle time Refresh interval Minimum row active time Yadda yadda yadda Controlled by PFB_TIMING0,PFB_TIMING1,PFB_TIMING2Ramaxel Technology LimitedRamaxel Technology
45、LimitedConfidentialWrite CycleRamaxel Technology LimitedRamaxel Technology LimitedConfidentialDLLsA DLL is a Delay-Locked Loop No transistor can switch in zero time,so there will be a delay between clock and DQS on reads But,it would make it easier if DQS was always in phase with clock.DLL-off clock
46、-DQS delay not in the spec Varies between memory vendorsRe-creates a delayed version of its input clock Keeps DQS on reads aligned with clocks Its an analog circuit and is sensitive to noise Can lose lock on the input clock if the signal is not clean or the DLL power supply is noisy.Ramaxel Technolo
47、gy LimitedRamaxel Technology LimitedConfidentialDLLs DLL on DLL offCLKDQSDATACAS#CLKDQSDATACAS#DQS delayed to simulate what the NV controller does.DQS delayed to simulate what the NV controller does.Ramaxel Technology LimitedRamaxel Technology LimitedConfidential tAA,tAC,tOH tRCD,tRP Set-up/Hold tim
48、e Vih,Vil Voh,Vol Ioh,IolTiming ParametersRamaxel Technology LimitedRamaxel Technology LimitedConfidentialSDRAM Timing DiagramRamaxel Technology LimitedRamaxel Technology LimitedConfidentialtAA,tAC,tOH(SDRAM)Ramaxel Technology LimitedRamaxel Technology LimitedConfidentialSetup/hold time Timing for l
49、atching data in Input buffer CLK rising edge is strobe for data(SDRAM)DQS rising&falling edge is strobe for data(DDR SDRAM)During Setup&time,there is no abnormal signal allowedRamaxel Technology LimitedRamaxel Technology LimitedConfidentialVIH/VILRamaxel Technology LimitedRamaxel Technology LimitedConfidentialVOH/VOLRamaxel Technology LimitedRamaxel Technology LimitedConfidentialIOH/IOLRamaxel Technology LimitedRamaxel Technology LimitedConfidentialDC SpecRamaxel Technology LimitedRamaxel Technology LimitedConfidentialThanks!
