Memories II

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Memories II

• Dr. T.Y. Chang
• NTHU EE
• 2007.12.18

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Contents

• CAM
• FPGA
• Flash
• FRAM
• Ref. Book D.A. Hodges, H. G. Jackson, R. A.
  Saleh, "Analysis and Design of Digital Integrated
  Circuits," 3rd Ed., McGraw Hill, 2004. Chapter 9.

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Content-Addressable Memory

• Called Associative Memory
• Lookup Scheme
• Tag Previous stored keyword
• Store randomly
• SRAM architecture
• Used in Cache
• As Internet routing
• Table

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CAM Lookup Array

• ? Diff XOR1
• NMOS on
• Machi 0
• ? Same XOR0
• NMOS off
• Machii1 (precharged)
• Select only one or none row

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CAM Cell

• M7, M8, M9, M10
• XOR
• Compare (q, q) with (Tagline, Tagline)
• 20 to 30 gt Area of SRAM cell
• Taglines
• Must start low
• To avoid discharge in precharge phase

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SRAM Array in CAM

• Invalid rows if not fully used
• Timing is critical since Matchlines are initially
  all prechaged
• Write data same as SRAM operations except
  Tagelines start low

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Modified CAM Cell

• Improve Speed
• M7 or M9 on if Gate1
• GND passes and waits for Tagline signals
• In Original Cell
• Tagline signals arrive
• Then GND can passes

Original Cell
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Field-Programmable Gate Array

• Rapid Implementation
• Verify function but not timing
• Overall architecture
• Routing Channel
• I/O blocks
• PLBs

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FPGA Architecture
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PLB Structure
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PLB Structure Example
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Programmable Connections
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I/O Block
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Flash Memory

• NOR Structure
• Write Hot Carriers Injection
• Erase Fowler-Nordheim Tunneling

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Write and Erase
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Flash Read Operation
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NAND Flash
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FRAM

• Ferroelectric material
• Nonvolatile
• Destructive read-out
• Need write back similar to DRAM
• Drawback (not semiconductor memory)
• Cost, Speed, Size
• Advantages
• Less power
• high density/reliability

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FRAM

• Cap Perovskite Crystal be polarized in 2
  directions
• Loigc-1 Vcc
• Logic-0 ?Vcc

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Summary of Semiconductor Memories
Memory EPROM EEPROM Flash FRAM
Prog type HCI FN HCI/FN Polarize
Erase typ UV FN FN Polarize
Erase Res. Full Mem Bit/Byte Block Bit
Endurance Cycle 102 105 -106 106 1010-1012
Cell Size S L S S
Speed Fast Med Fast Fast
Power High Med Low Low