Lecture17

Lecture17 - ECE ECE 124A VLSI Principles Lecture 17...

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CE 124A ECE 124A LSI Principles VLSI Principles ecture 17 Lecture 17 Semiconductor Memory Design Prof. Kaustav Banerjee Electrical and Computer Engineering E-mail: kaustav@ece.ucsb.edu @ Lecture 17, ECE 124A, VLSI Principles Kaustav Banerjee
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Semiconductor Memories Lecture 17, ECE 124A, VLSI Principles Kaustav Banerjee
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Memory Design. .. Increasing number of transistors in uprocessors are devoted to cache memories….more than 60%, see ITRS for more details…. . At the system level: high-performance workstations and desktops have several Gbytes of memory Audio (MP3), Video players (MPEG4) and GPUs require large amount of memory Can we store Memory using registers? ….yes but the area required will be excessive (need > 10 transistors/bit) Memory cells are therefore combined into large arrays, hich minimizes the overhead caused by the peripheral which minimizes the overhead caused by the peripheral circuits and increases storage density Memory design can be classified as high-performance, high Lecture 17, ECE 124A, VLSI Principles Kaustav Banerjee density, low-power circuit design
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emory Classification Memory Classification Size Timing Parameters Function ccess Pattern Access Pattern Lecture 17, ECE 124A, VLSI Principles Kaustav Banerjee
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Memory Size eo y S e Depends on the level of abstraction Bits : (used by circuit designers) are equivalent to the number of individual cells (FFs or Registers) to store data Bytes : (used by chip designers) are groups of 8 or 9 bits or their multiples: Kbyte, Mbyte, Gbyte, byte Tbyte Words : (used by system designers) represent a basic computational entity. For example, a group of 32 bits represent a word in a computer that operates on 32 bit data Lecture 17, ECE 124A, VLSI Principles Kaustav Banerjee
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iming Parameters Timing Parameters EAD ccess Time time it takes to retrieve (read) READ-Access Time : time it takes to retrieve (read) from the memory. This is equal to the delay between the read request and the moment the data becomes available at the O/P. WRITE-Access Time : time elapsed between a write quest and the final writing of the input data into the request and the final writing of the input data into the memory CYCLE Time : minimum time required between successive reads or writes Lecture 17, ECE 124A, VLSI Principles Kaustav Banerjee
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Memory Timing: Definitions Read cycle rite cycle READ Write cycle Read access Read access WRITE Write access Data valid Data written DATA ote: Read and Write cycles do not necessarily have the same length but Lecture 17, ECE 124A, VLSI Principles Kaustav Banerjee Note: Read and Write cycles do not necessarily have the same length but are considered to be equal for simplicity of system design.
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Function uc t o Read-Only Memory ( ROM ): ncode the information into the circuit topology y removing or encode the information into the circuit topology-by removing or adding transistors. The topology is hard wired and the data cannot be modified….can only be read.
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Lecture17 - ECE ECE 124A VLSI Principles Lecture 17...

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