Full custom design offers the highest performance and

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Full-custom design offers the highest performance and lowest part cost (smallest die size) for a given design The disadvantages of full-custom design include increased design time, complexity, design expense, and highest risk 4/2/18
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Microprocessors (strategic silicon) were exclusively full-custom, but designers are increasingly turning to semicustom ASIC techniques in this area as well Other examples of full-custom ICs or ASICs are requirements for high-voltage (automobile), analog/digital (communications), sensors and actuators, and memory (DRAM) 4/2/18 Full-Custom ASICs(HAND HELD) Contd….
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Standard-Cell-Based ASICs 4/2/18 A cell-based ASIC ( CBIC —“sea- bick”) Standard cells Possibly mega cells , mega functions , full-custom blocks , system-level macros( SLMs ), fixed blocks , cores , or Functional Standard Blocks ( FSBs ) All mask layers are customized - transistors and interconnect Automated buffer sizing, placement and routing Custom blocks can be embedded Manufacturing lead time is about eight weeks.
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Standard Cell Layout 4/2/18
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Standard Cell ASIC Routing A “wall” of standard cells forms a flexible block Metal2 may be used in a feedthrough cell to cross over cell rows that use metal1 for wiring Other wiring cells: spacer cells , row-end cells , and power cells 4/2/18
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Gate-Array-Based ASICs In a gate-array-based ASIC, the transistors are predefined on the silicon wafer The predefined pattern of transistors is called the base array The smallest element that is replicated to make the base array is called the base or primitive cell The top level interconnect between the transistors is defined by the designer in custom masks - Masked Gate Array (MGA) 4/2/18
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4/2/18 Design is performed by connecting predesigned and characterized logic cells from a library ( macros ) After validation, automatic placement and routing are typically used to convert the macro-based design into a layout on the ASIC using primitive cells Types of MGAs: Channeled Gate Array Channelless Gate Array Structured Gate Array
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Gate-Array-Based ASICs 4/2/18 Channeled Gate Array Only the interconnect is customized The interconnect uses predefined spaces between rows of base cells Manufacturing lead time is between two days and two weeks Channel less Gate Array There are no predefined areas set aside for routing - routing is over the top of the gate-array devices Achievable logic density is higher than for channeled gate arrays Manufacturing lead time is between two days and two weeks
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Gate-Array-Based ASICs (cont.) 4/2/18 Structured Gate Array Only the interconnect is customized Custom blocks (the same for each design) can be embedded These can be complete blocks such as a processor or memory array, or An array of different base cells better suited to implementing a specific function Manufacturing lead time is between two days and two weeks.
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Semi-Custom ASICs
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  • Fall '15
  • prasad
  • Logic, Transistor, Logic gate, Field-programmable gate array, Application-specific integrated circuit, logic cells

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