chap8_1 - Principles of VLSI Design Subsystem Design CMPE...

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Unformatted text preview: Principles of VLSI Design Subsystem Design CMPE 413 1 UMBC U M B C U N IV E R S I T Y O F M A R Y L A N D B A L T IM ORE COU NTY 1 9 6 6 Digital Device Components Asimpleprocessorillustratesmanyofthebasiccomponentsusedinanydig- ital system: Datapath: The core -- all other components are support units that store either the results of the datapath or determine what happens in the next cycle. Control Memory Datapath I n p u t-O u t p u t Principles of VLSI Design Subsystem Design CMPE 413 2 UMBC U M B C U N IV E R S I T Y O F M A R Y L A N D B A L T IM ORE COU NTY 1 9 6 6 Digital Device Components Memory: A broad range of classes exist determined by the way data is accessed: Read-Only vs. Read-Write Sequential vs. Random access Single-ported vs. Multi-ported access Or by their data retention characteristics: Dynamic vs. Static Stay tuned for a more extensive treatment of memories. Control: A FSM (sequential circuit) implemented using random logic, PLAs or memories. Interconnect and Input-Output: Parasitic resistance, capacitance and inductance affects performance of wires both on and off the chip. Growing die size increases the length of the on-chip interconnect, increasing the value of the parasitics. Principles of VLSI Design Subsystem Design CMPE 413 3 UMBC U M B C U N IV E R S I T Y O F M A R Y L A N D B A L T IM ORE COU NTY 1 9 6 6 Digital Device Components Datapath elements include adders, multipliers, shifters, BFUs, etc. The speed of these elements often dominates the overall system perfor- mance so optimization techniques are important. However, as we will see, the task is non-trivial since there are multiple equivalent logic and circuit topologies to choose from, each with adv./ disadv. in terms of speed, power and area. Also, optimizations focused at one design level, e.g., sizing transistors, leads to inferior designs. D a t a- I n R e g i s t e r s A d d e r S h i f t e r M u l t i p l e x e r D a t a-O u t Control Bit-sliced organization is common for datapaths. Bit 0 Bit 1 Bit 3 Bit 4 Bit 2 Principles of VLSI Design Subsystem Design CMPE 413 4 UMBC U M B C U N IV E R S I T Y O F M A R Y L A N D B A L T IM ORE COU NTY 1 9 6 6 Datapath Operators: Addition/Subtraction Lets start with addition, since it is a very common datapath element and often a speed-limiting element. Optimizations can be applied at the logic or circuit level. Logic-leveloptimizationtrytorearrangetheBooleanequationstoproduce a faster or smaller circuit, e.g. carry look-ahead adder. Circuit-leveloptimizationsmanipulatetransistorsizesandcircuittopology to optimize speed. Lets start with some basic definitions before considering optimizations: C i B A G(A.B) P(A+B)P(A + B)Sum C o 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 delete Carry status delete propagate propagate propagate propagate generate generate Principles of VLSI Design Subsystem Design CMPE 413 5 UMBC U M B C U N IV E R S I T Y O F M A R Y L A N D B A L T IM ORE...
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chap8_1 - Principles of VLSI Design Subsystem Design CMPE...

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