Spezielle Anwendungen des VLSI Entwurfs Special applications of VLSI design

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Spezielle Anwendungen des VLSI Entwurfs
Special applications of VLSI design

• Course and contest
• Results of Phase II
• Jan Skodzik

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Summary of old design

• All coefficients used
• RCA in use
• No redundant number representation used

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Optimization step 1

• Getting better coefficients
• 2 Goals
• Reducing the non zeroes
• Trying to get equal coefficients

New coefficients
Only 4 coefficients left
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Optimization step 2

• Implement a proper adder
• ? Brent-Kung-Adder
• Compromise of area and speed
• Produce all carries before in a tree-in-tree
  structure
• Produce of the sum bits after

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Brent Kung Adder example
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Optimization step 3

• Using Carry Save Adders for the multiplications
  and additions
• Less logic
• Constant delay (independent to bit depths)
• Unconnected line of Full Adders
• The mulitpliers work with 31 bit Carry Save
  Adders
• The last Adder is a Brent Kung Adder for
  producing the last result

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Optimization step 4

• Pipelining
• Just the Brent Kung Adder is piped
• CSA logic is not piped

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Design Overview
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Results summary

• Old Runtime
• TOTAL COST 5NK
• Definition N (Runtime of RCA)

• New Runtime
• TOTAL COST Log2(N)/pipesteps
• N for the bit depth in the Brent Kung Adder

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Behavior
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Behavior (deeper look)
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Behavior (deeper look 2)