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Spezielle Anwendungen des VLSI – Entwurfs Applied VLSI Design

Spezielle Anwendungen des VLSI – Entwurfs Applied VLSI Design. Group 3: Hagen Fischer, Jacob Maxa Results of Phase 2: Optimization 22.11.2012. Institute MD, University of Rostock. Challenge. Improve the foreign VHDL design with regard to the metric Optimize the filter structure

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Spezielle Anwendungen des VLSI – Entwurfs Applied VLSI Design

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  1. Spezielle Anwendungen des VLSI – EntwurfsApplied VLSI Design Group 3: Hagen Fischer, Jacob Maxa Results of Phase 2: Optimization 22.11.2012 Institute MD, University of Rostock

  2. Challenge • Improve the foreign VHDL design with regard to the metric • Optimize the filter structure • Optimize the multiplier • Optimize the adder • Step 1: Changing the direct form from I to II • Critical path only one adder instead of 8 • All multiplications in parallel + + + + + + Direct form I Direct form II

  3. Filter – Shrinking and pipelining <7> <9> <9> SAT SXT x_in <15>/<10> <15>/<10> y_out <7> + + + + + + + + * Metric from Phase 1: 10,93234718 kHz/area

  4. Filter – Multiplier • Move the sign extension to the filter input • Create specialized multipliers for each coefficient • No coefficient input needed • Based on shift operation and addition with ripple carry adders • Wallace structure for internal adders • Only 10 variable bit size adders for all multipliers Sign ext. b3 b2 b1 b0 Multiplier Sign Multiplier Sign ext. Sign ext. XOR XOR

  5. Filter – Adder + • Tried various adders • Carry Skip Adder • Carry Save Adder • Ripple Carry Adder • also pipelined • Carry Lookahead Adder • Special Structures • Brent Kung Adder • Kogge Stone Adder • Ling Adder • Result for heuristic analysis for the best metric • Ripple Carry Adder for adders in multiplier component and in filter structure

  6. Filter – Term sharing <7> <9> <9> SAT SXT x_in_r <10> <10> y_out <7> + + + + + + + + • Possible due coefficient optimization • 0xF9, 0x02, 0x1E, 0x42, 0x53 (left to right) • Save 4 multiplier units and pipeline register

  7. Results • Improvement from phase 1: • Synthesis: 222,04 • Possible further improvements: • Critical path in adders • Combine partial products in the multiplayer stage within all multipliers

  8. End • Thanks for your attention! • Questions?

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