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Numeric representation

Numeric representation

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Numeric representation

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  1. Numeric representation • Floating point: exponent+mantissa • Floating = data dependent • Larger dynamic range (largest/smallest) • More expensive • Fixed point: n-bits • Scaling factor = position binary point • Fixed = defined in the program

  2. Numeric representation

  3. Numeric representation • One’s complement • Negative num = bit_inverse(positive num) • Two’s complement • Negative num = bit_inverse(positive num) + 1 • Conversion to more bits via sign extension • E.g. 6 = 011 = 0011 = 00011 … • E.g. –6 = 101 = 1101 = 11101 … • Temporary overflow 1 0 1 1 1 -24 23 22 21 20

  4. Temporary overflow

  5. Integer, fractional and scaling Integer Fractional 1 0 1 1 1 1 0 1 1 1 Binary point -20 2-1 2-2 2-3 -24 23 22 21 20 2-4 -2(n-1)  x  2(n-1) -1 range -1 x  1-2-(n-1) Scaling is chosing dependent on the signal range

  6. Numeric representation: scaling • integer and fractional numbers are a special case of fixed point • fix <p,q> (ART designer & SystemC) p q 1 0 1 -19/8 = -2.375 1 1 1 fix <8,3> 1 0 -24 23 22 2-2 21 20 2-1 2-3 Scale factor 1/8 negative weight 2’s complement quantization error Same alu handles fix <8,1>, fix <8,2>, fix <8,3>, ... if q=0 then integer e.g. int <8,0> if q=p-1 then fractional e.g. int <8,7>

  7. Fixed point: addition -19/8 Int <8,3> 1 1 1 0 1 1 1 0 Int <8,4> 97/16 1 0 1 0 0 1 0 0 59/16 0 0 1 1 1 0 1 0 1

  8. Fixed point: multiplication -19/8 1 1 1 0 1 1 Int <8,3> 1 0 Int <8,4> 97/16 1 0 1 0 0 1 0 0 -1843/128 1 1 1 0 1 1 1 0 0 0 1 1 1 0 1 0

  9. Arithmetic Building Blocks

  10. A Generic Digital Processor

  11. Building Blocks for Digital Architectures Arithmetic unit Bit-sliced datapath adder - ( , multiplier, shifter, comparator, etc.) Memory - RAM, ROM, Buffers, Shift registers Control - Finite state machine (PLA, random logic.) - Counters Interconnect - Switches - Arbiters - Bus

  12. Bit-Sliced Design

  13. Full-Adder

  14. The Binary Adder

  15. Express Sum and Carry as a function of P, G, D

  16. The Ripple-Carry Adder

  17. Complimentary Static CMOS Full Adder

  18. Inversion Property

  19. Minimize Critical Path by Reducing Inverting Stages

  20. The better structure: the Mirror Adder

  21. The Mirror Adder • The NMOS and PMOS chains are completely symmetrical. This guarantees identical rising and falling transitions if the NMOS and PMOS devices are properly sized. A maximum of two series transistors can be observed in the carry-generation circuitry. • When laying out the cell, the most critical issue is the minimization of the capacitance at node Co. The reduction of the diffusion capacitances is particularly important. • The capacitance at node Co is composed of four diffusion capacitances, two internal gate capacitances, and six gate capacitances in the connecting adder cell . • The transistors connected to Ci are placed closest to the output. • Only the transistors in the carry stage have to be optimized for optimal speed. All transistors in the sum stage can be minimal size.

  22. Quasi-Clocked Adder

  23. NMOS-Only Pass Transistor Logic

  24. NP-CMOS Adder

  25. NP-CMOS Adder C o1 S 1 A 1 B 1 S 0 A 0 B 0 C i0

  26. Manchester Carry Chain

  27. Sizing Manchester Carry Chain

  28. Carry-Bypass Adder

  29. Manchester-Carry Implementation

  30. Carry-Bypass Adder (cont.)

  31. Carry Ripple versus Carry Bypass

  32. Carry-Select Adder

  33. Carry Select Adder: Critical Path

  34. Linear Carry Select

  35. Square Root Carry Select

  36. Adder Delays - Comparison

  37. LookAhead - Basic Idea

  38. Look-Ahead: Topology

  39. Logarithmic Look-Ahead Adder

  40. Brent-Kung Adder

  41. The Binary Multiplication

  42. The Binary Multiplication

  43. The Array Multiplier

  44. The MxN Array Multiplier— Critical Path Critical Path 1 & 2

  45. Carry-Save Multiplier

  46. Adder Cells in Array Multiplier

  47. Multiplier Floorplan

  48. Wallace-Tree Multiplier

  49. Multipliers —Summary

  50. The Binary Shifter