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Arithmetic Building Blocks

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Presentation on theme: "Arithmetic Building Blocks"— Presentation transcript:

1 Arithmetic Building Blocks

2 A Generic Digital Processor

3 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

4 Bit-Sliced Design

5 Full-Adder

6 The Binary Adder

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

8 The Ripple-Carry Adder

9 Complimentary Static CMOS Full Adder

10 Inversion Property

11 Minimize Critical Path by Reducing Inverting Stages

12 The better structure: the Mirror Adder

13 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.

14 Quasi-Clocked Adder

15 NMOS-Only Pass Transistor Logic

16 NP-CMOS Adder

17 NP-CMOS Adder C o1 S 1 A 1 B 1 S A B C i0

18 Manchester Carry Chain

19 Sizing Manchester Carry Chain

20 Carry-Bypass Adder

21 Manchester-Carry Implementation

22 Carry-Bypass Adder (cont.)

23 Carry Ripple versus Carry Bypass

24 Carry-Select Adder

25 Carry Select Adder: Critical Path

26 Linear Carry Select

27 Square Root Carry Select

28 Adder Delays - Comparison

29 LookAhead - Basic Idea

30 Look-Ahead: Topology

31 Logarithmic Look-Ahead Adder

32 Brent-Kung Adder

33 The Binary Multiplication

34 The Binary Multiplication

35 The Array Multiplier

36 The MxN Array Multiplier — Critical Path

37 Carry-Save Multiplier

38 Adder Cells in Array Multiplier

39 Multiplier Floorplan

40 Wallace-Tree Multiplier

41 Multipliers —Summary

42 The Binary Shifter

43 The Barrel Shifter Area Dominated by Wiring

44 4x4 barrel shifter Widthbarrel ~ 2 pm M

45 Logarithmic Shifter

46 0-7 bit Logarithmic Shifter
3 Out3 A 2 Out2 A 1 Out1 A Out0

47 Design as a Trade-Off

48 Layout Strategies for Bit-Sliced Datapaths

49 Layout of Bit-sliced Datapaths

50 Layout of Bit-sliced Datapaths


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