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Arithmetic Building Blocks
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A Generic Digital Processor
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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
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Bit-Sliced Design
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Full-Adder
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The Binary Adder
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Express Sum and Carry as a function of P, G, D
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The Ripple-Carry Adder
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Complimentary Static CMOS Full Adder
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Inversion Property
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Minimize Critical Path by Reducing Inverting Stages
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The better structure: the Mirror Adder
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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.
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Quasi-Clocked Adder
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NMOS-Only Pass Transistor Logic
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NP-CMOS Adder
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NP-CMOS Adder C o1 S 1 A 1 B 1 S A B C i0
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Manchester Carry Chain
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Sizing Manchester Carry Chain
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Carry-Bypass Adder
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Manchester-Carry Implementation
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Carry-Bypass Adder (cont.)
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Carry Ripple versus Carry Bypass
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Carry-Select Adder
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Carry Select Adder: Critical Path
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Linear Carry Select
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Square Root Carry Select
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Adder Delays - Comparison
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LookAhead - Basic Idea
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Look-Ahead: Topology
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Logarithmic Look-Ahead Adder
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Brent-Kung Adder
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The Binary Multiplication
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The Binary Multiplication
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The Array Multiplier
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The MxN Array Multiplier — Critical Path
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Carry-Save Multiplier
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Adder Cells in Array Multiplier
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Multiplier Floorplan
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Wallace-Tree Multiplier
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Multipliers —Summary
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The Binary Shifter
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The Barrel Shifter Area Dominated by Wiring
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4x4 barrel shifter Widthbarrel ~ 2 pm M
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Logarithmic Shifter
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0-7 bit Logarithmic Shifter
3 Out3 A 2 Out2 A 1 Out1 A Out0
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Design as a Trade-Off
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Layout Strategies for Bit-Sliced Datapaths
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Layout of Bit-sliced Datapaths
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Layout of Bit-sliced Datapaths
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