Digital Integrated Circuits A Design Perspective

Apresentação em tema: "Digital Integrated Circuits A Design Perspective"— Transcrição da apresentação:

1 Digital Integrated Circuits A Design Perspective
EE141 Digital Integrated Circuits A Design Perspective Jan M. Rabaey Anantha Chandrakasan Borivoje Nikolic Arithmetic Circuits January, 2003 (contém alterações feitas no âmbito da PSI-2452))

2 A Generic Digital Processor
EE141 A Generic Digital Processor

3 Building Blocks for Digital Architectures
EE141 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 An Intel Microprocessor
EE141 An Intel Microprocessor Itanium has 6 integer execution units like this

5 EE141 Bit-Sliced Design

6 EE141 Bit-Sliced Datapath

7 Itanium Integer Datapath
EE141 Itanium Integer Datapath Fetzer, Orton, ISSCC’02

8 EE141 Adders

9 EE141 Full-Adder

10 EE141 The Binary Adder

11 EE141 The Binary Adder Como é a implementação CMOS? Mãos à Obra !

12 Características da célula somador completo:
EE141 Características da célula somador completo: PMOS em série CL muito alta (em Cout) Inversor no caminho do carry A soma não é tão importante quanto o carry

13 The Ripple Carry-Adder
EE141 The Ripple Carry-Adder Como é a implementação CMOS? Esquematizar um somador de 4 bits e computar o caminho crítico (diagrama de atrasos)

14 The Ripple-Carry Adder
EE141 The Ripple-Carry Adder Worst case delay linear with the number of bits td = O(N) mais importante otimizar tcarry tadder = (N-1)tcarry + tsum Goal: Make the fastest possible carry path circuit

15 EE141 Inversion Property

16 Minimize Critical Path by Reducing Inverting Stages
EE141 Minimize Critical Path by Reducing Inverting Stages Exploit Inversion Property

17 Express Sum and Carry as a function of P, G, D
EE141 Express Sum and Carry as a function of P, G, D Define 3 new variable which ONLY depend on A, B Generate (G) = AB Propagate (P) = A  B Delete = A B Can also derive expressions for S and C based on D and P o Note that we will be sometimes using an alternate definition for Propagate (P) = A  B

18 EE141 Full-Adder P G D

19 CMOS Binary Adder with P and G
Generate (G) = AB Propagate (P) = A  B 28 transistors

20 A Better Structure: The Mirror Adder
EE141 A Better Structure: The Mirror Adder

21 EE141 The Mirror Adder The NMOS and PMOS chains are completely symmetrical. 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 Transmission Gate Full Adder
EE141 Transmission Gate Full Adder

23 Manchester Carry Gates
EE141 Manchester Carry Gates

24 Manchester Carry Chain
EE141 Manchester Carry Chain Tempo de propagação: tP = 0.69N(N+1)RC/2

25 EE141 Carry-Bypass Adder Also called Carry-Skip

26 Carry-Bypass Adder (cont.)
EE141 Carry-Bypass Adder (cont.) tadder = tsetup + Mtcarry + (N/M-1)tbypass + (M-1)tcarry + tsum

27 Carry Ripple versus Carry Bypass
EE141 Carry Ripple versus Carry Bypass

28 EE141 Carry-Select Adder

29 Carry Select Adder: Critical Path
EE141 Carry Select Adder: Critical Path

30 EE141 Linear Carry Select

31 Square Root Carry Select
EE141 Square Root Carry Select

32 Adder Delays - Comparison
EE141 Adder Delays - Comparison

33 EE141 Multipliers

34 EE141 Shifters

35 EE141 The Binary Shifter

36 EE141 The Barrel Shifter Area Dominated by Wiring

37 EE141 4x4 barrel shifter Widthbarrel ~ 2 pm M

38 EE141 Logarithmic Shifter

39 0-7 bit Logarithmic Shifter
EE141 0-7 bit Logarithmic Shifter A 3 Out3 A 2 Out2 A 1 Out1 A Out0

40 EE141 Conclusões Existem muitos módulos funcionais de processadores que podem ser descritos através de “geradores de módulos”. Mas, não todos. Exemplos: somadores, shifters, memórias, multiplicadores, registrador de deslocamento, multiplexadores, Estes módulos podem ser disponibilizados de duas formas: módulos hard do tipo bit-slice (leiaute pré- determinado) ou módulos soft através de descrições comportamentais utilizando o comando generate. Ambos permitem acelerar o projeto de CI´s complexos