Prof. Vojin G. Oklobdzija VLSI Prof. Vojin G. Oklobdzija References (used for creation of the presentation material): [1] Mead, Conway, “Introduction to VLSI Systems”, Addison Wesley Publishing. [2] Glasser, Dobberpuhl, “The Design and Analysis of VLSI Circuits”, Addison Wesley Publishing. [3] Weste, Eshraghian, “Principles of CMOS VLSI Design”, Addison Wesley Publishing. [4] Shoji, “CMOS Digital Circuits Technology”, Prentice Hall.

Prof. V.G. Oklobdzija: High-Performance System Design Historical Overview nMOS era: 1970-85 Pass-transistor design CMOS existed early but took off 1985 on Domino CMOS, 1982 NORA DCVSL CPL, DPL DCVS-PG SRPL LEAP SOI-CMOS Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. V.G. Oklobdzija: High-Performance System Design n-MOS Design Era 1970-85 LSI started with nMOS: pass-transistor design experience: Flourished at the beginning of the nMOS era (popularized by Mead-Conway book) Allows high density layout and compact design style Fast: outperforming gate based design Low in power Drawbacks: Not compatible with existing design tools Exhibiting testability and reliability problems Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. Vojin G. Oklobdzija Review of CMOS Prof. Vojin G. Oklobdzija

Prof. V.G. Oklobdzija: High-Performance System Design CMOS Basics Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. V.G. Oklobdzija: High-Performance System Design CMOS Basics Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. V.G. Oklobdzija: High-Performance System Design CMOS Basics Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. V.G. Oklobdzija: High-Performance System Design CMOS Basics A complex path example: Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. V.G. Oklobdzija: High-Performance System Design CMOS Basics More complex blocks are realizable in CMOS Primitive gates: Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. V.G. Oklobdzija: High-Performance System Design CMOS Deficiencies: Muli-Input NOR function in CMOS is slow Various remedies: Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

CMOS Deficiencies and Remedies Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

CMOS Deficiencies and Remedies Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. V.G. Oklobdzija: High-Performance System Design CMOS Basic Inverter Transfer function: Logic voltage levels are VOH and VOL and VIL and VIH The inverter transfer function lie within the shaded region Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

CMOS Basic: Inverter Characteristic Leakage Currents Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

CMOS Basic: Inverter Characteristic Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

CMOS Basic: Inverter Characteristic Transistors during the transition Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

CMOS Basic: Inverter Switching Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. V.G. Oklobdzija: High-Performance System Design CMOS Basic: Power During the static state there is no current Current is only present during transistion: Short circuit current (crow-bar current) Charging and discharging of the output capacitor Leakage Current Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. V.G. Oklobdzija: High-Performance System Design CMOS Basic: Power PCMOS=kCLV2DDfo This is an E=mc2 of low-power design There are three ways to control power: Reducing Power-Supply Voltage (most effective !!) Reducing the switching activity k (various ways) Reducing CL (technology scaling etc.) Reducing the required frequency of operation (?) Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. V.G. Oklobdzija: High-Performance System Design CMOS Basic: Delay Which one of the three designs is the fastest ? How can we find this out without simulation ? Learn about Logical Effort ! Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. V.G. Oklobdzija: High-Performance System Design CMOS Basic: Delay Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

CMOS Basic: Delay RND7Cin1+RNORCin2+RND2Cout Delay can be approximated with: RND7Cin1+RNORCin2+RND2Cout Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. V.G. Oklobdzija: High-Performance System Design CMOS Basic: Delay Delay of a signal path in CMOS logic is dependent on: Fan-in of a gate Represented as a resistance of the pull-up/down transistor path of the gate Fan-out of a gate Represented as a capacitive load at the output Number of CMOS blocks in the path. Wire delay connecting various blocks. Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. V.G. Oklobdzija: High-Performance System Design CMOS Basic: Delay Delay of a signal path in CMOS logic can be reduced by: Making the transistors larger in order to minimize resistance of a pull-up/down path in the gate Making the transistors smaller in order to minimize the capacitive load of each gate Reducing the number of CMOS blocks in the path. Bringing the blocks closer and/or choosing the less wire intensive topology. Note that these requirements are often contradictory Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. V.G. Oklobdzija: High-Performance System Design CMOS Basic: Delay How to estimate delay and critical timing in CMOS circuits ? How to determine the proper transistor sizing in order to make a compromise with contradicting requirements ? How to choose the right circuit topology ? The Answer: “Logical Effort” Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Pass-Transistor Design Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Pass-Transistor Design Another way of looking at Karnaugh Map: AND function Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Pass-Transistor Design Two-variable function Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Pass-Transistor Design “Threshold Voltage Drop” problem: Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Pass-Transistor Design Solving the “Threshold Voltage Drop” problem in CMOS: Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Pass-Transistor Design Function Generator Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Pass-Transistor Design Full 1-bit Adder Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Pass-Transistor Design Compact ALU Example (IBM PC/RT) Circ. 1984 Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Prof. V.G. Oklobdzija: High-Performance System Design Control Lines Output Control A - inputs B - inputs Odd Even Operation K1 K2 Qn A B Arithmetic A+B Add 1 A+B+1 A-B Subtract B-A B+1 Increment +1 2s compl A+1 Logical Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Pass-Transistor Design Compact ALU Example (IBM PC/RT) Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design

Using Pass-Transistor Design to Speed-up Addition Fall 2004 Prof. V.G. Oklobdzija: High-Performance System Design