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2. VLSI Basic. Hiroaki Kunieda Dept. of Communication and Integrated Systems Tokyo Institute of Technology. VLSI Design with Verification. Specification. System Design. System Verification. RTL. Logic Design. Logic Verification. Netlist. Layout Design. Layout Verification. Mask Data

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2 vlsi basic

2. VLSI Basic

Hiroaki Kunieda

Dept. of Communication and Integrated Systems

Tokyo Institute of Technology

2 vlsi basic

VLSI Design with Verification


System Design

System Verification


Logic Design

Logic Verification


Layout Design

Layout Verification

Mask Data

Test Data

2 vlsi basic

Logic Theory


  • Function {|}=NAND function: complete

    • 1: a|(a|a) = a|a’ = 1

    • 0: {a|(a|a}|{a|(a|a)} = 1|1 = 0.

    • a’: a|a = a’.

    • ab: (a|b)|(a|b) = ab

    • a+b: (a|a)|(b|b) = a’|b’=a+b

  • NOR function: complete

  • AND and OR function: not complete

    [Irredundant] no literal can be removed.

    redundant Ab+ab’=a

2 vlsi basic

  • “MOS” : sandwichstructure of Metal, Oxide, and Silicon (semiconductor substrate).

  • The positive voltage on the polysilicon forms gate attracts the electron at the top of the channel.

  • The threshold voltage (Vt) collects enough electrons at the channel boundary to form an inversion layer (p -> n).

Field Oxide

Gate Oxide

Transistor parasitics
Transistor Parasitics

  • Cg: gate capacitance

    = 0.9fF/μm2 (2 μprocess)

  • Cgs/Cgd: source/drain overlap capacitance

    =Cox W (Cox: gate/bulk overlap capacitance)

A simple transistor model
A Simple Transistor Model

Linear region

Saturated region

  • nMOS transistor become on by applying high voltage to gate to provide current.

  • pMOS transistor becomes on by applying low voltage to gate to provide current

Static complementary gates
Static Complementary Gates


Pullup network (pMOS)

  • output is connected to VDD





Pulldown network (nMOS)

  • Output is connected to VSS

Pull down

Pull up


2 vlsi basic

Vin-Vout DC Characteristics


Noise Margin






2 vlsi basic


Pullup network (pMOS)

  • output is connected to VDD

    when ab=0.


Pulldown network (nMOS)

  • Output is connected to VSS

    when ab=1.



si =aibici =(aibi)ci = Pici

ci+1=aici+bici+aibi=(aibi)ci+aibi =Pici+Gi

Gate delay delay model
Gate Delay (delay model)

Let’s suppose that Wp = 2 Wn which makes the same pull up and pull down current with ON-resistance of,


where Ro is the resistance per unit width. (ex. 200Ωum)

Load capacitance consisting of drain junction capacitance is corresponded by the area of the drain such as


where Co is the capacitance per unit width (ex. 50 fF/um)

Input capacitance is also represented by


L=35 nm=0.035 um (45nm)

Gate delay
Gate Delay





Pull down

Pull up

Pull up current is represented by VDD/Ron(p).

Pull down current is represented by VDD/Ron(n)

Gate Delay

(W=0.35um, L=0.035um)

= (Ro/W) x (CoW)

= Ro Co

= 200 Ωum x 50pF/um


Pull up/downcurrents are represented by ON resistance,

which are reversely corresponded by the channel width W.

2 stage gates without load
2 stage gates without load

  • The first term represents the delay of the 1st stage, where the output charge and the input charge of the 2nd stage is pull up or down by the current driven by the 1st gate. Both charge and current corresponds to the size or the channel width w.

  • The second term represents the delay of the 2nd stage. Without any load to the gates, the delay becomes identical to, which depends on the process.

Delay = 1st stage delay + 2nd stage delay

= (Ro/W1) (CoW1+CoW2) + (Ro/W2)(CoW2)

= RoCo (2+W2/W1)

= 10 psec x 3 = 30 psec

2 stage gates with load
2 stage gates with load

Load Capacitance is total sum of input capacitance CoWload

Delay = 1st stage delay + 2nd stage delay

= (Ro/W1) (CoW1+CoW2) + (Ro/W2)(CoW2+CoWload)

= RoCo (2+W2/W1+Wload/W2)

Case 1. W2=W1, Load=10W1

Delay = 10 psec (2+1+10) = 130.0 psec

Case 2. W2=3W1, Load=10W1

Delay = 10 psec (2+3+3.33) =83.3 psec

Wires delay elmore delay model
Wires DelayElmore Delay Model

Delta1=r1 x (C1+---+Cn) =n tc

Delta2=r2 x (C2+----+Cn) =(n-1)tc

DeltaN=rn x Cn =tc

total=Delta1+ ----- + DeltaN

=[n(n+1)/2] tc

Wire delay
Wire Delay

Rline=2.0 Ω-um


Ro=200 Ω*um

Co= 50 fF/um


Line=2N um

Delay=(R0/W1) (CoW1+CoW2+ClineLine) +(RlineLine) (CoW2+(Cline/2)Line)

=200 x (2x50f + 2xN)+2 x (10f+0.5N)

= 50 nsec + 26*N nsec (line =2xN um)

Delay = Ro/W1 (CoW1+CoW2) =2.5K x 20fF =50.0 nsec (line=0)

Wire delay1
Wire Delay

Rline=500 Ω/um

Cline=300 fF/um

Ro=25 kΩ*um

Co=0.5 fF/um



Delay=(R0/W1) (CoW1+CoW2+ClineLine) +(Ro/W1+RlineLine) (CoW2+(Cline/2)Line)

=50K x (0.5 f + 50K x (0.25+0.125)

= 37.5 nsec + 18.8 nsec =56.3 nsec (line =0.5 um)

Delay = Ro/W1 (CoW1+CoW2) =50K x 0.5fF =25 nsec (line=0)

Switch logic
Switch Logic

Logic 0 transfer

Logic 1 transfer


Charge sharing: the stored data of A is

connected to the latch’s output. Additional

buffer may be required to drive output load.

Clocked inverter
Clocked Inverter

  • tristate inverter produces restored output or Hi-Impedance Z

  • Used as latch circuit

Scan in dff
Scan in DFF

Functional Schematic of DFF with Scan

ACSEL Lab University of California, Davis

Memory structure
Memory Structure

Read-Only Memory (ROM)

Random Access Memory (RAM)

Static RAM (SRAM)

Dynamic RAM (DRAM)

Static ram cell
Static RAMCell

  • Read

    • Precharge bit and bit’

    • Asert Select line

  • Write

    • Bit and bit’ lines are set to desired values.

    • Select is set to 1.

2 vlsi basic

RAM Cell

  • Write

    • set bit line

  • Read

    • Precharge firstly bit line

    • Activate word line

2 vlsi basic

1.5 Data Path and

Control Circuit

Data path 2
Data Path 2

During Clk=2, adder operation must

be completed within 1 clock.