### 2. VLSI Basic

```2. VLSI Basic
Hiroaki Kunieda
Dept. of Communication and Integrated Systems
Tokyo Institute of Technology
VLSI Design with Verification
Specification
System Design
System Verification
Logic Design
Logic Verification
Layout Design
Layout Verification
RTL
Netlist
Test Data
1.3 Logic Gate
Logic Gate
Class
Static Logic
CMOS Logic
Pseudo NMOS
Logic
NMOS Logic
Dynamic Logic
CMOS Domino
Logic
Characteristics
Logic Delay
Rise Time
Fall Time
Fan-in/ Fan-out
Power
Consumption
Ｌｏｇｉｃ Ｔｈｅｏｒｙ
[Completeness]
•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
Data sheet for 45nm Process
Parameter
Symbols
Data
Oxide Thickness
Tox
1.3 (1.7) nm
Unit MOS Capacitor
Cox
15.67 fF/um2
Gate Capacitor (W=250nm, L=25nm)
Cg
0.160 fF
Sheet registance
Rsheet
875 Ω/□
Relative permittivity
εr
2.3
Vacuum permittivity
ε0
8.85418782 pF/m
NMOS On current（L=35nm)
Ion(n)
1360uA/um
PMOS Off current (L=35nm)
Ion(p)
1070uA/um
Off leak current (L=35nm)
Ioff
100nA/um
Data sheet for 45nm Process
Parameter
Symbols
Data
Power Supply Voltage
VDD
1.0 V
Gain factor
K
7.81 uA/V2
Threshold voltage
Vth
0.4 V
Gate delay
Tau
10 psec
Unit on resistor (L=35nm)
Ro
220.6 Ω-um
Unit Capacitor (L=35nm)
Co
45.3 fF/um
Wire R
Rline
500 Ω/mm
Wire C
Cline
300 fF/mm
#layer for wire
#layer
12
MOS



“MOS” : sandwich structure 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


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
Linear region
Vds  Vgs  Vt
W
1 2
Id  k ' [(Vgs  Vt )Vds  Vds ]
L
2
Saturated region
Id 


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
Vds  Vgs  Vt
1 W
k ' [(Vgs  Vt ) 2 ]
2 L
Static Complementary Gates
VDD
Pullup network
(pMOS)
•output is
connected
to VDD
Ro/W
CoW
Ro/W
CoW
VSS
Pulldown network
(nMOS)
•Output is
connected
to VSS
Pull up
Pull down
Vin-Vout DC Characteristics
VOH
Noise Margin
NML = VIL-VOL
NMH = VOH-VIH
VIH
VOL
VIL
CMOS NAND & NOR
Pullup network (pMOS)
•output is connected to VDD
when ab=0.
VDD
VSS
Pulldown network (nMOS)
•Output is connected to VSS
when ab=1.
Relation between nMOS and pMOS
Dual graph
And Or Inverter (AOI) gate
(ab+c)’
si =aibici
=(aibi)ci
= Pici
ci+1=aici+bici+aibi=(aibi)ci+aibi =Pici+Gi
1.3 Gate Delay and
Wire Delay
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,
Ro/W
where Ro is the resistance per unit width. (ex. 200 Ωum）
Either one
Becomes
On.
CoW
Load capacitance consisting of drain junction capacitance is
corresponded by the area of the drain such as
CoW
where Co is the capacitance per unit width (ex. 50 fF/um)
Ro/W
Ro/W
CoW
Input capacitance is also represented by
CoW
L=35 nm=0.035 um (45nm)
Gate Delay
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)
CoW
Ro/W
Either one
Becomes
On.
= (Ro/W) x (CoW)
Ro/W
Ro/W
= Ro Co
CoW
CoW
Ro/W
= 200 Ωum ｘ 50 pF/um
CoW
Pull up
Pull down
= 10 psec
Pull up/down currents are represented by ON resistance,
which are reversely corresponded by the channel width W.
Either one
Becomes
On.
CoW1
Ro/W1
Either one
Becomes
On.
Ro/W1
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.
Ro/W2
Ro/W2
CoW2
CoW1 CoW2
Delay = 1st stage delay + 2nd stage delay
= (Ro/W1) (CoW1+CoW2) + (Ro/W2)(CoW2)
= RoCo (2+W2/W1)
= 10 psec x 3 = 30 psec
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
Delay = 10 psec (2+1+10) = 130.0 psec
Delay = 10 psec (2+3+3.33) =83.3 psec
Wires Delay
Elmore 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
Rline=2.0 Ω-um
Cline=0.3 fF/um
Ro=200 Ω*um
Co= 50 fF/um
W1=W2=0.35u
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 Delay
Rline=500 Ω/um
Cline=300 fF/um
Ro=25 kΩ*um
Co=0.5 fF/um
W1=W2=0.35u
Line=0.5um
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)
1.4 Flipflop and Memory
Switch Logic
Logic 0 transfer
Logic 1 transfer
Latch
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


tristate inverter produces restored output or HiImpedance Z
Used as latch circuit
Latch
D Flip-flop Operation
Scan in DFF
Functional Schematic of DFF with Scan
31
ACSEL Lab University of California,
Davis
Memory Structure
Random Access Memory (RAM)
Static RAM (SRAM)
Dynamic RAM (DRAM)
Static RAM Cell
•Precharge bit and bit’
•Asert Select line
•Write
•Bit and bit’ lines are set
to desired values.
•Select is set to 1.
RAM Ｃｅｌｌ

Write


set bit line


Precharge firstly bit
line
Activate word line
1.5 Data Path and
Control Circuit
Data Path 1
Control Sequential Logic Circuit
Data Path 2
0
1
2
3
4
5
6
7
DA1
DB1
*
DC1
DA2
DB2
*
DC2
1
0
0
0
1
0
0
0
RegA
*
DA1
DA1
DA1
DA1
DA2
DA2
DA2
0
1
0
0
0
1
0
0
RegB
*
*
DB1
DB1
DB1
DB1
DB2
DB2
0
0
1
0
0
0
1
0
RegC
*
*
*
DC1
DC1
DC1
DC1
DC2
BUS