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CS/EE 3700 : Fundamentals of Digital System Design
Chris J. Myers
Lecture 3: Implementation Technology
Chapter 3
Logic value 1
Undefined
Logic value 0
Voltage
V DD
V 1,min
V 0,max
V SS (Gnd)
Figure 3.1 Logic values as voltage levels
Figure 3.2 NMOS transistor as a switch
Drain Source
x = "low" x = "high"
(a) A simple switch controlled by the input x
V D V S
(b) NMOS transistor
Gate
(c) Simplified symbol for an NMOS transistor
V G
Substrate (Body)
Figure 3.3 PMOS transistor as a switch
Gate
x = "high" x = "low"
(a) A switch with the opposite behavior of Figure 3.2 a
V G
V D V S
(b) PMOS transistor
(c) Simplified symbol for an PMOS transistor
V DD
Drain Source
Substrate (Body)
(a) NMOS transistor
V G
V D
V S = 0 V
V S = V DD
V D
V G
Closed switch whenV G =V DD
V D = 0 V
Open switch whenV G = 0 V
V D
Open switch whenV G =V DD
V D
V DD
Closed switch whenV G = 0 V
V D =V DD
V DD
(b) PMOS transistor
Figure 3.4 NMOS and PMOS transistors in logic circuits
(b) Simplified circuit diagram
V x
V f
V DD
x f
(c) Graphical symbols
x f
R
V x
V f
R +
-
(a) Circuit diagram
5 V
Figure 3.5 A NOT gate built using NMOS technology
Figure 3.6 NMOS realization of a NAND gate
V f
V DD
(a) Circuit
(c) Graphical symbols
(b) Truth table
f f
0 0 1 1
0 1 0 1
1 1 1 0
x 1 x 2 f
V x 2
V x 1
x 1
x 2
x 1
x 2
Figure 3.7 NMOS realization of a NOR gate
V x 1 V x 2
V f
V DD
(a) Circuit
(c) Graphical symbols
(b) Truth table
f
0
0
1
1
0
1
0
1
1
0
0
0
x 1 x 2 f
f x 1
x 2
x 1
x 2
Figure 3.8 NMOS realization of an AND gate
(a) Circuit
(c) Graphical symbols
(b) Truth table
f f
0 0 1 1
0 1 0 1
0 0 0 1
x 1 x 2 f
V f
V DD
A
V x 1
V x 2
x 1
x 2
x 1
x 2
V DD
Figure 3.9 NMOS realization of an OR gate
(a) Circuit
(c) Graphical symbols
(b) Truth table
f
0
0
1
1
0
1
0
1
0
1
1
1
x 1 x 2 f
f
V f
V DD
V x 2 V x 1
x 1
x 2
x 1
x 2
V DD
Figure 3.10 Structure of an NMOS circuit
V f
V DD
Pull-down network
V x 1
V x n
(PDN)
Figure 3.11 Structure of a CMOS circuit
V f
V DD
Pull-down network
Pull-up network
V x 1
V x n
(PUN)
(PDN)
Figure 3.12 CMOS realization of a NOT gate
(a) Circuit
V f
V DD
V x
(b) Truth table and transistor states
onoff
off on
1 0
0 1
f x
T 1
T 2
T 1 T 2
Figure 3.13 CMOS realization of a NAND gate
(a) Circuit
V f
V DD
(b) Truth table and transistor states
on
on
on
off
0
1 0
0
1
1
0
1
off
off
on
off
off
on
f
off
on
1
1
1
0
off
off on
on
V x 1
V x 2
T 1 T 2
T 3
T 4
x 1 x 2 T 1 T 2 T 3 T 4
(a) Circuit
V f
V DD
(b) Truth table and transistor states
on
on
on
off
0
1
0
0
1
1
0
1
off
off
on
off
off
on
f
off
on
1
0
0
0
off
off on
on
V x 1
V x 2
T 1
T 2
T 3 T 4
x 1 x 2 T 1 T 2 T 3 T 4
Figure 3.14 CMOS realization of a NOR gate
Figure 3.15 CMOS realization of an AND gate
V f
V DD
V x 1
V x 2
V DD
Figure 3.16 A CMOS complex gate
V f
V DD
V x 1
V x 2
V x 3
Figure 3.17 A CMOS complex gate
V f
V DD
V x 1
V x 2
V x 3
V x 4
Figure 3.18 Voltage levels in a CMOS circuit
(a) Circuit
V f
V DD
(b) Voltage levels
L
H
L
L
H
H
L
H
H
H
H
L
V x 1
V x 2
V x 1 V x 2
V f
Figure 3.19 Interpretation of voltage levels
(b) Positive logic truth table and gate symbol
f 0 0 1 1
0 1 0 1
1 1 1 0
x 1 x 2 f
x 1
x 2
(c) Negative logic truth table and gate symbol
1 1 0 0
1 0 1 0
0 0 0 1
x 1 x 2 f
f x 1
x 2
(a) Voltage levels
L H
L L H H
L H
H H H L
V x 1 V x 2
V f
Figure 3.20 Interpretation of voltage levels
(b) Positive logic
f 0 0 1 1
0 1 0 1
0 0 0 1
x 1 x 2 f
x 1
x 2
(c) Negative logic
1 1 0 0
1 0 1 0
1 1 1 0
x 1 x 2 f
f x 1
x 2
(a) Voltage levels
L H
L L H H
L H
L L L H
V x 1 V x 2
V f
Figure 3.43 a NMOS transistor when turned off
++++++++++ ++++++ +++ ++++++++++++ ++++++ ++++++
+++++++++ +++++++++ +++++++++++ +++++++++++
Drain (type n)Source (type n)
Substrate (type p)
SiO 2
(a) WhenV GS = 0 V, the transistor is off
V S
0 V =
V G
0 V =
V D
++++++
++++++++++++++++++
++++++++++ +++ ++++++++++++ ++++++
+++++++++ +++++++++++++++++++++ +++++++++++++++++
Channel (type n)
SiO 2
V DD
(b) WhenV GS = 5 V, the transistor is on
+++++++++
V D 0 V =
V G 5 V =
V S 0 V =
Figure 3.43 b NMOS transistor when turned on
Figure 3.44 Current-voltage relationship in the NMOS transistor
I
D
0
Triode
V DS
Saturation
V GS V T –
Figure 3.45 Voltage levels in the NMOS inverter
V DD
(b) V x = 5 V
I stat
R
R DS
V f V OL=
(a) NMOS NOT gate
V f
V DD
V x
Figure 3.46 Voltage transfer characteristics for the CMOS inverter
V f
V x
V OL 0 V =
V OH V DD=
V T V IL V IH V DD V T – V DD
V DD
2 —
Slope 1 – =
x f A
(a) A NOT gate driving another NOT gate
N 1 N 2
Figure 3.47 Parasitic capacitance in integrated circuits
(b) The capacitive load at node A
V f
V DD
V x
V DD
C
x f A
(a) A NOT gate driving another NOT gate
V A
N 1 N 2
Figure 3.48 Voltage waveforms for logic gates
Propagation delay
V DD
V DD
Gnd
Gnd
V x
V A
50% 50%
90%
Propagation delay
10%
t r
50%
90%
50%
10%
t f
Figure 3.49 Transistor sizes
+
+
(a) Small transistor
L
W 1
L
W 2
(b) Larger transistor
V DD
V x = 5 V
I stat
R
R DS
V f V OL= V f
V DD
V x
V f
V DD
V x
T 1
T 2
Figure 3.50 Dynamic current flow in CMOS circuits
VDD
Vf
Vx
IDVx
Vf
ID
(a) Current flow when input V x
changes from 0 V to 5 V
(b) Current flow when input V x
changes from 5 V to 0 V
Figure 3.51 Poor use of NMOS and PMOS transistors
(a) NMOS transistor
V DD
(b) PMOS transistor
V DD
A B
Figure 3.52 Poor implementation of a CMOS AND gate
(a) An AND gate circuit
V f
V DD
(b) Truth table and voltage levels
1.5 V 1.5 V
0 1
0 0 1 1
0 1
1.5 V 3.5 V
f
0 0 0 1
V x 1
V x 2
x 1 x 2 V f
Voltage Logic value
Logic value
Figure 3.53 High fan-in NMOS NAND gate
V f
V DD
V x 2
V x 1
V x 3
V x k
Figure 3.54 High fan-in NMOS NOR gate
x k
V f
V DD
V x 1 V x 2 V
Figure 3.55 The effect of fan-out on propagation delay
(b) Equivalent circuit for timing purposes
x f
(a) Inverter that drives n other inverters
To inputs ofn other inverters
To inputs ofn other inverters
C n
x V f
forn = 1 V f
forn = 4 V f
V DD
Gnd
Time0
(c) Propagation times for different values of n
N 1
Figure 3.56 A noninverting buffer
(a) Implementation of a buffer
V f
V DD
V x
x f
(b) Graphical symbol
Figure 3.57 Tri-state buffer
(b) Equivalent circuit
(c) Truth table
x f
e
(a) A tri-state buffer
0 0 1 1
0 1 0 1
Z Z 0 1
f e x
x f
e = 0
e = 1x f
f x
e
(d) Implementation
Figure 3.58 Four types of tri-state buffers
x f
e
(b)
x f
e
(a)
x f
e
(c)
x f
e
(d)
Figure 3.59 An application of tri-state buffers
f x 1
x 2
s
Figure 3.60 A transmission gate
(a) Circuit
f x
(b) Truth table
Z x
0 1
f s
s
s
s 0 =
s 1 =
x
x
f = Z
f = x
(c) Equivalent circuit (d) Graphical symbol
f x
s
s
Figure 3.61 a Exclusive-OR gate
(b) Graphical symbol(a) Truth table
0 0 1 1
0 1 0 1
0 1 1 0
x 1 x 2
x 1
x 2
f x 1 x 2 =
f x 1 x 2 =
(c) Sum-of-products implementation
f x 1 x 2 =
x 1
x 2
(d) CMOS implementation
x 1
x 2
f x 1 x 2 =
Figure 3.61 b CMOS Exclusive-OR gate
Figure 3.62 A 2-to-1 multiplexer built using transmission gates
x 1
x 2 f
s
Figure 3.21 A 7400-series chip
(a) Dual-inline package
(b) Structure of 7404 chip
V DD
Gnd
Figure 3.22 Implementation of f = x1x2 + x2x3
V DD
x 1 x 2 x 3
f
7404
7408 7432
Figure 3.23 The 74244 buffer chip
Pin 2
Pin 4
Pin 6
Pin 8
Pin 1
Pin 1
2
Pin 1
4
Pin 1
6
Pin 1
8
Pin 1
1
Pin 1
3
Pin 1
5
Pin 1
7
Pin 1
9
Pin 3
Pin 5
Pin 7
Pin 9
Figure 3.24 Programmable logic device as a black box
Logic gates and
programmableswitches
Inputs
(logic variables) Outputs
(logic functions)
Figure 3.25 General structure of a PLA
f 1
AND plane OR plane
Input buffers
inverters and
P 1
P k
f m
x 1 x 2 x n
x 1 x 1 x n x n
Figure 3.63 An example of a NOR-NOR PLA
VDD
VDD
VDD VDD VDD
S1
S2
S3
NOR plane
NOR plane
f1 f2
x1 x2 x3
Figure 3.26 Gate-level diagram of a PLA f1
P1
P2
f2
x1 x2 x3
OR plane
Programmable
AND plane
connections
P3
P4
Figure 3.27 Customary schematic of a PLA
f 1
P 1
P 2
f 2
x 1 x 2 x 3
OR plane
AND plane
P 3
P 4
V DD
V DD
V DD
S 1
S 2
S k
x 1 x 2 x n
(a) Programmable NOR-plane
= V e
(b) A programmable switch
V e
+++++++++
+ ++++++++++++++ +
(c) EEPROM transistor
Figure 3.65 A programmable version of a NOR-NOR PLAf1
S1
S2
f2
x1 x2 x3 NOR plane
NOR plane
S3
S4
x4
S5
S6
VDD
VDD
Figure 3.66 A NOR-NOR PLA used for sum-of-products f1
P1
P2
f2
x1 x2 x3 NOR plane
NOR plane
P3
P4
x4
P5
P6
VDD
VDD
Figure 3.28 An example of a PAL
f 1
P 1
P 2
f 2
x 1 x 2 x 3
AND plane
P 3
P 4
Figure 3.67 PAL programmed to implement two functions
f 2
P 1
P 2
x 1 x 2 x 3
NOR plane
P 3
P 4
x 4
P 5
P 6
V DD
f 1
Figure 3.29 Output circuitry
f 1
To AND plane
D Q
Clock
SelectEnable
Flip-flop
Figure 3.30 A PLD programming unit
Figure 3.31 A PLCC package with socket
Printed cir
cuit board
Figure 3.32 Structure of a CPLD
PAL-likeblock
I/O
blo
ck
PAL-likeblock
I/O b
lock
PAL-likeblock
I/O
blo
ck
PAL-likeblock
I/O b
lock
Interconnection wires
Figure 3.33 A section of a CPLD
D Q
D Q
D Q
PAL-like block (details not shown)
PAL-like block
Figure 3.34 CPLD packaging and programming
(a) CPLD in a Quad Flat Pack (QFP) package
Printed circuit board
To computer
(b) JTAG programming
Figure 3.35 Structure of an FPGA
Logic block Interconnection switches
I/O block
I/O block
I/O b
lock I/
O b
lock
Figure 3.36 A two-input lookup table
(a) Circuit for a two-input LUT
x 1
x 2
f
0/1
0/1
0/1
0/1
0
0
1
1
0
1
0
1
1
0
0
1
x 1 x 2
(b) f 1 x 1 x 2 x 1 x 2 + =
(c) Storage cell contents in the LUT
x 1
x 2
1
0
0
1
f 1
f 1
Figure 3.37 A three-input LUT
f
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
x 2
x 3
x 1
Figure 3.38 Inclusion of a flip-flop with a LUT
Out
D Q
Clock
Select
Flip-flop In1
In2
In3
LUT
Figure 3.39 A section of a programmed FPGA
0 1 0 0
0 1 1 1
0 0 0 1
x 1
x 2
x 2
x 3
f 1
f 2
f 1 f 2
f
x 1
x 2
x 3 f
Figure 3.68 Pass-transistor switches in FPGAs
1 0
V f 1
V A
0
0 0 0 1
x 1
x 2
f 1
SRAM SRAM SRAM
(to other wires)
Figure 3.69 Restoring a high voltage level
V DD
To logic block
1 SRAM
V A
V B
Custom Chips
• Created from scratch.
• Designer selects number, placement, and connections for each and every transistor.
• Are most dense and highest speed.
• Requires a substantial design effort.
• Used only when high performance and density is required: processors/memories.
Standard-Cell Chips
• Gates prebuilt and stored in a library.
• Gates needed for a design are selected and placed, and wires are routed between them.
• Standard-cell chips often called application specific integrated circuits (ASICs).
• Saves time since gates are reused.
• CAD tools exist to place and route gates.
Figure 3.40 A section of two rows in a standard-cell chip
f 1
f 2 x 1
x 3
x 2
Gate-Arrays
• Parts of chip are prefabricated (transistors).
• Parts of chip are custom fabricated (wires).
• Provides cost savings since all template wafers are identical.
• Many variants exist.
Figure 3.41 A sea-of-gates gate array
Figure 3.42 An example of a logic function in a gate array
f 1
x 1
x 3
x 2
Concluding Remarks
• Introduced basics of using transistors for digital logic.
• Described several types of IC chips:– Standard chips from the 7400 series.– Various types of PLDs.– Custom and semi-custom chips.
Figure P3.11 Circuit for problem 3.55
V f
V x 1
V x 2