# Fully Complementary CMOS Networks Complex Gates by alicejenny

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```									EE 5900 Advanced
Algorithms for Robust

CMOS Combinational Gate
CMOS Combinational Circuits
   Implementation of logic gates and other structures using
CMOS technology.
   Basic element: transistor
   2 types of transistors:
   n-channel (nMOS) and p-channel (pMOS)
   Type depends on the semiconductor materials used to implement
the transistor.
   We want to model transistor behavior at the logic level in order
to study the behavior of CMOS circuits  view pMOS and nMOS
transistors as swithes.

6-Oct-12                      Combinational Logic                PJF - 2
CMOS transistors as Switches
3 terminals in CMOS transistors:
 G: Gate
 D: Drain
 S: Source

nMOS transistor/switch                          pMOS transistor/switch
X=1 switch closes (ON)                          X=1 switch opens (OFF)
X=0 switch opens (OFF)                          X=0 switch closes (ON)
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Networks of Switches
   Use switches to create networks that
represent CMOS logic circuits.
   To implement a function F, create a network
s.t. there is a path through the network
whenever F=1 and no path when F=0.
   Two basic structures:
     Transistors in Series
     Transistors in Parallel

6-Oct-12                      Combinational Logic   PJF - 4
Transistors in Series/Parallel
nMOS in Series                                nMOS in Parallel
a     a    Path between                         a         a     Path between
X              X:X    points a and b                                       points a and b
exists if both      X            Y                   exists if either
X:X   Y:Y
X and Y are 1                                        X or Y are 1
Y             Y:Y     X•Y                                                 X+Y
b     b                                         b         b

pMOS in Series                                pMOS in Parallel
a     a                                         a         a     Path between
Path between                                         points a and b
X             X:X’   points a and b
X            Y                   exists if either
exists if both                           X:X   Y:Y
X or Y are 0
X and Y are 0                                         X’+Y’
Y                     X’•Y’
Y:Y’
b         b
b     b

6-Oct-12                         Combinational Logic                            PJF - 5
Networks of Switches (cont.)
         In general:
1.     nMOS in series is used to implement AND logic
2.     pMOS in series is used to implement NOR logic
3.     nMOS in parallel is used to implement OR logic
4.     pMOS in parallel is used to implement NAND logic
         Observe that:
      1 is the complement of 3, and vice-versa
      2 is the complement of 4, and vice-versa

6-Oct-12                       Combinational Logic             PJF - 6
CMOS Inverter
+V

X         F = X’                   X             F = X’

Logic symbol

GRD
Transistor-level schematic

Operation:
 X=1  nMOS switch conducts (pMOS is open)
and draws from GRD  F=0
 X=0  pMOS switch conducts (nMOST is open)
and draws from +V  F=1
6-Oct-12                      Combinational Logic                      PJF - 7
Fully Complementary CMOS Networks
Basic Gates

6-Oct-12    Combinational Logic   PJF - 8
Fully Complementary CMOS
Complex Gates
Given a function F:
1.  First take the complement of F to form F’
2.  Implement F’ as an nMOS net and connect it to GRD
(pull-down net) and F.
3.  Find dual of F’, implement it as a pMOS net and
connect it to +V (pull-up net) and F.
4.  Connect switch inputs.

6-Oct-12              Combinational Logic        PJF - 9
Fully Complementary CMOS Networks
Complex Gates - Example

F = (A+B)(A+C’)
F’ = A’B’+A’C=A’(B’+C)

6-Oct-12                  Combinational Logic   PJF - 10

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