Assignment 1 - Solution 1 - CMOS NOR Gate Logic

Oct 29, 2026

Transistor-level CMOS design tasks covering combinational logic implementation. The material includes constructing a transistor schematic for a 4-input NOR gate by deriving the truth table and mapping logic behavior to NMOS and PMOS connectivity. It also discusses how output states follow from series/parallel device behavior, distinguishing cases where inputs are all low versus when any input is high. Additional exercises combine CMOS gates to realize logic functions such as buffers, XOR, and related multi-input expressions.

LanguageEnglish

CategoryExam

FormatPDF

Pages15

Reading Time38 min

AccessFree to download

Sketch transistor-level CMOS for a 4-input NOR gate

Truth table analysis and device connectivity

CMOS gate combinations for logic functions

Buffer and XOR construction

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1.5 Sketch a transistor-level schematic for a CMOS 4-input NOR gate
the truth table for a 4-input NOR gate.

W X Y Z OUT 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1 0 0 1 0 0 0 0 1 0 1 0 0 1 1 0 0 0 1 1 1 0 1 0 0 0 0 1 0 0 1 0 1 0 1 0 0 1 0 1 1 0 1 1 0 0 0 1 1 0 1 0 1 1 1 0 0 1 1 1 1 0
Figure 1: Truth table for 4-input NOR gate.
Observe from the truth table that the output is high when all of the input are low and that the output is low when at least one of the inputs is high. This means that in the transistor schematic, the PMOS transistors must be in series and the NMOS transistors must be in

Observe from the schematic that when all of the inputs are low the 4 NMOS transistors areturned off so there is connection between the output and ground. The 4 PMOS transistorson the other hand will all be on so the output will get pulled up to . If one of the inputs is | | | | | | | | | | | | | | | | | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | | | | | | | | | | | | | | | | |
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+ AB (XNOR)
d) Y = AB + BC + AC (majority)
(a)
For the buffer we can just have two invertors in series so the following gate level schematic accomplishes the buffer.
(b)
For the given logic function, we
have A and the inverse of B ANDed and this is ORed with the AND of A inverse and B. Therefore the following gate level schematic accomplishes this logic function.

(c)
For the given logic function, we have A inverse and B inverse ANDed and this is ORed with the AND of A and B. Therefore the following gate level schematic accomplishes this logic function.
high then the output cannot get pulled up to ; instead one of the NMOS transistors will be turned on and the output will be pulled down to ground. Therefore this schematic acts exactly like a 4 input NOR gate.
1.7 Use a combination of CMOS gates (represented by their symbols) to generate the following functions from A, B, and C.
a) Y = A (buffer)
b) Y = A􀡮
+ 􀡭
B (XOR)
c) Y = 􀡭
􀡮
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FAQs

How is the truth table used to design a 4-input CMOS NOR gate?

The truth table shows the output is high only when all inputs are low and low when at least one input is high. This guides NMOS series/PMOS series placement to enforce the correct pull-up and pull-down behavior.

What transistor connectivity ensures the correct output for the 4-input NOR gate when all inputs are low?

When all inputs are low, the NMOS stack is turned off, disconnecting the output from ground. At the same time, the PMOS network conducts, pulling the output up.

How do you implement logic functions like a buffer or XOR using CMOS gates?

A buffer can be built from cascaded inverters, while XOR can be constructed from combinations of AND/OR structures using inverted inputs. The gate-level schematics follow the given Boolean expressions.

Oct 29, 2026

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