# Ch 3. Digital Circuits 3.1 Logic Signals and Gates (When N=1, 2 states)

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Ch 3. Digital Circuits 3.1 Logic Signals and Gates (When N=1, 2 states)

–Black-box representation and Truth table shows a logic circuit with input/output and ignores electrical behavior of the circuit Black-box Input Output

–AND gate produces 1 : Only if all of its inputs are 1 –OR gate produces 1 : One or more of its inputs are 1 –NOT gate produces an output that is opposite of its input value

–NAND Gate : Opposite of an AND gates output –NOR Gate : Opposite of an OR gates output

Black-box representationTruth table

–Timing diagram show how the circuit might respond to a time-varying pattern of input signals Lag Input Output

3.3 CMOS Logic Not expected to occur except during signal transition

High resistance : Off Transistor Low resistance : On Transistor NMOS PMOS

NMOS PMOS NMOS

CMOS inverter

On Z=1 On Z=0

PMOS NMOS PMOS NMOS PMOS NMOS

On Z=0 On Z=1

PMOS F NMOS F D F AND -> Series OR -> Parallel PMOS F NMOS F F = F A C A B B D C D

AND -> Series OR -> Parallel PMOS F NMOS F

Inverter + Inverter

NAND + Inverter More Transistors are needed than NAND

4x3+2 =14 Transistor 6 Transistor 4 Transistor 16 Transistor

4x3+2 =14 Transistor 6 Transistor 4 Transistor 6 Transistor 16 Transistor

3.4 Electrical Behavior of CMOS Circuits

3.5 CMOS Static Electrical Behavior Noise can be added in signals So, There are noise margins

High state Minimum value Low state Maximum value

Sink currentSource current

Pull-upPull-down

No Transition Time in ideal case (20% ~ 80%) (80% ~ 20%)

3.6 CMOS Dynamic Electrical Behavior Both the speed and the power consumption of a CMOS device depend to a large extent on AC device

High StateLow State

High State

50% Ideal case (No rise and fall times) Propagation delay

3.7 Other CMOS input and Output Structures

Open-drain output requires an external pull-up resistor

Increase because R=1.5K Pull-up Resistor

X Y W

Burn !

Low output must sink 0.4mA

In high state, typical open-drain outputs have a maximum leakage current 5uA and typical LS-TTL inputs require 20uA of a source current

3.8 CMOS Logic Families High-speed CMOSHigh-speed CMOS, TTL compatible

3.9 Low-Voltage CMOS Logic and Interfacing

Clamp overshoot Clamp diode To Clamp overshoot Clamp undershoot 0.6V -0.6V

G G S D S OFF S D G S D D

3.10 Bipolar Logic

AND

pnp

Diode AND Gate Output stage = Totem pole Phase Splitter

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