transistor and gate

8/8/2019 Transistor and Gate

1/16

Transistor AND Gate

AND Gate

OR GateNAND

Gate

NOR Gate

Double

Transistor

NOR Gate

Single

Transistor

The use oftransistorsfor

the construction oflogic gatesdepends upon

their utility asfastswitches. When the

base-emitter diode is

turned on enough to be

driven intosaturation, thecollector voltage with

respect to ground may be

less than a volt and can beused as a logic 0 in

the TTL logic family.

Basic Gates

Index

Electronicsconcepts

Digital

Electronics

Reference

MimsDigital

Logic

Circuits

HyperPhysics*****Electricity and magnetismR

Nave

Go Back
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c2%23c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/transwitch.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/transwitch.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans2.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/logfam.html#c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/logfam.html#c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electric/eleref.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hph.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#c1http://history.go%28-1%29/http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c2%23c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c2%23c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/transwitch.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans2.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/logfam.html#c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electric/eleref.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hph.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#c1http://history.go%28-1%29/


2/16

Transistor OR Gate

AND Gate

OR GateNAND

Gate

NOR Gate

Double

Transistor

NOR Gate

Single

Transistor

The use oftransistors for


their utility asfast switches. When the


turned on enough to bedriven intosaturation, the

collector voltage with

respect to ground may beless than a volt and can be

used as a logic 0 in

theTTL logic family.

Basic Gates

Index

Electronicsconcepts

DigitalElectronics

ReferenceMims

Digital

Logic

Circuits


Nave

Go Back
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/transwitch.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans2.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/logfam.html#c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/logfam.html#c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electric/eleref.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hph.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#c1http://history.go%28-1%29/http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/transwitch.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans2.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/logfam.html#c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electric/eleref.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hph.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#c1http://history.go%28-1%29/


3/16

Transistor NAND Gate

AND Gate

OR GateNAND

Gate

NOR Gate

Double

Transistor

NOR Gate

Single

Transistor


the construction of

logicgates depends upontheir utility as

fast switches. When the

base-emitter diode isturned on enough to be

driven into saturation,

the collector voltage withrespect to ground may be

less than a volt and can

be used as a logic 0 in


Basic Gates

Index

Electronics

concepts

Digital

Electronics

ReferenceMims

Digital

LogicCircuits


Nave

Go Back

Transistor NOR Gate

AND Gate

OR Gate

NAND

Gate

NOR Gate

DoubleTransistor

NOR Gate

Single

Transistor



their utility as

fastswitches. When thebase-emitter diode is


driven intosaturation, thecollector voltage with


less than a volt and can beused as a logic 0 in

the TTL logic family.

Basic Gates

Index

Electronics

concepts

Digital

Electronics

Reference

Mims

DigitalLogic

Circuits
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c2%23c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/transwitch.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans2.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/logfam.html#c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/logfam.html#c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electric/eleref.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hph.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#c1http://history.go%28-1%29/http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c2%23c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/transwitch.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/transwitch.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans2.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/logfam.html#c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electric/eleref.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c2%23c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c2%23c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c2%23c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/transwitch.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans2.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/logfam.html#c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electric/eleref.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hph.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#c1http://history.go%28-1%29/http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c2%23c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/transwitch.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans2.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/logfam.html#c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electric/eleref.html#c1


4/16


Nave

Go Back

Transistor NOR Gate

AND Gate

OR Gate

NAND

Gate

NOR Gate

Double

Transistor

NOR Gate

Single

Transistor

The use oftransistors forthe construction of

logicgates depends upon

their utility asfast switches. When the



driven into saturation, thecollector voltage with


less than a volt and canbe used as a logic 0 in


Basic Gates

Index

Electronics

concepts

Digital

Electronics

Reference

MimsDigital

Logic

Circuits


Nave

Go Back
http://hyperphysics.phy-astr.gsu.edu/hbase/hph.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#c1http://history.go%28-1%29/http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c2%23c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/transwitch.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans2.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/logfam.html#c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/logfam.html#c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electric/eleref.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hph.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#c1http://history.go%28-1%29/http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c2%23c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/hph.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#c1http://history.go%28-1%29/http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c2%23c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html#c4%23c4http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/transwitch.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans2.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/logfam.html#c2http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/gate.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/digcktcon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electric/eleref.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/hph.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#c1http://history.go%28-1%29/


5/16

written byJonathan Dunder

Logic gates take binary values and perform

functions on them, similar to the functions found

in simple algebra. Binary algebra is the set of

mathematical laws that are valid for binary values.A binary value can only be a 1 or a 0. 1 is a high

value, representing true and high voltage. 0 is a

low value, representing a false value and low

voltage.
http://www.freeinfosociety.com/profile.php?id=1http://www.freeinfosociety.com/profile.php?id=1


6/16

Logic gates are typically packaged in integrated

circuits, although they can be constructed using

analogue components. Integrated circuits allow

multiple logic gates to be packaged in one chipand are usually quite reliable. Logic gates

typically come in two flavors, TTL (transistor-

transistor logic) and CMOS (Complementary Metal

Oxide Semiconductor). One must be careful

mixing the two types, there logic low and logic

high are different voltages. A CMOS might take a

TTL high as a LOW and a TTL will accept a CMOS

low as a high. Because of this they are generally

incompatible, but there are a few CMOS that can

accept TTL inputs and vice versa.

The buffer and NOT gates are the simplest of the

logic gates. The buffer would be used as a digital

signal booster, if a logic signal was to travel for

some distance voltage drop from wire resistance
http://www.freeinfosociety.com/media.php?id=781http://www.freeinfosociety.com/media.php?id=780


7/16

would lower a logic high voltage so low that when

it reaches its destination its read as a logic low,

putting this in between would solve that problem.

The buffer's algebra function is B = A.

NOT gates simply change the input from a 1 to a 0

or vice versa. It is also called an inverter and has

many uses in logic circuits. For example, you

have 2 lights, but you only want 1 on at any one

time, you would put a NOT gate between one light

so when there is a logic high input 1 light is onand the other connected to the NOT gate is off

and when there is a logic low input the second

comes on because of the NOT gate. The circle on

the end of the triangle indicates that its an

inverting gate and you can recognize any

inverting logic device by this circle.

The equivalent binary algebra function is B = A',

where B is the output and A is an input value.


8/16

The AND gate most commonly come in IC

packages of 2 and 3 input versions. The outputonly produces a logical 1 when all of the inputs

are 1. An AND gate could be used in an alarm

circuit, where input A would be a reed switch

input and B would be an armed control, So the

alarm would only be activated if the alarm was

active AND the reed switch was circuit was

opened (opened door ect.).

The equivalent binary algebra function is C = A * B

* ... * N, where C is the output and A and B are two

of N total inputs.


9/16

The OR gate has a minimum of two inputs and

produces an output of 1 if at least one of theinputs has a value of 1. An OR gate could be used

to expand the number of reed switches in the

previous example.

The equivalent binary algebra function is C = A +

B + ... + N, where C is the output and A and B are

two of N total inputs.
http://www.freeinfosociety.com/media.php?id=784


10/16

The NAND gate has a minimum of two inputs and

is the equivalent of an AND gate with a NOT gateon the output. It produces a 0 only if all of the

inputs are 1. A NAND gate could be used to

switch a device off if it gets too hot or a cooling

fan stops working, so a temperature sensor would

be connected to input A and a tachometer output

filtered so its a logical high when there is rotation

and logical low when there is no rotation, is

connected to input B. The equivalent binary

algebra function is C = (A * B * ... * N)', where C is

the output and A and B are two of N total inputs.


11/16

The NOR gate has a minimum of two inputs and is

the same as an OR gate with a NOT gate on theoutput. The NOR gate produces a 1 only if all of

the inputs are 0. The NOR gate can be used to

shutdown a device if either of 2 temperature

sensors measure a temperature too high for the

circuit.

The equivalent binary algebra function isF=(A+B+...+N)', where F is the output and A and B

are two of N total inputs.


12/16

The XOR aka EOR gate has a minimum of two

inputs. The NOR gate produces a 1 only if one ofthe inputs is a 1. The equivalent binary algebra

function is C = AB'+ A'B, where C is the output

and A and B are two inputs.

The XNOR aka ENOR gate has a minimum of twoinputs. The XNOR gate produces an output of 1 if

inputs A and B match. The most obvious

application for this logic gate is a comparator, this

could be used as error checking in data


13/16

transmission or it can form the basis of a

combination keypad. The equivalent binary

algebra function is C = AB + A'B', where C is the

output and A and B are two inputs.

Discrete logic gates

I often use discrete component implementations of logic gates in my projects,often consisting of AND and OR gates made from diodes and resistors. I"invented" or "discovered" how to make these gates when I was about 14 andhave been happily using them ever since.

The reason I use these gates is often to save space: if all I need is one ANDgate, for example to reset a counter, then I can easily implement it with 2 diodesand a resistor. It saves using a whole additional IC such as a 74HC08 containingfour AND gates, of which I only need one. At other times, it can be convenient tobe able to build a logic gate with as many inputs as I like. For example, a 7 inputOR-gate is easily implemented just by adding more diodes to the basic 2-input

gate. I might not have the IC's I would need in my junkbox, so I'd have to orderthem and wait for the delivery to arrive. But I'll always have resistors and diodes,so this is sometimes another reason for using logic gates made from discretecomponents.

There are disadvantages to these very simple logic gates too. The mostnoticeable is that the output current ability of the gates is low. It is determined bythe resistor used, and by the current handling ability of the signals driving the


14/16

gate inputs. If the discrete logicgate output is driving a highimpedance IC input such as arefound on the modern 74HC-series IC's, there is no problem.

The 0.7V voltage drop acrossthe diodes means that youcannot cascade the simplediscrete component logic gates,because you may easily violate

the input voltage logic level specifications of the IC's following the gate: thevoltage will fall below what is recognised as a "1" for example. Finally, thediscrete component implementations of logic gates might be slower than their"proper" IC equivalents. I do not currently know how much of a problem this islikely to be.

Now I'll try to explain the various types of gates which I commonly use.

OR gate

I'll start with this one because it is the easiest to understand. The easiest way tounderstand the operation of these gates is to consider the diode as a simpleswitch, which is closed (on) when the voltage on one side (the anode) is higherthan the other (the cathode). The current then flows in the direction of the arrowin the diode's circuit diagram symbol. In the diagram (right) I show the logicsymbol, my discrete component implementation, and the truth table. In an ORgate, the output is "1" (high) if either of the inputs are "1". In this diagram, if either

of the inputs has a "high" voltage, its diode will conduct and current will flow tothe output. A "high" voltage will develop across the resistor, equivalent to theinput voltage minus 0.7V drop, as is usual across silicon diode junctions. If bothof the inputs are low voltage "0", then the diodes don't conduct. In this instancethe gate's output is tied low by the 10K resistor.

AND gate

Now look at my AND gate. It's similar to the OR gate except that the diodes point

in the other direction, and the resistor goes to +5V not ground. The output of anAND gate is "1" only if BOTH the inputs are "1". In my diode-resistorimplementation, if either input is "low" voltage (logic "0") then the diode willconduct and the output is effectively shorted to ground. If both of the inputvoltages are "high" (logic "1") then neither of the diodes will conduct, so theoutput is not shorted to ground: it remains at +5V (logic "1") via the 10K resistor.This gives the desired result. Note that again, due to the silicon junction voltage,the actual "low" output voltage is 0.7V higher than the "low" input voltage.


15/16

NOT gate

(inverter)

You cannot implement an inverting function with diodes and resistors alone. Youalso now need a transistor, to provide the inverting action. There's nothingparticularly special about the transistor to be used, almost any small signal NPNtransistor will suit, since it's driven into saturation (unbiased). If the voltage

presented to the base of the transistor is above 0.7, the transistor will conductwhich drags the output to logic "0", low voltage. If the input voltage is logic "0",then the transistor does not conduct, and the resistor will just tie the output to+5V. You always need that 10K current limiting resistor in the base, or excessivebase-emitter current will destroy the transistor.

NAND and NOR gates

These are easy: just use AND or OR followed by a NOT (inverter). In the case ofthe NAND gate, the transistor's base resistor can be omitted since the maximumcurrent is already limited by the 10K resistor in the diode-resistor AND gate. Thebase resistor is still needed in a NOR gate.

XOR gate

This one is a little more complicated. If we start off imagining an OR gate, thatworks for the first three of the possible four states in the truth table. But not thefinal one, where both inputs are "1". So we need a way of forcing the output to

zero. I accomplised this using a transistor as a switch, with its base driven by anAND gate on the two inputs. So that when both inputs are "1", the AND gate willactivate the transistor, which will force the output to zero. So the XOR gate canbe considered as an OR gate, plus an AND gate, plus a switch to zero theoutput. The additional diode in the base lead of the transistor is to create anadditional 0.7V drop, without it the 0.7V of the AND gate output (even when oneof the inputs is zero) would be enough to put the transistor into partialconduction.


16/16

Signal gate

I like this one for gating incoming pulse trains. I use this circuit sometimes forfrequency counter inputs for example. In the example to the right, the pulse isonly allowed from IN to OUT when both the A and B inputs are "1". It's really justanother kind of AND gate I suppose, effectively having three inputs. But savesone diode compared to an AND-gate implementation as above. (Well, even a 2-input AND gate or OR gate can be reduced to a single resistor and a singlediode, in that case - but somehow I prefer the more balanced approach with twodiodes and a resistor). In the diagram to the right, the diodes could be reversedand the output would then be forced to "1" if either of A or B were a "1". Thiscould be useful to drive a negative edge triggered counter clock input, forexample.

Other notes

1. Gates with more than two inputs: Easy! Just add more diodes, one for eachinput!

2. The 10K resistor: I have shown 10K for the purposes of illustration only. Inreality resistance value needs to be chosen depending on the input resistance ofthe following circuit that needs to be driven by the output. It needs to be relativelysmall in comparison. If the gate is driving a single 4000-series CMOS or 74HC-series logic IC input, then the resistor could easily be made upwards of 100K or

even 1M, depending on the application.

transistor and gate

Documents