Multiplexers and DeMultiplexers

Summary

This video script offers an insightful explanation of multiplexers and demultiplexers, essential components in digital signal processing. A multiplexer (MUX) is a digital switch that consolidates multiple inputs into a single output, allowing users to select the desired input source for an output device, such as a stereo system. Conversely, a demultiplexer (DEMUX) takes a single input and routes it to one of several outputs, useful for devices like printers. The script delves into the symbols and functions of these components, their practical applications in home electronics, and how they work in tandem. It also provides a detailed look at the internal circuitry of these devices, built from basic logic gates, and their configurations in simulation software, highlighting the enable pins and inverted outputs.

Takeaways

• 🔌 A multiplexer (MUX) is a digital switch that allows multiple inputs to be selected and sent to a single output.
• 🎧 Common uses for multiplexers include routing audio from various sources like MP3 players, laptops, and satellite boxes to a single output device like speakers.
• 🔄 The opposite of a multiplexer is a demultiplexer (DEMUX), which takes a single input and routes it to multiple outputs, such as printing a document to various devices like printers or fax machines.
• 🔗 Multiplexers and demultiplexers often work together, with the former combining multiple inputs into one signal for transmission and the latter routing that signal to the correct output.
• 📊 The number of inputs or outputs in a multiplexer or demultiplexer is always a power of 2 (e.g., 2, 4, 8, 16), requiring a corresponding number of selector inputs to determine the active path.
• ⚙️ Internally, multiplexers are constructed using basic logic gates like AND, OR, and NOT gates, with the specific configuration depending on the number of inputs and outputs.
• 🛠️ To select a specific input in a multiplexer, the selector inputs are set to enable the corresponding logic path, allowing the desired input signal to pass through to the output.
• 🔄 In a demultiplexer, the process is reversed; selector inputs determine which output path is enabled, allowing the single input signal to be routed to the desired output.
• 💡 The concept of multiplexing is essential for efficient data transmission, as it allows multiple signals to be sent over a single communication line, reducing the need for physical wiring.
• 📚 Understanding the operation of multiplexers and demultiplexers is fundamental to grasping digital communication systems and their applications in everyday technology.

Q & A

What is a multiplexer?

A multiplexer is a digital switch that allows multiple inputs and a single output, enabling the selection of which input signal is sent to the output.

How does a multiplexer select which input to send to the output?

A multiplexer uses a set of selector inputs, typically binary, to determine which of the multiple inputs is connected to the single output.

What is the abbreviation for a demultiplexer?

The abbreviation for a demultiplexer is 'DEMUX', which is the opposite of a multiplexer.

How does a demultiplexer differ from a multiplexer?

A demultiplexer has a single input and multiple outputs, allowing it to select which output should receive the input signal.

What is the relationship between multiplexers and demultiplexers in a system?

Multiplexers and demultiplexers often work together, with the multiplexer combining multiple inputs into a single output line, and the demultiplexer then routing that single input to the correct output among many.

How are multiplexers and demultiplexers represented in circuit diagrams?

In circuit diagrams, multiplexers and demultiplexers are represented by trapezoidal symbols. A multiplexer (MUX) has multiple inputs and a single output, while a demultiplexer (DEMUX) has a single input and multiple outputs.

What is the significance of the number of inputs in a multiplexer?

The number of inputs in a multiplexer is always a power of 2 (e.g., 2, 4, 8, 16), which corresponds to the number of binary combinations needed to select one input out of the many.

Can you explain how a 4-to-1 multiplexer works using basic gates?

A 4-to-1 multiplexer uses a combination of AND, OR, and NOT gates to select one of the four inputs based on two selector inputs. The selector inputs determine which path is enabled, allowing the corresponding input to pass through to the output.

What is the purpose of the enable pin on a multiplexer chip?

The enable pin on a multiplexer chip is used to activate the chip. It is active low, meaning the chip is enabled when a 0 is sent to this pin.

How does the number of selector inputs relate to the number of outputs in a demultiplexer?

The number of selector inputs in a demultiplexer is determined by the number of outputs. For example, to select one output from 16, you would need 4 selector inputs, as 4 bits are required to represent 16 different combinations.

What does the bubble symbol next to the output of a multiplexer or demultiplexer indicate?

The bubble symbol next to the output of a multiplexer or demultiplexer in a circuit diagram indicates that the output is inverted, meaning a 0 input will result in a 1 output, and vice versa.

Outlines

00:00

🔌 Introduction to Multiplexers and Demultiplexers

The speaker begins by introducing the concept of multiplexers (MUX) and demultiplexers (DEMUX), explaining that a multiplexer is a digital switch that consolidates multiple input signals into a single output. Examples include connecting various devices like an MP3 player or a laptop to a stereo system. The multiplexer is represented by a diagram with four inputs and one output, where the output can be selected from the inputs. The video also touches on the concept of demultiplexers, which work in reverse, taking a single input and distributing it to multiple outputs. The speaker uses the example of sending a document to various output devices like a printer or a fax machine. The symbols for both MUX and DEMUX are shown, highlighting their respective functions and the way they are represented in circuit diagrams.

05:01

🛠️ Inside a Multiplexer: Basic Gates and Logic

This section delves into the internal workings of a multiplexer, revealing that it is constructed from fundamental logic gates such as AND, OR, and NOT gates, as well as inverters. The speaker explains the logic behind a 4-to-1 multiplexer, where four inputs are selected and sent to a single output based on the settings of two selector inputs. The concept of using binary signals to enable or disable gates within the multiplexer is discussed, with a focus on how a NAND gate behaves when provided with a zero input. The speaker uses a table to illustrate the relationship between the selector inputs and the corresponding output, demonstrating how specific input combinations result in the transmission of a particular input signal to the output.

10:02

🔄 Demultiplexers: Function and Internal Structure

The final paragraph shifts focus to demultiplexers, explaining their function as the counterpart to multiplexers. A demultiplexer takes a single input and routes it to one of several outputs, determined by the settings of selector inputs. The internal structure of a demultiplexer is explored, which, like a multiplexer, is composed of basic logic gates. The speaker uses a table to demonstrate how different combinations of selector inputs result in the input signal being sent to specific output lines. The concept of power-of-two relationships between inputs and outputs for both multiplexers and demultiplexers is reiterated, with an explanation of how the number of selector inputs is determined by the number of possible output combinations. The video concludes with a brief look at how multiplexers and demultiplexers are represented in a simulation software, highlighting the enable pins and the concept of active-low signals.

Keywords

💡Multiplexer (MUX)

A multiplexer is a digital switch that consolidates multiple input signals into a single output line. In the context of the video, it's likened to a device that allows one to select which of several audio sources, such as an MP3 player or a laptop, is sent to a stereo system. The video script uses the term to explain how multiplexing works, where several inputs are combined into one output, which is crucial for understanding data transmission in systems like fiber-optic cables.

💡Demultiplexer (DEMUX)

A demultiplexer is the counterpart to a multiplexer; it takes a single input signal and distributes it across multiple output lines. The video script describes it as a device that can route a document from a single source, like an old computer, to various output devices such as printers or fax machines. This concept is essential for understanding how data is directed to specific destinations in a network.

💡Digital Switch

A digital switch is a fundamental concept in digital electronics, used to control the flow of digital signals. In the video, the multiplexer is described as a type of digital switch that allows for the selection of one input from many to be sent to an output. This concept is key to understanding how multiplexers manage multiple data streams.

💡Input and Output

In the context of the video, inputs and outputs refer to the points at which data enters and leaves a system or device. A multiplexer has multiple inputs and a single output, while a demultiplexer has a single input and multiple outputs. These terms are central to understanding the functionality of multiplexers and demultiplexers.

💡Power of 2

The video script mentions that the number of inputs and outputs in a multiplexer or demultiplexer is always a power of 2 (e.g., 2, 4, 8, 16). This is because digital systems often use binary counting, which is based on powers of 2. Understanding this concept helps to grasp why multiplexers and demultiplexers have a specific number of inputs and outputs.

💡NAND Gate

A NAND gate is a type of logic gate used in digital circuits. The video explains how a multiplexer is built using basic gates like NAND gates. The script uses the NAND gate as an example to demonstrate how a multiplexer can be constructed to select which input is sent to the output.

💡AND Gate

An AND gate is another type of logic gate that the video uses to explain the inner workings of a multiplexer. The script describes how an AND gate can be used to enable certain pathways within a multiplexer, allowing specific inputs to be routed to the output.

💡Inverter Gate

An inverter gate, also known as a NOT gate, is used in the video to describe the components of a demultiplexer. The script mentions these gates as part of the basic building blocks that make up the circuitry inside a demultiplexer, which is used to invert signals to control the routing of data.

💡Selectors

Selectors in the context of the video refer to the inputs used to choose which of the multiple inputs is sent to the output in a multiplexer, or which output is activated in a demultiplexer. The script explains that the number of selectors needed corresponds to the number of inputs or outputs, which must be a power of 2.

💡Enable Pin

The enable pin is a specific input on a multiplexer or demultiplexer chip that must be activated (usually by a low signal, indicated by a circle on the schematic) to enable the device to operate. The video script mentions this as a necessary component for the proper functioning of the multiplexer chip, highlighting its importance in practical applications.

Highlights

A multiplexer is a digital switch that allows multiple inputs to be selected for a single output.

Examples of multiple inputs include an MP3 player, laptop, sound card, digital satellite box, or cable TV box.

A multiplexer is useful for selecting which input device's signal is sent to a single output device, like stereo speakers.

Demultiplexers (or 'DEMUX') are the opposite of multiplexers, having a single input and multiple outputs.

Demultiplexers can route a single input signal to the correct output device, such as a printer or fax machine.

Multiplexers and demultiplexers often work together, with the former combining signals and the latter routing them to specific outputs.

In telecommunications, multiplexing combines multiple signals into one high-speed line, while demultiplexing routes them to the correct recipient.

A multiplexer is constructed from basic logic gates, such as AND, OR, and NOT gates.

The number of inputs in a multiplexer is always a power of 2 (e.g., 2, 4, 8, 16).

Selectors are used to determine which input is routed to the output in a multiplexer.

A demultiplexer is also made from basic logic gates and has a single input with multiple outputs.

The number of outputs in a demultiplexer is a power of 2, and the number of inputs is determined by the number of outputs.

In a multiplexer, enabling a specific input path requires setting all other inputs to '1'.

The operation of a demultiplexer is similar to that of a multiplexer, but in reverse, selecting an output path for a single input.

Multiplexers and demultiplexers can be visualized and simulated using software like Multisim.

In practical applications, multiplexer chips have an enable pin that needs to be set to '0' to activate the chip.

Demultiplexer chips may have inverted outputs, indicated by a bubble on the output pin, which is a design choice for simplicity inside the chip.

Both multiplexers and demultiplexers are essentially switches that can be controlled to direct signals to specific inputs or outputs.

Transcripts

in this video I'm going to talk about

multiplexers and demultiplexers

this is a diagram of a multiplexer a

multiplexer is really just a digital

switch that allows multiple inputs so

here are my multiple inputs right here I

have four inputs my mp3 player my laptop

sound court card and so forth I might

have a digital satellite box or a cable

TV box and I want to be able to select

which of these inputs goes to my output

in this case my output might be my

stereo speakers right here so a

multiplexer has multiple inputs and a

single output and you can select which

of these inputs goes to your output and

this actually might be something that

you have connected at home at least I do

I have a bunch of things to connect it

into my stereo and I can select which

one I want to play over my my sound

system to play over my speakers so again

multiplexing or a multiplexer is several

inputs multiple inputs a single output

and you can select which one of those

inputs goes to that output

ad multiplexer or D max as it's

sometimes abbreviated as is the opposite

of a multiplexer as you might have

expected so I have one input here's my

one input this very old-looking computer

right here my single input and I have

several output choices so perhaps I have

a document that I want to print and I

can select which of these outputs I want

to send my document it might be my laser

printer a fax machine and jet or a pen

plot or so forth so ad multiplexer it's

the opposite of a multiplexer I have one

input and multiple output and perhaps

you noticed that the multiplexer

abbreviated MUX was was the same symbol

as the D multiplexer but it was the

other way around so my D multiplexer

they're both trapezoids one input

multiple outputs that's my D multiplexer

my multiplexer was the exact

in terms of its symbol it looked like

that looked like that right it was had

multiple inputs multiple inputs and a

single output that was my multiplexer

abbreviated MUX this is my D multiplexer

a single input multiple outputs and you

can select where that output should go

where you have a bunch of different

destinations

as you might have expected multiplexers

and demultiplexers

often work together so here on the Left

I have a multiplexer showing multiple

inputs combined into one output now this

output might be like a high-speed

fiber-optic cable or something like that

and on the other side I have a d

multiplexer taking that single input and

routing it to the correct output so

multiplexer multiple inputs I have a

bunch of inputs here one output D

multiplexer that single input and it's

it's sending it to the correct output

and in this illustration it shows that I

have a bunch of conversations all

happening at once and these could be

conversations between people or

computers or whatever and they're all

getting combined into this single

high-speed line and then it's getting

routed to the correct

recipient on the other end using

multiplexing to combine the inputs and

de-multiplexing to take the input and

send it to the correct output

here's another diagram showing a similar

thing actually as the previous diagram

where I have a multiplexer in this case

it's called a multiplexer demultiplexer

because I might have several inputs

that's the multiplexing part several

inputs going to a single output a fast

line as it says and then getting

demultiplexed going to the correct

output perhaps so that's the D

multiplexing part but then on this side

the communication might go the other

direction as well where I have several

inputs so this box is actually a

multiplexer demultiplexer here I have

might have several inputs

going to my fast

and then again getting sent to my

correct output so depending on which way

the communication is going the these

boxes could either be multiplexing or D

multiplexer either combining several

inputs to a single output or taking that

single input and sending it to the

correct output I just thought this was a

nice additional diagram to add

now it's time to look inside a

multiplexer and see how they work a

multiplexer is just built out of basic

gates here's a three input and gate for

input or gate here's a couple of knock

dates a couple of inverter gates and

let's see what's going on inside here so

this is a 4 to 1 multiplexer I have 4

inputs the number of inputs is always

going to be some power of 2 it's always

going to be 2 to the n in this case it's

2 squared 2 squared is 4 but it could be

4 inputs a to put 16 and so forth and on

the bottom here this is out how I select

which of these inputs goes to the output

so just real quick before we get into

how this works just a jog your memory

about how and gates work if I send in a

0 to a NAND gate that output is always

going to be 0 no matter what the input

is so let's let's say I have a switch

here called an e if I send in a zero to

the other input the outputs always going

to be 0 so if you send in a zero to a

NAND gate you've effectively disabled a

NAND gate it's always going to be 0

here's another end date this time I'm

going to send in a 1 to this and gate

now I have a switch called a so I'm

ending together a with a 1 that output

is going to be whatever a is in other

words if I switch a on I'll get a 1 out

if I switch a to the 0 I'll get a 0 out

so effectively if I make all the other

inputs to a NAND gate ones the output

will be whatever data is coming in on

line a and that's the basics that's the

basis for how these things work in other

words if I want d0 to be transmitted to

my output I have got to make sure that

all the other inputs both these inputs

are ones well how am I going to do that

look at the table right here it says if

I make a and B both zeros my output will

be d0 let's see why if I if I make these

both zeros I'm nodding them right here

so that means they're gonna be ones I'll

have a 1 going into both of these things

and so yes in fact whatever d0 is will

be my output and if we take a quick look

at the other end dates at the same time

let's see remember I have if I have 0 is

going in so these two lines will be 0

let's just check out the other ones real

quick so this would be a 1 0 this would

be a

0 1 and this would be a it looks like I

have a 0 0 yeah so notice when the

inputs are 0 0 the only the only and

gate that's enabled the only one that

has two ones is this top one right here

and I think if you if you follow the

other

examples like if I wanted to check out

what happens when B is 0 and a is a 1 I

think you will find that d1 will get 2

ones and the output will come from this

and gate it's really not that

complicated but I hopefully you get

what's going on here so again a

multiplexer just built out of basic

hands and or gates and it's always going

to be some power of 2 in this case I

have 4 inputs and I need to

two digits to select which of the inputs

goes to the output

imagine I had 8 inputs let's say I had 2

to the 3rd or 8 inputs how many how many

different

inputs what I need on the bottom to

select which one I which one went to the

output well it would be 3 why could I

need 3 well because in binary you need 3

bits to get 8 possible combinations from

0 0 0 to 1 1 1 that's 0 to 7 that's 8

possible combinations so I already need

3 inputs on the bottom for my selectors

if I had eight data inputs and of course

if I had sixteen data inputs I would

need four different selectors a B C and

D perhaps on the bottom hopefully this

makes sense now let's take a look at D

multiplexers so here is what the inside

of a demultiplexer looks like and

amazingly it is also made out of basic

AIDS so here are a bunch of three input

NAND gates here's a couple of not gates

or inverter gates and let's see how this

works remember D multiplexer I have my 1

input source and I can decide where I'm

going to send that and put which one of

these 4 outputs and of course as you

guessed it the number of outputs is

always going to be a power of 2 it's

going to be 2 to the something to be n 2

4 8 16 32 and so forth and the number of

inputs is is n if well well go so let's

say that I want my output to go to d0

well as you already know if you want to

transmit whatever the input is I've got

to make the other inputs both ones well

how am I going to do that let's look at

this table right here if I make them

both zeros let's do that I'll make a and

B both zeros so if a 0 and B is a 0

coming out of here I will have a 1 and 1

and going into here yes I have two ones

so my my input coming from X will be

transmitted to d0 if I make them both 0

so yes the output will be

d0 the others will be just zeros if I

want my data to come out of d1 or to be

sent to d1 I make be a 0 and a 1 and you

can follow through this this is very

similar to the multiplexer diagram the

whole idea is if you want to enable a

NAND gate you've got to send all of the

other inputs ones and then this last imp

in this case it will be coming from X

whatever X's will be transmitted to your

output and again I'm over here this is

the diagram of a demultiplexer one input

multiple outputs and you can select

where your input gets sent by using

these selectors on the bottom and if I

have let's say for example let's say I

have

16 outputs also known as two to the

fourth I will need four different input

selectors right because to get 16

possible numbers in binary I need 4 bits

I need to go from 0 0 0 0 to 1 1 1 1

that's from 0 to 15 that's 16 possible

combinations alright well hopefully that

makes sense a couple more slides to go

so here is a look at what a multiplexer

will look like if you work in multi sim

and here's a bunch of different

multiplexer chips here's a 4 input

multiplexer right I have 4 inputs and

you can see that I will need 2 switches

to select which of these 4 inputs I want

and here is an 8 input multiplexer in

this case I'm going to need 3 inputs to

select which which of these inputs goes

to my output and of course if I have a

16 input multiplexer I'm going to need 4

switches this this other little pin here

this is an enable pin and notice it has

a little bubble a little circle right

there that circle means in order to

enable this particular chip you need to

send it a 0 that little circle indicates

that it wants a 0 to do its job so

another way of saying it is it's active

low you will activate this chip if you

send it a 0 notice that all the chips

have have that little enable right there

so in order for this chip to work

properly and I don't know why they

designed it this way in addition to your

inputs and selectors and all that kind

of stuff you have to send this little

activation pin a 0 all right let's take

a look at Dien bulky flexors finally

let's take a look at the diagrams of

demultiplexers so this is what it's

going to look like in multi-sim if you

work with demultiplexers here i have a a

for output d multiplexer and of course i

need two switches to determine which

output it goes to this is my input right

here here I have a one to eight D

multiplexer then this is my data input

line and I need of course three switches

to determine which of these outputs it

goes to and then I have my sixteen

twenty multiplexer I need four switches

to determine where my data is going to

sent be sent from these sixteen right

four switches 0 0 0 0 2 1 1 1 1 is 15 or

rather 16 possible combinations i need

16 combinations to determine which of

these 16 outputs it's going to go to and

notice also at the end these little

bubbles here mean that the output is

going to be inverted it's done that I

it's I know that seems weird some chips

are built like this and I presumably

it's because it made the logic inside

the chip a little bit simpler you really

don't need to worry about that too much

with multiplexers we'll talk more about

that when we talk about other chips so

hopefully you have a basic understanding

of the difference between a multiplexer

and a demultiplexer again they're just

switches multiplexer multiple inputs 1

output D multiplexer 1 data input

multiple outputs and you can select

where you want that output to go all

right that's it