What Is A Set Top Box or STB Working And Architecture ?

what is a set top box


There is one most important part of Digital Headend which should be considered, known as STB or Set Top Box. Because overall the output of digital headend we are measuring on STB.

So we are going to discuss in this article What Is a Set Top Box STB working and Architecture. below.

Overview Of STB

In simple words A hardware device which demodulate or decode the signal of headend and provides the output known as STB or Set Top Box. It is small compact user end device which enable the user to view the services in a proper manner. These services can be Digital Television Service  and Internet Service.

STBs have two way communication which enable to provide interactive features like adding of premium channels.

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STB Internal Architecture And STB Working

STB Working what is a set top box

As shown above in the figure we have taken a standard internal diagram of STB’s internal architecture. This is Standard Definition STB. This diagram explains many components of STB internal architecture widely.Lets describer each part step by step,

Power Port:

In this stb architecture the power port accepts 5.5 Volt DC supply via AC to DC adaptor. This supply goes into the ON OFF switch of the STB and then it forward into the circuit.

Zener Diode:

A zener diode is used to prevent the STB from shor circuit. if in case we uses 12 Volt DC adaptor by mistake then this zener diode will burn out to prevent the STBs next circuit.

2.5 Volt IC:

2.5 Volt IC’s work is to forward stable 2.5 volt to circuit.

3.3 Volt IC:

This ic forward stable 3.3 Volt to circuit for proper functioning.

1.8 Volt IC:

as usual it is responsible to provide 1.8 Volt to its forwarding circuit.

You can get these ICs from here,

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RAM stands for Random Access Memory. RAM is used to store necessary information of stb. It is also known as Flash.


CPU stands for Central Processing Unit. CPU is responsible to perform different functions of stb from booting. It gives audio output and video output. The audio output goes into the audio ic first then it goes into the A/V section of STB. The video output goes into the A/V section of stb.

O/P Front Panel Port:

A STBs front panel is connected to this port. The front panel is different PCB which is connected to this port. Which control the remote functions of stb because a remote sensor is mounted there. Also front panel PCB plate is responsible for touch button functions of stb.

Tuner IC:

It is responsible to tune the Transport Streams and channels available in it. It is mounted in the RF section of the STB. If we provide high or low RF signal to the tuner ic then its behavior is abnormal. It tunes less number of streams.

Low signal level in stb makes hard to tune the services while on the other hand high signal level in the stb is harmful for its tuner ic. Thus a proper signal level should be given to stb for proper reception of services.  Signal level depends upon the resistivity of tuner ic. The practicaal input RF level is seen around 45-55 dB.

RF Port Section:

This RF port section have two RF ports. One is for input RF port and second one is for loop out. Generally the is 10 dB of loss in loop out port.

A/V Port:

A/V port gives composite video output. Which directly goes into the Television.

RS232 Port:

RS 232 Port is used to upgrade the release of STB. A USB to RS 232 port cable is used to connect this port to the Laptop and upgrade the software of STB. Whenever a new network is setup then we use Test release to upgrade a particular STB.

Thus a Test release is used in  a particular stb to see how does it work. After we complete the testing OTA is done from headend to upgrade all the stbs in field. So this port is very useful to upgrade a particular stb for testing.

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Conclusion Of STB Working

A STB is used to decode the digital headend signal and enable users for television services, VOD, Radio and Internet etc. We have discussed here about a basic internal architecture of STB which makes us easy to understand its functioning.

You can buy STBs Audio IC, Power IC and Tuner IC etc spare parts from our Headend INFO Store

Thus this is all about what is set top box and how it works .

 Know More About  Digital Headend Mainteance

reference : itv


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