3. Using Block Diagrams To Understand How Cell Phones Work

In this lesson we are going to take a brief familiarization of a typical block diagram of a cell phone.

Block Diagram can help us understand the flow of a certain part of a cell phone’s circuit.

A Cell-phone handset is basically composed of two sections, which is RF and Baseband Sections.

RF
RF refers to Radio Frequency, the mode of communication for wireless technologies of all kinds,

including cordless phones, radar, ham radio, GPS, and radio and television broadcasts. RF technology is so much a part of our lives we scarcely notice it for its ubiquity. From baby monitors to cell phones, Bluetooth to remote control toys, RF waves are all around us.

RF waves are electromagnetic waves which propagate at the speed of light, or 186,000 miles per second (300,000 km/s). The frequencies of RF waves, however, are slower than those of visible light, making RF waves invisible to the human eye.


Baseband
In signal processing, baseband describes signals and systems whose range of frequencies is measured from zero to a maximum bandwidth or highest signal frequency. It is sometimes used as a noun for a band of frequencies starting at zero. In telecommunications, it is the frequency range occupied by a message signal prior to modulation. It can be considered as a synonym to low-pass.

Baseband is also sometimes used as a general term for part of the physical components of a wireless communications product. Usually it includes the control circuitry (microprocessor), the power supply, and amplifiers. A baseband processor is an IC that is mainly used in a mobile phone to process functions of communication.

Basically Baseband is also composed of two sections - the Analog, and Digital Processing Sections. So, we are going to separate each other for better understanding.

Let’s try to understand these in the simplest possible way so that it is easy for us to understand the concepts and methods of how basically a cell phone works.

Cell phones have three sections since baseband is divided into two - the Analog and Digital functions - while the RF section remains as a whole circuit section

1. Radio Frequency (RF Section)
2. Analog Baseband Processor
3. Digital Baseband Processor. 

Radio Frequency Processing Section
The RF section is the part of the cell-phone circuit is also known as RF Transceiver.
It is the section that transmits and receives certain frequencies to a network and synchronizes the same to another phone.

A simple mobile phone uses these two circuits to correspond to another mobile phone.

The RF - A radio section is based on two main Circuits:
1 Transmitter
A Transmitter is a circuit or device which is used to transmit radio signals in the air.

2 Reciever

A reciever is simply like radios which are used to receive transmissions (Radiation) which is spread in the air by any transmitter on a specific frequency.

The two way communication is made possible by setting two transmitters and two receivers sycronized in such a way that a trasmitter in a cell phone is syncronised with the frequency of another cell phone's recieving frequency and vice versa. So, the first cell phone transmits its radiation in the air while the other phone listens for it. And the same process is present in the opposite side as well. So, these two hand-held cell phones correspond to one another - more or less simultaneously.
The technology used these days is a little bit different, but is based on the basic theory as used previously. Today's technology will be discussed later on.

Analog Baseband Processor
A/D and D/A section
The analog baseband processing section is composed of different types of circuits.
This section  converts and processes the analog to digital (A/D) signals and digital to analog (D/A) signals.

Control section 
This is the section which acts as the controller of the the input and output of any analog and digital signal.

Power Management
A power management section in mobile phones is designed to handle energy consumed in mobile phones. There are two main sub sections in a single power section.

• Power Distribution and switching section
A power distribution section is designed to distribute desired Voltages and currents to the other sections of a phone. This section takes power from a battery (which is figured commonly at 3.6 Volts) and in some places it converts or steps down to various volts like 2.8V, 1.8V, 1.6V etc., while in other places it also steps up the voltage to higher voltages like 4.8 V. This section is commonly designed around a power IC (integrated circuit) which is used to distribute and regulate the voltage used in other components.
 
• Charging Section
The Charging section is based on a charging IC which takes power from an external source and gives it to the battery to power it up again when it is exhausted. This section uses convertability of 6.4V from an external battery charger, and regulates it to 5.8V while giving it to the battery. The battery is charged by this process and it is ready to use for the next session (a battery session is a time which is provided by the manufacturer of a cell phone for standby or talk time.) Please refer to the first diagram in this post as refeence.


Audio Codecs Section
This section is where analog and digital audio properties are processed - like the microphone, earpiece, speaker, headset, ring-tones, and also the vibrator circuits.

Digital Baseband Processor
This is the part where All Applications are process. Digital Baseband Processor section is used in mobile phones to handle data input and ouput signal like switching, driving application commands, and memory accessing and executing.

These are the parts and sections of a Digital Baseband Circuit:

CPU( Centeral Processing Unit)
The Central Processing Unit (CPU) is responsible for interpreting and executing most of the commands from the user interface. It is often called the "brain" of the microprocessor, or the central processor.

Flash and Memory Storage Circuits
*RAM( Random Access Memory)
*ROM, Flash(Read Only Memory)

Interfaces such as the following are also part of this section:
*Blutooth
*Wi-fi
*Camera
*Screen  Display
*Keypads
*USB
*SIM-Card

Here a typical overview of a block diagram on latest mobile phone designs.

Every mobile phone has a different concept and design in various aspects, but the methods and operational flow are all exactly the same. It differs on how and what certain IC chips and parts are being used and installed in a certain mobile phone circuitry.

Credits:
cellphonerepairtutorials.blogspot.com