Inside a Digital Cell Phone

On a "complexity per cubic inch" scale, cell phones are some
of the most intricate devices people use on a daily basis.
Modern digital cell phones can process millions of
calculations per second in order to compress and decompress
the voice stream.

If you take a basic digital cell phone apart, you find that
it contains just a few individual parts:

* An amazing circuit board containing the brains of the
phone.
* An antenna.
* A liquid crystal display (LCD).
* A keyboard (not unlike the one you find in a TV remote
control).
* A microphone.
* A speaker.
* A battery.

The circuit board is the heart of the system. Here is one
from a typical Nokia digital phone:

In the photos, you see several computer chips. Let's talk
about what some of the individual chips do. The
analog-to-digital and digital-to-analog conversion chips
translate the outgoing audio signal from analog to digital
and the incoming signal from digital back to analog. You can
learn more about A-to-D and D-to-A conversion and its
importance to digital audio in How Compact Discs Work. The
digital signal processor (DSP) is a highly customized
processor designed to perform signal-manipulation
calculations at high speed.

The microprocessor handles all of the housekeeping chores for
the keyboard and display, deals with command and control
signaling with the base station and also coordinates the rest
of the functions on the board.

The ROM and Flash memory chips provide storage for the
phone's operating system and customizable features, such as
the phone directory. The radio frequency (RF) and power
section handles power management and recharging, and also
deals with the hundreds of FM channels. Finally, the RF
amplifiers handle signals traveling to and from the antenna.

The display has grown considerably in size as the number of
features in cell phones have increased. Most current phones
offer built-in phone directories, calculators and games. And
many of the phones incorporate some type of PDA or Web
browser.

Some phones store certain information, such as the SID and
MIN codes, in internal Flash memory, while others use
external cards that are similar to SmartMedia cards.

Cell phones have such tiny speakers and microphones that it
is incredible how well most of them reproduce sound. As you
can see in the picture above, the speaker is about the size
of a dime and the microphone is no larger than the watch
battery beside it. Speaking of the watch battery, this is
used by the cell phone's internal clock chip.

What is amazing is that all of that functionality -- which
only 30 years ago would have filled an entire floor of
an office building -- now fits into a package that sits
comfortably in the palm of your hand!