On a "complexity per cubic inch" scale, cell phones are some of the most
intricate devices people play with 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 have read the How Stuff Works
article on cell phones you know that they can
transmit and receive on hundreds of FM channels, switching channels in
sync with base stations as the phone moves between cells.
If you ever take a cell phone apart you will find that it contains
just a few individual parts:
The circuit board is the heart of the system. Here is one from a typical
Ericsson digital phone:
- A microscopic microphone
- A speaker
- An LCD or plasma display
- A keyboard not unlike the one we saw in a TV remote control
- An antenna
- A battery
- An amazing circuit board containing the guts of the phone
In this picture several of the components are identified. Starting from the
left you the see the Analog-to-Digital and Digital-to-Analog conversion chips.
You can learn more about A-to-D and D-to-A conversion and its importance
to digital audio in the How Stuff Works article on compact disks.
The DSP is a "Digital Signal Processor" - a highly customized processor designed to
perform signal manipulation calculations at high speed. This DSP is rated at about
40 MIPS (Millions of Instructions per Second) and handles all the signal compression
and decompression. The microprocessor (Ericsson phones use an ASIC version of the Z-80) and memory
handle all of the housekeeping chores for the keyboard and display, deal with
command and control signaling with the base station and also
coordinate the rest of the functions on the board. The RF and power
section handles power management and recharging and also deals with the hundreds
of FM channels. Finally the RF (Radio Frequency)
amplifiers handle signals in and out of the antenna.
What is amazing is that all of that functionality - which only 30 years ago would have filled
the entire floor of an office building - now fits into a package that sits comfortably
in the palm of your hand!