er Keypad Communications Processor Components Microphone Figure 3.1 Portable phone components. phone. In addition, innovative technologies include hand-powered generators that recharge cell phones. The battery is a crucial component of mobile telephone design. Increased power in batteries of smaller size and lower weight has been a critical component of the techno- logical revolution in mobile electronics, including battery-powered laptops, personal digital assistants (PDAs), and mobile telephones. The market for more compact, lighter sources of power has driven a remarkable engineering effort for more than a decade. For mobile telephones, the result has been a decrease in size and weight of about 25 percent per year. If this trend continued for another century, mobile telephones would become subatomic in size. More realistically, we are reaching the point where the bat- tery is no longer the primary limit in the size of the mobile telephone. For phones to shrink any further, the keypad will have to be replaced with voice-activated dialing and controls, and indeed, this is beginning to happen. The major drive in battery technol- ogy probably will be used to deliver larger battery capacity at roughly the current weight and size. This larger capacity will be used primarily to increase the recharge interval of the cell phone rather than to increase radio power for greater system coverage. The battery powers all components of the mobile unit; however, only the transmitter amplifier uses a great deal of power. This is why a typical mobile telephone can be ac- tive and ready to receive calls for 72 hours on one battery charge but only lasts for 3 hours of actual call time. Improved battery life, therefore, depends primarily on devel- oping better batteries and increasing the efficiency of transmission through the trans- mitter, amplifier, and antenna. The subscriber uses the keypad to direct the mobile telephone to perform its various functions. Sophisticated microprocessors in the mobile telephones provide a choice of