Three factors combine to distinguish one cell phone from another—small size, increased functionality, and high performance. Miniaturization of the electronics is key to shrinking size while improving or maintaining functionality, performance, and reliability.
Today's leading-edge cell phones typically consist of eight to 14 ICs that have a total active-device area of 3 cm2 (i.e., the total die area). The packaged area for these devices has shrunk from an average of 18.9 cm for phones made before 2000 to an average of 8.6 cm for phones made after 2000. The related die-to-package ratios are 0.17 (before 2000) and 0.27 (after 2000).1 The efficiencies in packaging-area ratios are reflected in technology integration. In other words, more functionality is offered in each generation of handsets, as is miniaturization of the entire phone.
A typical 2001 handset weighs only 3 to 6 ounces.2 The four main subsystems a cell-phone handset comprises are:
- The radio-frequency (RF) section receives and transmits signals through the antenna. RF functions include modulation, synthesis, up and down conversion, filtering, power amplification, and others. It's estimated that the RF portion of a handset consumes 65% of the cell phone's total power. Typically, four ICs reside in the RF section, with an average semiconductor area of 0.2 cm2.
- A DSP, microcontroller, and memory make up the digital baseband section. This portion is the heart of digital wireless, performing the high-speed encoding and decoding of the digital signal, as well as managing the keyboard and other system-level operations. The logic section usually consists of two ICs and has an average of 1.0 cm2 of silicon area.
- For analog voice and radio signals to become DSP-processible digital signals, they must be converted in the analog baseband section. The voice and RF coding/decoding devices (codecs) perform analog-to-digital and digital-to-analog signal conversion and filtering, along with various other functions. Typically, with five ICs, the analog section covers an average silicon area of 0.5 cm2. This includes ICs performing power-management and user-interface functions.
- Today's cell phones have two primary forms of memory: Flash (nonvolatile) and SRAM (volatile). Flash memory stores personal information (e.g., phone numbers), while SRAM is necessary for the phone's operating system. Normally, three ICs reside in the memory section, which has an average silicon area of 1.3 cm2.
This ongoing consolidation and concentration of the electronics is expected to continue for the foreseeable future. The cell handset itself may not shrink any further because of the size limitation imposed by the human interface. However, functionality and performance will continue to make gains.