Authorities on analog and mixed-signal technology believe that handheld electronics will soon incorporate an unprecedented number of features. Cellular telephones will likely have a color screen, a wireless Internet browser, the address book and calendar functions of a PDA, even an FM radio and MP3 music player. The big issue, technologists say, is how to pack all these features together without using a battery the size of a brick, or reducing battery life to 30 seconds.
At the same time, the digital guts of a pocket computer, personal digital assistant or cell phone are being built in increasingly fine-geometry, low-voltage CMOS, which allows very high levels of functionality with relatively small hits on battery life.
As a result, the analog interfaces to "the real world" the radio modules of cell phones and wireless PDAs, the color video displays, the voice codecs and audio playback systems become the focus of power conservation and sophisticated battery-management techniques. In 2002 and the years that follow, a lot of attention will be devoted to power-management architectures and the technologies required to most efficiently implement radio transceivers, miniature displays and audio interfaces. Also likely is an increasing reliance on bipolar circuitry and bipolar implants on CMOS substrates particularly silicon germanium for high-frequency circuits like radio transceivers.
If only the industry could agree on what the integrated handheld should actually include. "It's getting so that you could pick up any box and find it does most anything you want," said Jim Williams, staff scientist at Linear Technology Corp. (Milpitas, Calif.). Linear designed the power-management circuits for the Apple iPod, a device the size of a deck of cards that holds 1,000 MP3 songs and runs for 10 to 13 hours on a single battery charge.
But technology managers worry that many of the features bolted onto cell phones or PDAs will do little more than consume space and battery power (as well as add costs) unless consumers want and use them. A cell phone built into a portable CD player can seem like "an awful kluge," said Alun Roberts, strategic marketing manager for Texas Instruments Inc. (Dallas). "Who wants it?"
Peter Henry, director for portable power at National Semiconductor Corp. (Santa Clara, Calif.), cited a number of examples of interesting combo devices, including Kyocera's Palm Phone and Nokia's 7560 color PDA-and-Bluetooth handset. National's own Origami experiment, a feature-laden Web pad shown at Comdex last November, is something of a "Swiss army knife," Henry acknowledged.
But though cell phones outsell PCs four to one, Henry wonders whether the cell phone is being asked to do too much. "People want to browse the Internet and collect e-mail," he said. "The cell phone is still an atrocious Internet device companies are now starting to figure that out."
Implementing third-generation communications encouraging people to cruise the Internet or conduct videoconferences through their wireless telephone modems would be extraordinarily taxing on bandwidth and battery life. Other forms of wireless connectivity, such as the short-range Bluetooth spec or IEEE-802.11b wireless LANs, may offer more efficient means of Internet connectivity in the same portable package.
The issue is whether to tax packaging and battery life for a handheld by including both cell phone and wireless LAN interface; to strip the cellular telephone function from the handheld; or to find some sort of radio architecture, such as the software-defined radio, that does both.
In addition to modularity, the latter option would require some type of universal radio architecture and an extremely versatile baseband processor. "If we look at the handset as a modem, not necessarily a 'voice transmitter,' it is possible to add consumer features without sucking down your battery," said National's Henry. This change in thinking, he suggested, would open a "golden age of Internet devices." Getting there, Henry said, will involve creating new battery technologies (though rechargeable lithium ion will be more widespread).
In addition to more sophisticated baseband processing, wireless e-mail and Internet access will create larger opportunities for digital signal processing, said TI's Roberts. Also, security issues especially encryption, character recognition and pattern recognition will require more resolution from both the processor and the front-end data converter. Dc-accurate converters, capable of resolving 16 bits (that is, one part in 65,535) can now sample at 100-kHz rates. Accurate devices that sample even faster are coming soon, Roberts said.
While CMOS paves the way for higher levels of digital circuit integration, its lower voltage requirements are a nightmare for designers of power-management devices (such as voltage regulators) and for RF circuit designers.
Portable cell phones and PDAs typically require multiple power supply rails, said David Bell, general manager of Linear Technology's power products group: 1.5 volts for the processor core, 1.8 to 2.5 V for the I/O, 3.3 V for glue logic, 15 V for LCD contrast lighting and 4.5 V for the white LED backlights. MP3 players and other audio amplifiers, in addition, typically require a 5-V supply rail.
This creates a trend toward the use of multiphase switching regulators, which increase the efficiency of multiple voltage generators by switching them somewhat out of phase with one another. Bell also foresees increasing use of synchronous rectification.
In most power supply circuits, even switching regulators, a diode is used to hold the source of the switching MOSFET at a certain level above ground, Bell explained. The diode, in effect, is always "on." But as power supplies follow the CMOS trend toward lower and lower voltages, the diode looks "really tall," Bell said. An additional switching MOSFET, one with low RDSON, allows the voltage to sink to a lower level and ensures higher efficiency.
"Denser CMOS processes mean we can do a much better FET," said Len Sherman, staff scientist at Maxim Integrated Circuits (Sunnyvale, Calif.). The process makes it possible to integrate the power MOSFET switches for a regulator circuit on the same die as the pulse-width modulator controller.
"Formerly, if you tried to do more than an amp with an integrated device, you were really pushing it," Sherman said. "It was more economical to use separate FETs in a battery-powered device and in terms of heat dissipation, you don't want the thing to cook. But the scale is sliding," he added. "Low-voltage CMOS means there are more cases for integration."
Lew Counts, vice president of the linear products group at Analog Devices Inc. (Norwood, Mass.), envisions a credit card-size PDA, but worries that line-geometry CMOS will offer little help for radio-frequency circuitry. Complementary bipolar devices are more power efficient than CMOS at high frequencies, he said.
The huge interest in RF and in signal processing in the microwave and gigahertz domain has fueled a move toward building high-frequency devices in BiCMOS with silicon germanium implants on bipolar substrates, Counts said. BiCMOS is readily available from foundries like IBM and Taiwan Semiconductor Manufacturing, he said. Such a process is not useful for commodity products, like Bluetooth transceivers, but will certainly be mainstream in cell phones with GSM and CDMA modulation schemes.