Electronic Design

Inside iPod

Apple doesn't want to spill the secret sauce, but we tear down its mega-seller music machine.

It was an unusual strategy for a design engineer, but it was appropriate for the job. Elaine Wherry, manager of usability and design at Synaptics Inc., put on her hooded sweatshirt so she would blend in at college campuses. Her mission was to understand user requirements for a digital music player.

On campus, she observed people jog, ride bikes, walk, sit quietly, and in myriad other ways, enjoy their tunes. She made similar observations in libraries, airports, and other venues where individuals carry music to speed up, slow down, or blend with the pace of their lives. She carried a player herself, but she avoided the urge to tweak an interface according to her own preferences.

Apple Computer's market-redefining iPod and iPod mini benefit from Synaptics' user interface design and capacitive sensor technology. Synaptics didn't create the original iPod interface, which was done by Apple employees with the help of independent designer Tony Fadell and others who may never receive due credit for the iPod's success. But part of Synaptics' contribution was to understand that less is more; that users want to get their music into the player quickly and easily, navigate smoothly from one song to another, and hear their music faithfully reproduced.

Apple won't say much about the iPod, especially about its inner workings. Those who supply electronic components for the machine, wrapped as they are in nondisclosure agreements, still won't reveal much either. But the iPod's success is clearly due to the combination of its sleek design, its deceptively simple user interface, and the holistic nature of its find-the-music/save-the-music/hear-the-music solution.

Apple launched the iPod in October 2001. But in January that year, the company introduced digital jukebox software called iTunes. It lets Mac users import songs from CDs by converting audio files to the MP3 format and storing them on the computer's hard drive.

When it set out to develop a digital music player, Apple faced the decision of using a hard-disk drive or flash as a storage medium. The hard disk offered the advantage of capacity and the disadvantages of size and cost, while the case for flash was just the opposite.

Toshiba America Information Systems, which had pioneered 2.5-in. hard-disk technology, offered Apple a compromise of sorts. With its protective cover, its 1.8-in. hard disk measured just slightly more than 2 by 3 in. and weighed less than 2 oz., but it could store 5 Gbytes of data. That's enough for approximately 1000 songs, or about 100 CDs.

The first-generation iPod, an all-white model (including the headphones), debuted in time for Christmas 2001. Priced at $399, far beyond the tag for most competing players, the 6.5-oz. device sported a 160- by 128-pixel monochrome screen with a white LED backlight for displaying song title, artist, album, playlist, and genre information. Just beneath the screen were four buttons (Back, Menu, Play/Pause, and Forward) to help users navigate their music files.

Below the navigation buttons, visually complementing the rectangular display screen, was a mechanical scroll wheel that users could turn with a thumb or finger to select music by playlist/album, artist, or song. Along with the 1.8-in. disk, the scroll wheel is widely considered to be the iPod's most significant innovation.

With the desired selection highlighted, users click a button at the center of the wheel—as they would click a mouse—and the music begins to play. In "Play" mode, the scroll wheel functions as a volume-control knob. Click the center button again, and the wheel provides an accelerated scrolling capability. Other features in the first-generation iPod included shuffle and repeat settings, customizable startup volume, and a sleep timer. Menus were available in English, French, German, and Japanese, and song data could be displayed in any of those languages.

Along with the iPod, Apple announced an enhanced version of iTunes that included a 10-band equalizer with more than 20 presets, as well as a cross fading feature for smoother transitions from one song to another. An Auto-Sync capability facilitated the downloading of music from a Mac to the new portable media device. All users had to do was connect the iPod to the Mac through the machines' respective FireWire ports via the FireWire cable that came with the iPod. Then, Auto-Sync would automatically download songs and playlists from iTunes to the iPod. Apple estimated that downloading via FireWire was approximately 30 times faster than downloading elsewhere via USB cable connection.

Once music was downloaded, Apple promised 10 hours of continuous play from the iPod's rechargeable lithium-polymer battery. The device supported MP3, with bit rates of up to 320 kbits/s, as well as AIFF and WAV file formats. Its 60-mW amplifier could deliver 20- to 20,000-Hz frequency response. And, its earbud headphones were built with neodymium magnets for enhanced sound quality.

In March 2002, just five months after its initial product launch, Apple introduced a $499 iPod with a 10-Gbyte hard drive—enough for 2000 songs. To put that quantity in perspective, Apple chief executive officer Steve Jobs told an audience at Macworld Expo in Tokyo that they could fly six round trips between San Francisco and Tokyo, should they want to, without hearing the same song twice.

The ability to do something doesn't necessarily make it a good idea. Apple offered software that took the iPod down what some would call a rabbit trail, enabling users to download and store as many as 1000 contacts from Entourage, Palm Desktop, or a Mac OS X address list. The company has done little to promote the Contacts capability or the Calendar, Games, or other extras provided in subsequent models. While the extras are there for users who want them, they can easily be ignored by those who simply want to download and play lots of music.

In the summer of 2002, Apple began to flesh out its second-generation iPod line, which differed only slightly from the first generation. The company introduced a 5-Gbyte iPod for $299; a 10-Gbyte unit, estimated to be some 10% thinner than its predecessors, for $399; and a 20-Gbyte (4000-song) model for $499. Thus, for the same price, Apple offered twice the capacity of the version launched just four months earlier.

The 10- and 20-Gbyte iPods were fitted with a solid-state touch wheel, Synaptics' interface, in place of the mechanical wheel. This eliminated a potential source of failure while also enabling a thinner device. Apple touted the solid-state touch wheel as an industry first. Synaptics' capacitive sensing technology consists of an array of conductive metal electrodes covered by an insulating layer that protects the electrodes from wear. Analog circuitry measures the changes in capacitance that occur as a user's finger moves around the wheel's surface, pinpointing the finger's location at any given moment with accuracy in excess of 1/1000th of an inch (Fig. 1).

Equally, if not more important, from a marketing standpoint, both Mac and Windows customers could use the new models. The Windows version included the Musicmatch jukebox, widely popular among Windows users, while Mac users were treated to a new version of iTunes with smart (automatically updatable) playlists, a sound-check feature for consistent volume during playback, and support for programming from Audible.com.

Though barely midway into its first year of shipments, the iPod had generated sufficient buzz to warrant a "teardown" by Portelligent Inc., which makes its living in techno-archaeology. As though he were dictating notes from an autopsy, Portelligent president David Carey describes a 2-cm thick enclosure that combines a stainless-steel lower shell and dual-plastic top casing, with the latter co-molding clear resin for the viewing window and white resin for the rest. The two halves of the enclosure are held together by a snap-lock design that Carey says is likely to outlast the electronics in a drop test.

In first- and second-generation iPods, the navigation wheel assembly used contactless construction, with a ball-bearing axle and optical "chopper" for smooth menu selections. Synaptics' touch-scroll technology required a separate board for the touchplate and supporting electronics. The board, which also connects the monochrome LCD and backlight, includes a Synaptics ASIC and a sawtooth electrode pattern.

Components inside the iPod include Toshiba's 1.8-in. disk drive, stacked with a 3-mm Sony lithium-polymer battery and system electronics. Apple used four screws to fasten the electronics, display, and control interface assemblies to the top casing of the plastic enclosure. The disk drive and battery are attached to the stack with adhesive strips. The stacked assembly weighs 185 g and leaves virtually no extra room inside the enclosure. Carey reports that the frame for the navigation-wheel assembly has cutouts for nesting high-profile components, honing thickness by a few millimeters.

The iPod's central processor is a PP5002 system-on-a-chip from PortalPlayer Inc., based on a 32-bit ARM7 processor core (Fig. 2). Supplied by Sharp Microelectronics of the Americas, 1 Mbyte of memory stores system operating code. To buffer songs, 32 Mbytes of DRAM from Samsung Electronics USA is used--eight songs at about 4 Mbytes each, according to Carey. This provides 20 minutes of skip protection. The DRAM buffer lightens the disk drive's workload and prolongs battery life.

Other components found in first-generation iPods include a chip from Texas Instruments dedicated to the IEEE 1394 (FireWire) interface. The interface handles both data transfer and battery charging. A chip from Wolfson Microelectronics plc that integrates a digital-to-analog converter and a headphone driver amplifier controls audio output.

For power management, first-generation iPods include two chips from Linear Technology Corp.: the LTC1731 and LTC1726. Packaged in an MSOP-8, the LTC1731 is a complete, constant-current/constant-voltage linear charge controller for fast charging of single-cell lithium-ion (Li-ion) batteries. The LTC1726, also in an MSOP-8, combines the ability to monitor three supply voltages, at 61.5% threshold accuracy, with adjustable reset and watchdog functions. PowerFETs from International Rectifier round out the power management and control support.

When he first opened up an iPod, Carey estimated the bill of materials cost at less than $250, or roughly 50% of the retail price. By that tally, he suggested that the iPod "may be as much a hook to sell Macs as a profit generator in itself." While Apple won't say whether or not Mac sales were among its goals for the iPod, the music player has had a major halo effect on Apple.

Apple launched its third-generation iPod in April 2003, offering a 10-Gbyte model for $299, 15 Gbytes for $399, and 30 Gbytes for $499, each in an enclosure described as lighter and thinner than two CDs. Other features touted at the announcement were backlit, solid-state buttons as well as a solid-state wheel, an "on-the-go" playlist, and a customizable main menu. The 15- and 30-Gbyte models came with a dock for easier connection to either a Mac or a Windows PC. An audio line out provided easier connection to powered speakers or a home stereo.

For its third generation, Apple down-shifted its continuous play spec from 10 hours to eight. Perhaps by factoring in the effect of more compact file formats, it upped the song capacity of the 30-Gbyte models from 6000, which would have been expected in a linear progression, to 7500.

Comparing the third-generation iPod to the first, Portelligent's Carey found the enclosure, hard-disk drive, solid-state touch-scroll wheel, SoC, flash, DRAM buffer, FireWire interface, and audio chip to be about the same in each (Fig. 3). The third-generation units are 1.57 cm thick. This is due in part from Apple's swapping of the lithium-polymer battery in its first-generation iPods for a smaller, less-expensive Li-ion cell. In addition, Apple set both the new battery and the hard drive into a cutout on the main board, reducing the profile of each. Plus, third-generation players include a USB interface chip from Cypress Semiconductor Inc.

The third-generation iPod contains two power-management chips from Royal Philips Electronics, a TEA1211 and a PCF50605. The TEA1211 is a dc-dc converter that can switch automatically between step-down and step-up operation in response to changing input voltage. The PCF50605, a single-chip power-management unit (PMU), can adjust power-supply voltages to the lowest thresholds needed for functions in a particular power domain.

In September 2003, Apple unveiled a 20-Gbyte model priced at $399--the same price as the 15-Gbyte model introduced just five months earlier--and a 40-Gbyte model priced at $499 that holds up to 10,000 songs.

Soon afterward, Apple made iPod software available to Mac and Windows users, adding support for Belkin voice recording and photo storage accessories for dockable iPods. Thus, users could record hundreds of hours of audio and store thousands of digital photos on their iPod.

By January 2004, Apple had shipped some 2 million iPods. That month, it introduced the iPod mini. With room for 1000 songs, plus extras, the 3.6-oz., 1.27-cm mini presented a cleaner look than earlier iPods. The buttons below the display screen were eliminated, and their functions were transferred to the outer ring of the scroll wheel.

Tearing down the mini, Portelligent's Carey found a new PortalPlayer CPU chip (PP5020D-TF) that, for the first time, integrated USB and FireWire controller functions (Fig. 4). In lieu of Toshiba's 1.8-in. drive, the mini employs a 1-in., 4-Gbyte Microdrive from Hitachi Global Storage Technologies. A Linear Technology LT4055 USB power controller/Li-ion linear charger can detect the presence of a wall adapter and use it as an alternative power source to charge the battery while simultaneously providing power to the load. Other power-management devices include a Texas Instruments TPS62046 step-down dc-dc converter and an LM3485 PFET switching regulator controller from National Semiconductor Corp.

One of the latest additions is iPod Photo. It comes in 40- and 60-Gbyte models that hold 10,000 or 15,000 songs, respectively, as well as up to 25,000 digital photos. The units feature up to 15 hours of music playback or up to five hours of slideshows. Both Mac and Windows users can exploit iPod Photo via Auto-Sync.

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