Apple's iPad: New Computing Form Factor or Passing Fad?

Tablet-style computers running both Unix and Windows operating systems have for many years been an enduring presence on the tech landscape, primarily by virtue of the innumerable product failures. In early April, Apple began selling its first-generation OS X-based iPad. Is Apple's tablet destined for greater success than its predecessors, and what hardware building blocks compose it? My friends at iFixit helped me answer these questions.

(Figure 1) At approximately 4.5 in. wide, the iPad's primary PCB (printed-circuit board) is about the same size as that in an Apple handheld device, leaving plenty of room in the system cavity for the 25-Whr lithium-polymer battery. With the iPad, Apple also used many of the same chips it used in both the iPod touch and the iPhone, thereby giving a measure of validity to the oft-repeated observation that the iPad is little more than a big iPod touch.


FIGURE 1

The display interface employs Broadcom's BCM5973 microcontroller IC and BCM5974 capacitive-touchscreen-controller IC, plus Texas Instruments' CD3240A touchscreen-line-driver IC, rather than a more leading-edge approach with greater integration. This design choice likely reflects the fact that the iPad has a larger, higher-resolution screen than does either the iPhone or the iPod touch. It also has comparatively more PCB real estate.

Die analysis and software profiling both suggest that the 1-GHz, ARM-based Apple A4 microprocessor combines a Cortex A8 single-core CPU and a PowerVR SGX 535 graphics processor. Although Apple more than two years ago bought PA Semiconductor-notably, the company's ARM-design expertise-persistent rumor suggests that Intrinsity, which Apple reportedly also acquired, spearheaded this project. The package also includes two 1-Gbit Samsung DRAM die, for 256 Mbytes of total system memory, the same amount as the latest-generation iPod touch.

Other notable ICs include an NXT-developed DisplayPort and PCIe (Peripheral Component Interconnect Express) multiplexer/demultiplexer and an STMicroelectronics-supplied accelerometer. The identity and location of the silicon compass, an IC that made its debut in Apple's product line with the iPhone 3GS, are currently unknown. More generally, Apple's insistence on employing proprietary package markings complicates function and sourcing identification of many devices inside the iPad.

(Figure 2) This particular iPad is a Wi-Fi-only unit, lacking the 3G (third-generation) UMTS (Universal Mobile Telecommunications System) HSPA (high-speed-packet-access) cellular-data capabilities found in more expensive iPad versions. As such, you won't find relevant ICs, which mount on an add-in module in one corner of the unit. These ICs include Infineon's PMB 8878 X-Gold baseband chip and PMB 6952 dual-mode RF transceiver; Skyworks' Sky77340 power-amplifier module; Triquint's TQM616035A, TQM666032B, and TQM676031A power-amplifier/filter combinations; Numonyx's 36MY1EE NOR-flash memory containing additional system firmware; and Broadcom's BCM4750 implementing the A-GPS (assisted global-positioning-system) function that's also unique to the cellular-cognizant iPad.


FIGURE 2

The discrete wireless-communications module resides on the cable that interconnects the primary PCB and the bottom-edge dock connector. Broadcom's BCM4329 transceiver supports Bluetooth Version 2.1 EDR (enhanced-data-rate) and dual-band 802.11a/b/g/n Wi-Fi capabilities. Curiously, the Broadcom IC also supports FM radio reception and transmission, neither of which is a documented iPad feature.

PLEASE PUT FIGURE 3 HERE

(Figure 3) Nonvolatile memory on the iPad comprises two 64-Gbit MLC (multilevel-cell) NAND-flash-memory ICs for 16 Gbytes of total resident storage on the primary PCB's front side; 32- and 64-Gbyte iPad variants are also available. An 8-Mbit SPI (serial-peripheral-interface) flash-memory IC, presumably containing system boot code, resides on the PCB's backside. This iPad employs Samsung-sourced NAND devices, whereas the FCC (Federal Communications Commission) characterized a unit that used Toshiba-fabricated silicon. The Atmel-stored system-firmware selection mimics Apple's choice on the second-generation iPod touch (see "Studying the second-generation Apple iPod touch," EDN, Sept 30, 2008) and marks a departure from the Intel IC on the first-generation iPhone (see "Inside Apple's iPhone: more than just a dial tone," EDN, July 27, 2007).