If I am to take press reports to be accurate, Samsung's newest smartphone, the Galaxy S4, is a marvel to behold. Looking past the high-profile features that have already gotten a lot of press, sensors seem to have attained higher status with the addition of an infrared device to sense when a finger is hovering over the screen. Even more interesting to me, however, is a new and somewhat untested sensor application: eye tracking using the camera's CCD.
It seems to me that eye-tracking could increase the duty cycle of the CMOS sensor quite a bit and, with it, power consumption. There are other power consuming features such as the 5-inch, 1,920-by-1,080-pixel (1080p) AMOLED screen. So it's little wonder the S4 packs a 2,600mAh battery — 500mAh (25 percent) greater capacity than the S3's.
I'm taking the “run-all-day” with recharge claim with a grain of salt. (I know. It depends on the application.)
This brings me to the real topic of this blog: power management. Designers of mixed signal power management chips must have nerves of steel to meet the constantly evolving specs and features of smartphones that have six-month product cycles. System architects seem to have little compassion for chip designers and the marketing guys, of course… Well, they have active imaginations. (One of the interesting trends in smartphone reviews recently is the increasing incidence of a reviewer saying that a feature is interesting, but unlikely to be used.)
While we users seek the thrill of scaling the new-feature summit and doing a victory dance, it means some analog designer has had to dance the how-low-can-you-go limbo to get us there.
How many smartphone users know (or care) that about half the board area of conventional smartphones is occupied by power, analog, mixed-signal, and passive components. This is a statistic that we typically don't see in teardowns, which tend to focus on the obvious but relatively less important digital devices, such as the processor.
Integration is the obvious answer, and there is plenty to integrate in a full-featured (dare we say “over-featured”) smartphone: battery management, display, LED indicators, sensors requiring miscellaneous ADC channels, and last — but certainly not least — processor and system power that require DC-DC converters with DVFS (dynamic voltage and frequency scaling) and low-noise, high-PSRR (power supply rejection ratio) LDOs.
A complete, highly-integrated SoC power management solution for smartphones would ideally have 2 ICs, 70-odd components, and take up about 120mm2 on the board. Compare this to a conventional solution with 9 ICs, 120-odd components and about 160mm2 of board space. Let me be among the first to publicly congratulate the power management IC designers that made the Galaxy S4 possible.
Earlier I noted that sensors seem to be getting a bit more respect from smartphone reviewers. I'm wondering when power management solutions — particularly SoC solutions — will get their day in the sun.