Single-chip solutions have an obvious appeal, but don't expect them to become common any time soon.
Last week TI announced the C5506, its lowest-power DSP. One of the things I found interesting about this announcement was that TI touted the relatively large on-chip memory as a key power-saving feature. TI has a point. As I noted in my October 16 blog, moving code and data on-chip is one of the simplest and most effective ways to cut power.
The same is true for the more general case of bringing system components on-chip. Reducing off-chip transactions—which are relatively high-voltage, high-impedance transactions—tends to reduce power. That's not all: Increasing on-chip integration tends to also reduce costs and system size.
Not surprisingly, there is a clear trend of DSPs offering more and more integration. Just a few years ago, the typical DSP offered little more than a few kilobytes of memory and a couple of serial ports. Today, chips are packed to the gills with multiple processor cores, tons of memory, and long lists of peripherals. So what's next? Will DSPs gobble up all of the components around them, leaving us with single-chip solutions?
In a word, no. For one thing, most applications move too fast for single-chip solutions to be practical. This is particularly problematic as shrinking fabrication processes drive up the cost of chip design. For example, a typical 90nm mask costs more than $1 million! Thus, you can only afford to design a single-chip solution if you have an application with high volumes and stable requirements. (The best example of this is the low-cost cell phone market, where single-chip solutions have started to appear.)
The other factor to consider is that most DSP systems have significant analog circuitry. Integrating the analog and digital circuitry on one chips requires some serious compromises, so these components are usually left on separate chips.
All of this make me think that we will see more multi-chip packages in the future. These packages cram multiple die into a single package. This doesn't give all of the benefits of bringing everything onto one die. However, it does let the manufacturer retain flexibility to meet changing market demands quickly, and it sidesteps the problems associated with mixed-signal chips. I think this is a technology to keep a close eye on.