As the Chief Technologist for PowerWise® Solutions at National Semiconductor, I’m often asked why there is so much emphasis on improving the energy efficiency of semiconductors while there are so many large consumers of power elsewhere. The reasons are many, however there are semiconductors in just about every product on the planet these days and once the function provided by the electronics is accomplished, and the energy that went in comes out as heat.
So if most everything that goes into a semiconductor based product winds up as useless heat, the less it consumes the lower the energy cost of the system. Again, people often say, "Who cares... cars use far more energy than any electronic device so why put effort into saving a few watts here or there". I agree that large energy consumers such as transportation have their own challenges, but energy efficiency is not all about saving energy... it is also about enabling new technologies.
For example, terrorists would like to wreak havoc on modern civilization and they’ll do anything to accomplish their mission. The possibility of a weapon of mass destruction (WMD) being transported into a country inside of an Intermodal Container is a real threat. So how do you protect the estimated 14 million containers in operation worldwide from being compromised? The Department of Homeland Security in the United States is working on this problem... if someone were to cut a hole in the side of a container and place a WMD inside and then weld it shut (plus repaint the side), how would you know? This is a classic application for extremely low power electronics.
Most of the time any particular container is in transit from point A to point B and is uninterrupted in its journey to its final destination. This means that any monitoring electronics placed inside the container to "watch" for intrusion must either sleep most of the time or use very little power. It is impractical and expense to use large batteries inside the container (as well as being potentially dangerous), so only small batteries or energy harvesting can be used. If the goal is to provide intrusion detection for the container for 3 years (the interval between container refurbishment), then it doesn’t take much math to calculate how much energy you can use to solve the problem.
This is a classic application of Analog to Information or A-to-I. Using a DSP to analyze the environment inside the container is extremely power hungry and it would need to operate pretty much all the time. What if you could put the DSP to sleep and use an analog processor capable of performing a subset of the DSP algorithms in real time and at extremely low power? Once the analog processor "detected" a suspect intrusion it could then wake up the DSP and begin analyzing the situation. The detection might be a normal environmental event or it might be someone with a torch or grinder trying to get inside. The analog function block is producing information (i.e. suspected intrusion) from inputs from analog sensors and working in concert with the DSP based algorithms to dramatically lower the system power consumption.
Another example where energy efficiency enables new capabilities is in infrastructure monitoring. There are approximately 600,000 bridges in America and many of them are aging. If the department of transportation wanted to monitor each bridge for subtle changes that may indicate imminent failure you’d need to instrument each bridge. The instruments would continuously monitor various sensors located around the bridge and analyze the input for signs of failure. Again, this is another great application for A-to-I. Putting the instrument’s DSP to sleep and using ultra low power analog processors to perform the function of detecting possible failure modes can greatly reduce the overall system energy consumption. In this application, the vibration of vehicles moving over the bridge might be enough to run all the equipment.
The DSP cycles only need to be used to perform the detailed analysis to verify the detection seen by the analog processing so the higher power electronics are used very infrequently. It is a great marriage between analog and digital functions. This is like having a lookout at a post watching for enemy activity. Once something is detected, more troops can be called in to verify the incursion. Sometimes it might just be a rouge moose and other times it might be the real thing. In all cases, only a single lookout is being used allowing the main troops to rest in case of real attack.
So, is analog processing dead? Analog is more important now in the 21st century than it was 20 years ago! I’ll have more on A-to-I in future blog posts. I welcome your comments... till next time.