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August 21, 2008

Creating Efficient Architectures

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Back in April, I sat on a panel at the 2008 Globalpress Electronics Summit held in San Francisco along with several esteemed collogues.  We were asked a question at the end of the discussion - "What single thing could the electronics industry do to help save energy?" My original answer was to implement a set of metrics to allow engineers to quickly evaluate the energy consumed by a device or system in relation to the function that device or system provides.  This would provide engineers a way to accurately evaluate competing devices and sub-systems to find the most energy efficient solutions. National Semiconductor has adopted a set of metrics for their PowerWise® Solutions Family of devices which defines these parameters.  But over the months since the conference, I also thought there could be more.

Today we are facing a crisis... one that is undeniable and visible every day we turn on the news.  Energy is in growing demand and heavily influences our economy.  Without it, our modern civilization would grind to a halt.  For example, at the current growth rate of electrical consumption it is predicted that by 2030 over 300 new gigawatt power plants will need to be built to keep pace. There are two choices - we can find more usable energy or we can be more efficient with what we have.  The final solution will be a combination of both.

Part of being efficient is understanding what is required and what is superfluous.  Efficiency experts study process flows to see where time is being wasted in the production of some item or items.  Assembly lines are case studies for this type of exercise.  Early in the 20th century, Charles Sorensen and Charlie Lewis employed by Ford Motor Company figured out how to build a moving assembly line for the Model T which greatly simplified the production of the vehicle reducing both time and cost.  This change - moving the car to each work station instead of moving the workers - was a major efficiency improvement in the production of automobiles.

Engineers have a responsibility to be efficient which is often overlooked.  In 1908 William A. Smith stated, "Engineering is the science of economy, of conserving the energy, kinetic and potential, provided and stored up by nature for the use of man. It is the business of engineering to utilize this energy to the best advantage, so that there may be the least possible waste." Just because you have 2000 watts of power available at an electrical outlet doesn’t mean you can use it all to solve your problem.  Sure, it’s easier to provide a function without concern for the method or implementation of the product. However, engineers must consider their choice in components to best solve their problem using the least amount of energy.

But even more important is how these components are used together to solve a problem.  This is the architecture of the design - the combination of subsystems that best solves the problem.  Architectures can evolve over time based on the availability of certain technologies.  For example, modern LCD HDTV units have used LCD glass with red, green and blue (RGB) color filters to turn the white light of the cold cathode florescent light (CCFL) tubes in the back-light into color pixels.  Over 85% of the backlight energy is absorbed by these color filters.  Converting the backlight to white LEDs and controlling the brightness dynamically across the image frame greatly reduces power and improves the contrast ratio. This modification of the backlight is an architectural change.

Possibly the next big architectural change in LCDs will be frame sequential scan technology which removes the color filters completely.  It also replaces the white LEDs with RGB LEDs which are sequenced - red, green, blue - along with the LCD image (running 3 to 6 times faster than the frame rate).  Each new complete image frame is composed of a red, green and blue frame which sequences so fast, the human eye cannot detect it.  A 42 inch HDTV that today draws 500 watts could be reduced to fewer than 100 watts using this architecture.

Some of the greatest gains in energy efficiency can be found in improving the system architecture.  Intel and AMD have known this for years.  Single execution pipelines can only run so fast, so by creating multiple execution paths, the processing speed can be increased.  From a perspective of saving energy, the parts can run slower and provide the same amount of processing power thus improving the performance to energy consumed.  This advancement in architecture enabled the notebook computing revolution we see today and is also helping reduce the power consumption of server farms.

In the analog semiconductor world architecture is equally important. High speed analog to digital converters (ADCs) can require a large amount of energy to perform the function of converting analog signals to digital bits.  In medical imaging systems such as ultrasound equipment, large numbers of ADCs are required to convert the analog image data into digital form so the image processors can create a picture.  To create a portable ultrasound that runs from batteries, you either need very large battery packs or a way to reduce the overall power consumption. 

Typical ADCs used in ultrasound equipment use a pipeline architecture which is very similar to the assembly line approach envisioned by Sorensen and Lewis.  Each step of the way, the system converts a piece of the analog signal to bits and passes the analog remainder to the next stage.  This architecture works very well and is found in many high speed ADCs.  However, it does take a certain amount of power to keep the "assembly line" running.  Alternative ADC architectures, such as Delta Sigma ADCs used switched capacitor modulators and filters which become very inefficient at higher conversion speeds.  National Semiconductor figured out how to substitute the switched capacitor stages for continuous time versions which dramatically lowers the power.  The first component, the ADC12EU050, debuted with 30% lower power consumption when compared to its nearest competitor.  This type of ADC also eliminated the requirement for external anti-aliasing filters which again reduced the cost and power consumption of the overall system.

As engineers, we need to continuously examine how we design things and try to look beyond our normal methods.  Sorensen and Lewis looked beyond the limits of their current methods to fundamentally change the way automobiles were assembled - these methods are still in use almost 100 years later.  Thinking "outside the box" sometimes provides an insight never seen before and could solve many of our troubling problems that we face today...

So, the next time you are about to design a new product, try and avoid starting the project with the "let’s look how we did it the last time and start there" approach.  One of my old professors once told me "a new problem requires a clean sheet of paper..." pretty good advice even 30 years later.  Till next time...


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