By David Bourner, Micrel Corp.
Real limits in power technology occur in systems that are supporting optical fiber applications. In the optical realm, data rates and available bandwidth go up every month without any performance penalties and reduced cost.
By David Bourner, Micrel Corp.
By David Bourner, Micrel Corp.
Real limits in power technology occur in systems that are supporting optical fiber applications. In the optical realm, data rates and available bandwidth go up every month without any performance penalties and reduced cost. Well-behaved electronics that do not impair the optic pathway capabilities are a key necessity.
The counterparts to the digital data waterfalls seen in these record-breaking high-speed circuits that process massive bitstreams are precision circuits which are often used for controlling laser sources and receivers. These elements drip-drip low-level signals into a data processing environment from a comparatively slow, band-limited external world. These circuits have power requirements that are tiny but myriad: they have high positive and negative voltages for bias, precisely programmed voltages that sit between those high and low voltage extremes, and they have to be very “clean” as the signal processes they supply energy to “sift” low energy signals out of noise. All these considerations need Smarter Power.
Smarter Power Approaches
On the one hand you have a need for elevating current densities at sub-1V voltages (with the attendant need for fast transient response) and then there is the issue of supporting lots of rails (calling for low noise and simple, fast programmability).
Smart power encompasses a power semiconductor with an area on its substrate, much like a castle with a moat around it, housing the control circuitry for that power device. The brain of the power module would need to be protected from the intense E-fields and noise emanating from the power switch, the brawn of a power module.
It can now be argued that smart power means more than this – it needs to be Smarter than Ever. Some semiconductor manufacturers have worked out ways of integrating several functions to strike very attractive design tradeoffs in the size, utility and performance: An example of this is the MIC38300, a buck switching regulator, its attendant inductor and a low-dropout regulator all on one chip giving a massive power density advantages over other solutions while maintaining enviable efficiency ratings [1].
Addressing Challenges
We take control mechanisms for granted, particularly the feedback loop of a power regulator setting the output, be it a current or a voltage. Micrel continues to cleverly re-engineer the feedback loop of regulators, both of the linear and switching kinds, so that they have wider frequency responses. Optimal noise control and fast transient response gets to be paired with using fewer as well as smaller filtering and stabilizing passive components. A prime example of this design approach is used in certain buck regulators in the Micrel power portfolio: the Hyperlight load concept [2] features a simple, high-bandwidth switched feedback loop that can achieve rapid transient heavy load responses whilst maintaining high efficiency when the load is small.
Add to this the use of simple, but lean and fast digital interfaces to address and alter the output levels of individual outputs in a highly parallel regulator architectures and you have Smarter power for all sorts of applications where power levels settle quickly in transient situations and are verniered as needed to conform with efficiency and power saving dictates for a given application. An example of such a device that is close to release is the MIC2826, whose switcher and 3 LDOs can be dynamically sequenced and scaled using an I2C control interface.
The ultimate challenge surely lies in the clever integration of power provisioning on sophisticated, ULSI+ state-of-the-art signal processors, where there may be a need for different bias or core voltages for mixed signal circuits. We often see much of the control circuitry for a linear regulator integrated into the signal processing substrate. Although inefficient, this is a low noise solution. Switching noise would appear to be such a serious interference source that it obviates the use of fully integrated switchers on a signal processing chip. However, as an example of bucking the trend, Micrel’s engineers have been able to integrate much of a boost regulator into QuikRadio ICs such as the MICRF104, a 1.8V DC powered UHF ASK radio operating in the 300 to 470 MHz range [3].
The insistent demand is perfecting higher power efficiencies at low noise in high current density supply systems. Radical approaches in integrated circuit design and fabrication promise to bring together heavy power switching modules and the complex signaling circuits that form the majority of the gate count of ASICs and mixed-signal FPGAs.
References
[1] “Maintain Power-Conversion Efficiency While Saving PCB Space” by P Khairolomour Fairchild Semiconductor pp 53, 54 in Electronic Design June 12, 2008.
[2] “Beyond LDOs and Switching Regulators” by B Huang Micrel Semiconductor pp 42-44 in Bodo’s Power Systems Oct 2007
[3] http://www.micrel.com/ Micrel’s webportal: Search on MICRF104
About the Author
David Bourner is a field applications engineer serving Micrel’s Midatlantic region. He has had a diverse career that has seen him working as a Royal Navy instructor officer, a senior design engineer working on digital audio at Philips Semiconductor (now NXP) and on RF communications systems at Hughes Network Systems following his move over to the USA. Working for Analog Devices and National Semiconductor in field applications, he went back to school to offer his broad experience as a non-tenured Professor of the Practice, in the roles of teaching and offering consultation on RF and sensor technology to start-up companies through the Maryland Industrial Partnership program. He is the architect of the computer engineering undergraduate capstone course which is conducted within the computer science and electrical engineering school at the University of Baltimore County Maryland.
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