Near-Threshold Voltage Technology
The near-threshold voltage is the point at which transistors turn on and conduct electricity. Operating certain devices near this threshold can increase energy efficiency by an order of magnitude over running a device at normal power levels. Further, by moving the supply voltage closer to but still above the transistor threshold voltage, the effects of common transistor leakage current can be dramatically reduced.
Intel first introduced a near-threshold voltage (NTV) processor, code-named during the 2011 Intel Developer Forum (IDF). The Claremont,was a prototype chip that could allow a computer to power up on a solar cell the size of a postage stamp. My tweet from the IDF event referenced a solar-powered Claremont demonstration in which the Claremont powered a short video clip of a playful kitten. When the sunny was out, the NVT-powered video had enough power for the cat to dance. But when it rained (i.e., the sun’s energy was clouded over), then the cat video froze and the dancing stopped.
The Claremont relied on an ultra-low-voltage circuit to greatly reduce energy consumption. This class of processor operated close to the transistor’s turn-on threshold voltage. Not surprisingly, threshold voltages varied with transistor type. Typically, though, they are low enough to be powered by a postage-stamp-sized solar cell.
The other goal for the Claremont prototype, fabricated at 32nm, was to extend the processor’s dynamic performance – from NTV to higher, more common computing voltages – while maintaining energy efficiency.
The Claremont prototype showed that the technology works for ultra-low-power applications that require only modest performance. Reliable NTV operation was achieved using unique, IA-based circuit-design techniques for logic and memories.
Unfortunately, further developments were needed to create standard NTV circuit libraries for common, low-voltage CAD methodologies. Specifically, NTV designs required a re-characterized, constrained standard-cell library to achieve such low corner voltages. Creating such libraries took time and money plus the support of EDA tool vendors and foundries. To date, that support has not been forthcoming. For these reasons, the adoption of NTV technology in the commercial market has been very slow.
Fortunately, the continued march of Moore’s Law beyond the 32nm geometry of the original Clairmont prototype has improved the power efficiency of silicon chips – thus removing the urgency for the NTV technology.
|Image source: Intel / IDF 2011 / Claremont|