Dynamic Voltage and Frequency Management for a Low-Power Embedded Microprocessor

Takahiro SEKI
Satoshi AKUI
Katsunori SENO
Masakatsu NAKAI
Tetsumasa MEGURO
Tetsuo KONDO
Akihiko HASHIGUCHI
Hirokazu KAWAHARA
Kazuo KUMANO
Masayuki SHIMURA

Publication
IEICE TRANSACTIONS on Electronics   Vol.E88-C    No.4    pp.520-527
Publication Date: 2005/04/01
Online ISSN: 
DOI: 10.1093/ietele/e88-c.4.520
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Low-Power LSI and Low-Power IP)
Category: Digital
Keyword: 
adaptive supply voltage control,  autonomous clock frequency control,  leakage power compensation,  embedded DRAM,  wideband bus architecture,  

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Summary: 
In this paper, a Dynamic Voltage and Frequency Management (DVFM) scheme introduced in a microprocessor for handheld devices with wideband embedded DRAM is reported. Our DVFM scheme reduces the power consumption effectively by cooperation of the autonomous clock frequency control and the adaptive supply voltage control. The clock frequency is controlled using hardware activity information to determine the minimum value required by the current processor load. This clock frequency control is realized without special power management software. The supply voltage is controlled according to the delay information provided from a delay synthesizer circuit, which consists of three programmable delay components, gate delay, RC delay and a rise/fall delay. The delay synthesizer circuit emulates the critical-path delay within 4% voltage accuracy over the full range of process deviation and voltage. This accurate tracking ability realizes the supply voltage scaling according to the fluctuation of the LSI's characteristic caused by the temperature and process deviation. The DVFM contributes not only the dynamic power reduction, but also the leakage power reduction. This microprocessor, fabricated in 0.18 µm CMOS embedded DRAM technology achieves 82% power reduction in a Personal Information Management scheduler (PIM) application and 40% power reduction in a MPEG4 movie playback application. As process technology shrinks, the DVFM scheme with leakage power compensation effect will become more important realizing in high-performance and low-power mobile consumer applications.