Image Processing Reference
In-Depth Information
The maximum local supply noise measured by VMON5 was 30.9 mV, and the average voltage
drop was smaller than that when executing the Dhrystone benchmark program. This result
confirms that good power efficiency was attained using hardware accelerators. Measured
maps of the typical situations are shown in Fig. 14. Figure 14(a) is a snapshot taken when
neither CPU was operating but both were consuming clock power; it also shows the location
of each VMON. Note that the APL-RT CPU was running at 312 MHz, and the AP-SYS CPU
was running at 208 MHz. Figure 14(b) is a snapshot when the APL-RT CPU was initializing
the MPEG4 accelerator. Figure 14(c) depicts the situation when the local supply noise was at
its maximum. The image in Fig. 14(d) illustrates the period when the execution of the MPEG4
accelerator was dominant. Figure 14(e) is a snapshot when the APL-RT CPU was executing an
interruption operation from the MPEG4 accelerator, and Fig. 14 (f) shows the typical situation
where the MPEG4 accelerator was encoding a QCIF-size image.
This measurement was done using simple picture-encoding programs, so frequent
interruptions were necessary to manage the execution of the program. However, in real
situations, since operation would not be carried out with frequent interruptions , and the
APL-RT CPU might be in the sleep mode, the power consumption of the APL-RT CPU would
be reduced, and the map would show a calmer surface.
These results show that by using a hardware accelerator, the power consumption was also
distributed over the chip, resulting in a reduction in the total power consumption. This
voltage-drop map therefore visually presents the effectiveness of implementing a hardware
accelerator.
4. Conclusion
An in-situ power supply noise measurement scheme for obtaining supply-noise maps
was developed. The key features of this scheme are the minimal size of simple on-chip
measurement circuits, which consist of a ring oscillator based probe circuit and analog
amplifier, and the support of off-chip high resolution digital signal processing with frequent
calibration. Although the probe circuit based on the ring oscillator does not require a
sampling-and-hold circuit, high accuracy measurements were achieved by off-chip digital
signal processing and frequent calibrations. The frequent calibrations can compensate for
process and temperature variations. This scheme enables voltage measurement with millivolt
accuracy and nanosecond-order time resolution, which is the period of the ring oscillator.
Using the scheme, we demonstrated the world's first measured animation of a supply-noise
map in product-level LSIs, that is, 69-mV local supply noise with 5-ns time resolution in a
3G-cellular-phone processor.
5. Acknowledgment
This work was done in cooperation with H. Mizuno, S. Komatsu, and Y. Kondoh
of the Hitachi, Ltd., and T. Irita, K. Hirose, R. Mori, and Y. Yasu of the Renesas
Electronics Corporation. We thank T. Yamada and N. Irie of Hitachi Ltd., and T. Hattori,
T. Takeda of Renesas Electronics Corporation, and K. Ishibashi of The University of
Electro-Communications, for their support and helpful comments. We also express our
gratitude to Y. Tsuchihashi, G. Tanaka, Y. Miyairi, T. Ajioka, and N. Morino of Renesas
Electronics Corporation for their valuable advice and assistance.
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