**4. Conclusion**

14 Will-be-set-by-IN-TECH

(b)

(f)

(d)

**VMON1**

**VMON6**

**VMON7**

**VMON4 VMON5**

**VMON2 VMON3**

(a)

(c)

(e)

Fig. 14. Measured supply-noise maps for MPEG encoding operation. (a) neither CPU was operating but was consuming clock power; (b) the APL-RT CPU was initializing the MPEG4 accelerator; (c) the local supply noise was at its maximum; (d) the execution of the MPEG4 accelerator was dominant; (e) the APL-RT CPU was executing an interruption operation from the MPEG4 accelerator and (f) the MPEG4 accelerator was encoding a QCIF-size picture.

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
