Image Processing Reference
In-Depth Information
(
GHz). Especially, the low-frequency domain is important in the case such as the operational
mode switching and the power gating by on-chip power switches. Thus, in these cases, the
accuracy of this method is sufficient to the tracking with high accuracy and the time resolution.
Recently measurement of the influence of the on-chip power gating is reported (Fukuoka,
2007). Although the measured voltage is averaged out in the period of the VMON, however,
the measurement of the voltage fluctuations at the actual operational mode in the product
level LSI is innovative.
The higher the frequency of the ring oscillator, the higher the time resolution and improving
the tracking accuracy; however, signal transmission at a higher frequency limits the length of
the transmission line between the VMONs and VMONC due to the bandwidth limitation of
the transmission line. There is therefore a trade-off between time resolution and transmission
length. Although bandwidth can be widened by adding a repeater circuit, isolation cells,
>
I/O
s (Kanno, et al., 2002), are needed when applying many power domains, and, thus, the design
will be complicated.
μ
2.2 Accuracy of waveform analysis
Accurate measurement of the VMON output frequency is also important in the in-situ
measurement scheme. The accuracy also depends on the resolution of the oscilloscope
φ = 0
φ = 0
φ = π/4
φ = π/4
φ = π/2
φ = π/2
φ = 3π/4
φ = 3π/4
φ = π
φ = π
φ = 5π/4
φ = 5π/4
φ = 3π/2
φ = 3π/2
φ = 7π/4
φ = 7π/4
mu
ltiple
multiple
(a)
(b)
Fig. 7. Simulated results of voltage calculated by ring oscillator frequency: voltage
fluctuation was (a) 150 MHz and (b) 300MHz.
is the initial phase difference between
voltage fluctuation and VMON output. The solid lines are voltage fluctuations and the dots
are the calculated voltage from the VMON output.
φ
