Image Processing Reference
In-Depth Information
there is no flat (global) reference voltage in an LSI. Dual-ended signal transmission is
a promising technique to get around this problem; however, this method gives rise to
another issue: the difficulty of routing by using a ready-made EDA tool. Noise immunity
of the transmission is another concern, because analog signal transmission is still needed.
3. The third point is the dynamic range of the voltage measurement.
To measure supply-voltage fluctuation, a dedicated supply voltage for the probes needs to
have a greater range than that of the measured local supply voltage difference.
2. In-situ supply-noise map measurement
An in-situ power-supply-noise map measurement scheme was developed by considering the
above key points. Figure 4 shows the overall configuration of our proposed measurement
scheme. The key feature of this scheme is the minimal size of the on-chip measurement circuits
and the support of off-chip high resolution digital signal processing with frequent calibration
(Kanno, et al., 2006),(Kanno, et al., 2007). The on-chip measurement circuit therefore does not
need to have a sample-and-hold circuit.
VDD 1
VMONC
VMON1
off-chip
PC
AVDD
VSS1
VDD 2
calibration
VMON2
+
VSS2
V DDn
VMONn
VSSn
time-domain
analyzer
Fig. 4. In-situ supply-noise-map measurement scheme
The on-chip circuits consist of several voltage monitors (VMONs) and their controller
(VMONC). The VMON is a ring oscillator that acts as a supply-voltage-controlled oscillator,
so that the local supply difference (LSD) between V DD1 and V SS1 can be translated to a
frequency-modulated signal (see Fig. 5). The VMONC activates only one of the VMONs
and outputs the selected frequency-modulated signal to the external part of the chip. Every
VMON can be turned off when measurement is not necessary.
The output signal is then demodulated in conjunction with time-domain analysis by an
oscilloscope and calibrations by a PC. The frequency-modulated signal between the VMONs
and VMONC is transmitted only via metal wires, so dozens of power-domain partitions can
be easily implemented in an LSI (Kanno, et al., 2006). The frequency-modulated signal has
high noise immunity for long-distance, wired signal transmission. Although the measurement
results are averaged out in the nanoseconds of the VMON's sampling period, this method can
analyze voltage fluctuation easily as the voltage fluctuation map in LSIs by using multi-point
measurement.
The dynamic range of the measuring voltage is not limited despite requiring no additional
dedicated supply voltage. This is because we measure a frequency fluctuation as a voltage
 
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