A verilog based simulation methodology for estimating statistical test for the time constancy of scaling exponents power and area

IJSRD - International Journal for Scientific Research & Development| Vol. 2, Issue 08, 2014 | ISSN (online): 2321-0613
All rights reserved by www.ijsrd.com 56
A Verilog Based Simulation Methodology for Estimating Statistical Test
for the Time Constancy of Scaling Exponents Power and Area
Lokeshwari Sharma1
1
Research Scholar
1
Department of Electronics and Communication
1
Institute of Technology and Management, Bhilwara
Abstract— The low Power estimation is an important aspect
in digital VLSI circuit design. The estimation includes a
power dissipation of a circuit and hence this to be reduces.
The power estimations are specific to a particular
component of power. The process of optimization of circuits
for low power, user should know the effects of design
techniques on each component. There are different power
dissipation methods for reduction in power component. In
this paper, estimating the power like short circuit and the
total power, power reduction technique and the application
of different proposed technique has been presented here.
Hence, it is necessary to provide the information about the
effect on each of these components.
Keywords: Power estimation, Verilog Based Simulation
Methodology, Power Theater.
I. INTRODUCTION
Power consumption was a part of the design process but not
very visible. The reduced area of digital circuits is not a big
point of matter today because with new IC production
techniques, many millions of transistors can be fabricated in
a single IC. But, reducing the sizes of circuits have paved
the way for reduced power consumption in order to have an
extended battery life. Generally, power is consumed when
capacitors in the circuits are either charged or discharged
due to the switching activities of CMOS. Estimating the
short circuit dissipation has been coupled with the dynamic
dissipation and report the switching energy. So at higher
order of a system this power dissipation is well-kept by
reducing the switching activities which is done by shutting
down portions of the system when they are not in use. The
short circuit models are proposed and studied .The correct
model taken into account of capacitance load effect, the
input rise and fall times. The overall current flow can be
determined by the rise and fall time. Large VLSI circuits
comprise of number of components like a processor,
controllers and a functional unit. The power reduction has to
stop in any of the components of the processor which is not
in use, so that less power will be dissipated when the
processor is operating. The circuit level power estimation
can accurately and efficiently estimate various power
components and the total power and provide information to
a designer. With the modification and significant advances
made in logic simulation, timing analysis and delay areas
through the use of the bounded delay model and also be
extended to include leakage power.
II. POWER DISSIPATION IN CMOS CIRCUITS
Three prime sources of power dissipation in CMOS circuits:
 Dynamic power
 Short circuit power
 Leakage power
The average power dissipation of a digital CMOS
circuits can be calculated by
P avg = P dynamic + P short-circuit + P leakage + P static
Where Pavg is the average power dissipation, P
dynamic is the dynamic power dissipation due to switching of
transistors, P short-circuit is the short-circuit current power
dissipation when there is a direct current path from power
supply down to ground, P leakage is the power dissipation due
to leakage currents, P static and is the static power
dissipation[12].
A. Dynamic power
Dynamic Power is the dominant source of power dissipation
in hardware design, and is highly dependent on the
application and architecture. A lot of opportunities to reduce
dynamic power exist at high-level. Power reduction
techniques discussed in this thesis concentrate on reducing
the dynamic power consumption of the hardware design.
Switching activity and capacitance are two most important
factors to keep in mind at high level because small changes
in hardware architecture may impact the capacitance and
activity proﬁle of the design.
Fig. 1: Dynamic Power in CMOS Invertor
Fig. 2: Static Power in CMOS Invertor
B. Leakage power
It is the static component of the power dissipation and
occurs due to spurious currents in the non-conducting state
of the transistors. Static power has two important factors,
namely Sub-threshold leakage and gate to source leakage.
As process technology node size is decreasing sub-threshold
leakage is increasing. This factor exponentially in- creases
with newer technology node. Some of the prominent
techniques to reduce leakage power include power-gating
and stacking of transistors. These techniques are applied
after the net list is ﬁnalized for the design. Gate to source

A Verilog Based Simulation Methodology for Estimating Statistical Test for the Time Constancy of Scaling Exponents Power and Area
(IJSRD/Vol. 2/Issue 08/2014/014)
leakage can be reduced by improving the gate insulation of a
node of transistor.
C. Short-circuit Power:
It occurs due to the stacked P and N devices in a CMOS
logic gate that are in the ON state simultaneously, and can
be minimized by reducing the signal transition times. It is
hard to reduce this component of power through synthesis-
time optimizations. After the netlist is finalized, a lot of care
is given to place the design so that there is not much voltage
drop for some transistors. Voltage drop on nodes may not
only cause timing issues but also short circuit power issues.
If short circuit power persists for longer time it may cause
extremely high power consumption.
Various tools exist in industry that can perform
power estimation accurately at the RTL or lower- level such
as Power Theater [11].Power Theater [11] is an RTL/gate-
level power estimation tool, which provides good accuracy
for RTL power estimation with respect to the corresponding
gate-level and silicon implementation. These tools require
design information for models in Verilog/VHDL, simulation
dump from the RTL or lower-level simulation (such as
Value Change Dump (VCD) or FSDB) for activity analysis,
and technology library etc. Such information helps in doing
power estimation accurately and efficiently at the RTL and
lower level.
III. HIGH LEVEL POWER ESTIMATION
Accurate power estimation at high level is very important
for any successful design methodology. In this section, we
include spread sheet based approach, Power Estimation
Approaches utilizing Power Models, commercial tools
available for RTL and gate-level power estimation etc.
A. Spreadsheet Based Approaches:
Spreadsheets are very useful in the early stage of design
process, when initial planning is going on and a lot of
important decisions are being taken [13]. One of the biggest
advantages of spreadsheet based analysis is that the user
does not really need to learn any complex/sophisticated tool
for taking design decisions. One of the basic application of
spreadsheet is area estimation. He/She can easily get an
estimate on area by using data sheets from intellectual
property (IP) provider, library cell estimates, etc.
Spreadsheet provides a capability to capture such
information, which can be utilized for quick area estimation.
Similarly, some decisions to control power can also be taken
using spreadsheet based approach. Power calculating
approaches using spreadsheets are very helpful for voltage
regulators , heat sink, printed circuit board (PCB), power
supplies, and cooling systems.
B. Power Estimation Approaches utilizing Power Models
One of the first works in the area of model based power
estimation was proposed by Tiwari et al. [14] for the
architecture level power estimation of microprocessors.
They provide a method to estimate power/energy number of
a given program on a given processor. It states “By
measuring the current drawn by the processor as it
repeatedly executes certain instruction sequences, it is
possible to gain most of the information that is needed to
estimate the power cost of a program for that processor”
[14].
Power consumption of a microprocessor can be
represented as P = VCC x I, where VCC is operating voltage
and I is the current drawn by the microprocessor. In their
approach, they measured the current drawn by the processor
and then utilize it for power measurement purpose. They
assumed that during the calculation, the operating voltage
for the processor will not change. For average power
estimation purpose they had first estimated energy over
different cycles and then averaged it. To conclude with, they
have proposed a way in which one can gauge the impact on
average current from the execution of an instruction. This
also proposed a method to measure inter- instruction effects
on prevailing values. To compute the average power
consumption of a processor while executing a software
program, these values are used.
Most of the approaches for power models are
proposed for CPU or micro architecture of processors. In an
ASIC design flow where mainly design stage starts at RTL
and mostly design is represented as a Finite State Machine
with Data path (FSMD), similar approach may not be useful.
IV. POWER REDUCTION AT THE RTL AND HIGH LEVEL
Clock-gating is implemented at the RTL by tools such as
Power Theater [15], Power compiler [16], etc. Power
Theater suggests opportunities to clock-gate registers for
which there is no multiplexer in the feedback path. They
find the conditions under which clock is required when and
only when there is a change in data input to a register.
Power compiler recommends particular RTL coding styles
to enable clock-gating during synthesis.
Clock gating and operand isolation are two
techniques to reduce the power consumption in state- of-the
art hardware designs. Both approaches basically follow a
two-step procedure: first, a hardware circuit is statically
analyzed to determine irrelevant computations. Secondary,
all parts that are responsible for these computations are
replaced by others that consume less power in the average
case, either by gating clocks or by isolating operands. Jens
et al. [17] defines the theoretical basis for adoption of these
approaches in their entirety. They show how irrelevant
computation can be eliminated using their approach. They
present passiveness conditions for every signal x, that shows
that the value currently carried by x does not contribute to
the final result of the system. After showing how their
theory can be generally used in the context of clock gating
and operand isolation a classification of many state-of-the-
art approaches is performed and shown that most of the
approaches in the literature are conservative approximations
of their general setting.
Recently power reduction techniques have also
been used for security purpose. With increased outsourcing,
confirming the genuineness of third party manufactured ICs
has emerged as a major challenge. Researchers have
effectively used various side-channel analysis techniques to
finger- print ICs viz. power, timing, EM-radiation. In [18],
[19] authors have used circuit partitioning techniques to
selectively exaggerate power consumption in targeted
portions while reducing the overall power of the chip.

Fig. 3: Dynamic Power Control Lower Power Consumption
and Eliminates Power Loss
Fig. 4: Static Power Versus Normalized delay
V. APPLICATION OF THE PROPOSED TECHNIQUES
In this paper, propose techniques that can be utilized with
HLS or high-level design flows. Here we briefly discuss the
application of the proposed techniques.
A. Early Power Estimation
This approach is applicable in scenarios where designers
want to measure power consumption of the target hardwares
using models that can be utilized at higher abstraction levels
than the RTL. It is given that the RTL or gate-level power
estimation is extremely time consuming, such techniques
can save time if proven to be accurate enough for crucial
design decisions. A technique to characterize power model
that is parameterized by the switching activity of each state
of Finite State Machine with Datapath (FSMD) model of the
design. Such a power model can then be simulated with
high-level models. One could use such vectors or assertions
to bring a high level simulation to a target state to measure
state specific power consumption.
Since power consumption is very much design and
technology dependent, it might be difficult to create power
models that characterize power consumption of a target
hardware at high-level. To perform power calculation at the
RTL, the largest bottlenecks are simulating, processing and
extraction of the activity information.
B. Power Reduction from high-level:
We consider clock-gating as a primary candidate for power
reduction. We investigate how this can be enabled from
high-level. A designer is operating on a behavioral
description of the design at high-level. Clock-gating is
needed to be insert from the behavioral description before
synthesis. Similarly, sequential clock-gating requires
optimizations across the register boundaries. Such
optimizations may cause a lot of verification problems.
Also, how system-level simulation can guide HLS to select
the appropriate clock-gating candidates among all the
registers. This approach is also useful to find out if
aggressive application of clock-gating will lead to wastage.
VI. CONCLUSION
The estimation techniques are implemented for logic gate
level estimation tool. The tool can estimate the different
power dissipation components and also estimate the power
dissipation while maintaining efficiency .Also capable of
separating and estimating the different power dissipation
components. The above technique can be used for
estimating the power dissipation. There have been other
notable works focusing on particular power components.
For the power estimation Techniques discussed
above show that power modeling of a hardware block can be
very complex and application dependent. On enhancing the
levels of abstraction, power estimation of a hardware block
becomes crucial. Different techniques at different
abstraction levels exist to obtain the power consumption
starting from spread-sheet, power model to macro-model
based power estimation. The most popular approaches in
industry are mainly power model based approach or by
performing power estimation at RTL/gate-level description
of a hardware design. While, at the lower level of
abstraction, commercial tools contribute good certainty with
respect to silicon, but as we go to higher levels of
abstraction accuracy of the power estimation methodologies
reduces.
Dynamic power is one of the most important
components of power consumption of a design, and thus its
reduction is targeted during most power-aware high-level
synthesis processes. Most of the approaches do not provide
any support for power reduction from the behavioral
specifications itself. In this paper, propose approaches to
enable clock-gating itself for various granularities of clock-
gating such as fine grain at variable level and coarse grain at
function or scope level. We also show how to extend this
approach for sequential clock-gating. Finally, we present
how to utilize power models to guide power reduction
process at high-level. The advantage of such an approach is
facilitation of power reduction features at the high-level.
Also, the approaches for power estimation, which will be
discussed later in detail, combined with power reduction
approach can make the design flow completely at high-level.
This will help in providing power aware design
methodology at high-level with faster turnaround time.
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A verilog based simulation methodology for estimating statistical test for the time constancy of scaling exponents power and area

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A verilog based simulation methodology for estimating statistical test for the time constancy of scaling exponents power and area