IRJET- Reliability Enhancement of Low-Power Sequential Circuits using Power Gating Technology

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 06 Issue: 05 | May 2019 www.irjet.net p-ISSN: 2395-0072
© 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 5321
RELIABILITY ENHANCEMENT OF LOW-POWER SEQUENTIAL CIRCUITS
USING POWER GATING TECHNOLOGY
Deepa Jose1, Juby Raju2, Saju A3
1PG Scholar, Dept of ECE, MCET, Kerala
2Associate professor, Dept of ECE, MCET, Kerala
3Research Scholar, VTU, Karnataka
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Abstract – This paper deals with low-powerASICdesigns with
power gating technology. They compromises with high
performance and low area and power consumption, taking
advantage of both latch and flip-flop features. While the
circuit reliability and robustness against different process,
voltage, and temperature variations are consideredascritical
issues with current technologies, no significant reliability
study was proposed for traditional transmission gate pulsed
latch circuits. In this paper, present a study on the effect of
different PVT variations on the behavior traditional
transmission gate pulsed latch circuits with power gating
technology , while keeping their main advantages of high
performance, low power, and smallarea. Theproposeddesigns
have negligible power overhead when running at nominal
supply voltage, and they have higher yield per unit power
when compared with the traditional design at different
voltages and temperatures. The proposed circuit is
implemented using Tanner v13 in 45 nm technology.
Key Words: Pulsed latches, power gating techniques, low
power, voltage scaling etc
1. INTRODUCTION
FLIP-FLOPS are considered the most popular sequential
elements used in conventional ASIC designs. This is mainly
because of the simplicity of their timing model,whichmakes
the design and timing verification processes much easier.
The high performance custom designs tend to use latches
due to their lower timing in some designs. Although latch
based designs are typically robust to clock skew and jitter
(due to the latch transparency period), latches have a
complicated timing model, which, in turn, complicates the
design and the verification processes and increases the risk
of hold time violations, especially with PVT variations.
Pulsed latches have been always proposed to decrease
power consumption and increase performance. In PLs with
relatively wide pulse widths were used to allow cycle
borrowing and tolerate any clock skew. In order, to
compensate for any data before the end of the pulse. The
structure of transmission gate pulsed latch is similar to
differential latch structure, due to the presence of weak
PMOS transistors in the master latch it is very difficult for
the transition to take place when there is a change in input.
Fig -1: Simple diagram of a transmission gate pulsed latch
Pulsed latches are used in above figured;singlepulsercan be
shared by more than one latch. The advantagesofthiscircuit
are area and power consumption savings.Pulser usage can
eliminate the need for some of theclock buffers inthecircuit.
2. Overview of Power Gating Technology
Power gating is a technique used in integrated circuitdesign
to reduce power consumption, by shutting off the current to
blocks of the circuit that are not in use. In addition to
reducing stand-by or leakage power, power gating has the
benefit of enabling Iddq testing. Power Gating is effectivefor
reducing leakage power. Power gating is the technique
wherein circuit blocks that are not in use are temporarily
turned off to reduce the overall leakage power of the chip.
This temporary shutdown time can also call as "low power
mode" or "inactive mode". When circuit blocks are required
for operation once again they are activated to "activemode".
These two modes are switched at the appropriate time and
in the suitable manner to maximize power performance
while minimizing impacttoperformance.Thusgoal ofpower
gating is to minimize leakage power by temporarily cutting
power off to selective blocks that are not required in that
mode.
2.1 Fine-grain power gating
Adding a sleep transistor to every cell that is to be turned off
imposes a large area penalty, and individually gating the
power of every cluster of cells creates timing issues
introduced by inter-clustervoltagevariationthataredifficult
to resolve. Fine-grain power gating encapsulates the
switching transistor as a part of the standard cell logic.

Switching transistors are designed by either library IP
vendor or standard cell designer.
The size of the gate control is designed with the worst case
consideration that this circuit will switch during every clock
cycle resulting in a huge area impact. Some of the recent
designs implement the fine-grain power gating selectively,
but only for the low threshold cells. If the technology allows
multiple low threshold libraries, the use of low threshold
devices is minimum in the design (20%), so that the area
impact can be reduced. When using power gates on the low
threshold cells the output must be isolatedifthenextstageis
a high threshold cell. Otherwise it can cause the neighboring
high threshold cell to have leakage when output goes to an
unknown state due to power gating.
Fig -2: Fine-grain power gating
Gate control slew rate constraint is achieved by having a
buffer distribution tree for the control signals. The buffers
must be chosen from a set of always on buffers (buffers
without the gate control signal) designed with high
threshold cells. The inherent difference between whena cell
switches off with respect to another, minimizes the rush
current during switch-on and switch-off.
2.2 Coarse-grain power gating
The coarse-grained approach implements the grid style
sleep transistors which drives cells locally through shared
virtual power networks. This approach is less sensitive to
PVT variation, introduces less IR-drop variation, and
imposes a smaller area overhead than the cell- or cluster-
based implementations. In coarse-grain power gating, the
power-gating transistor is a part of the power distribution
network rather than the standard cell.
3. OVERVIEW OF ARCHITECTURE
The new architecture for transmission gate pulsed latch is
designed by power gating technology. Here we used stack
technique. In which the basic circuit is connected with both
header an footer switches. The PMOS transistorisconnected
to the vdd. During active mode the header switch will be
conduct and transfer the drain voltage to the given circuit.
But in stand by mode it cannot work. So, that leakage power
is reduced. The similar operation is carried out in footer
switch, it will conduct on the stand by mode .The NMOS
transistor is connected as a footer switch. Due to this power
dissipation is grounded.
Fig -3 PROPOSED DIAGRAM
3.1 SIMULATION RESULT
Fig -4:Simulation of proposed design
Fig -5:OUTPUT WAVEFORM

Table -1: Comparison Table
Voltage
(vdd)
Power TECHNOLOGY
Traditional
transmissi
on gate
pulsed
latch
3v 4.27w 90nm
Proposed
system
5v 2.204w 45nm
3. CONCLUSION
In this paper presented the effect of PVT variations on the
pulsed latch performance in low power circuit. The circuit is
implemented using Tanner v13 in 45 nm technology. The
analysis considered both the pulser and the latchtoevaluate
the reliability of the entire pulsed latch circuit. In addition,
the benefits of having a power gating technique were
discussed. Stack technique is used in the proposedsystem to
reduce power. Finfet and CNT can be viewed as the future
implantation for this design for standard cell ASICs.
REFERENCES
[1] M. Alioto, E. Consoli, and G. Palumbo, “Variations in
nanometer CMOS flip-flops: Part Energy variability and
impact of other sources of variations,” IEEE Trans.
Circuits Syst. I, Reg. Papers, vol. 62, no. 3,pp. 835–843,
Mar. 2015.
[2] S. Paik, G.-J. Nam, and Y. Shin, “Implementation of
pulsed-latch and pulsed-register circuits to minimize
clocking power,” in Proc. IEEE/ACM Int. Conf. Comput.-
Aided Design (ICCAD), Nov. 2011, pp. 640–646.
[3] E. Consoli, G. Palumbo, J. M. Rabaey, and M. Alioto,
“Novel class of energy-efficient very high-speed
conditional push–pull pulsed latches,” IEEE Trans. Very
Large Scale Integr. (VLSI) Syst., vol. 22, no. 7, pp. 1593–
1605, Jul. 2014.
[4] M. Alioto, E. Consoli, and G. Palumbo, “Variations in
nanometer CMOS flip-flops: Part II—Energy variability
and impact of other sources of variations,” IEEE Trans.
Circuits Syst. I, Reg. Papers, vol. 62, no. 3, pp. 835–843,
Mar. 2015.

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IRJET- Reliability Enhancement of Low-Power Sequential Circuits using Power Gating Technology