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International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
DOI : 10.5121/vlsic.2012.3510 123
DESIGN & ANALYSIS OF A CHARGE RE-CYCLE
BASED NOVEL LPHS ADIABATIC LOGIC CIRCUITS
FOR LOW POWER APPLICATIONS
Sanjeev Rai1
, Govind Krishna Pal2
, Ram Awadh Mishra3
and Sudarshan Tiwari4
1
Department of Electronics & Communication Engineering, Motilal Nehru National
Institute of Technology, Allahabad, India
srai@mnnit.ac.in
2
Apache Design Solutions, Noida, India
govind@gmail.com
3
Department of Electronics & Communication Engineering, Motilal Nehru National
Institute of Technology, Allahabad, India
ramishra@mnnit.ac.in
4
Director National Institute of Technology, Raipur, Chhatisgarh, India
director@nitrr.ac.in
ABSTRACT
This paper focuses on principles of adiabatic logic, its classification and comparison of various adiabatic
logic designs. An attempt has been made in this paper to modify 2PASCL (Two Phase Adiabatic Static
CMOS Logic) adiabatic logic circuit to minimize delay of the different 2PASCL circuit designs. This
modifications in the circuits leads to improvement of Power Delay Product (PDP) which is one of the
figure of merit to optimize the circuit with factors like power dissipation and delay of the circuit. This
paper investigates the design approaches of low power adiabatic gates in terms of energy dissipation and
uses of Simple PN diode instead of MOS diode which reduces the effect of Capacitances at high transition
and power clock frequency. A computer simulation using SPECTRE from Cadence is carried out on
different adiabatic circuits, such as Inverter, NAND, NOR, XOR and 2:1 MUX.
KEYWORDS
Adiabatic logic, Low-power, Two phase clocked, Energy recovery, Split-level, Diode based logic, Power
Delay Product (PDP), LPHS (Low Power High Speed).
1. INTRODUCTION
The popularity of complementary MOS (CMOS) technology can be gauged from the fact that it
has lower power consumption and high speed. However, the current trend towards ultra low-
power has made researchers search for techniques to recycle energy from the circuits within. In
conventional CMOS level-restoring logic, the switching event of circuits with rail-to-rail output
voltage swing, causes an energy transfer from the power supply to the output node or from the
output node to the ground. During a 0-to-VDD transition of the output, the total output charge Q =
Cload VDD is drawn from the power supply at a constant voltage. Thus, an energy of E = CL VDD
2
is
drawn from the power supply during this transition. Charging the output node capacitance to the
voltage level VDD means that at the end of the transition, the amount of stored energy in the output
node is E = ½ CL VDD
2
. Thus, half of the injected energy from the power supply is dissipated in
the PMOS network while only one half is delivered to the output node. During a subsequent
VDD-to-0 transition of the output node, no charge is drawn from the power supply and the energy
stored in the load capacitance is dissipated in the NMOS network.
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
124
To reduce the dissipation, the circuit designer can minimize the switching events, decrease the
node capacitance, reduce the voltage swing, or apply a combination of these methods. Yet in all
these cases, the energy drawn from the power supply is used only once before being dissipated.
To increase the energy efficiency of the logic circuits, other measures can be introduced for
recycling the energy drawn from the power supply. A novel class of logic circuits called adiabatic
logic [1],[2] offers the possibility of further reducing the energy dissipated during the switching
events, and the possibility of recycling, or reusing, some of the energy drawn from the power
supply. To accomplish this goal, the circuit topology and the operating principles have to be
modified as per the need arises. The amount of energy recycling [3] achievable using adiabatic
techniques is also determined by the process technology, switching speed, and the voltage swing.
In conventional CMOS logic we use constant voltage source to charge the load capacitance but in
case of adiabatic logic switching circuits we use constant current source instead of constant
voltage source. Figure 1. depicts clearly how this can be achieved with subsequent explanation.
Figure 1. Constant current source used for adiabatic logic circuit
Dissipation in the switch = I2
*R
Energy during charging E=( I2
*R)*T
Also,
The voltage across the switch = I*R
Q=CL*Vdd , I = (CL *Vdd)/T (1.1)
E=( I2
*R)*T = (R CL) / T * CL *Vdd2
(1.2)
Where,
E is the energy dissipated during charging time
Q is the charge transferred to the load
CL is the value of the load capacitance
R is the on resistance of the PMOS switch
VDD is the final value of the voltage at the load
T is the charging time
As explained above, the adiabatic switching power dissipation is asymptotically proportional to
inverse of the charging time therefore, one can achieve very low energy dissipation [4] by
slowing down the speed of operation and also the charge stored in the load capacitors can be
recycled by using AC type power supply rather than DC.
Now, couple of observations can be made based on Equation (1.2) as follows:
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
125
i. The energy dissipated for adiabatic circuits is smaller if the charging time T is
larger than 2RCL.
ii. Since, the dissipated energy is proportional to R thus reducing the on-resistance
of the PMOS reduces the energy dissipation.
Figure 2 shows the model of an adiabatic logic showing an ideal switch in series with resistance
and two complementary voltage supply clocks.
Figure 2. Model of adiabatic logic.
In this paper, we propose a low-power high speed (LPHS) adiabatic logic circuit to achieve an
optimized result between power dissipation and delay which significantly reduces PDP upto 40%
when compared with 2PASCL logic circuit,also power consumption is compared with that of a
conventional CMOS circuit.
2. PREVIOUS WORK
Several adiabatic or Energy recovery logic architectures have been proposed over the years. They
are based on the similar principle, but the structure and complexity, differ by, number of
operation clock, Single- Dual rail style, Charging and discharging path etc.
2.1. Adiabatic logic structures are mainly of two types:
Partially adiabatic logic. They are classified as –
i) Efficient charge recovery logic (ECRL)
ii) Quasi Adiabatic Logic(QAL) [5]
iii) Positive feedback adiabatic logic (PFAL)
iv) NMOS energy recovery logic
v) True single phase adiabatic logic (TSAL)
Fully adiabatic logic. They are classified as-
i) Pass transistor adiabatic logic
ii) 2 Phase adiabatic Static CMOS logic (2PASCL)
iii) Split rail charge recovery logic (SCRL)
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
126
The previous work, using 2PASCL adiabatic logic shows that the power dissipation reduces by
60-70 % but delay of the circuit increases by as much as 30% as compared to the conventional
CMOS circuit. These delays of the circuit occurred due to the MOS diode present in the
discharging path of the circuit, because of the circuit operating at very high frequencies (10-100
MHz.) and at high frequency large number of capacitors are present which affects the time
constant of the circuit. Time constant of the circuit increases due to charging and discharging of
these capacitors at high power clock frequencies [6]. Therefore, delay of the circuit increases.
3. DESIGN APPROACHES AND PROPOSED CIRCUIT
Before we discuss more about the proposed and 2PASCL circuit, let us discuss a Partially
adiabatic logic circuit for e.g QAL (Quasi Adiabatic Logic). Figure 3 shows the schematic of
Quasi adiabatic logic circuit design which can be extended to 4 Inverter chain.
Figure 3. Quasi adiabatic logic.
In the Quasi Adiabatic Logic circuit, the circuit components are driven by a sinusoidal supply
power clock instead of a constant supply (DC supply) as used in Conventional CMOS circuit. The
QAL inverter shown above in the schematic uses a power clock of sinusoidal supply, therefore,
the power dissipation of the circuit improves 60-70%.
Also the present paper discusses QAL using Pseudo nMOS, with MOS diode in charge recovery
path. Due to these changes, we can save energy upto 15% as compared to conventional QAL.
Both the schematic designs using Pseudo nMOS are shown below-
Figure 4. Proposed inverter (Pseudo nMOS implemented with Adiabatic Logic)
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
A novel method for reducing delay in
adiabatic circuit involves Simple PN diode instead of MOS dio
At high frequencies of 10-100MHz, capacitances acting on MOS diode in 2PASCL charges and
discharges at every power clock cycle which would effectiv
circuit that leads to increases in
digital design [7] it has always been the focus point of the engineers to keep the load capacitance
under control so that the delay is under check.
Figure 5. General diagram of LPHS Adiabatic logic circuit
LPHS Adiabatic logic is similar to CMOS circuits except few changes which make this logic
much more energy efficient than CMOS
some other adiabatic logic circuits
CMOS logic gate is the two diodes, one from the output node to the power clock supply and
another one is placed next to the nMOS logic to another power clock. Both PN diodes are used to
re-cycle the charges from the output node, to improve d
This is especially advantageous for signal nodes with a long chain of switches
The other difference is that split-
replace the Vdd and the Vss. Substrate of pMOS is connected to Vø whereas for nMOS, it is
connected to Vø bar. From the simulation, we found that split
energy dissipation compared to trapezoidal power clock supply even if we set the T
the trapezoidal waveforms to maximum values. By using two split
where each peak-to-peak is 0.9 V, we can reduce the voltage difference, thus reducing the
charging and discharging activities. Sinusoidal waveforms can also be
energy efficiency than trapezoidal waveforms.
The circuit operates in 2 phases –
I. Evaluation phase: When the output node is LOW and pMOS tree is turned ON, Load
capacitor is charged through pMOS transistor resulting in the HIGH state at the
When the output is LOW and nMOS is ON, no transition occurs. The same result is
obtained when the output node is HIGH and pMOS is ON. Finally, when
HIGH and nMOS is ON, discharging via nMOS
output voltage to Vt(threshold voltage)
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
A novel method for reducing delay in the Proposed circuit, Low Power High Speed (LPHS)
adiabatic circuit involves Simple PN diode instead of MOS diode uses in 2PASCL logic circuit
100MHz, capacitances acting on MOS diode in 2PASCL charges and
discharges at every power clock cycle which would effectively increase the capacitances of
in the time constant resulting in increases of delay. For low power
digital design [7] it has always been the focus point of the engineers to keep the load capacitance
under control so that the delay is under check.
. General diagram of LPHS Adiabatic logic circuit
LPHS Adiabatic logic is similar to CMOS circuits except few changes which make this logic
more energy efficient than CMOS with lesser delay as compared to 2PASCL as well as
circuits also [8]. The notable difference between LPHS and static
CMOS logic gate is the two diodes, one from the output node to the power clock supply and
another one is placed next to the nMOS logic to another power clock. Both PN diodes are used to
cycle the charges from the output node, to improve discharging speed of internal signal nodes.
This is especially advantageous for signal nodes with a long chain of switches.
-level sinusoidal power clock supplies, Vø and Vø bar are used to
Substrate of pMOS is connected to Vø whereas for nMOS, it is
connected to Vø bar. From the simulation, we found that split- level sinusoidal gives a lower
energy dissipation compared to trapezoidal power clock supply even if we set the Trise
the trapezoidal waveforms to maximum values. By using two split-level sinusoidal waveforms
peak is 0.9 V, we can reduce the voltage difference, thus reducing the
charging and discharging activities. Sinusoidal waveforms can also be generated with higher
energy efficiency than trapezoidal waveforms.
–
hen the output node is LOW and pMOS tree is turned ON, Load
capacitor is charged through pMOS transistor resulting in the HIGH state at the
is LOW and nMOS is ON, no transition occurs. The same result is
when the output node is HIGH and pMOS is ON. Finally, when output
HIGH and nMOS is ON, discharging via nMOS takes place resulting in the decrease of
(threshold voltage) value where the logical state is “0” [9
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
127
Proposed circuit, Low Power High Speed (LPHS)
de uses in 2PASCL logic circuit.
100MHz, capacitances acting on MOS diode in 2PASCL charges and
capacitances of
For low power
digital design [7] it has always been the focus point of the engineers to keep the load capacitance
LPHS Adiabatic logic is similar to CMOS circuits except few changes which make this logic
2PASCL as well as
PHS and static
CMOS logic gate is the two diodes, one from the output node to the power clock supply and
another one is placed next to the nMOS logic to another power clock. Both PN diodes are used to
ischarging speed of internal signal nodes.
level sinusoidal power clock supplies, Vø and Vø bar are used to
Substrate of pMOS is connected to Vø whereas for nMOS, it is
level sinusoidal gives a lower
rise and Tfall of
level sinusoidal waveforms
peak is 0.9 V, we can reduce the voltage difference, thus reducing the
ated with higher
hen the output node is LOW and pMOS tree is turned ON, Load
capacitor is charged through pMOS transistor resulting in the HIGH state at the output.
is LOW and nMOS is ON, no transition occurs. The same result is
output node is
resulting in the decrease of
9].
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
II. Hold phase: Now due to the diodes, the state of
remains unchanged. When the preliminary state of the output node is HIGH, it will
change to Vt, the threshold voltage of the diode. At this point, discharging via diode D1
occurs.
From the operation of LPHS adiabatic logic as explained in
dynamic switching are observed as circuit nodes are not necessarily
every clock cycle which reduces the node switching activities significantly. Th
lowers the switching activity lowering the
4. CIRCUIT SIMULATION
Schematic design and simulation
shown where comparison has been made for
conventional CMOS and 2PASCL logic circuits with their power dissipation, delay and PDP.
These results well conform for ul
The simulation in this paper were performed using a SPECTRE circuit simulator with a 0.18 um,
1.8 V standard CMOS process. The width and Length of the nMOS and pMOS logic gates were
0.6 um and 0.18 um respectively. A load capacitance of 0.01 pF was connected to the output
node. The frequency of the power supply clock was set to a value same as the transition
frequency. In this era of digital integrated circuits [
degradation in the logic levels is the objective and the authors with the result have tried to prove
this point.
4.1. Simulation Results
The logic function of these fundamental logic
are based on LPHS Adiabatic logic
accordingly as shown in the corresponding
tabulated. The time scale on the horizontal axis is in terms of nsecs. Th
usual meaning.
i. Schematic and Simulated waveforms of
Vø
Figure 6(a). Schematic and simulated waveform of LPHS Adiabatic
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
ue to the diodes, the state of output when preliminary state is LOW
remains unchanged. When the preliminary state of the output node is HIGH, it will
to Vt, the threshold voltage of the diode. At this point, discharging via diode D1
From the operation of LPHS adiabatic logic as explained in evaluation and hold
dynamic switching are observed as circuit nodes are not necessarily charging and discharging
every clock cycle which reduces the node switching activities significantly. This
lowering the energy dissipation.
IMULATION AND RESULTS
and simulation results of INVERTER, NAND, NOR, XOR and 2:1 MUX
where comparison has been made for a non cascaded gate to those design using
conventional CMOS and 2PASCL logic circuits with their power dissipation, delay and PDP.
These results well conform for ultra low power applications using these logic gates [9].
were performed using a SPECTRE circuit simulator with a 0.18 um,
1.8 V standard CMOS process. The width and Length of the nMOS and pMOS logic gates were
m respectively. A load capacitance of 0.01 pF was connected to the output
node. The frequency of the power supply clock was set to a value same as the transition
In this era of digital integrated circuits [10] maintaining the logic level with le
degradation in the logic levels is the objective and the authors with the result have tried to prove
of these fundamental logic circuits which may form a basic cell for a design
based on LPHS Adiabatic logic and has been observed that the circuits conform
corresponding figures. The results have been categorized
The time scale on the horizontal axis is in terms of nsecs. The other symbols have their
Schematic and Simulated waveforms of different logic circuits
Vout
CL
Schematic and simulated waveform of LPHS Adiabatic Inverter.
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
128
when preliminary state is LOW
remains unchanged. When the preliminary state of the output node is HIGH, it will
to Vt, the threshold voltage of the diode. At this point, discharging via diode D1
hold phase, less
charging and discharging on
is significantly
of INVERTER, NAND, NOR, XOR and 2:1 MUX are
a non cascaded gate to those design using
conventional CMOS and 2PASCL logic circuits with their power dissipation, delay and PDP.
tra low power applications using these logic gates [9].
were performed using a SPECTRE circuit simulator with a 0.18 um,
1.8 V standard CMOS process. The width and Length of the nMOS and pMOS logic gates were
m respectively. A load capacitance of 0.01 pF was connected to the output
node. The frequency of the power supply clock was set to a value same as the transition
] maintaining the logic level with less
degradation in the logic levels is the objective and the authors with the result have tried to prove
circuits which may form a basic cell for a design
conform to operate
results have been categorized and well
e other symbols have their
Inverter.
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
Vø
Va
Vø
Figure 6(b). Schematic and simulated waveform of LPHS Adiabatic
Vø
Vø
Va
Vb
Figure 6(c). Schematic and simulated waveform of LPHS Adiabatic
V
Vb
Vø
Va
Figure 6(d). Schematic and simulated
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
ø
CL
Vout
Schematic and simulated waveform of LPHS Adiabatic NAND Gate
Vout
Schematic and simulated waveform of LPHS Adiabatic XOR Gate
Vø
CL
Vout
Schematic and simulated waveform of LPHS Adiabatic NOR Gate
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
129
NAND Gate
XOR Gate
OR Gate
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
Vø
S
Vø
A
S
B
A
S
S
B
Figure 6(e).Schematic and simulated waveform of LPHS Adiabatic
Figure 6(a) to 6(e) shows the simulated waveforms for the corresponding circuits of different
gates where for each gate the current and output voltage has been shown for the applied inputs.
The symbols shown in the figure have their usual meaning.
i. Tables.
Table 1 describes the power dissipation comparison of different logic gates for PD
2PASCL & PD-LPHS structures at 10fF capacitance and transition frequency of 25 MHz.
Table 1.PD comparison at
Designed Logic PD
Inverter 7.1224 E
NAND 7.12 E
NOR 7.088 E
XOR 7.782 E
2:1 MUX 7.244 E
Table 2 describes the delay comparison of different logic gates for PD
PD-LPHS structures at 10fF capacitance and transition frequency of 25 MHz.
has also been used in the comparison of different structures.
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
C
B Vout
Schematic and simulated waveform of LPHS Adiabatic 2:1 MUX Gate
6(a) to 6(e) shows the simulated waveforms for the corresponding circuits of different
gates where for each gate the current and output voltage has been shown for the applied inputs.
The symbols shown in the figure have their usual meaning.
describes the power dissipation comparison of different logic gates for PD
LPHS structures at 10fF capacitance and transition frequency of 25 MHz.
PD comparison at CL= 10fF and transition frequency = 25 MHz
PD- CMOS PD- 2PASCL PD- LPHS
7.1224 E-7 3.5568 E-7 3.5857 E-7
7.12 E-7 3.55 E-7 3.604 E-7
7.088 E-7 3.423 E-7 3.6631 E-7
7.782 E-7 1.88 E-7 2.135 E-7
7.244 E-7 2.412 E-7 2.614 E-7
comparison of different logic gates for PD-CMOS,PD
LPHS structures at 10fF capacitance and transition frequency of 25 MHz. Note that 2:1 MUX
has also been used in the comparison of different structures.
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
130
2:1 MUX Gate
6(a) to 6(e) shows the simulated waveforms for the corresponding circuits of different
gates where for each gate the current and output voltage has been shown for the applied inputs.
describes the power dissipation comparison of different logic gates for PD-CMOS,PD-
LPHS structures at 10fF capacitance and transition frequency of 25 MHz.
25 MHz
CMOS,PD-2PASCL &
Note that 2:1 MUX
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
131
Table 2. Delay comparison CL= 10fF and transition frequency =25 MHz
Designed Logic CMOS Delay 2PASCL
Delay
LPHS Delay
Inverter 5.7878 E-11 9.05454E11 3.302 E-11
NAND 3.254 E-11 4.665 E-11 1.928 E-11
NOR 1.4094 E-11 2.251 E-11 1.1587E-11
XOR 5.925 E-11 7.225 E-11 4.9842E-11
2:1 MUX 3.442 E-11 4.4572 E-9 3.29189E-9
Table 3 describes the power delay product of different logic gates for PD-CMOS,PD-2PASCL &
PD-LPHS structures at 10fF capacitance and transition frequency of 25 MHz.
Table 3.PDP comparison at CL= 10fF and transition frequency 25= MHz
Designed Logic PDP -CMOS PDP -2PASCL PDP - LPHS
Inverter 4.122 E-17 3.22 E-17 1.84 E-17
NAND 2.2897 E-17 1.224 E-17 0.695 E-17
NOR 9.122 E-17 6.872 E-17 4.244 E-17
XOR 1.064 E-16 8.232 E-16 6.325 E-16
2:1 MUX 13.38 E-16 11.64 E-16 8.62-16
iii. Figures:PD comparison between CMOS, 2PASCL and LPHS Adiabatic logic
Figures 7 to Figure 10 shows the power dissipation comparison of CMOS, LPHS & 2PASCL
structures at different output load capacitances which have been plotted for different logic gates.
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
Figure 7
Figure
Figure 9
0
1
2
3
4
5
6
7
8
0 20
0
1
2
3
4
5
6
7
8
0 20 40
0
1
2
3
4
5
6
7
8
0 20 40
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
Load Capacitance(fF)
Figure 7. PD Versus CL Comparison(Inverter)
Load Capacitance(fF)
Figure 8. PD Versus CL Comparison(NAND)
Load Capacitance (fF)
Figure 9. PD Versus CL Comparison (NOR)
40 60 80 100 120
CMOS
LPHS
2PASCL
40 60 80 100 120
CMOS
2PASCL
LPHS
40 60 80 100 120
CMOS
2PASCL
LPHS
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
132
CMOS
LPHS
2PASCL
CMOS
2PASCL
LPHS
CMOS
2PASCL
LPHS
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
Figure
iv. Figures: Four Inverter chain
Figures 11 shows the power dissipation comparison of four inverter chain for CMOS, QAL,
Pseudo NMOS QAL, Pseudo NMOS structures at different output load capacitances. Figure 12
shows the delay comparison for the mentioned structures at different loads and Figure 13 shows
the Power Delay Product for the different structures at different load.
verified using Cadence tool.
Figure11
0
1
2
3
4
5
6
7
8
0 20 40
0
1
2
3
4
5
6
7
8
0 20 40
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
Load Capacitance (fF)
Figure 10. PD Versus CL Comparison (XOR)
Inverter chain Comparisons.
Figures 11 shows the power dissipation comparison of four inverter chain for CMOS, QAL,
Pseudo NMOS QAL, Pseudo NMOS structures at different output load capacitances. Figure 12
the delay comparison for the mentioned structures at different loads and Figure 13 shows
the Power Delay Product for the different structures at different load. The results have been
Load Capacitance (fF)
Figure11. PD(Âľw) Versus CL Comparison
40 60 80 100 120
CMOS
2PASCL
LPHS
40 60 80 100 120
QAL
Pseudo nmos QAL
Pseudo nmos
CMOS
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
133
Figures 11 shows the power dissipation comparison of four inverter chain for CMOS, QAL,
Pseudo NMOS QAL, Pseudo NMOS structures at different output load capacitances. Figure 12
the delay comparison for the mentioned structures at different loads and Figure 13 shows
The results have been
CMOS
2PASCL
LPHS
Pseudo nmos QAL
Pseudo nmos
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
134
Load Capacitance (fF)
Figure 12. Delay (ns) Versus CL comparison
Load Capacitance (fF)
Figure 13. PDP Versus CL comparison
The functionality of the proposed circuit with variation in different parameters (like load
capacitance, frequency and voltage) has been examined. Using proposed adiabatic logic [11], we
can reduce delay upto 40% compared with the 2PASCL. LPHS reduces delay at the cost of power
dissipation and output swing of the circuit. Output swing reduces from 0.5-1.8 to 0.7-1.8.
Further, it is important to note that the clock plays a very important role for these type of digital
circuits not because charge recycling has been employed but due the dependence power
consumption on it, there whether single phase clock is being used on two phase it is utmost
important to control the clock [11-14].
5. CONCLUSION
This paper primarily focuses on the design of low power high speed CMOS cell structures. A
family of full-custom conventional CMOS Logic and an Adiabatic Logic units were designed in
Cadence Design Architect using standard TSMC 0.18 Âľm technology and further the analysis of
0
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150
CMOS
QAL
Pseudo nmos QAL
Pseudo nmos with
diode adiabatic
0
1
2
3
4
5
6
7
0 50 100 150
QAL
Pseudo nmos QAL
Pseudo nmos with
diode
CMOS
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
135
the average dynamic power dissipation and delay with respect to the load capacitance was done.
It was found that the Proposed adiabatic logic style is advantageous in applications where power
reduction as well as speed is of prime importance as in high performance battery-portable digital
systems running on batteries such as note-book computers, cellular phones, personal digital
assistants, etc. We have achieved an improvement of 60 to 70% in power consumption as
compared with Conventional CMOS circuits. This reduction in power consumption is achieved
by adiabatic logic with split level power supply. The comparison of the 2PASCL circuit with
Conventional CMOS has proved that power consumption with 2PASCL logic is far less as
compared to CMOS based technique but delay increases. Delay comparatively increases in
2PASCL but using modified logic we can optimize the circuit between delay, power and output
swing.
ACKNOWLEDGEMENTS
The authors duly acknowledged with gratitude the support from ministry of communication and
information technology, DIT Govt. of India, New Delhi, through special manpower Development
program in VLSI and related Software’s Phase-II (SMDP-II) project in ECE Department, MNNIT
Allahabad-211004, India.
REFERENCES
[1] N. Anuar, Y. Takahashi and T. Sekine, “Two phase clocked adiabatic static CMOS logic and its
Logic Family,” Joural of Semiconductor Technology & Science. Vol.10 No.1, Mar. 2010.
[2] N. Anuar, Y. Takahashi and T. Sekine, “Two phase clocked adiabatic static logic circuit: a proposal
for digital low power applications,” Proc. IEICE Gen. Conf., p.102, Mar. 2009.
[3] T. Indermauer and M. Horowitz, “Evaluation of Charge Recovery Circuits and Adiabatic Switching
for Low Power Design,” Technical Digest IEEE Symposium Low Power Electronics, San Diego, pp.
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[4] W. C. Athas, J. G. Koller, L. Svensson, “An Energy- Efficient CMOS Line Driver using Adiabatic
Switching,” Fourth Great Lakes symposium on VLSI, California, March 2005.
[5] Y. Ye, and K. Roy, “QSERL: Quasi-static energy recovery logic,” Solid-States Circuits., IEEE
Journal, Vol.36, Issue 2, Feb., 2001, pp. 239-248.
[6] N. Waste and K. Eshraghian, Principle of CMOS VLSI Design: A System Prospective, 2nd ed. New
York: Addison – Wesley, 1993.
[7] A. P. Chandrakashan, S. Sheng, and R. W. Brodersen, “Low Power CMOS Digital Design,” IEEE
Journal of Solid-state Circuits, Vol. 27, No. 04, pp. 473-484, April 1999.
[8] W.C.Athes, L.J. Svensson, J.G. Koller, et al., “Low-power digital systems based on adiabatic-
switching principles,” IEEE Trans. On VLSI Systems, 2(4): 398-407, December 1994.
[9] A.Blotti and R. Saletti, “Ultralow- Power Adiabatic Circuit Semi-Custom Design,” IEEE
Transactions on VLSI Systems, vol. 12, no. 11, pp. 1248-1253, November 2004.
[10] Sung Mo Kang and Yusuf Leblebici, CMOS Digital Integrated Circuits - Analysis and Design,
McGraw-Hill, 2003.
[11] S. Samantha “Adiabatic computing: A Contemporary Review,” International conference on
computers and devices for communication, Dec. 2009, pp.1-4
[12] J. Marjonen and M Aberg, “A single clocked adiabatic static logic – a proposal for digital low power
application,” J. VLSI signal processing, vol.27, no. 27, Feb.2001, pp.253-268.
[13] B.Voss and M. Glesner, “A Low Power Sinusoidal Clock,” In Proc. of the International Symposium
on Circuits and Systems, ISCAS 2001.
[14] Y. Moon and D. K. Jeong, “An Efficient Charge Recovery Logic Circuit,” IEEE JSSC, Vol. 31, No.
04, pp. 514-522, April 1996.
International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012
136
Authors
Short Biography
Mr. Sanjeev Rai – Was born on 21st
July 73 in a remote village of District Ballia, State Uttar Pradesh,
India and completed graduation from Government Engineering College, Raipur, now known as NIT
Raipur, did Masters in Digital Systems from Motilal Nehru Regional Engineering College, Allahabad,
now known as MNNIT, Allahabad. Presently serving as Assistant Professor in the Department of
Electronics & Communication Engineering, MNNIT Allahabad, India. Primarily the research interest
includes Microelectronics & VLSI Design & Semiconductor Device Modeling.
Mr. Govind Krishna Pal – is currently working with Apache Design Solutions as Application Engineer
his area of interest is VLSI Design and its applications
Dr. Ram Awadh Mishra – Currently working as Associate Professor in the Department of Electronics &
Communication Engineering, MNNIT Allahabad, India. Primarily the research interest includes
Semiconductor Device Modeling.
Dr.Sudarshan Tiwari – Is currently working as Director, NIT Raipur, Chattisgarh. He has formerly
worked as Professor & Head Department of Electronics & Communication Engineering, MNNIT
Allahabad, India. Primarily the research interest includes Microelectronics & Optical Communication.

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DESIGN & ANALYSIS OF A CHARGE RE-CYCLE BASED NOVEL LPHS ADIABATIC LOGIC CIRCUITS FOR LOW POWER APPLICATIONS

  • 1. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 DOI : 10.5121/vlsic.2012.3510 123 DESIGN & ANALYSIS OF A CHARGE RE-CYCLE BASED NOVEL LPHS ADIABATIC LOGIC CIRCUITS FOR LOW POWER APPLICATIONS Sanjeev Rai1 , Govind Krishna Pal2 , Ram Awadh Mishra3 and Sudarshan Tiwari4 1 Department of Electronics & Communication Engineering, Motilal Nehru National Institute of Technology, Allahabad, India srai@mnnit.ac.in 2 Apache Design Solutions, Noida, India govind@gmail.com 3 Department of Electronics & Communication Engineering, Motilal Nehru National Institute of Technology, Allahabad, India ramishra@mnnit.ac.in 4 Director National Institute of Technology, Raipur, Chhatisgarh, India director@nitrr.ac.in ABSTRACT This paper focuses on principles of adiabatic logic, its classification and comparison of various adiabatic logic designs. An attempt has been made in this paper to modify 2PASCL (Two Phase Adiabatic Static CMOS Logic) adiabatic logic circuit to minimize delay of the different 2PASCL circuit designs. This modifications in the circuits leads to improvement of Power Delay Product (PDP) which is one of the figure of merit to optimize the circuit with factors like power dissipation and delay of the circuit. This paper investigates the design approaches of low power adiabatic gates in terms of energy dissipation and uses of Simple PN diode instead of MOS diode which reduces the effect of Capacitances at high transition and power clock frequency. A computer simulation using SPECTRE from Cadence is carried out on different adiabatic circuits, such as Inverter, NAND, NOR, XOR and 2:1 MUX. KEYWORDS Adiabatic logic, Low-power, Two phase clocked, Energy recovery, Split-level, Diode based logic, Power Delay Product (PDP), LPHS (Low Power High Speed). 1. INTRODUCTION The popularity of complementary MOS (CMOS) technology can be gauged from the fact that it has lower power consumption and high speed. However, the current trend towards ultra low- power has made researchers search for techniques to recycle energy from the circuits within. In conventional CMOS level-restoring logic, the switching event of circuits with rail-to-rail output voltage swing, causes an energy transfer from the power supply to the output node or from the output node to the ground. During a 0-to-VDD transition of the output, the total output charge Q = Cload VDD is drawn from the power supply at a constant voltage. Thus, an energy of E = CL VDD 2 is drawn from the power supply during this transition. Charging the output node capacitance to the voltage level VDD means that at the end of the transition, the amount of stored energy in the output node is E = ½ CL VDD 2 . Thus, half of the injected energy from the power supply is dissipated in the PMOS network while only one half is delivered to the output node. During a subsequent VDD-to-0 transition of the output node, no charge is drawn from the power supply and the energy stored in the load capacitance is dissipated in the NMOS network.
  • 2. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 124 To reduce the dissipation, the circuit designer can minimize the switching events, decrease the node capacitance, reduce the voltage swing, or apply a combination of these methods. Yet in all these cases, the energy drawn from the power supply is used only once before being dissipated. To increase the energy efficiency of the logic circuits, other measures can be introduced for recycling the energy drawn from the power supply. A novel class of logic circuits called adiabatic logic [1],[2] offers the possibility of further reducing the energy dissipated during the switching events, and the possibility of recycling, or reusing, some of the energy drawn from the power supply. To accomplish this goal, the circuit topology and the operating principles have to be modified as per the need arises. The amount of energy recycling [3] achievable using adiabatic techniques is also determined by the process technology, switching speed, and the voltage swing. In conventional CMOS logic we use constant voltage source to charge the load capacitance but in case of adiabatic logic switching circuits we use constant current source instead of constant voltage source. Figure 1. depicts clearly how this can be achieved with subsequent explanation. Figure 1. Constant current source used for adiabatic logic circuit Dissipation in the switch = I2 *R Energy during charging E=( I2 *R)*T Also, The voltage across the switch = I*R Q=CL*Vdd , I = (CL *Vdd)/T (1.1) E=( I2 *R)*T = (R CL) / T * CL *Vdd2 (1.2) Where, E is the energy dissipated during charging time Q is the charge transferred to the load CL is the value of the load capacitance R is the on resistance of the PMOS switch VDD is the final value of the voltage at the load T is the charging time As explained above, the adiabatic switching power dissipation is asymptotically proportional to inverse of the charging time therefore, one can achieve very low energy dissipation [4] by slowing down the speed of operation and also the charge stored in the load capacitors can be recycled by using AC type power supply rather than DC. Now, couple of observations can be made based on Equation (1.2) as follows:
  • 3. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 125 i. The energy dissipated for adiabatic circuits is smaller if the charging time T is larger than 2RCL. ii. Since, the dissipated energy is proportional to R thus reducing the on-resistance of the PMOS reduces the energy dissipation. Figure 2 shows the model of an adiabatic logic showing an ideal switch in series with resistance and two complementary voltage supply clocks. Figure 2. Model of adiabatic logic. In this paper, we propose a low-power high speed (LPHS) adiabatic logic circuit to achieve an optimized result between power dissipation and delay which significantly reduces PDP upto 40% when compared with 2PASCL logic circuit,also power consumption is compared with that of a conventional CMOS circuit. 2. PREVIOUS WORK Several adiabatic or Energy recovery logic architectures have been proposed over the years. They are based on the similar principle, but the structure and complexity, differ by, number of operation clock, Single- Dual rail style, Charging and discharging path etc. 2.1. Adiabatic logic structures are mainly of two types: Partially adiabatic logic. They are classified as – i) Efficient charge recovery logic (ECRL) ii) Quasi Adiabatic Logic(QAL) [5] iii) Positive feedback adiabatic logic (PFAL) iv) NMOS energy recovery logic v) True single phase adiabatic logic (TSAL) Fully adiabatic logic. They are classified as- i) Pass transistor adiabatic logic ii) 2 Phase adiabatic Static CMOS logic (2PASCL) iii) Split rail charge recovery logic (SCRL)
  • 4. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 126 The previous work, using 2PASCL adiabatic logic shows that the power dissipation reduces by 60-70 % but delay of the circuit increases by as much as 30% as compared to the conventional CMOS circuit. These delays of the circuit occurred due to the MOS diode present in the discharging path of the circuit, because of the circuit operating at very high frequencies (10-100 MHz.) and at high frequency large number of capacitors are present which affects the time constant of the circuit. Time constant of the circuit increases due to charging and discharging of these capacitors at high power clock frequencies [6]. Therefore, delay of the circuit increases. 3. DESIGN APPROACHES AND PROPOSED CIRCUIT Before we discuss more about the proposed and 2PASCL circuit, let us discuss a Partially adiabatic logic circuit for e.g QAL (Quasi Adiabatic Logic). Figure 3 shows the schematic of Quasi adiabatic logic circuit design which can be extended to 4 Inverter chain. Figure 3. Quasi adiabatic logic. In the Quasi Adiabatic Logic circuit, the circuit components are driven by a sinusoidal supply power clock instead of a constant supply (DC supply) as used in Conventional CMOS circuit. The QAL inverter shown above in the schematic uses a power clock of sinusoidal supply, therefore, the power dissipation of the circuit improves 60-70%. Also the present paper discusses QAL using Pseudo nMOS, with MOS diode in charge recovery path. Due to these changes, we can save energy upto 15% as compared to conventional QAL. Both the schematic designs using Pseudo nMOS are shown below- Figure 4. Proposed inverter (Pseudo nMOS implemented with Adiabatic Logic)
  • 5. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 A novel method for reducing delay in adiabatic circuit involves Simple PN diode instead of MOS dio At high frequencies of 10-100MHz, capacitances acting on MOS diode in 2PASCL charges and discharges at every power clock cycle which would effectiv circuit that leads to increases in digital design [7] it has always been the focus point of the engineers to keep the load capacitance under control so that the delay is under check. Figure 5. General diagram of LPHS Adiabatic logic circuit LPHS Adiabatic logic is similar to CMOS circuits except few changes which make this logic much more energy efficient than CMOS some other adiabatic logic circuits CMOS logic gate is the two diodes, one from the output node to the power clock supply and another one is placed next to the nMOS logic to another power clock. Both PN diodes are used to re-cycle the charges from the output node, to improve d This is especially advantageous for signal nodes with a long chain of switches The other difference is that split- replace the Vdd and the Vss. Substrate of pMOS is connected to Vø whereas for nMOS, it is connected to Vø bar. From the simulation, we found that split energy dissipation compared to trapezoidal power clock supply even if we set the T the trapezoidal waveforms to maximum values. By using two split where each peak-to-peak is 0.9 V, we can reduce the voltage difference, thus reducing the charging and discharging activities. Sinusoidal waveforms can also be energy efficiency than trapezoidal waveforms. The circuit operates in 2 phases – I. Evaluation phase: When the output node is LOW and pMOS tree is turned ON, Load capacitor is charged through pMOS transistor resulting in the HIGH state at the When the output is LOW and nMOS is ON, no transition occurs. The same result is obtained when the output node is HIGH and pMOS is ON. Finally, when HIGH and nMOS is ON, discharging via nMOS output voltage to Vt(threshold voltage) International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 A novel method for reducing delay in the Proposed circuit, Low Power High Speed (LPHS) adiabatic circuit involves Simple PN diode instead of MOS diode uses in 2PASCL logic circuit 100MHz, capacitances acting on MOS diode in 2PASCL charges and discharges at every power clock cycle which would effectively increase the capacitances of in the time constant resulting in increases of delay. For low power digital design [7] it has always been the focus point of the engineers to keep the load capacitance under control so that the delay is under check. . General diagram of LPHS Adiabatic logic circuit LPHS Adiabatic logic is similar to CMOS circuits except few changes which make this logic more energy efficient than CMOS with lesser delay as compared to 2PASCL as well as circuits also [8]. The notable difference between LPHS and static CMOS logic gate is the two diodes, one from the output node to the power clock supply and another one is placed next to the nMOS logic to another power clock. Both PN diodes are used to cycle the charges from the output node, to improve discharging speed of internal signal nodes. This is especially advantageous for signal nodes with a long chain of switches. -level sinusoidal power clock supplies, Vø and Vø bar are used to Substrate of pMOS is connected to Vø whereas for nMOS, it is connected to Vø bar. From the simulation, we found that split- level sinusoidal gives a lower energy dissipation compared to trapezoidal power clock supply even if we set the Trise the trapezoidal waveforms to maximum values. By using two split-level sinusoidal waveforms peak is 0.9 V, we can reduce the voltage difference, thus reducing the charging and discharging activities. Sinusoidal waveforms can also be generated with higher energy efficiency than trapezoidal waveforms. – hen the output node is LOW and pMOS tree is turned ON, Load capacitor is charged through pMOS transistor resulting in the HIGH state at the is LOW and nMOS is ON, no transition occurs. The same result is when the output node is HIGH and pMOS is ON. Finally, when output HIGH and nMOS is ON, discharging via nMOS takes place resulting in the decrease of (threshold voltage) value where the logical state is “0” [9 International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 127 Proposed circuit, Low Power High Speed (LPHS) de uses in 2PASCL logic circuit. 100MHz, capacitances acting on MOS diode in 2PASCL charges and capacitances of For low power digital design [7] it has always been the focus point of the engineers to keep the load capacitance LPHS Adiabatic logic is similar to CMOS circuits except few changes which make this logic 2PASCL as well as PHS and static CMOS logic gate is the two diodes, one from the output node to the power clock supply and another one is placed next to the nMOS logic to another power clock. Both PN diodes are used to ischarging speed of internal signal nodes. level sinusoidal power clock supplies, Vø and Vø bar are used to Substrate of pMOS is connected to Vø whereas for nMOS, it is level sinusoidal gives a lower rise and Tfall of level sinusoidal waveforms peak is 0.9 V, we can reduce the voltage difference, thus reducing the ated with higher hen the output node is LOW and pMOS tree is turned ON, Load capacitor is charged through pMOS transistor resulting in the HIGH state at the output. is LOW and nMOS is ON, no transition occurs. The same result is output node is resulting in the decrease of 9].
  • 6. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 II. Hold phase: Now due to the diodes, the state of remains unchanged. When the preliminary state of the output node is HIGH, it will change to Vt, the threshold voltage of the diode. At this point, discharging via diode D1 occurs. From the operation of LPHS adiabatic logic as explained in dynamic switching are observed as circuit nodes are not necessarily every clock cycle which reduces the node switching activities significantly. Th lowers the switching activity lowering the 4. CIRCUIT SIMULATION Schematic design and simulation shown where comparison has been made for conventional CMOS and 2PASCL logic circuits with their power dissipation, delay and PDP. These results well conform for ul The simulation in this paper were performed using a SPECTRE circuit simulator with a 0.18 um, 1.8 V standard CMOS process. The width and Length of the nMOS and pMOS logic gates were 0.6 um and 0.18 um respectively. A load capacitance of 0.01 pF was connected to the output node. The frequency of the power supply clock was set to a value same as the transition frequency. In this era of digital integrated circuits [ degradation in the logic levels is the objective and the authors with the result have tried to prove this point. 4.1. Simulation Results The logic function of these fundamental logic are based on LPHS Adiabatic logic accordingly as shown in the corresponding tabulated. The time scale on the horizontal axis is in terms of nsecs. Th usual meaning. i. Schematic and Simulated waveforms of Vø Figure 6(a). Schematic and simulated waveform of LPHS Adiabatic International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 ue to the diodes, the state of output when preliminary state is LOW remains unchanged. When the preliminary state of the output node is HIGH, it will to Vt, the threshold voltage of the diode. At this point, discharging via diode D1 From the operation of LPHS adiabatic logic as explained in evaluation and hold dynamic switching are observed as circuit nodes are not necessarily charging and discharging every clock cycle which reduces the node switching activities significantly. This lowering the energy dissipation. IMULATION AND RESULTS and simulation results of INVERTER, NAND, NOR, XOR and 2:1 MUX where comparison has been made for a non cascaded gate to those design using conventional CMOS and 2PASCL logic circuits with their power dissipation, delay and PDP. These results well conform for ultra low power applications using these logic gates [9]. were performed using a SPECTRE circuit simulator with a 0.18 um, 1.8 V standard CMOS process. The width and Length of the nMOS and pMOS logic gates were m respectively. A load capacitance of 0.01 pF was connected to the output node. The frequency of the power supply clock was set to a value same as the transition In this era of digital integrated circuits [10] maintaining the logic level with le degradation in the logic levels is the objective and the authors with the result have tried to prove of these fundamental logic circuits which may form a basic cell for a design based on LPHS Adiabatic logic and has been observed that the circuits conform corresponding figures. The results have been categorized The time scale on the horizontal axis is in terms of nsecs. The other symbols have their Schematic and Simulated waveforms of different logic circuits Vout CL Schematic and simulated waveform of LPHS Adiabatic Inverter. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 128 when preliminary state is LOW remains unchanged. When the preliminary state of the output node is HIGH, it will to Vt, the threshold voltage of the diode. At this point, discharging via diode D1 hold phase, less charging and discharging on is significantly of INVERTER, NAND, NOR, XOR and 2:1 MUX are a non cascaded gate to those design using conventional CMOS and 2PASCL logic circuits with their power dissipation, delay and PDP. tra low power applications using these logic gates [9]. were performed using a SPECTRE circuit simulator with a 0.18 um, 1.8 V standard CMOS process. The width and Length of the nMOS and pMOS logic gates were m respectively. A load capacitance of 0.01 pF was connected to the output node. The frequency of the power supply clock was set to a value same as the transition ] maintaining the logic level with less degradation in the logic levels is the objective and the authors with the result have tried to prove circuits which may form a basic cell for a design conform to operate results have been categorized and well e other symbols have their Inverter.
  • 7. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 Vø Va Vø Figure 6(b). Schematic and simulated waveform of LPHS Adiabatic Vø Vø Va Vb Figure 6(c). Schematic and simulated waveform of LPHS Adiabatic V Vb Vø Va Figure 6(d). Schematic and simulated International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 ø CL Vout Schematic and simulated waveform of LPHS Adiabatic NAND Gate Vout Schematic and simulated waveform of LPHS Adiabatic XOR Gate Vø CL Vout Schematic and simulated waveform of LPHS Adiabatic NOR Gate International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 129 NAND Gate XOR Gate OR Gate
  • 8. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 Vø S Vø A S B A S S B Figure 6(e).Schematic and simulated waveform of LPHS Adiabatic Figure 6(a) to 6(e) shows the simulated waveforms for the corresponding circuits of different gates where for each gate the current and output voltage has been shown for the applied inputs. The symbols shown in the figure have their usual meaning. i. Tables. Table 1 describes the power dissipation comparison of different logic gates for PD 2PASCL & PD-LPHS structures at 10fF capacitance and transition frequency of 25 MHz. Table 1.PD comparison at Designed Logic PD Inverter 7.1224 E NAND 7.12 E NOR 7.088 E XOR 7.782 E 2:1 MUX 7.244 E Table 2 describes the delay comparison of different logic gates for PD PD-LPHS structures at 10fF capacitance and transition frequency of 25 MHz. has also been used in the comparison of different structures. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 C B Vout Schematic and simulated waveform of LPHS Adiabatic 2:1 MUX Gate 6(a) to 6(e) shows the simulated waveforms for the corresponding circuits of different gates where for each gate the current and output voltage has been shown for the applied inputs. The symbols shown in the figure have their usual meaning. describes the power dissipation comparison of different logic gates for PD LPHS structures at 10fF capacitance and transition frequency of 25 MHz. PD comparison at CL= 10fF and transition frequency = 25 MHz PD- CMOS PD- 2PASCL PD- LPHS 7.1224 E-7 3.5568 E-7 3.5857 E-7 7.12 E-7 3.55 E-7 3.604 E-7 7.088 E-7 3.423 E-7 3.6631 E-7 7.782 E-7 1.88 E-7 2.135 E-7 7.244 E-7 2.412 E-7 2.614 E-7 comparison of different logic gates for PD-CMOS,PD LPHS structures at 10fF capacitance and transition frequency of 25 MHz. Note that 2:1 MUX has also been used in the comparison of different structures. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 130 2:1 MUX Gate 6(a) to 6(e) shows the simulated waveforms for the corresponding circuits of different gates where for each gate the current and output voltage has been shown for the applied inputs. describes the power dissipation comparison of different logic gates for PD-CMOS,PD- LPHS structures at 10fF capacitance and transition frequency of 25 MHz. 25 MHz CMOS,PD-2PASCL & Note that 2:1 MUX
  • 9. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 131 Table 2. Delay comparison CL= 10fF and transition frequency =25 MHz Designed Logic CMOS Delay 2PASCL Delay LPHS Delay Inverter 5.7878 E-11 9.05454E11 3.302 E-11 NAND 3.254 E-11 4.665 E-11 1.928 E-11 NOR 1.4094 E-11 2.251 E-11 1.1587E-11 XOR 5.925 E-11 7.225 E-11 4.9842E-11 2:1 MUX 3.442 E-11 4.4572 E-9 3.29189E-9 Table 3 describes the power delay product of different logic gates for PD-CMOS,PD-2PASCL & PD-LPHS structures at 10fF capacitance and transition frequency of 25 MHz. Table 3.PDP comparison at CL= 10fF and transition frequency 25= MHz Designed Logic PDP -CMOS PDP -2PASCL PDP - LPHS Inverter 4.122 E-17 3.22 E-17 1.84 E-17 NAND 2.2897 E-17 1.224 E-17 0.695 E-17 NOR 9.122 E-17 6.872 E-17 4.244 E-17 XOR 1.064 E-16 8.232 E-16 6.325 E-16 2:1 MUX 13.38 E-16 11.64 E-16 8.62-16 iii. Figures:PD comparison between CMOS, 2PASCL and LPHS Adiabatic logic Figures 7 to Figure 10 shows the power dissipation comparison of CMOS, LPHS & 2PASCL structures at different output load capacitances which have been plotted for different logic gates.
  • 10. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 Figure 7 Figure Figure 9 0 1 2 3 4 5 6 7 8 0 20 0 1 2 3 4 5 6 7 8 0 20 40 0 1 2 3 4 5 6 7 8 0 20 40 International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 Load Capacitance(fF) Figure 7. PD Versus CL Comparison(Inverter) Load Capacitance(fF) Figure 8. PD Versus CL Comparison(NAND) Load Capacitance (fF) Figure 9. PD Versus CL Comparison (NOR) 40 60 80 100 120 CMOS LPHS 2PASCL 40 60 80 100 120 CMOS 2PASCL LPHS 40 60 80 100 120 CMOS 2PASCL LPHS International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 132 CMOS LPHS 2PASCL CMOS 2PASCL LPHS CMOS 2PASCL LPHS
  • 11. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 Figure iv. Figures: Four Inverter chain Figures 11 shows the power dissipation comparison of four inverter chain for CMOS, QAL, Pseudo NMOS QAL, Pseudo NMOS structures at different output load capacitances. Figure 12 shows the delay comparison for the mentioned structures at different loads and Figure 13 shows the Power Delay Product for the different structures at different load. verified using Cadence tool. Figure11 0 1 2 3 4 5 6 7 8 0 20 40 0 1 2 3 4 5 6 7 8 0 20 40 International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 Load Capacitance (fF) Figure 10. PD Versus CL Comparison (XOR) Inverter chain Comparisons. Figures 11 shows the power dissipation comparison of four inverter chain for CMOS, QAL, Pseudo NMOS QAL, Pseudo NMOS structures at different output load capacitances. Figure 12 the delay comparison for the mentioned structures at different loads and Figure 13 shows the Power Delay Product for the different structures at different load. The results have been Load Capacitance (fF) Figure11. PD(Âľw) Versus CL Comparison 40 60 80 100 120 CMOS 2PASCL LPHS 40 60 80 100 120 QAL Pseudo nmos QAL Pseudo nmos CMOS International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 133 Figures 11 shows the power dissipation comparison of four inverter chain for CMOS, QAL, Pseudo NMOS QAL, Pseudo NMOS structures at different output load capacitances. Figure 12 the delay comparison for the mentioned structures at different loads and Figure 13 shows The results have been CMOS 2PASCL LPHS Pseudo nmos QAL Pseudo nmos
  • 12. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 134 Load Capacitance (fF) Figure 12. Delay (ns) Versus CL comparison Load Capacitance (fF) Figure 13. PDP Versus CL comparison The functionality of the proposed circuit with variation in different parameters (like load capacitance, frequency and voltage) has been examined. Using proposed adiabatic logic [11], we can reduce delay upto 40% compared with the 2PASCL. LPHS reduces delay at the cost of power dissipation and output swing of the circuit. Output swing reduces from 0.5-1.8 to 0.7-1.8. Further, it is important to note that the clock plays a very important role for these type of digital circuits not because charge recycling has been employed but due the dependence power consumption on it, there whether single phase clock is being used on two phase it is utmost important to control the clock [11-14]. 5. CONCLUSION This paper primarily focuses on the design of low power high speed CMOS cell structures. A family of full-custom conventional CMOS Logic and an Adiabatic Logic units were designed in Cadence Design Architect using standard TSMC 0.18 Âľm technology and further the analysis of 0 0.2 0.4 0.6 0.8 1 1.2 0 50 100 150 CMOS QAL Pseudo nmos QAL Pseudo nmos with diode adiabatic 0 1 2 3 4 5 6 7 0 50 100 150 QAL Pseudo nmos QAL Pseudo nmos with diode CMOS
  • 13. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 135 the average dynamic power dissipation and delay with respect to the load capacitance was done. It was found that the Proposed adiabatic logic style is advantageous in applications where power reduction as well as speed is of prime importance as in high performance battery-portable digital systems running on batteries such as note-book computers, cellular phones, personal digital assistants, etc. We have achieved an improvement of 60 to 70% in power consumption as compared with Conventional CMOS circuits. This reduction in power consumption is achieved by adiabatic logic with split level power supply. The comparison of the 2PASCL circuit with Conventional CMOS has proved that power consumption with 2PASCL logic is far less as compared to CMOS based technique but delay increases. Delay comparatively increases in 2PASCL but using modified logic we can optimize the circuit between delay, power and output swing. ACKNOWLEDGEMENTS The authors duly acknowledged with gratitude the support from ministry of communication and information technology, DIT Govt. of India, New Delhi, through special manpower Development program in VLSI and related Software’s Phase-II (SMDP-II) project in ECE Department, MNNIT Allahabad-211004, India. REFERENCES [1] N. Anuar, Y. Takahashi and T. Sekine, “Two phase clocked adiabatic static CMOS logic and its Logic Family,” Joural of Semiconductor Technology & Science. Vol.10 No.1, Mar. 2010. [2] N. Anuar, Y. Takahashi and T. Sekine, “Two phase clocked adiabatic static logic circuit: a proposal for digital low power applications,” Proc. IEICE Gen. Conf., p.102, Mar. 2009. [3] T. Indermauer and M. Horowitz, “Evaluation of Charge Recovery Circuits and Adiabatic Switching for Low Power Design,” Technical Digest IEEE Symposium Low Power Electronics, San Diego, pp. 102-103, October 2002. [4] W. C. Athas, J. G. Koller, L. Svensson, “An Energy- Efficient CMOS Line Driver using Adiabatic Switching,” Fourth Great Lakes symposium on VLSI, California, March 2005. [5] Y. Ye, and K. Roy, “QSERL: Quasi-static energy recovery logic,” Solid-States Circuits., IEEE Journal, Vol.36, Issue 2, Feb., 2001, pp. 239-248. [6] N. Waste and K. Eshraghian, Principle of CMOS VLSI Design: A System Prospective, 2nd ed. New York: Addison – Wesley, 1993. [7] A. P. Chandrakashan, S. Sheng, and R. W. Brodersen, “Low Power CMOS Digital Design,” IEEE Journal of Solid-state Circuits, Vol. 27, No. 04, pp. 473-484, April 1999. [8] W.C.Athes, L.J. Svensson, J.G. Koller, et al., “Low-power digital systems based on adiabatic- switching principles,” IEEE Trans. On VLSI Systems, 2(4): 398-407, December 1994. [9] A.Blotti and R. Saletti, “Ultralow- Power Adiabatic Circuit Semi-Custom Design,” IEEE Transactions on VLSI Systems, vol. 12, no. 11, pp. 1248-1253, November 2004. [10] Sung Mo Kang and Yusuf Leblebici, CMOS Digital Integrated Circuits - Analysis and Design, McGraw-Hill, 2003. [11] S. Samantha “Adiabatic computing: A Contemporary Review,” International conference on computers and devices for communication, Dec. 2009, pp.1-4 [12] J. Marjonen and M Aberg, “A single clocked adiabatic static logic – a proposal for digital low power application,” J. VLSI signal processing, vol.27, no. 27, Feb.2001, pp.253-268. [13] B.Voss and M. Glesner, “A Low Power Sinusoidal Clock,” In Proc. of the International Symposium on Circuits and Systems, ISCAS 2001. [14] Y. Moon and D. K. Jeong, “An Efficient Charge Recovery Logic Circuit,” IEEE JSSC, Vol. 31, No. 04, pp. 514-522, April 1996.
  • 14. International Journal of VLSI design & Communication Systems (VLSICS) Vol.3, No.5, October 2012 136 Authors Short Biography Mr. Sanjeev Rai – Was born on 21st July 73 in a remote village of District Ballia, State Uttar Pradesh, India and completed graduation from Government Engineering College, Raipur, now known as NIT Raipur, did Masters in Digital Systems from Motilal Nehru Regional Engineering College, Allahabad, now known as MNNIT, Allahabad. Presently serving as Assistant Professor in the Department of Electronics & Communication Engineering, MNNIT Allahabad, India. Primarily the research interest includes Microelectronics & VLSI Design & Semiconductor Device Modeling. Mr. Govind Krishna Pal – is currently working with Apache Design Solutions as Application Engineer his area of interest is VLSI Design and its applications Dr. Ram Awadh Mishra – Currently working as Associate Professor in the Department of Electronics & Communication Engineering, MNNIT Allahabad, India. Primarily the research interest includes Semiconductor Device Modeling. Dr.Sudarshan Tiwari – Is currently working as Director, NIT Raipur, Chattisgarh. He has formerly worked as Professor & Head Department of Electronics & Communication Engineering, MNNIT Allahabad, India. Primarily the research interest includes Microelectronics & Optical Communication.