Design of Ultra-Low Power PMOS and NMOS for Nano Scale VLSI Circuits

CMOS devices play a major role in most of the digital design, since CMOS devices have larger density and consume less power. The integrated circuit performance mostly depends on the basic devices and its scaling methods, but in conventional CMOS devices in ultra deep submicron technology, leakage power becomes the major portion apart of dynamic power. The demerits of the conventional CMOS is less speed and, more leakage, for any digital design PDP is the figure of merit which can be used to determine energy consumed per switching event, hence we designed a NOVEL NMOS and PMOS which has superior performance than conventional PMOS and NMOS, the design and performance checked at 90 nm, 180 nm and 45 nm technology and calculate the performance values.


Introduction
The need for low power chips is the increased marked demand for portable consumer electronics powered by the batteries, which have not experienced the similar rapid density growth compared to electronics circuits.It has been concluded that battery technology alone will not solve power problems in the near future.Therefore designing a chip with low power is becoming a major concern in the chip design industry.The different power reduction techniques from device level to circuit level and system level have been shown as a low power taxonomy [1].
In ultra-deep submicron technology especially below 45 nm technology, leakage power is becoming a major concern than the dynamic power.As the technology is going on scaling down, and we are now in 20 nm/15 nm/ 10 nm technology proper controlling of leakage power is becoming challenge factor.Any power reduction techniques at device level will certainly lower the overall power consumption at system level (power reduction means it should be applicable from device level to system level, there is no guarantee that device level power reduction always applicable at system level) [2].
Related work: The existing numerous power reduction techniques in the field of VLSI are suitable for only 90 nm and above, but continuous scaling of the device in the present VLSI technology many of them may not be suitable.Moreover if the technique is suitable for power reduction than it fails for high speed, hence a new technique is required that is suitable for both power and speed [3].
Sources of power dissipations are The major source in the overall power dissipation is the dynamic power As the technology shrinks leakage power is to be dealt very carefully.

Taxonomy of Low Power
In Figure 1 different power dissipation and power reduction techniques are clearly shown, all these techniques are applicable in low power design [4].

Problem Statement
Here an attempt has been made to control leakage power by proposed PMOS and NMOS, the fundamental limit of conventional PMOS and NMOS is higher leakage and lower sped in deep submicron technology sine power supply reduction lowers three times the threshold voltage will degrade the speed of the circuit considerably, as we are striving forward to higher level of integration, area is not having that much of concern, now we are in position to keep millions of transistors in a single die, the other performance parameters like power, speed and delay moreover power delay product are important parameters which can decide the role of the device in nano scale regime [5].In design abstraction we are approaching bottom up design as shown in the below Figure 2, basically CMOS device level analysis is done and comparative study is done among different MOS devices.Working of proposed PMOS and NMOS: in Figure 5 for top transistor (PM0) a reference voltage of 0.8 V is applied, and input is applied to the gate terminals of bottom transistor (PM2) and output is taken across the drain terminals of the right transistor (PM1) [6].

Demerits of Conventional PMOS & NMOS
Both the conventional PMOS and NMOS, DT PMOS, DT NMOS and proposed PMOS and proposed NMOS are implemented using 45 nm technology and all are simulated using Cadence Virtuoso Design Environment and simulated and results are shown Table 1 Comparison table for the conventional PMOS and NMOS, DT PMOS, DT NMOS and proposed PMOS and proposed NMOS are implemented using 90 nm technology and all are simulated using Cadence Virtuoso Design Environment and simulated and results are shown Table 2.
Comparison table for the conventional PMOS and NMOS, DT PMOS, DT NMOS and proposed PMOS and proposed NMOS are implemented using 180 nm technology and all are simulated using Cadence Virtuoso Design Environment and simulated and results are shown Table 3.The PMOS and NMOS are good transfer of 1 and good transfer of 0, the comparative study is done on various types of MOS devices like PMOS, DTMOS and proposed MOS devices, the average power, delay and PDP is calculated by using the cadence virtuoso design environment tool for 45 nm, 90 nm, 180 nm technology [7].

Conventional CMOS Inverter
Figure 6 shows a conventional CMOS inverter which is simulated using Cadence Virtuoso Design tool and simulated outputs are shown in Figure 7, Figure 8 shows CMOS output when all Zero's Applied and Figure 9 shows CMOS output when All one's Applied.

Inverter with Proposed PMOS and NMOS
From the     There may be an area overhead but this circuit is certainly suitable for high speed and low leakage in deep submicron technology, as area is not a problem since we are in a position to keep millions of transistors in single die, performance parameters like speed will increase and leakage will [9].
Hence an attempt has been made with proposed MOS devices to improve the performances.

Leakage Current Mechanism
Reverse biased junction leakage and subthreshold leakage have very much similar characteristics both will be in order of pico amperes per device and very sensitive to process variations.Leakage current cannot be ignored in deep submicron region and leakage current is the beyond the digital designer control [10].In large scale high performance digital chips performing operations with high frequency.In ultra submicron region leakage power is playing a major contribution apart of dynamic power [11].Subthreshold channel leakage: the subthreshold conduction current is given by where alpha is parameter depends on fabrication process v th is the threshold voltage, v th is the thermal voltage, even though a transistor is logically turned off there may be non zero leakage current through the channel this current is known as Subthreshold leakage current Since it occurs below threshold voltage [12].

Conclusion
We designed a Novel PMOS and NMOS which could give superior performance in deep submicron technology.
The MOS devices like PMOS, DTMOS, and Novel MOS are studied and PDP is comparatively calculated.The leakage power is calculated for normal CMOS inverter and Novel CMOS inverter and it is observed that Novel CMOS inverter has less leakage power compared to Normal CMOS inverter.There may be area overhead but performance is better.It is concluded that Novel PMOS and NMOS are certainly suitable for low leakage and low power in ultra-deep submicron technology [13].
activity factor, V DD = supply voltage, C L = load capacitance, f = frequency of operation.

Figure 3 (
Figure 3(a) and Figure 3(b) show the conventional PMOS and NMOS and having the following demerits.• Lower speed.• Higher leakage in deep submicron technology.Figure4in DT PMOS and DT NMOS body is connected to gate terminal of the MOS device and as the gate voltage is changing body biasing takes place.Working of proposed PMOS and NMOS: in Figure5for top transistor (PM0) a reference voltage of 0.8 V is applied, and input is applied to the gate terminals of bottom transistor (PM2) and output is taken across the drain terminals of the right transistor (PM1)[6].Both the conventional PMOS and NMOS, DT PMOS, DT NMOS and proposed PMOS and proposed NMOS are implemented using 45 nm technology and all are simulated using Cadence Virtuoso Design Environment and simulated and results are shown Table1.From Table1the proposed PMOS and NMOS have low PDP value.Comparison table for the conventional PMOS and NMOS, DT PMOS, DT NMOS and proposed PMOS and proposed NMOS are implemented using 90 nm technology and all are simulated using Cadence Virtuoso Design Environment and simulated and results are shown Table2.Comparison table for the conventional PMOS and NMOS, DT PMOS, DT NMOS and proposed PMOS and proposed NMOS are implemented using 180 nm technology and all are simulated using Cadence Virtuoso Design Environment and simulated and results are shown Table3.
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Figure 10 ,
V dc = 1.1 v and V ref 0.8 v is applied to the transistors PM0 and NM3 and v in = 0 v is applied to the transistors NM2 and PM2 PM2 becomes ON and NM2 becomes OFF, output will be 1 v, when v in = 1 v applied to the transistors NM2 and PM2, NM2 ON and PM2 OFF output becomes 0 v[6].And output results are shown in Figures11-13.

Figure 9 .
Figure 9. CMOS output when all one's applied.

Figure 12 .
Figure 12.Proposed CMOS output for all zero's.

Figure 13 .
Figure 13.Proposed CMOS output for all one's.

.
From Table 1 the proposed PMOS and NMOS have low PDP value.