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DESIGN OF PARALLEL PREFIX ADDERS USING REVERSIBLE LOGIC GATES

Abstract: The coexistence of different cellular system demands reconfigurable mobile terminals. For greater degree of application such as Text, graphics, audio and games etc are required to handle by modern handset. These demands can be fulfilled by integrating some Complementary technologies such as WLAN or Bluetooth, UWB for high bandwidth local or personal services and 2G — 3G standards for voice low data rate communication with wide area coverage together in same handset. Frequency dividers are useful in many communication applications such as Frequency synthesizers, Timing recovery circuits and clock generations. The design of frequency divider is an important factor in performance of PLL as it is in feedback path and so locking gets difficult.

Keywords: Keywords— High Operating Frequency, Minimum Power consumption, Minimum Area, Cmos Frequency Divider.

I   INTRODUCTION

Prescaler is a critical block in power conscious PLL design. A new design technique that improves operating speed of true single-phase clock-based (TSPC) prescalers is presented. A reset signal is added to the positive edge triggered TSPC DFF to obtain the objective of multi modulus prescaler that is frequency division (High frequency to low frequency). Two Dual-modulus prescalers 2/3 and 3/4 prescalers are designed using TSPC positive edge triggered DFF and CM OS nor gates. By using the two dual modulus prescalers, multi modulus prescaler is designed to provide multiple division ratios and their performances are compared with previous work. The speed of the 2/3 and 3/4 prescaler are improved at the maximum operating frequency. The power efficient multi modulus prescaler is designed using dsch tool and its performance are compared. A Simulation and measurement results shows high-speed, low-power, low PDP and multiple division ratio capa biIities of the power efficient technique. The improved speed, the power efficiency, and the flexibility will promote its wide deployment i n Multi gigahertz range applications.

A new design technique that improves operating speed of true single-phase clock-based (TSPC) prescalers is presented. We implement dual-modulus prescalers without using any extra logic gates by exploiting the behavior of the second branch in a TSPC flip-flop. The proposed design technique is applied to ÷2/3 and ÷3/4 prescalers, and their performances are compared with previous work. Implemented in a 130-nm CMOS technology and compared at same process-voltage-temperature conditions, the maximum speed of the ÷2/3 prescaler reaches 88% of the maximum operating frequency of a single TSPC flip-flop, and the ÷3/4 prescaler reaches 75%. In addition, the proposed divide-by-3 prescaler is able to work almost at the speed of the single TSPC flip-flop. A frequency divider that provides dividing ratios of 7, 8, and 9 is implemented as a part of a 3.4-5-GHz integer- Nphase-locked loop in a 65-nm CMOS technology. Simulation and measurement results demonstrate high-speed, low-power, and multiple division ratio capabilities of the proposed technique.

II.    BACK GROUND

FIGURE 1:general diagram of prescalar:

With the expanding need in terms of the low power consumption and increasing frequency of operation, CMOS has been the key element to fabricate the components. Also, the highest operating frequencies of prescalers implemented in GaAs and SiGe bipolar technologies have reached 5.4 GHz [3] and 3.6GHz [4]. Bipolar technologies do offer a high range of frequency of operation but at the expense of power consumption. So, to minimize the power is of prime importance. The prescaler block do consists of various submodules which comprises of nMOS and pMOS. These transistors can be effectively used so as to reduce the area as well as the power consumption. The D flip Flop internal circuit is also shown here along with the

waveform and the power consumption has been brought to 5.4 gW. Compared with these, the prescalers fabricated in CMOS processes usually operate at lower frequencies. The highest reported operating frequency for CMOS prescalers is 1.5GHz [6], [7]. The circuit has been fabricated in a 65-nm technology and consumes relatively high power (115mW).Extra feedback networks were used [5] to increase the operating frequency to 5.4 GHz in a 0.18 gm CMOS process. A phase-shifting prescaler switches among signals with varying phases to achieve two or more divide ratios. The highest operating frequency for phase shifting prescalers [6] is 1.3 GHz and consumes 41 mW of power.

III. TSPC STRUCTURE:

 .

In this paper True Single Phase Clock (TSPC) based on Ratio logic D flip-flop and Transmission Gates (TGs) is implemented in 0.18μm CMOS process. A Glitch elimination TSPC D-flip flop is used in the synchronous counter. TGs are used in the critical path and the control logic for mode selection. The power efficient TSPC design technique is applied to 3/4 and 15/16 prescalers, and their performances are compared. Simulation and measurement results show high-speed, low-power, low PDP and multiple division ratio capabilities of the power efficient technique with a frequency range of 1.0-5.8GHz. The improved speed, the power efficiency, and the flexibility will promote its wide deployment in Multi gigahertz range applications.

 TSPC dynamic CMOS circuit is operated with one clock signal only to avoid clock skew problems. One reset signal is added with the TSPC circuit. Fig.1. below shows the TSPC flip-flop with reset. This TSPC circuit is used in the 2/3 and 3/4 prescaler. Fig.2. below shows the symbol of TSPC positive edge triggered d flip-flop. This symbol is used in 2/3 prescaler and 3/4 prescaler designs.

 1V EXISTING CIRCUIT DIAGRAM:

PROPOSED 16/17 PRESCALAR:

In  the transistor level forward body biasing technique can improve the speed by decreasing  threshold voltage of nmos transistors.How ever it suffers from high minimum working frequency as well as increased cost decreased robustness. A divide counter (M) is inserted in the feedback loop to increase the VCO frequency above the input reference frequency.Dynamic logic multiband flexible integer-n divider based on pulse-swallow topology uses a low-power wideband 2/3 prescaler and a wideband multi modulus 16/17 prescaler .The divider also uses an improved low power loadable bit-cell for the Swallow S-counter.Saves a considerable amount of power and also reduces the complexity of multi band divider. Here the clock divider uses a wide band 2/3 prescaler and a multimodulus prescaler.

As well as the conventional circuit, the maximum working frequency of proposed prescaler is decided by its divide-by-17 operation mode. In addition, the key operation in divide-by-17 mode is the divide-by-3 operation of pseudo divide-by-2/3 prescaler. Fig. 4 shows

the timing diagram of this key operation of proposed circuit. In the first rising edge of Fin, QN1 and QN2 switch to high, then MC1

switches to high and holds for two periods. In the second rising edge,QN0 and D1 switch to low for two periods. In the third rising edge,

QN1 switches to high and holds for two periods. From the second to the fifth rising edge of Fin, DFF1 outputs a divide-by-3 signal in node

QN1 and the pseudo divide-by-2/3 prescaler accomplishes a divideby-3 operation. After this, the pseudo divide-by-2/3 prescaler will

carry out seven times divide-by-2 operation. A divide-by-17 signal will be obtained in node Fout.

 The pseudo divide-by-2/3 prescaler can exactly accomplish a single,but not continuous divide-by-3 operation. In addition, it is enough

for divide-by-16/17 prescaler because it only needs less than one divide-by-3 operation in a cycle. By adopting the pseudo divide-by-

2/3 prescaler, an OR gate is saved and there leaves only one AND gate in front of DFF0. As a result, the critical path #1 in conventional

circuit is disappeared and the length of critical path #2 is reduced.Second, QN1 and QN2 node (instead of Q1 and Q2 node in conventional circuit) of DFF1, DFF2, and DFF3, is connected to the input CLK node of DFF2, DFF3, and DFF4, respectively. The propagation

delay of DFF1, DFF2, and DFF3 will all decrease from td− Q to

td−QN. Thus, the length of critical path will be further reduced.

The operation mode of proposed circuit is as follows. When MC = 1, MC1 changes its value according to (QN2, QN3, QN4).The pseudo divide-by-2/3 prescaler controlled by MC1 accomplishes seven times of divide-by-2 operations and one time of divide-by-3

operation in a cycle. The whole circuit operates in divide-by-17mode. When MC = 0, MC1 keeps low and the pseudo divide-by-2/3

prescaler keeps on divide-by-2 operation. The whole circuit works in divide-by-16 mode.

V. PROPOSED TSPC  D FLIPFLOP:

Figure for tspc dflipflop:

GDI TECHNIQUE:

GDI (Gate Diffusion Input) - a new technique of low power digital circuit design is described. This technique allows reducing power consumption, delay and area of digital circuits, while maintaining low complexity of logic design. Performance comparison with traditional CMOS and various PTL design techniques is presented, with respect to the layout area, number of devices, delay and power dissipation, showing advantages and drawbacks of GDI as compared to other methods. A variety of logic gates have been implemented in 0.35 μm technology to compare the GDI technique with CMOS and PTL. A prototype test chip of 8-bit CLA adder has been fabricated, based on GDI and CMOS cell libraries, showing up to 45% reduction in power-delay product in GDI.

AND GATE USING GDI TECHNIQUE:

           From the above figure,by using gdi technique we can reduce the area and power consumption.such that the overall power consumption can be reduced.

V1.simulation results:

Xilinx simulation results for 16/17 prescalar

Simulation results in microwind tool

Layout for proposeed circuit:

Power consumption for existing system:

Power consumption for proposed system:

VI1 APPLICATION:

The major applications of frequency dividers are mainly used inFor greater degree of application such as Text, graphics, audio and games etc are required to handle by modern handset. These demands can be fulfilled by integrating some Complementary technologies such as WLAN or Bluetooth, UWB for high bandwidth local or personal services and 2G — 3G standards for voice low data rate communication with wide area coverage together in same handset. Frequency dividers are useful in many communication applications such as Frequency synthesizers

VIII CONCLUSION:

By using gdi technique and tspc flipflop with 9 transistors can reduce the power consumption of the circuit.hence we can design frequency dividers such as 31/32,127/128 and so on with less power consumption.hence this can be helpful.

References

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