Most of the current portable devices are powered by rechargeable batteries. But the battery based systems have many jobs such as the demand to reload or replace these batteries with the clip. Besides the batteries have a important weight and size of the whole system and this size increases as the engineering scales down. Another option for batteries is to use environmental beginnings energy.
Geting the environmental beginnings energy and change overing it into a useable electrical energy is called Energy harvest home.
Energy harvest home has been around for centuries in the signifier of windmills, watermills and inactive solar power systems. This engineering offers two advantages over battery-powered systems, virtually unlimited beginnings and no bad environmental effects. Because of these advantages, this engineering is considered a good subscriber to the universe ‘s energy demands.
In energy reaping systems, milliwatts of energy can be scavenged from solar, vibrational, thermic and biological beginnings. Human organic structure can be employed as input energy beginning for the energy reaping transducers.
In human organic structure, energy can be harvested from the temperature difference between the organic structure and the room, the organic structure here is employed as a Thermal beginning, or from body gestures and activities, the organic structure is employed in this instance employs as a kinetic energy beginning. Our involvement here is the thermic energy generator ( TEG ) that transforms the temperature difference between the environment and the human organic structure into electrical energy.
A TEG consists of a big figure of thermocouples sandwiched between a hot and a cold home base as shown in figure 1.
A thermocouple is made of a hole conducting ( P-type ) stuff and an negatron conducting ( n-type ) stuff connected in series as in figure. When heat flows from the hot to the cold home base, free charge bearers ( negatrons or holes ) move in the way of heat flow doing a current and a net electromotive force is produced that can be driven through a burden. Due to TEG ‘s little size and working independent ability, they can be used in many applications like attachable medical devices, electronic carpus tickers, ego powered heat detectors and Bluetooth headsets.
Teg can be modeled electrically as a electromotive force beginning, relative to the temperature difference across it, in series with a resistance R. In many applications, such as reaping power from the human organic structure, this temperature difference is merely a few grades in the scope of lone 5-10 K. so the TEG ‘s open-circuit electromotive force is in the scope of Millivolts.
A big figure of TEG ‘s are connected electrically in series and thermally in analogue to acquire higher end product electromotive force but this consequences in a larger volume and higher cost. Another practical solution is to hike TEG ‘s end product electromotive force to a higher electromotive force in order to accommodate any application. Two chief techniques are used to implement a step-up DC-DC convertor: switched-capacitor charge pump and hike convertor with external LC. To accomplish to the full incorporate system, a switched capacitance charge pump is chosen for this design.
The end product electromotive force of thermic electrical generator is really low, less than 1V so it ca n’t be used straight to power any electronic circuits. The minimal electromotive force required for any transistor to turn on is about 0.7v. Step-up convertors are used after the TEG to bring forth a higher electromotive force from the available low electromotive force.
Two chief techniques are used to implement a step-up DC-DC convertor: switched-capacitor charge pump and encouragement convertor. The charge pump merely consists of some capacitances and switches. Boost convertor needs external constituents such as inductances and capacitances to be implemented. To accomplish a to the full incorporate system, a switched capacitance charge pump is chosen for this design.
The operation of the Charge pump merely depends on bear downing and dispatching electrical capacities during consecutive stages and reassigning the charge to the end product burden. To demo this thought, see the circuit in figure 2.1, it is called the electromotive force doubler and it consists of a capacitance and three switches. The operation is as follows, the capacitance C charges to VDD during the stage I¦ in which S1and S3 are closed and S2 is unfastened. After this stage the capacitance C has a charge of C*VDD.In the following stage S1 and S3 are unfastened and S2 is unfastened. Due to bear down preservation concept the end product electromotive force will be 2VDD. To acquire a electromotive force larger than 2VDD, this phase is cascaded.This chapter discusses the conventional architectures used in planing the charge pumps.
2.1 Dickson Charge Pump
Dickson charge pump is the most celebrated and basic charge pump because it is the first to the full integrated pump and interior decorators built any pump based on its thought. Dickson phase is composed of a rectifying tube -connected NMOS and a capacitance. Diode connected-NMOS plants as the charge transportation device. The two redstem storksbills I¦1 and I¦2 are out of stage with amplitude VI¦ , and are connected to jump node through the capacitances.Figure 2.2 shows five phases of the Dickson charge pump
2.1.1 Dickson Charge Pump operation
The operation of Dickson charge pump is as follows, ab initio when I¦1 is low and I¦2 is high, MD1 is ON & A ; MD2 is OFF and the electromotive force at node 1 is, Where is the threshold electromotive force of NMOS diode-connected. When I¦1 is high and I¦2 is low, MD1 is OFF and MD2 is ON and the electromotive force at node 1 becomes
. MD2 will carry on until the electromotive force at node 2 is equal to
In the following half rhythm, when I¦2 is high, the electromotive force at node 2 is
By and large the electromotive force at node N can written as
And the end product electromotive force after the last diode-connected is expressed as
This equation is derived presuming ideal status, but if isolated electrical capacities are taken into consideration, the transferred clock amplitude will be reduced by a factor and the end product electromotive force can be written as
Besides if a burden is added, so a dc current will be driven from the pump and the end product electromotive force will be reduced by the sum, where is the electromotive force bead per phase when the pump is providing an end product current. Since the entire charge pumped by each phase per clock rhythm is, the current supplied by the pump at a clock frequence, degree Fahrenheit, is given by
Rewrite the equation including the consequence of the burden current, the end product electromotive force becomes
From ( 6 ) , the pump will work merely if
2.1.2 Dickson Equivalent circuit
Equation ( 6 ) can be written as
Equation ( 8 ) leads to an tantamount circuit to the charge pump as shown in figure 2.3 where V0 and Rout are defined as the open-circuit end product electromotive force and end product series opposition of the Pump severally.
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The end product node is bear downing and dispatching through the burden opposition RL. This will take to a rippling, VR, at the end product electromotive force. VR can be written as in equation ( 11 )
As noticed from equation ( 11 ) , increasing the value of the end product capacitance or increasing the clock frequence will assist to hold a little rippling compared to. But increasing the clock frequence should be within a bound to non impact severely on the pump efficiency and power ingestion.
2.1.3 Voltage fluctuating and pumping addition
There are two utile measures should be defined here, Voltage fluctuation at each node, I”V, and electromotive force pumping addition per phase, Gv. I”V is defined as the alteration in electromotive force that occurs at each node from one clock rhythm to the following. I”V can be expressed as
by replacing from ( 11 ) in ( 6 ) , the end product electromotive force can now expressed as
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The electromotive force pumping addition per phase, Gv, is defined as the addition in electromotive force that occurs from one node to the following. Gv can be expressed as in the undermentioned equation
for Dickson Charge pump, the addition is
Figure 2.4 shows the electromotive force fluctuation at each point and the threshold bead from node to the following node.
2.1.4 Dickson charge pump jobs
Although Dickson charge pump has really simple architecture, it has a hapless public presentation at low electromotive force input degrees. Dickson ‘s chief job is the threshold bead per phase as indicated in equation ( 2.15 ) and therefore I”V should be larger than to obtain a positive electromotive force measure in each phase. Since the clock amplitude is normally equal to VDD, so at low electromotive force supply degrees the value of I”V will be decreased and this will impact severely on the addition.
Besides organic structure consequence job is considered a important job in the Dickson charge pump. Body consequence job occurs due to increasing the beginning terminal electromotive force of NMOS from a phase to the following ( V2 & lt ; V3 & lt ; aˆ¦.. ) . Due to this job, threshold electromotive force of Diode connected-NMOS additions with each phase. This means that as the end product electromotive force of each phase additions, the electromotive force addition per phase lessenings due to increasing organic structure consequence. When the threshold electromotive force of the last phase ‘s transistor becomes equal to I”V the end product electromotive force will non increase even with the add-on of subsequent phases.
These full brand Dickson Charge pump is non suited for low electromotive force applications. Several methods have been proposed to avoid jobs of bead and to increase the circuit efficiency such as the boosted pump clock strategy, a CTS strategy, and several intercrossed versions of these combinations.
2.2 Charge Transfer Switch Scheme ( CTS )
In Charge transportation switch strategy ( CTS ) , Pass transistors are used in analogue with the rectifying tube connected devices. CTS are used alternatively of the rectifying tubes to reassign the charge between nodes, while rectifying tubes are used merely for puting up the initial electromotive force at each pumping node. Charges are transfer from one phase to the following without enduring the job of threshold electromotive force bead. The electromotive force pumping addition per phase can be now expressed as
Two techniques are used to command the CTS, Static and dynamic control. In both control schemes, the gate of the base on balls transistor is controlled by the following phase electromotive force, which is in opposite stage.
As shown in Figure 2.5 Static CTS uses the following phase higher electromotive force as a inactive control for the CTS ‘s. For illustration, gate of MS1 is ever connected to node 2.
The electromotive force at each pumping node at each stage is indicated in table 2.1, where V1 peers and is defined as in equation ( 2.13 )
The operation is as follows ; when I†1 is high and I†2 is low, MD2 will be turned ON to put the initial electromotive force at node 2. The gate-to- beginning electromotive force of MS2 is the difference between node 3 and node 2 which is equal to 2I”V, if
Then MS2 is ON where Vtn is the threshold electromotive force of NMOS. In the following half rhythm, I†1 is low and I†2 is high, MD2 will be turned OFF and the gate-to-source electromotive force of MS2 is now the difference between node 3 and node 1 which is equal to 2I”V also.MS2 will be turned OFF merely if
which is non valid. This will make rearward charge sharing job. Although inactive CTS achieves higher addition than Dickson, it suffers from rearward charge sharing job due to incompletely turning OFF of MS2 and this will cut down the efficiency.
The job of Inactive CTS is solved by utilizing dynamic control of the CTS ‘s. As shown in Figure 2.6, each CTS is accompanied by an subsidiary circuit that contains of NMOS and PMOS transistors. So CTS ‘s can be turned off wholly in the needed period and can be turned on by following phase high electromotive force as in Inactive CTS.
As shown in figure ( 2.6 ) gate of Mp2 and Mn2 are connected to node 2.the beginning of Mp2 is connected to node 3 while the beginning of MN1 is connected to node 1. The electromotive force at each pumping node is still defined as in table 2.1.The operation of dynamic CTS is explained as follows. When is high and is low, the source-to-gate electromotive force of MP2 is V32 which is equal to, the gate-to-source electromotive force of MN2 is V21 which is zero, and MS2 will be turned ON if
where is the threshold electromotive force of PMOS and is the threshold electromotive force of NMOS. When is low and is high, the source-to-gate electromotive force of MP2 now is zero so MP2 will be turned OFF and the gate-to beginning electromotive force of MN2 is 2I”V, so Mn1will be turned ON If
and MS2 will be wholly turned OFF. From equation ( 2.19 ) , CTS ‘s are hard to turn ON in low electromotive force environment. So Dynamic CTS is non effectual at low electromotive force applications.
In inactive and dynamic CTS, CTS ‘s ca n’t be used in the end product phase since no signal is available for commanding CTS ‘s. The circuit shown in figure 2.7 is used as the end product phase of the pump. It contains of two diode-connected NMOS, MD0 and MD5. MD0 is used to force the charge to the end product node while MD5 is used to bring forth a fluctuating electromotive force wave form to command the old phase. MD5 is coupled to the clock by a capacitance C5.
The operation of end product phase is as follows, the beginning of MS4 is connected to node x and its gate is connected to node 4. When is high and is low, the electromotive force at node ten peers where is the electromotive force fluctuation at node ten which is larger than the nominal due to the absence of burden current.The electromotive force at node 4 peers, so for Mp4
Where can be expressed as
By replacing from equation ( 2.22 ) in to equation ( 2.21 ) , becomes
And the status for MP4 to be ON is
Besides the status for MS4 to be ON is
Equations ( 2.24 ) and ( 2.25 ) limit the minimal degree of the input supply electromotive force and the maximal accomplishable end product electromotive force particularly if increasing of among the phases due to body consequence is taken into consideration. This restriction can be reduced by increasing the value of and this can be done by utilizing a clock of higher amplitude alternatively of the normal clock I¦1. A clock supporter is required here to bring forth the higher amplitude clock. The impulsive capableness of the needed clock supporter is non big since the burden of the generated clock is comparatively little. Finally, the end product phase will be as in figure 2.8.
One phase of the charge pump proposed by Pelliconi is shown in Figure 2.9. The clock amplitude is equal to. The operation is as follows. After the initial transient, when is high and is low, is set to through M1 and is charged to and connected to through M2.
When is low and is high, V1 is set to through M0 and is charged to and connected to through M3. So the end product is ever after first phase. Pelliconi ‘s phase may be cascaded as shown in figure 2.10 to bring forth an end product electromotive force larger than.
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The addition of one phase is but this addition may be reduced due to the parasitic electrical capacity and phase end product opposition. The addition after N phases is about given in equation
Where Cs is the parasitic electrical capacity on the internal nodes of the phase, and Rout is the phase end product opposition. Besides the end product electromotive force after N phases can be written as in equation
Pelliconi charge pump have many advantages. First, its addition is larger than Dickson addition since it does non endure from threshold bead. Second, organic structure consequence is eliminated by linking each device substrate to its beginning so triple-well NMOS transistors are used. It besides uses really simple non-overlapping clocking strategy, No specific end product phase is needed and it has a wholly symmetrical strategy.
The jobs of Pelliconi appear at really low electromotive force degrees applications. Since at really low electromotive force degrees, cascading big figure of phases is necessary to obtain the coveted end product electromotive force and this will ensue in big end product opposition as indicated in equation ( 2.27 ) so the charge pump will be inefficient.
There are some issues should be taken in consideration while planing a charge pump. Some of these issues are power efficiency of the pump, end product current demands, end product electromotive force ripplings, pump power supply and die country. Power efficiency is a chief issue in our design since the upper limit end product power of the TEG ‘s is highly little, about merely a few milliwatts. Therefore, the charge pump should be carefully designed to pull out every bit much power as possible from the TEG and reassign it to the electronic system.
Besides input electromotive force degrees or pump power supply is another of import issue in our design, since the unfastened electromotive force of the TEG is a few mVs and is dependent on temperature difference. So the capableness of working at really low electromotive force degrees and high power efficiency are the two chief issues in our charge pump design.
Comparison is done between assorted charge pumps ‘ architectures in table 3.1 to take the suited architecture for our design. For addition point of position, It is clear that Dickson charge pump has the lowest addition per phase due the threshold electromotive force bead while the other charge pumps do n’t endure from this job. The inactive CTS charge pump has a charge sharing job due to incompletely turning OFF of the CTS ‘s and this will impact severely on the efficiency which is a chief issue in our design.
In the dynamic CTS charge pump, CTS ‘s have a status to turn ON as indicated in equation 2.19. So CTS ‘s are hard to turn on in low electromotive force environment and therefore dynamic charge pump is hard to be used at low electromotive force degrees. In Pelliconi, Cascading larger figure of phases consequences in higher end product opposition and lower efficiency. This job can be solved if the figure of phases can be controlled. So Pelliconi architecture is the most suited for our design.
Threshold bead per phase
Charge sharing job
CTS ‘s are hard to turned on in low electromotive force environment
Cascading big figure of phases
The architecture of the proposed charge pump is based on Pelliconi but the PMOS transistors are replaced with diode-connected NMOS transistors due to their low threshold electromotive force compared to that of the PMOS 1s and this is shown in figure3.1. The threshold of the low threshold NMOS transistor in the TSMC 0.25I?m CMOS engineering is somewhat less than 200mV, while regular PMOS transistor threshold electromotive force is about 0.7.
The rectifying tube threshold electromotive force bead will restrict the public presentation of the proposed charge pump particularly at low electromotive force input. To hold a better public presentation an subsidiary circuit is added to each rectifying tube connected to do it more efficient in reassigning charge. Besides to get the better of the job of cascading a big figure of phases, higher clock amplitude is used. The proposed charge pump now is composed of three blocks, the charge pump nucleus, the subsidiary circuit and the clock supporter.
Figure 3.2 shows two phases of the proposed charge pump with the subsidiary circuit added to each diode-connected The subsidiary circuit is composed of 2 NMOS transistors ( Ms ‘s and Mn ‘s ) and one PMOS ( Mp ‘s ) . The gate of Mp11 is connected to while its beginning is connected to. The gate of Mn11 is connected to and its beginning is connected to. The operation of the subsidiary circuit is explained as follows. when I¦1 is low and I¦2 is high ( ) , the electromotive force at the nodes, , , and are, , , and,
severally. The source-to-gate electromotive force of Mp11 is so
Then MP11 is turned ON doing MS11 to turn ON besides. Mn11 is turned OFF since its gate-to beginning electromotive force is zero. When I¦1 is high and I¦2 is low, the electromotive force at the nodes, , , and and are, , , and, severally. The source-to-gate electromotive force of Mp11 is zero so it will be turned OFF. The gate-to -source electromotive force of Mn11 is. So if:
so Mn11 is turned ON doing MS11 to turn OFF. Comparing ( 3.1 ) with ( 2.19 ) , the proposed charge pump is more suited for low electromotive force applications.
The end product phase of the proposed charge pump is shown in Figure 3.3. It has no subsidiary circuit since no signal is available to command it. The controlling signal for the old phase already exist at the nodes Vn1and Vn2, so no particular end product phase is required
The clock supporter circuit shown in Figure 3.4 is used to hold a clock amplitude of. Clock hiking chief function is to hold a swing of at each node. Hiking the clock is a must for the subsidiary circuit to work and it besides helps in bettering the Charge pump public presentation. Besides by clock hiking higher end product electromotive force can be obtained with fewer phases and this will take to smaller end product tantamount opposition. As a consequence the efficiency will be improved.
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The operation of the supporter is explained as follows. When is high and
is low, so, , and are ON while, , and are OFF. Node x will bear down to through. And the node will be connected to land through. When When is low and is high, , , and are OFF while, , and are ON. The Node now will put to through. The same operation is done for the node
Simulations are done in this chapter to prove the public presentation of the proposed charge pump and the clock supporter. Besides simulations are done to compare between the proposed charge pump and conventional architectures.
Simulation is performed utilizing TSMC 0.25I?m CMOS engineering in SpectreA® to prove the public presentation of six-stage charge pump while altering some parametric quantities as current sink to the end product, input electromotive force and clock frequence.
The end product electromotive force versus clip curve is shown in figure 4.1, the transient analysis is performed at no burden current and at a clock frequence of 1MHz.When the supply electromotive force is 300mV, the ideal end product electromotive force after six phases is expected to be 3.9V but due to parasitic electrical capacities the end product electromotive force is reduced to 3.75V.
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The end product electromotive force rippling is 16mV when the burden electrical capacity is 25pF.This rippling is shown in figure 4.2.At the same burden electrical capacity, the clip required for the end product to make 90 % of its steady province value is equal to 63.84Aµs.
Figure 4.3 shows the efficiency of the proposed charge pump versus end product load current at different frequences. The simulations are done at supply electromotive force of 0.3V and at different frequences. The maximal efficiency at 500 kilohertz, 1 MHz and 1.5 MHz is 68.46 % , 66.19 % and 61.1 % severally.
In this analysis pump end product electromotive force is plotted versus pump end product current. Simulations are done at frequence of 1MHz and at supply electromotive forces of 0.3V, 0.4V and 0.5V. The simulation consequences are shown in figure 4.4.
Simulations are performed to prove the public presentation of clock supporter block
Figure 3.5 shows the input clock which has amplitude of 0.3V and a frequence of 1MHz and the clock after hiking. The boosted clock amplitude is 5. 7V and it has the same frequence. It is clear from figure 3.6 that the two boosted redstem storksbills have the same amplitude but they are out of stage.
Figure 4.7 shows the simulations consequences of the boosted clock at different input clock amplitude. The simulations are done at input power supply of 0.3V, 0.4V and 0.5 V.
Simulation is performed utilizing TSMC 0.25I?m CMOS engineering in SpectreR to compare between all NMOS Pelliconi charge pump shown in figure 4.8 and the proposed charge pump. To hold a just comparing, the same clock hiking strategy has been used for both circuits with the same value ( 25pF ) of pumping capacitances. All simulations are performed at a clock frequence of 1MHz.
Figure 4.9 shows comparison consequences of end product electromotive force versus figure of phases at VDD of 0.3V and Io = 2.8I?A. It is clear from the figure that the proposed charge pump offers about 10 % higher end product electromotive force at the same figure of phases ( e.g. for six phases, the end product electromotive force of the proposed charge pump is 3.04V while it is 2.72V in boosted Pelliconi ) .
The efficiency versus burden opposition comparing is shown in Figure 4.10. Simulation are done at VDD = 0.3V and N = 6. The proposed pump maximal efficiency reaches 66 % while it is about 57 % in Pelliconi with clock boosting.
The comparing consequences of the end product electromotive force versus input electromotive force are given
in Figure 4.11. The proposed charge pump has higher addition than Pelliconi charge pump with clock boosting as shown in the figure.
The comparing consequences of the end product electromotive force versus end product current are given in Figure 4.12. The proposed charge pump has better thrust capableness than Pelliconi charge pump with clock boosting as shown below.