Lee et al. The conceptual diagrams of operation of RCP circuit are shown in Figures 2 a , 2 b , and 2 c , where weak, moderate, and strong sunlight conditions are illustrated, respectively. In Figure 1 a , we can know that VSC and 7SC in weak sunlight are smaller than moderate and strong sunlight conditions. In Figure 2 a VSC in weak sunlight is as low as 1. On the contrary, the output voltage, VBAT, should be the same with the charging voltage of lithium ion batteries, that is, as high as 4.
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Thus the number of stages of charge pump's architecture should be large enough to generate 4. One more thing to consider here is that an amount of pumping current should be small in weak sunlight because the solar cell can deliver only small amounts of VSC and 7SC to the load. Here we can think that the serial architecture of charge pump in Figure 2 a is more suitable than the parallel-serial and parallel architectures that are shown in Figures 2 b and 2 c , respectively.
In the serial architecture, 4 unit pumps UPs are connected in series, as shown in Figure 2 a. In Figure 2 b , we assume that sunlight intensity is moderate, where VSC becomes 2. For the amount of 7SC, 7SC in moderate sunlight is larger than weak sunlight, as shown in Figure 1 a.
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Owing to these higher VSC and larger 7SC in the moderate sunlight condition than the weak condition, we can consider the parallel-serial architecture more suitable. In the parallel-serial architecture, two UPs are in parallel and two parallel-connected pumps are in series, as shown in Figure 2 b. Figure 2 c shows the parallel architecture that has four UPs in parallel. This parallel architecture can be thought to be suitable to deliver the largest amount of output current to the load than the serial and parallel-serial architectures in Figures 2 a and 2 b , respectively.
As explained just earlier, RCP circuit can maximize the amount of output current, by choosing the most suitable architecture among the serial, parallel-serial, and parallel architectures at a given sunlight condition . However, performance of RCP circuit can be improved more by adding variable pumping frequency VPF scheme to the reconfigurable architecture. By merging the VPF scheme with the reconfigurable architecture, the charge pump which is proposed in this paper can track MPPs better than charge pumps only with the reconfigurable architecture.
Figures 3 a , 3 b , and 3 c show the amounts of output current of RCP circuit for weak, moderate, and strong sunlight, respectively, with varying the pumping frequency. In Figure 3 a with weak sunlight intensity from 1.
If the sunlight intensity becomes 2 mA, the best. Figure 2: a Conceptual diagram of operation of RCP circuit and the serial architecture in weak sunlight condition, b conceptual diagram of operation of RCP circuit and the parallel-serial architecture in moderate sunlight condition, and c conceptual diagram of operation of RCP circuit and the parallel architecture in strong sunlight condition.
For the light intensity as much as 2. Here we can know that pumping frequency for MPP becomes higher with increasing the sunlight intensity.
Similarly, with moderate sunlight, we varied the pumping frequency to find the MPPs, where the largest amount of power can be harvested from environmental solar energy. For the moderate sunlight intensities of 3 mA, 9 mA, and. Figure 3 c shows the amounts of output current with strong sunlight intensities such as 18 mA, 38 mA, and 58 mA. The circuit simulation indicates that the pumping frequencies of 9 MHz, 15 MHz, and 23 MHz can deliver the maximum amounts of output current to the load for the sunlight intensities of 18 mA, 38 mA, and 58 mA, respectively.
From Figures 3 a , 3 b , and 3 c , we can know that the VPF scheme that is merged with the reconfigurable. Figure 3: a Output current of RCP circuit in weak sunlight intensities with varying pumping frequency. Figure 3 d shows the pumping frequencies at MPPs with varying sunlight intensity from 1. From Figure 3 d , it is indicated that the pumping frequency as low as 2.
Charge pump circuit design / Feng Pan, Tapan Samaddar.
For the largest sunlight intensity as large. On the contrary, if the intensity is increased stronger than However, for lighter intensities, the fixed pumping frequency of 15 MHz cannot give the output current as much as MPPs. From Figure 4, we can know that no fixed frequency can have the amounts of output current that are similar with the MPPs in the entire range of sunlight intensity.
Thus, we need to propose the VPF scheme that can be added to the previous RCP circuit, where the pumping frequency can be changed according to a given sunlight condition to deliver the largest amount of output current to the load at this given intensity.
In this paper, we can think that the solar cell delivers the input current to RCP circuit with the additional control circuit which is needed to adjust the architecture and pumping frequency according to. Here 7dc means the static current which is consumed in RCP circuit and the controller circuit. By combining 1 and 2 , we can calculate 7OUT with. Thus, we can have an optimum pumping frequency for a given sunlight condition, at which the charge pump circuit can deliver the largest amount of output current to the load.
The good agreement between the simulation and the model in 4 indicates that 3 can describe the charge pump's output current well. In this session, a new RCP circuit is proposed, where the reconfigurable architecture is merged with the VPF scheme, as shown in Figure 6 a. Here the solar cell is connected to the voltage divider with the division ratio as much as 0. Thus we can have a voltage as high as 0.
Here it should be noted that 0. For VCO circuit, the general scheme which is based on simple ring oscillator is used in this paper . Figure 6 c shows the voltage and current waveforms in Figure 6 a. Now let us explain the closed-loop operation of VPF scheme in Figure 6 a more in detail, as shown in Figure 6 c. First, we can assume that 0. As the pumping frequencybecomes higher, 0. As well explained in , three modes of RCP circuit are available in Figure 6 a.
They are the serial, parallel-serial, and parallel architecture, respectively. The sampled 0. C1 and C2 are the comparators for the architecture reconfiguration. When 0.
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The 0. Here k is a fractional constant of VOC and the value used in this simulation is 0. The capacitance used in the simulation is 50 pF. Figure 7 a compares the percentage amounts of output current among 3 schemes of the reconfigurable charge pump circuit, with respect to MPPs. In Figure 7 a , "VPF" means that the pumping frequency of the reconfigurable charge pump can be variable according to the sunlight conditions.
Here the pumping frequency is decided to meet the condition where the solar cell's voltage, 0. This variable frequency for each sunlight condition can be tracked by the circuit shown in Figures 6 a and 6 b. The maximum amounts of 7OUT. Figure 6: a Block diagram of the new RCP circuit that is proposed in this paper. If sunlight intensity becomes different from the moderate condition, percentage of 7OUT with respect to the MPP becomes much smaller.
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Charge pumps are finding increased attention and diversified usage in the new era of nanometer-generation chips used in different systems. This book explains the different architectures and requirements for an efficient charge pump design and explains each step in detail.
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