JP6789524B2 - Energy harvesting circuit - Google Patents

Description

The present invention relates to an energy harvesting circuit that generates energy from high frequency (RF) electromagnetic waves existing in the environment, and more particularly to an energy harvesting circuit having a function of maximizing the electric power harvested from an antenna.

As one of the devices that enrich human life, sensor nodes and embedded devices are being studied. Here, in applications such as wireless sensor nodes and implantable medical devices, it is not possible to constantly supply electric power from the outside, so a power supply method for supplying electric power to the circuits constituting the device has become an important issue. There is. Generally, in such applications, an external battery is installed in the device to charge or replace it after the power is consumed, but the external battery has a burden related to its replacement. Since it is large, a power supply method that does not require battery replacement is being studied.

An energy harvesting device is being studied as a power supply method that does not require battery replacement. Various types of energy harvesting devices that harvest energy have been proposed, such as those that use light, vibration, heat, and ultrasonic waves, but in communication devices and broadcast radio waves used in human life. RF harvesting, which performs energy harvesting from electromagnetic waves, is also considered to be an effective method.

However, when performing energy harvesting from electromagnetic waves, as shown in FIG. 11, the radio waves arriving at the antenna are boosted by a booster circuit, converted to direct current by a rectifier circuit, stored in a capacitance, and driven by a voltage detection circuit. It is configured to supply the load. In the case of the method of generating energy from electromagnetic waves, the energy of electromagnetic waves obtained from the environment is small, so it is a very important issue to efficiently acquire this and store it in a form that can be used by electronic circuits. There is.

For example, the circuit of Non-Patent Document 1 includes an antenna having an inductance component, a variable capacitance, a rectifier circuit, and an external control circuit, and uses the control circuit to connect to the antenna based on the inclination of the voltage rise of the rectifier circuit. By optimally controlling the resonance frequency with a variable capacitance, energy harvesting is performed to harvest power in the most efficient form from incoming electromagnetic waves. The method of Non-Patent Document 1 can operate with an input of −32 dBm, and is expected as a promising method with high harvesting efficiency.

M. Stoopman, et al., “Co-Design of a CMOS Rectifier and Small Loop Antenna for Highly Sensitive RF Energy Harvesters,” IEEE JSSC, 2014. T. Someya, H. Fuketa, K. Matsunaga, H. Morimura, T. Sakurai and M. Takamiya, "248pW, 0.11mV / ℃ glitch-free programmable voltage detector with multiple voltage duplicator for energy harvesting," ESSCIRC Conference 2015- 41st European Solid-State Circuits Conference (ESSCIRC), Graz, 2015, pp. 249-252.

However, in the energy harvesting circuit of Non-Patent Document 1, in order to drive the control circuit, it is necessary to wait for charging in a state where the resonance frequency is mismatched in the initial period of charging, and the control circuit starts driving. There is a problem that it takes time to complete and the efficiency of power harvesting deteriorates.

The present invention has been made to solve such a problem, and provides an energy harvesting circuit capable of reducing the time until the control circuit starts operation and increasing the harvesting efficiency of energy harvesting. The purpose is to do.

In order to solve the above problems, in the energy harvesting circuit of the present invention, an antenna, a resonance circuit that resonates with the antenna at a desired frequency, and a first capacitor are connected to the output side, and the output of the resonance circuit is output. In an energy harvesting circuit including a first step-up rectifying circuit that rectifies and boosts the load and supplies the load, and a control circuit that controls the resonance frequency of the resonance circuit so that the output voltage of the resonance circuit becomes large. A second capacitor is connected to the output side, and includes a second boost rectifying circuit that rectifies and boosts the output of the resonant circuit and supplies the output to the control circuit. The second capacitor is larger than the first capacitor. Having a small capacitance value, the control circuit controls the resonant frequency of the resonant circuit based on the output voltage amplitude of the resonant circuit.

Further, the resonance circuit is an LC resonance circuit having a plurality of variable capacitance capacitors connected in series between a switch and a capacitor, and the control circuit is a rectifying circuit that rectifies the output of the LC resonance circuit. , Driven according to the first clock signal, alternately charges the outputs of the rectifier circuit to the two capacitors, and drives according to the first voltage comparison circuit for comparing the charging voltages of the two capacitors and the first clock signal. A counter circuit that outputs a counter value that goes up or down based on the output of the first voltage comparison circuit is provided, and each of the switches of the variable capacitance capacitor is turned ON or OFF according to the counter value. May be good.

Further, when the control circuit detects that the output of the rectifier circuit gradually increases according to the counter value and then decreases , the control circuit changes the counter value so that the output of the rectifier circuit increases again. The supply of the first clock signal may be stopped.

Further, the control circuit is driven according to a second clock signal which is a clock signal slower than the first clock signal, and the output voltage of the rectifier circuit is alternately charged to the two capacitors of the two capacitors. A second voltage comparison circuit for comparing the charging voltage is further provided, and the second voltage comparison circuit resets the counter value when the fluctuation of the output of the rectifier circuit exceeds a predetermined threshold value. A signal may be output.

Further, a voltage multiplication circuit for multiplying the output signal of the counter circuit may be provided, and the switch of the variable capacitance capacitor may be controlled according to the output of the voltage multiplication circuit.

Further, the LC resonance circuit may further include a laser calibration capacitor connected in parallel with the variable capacitance capacitor and laser trimmed.

According to the present invention, it is possible to provide an energy harvesting circuit capable of reducing the time until the control circuit starts operation and increasing the harvesting efficiency of energy harvesting.

FIG. 1 is a configuration example of an energy harvesting circuit according to the first embodiment of the present invention. FIG. 2 is a configuration example of the energy harvesting circuit according to the second embodiment of the present invention. FIG. 3 is a configuration example of the variable capacitance capacitor according to the second embodiment of the present invention. FIG. 4 is a diagram for explaining the control of the variable capacitance capacitor in the second embodiment of the present invention. FIG. 5 is a configuration example of the energy harvesting circuit according to the third embodiment of the present invention. FIG. 6 is a configuration example of the comparison circuit according to the third embodiment of the present invention. FIG. 7 is a diagram for explaining control of a variable capacitance capacitor using a voltage multiplication circuit according to a fourth embodiment of the present invention. FIG. 8 is a configuration example of the voltage multiplication circuit according to the fourth embodiment of the present invention. FIG. 9 is a configuration example of an energy harvesting circuit including a laser calibration capacitor according to another embodiment of the present invention. FIG. 10 is a configuration example of a laser calibration capacitor according to another embodiment of the present invention. FIG. 11 is a configuration example of a conventional energy harvesting circuit.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention can be implemented in many different forms, and is not construed as being limited to the description of the embodiments described below.

<First Embodiment>
FIG. 1 is a configuration example of the energy harvesting circuit 1 according to the first embodiment of the present invention. The energy harvesting circuit 1 includes an antenna 10, an LC resonance circuit 11 that resonates with the antenna 10 at a desired frequency, and a first boost rectification for a main power supply that boosts the output of the LC resonance circuit 11 and converts it into a DC voltage. It has a circuit 12 and a second boost rectifier circuit 20 for a control circuit, and a capacitor (13, 21) and a voltage detection circuit (14, 22) are connected to the output of each boost rectifier circuit, and the voltage detection circuit It is configured to control the power supply to the load 15 and the control circuit 23 by a switch that is ON / OFF controlled according to the output of. The control circuit 23 uses a digital control signal based on the output voltage amplitude of the LC resonance circuit 11 to control the resonance frequency so that the output of the LC resonance circuit 11 is maximized.

In the energy harvesting circuit 1 of the present embodiment, the capacitance of the second capacitor 21 connected to the second boost rectifier circuit 20 for the control circuit is connected to the first boost rectifier circuit 12 for the main power supply. It is set to be smaller than the capacity of the first capacitor 13. By making the time constant when the second capacitor 21 that drives the control circuit 23 is charged smaller than the time constant of the first capacitor 13 for the main power supply, before the load 15 is supplied with power. It is possible to set the control circuit 23 to start driving.

According to the present embodiment, the time until the control circuit starts driving can be shortened, so that the harvesting efficiency of energy harvesting at the start of charging can be improved.

<Second Embodiment>
FIG. 2 is a configuration example of the energy harvesting circuit according to the second embodiment of the present invention. In the second embodiment, the LC resonance circuit 11 is an LC resonator having a variable capacitance capacitor 16 in which a plurality of switches and capacitors are connected in series in parallel, and the control circuit 23 is an LC resonance circuit. Voltage comparison with a rectifying circuit 33 that rectifies the output of 11 and a voltage comparison circuit 30 that alternately charges two capacitors with outputs (Vrec) from the rectifying circuit 33 according to a predetermined clock signal and compares their charging voltages. It is composed of a counter circuit 32 that outputs a counter value that goes up or down based on the output of the circuit 30, a voltage comparison circuit 30, and an oscillation circuit 31 that supplies a clock signal to the counter circuit 32, and a counter output by the counter circuit 32. The capacitance of the variable capacitor 16 of the LC resonance circuit 11 is controlled by the value.

FIG. 3 is a configuration example of the variable capacitor 16 according to the second embodiment of the present invention. In the variable capacitance capacitor 16, a plurality of switches and capacitors are connected in series in parallel, and the capacitance is switched by switching ON / OFF according to the counter value (Q0-Qn) output by the counter circuit 32. It controls.

An example of the control of the variable capacitance capacitor in the second embodiment will be described with reference to FIG. In FIG. 4, after outputting a counter value that increases the capacitance of the variable capacitance capacitor 16 so that the Vrec value gradually increases ((a) → (b) → (c)), a decrease in the Vrec value is detected. At that time, after outputting a counter value that reduces the capacitance of the variable capacitor 16 so that the Vrec value increases again, the counter value from the counter circuit 32 is calculated by stopping the supply of the clock from the oscillation circuit 31. It is fixed and the value of Vrec is focused on the value of (e). By switching ON / OFF of the switch connected in series with the capacitor, it is possible to control the capacitance of the LC resonance circuit 11 so that the output of the LC resonance circuit 11 becomes the maximum value.

In the present embodiment, since the control circuit of the energy harvesting circuit is configured by a simple circuit configuration of a rectifying circuit, a voltage comparison circuit, a counter circuit, and an oscillation circuit, it is possible to reduce the power consumption of the control circuit and it is efficient. It becomes possible to provide an energy harvesting circuit. This makes it possible to integrate the circuit including the control circuit into a single chip.

Further, since the control circuit is stopped when the parameter of the LC resonance circuit reaches the optimum value, the power required for the operation of the control circuit can be further reduced. It should be noted that a voltage detection circuit having low power consumption has also been developed. For example, the voltage detection circuit described in Non-Patent Document 2 can be used to reduce power consumption.

<Third embodiment>
FIG. 5 is a configuration example of the energy harvesting circuit according to the third embodiment of the present invention. In the third embodiment, in addition to the first voltage comparison circuit 30 in the second embodiment, the second voltage comparison circuit 40 driven by a clock signal slower than the first voltage comparison circuit 30. The second voltage comparison circuit 40 resets the counter value of the counter circuit 32 when the output of the LC resonance circuit 11 fluctuates significantly.

In the second embodiment, the output of the LC resonance circuit 11 can be stably converged under a certain operating environment of the energy harvesting circuit 1. However, when the operating environment changes, for example, when it is applied to a moving object, it frequently attaches to or detaches from another object, or when the power that is the source of energy harvesting fluctuates frequently. In such cases, the output of the antenna and the rectifier circuit 33 changes rapidly, so that it becomes difficult to stably converge the output of the LC resonance circuit 11. Here, even if the control is stopped at a certain convergence value, once the parameters of the LC resonance circuit 11 are fixed, it is not possible to deal with such a sudden change in voltage. Therefore, in the third embodiment, when the output of the rectifier circuit 33 suddenly changes to a predetermined threshold value or more, the output of the counter circuit 32 is reset to perform control for converging to the optimum point again. ..

In FIG. 5, the energy harvesting circuit 1 of FIG. 2 is further provided with a second transmission circuit 41 that supplies a second clock signal to the second voltage comparison circuit 40 and the second voltage comparison circuit 40. Similar to the first comparison circuit, the output of the rectifying circuit 33 is input to the second voltage comparison circuit, the output is connected to the counter circuit, and the output of the rectifying circuit 33 suddenly changes above a predetermined threshold value. In some cases, it is configured to output a signal that resets the counter value. Here, the second clock signal is set to be slower than the first clock signal so that the reset control cycle is longer than the control cycle that maximizes the output of the LC resonance circuit 11. There is. The speed of the second clock signal may be appropriately set according to the operating environment of the energy harvesting circuit 1.

A specific configuration of the second voltage comparison circuit according to the third embodiment will be described with reference to FIG. The voltage comparison circuit of FIG. 6 includes a latch circuit that outputs the voltage comparison result of the + terminal / − terminal, and a core circuit consisting of a core transistor having a gate connected to each of the + terminal / − terminal. A surplus drive transistor that supplies surplus driving force with a gate connected to each of the + and-terminals and a control transistor that controls ON / OFF of the surplus drive transistor are added to this control transistor. Is configured so that one is always ON. Further, in the configuration example of FIG. 6, a clock signal decelerated by the frequency dividing circuit is supplied to the gate of the latch circuit and the control transistor, and is configured to be driven based on the decelerated clock signal.

When the output voltage of the current rectifier circuit 33 is applied to the + terminal, the output voltage of the current rectifier circuit 33 is compared with the previous output voltage stored in the capacitance of the − terminal. Here, if the control transistor on the + terminal side is turned on and the control transistor on the-terminal side is turned off so as to operate the surplus driving transistor on the + terminal side, the surplus driving force has been added to the + terminal side. Output voltage is applied. For example, if the core transistor has a driving force of 1 and the surplus driving transistor has a driving force of x, the driving force on the + terminal side is 1 + x, and the driving force on the-terminal side remains 1. It is possible to emphasize the current output voltage by the driving force of the surplus driving transistor.

In such a circuit configuration, the value of the driving force emphasized by the value of x determines the threshold value in the voltage comparison circuit. In the latch circuit, even if the current output voltage on the + terminal side is lower than the previous output voltage on the-terminal side, the voltage input to the latch circuit is emphasized, so the output of the latch circuit is not inverted. However, the output of the latch circuit only occurs when the current voltage emphasized is lower than the previous voltage, that is, when the current voltage on the + terminal side drops significantly beyond the value of the emphasized driving force. Can be inverted. If the counter value is reset based on the output signal of this latch circuit, even if the output of the rectifying circuit suddenly changes above a predetermined threshold value, the output of the counter circuit is reset and the control for converging to the optimum point again is performed. It can be carried out. The value of the driving force x of the surplus transistor that determines the threshold value when performing this reset control may be appropriately set according to the operating environment of the energy harvesting circuit 1.

According to the present embodiment, even if the operating environment of the energy harvesting circuit suddenly changes and the harvested electric power drops significantly, the control for converging to the optimum point can be performed again. It is possible to provide an energy harvesting circuit that operates robustly to the environment.

<Fourth Embodiment>
A fourth embodiment will be described with reference to FIG. 7. In the fourth embodiment, as shown in FIG. 7, the counter value of the counter circuit in the first to third embodiments is input to the voltage multiplication circuit 50, and the output of the voltage multiplication circuit causes the LC resonance circuit 11 to operate. It drives the switch.

According to this configuration, in a general switch composed of active elements such as MOS transistors, a sufficient voltage can be applied to the gate of the MOS transistor, so that the on-resistance of the switch can be reduced. Become. Since the on-resistance of this switch is mainly seen as a loss in the LC resonance circuit, it is possible to improve the power efficiency of the entire energy harvesting circuit by reducing the on-resistance. A specific example of the voltage multiplication circuit 50 is shown in FIG. The circuit configuration as shown in FIG. 8 is useful as a voltage multiplication circuit in an energy harvesting circuit because the multiplication factor can be increased by increasing the number of stages.

<Other embodiments>
As shown in FIG. 9, the laser calibration capacitor 60 may be connected in parallel to the variable capacitance capacitor 16 of the LC resonance circuit 11. Since it is easier to handle the capacitor of the LC resonance circuit if there is a coarse adjustment range according to the environment, a laser calibration capacitor as shown in FIG. 10 is connected in parallel to the variable capacitance capacitor 16 of the LC resonance circuit 11. Then, the coarse adjustment by laser trimming may be performed.

1 ... Energy harvesting circuit, 10 ... Antenna, 11 ... LC resonance circuit, 12 ... Boost rectifier circuit (for main power supply), 13 ... Capacitor (for main power supply), 14 ... Voltage detection circuit (for main power supply), 15 ... Load, 16 ... variable capacitance capacitor, 20 ... boost rectifier circuit (for main power supply), 21 ... capacitor (for control circuit), 22 ... voltage detection circuit (for control circuit), 23 ... control circuit, 30 ... voltage comparison circuit, 31 ... Oscillation circuit, 32 ... Counter circuit, 33 ... Rectifier circuit.

Claims (6)

With the antenna
A resonant circuit that resonates with the antenna at a desired frequency,
A first boost rectifier circuit in which a first capacitor is connected to the output side, rectifies and boosts the output of the resonance circuit, and supplies the load.
A control circuit that controls the resonance frequency of the resonance circuit so that the output voltage of the resonance circuit becomes large,
In an energy harvesting circuit equipped with
A second capacitor is connected to the output side, and a second boost rectifier circuit that rectifies and boosts the output of the resonance circuit and supplies it to the control circuit is provided.
The second capacitor has a capacitance value smaller than that of the first capacitor, and the control circuit controls the resonance frequency of the resonance circuit based on the output voltage amplitude of the resonance circuit. Energy harvesting circuit. The resonance circuit is an LC resonance circuit having a variable capacitance capacitor in which a plurality of switches and capacitors are connected in series in parallel.
The control circuit
A rectifier circuit that rectifies the output of the LC resonance circuit and
A first voltage comparison circuit, which is driven according to a first clock signal, alternately charges the outputs of the rectifier circuit into two capacitors, and compares the charging voltages of the two capacitors.
A counter circuit that is driven according to the first clock signal and outputs a counter value that goes up or down based on the output of the first voltage comparison circuit is provided.
The energy harvesting circuit according to claim 1, wherein each of the switches of the variable capacitance capacitor is turned ON or OFF according to the counter value. When the control circuit detects that the output of the rectifier circuit gradually increases according to the counter value and then decreases , the control circuit changes the counter value so that the output of the rectifier circuit increases again . The energy harvesting circuit according to claim 2, wherein the supply of the clock signal of 1 is stopped. The control circuit
A second clock signal driven according to a second clock signal, which is a clock signal slower than the first clock signal, alternately charges the output voltages of the rectifying circuit to the two capacitors, and compares the charging voltages of the two capacitors. Voltage comparison circuit and
With more
The energy according to claim 2 or 3, wherein the second voltage comparison circuit outputs a signal for resetting the counter value when the fluctuation of the output of the rectifier circuit exceeds a predetermined threshold value. Harvesting circuit. A voltage multiplication circuit for multiplying the output signal of the counter circuit is provided.
The energy harvesting circuit according to any one of claims 2 to 4, wherein the switch of the variable capacitance capacitor is controlled according to the output of the voltage multiplication circuit. The energy harvesting circuit according to any one of claims 2 to 5, wherein the LC resonance circuit further includes a laser calibration capacitor connected in parallel with the variable capacitance capacitor and laser trimmed.

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