Patent Description:
This disclosure is directed to the field of wireless power transmission and, in particular, to hardware, operating techniques for the hardware, and methods for increasing the amount of power transmittable in a given unit of time via wireless power transmission.

Portable electronic devices, such as smartphones, smartwatches, audio output devices (earbuds, headphones), and wearables operate on battery power, and not from wired power transmitted thereto over wired transmission lines and distribution systems. The batteries used for such devices are typically rechargeable and, therefore, a way to recharge the power of such batteries is necessary.

Most portable electronic devices include a charging port, typically conforming to the Micro USB or USB-C standards, into which a power cord connected to a power source can be inserted to provide for recharging of their batteries. However, such charging ports may make it difficult to enhance the water resistance of the electronic device, and are subject to damage from repeated use. In addition, some smaller portable electronic devices (for example, earbuds and smartwatches) lack the available space to provide for a charging port. Still further, some users may find it cumbersome to plug a power cord into the charging port of an electronic device to charge the battery of that device.

Therefore, to address these issues, wireless power transmission has been developed as, for example, described in <CIT> related to a multi-mode wireless power receiver circuit and control method thereof. Wireless power transmission systems utilize a coil transmitter (a primary), driven by electric power from a power source (typically a wired connection, but in some cases a battery), that generates a time-varying electric field, and a coil receiver (a secondary) in which the time-varying electric field induces a current. Receiver hardware extracts the power transmitted to the coil receiver, and provides it to a load, such as the battery of the electronic device into which the coil receiver and receiver hardware are incorporated.

Standards governing the hardware and how the transmitter and receiver communicate have been developed, allowing for easy implementation of wireless charging into electronic devices. However, existing wireless transmission standards can only transfer a limited amount of power, which may be insufficient or undesirable in some situations where it is desired to transmit an increased amount of power per unit of time. As such, despite the existence of well-established and well-functioning wireless transmission standards, further development into this area is still needed.

The invention is set out by the appended claims.

An embodiment provides a wireless power transmission system including at least one wireless power transmission circuit, a first wireless power reception circuit, a second wireless power reception circuit, and control circuitry. Note that the first wireless power reception circuit is a master and that the second wireless power reception circuit is a slave, and that there may be multiple slaves. However, for brevity, in this summary section, just one second wireless power reception circuit (slave) is described.

The first wireless power reception circuit has a first amplifier circuit configured to compare a reference voltage to a feedback voltage representative of an output node voltage produced from power received from the at least one wireless power transmission circuit, and adjust a first transistor supplying a first rectified voltage until the feedback voltage is equal to the reference voltage, with the first rectified current being delivered to the output node.

The second wireless power reception circuit has a second amplifier circuit configured to modify a gate bias for a second transistor sourcing a second rectified current produced from power received from the at least one wireless power transmission circuit to thereby modify the second rectified current, based upon a comparison of a reference current to a current representative of the second rectified current, with the second rectified current being delivered to the output node.

The control circuitry is configured to adjust the reference current until a first rectified voltage generated by the first wireless power reception circuit and a second rectified voltage generated by the second wireless power reception circuit are equal.

The first wireless power reception circuit may also include a first capacitor across which the first rectified voltage forms, and the second wireless power reception circuit may also include a second capacitor across which the second rectified voltage forms.

The first amplifier circuit may also include a first n-channel transistor having a drain coupled to receive the first rectified voltage, a source coupled to the output node, and a gate. The first amplifier circuit may also include a voltage divider coupled between the output node and ground, and a first amplifier having a non-inverting terminal coupled to the reference voltage, an inverting terminal coupled to a tap of the voltage divider to receive the feedback voltage, and an output coupled to the gate of the first n-channel transistor.

The second amplifier circuit may include a second n-channel transistor having a drain coupled to the second rectified voltage, a source coupled to the output node, and a gate. The second amplifier circuit may also include a second amplifier having a non-inverting terminal coupled to receive the current representative of the second rectified current, an inverting terminal coupled to receive the reference current, and an output coupled to the gate of the second n-channel transistor.

An equalizer switch controlled by the control circuitry may selectively couple the first rectified voltage to the second rectified voltage when the control circuitry is unable to adjust the reference current until the first and second rectified voltage are equal. The equalizer switch may selectively couple the first rectified voltage to the second rectified voltage when the control circuitry is unable to adjust the reference current until the feedback voltage is equal to the reference voltage and the current representative of the second rectified current is equal to a reference current.

The first amplifier may be a low dropout amplifier.

The control circuitry may adjust the reference current until the first rectified voltage and the second rectified voltage are equal by: requesting that the at least one power transmission circuit transmit, to the first wireless power reception circuit, a portion of power it is capable of transmitting; and adjusting the reference current until a first balance point, at which the first and second rectified voltages are equal are reached. The reference current may be adjusted until the first balance point by: requesting that the at least one power transmission circuit increase the portion of its power that it is transmitting to the first wireless power reception circuit, if the first rectified voltage is greater than an output voltage at the output node and if the output voltage is greater than the second rectified voltage; increasing a magnitude of the reference current if the second rectified voltage is greater than the first rectified voltage and the first rectified voltage is greater than the output voltage; and decreasing the magnitude of the reference current if the first rectified voltage is greater than the second rectified voltage and the second rectified voltage is greater than the output voltage.

The control circuitry may adjust the reference current until the first rectified voltage and the second rectified voltage are equal by additionally: requesting that the at least one power transmission circuit transmit, to the second wireless power reception circuit, a portion of power it is capable of transmitting; and adjusting the reference current until a second balance point, at which the first and second rectified voltages are equal. The reference current may be adjusted until the second balance point is reached by: increasing a magnitude of the reference current, if the second rectified voltage is greater than the first rectified voltage and the first rectified voltage is greater than the output voltage; and decreasing the magnitude of the reference current if the first rectified voltage is greater than the second rectified voltage and the second rectified voltage is greater than the output voltage.

The control circuitry may adjust the reference current until the first rectified voltage and the second rectified voltage are equal by additionally: requesting that the at least one power transmission circuit transmit, to the first and second wireless power reception circuits, all of power it is capable of transmitting; and adjusting the reference current until a third balance point, at which the first and second rectified voltages are equal. The reference current may be adjusted until the third balance point is reached by: increasing a magnitude of the reference current, if the second rectified voltage is greater than the first rectified voltage and the first rectified voltage is greater than the output voltage; and decreasing the magnitude of the reference current if the first rectified voltage is greater than the second rectified voltage and the second rectified voltage is greater than the output voltage.

A further embodiment provides a wireless power transmission system comprising at least one wireless power transmission circuit; a master wireless power reception circuit; and a plurality of slave wireless power reception circuits.

The master wireless power reception circuit comprises a voltage reference circuit configured to adjust an output voltage at an output node until a feedback voltage is equal to a reference voltage, with the feedback voltage being representative of a first output voltage produced from power received from the at least one wireless power transmission circuit.

Each slave wireless power reception circuit comprises a current reference circuit configured to adjust a respective rectified current produced from power received from the master wireless power reception circuit by that slave wireless power reception circuit and delivered to the output node until a first rectified voltage generated by the master wireless power reception circuit and a second rectified voltage generated by that slave wireless power reception circuit are equal.

The master wireless power reception circuit may further comprises a first capacitor across which the first rectified voltage forms; and each wireless power reception circuit may further comprises a second capacitor across which the second rectified voltage forms.

The voltage reference circuit may comprise: a three terminal device or set of devices having a first terminal coupled to receive the first rectified voltage, a second terminal coupled to an output node, and a control terminal; a voltage divider coupled between the output node and ground; and a first amplifier having a non-inverting terminal coupled to the reference voltage, an inverting terminal coupled to a tap of the voltage divider to receive the feedback voltage, and an output coupled to the control terminal of the three terminal device or set of devices.

Each current sourcing circuit may comprise: a three terminal device or set of devices having a first terminal coupled to the second rectified voltage, a second terminal coupled to the output node, and a control terminal; and a second amplifier having a non-inverting terminal coupled to receive a current representative of the rectified current, an inverting terminal coupled to receive a reference current, and an output coupled to the control terminal of the three terminal device or set of devices of the current sourcing circuit.

The wireless power transmission system may further comprise an equalizer switch to selectively couple the first rectified voltage to the second rectified voltage when the current reference circuit is unable to adjust the reference current until the first and second rectified voltages are equal.

A further embodiment provides a method of wireless transmitting power, the method comprising: causing at least one power transmission circuit to transmit, to a master wireless power reception circuit, a portion of power it is capable of transmitting; adjusting operation of at least one slave wireless power reception circuit until a first rectified voltage produced by the master wireless power reception circuit and a second rectified voltage produced by the at least one slave wireless power reception circuit are equal by: requesting that the at least one power transmission circuit increase the portion of its power that it is transmitting to the master wireless power reception circuit, if the first rectified voltage is greater than an output voltage at an output node and if the output voltage is greater than the second rectified voltage; adjusting operation of the at least one slave wireless power reception circuit if the second rectified voltage is greater than the first rectified voltage and the first rectified voltage is greater than the output voltage; and adjusting operation of the at least one slave wireless power reception circuit if the first rectified voltage is greater than the second rectified voltage and the second rectified voltage is greater than the output voltage.

The operation of a plurality of slave wireless power reception circuits may be adjusted until the first rectified voltage and second rectified voltages produced by each of the plurality of slave wireless power reception circuits are equal by: requesting that the at least one power transmission circuit increase the portion of its power that it is transmitting to the master wireless power reception circuit, if the first rectified voltage is greater than an output voltage at an output node and if the output voltage is greater than the second rectified voltages; adjusting operation of the plurality of slave wireless power reception circuits if the second rectified voltages are greater than the first rectified voltage and the first rectified voltage is greater than the output voltage; and adjusting operation of the plurality of slave wireless power reception circuits if the first rectified voltage is greater than the second rectified voltages and the second rectified voltages are greater than the output voltage.

Now described with reference to <FIG> is an embodiment of wireless transmission system <NUM> in which first and second transmitters <NUM> and <NUM>, respectively, wirelessly transmit power to first and second receivers <NUM> and <NUM>, respectively, operating in parallel. First, the hardware itself will be described, and thereafter, the operation of the hardware will be described.

The transmitter <NUM> is comprised of an AC power source <NUM> connected to a primary coil (schematically represented by capacitance Cp1 in series with inductor Lp1 and resistance Rp1).

The receiver <NUM> is comprised of a secondary coil (schematically represented by capacitance Cs1 in series with inductor Ls1 and resistance Rs1) connected to a rectifier <NUM> that rectifies an AC current Is output by the secondary coil to produce a DC output current I1. The inputs of the rectifier <NUM> are connected to the secondary coil, and the output of the rectifier <NUM> is coupled between node N1 and ground.

A current sensor <NUM> is coupled between nodes N1 and N2 and configured to sense the current I1 output by the rectifier <NUM>. The current sensor <NUM> is comprised of a resistor R1 coupled between nodes N1 and N2, and an amplifier <NUM>. The amplifier <NUM> has a non-inverting terminal coupled to node N1 and an inverting terminal coupled to node N2. The output of the amplifier <NUM> is a first sense current I1_s, which is representative of the current I1 output by the rectifier <NUM>. The output of the amplifier <NUM> is selectively connected to the inverting terminal of amplifier <NUM> through switch S2 which is controlled by the mode signal Mode.

An n-channel MOSFET transistor T1 has its drain connected to node N2, its source connected to node N3, and its gate connected to be biased by the output of amplifier <NUM>. The amplifier <NUM> has its non-inverting terminal selectively connected to either a reference voltage Vref or a reference current Iref via a switch S4 that is controlled by the mode signal Mode, and has its inverting terminal selectively connected to node N4 through a switch S3 that is controlled by the Mode signal.

A resistor R2 is connected between nodes N3 and N4, and a resistor R3 is connected between nodes N4 and ground. A load <NUM> (for example, a battery of an electronic device into which the receivers <NUM> and <NUM> are incorporated) is connected between node N3 and ground. A capacitor C1 is connected between node N2 and ground, and a first rectified voltage Vrect1 forms across the capacitor C1.

Note that the switch S2, S3, and S4 in the receiver <NUM> all operate based upon the mode signal Mode, but operate differently. When the mode signal Mode indicates that the receiver <NUM> is to operate based on an output voltage control mode (hereinafter referred to as voltage feedback), the mode signal Mode serves to open switch S2, close switch S3 to receive the feedback voltage Vfbk1 from node N4 and set switch S4 so as to connect the non-inverting terminal of the amplifier <NUM> to the reference voltage Vref. On the other hand, when the mode signal Mode indicates that the receiver <NUM> is to operate based on output current control mode (hereinafter referred to as current feedback), the mode signal Mode serves to close switch S2, open switch S3, and set switch S4 so as to connect the non-inverting terminal of the amplifier <NUM> to the reference current Iref.

The transmitter <NUM> is further comprised of an AC power source <NUM> connected to a primary coil (schematically represented by capacitance Cp2 in series with inductor Lp2 and resistance Rp2).

The receiver <NUM> is further comprised of a secondary coil (schematically represented by capacitance Cs2 in series with inductor Ls2 and resistance Rs2) connected to a rectifier <NUM> that rectifies an AC current Is output by the secondary coil to produce a DC output current I2. The inputs of the rectifier <NUM> are connected to the secondary coil, and the output of the rectifier <NUM> is coupled between node N5 and ground.

A current sensor <NUM> is coupled between nodes N5 and N6 and configured to sense the current I2 output by the rectifier <NUM>. The current sensor <NUM> is comprised of a resistor R4 coupled between nodes N5 and N6, and an amplifier <NUM>. The amplifier <NUM> has a non-inverting terminal coupled to node N5 and an inverting terminal coupled to node N6. The output of the amplifier <NUM> is a second sense current I2_s, which is representative of the current I2 output by the rectifier <NUM>. The output of the amplifier <NUM> is selectively connected to the inverting terminal of amplifier <NUM> through switch S7 which is controlled by the mode signal Mode.

An n-channel transistor T2 has its drain connected to node N6, its source connected to node N3, and its gate connected to be biased by the output of amplifier <NUM>. Note that instead of the n-channel transistor T2, any three terminal device or combination of devices may be used.

A resistor R5 is connected between node N3 and N8, and a resistor R6 is connected between node N8 and ground.

The amplifier <NUM> has its non-inverting terminal selectively connected to a reference current Iref via a switch S9 that is controlled by the mode signal Mode, and has its inverting terminal connected to selectively receive the current I2_s from the output of the amplifier <NUM> through a switch S7 that is controlled by the mode signal Mode, or selectively connected to receive the feedback voltage Vfbk2 from node N8 through a switch S8 that is controlled by the mode signal Mode.

A capacitor C2 is connected between nodes N6 and ground, and a second rectified voltage Vrect2 forms across the capacitor C2.

Note that the switches S7, S8, and S9 in the receiver <NUM> all operate based upon the mode signal Mode, but operate differently. When the mode signal Mode indicates that the receiver <NUM> is to operate based on voltage feedback, the mode signal Mode serves to open switch S7, close switch S8, and set switch S9 so as to connect the non-inverting terminal of the amplifier <NUM> to the reference voltage Vref. On the other hand, when the mode signal Mode indicates that the receiver <NUM> is to operate based on current feedback, the mode signal Mode serves to close switch S7, open switch S8, and set switch S9 so as to connect the non-inverting terminal of the amplifier <NUM> to the reference current Iref.

A person skilled in the art will notice that in voltage feedback, the elements <NUM>, T1, R2, R3, S2, S3, S4 (and their respective counterparts <NUM>, T2, R5, R6, S7, S8, S9) are forming a conventional voltage regulator configuration represented here using n-channel MOSFET. However, this function could also be realized using a p-channel LDO conventional structure. A p-channel transistor T1 would have its drain connected to node N3, its source connected to node N2, and its gate connected to be biased by the output of amplifier <NUM> for which the positive and negative inputs would be swapped. A p-channel transistor structure would also accommodate the current feedback functionality. And more broadly, any receiver realized for being configurable between voltage control mode (conceptually a voltage source) and output current control mode (conceptually a current source) could be used to realize the disclosures herein.

A switch S1, operated by a control signal Eq, is connected between nodes N2 and N6. When the switch S1 is closed, Vrect1 and Vrect2 equalize.

A control unit <NUM> receives the reference voltage Vref, the output voltage Vout, the first rectified voltage Vrect1, the second rectified voltage Vrect2, the first rectified current I1_s, and the second rectified current I2_s, and from them generates the reference current Iref and the control signal Eq for the switch S <NUM>.

Note that there may be but one control unit <NUM> or <NUM>, or that both control units <NUM> and <NUM> are present. When both control units <NUM> and <NUM> are present, each is associated with one of the receivers <NUM> or <NUM>. As will be explained below, one receiver <NUM> or <NUM> operates as a master, while the other receiver <NUM> or <NUM> operates as a slave. In the case where both control units <NUM> and <NUM> are present, the control unit <NUM> or <NUM> associated with the receiver <NUM> or <NUM> designated as the master is operational, while the other control unit idles.

The Master control unit (not idle) is in charge of directly controlling Vref for the Master and Iref for the Slave and asking for power increase/decrease for both transmitters.

In case of in-band communication, despite a control unit being idle as a Slave, it may be requested by the Master control unit to wake-up and communicate (ASK modulation in Qi standard for example) with the associated transmitter for adjusting power, simply because the Master control unit do not have access to the physical communication link to the transmitter. This may not be used in the case of out-of-band communication.

In operation, one of the receivers <NUM> or <NUM> operates in a voltage mode feedback loop as a "master", while the other operates in a current mode feedback loop as a "slave". As illustrated in <FIG>, the receiver <NUM> is operating as the master, while the receiver <NUM> is operating as the slave. In particular, the receiver <NUM> (operating as the master) sets and controls the rectified output voltage Vout (conceptually as a voltage source would do), while the receiver <NUM> (operating as the slave) increases the power delivered (conceptually as a current source would do) at that output voltage Vout.

In greater detail, the amplifier <NUM>, transistor T1, and resistors R2 and R3 form a voltage regulator. The amplifier <NUM> compares the reference voltage Vref to a feedback voltage Vfbk1 at node N4, and modulates the bias applied to the gate of the n-channel transistor T1 such that the feedback voltage Vfbk1 is equal to Vref. This has the effect of modulating the current I1 supplied by the transistor T1 to the load to maintain the output voltage Vout at a set, stable voltage.

The receiver <NUM> operates in a current mode loop as a "slave" by adding the current I2 to the output current I1 of the receiver <NUM>, without changing the voltage Vout. The parameters of the system are linked through the following relationships: <MAT>.

The control unit <NUM> monitors Vrect1 and Vrect2, and adjusts Iref such that, when the amplifier <NUM> modulates the bias voltage on the gate of the n-channel transistor T2 to maintain the current I2_s as being equal to the reference current Iref, the second rectified voltage Vrect2 matches the first rectified voltage Vrect1. When Vrect1 and Vrect2 match, then I1 and I2 are governed by I2 = Iref and I1 = Vout / Rload - Iref with Iref = <MAT>. k1 (and respectively k2) represent the power transfer factor from TX1 to RX1 (resp. TX2 to RX2), and α represents the ratio between the amount of power P2 provided by TX2 and the amount of power P1 provided by TX1, such that P2=α. P0 while P1=P0. For the system to reach the equilibrium point (Vrect1 = Vrect2), the overall incoming power P1+P2 = (<NUM>+α)P0 should be sufficient so that Vout can reach Vref while delivering Vref<NUM>/Rload. In case the incoming power is not enough, the system would alter the parameters Iref & Vref so as to comply with the relationship tying up the two parameters. It is to be highlighted that in case k1=k2 and α=<NUM>, Iref = <NUM> × I1 = <NUM> × I2 = Vout / (<NUM>.

The receivers <NUM> and <NUM> each contribute to providing power to the load <NUM> at the output voltage Vout, effectively increasing the power provided to the load <NUM> over the case where but one of the receivers <NUM> or <NUM> is operational.

If it is impossible during a given operational condition (for example - but not only- in situations where the incoming power is too low), to sufficiently adjust Iref - for a given Vref - such that Vrect2 is substantially equal to Vrect1, the control unit <NUM> may assert the equalization signal Eq to thereby close switch S1, shorting nodes N2 and N6, thereby resulting in Vout possibly moving away from target and some current possibly flowing from Vrect1 to Vrect2 (or vice versa) through S1.

The current flowing from one of the two Vrect voltages (Vrect1, Vrect2) to the other can be read through the current sensors, and both and Vout information (captured by Vout voltage measurement) can be used by the system to understand on which parameter to play with for reaching the steady operation. Ultimately the steady operation is governed by: <MAT> When P0, Iref, and Vref set properly, it would result to zero current flowing through the switch S1, and system being able to release the Equalization.

The operations performed by the receiver <NUM> are instead performed by the receiver <NUM> if the receiver <NUM> is instead configured as the master, and the operations performed by the receiver <NUM> are instead performed by the receiver <NUM> if the receiver <NUM> is instead configured as the slave.

Greater details of operation of the wireless power transmission system <NUM> are now described with additional reference to the flowchart of <FIG> that illustrate one potential operating technique for the wireless power transmission system <NUM>, with it being understood that other operating techniques may also be used. To begin wireless power transmission, the receivers <NUM> and <NUM> are placed in position to receive power from the transmitters <NUM> and <NUM> (Block <NUM>). For instance, if the receivers <NUM> and <NUM> are within a smartphone and the transmitters <NUM> and <NUM> are within a wireless charging pad, the smartphone here would be placed on the wireless charging pad.

Then, a master/slave assignment operation is performed (Block <NUM>). In the instance shown in <FIG>, the receiver <NUM> is configured as the master, while the receiver <NUM> is configured as the slave. Details on this master/slave assignment (Block <NUM>) will be given below.

Next, the transmitters <NUM> and <NUM> ping the receivers <NUM> and <NUM> (Block <NUM>), resulting in the receivers <NUM> and <NUM> waking up, the control unit <NUM> setting the reference current Iref to a set initial value, and hardware within the electronic device containing the system <NUM> setting the reference voltage Vref to a set initial value (Block <NUM>). Then, the controller <NUM> sends a power request to the transmitter <NUM> via the receiver <NUM> using in-band or out-of-band data communication, and the load <NUM> is connected to node N3 (Block <NUM>).

Thereafter, a first feedback loop process (Block <NUM>) is performed so as to find a first balance point in which the output voltage Vout is approximately equal to the reference voltage Vref, the current I2 is approximately equal to the reference current Iref (which is set to approximately zero), the current I1 is approximately equal to the output voltage Vout divided by the impedance of the load <NUM>, the power transmitted by the second transmitter <NUM> to the second receiver <NUM> is approximately equal to Vout*I2, the power transmitted by the first transmitter <NUM> to the first receiver <NUM> is approximately equal to Vout*I1, the current into the load is equal to I1+I2, and I1 is providing most of the load current while I2 is still approximately zero. The goal of the first feedback loop process is for the transmitter <NUM> to reach Vout=Vref output voltage and deliver approximately <NUM>% of the power it is capable of delivering to the receiver <NUM>, while the transmitter <NUM> is delivering a small amount of power for biasing receiver <NUM> and Vrect2 is actually balanced with Vrect1 level. In other words, when exiting the loop <NUM> the receiver <NUM> is receiving just enough power for being alive and supplied, without contributing yet to the load current, while receiver <NUM> does provide to the load <NUM>% of what it is capable of.

The first feedback loop begins with the controller <NUM> reading the rectified voltages Vrect1 and Vrect2, and reading the output voltage Vout. If Vrect1 is greater than Vout and Vout is greater than Vrect2, then the controller <NUM> requests power transfer from the transmitter <NUM> to the receiver <NUM> (Block <NUM>) by transmitting the request from the receiver <NUM> to the transmitter <NUM> in view of increasing Vrect2 as the incoming power to receiver <NUM> will at a point exceed the receiver's demand which is set to a low Iref value. Subsequently to transmitter <NUM> power increases, the system will enter Block <NUM> or even Block <NUM> when the first feedback loop begins anew. On the other hand, if Vrect2 is greater than Vrect1 and Vrect1 is greater than Vout (Block <NUM>), the controller <NUM> increases Iref, changing the operation of the amplifier <NUM> such that the n-channel transistor T2 increases I2 resulting in Vrect2 decreasing (Block <NUM>), and the feedback loop begins anew. If, instead, Vrect1 is greater than Vrect2 and Vrect2 is greater than Vout (Block <NUM>), the controller <NUM> decreases Iref, changing the operation of the amplifier <NUM> such that the n-channel transistor T2 decreases I2 resulting in Vrect2 increasing (Block <NUM>), and the first feedback loop begins anew. Once Vrect1 is equal to Vrect2 and greater than Vout (Block <NUM>), the first balance point has been reached and the first feedback loop process is complete (Block <NUM>).

After the first balance point is reached, then the controller <NUM> (acting as the Master) requests additional power be transmitted from the transmitter <NUM> to the receiver <NUM>. In case of in-band communication, the controller <NUM> may not have capability to control the receiver <NUM> hardware communication channel to its associated transmitter <NUM>. Therefore, the controller <NUM> may instruct the controller <NUM> to wake-up and do so. The controller <NUM> ramps up the reference current Iref accordingly (Block <NUM>) to increase power delivery into the load <NUM>. This ramp-up (Block <NUM>) will be described in further detail below. After the ramp-up, a second feedback loop process begins (Block <NUM>).

The second feedback loop is performed so as to find a second balance point in which the output voltage Vout is approximately equal to the reference voltage Vref, the current I2 is approximately equal to the reference current Iref, the current I1 is approximately equal to the output voltage Vout divided by the load impedance Zload with the current I2 being subtracted from the result, the power transmitted by the second transmitter <NUM> to the second receiver <NUM> is approximately equal to Vout*I2, and the power transmitted by the first transmitter <NUM> to the first receiver <NUM> is approximately equal to Vout*I1 (Block <NUM>). The goal of the second feedback loop process is for the transmitters <NUM> and <NUM> to each deliver approximately <NUM>% of the power they are capable of delivering to the receivers <NUM> and <NUM>.

The second feedback loop begins with the controller <NUM> reading the rectified voltages Vrect1 and Vrect2, and reading the output voltage Vout. If Vrect2 is greater than Vrect1 and Vrect1 is greater than Vout (Block <NUM>), then the controller <NUM> increases Iref, changing the operation of the amplifier <NUM> such that the n-channel transistor T2 increases I2 resulting in Vrect2 decreasing (Block <NUM>), and the second feedback loop begins anew. If, instead, Vrect1 is greater than Vrect2 and Vrect2 is greater than Vout (Block <NUM>), the controller <NUM> decreases Iref, changing the operation of the amplifier <NUM> such that the n-channel transistor T2 decreases I2 resulting in Vrect2 increasing (Block <NUM>), and the second feedback loop begins anew. Once Vrect1 is equal to Vrect2 and greater than Vout (Block <NUM>), the second balance point has been reached and the second feedback loop process is complete (Block <NUM>).

After the second balance point is reached, then the controller <NUM> evaluates a value k1, calculated as the power delivered to the receiver <NUM> divided by the power transmitted by the transmitter <NUM>, and a value k2, calculated as the power delivered to the receiver <NUM> divided by the power transmitted by the transmitter <NUM> (Block <NUM>). These values of k1 and k2 may be stored and used at step <NUM> (at the next time the system <NUM> is used) to determine the master/slave assignment -- whichever receiver <NUM> or <NUM> has the higher k value can be set as the master at step <NUM>.

Thereafter, the controller <NUM> may instruct controller <NUM> to request additional power be transmitted from the transmitter <NUM> to the receiver <NUM>. It may also directly send power request to any of the two transmitters in case of out-of-band communication. The controller <NUM> ramps up the reference current Iref accordingly (Block <NUM>). This ramp-up (Block <NUM>) will be described in detail below, and serves to bring transmitters <NUM> and <NUM> to be transmitting <NUM>% of the power they are capable of transmitting to the receivers <NUM> and <NUM>. After the ramp-up, a third balance point is reached in which the output voltage Vout is approximately equal to the reference voltage Vref, the current I2 is approximately equal to the reference current Iref, the current I1 is approximately equal to the output voltage Vout divided by the load impedance Zload with the current I2 being subtracted from the result, the power transmitted by the second transmitter <NUM> to the second receiver <NUM> is approximately equal to Vout*I2, and the power transmitted by the first transmitter <NUM> to the first receiver <NUM> is approximately equal to Vout*I1 (Block <NUM>). Thereafter, the transmitters <NUM> and <NUM> will each be delivering <NUM>% of the power they are capable of delivering to the receivers <NUM> and <NUM>, and further adjustment is not needed. Power transfer continues to occur until the battery within the electronic device is fully charged or until the receivers <NUM> and <NUM> are no longer in proximity to the transmitters <NUM> and <NUM>, for example by the electronic device being removed from the charging pad.

It should be appreciated that in some instances, it may not be possible for the currents I1 and I2 to be equalized, and therefore it may not be possible for the transmitters <NUM> and <NUM> to each reach <NUM>% of their potential power output, and may not be possible for the receivers <NUM> and <NUM> to each reach <NUM>% of their potential power output to the load <NUM>. However, the above described feedback loops will still function to balance the rectified voltages Vrect1 and Vrect2, allowing each transmitter <NUM> and <NUM> to deliver different amounts of power.

Step <NUM> includes three events which are to happen simultaneously. The load demand adjusts to a higher value while the transmitter provides the additional required power and the control unit adjusts the Iref to help ensure smooth transition. It involves three independent items of hardware and time constants, and could result in Vrect excessively increasing or droping without proper synchronization between the demand, the supply and the balancing. Step <NUM> breaks this process in <NUM> phases. In the first instance, the power demand and Iref adjustment (supply & balancing) are performed while a dummy load is connected (steps 115a, 115b, 115c), which now allows simultaneously handling two items of hardware - transmitter & receiver - and more easily manage the sequencing as the dummy load is part of the receiver which is the one to instruct to the transmitter. Once the system stabilized in first instance, at second instance (step 115d), the dummy load is disconnected and the actual load demand is set which allows dealing again with the two items of hardware at a time, the receiver and its load, which could be for example a host in case of a battery charger.

The power request by the controller <NUM> for the transmitter <NUM> to send <NUM>% of the power it is capable of delivering to the receiver <NUM> (Block <NUM>) is now further described with additional reference to <FIG>. First, a dummy load is connected to the receiver <NUM>, and the controller <NUM> increases the reference current Iref to match the current through the dummy load (Block 115a).

Then, the controller <NUM> requests (or instructs controller <NUM> to do so in case of in-band communication) that the second transmitter <NUM> deliver additional power to the second receiver <NUM>. In particular the controller <NUM> requests that the second transmitter deliver up to <NUM>% of the power that it is capable of delivering to the receiver <NUM> (Block 115b). Then, the controller <NUM> reads the rectified voltages Vrect1 and Vrect2, as well as the output voltage Vout (Block 115c). If Vrect1 is greater than Vrect2 (which occurs if the controller <NUM> requested less than <NUM>% power from the second transmitter <NUM>, at Block 115c-<NUM>), then the controller <NUM> once again requests additional power from the second transmitter <NUM> (Block 115b). Once Vrect1 is equal to Vrect2 and greater than Vout (Block 115c-<NUM>), then the controller <NUM> disconnects the dummy load after making sure that the actual load requested the same amount of power (receiver to host transaction though I2C for example), resulting in the load <NUM> actually requesting additional current (Block 115d).

The power request by the controller <NUM> for the transmitters <NUM> and <NUM> to increase the power they are delivering to the receivers <NUM> and <NUM> (Block <NUM>) is now described with additional reference to <FIG>. First, as stated, the controller <NUM> requests the transmitters <NUM> and <NUM> (either directly through out-of-band communication, or via the controller <NUM>) to increase the power they are delivering to the receivers <NUM> and <NUM> by <NUM>% so that they are delivering the maximum power they can deliver (Block 124a). Therefore, the power delivered by the transmitter <NUM> is increased by <NUM>%, the power delivered by the transmitter <NUM> is increased by <NUM>% and the current I2 accordingly increases by <NUM>% (Block 124b). Thereafter, a third feedback loop process is performed (Block 124c).

The third feedback loop is performed so as to find a third balance point in which the output voltage Vout is approximately equal to the reference voltage Vref, the current I2 is approximately equal to the reference current Iref, the current I1 is approximately equal to the output voltage Vout divided by the load impedance Zload with the current I2 being subtracted from the result, the power transmitted by the second transmitter <NUM> to the second receiver <NUM> is approximately equal to Vout*I2, and the power transmitted by the first transmitter <NUM> to the first receiver <NUM> is approximately equal to Vout*I1 (Block 124c). The goal of third feedback loop process is for the transmitters <NUM> and <NUM> to each deliver <NUM>% of the power they are capable of delivering to the receivers <NUM> and <NUM>.

The third feedback loop begins with the controller <NUM> reading the rectified voltages Vrect1 and Vrect2, and reading the output voltage Vout. If Vrect2 is greater than Vrect1 and Vrect1 is greater than Vout (Block 124c-<NUM>), then the controller <NUM> increases Iref, changing the operation of the amplifier <NUM> such that the n-channel transistor T2 increases I2 resulting in Vrect2 decreasing (Block 124c-<NUM>), and the third feedback loop begins anew. If, instead, Vrect1 is greater than Vrect2 and Vrect2 is greater than Vout (Block 124c-<NUM>), the controller <NUM> decreases Iref, changing the operation of the amplifier <NUM> such that the n-channel transistor T2 decreases I2 resulting in Vrect2 increasing (Block 124c-<NUM>), and the third feedback loop begins anew. Once Vrect1 is equal to Vrect2 and greater than Vout (Block 125c-<NUM>), the third balance point has been reached and the third feedback loop process is complete (Block <NUM>).

The master/slave assignment operation (Block <NUM>) is now described in detail with additional reference to <FIG>. Initially, the transmitters <NUM> and <NUM> ping the receivers <NUM> and <NUM> (Block 102a), and the receivers <NUM> and <NUM> in turn wake up and identify themselves to the controller <NUM> (Block 102b). Initially, the first receiver <NUM> starts as the master and the reference voltage Vref is set to an initial startup value, and the second receiver <NUM> starts as the slave and the reference current Iref is set to an initial startup value, and the controller <NUM> requests power transfer from the transmitter <NUM> to the receiver <NUM> while the load <NUM> is not yet connected to node N3 and the controller reads the rectified voltage Vrect1 (Block 102c) and stores the value of Vrect1. When the receiver <NUM> is set as the master, it has the electrical components and connections it is shown as having in <FIG>. When the receiver <NUM> is set as the slave, it has the electrical components and connections it is shown as having in <FIG>.

Next, the receiver <NUM> is switched to be the master and the receiver <NUM> is switched to be the slave, and the receivers <NUM> and <NUM> are thereafter shut down (Block 102d). Here, note that by setting the receiver <NUM> to be the master, the receiver <NUM> has the same electrical components and connections as the receiver <NUM> is shown as having in <FIG>, and by setting the receiver <NUM> to be the slave, the receiver <NUM> has the same electrical components and connections as the receiver <NUM> is shown as having in <FIG>.

Now, the transmitters <NUM> and <NUM> again ping the receivers <NUM> and <NUM> (Block 102e), Vref and Iref are reinitialized to their initial startup values, the load <NUM> is still not connected to node N3, the controller <NUM> requests power transfer from the transmitter <NUM> to the receiver <NUM>, and the controller <NUM> reads the rectified voltage Vrect2 (Block 102f) and stores the value of Vrect2. Finally, the controller <NUM> determines which receiver <NUM> or <NUM> is to be the master and which is to be the slave based upon whether Vrect1 or Vrect2 is higher (Block <NUM>). It is to be noted that along with the Master/Slave assessment the control turns the receivers on and off. Therefore, as for being able to keep trace of Master/Slave assignment, the receivers should either embed NVM capability or either use the host memory capability for storing and retrieving the information.

An alternative technique for the master/slave assignment operation (Block <NUM>) is now described in detail with additional reference to <FIG>. Initially, the transmitters <NUM> and <NUM> ping the receivers <NUM> and <NUM> (Block 102a'), and the receivers <NUM> and <NUM> in turn wake up and identify themselves to the controller <NUM> (Block 102b'). Here, both receivers <NUM> and <NUM> are initially started in the slave configuration (e.g., both have the same electrical components and connections as the receiver <NUM> is shown as having in <FIG>), the load <NUM> is not connected to node N3, and the controller <NUM> requests power transfer to the receivers <NUM> and <NUM> from the transmitters <NUM> and <NUM> while reading Vrect1 and Vrect2 and storing their values (Block 102c').

Thereafter, the receiver <NUM> is switched to be the master and the receiver <NUM> is switched to be the slave, the controller <NUM> requests power transfer to the receivers <NUM> and <NUM> from the transmitters <NUM> and <NUM> while reading Vrect1 and storing its value (Block 102d'). Then, the receivers <NUM> and <NUM> are shut down. The controller <NUM> then determines which receiver <NUM> or <NUM> is to be the master and which is to be the slave based upon whether Vrect1 or Vrect2 is higher (Block 102e') at Block 102c', and whether Vrect2 from Block 102c' is higher than Vrect1 from Block 102d'.

Now described with reference to <FIG> is a second embodiment of wireless transmission system <NUM>' in which a single transmitter <NUM> wirelessly transmits power to first and second receivers <NUM> and <NUM> operating in parallel. The transmitter <NUM> is comprised of an AC power source <NUM> connected to a primary coil (schematically represented by capacitance Cp in series with inductor Lp and resistance Rp).

The receivers <NUM> and <NUM> are as described above.

Operation of the wireless power transmission system <NUM>' proceeds the same as the wireless power transmission system <NUM> as described above, except that the transmitter <NUM> is turned on when either of the transmitters <NUM> or <NUM> is turned on, that the transmitter <NUM> is turned off when both of the transmitters <NUM> and <NUM> are turned off.

While the cases of one transmitter paired with two receivers, and two transmitters paired with two receivers, has been shown, it should be appreciated that other configurations are possible. For example, there may be three or more receivers, with one receiver acting as a master (and performing the functions described above), and the other two or more receivers acting as slaves (and performing the functions described above).

Claim 1:
A wireless power transmission system (<NUM>; <NUM>'), comprising:
at least one wireless power transmission circuit (<NUM>, <NUM>; <NUM>);
a first wireless power reception circuit (<NUM>) configured to adjust an output voltage (Vout) at an output node produced from power received from the at least one wireless power transmission circuit until a feedback voltage (Vfbk1, Vfbk) is equal to a reference voltage (Vref), wherein the feedback voltage is representative of the output voltage; and
a second wireless power reception circuit (<NUM>) configured to adjust a first rectified current (I2) produced from power received from the at least one wireless power transmission circuit by the second wireless power reception circuit and delivered to the output node until a first rectified voltage (Vrect1) generated by the first wireless power reception circuit and a second rectified voltage (Vrect2) generated by the second wireless power reception circuit are equal,
wherein the first wireless power reception circuit (<NUM>) comprises a first amplifier circuit configured to compare the reference voltage (Vref) to the feedback voltage (Vfbk1), and adjust a first transistor (T1) sourcing a second rectified current (I1) until the feedback voltage is equal to the reference voltage, the second rectified current (I1) being delivered to the output node;
wherein the second wireless power reception circuit (<NUM>) comprises a second amplifier circuit configured to modify a gate bias for a second transistor (T2) sourcing the first rectified current (I2) to thereby modify the first rectified current, based upon a comparison of a reference current (Iref) to a current representative (I2_s) of the first rectified current (I2);
and wherein the wireless power transmission system further comprising a control circuitry (<NUM>, <NUM>) configured to adjust the reference current until the first rectified voltage (Vrect1) and the second rectified voltage (Vrect2) are equal.