Advanced protection circuit for q-factor sensing pads

Abstract

Advanced protection circuits for Q-factor sensing pads are disclosed. A wireless power system includes a bridge rectifier having first and second inputs coupled to first and second terminals of a coil and an output coupled to a rectified voltage node. An excitation circuit is coupled to the first input. A protection circuit has a first connection node capacitively coupled to the first terminal. The protection circuit clamps the first connection node when the first input is coupled to ground and connects the first connection node to the rectified voltage node when the first input is coupled to a supply voltage in a Q-factor measurement mode. The protection circuit functions as a pin of the rectifier in a wireless power mode. A pass gate circuit is between the first connection node and a sense node to which a sense circuit is connected to measure a Q-factor of the wireless power system when the protection circuit is in the Q-factor measurement mode.

Description

Technical Field

[0001] This disclosure relates to the field of wireless power transmission, and in particular to a protection circuit for a Q-factor measurement circuit device within a wireless power transmission system. Background Technology

[0002] Portable electronic devices, such as smartphones, smartwatches, audio output devices (earphones, headphones), and wearable devices, rely on battery power to operate, rather than from wired power transmitted to them via wired transmission lines and power distribution systems. Batteries used in such devices are typically rechargeable; therefore, a method for charging these batteries is required.

[0003] Most portable electronic devices include a charging port, typically compliant with Micro USB or USB-C standards, into which a power cord can be plugged in to charge its battery. However, such charging ports may not enhance the device's water resistance and can be damaged by repeated use. Furthermore, some smaller portable electronic devices (such as earbuds and smartwatches) may lack the space available to provide a charging port. Additionally, some users may find it inconvenient to plug a power cord into an electronic device's charging port to charge its battery.

[0004] Therefore, wireless power transmission has been developed to address these issues. For example... Figure 1 As shown, the wireless power transmission system 10 can be composed of a first device 11 and a second device 15. The first device 11 can be a device for wireless charging, such as a charging case for a pair of wireless earbuds, while the second device 15 can be a device that can both transmit and receive wireless power, such as a smartphone.

[0005] The first device 11 includes a receiving coil Ls (secondary; capacitor Cs represents the capacitance of the receiving coil), in which a time-varying current is induced by a time-varying electric field, and receiver hardware 12 that rectifies, regulates, and utilizes the time-varying current induced in the receiving coil Ls to provide power to the device 11, for example, to charge its battery.

[0006] The second device 15 includes a controlled-switching bridge circuit (operable as a bridge rectifier or a DC-AC inverter) 16, coupled to the transceiver coil Lxcvr at nodes Ac1 and Ac2. Discrete capacitor Cxcvr is used to tune the second device 15. The controlled-switching bridge circuit 16 consists of transistors T1-T4, which are controlled by gate voltages G1-G4.

[0007] A storage capacitor Ctank is coupled between node Nin and node N. Voltage regulator 17 has an input coupled to node Nin and an output coupled to node Nout. Battery 18 is selectively coupled between node Nout and node N via switch SW1, and selectively coupled between node N and node Nin via switch SW2. Switches SW1 and SW2 operate out of phase with each other. When the second device 15 operates as a receiver in power receiving mode, switch SW1 is closed and switch SW2 is open, and circuit 16 operates as an AC-DC rectifier, with a regulator used to generate a regulated voltage Vreg for charging the battery of the second device 15. When the second device 15 operates as a transmitter in power transmitting mode, switch SW1 is open and switch SW2 is closed, and circuit 16 operates as a battery-powered DC-AC inverter in one mode, transmitting the power supplied by battery 18 to the first device 11. Controller 19 generates gate voltages G1-G4 to control bridge 16 to operate in the desired rectifier / inverter mode.

[0008] When the second device 15 operates as a receiver, the controlled switching bridge circuit 16 rectifies the alternating current flowing into the transceiver coil Lxcvr to generate a direct current. This direct current charges the energy storage capacitor Ctank connected to node Nin, forming a rectified voltage Vrect across Ctank. The voltage regulator 17 generates a regulated output voltage Vreg at its output node Nout, which is supplied to the battery 18 to charge it.

[0009] When the second device 15 operates as a transmitter, the voltage of the battery 18 is applied to node Nin via switch SW2 and becomes voltage Vrect. Then, the gate voltages G1-G4 are driven by controller 19 to generate a time-varying current flowing through the transceiver coil Lxcvr.

[0010] In this wireless power transmission system 10, Q-factor measurements can be performed to enable object detection and evaluate the efficiency of wireless power transmission. Q-factor measurements are performed by scanning the frequency of the time-varying electric field generated by the transceiver 15 while simultaneously measuring the peak voltage generated at node AC1, and then dividing the peak voltage by the DC voltage generated at node Nin. To accommodate this, a sensing block 9 is coupled to a coil Lxcvr. The Q-factor measurement period can be interleaved with the power transmission / reception period, but they will not occur simultaneously.

[0011] The problem is that, without protective measures, components of sensing block 9, such as transistors, may be damaged during normal power transmission / reception cycles. Therefore, further development is needed. Summary of the Invention

[0012] The wireless power system includes: a coil having first and second terminals; a bridge rectifier having a first input and a second input coupled to the first and second terminals of the coil, respectively, and an output coupled to a rectified voltage node; an excitation circuit coupled to the first input of the coil; and a protection circuit having a first connection node coupled to the first terminal of the coil via a capacitor.

[0013] When in Q-factor measurement mode, the protection circuit is configured to: clamp the first connection node when the first input of the bridge rectifier is coupled to ground; and connect the first connection node to the rectified voltage node when the first input of the bridge rectifier is coupled to the power supply voltage.

[0014] When in wireless power mode, this protection circuit is configured to be disabled.

[0015] The wireless power system also includes a pass gate circuit coupled between a first connection node of the protection circuit and a sensing node; and a sensing circuit coupled to the sensing node and configured to measure the Q factor of the wireless power system when the protection circuit is in Q factor measurement mode.

[0016] This document also discloses a method for operating a wireless power system including a bridge rectifier. The method includes, in wireless power mode: receiving a time-varying electric field at a coil; operating the bridge rectifier to rectify an AC signal induced in the coil by the time-varying electric field to generate a rectified voltage at a voltage rectifier node; clamping a first connection node coupled to the coil via a capacitor when the low-side transistor of the bridge rectifier is coupled to ground; and connecting the first connection node to the rectified voltage when the high-side transistor of the bridge rectifier, which is directly electrically connected to the low-side transistor, is turned on.

[0017] The method further includes, in Q-factor measurement mode: turning off the high-side transistor of the bridge rectifier and turning on the low-side transistor of the bridge rectifier; turning on the pass-gate transistor to couple the first connection node to the sensing node; energizing the coil; stopping the energizing coil and sensing the voltage at the first connection node; and determining the Q-factor of the wireless power system based on the voltage sensed at the first connection node. Attached Figure Description

[0018] Figure 1 This is a schematic block diagram of a wireless power transmission system based on existing technology.

[0019] Figure 2 This is a schematic block diagram of the transceiver device described in this article, which may be used as a substitute for... Figure 1 Transceiver devices for wireless power transmission systems.

[0020] Figure 3This is a schematic block diagram of the transceiver device including protection circuitry described herein, which may be used as a substitute for... Figure 1 Transceiver devices for wireless power transmission systems. Detailed Implementation

[0021] The following disclosure enables those skilled in the art to make and use the subject matter disclosed herein. The general principles described herein can be applied to embodiments and applications other than those detailed above without departing from the spirit and scope of this disclosure. This disclosure is not intended to be limited to the embodiments shown, but rather to be given the broadest scope consistent with the principles and features of this disclosure or recommendations.

[0022] refer to Figure 2 The description refers to a transceiver device 15', for example, that can be used with... Figure 1 It is used in conjunction with the wireless power transmission system 10.

[0023] The transceiver device 15' includes a controlled-switching bridge circuit (which can operate as a bridge rectifier or a DC-AC inverter) 16, which is coupled to the transceiver coil Lxcvr at nodes Ac1 and Ac2, where Cxcvr represents a tuning capacitor to adjust impedance matching, and capacitor Cpar represents a parasitic capacitance intentionally added between nodes Ac1 and Ac2 to adjust the system impedance.

[0024] The controlled switch bridge circuit 16 consists of transistors T1-T4, which are controlled by gate voltages G1-G4. More specifically: transistor T1 has a drain coupled to node Nin, a source coupled to node Ac1, and a gate coupled to gate voltage G1; transistor T3 has a drain coupled to node Ac1, a source coupled to node N (which may be ground or another reference voltage), and a gate coupled to gate voltage G3; transistor T2 has a drain coupled to node Nin, a source coupled to node Ac2, and a gate coupled to gate voltage G2; and transistor T4 has a drain coupled to node Ac2, a source coupled to node N, and a gate coupled to gate voltage G4.

[0025] A storage capacitor Ctank is coupled between node Nin and node N. Voltage regulator 17 has an input coupled to node Nin and an output coupled to node Nout. Battery 18 is selectively coupled between node Nout and node N via switch SW1, and selectively coupled between node N and node Nin via switch SW2. Switches SW1 and SW2 operate out of phase with each other; when transceiver device 15' operates as a receiver in power receiving mode, switch SW1 is closed and switch SW2 is open, and circuit 16 operates as an AC-DC rectifier, with the regulator operating to generate a regulated voltage Vreg for charging battery 18; when transceiver device 15' operates as a transmitter in power transmitting mode, switch SW1 is open and switch SW2 is closed, and circuit 16 operates as a battery-powered DC-AC inverter. Controller 19 generates gate voltages G1-G4 to control bridge 16 to operate in the desired rectifier / inverter mode.

[0026] When transceiver device 15' operates as a receiver, the controlled switching bridge circuit 16 rectifies the alternating current to generate direct current, charging the energy storage capacitor Ctank connected to node Nin and forming a rectified voltage Vrect across the energy storage capacitor Ctank. Voltage regulator 17 generates a regulated output voltage Vreg at its output node Nout, which is supplied to battery 18 to charge battery 18.

[0027] When transceiver 15' operates as a transmitter, the voltage of battery 18 is applied to node Nin via switch SW2, becoming voltage Vrect. Then, gate voltages G1-G4 are driven by controller 19 to generate a time-varying current flowing through transceiver coil Lxcvr. Details of this control scheme can be found in U.S. Patent Application No. 16 / 669,068, filed October 30, 2019, the contents of which are incorporated herein by reference in their entirety.

[0028] The excitation circuit 21 is coupled between the power supply Vdd voltage and the node Ac1 of the transceiver coil Lxcvr (because capacitors Cxcvr and Cpar represent capacitors rather than physical components).

[0029] Capacitor Cq is coupled between excitation circuit 21 and pad Qs. n-channel transistor MN1 has a drain coupled to pad Qs, a source coupled to the source of n-channel transistor MN2, and a gate coupled to the Q-factor measurement enable signal Q_En. The source of transistor MN2 is coupled to the source of transistor MN1, its drain is coupled to a tap between resistors R1 and R2 (coupled in series between Vdd and ground), and its gate is coupled to the Q-factor measurement enable signal Q_En. Sensing circuit device 23 is coupled to the tap between resistors R1 and R2.

[0030] The second device 15' can operate in transceiver mode (Rx or Tx) or Q-factor measurement mode.

[0031] In Q-factor measurement mode, the Q-factor measurement enable signal Q_En is asserted by controller 19 to turn on transistors MN1 and MN2, thereby establishing a connection from the Qs pad to the center tap of series-connected resistors R1 and R2. Furthermore, transistors T3 and T4 are simultaneously turned on by controller 19 asserting gate voltages G3 and G4, thereby shorting nodes Ac1 and Ac2 to ground. Then, excitation circuit 21 excites coil Lxcvr until it reaches a steady state. Once excitation stops, the response of voltage VLC at node Nf (which will be a decaying sine wave oscillating around the common-mode voltage Vcm set at the tap between resistors R1 and R2) is sensed by sensing circuit device 23 through capacitor Cq. The amplitude and timing information sensed by sensing circuit device 23 can then be used to determine the Q-factor of the second device 15'.

[0032] During transceiver mode, controller 19 generates control signals G1-G4 to enable circuit 16 to function as either a receiver or an inverter, as described above. Additionally, during transceiver mode, the Q-factor measurement enable signal Q_En is deasserted, turning off transistors MN1 and MN2 to effectively isolate node Qs from Vcm. Simultaneously, the internal circuitry of excitation circuit 21 effectively blocks transmit / receive signals from excitation circuit 21, while the switching action of circuit 16 causes the voltage VLC on coil Lxcvr to switch between positive and negative maximum amplitudes, e.g., -50V and 50V. Because transistors MN1 and MN2 are off, pad Qs floats and therefore follows voltage VLC as it is AC-coupled to node Qs through capacitor Cq. This can be problematic as it can cause transistors MN1 and subsequently MN2 to break down. Specifically, transistor MN1 may break down when the voltage amplitude at pad Qs becomes sufficiently positive, and may inadvertently turn on when the voltage amplitude at pad Qs becomes sufficiently negative. In transceiver mode, this problem can be solved by using appropriate clamping circuitry to clamp the Qs pad to ground.

[0033] However, clamping circuits dissipate power, and for some applications requiring high-efficiency wireless power transmission, the level of power dissipation is not negligible.

[0034] To allow Q-factor measurement in applications requiring high-efficiency wireless power transmission, a method was developed. Figure 3 The transceiver device is 15".

[0035] Now for reference Figure 3 Transceiver device 15" and Figure 2The transceiver device 15' has the same connection and topology, except that a protection circuit 22 is coupled between the pad Qs and the drain of the transistor MN1, and the function of the controller 19' is modified.

[0036] The controller 19' includes a logic core 23 that generates Gate_G1, Gate_G2, Gate_G3, and Gate_G4 control signals, and a Q-factor measurement enable signal Q_En, which is inverted to generate Q_En_B. A first AND gate 31 performs a logical AND operation on Gate_G1 and Q_En_B to generate gate voltage G1. A second AND gate 32 performs a logical AND operation on Gate_G2 and Q_En_B to generate gate voltage G2. An OR gate 33 performs a logical OR operation on Gate_G3 and Q_En to generate gate voltage G3. An OR gate 34 performs a logical OR operation on Gate_G4 and Q_En to generate gate voltage G4. A third AND gate 35 performs a logical AND operation on Gate_G1 and Q_En_B to generate gate voltage G1a. A fourth AND gate 36 performs a logical AND operation on Gate_G3 and Q_En_B to generate gate voltage G3a.

[0037] Protection circuit 22 includes a p-channel transistor T1a, whose source is coupled to node Nin (therefore, the source of T1a is coupled to the drains of transistors T1 and T2), its drain is coupled to the Qs pad, and its gate is coupled to node N2. Protection circuit 22 also includes an n-channel transistor T3a, whose gate is coupled to the gate voltage G3a, its drain is coupled to the drain of transistor T1a, and its source is coupled to ground. The anode of a Zener diode Dz is coupled to node N2, and its cathode is coupled to node Nin. Resistor R3 is coupled in parallel with diode Dz between nodes Nin and N2. Resistor R4 is coupled between node N2 and the drain of n-channel transistor MN3. The source of n-channel transistor MN3 is coupled to ground, and its gate is coupled to the gate voltage G1a.

[0038] In transceiver mode, the Q-factor measurement enable signal Q_En is driven low by logic core 23, thus driving Q_En_B high. Additionally, during transceiver mode, logic core 23 generates Gate_G1, Gate_G2, Gate_G3, and Gate_G4 control signals to cause bridge 16 to either induce a time-varying current in the rectifier coil Lp or generate a time-varying current in coil Lp, thereby creating a time-varying electric field, depending on whether it is in receiver or transmitter mode.

[0039] Since transistor T3a is driven by gate voltage G3a and Q_En_B is high in transceiver mode, it is clear that in transceiver mode, transistor T3a is on when transistor T3 is on and off when transistor T3 is off. Similarly, since G1 and Q_En_B are high, transistor MN3 is turned on when gate voltage G1a goes high, thus sinking current from node N2 to turn on transistor T1a. Therefore, transistor T1a is on when transistor T1 is on. When Vrect is positive, transistor T1 is off; therefore, when Vrect exceeds the breakdown voltage of Zener diode Dz, Zener diode Dz breaks down and connects the gate of transistor T1a to Vrect. When transistor T1 is off, transistor T1a is off.

[0040] As previously stated, during transceiver mode, the Q-factor measurement enable signal Q_En is deasserted. This shuts down transistors MN1 and MN2. Since node Qs is AC coupled to voltage VLC through capacitor Cq, the voltage at node Qs follows voltage VLC. However, despite this, without protection circuit 22 (if node Qs is directly electrically connected to the drain of transistor MN1), the voltage at node Qs could spike high enough to damage transistors MN1 and MN2 unless transistors MN1 and MN2 are specifically designed to prevent potential voltages at node Qs. However, this would negatively impact the ability of transistors MN1 and MN2 to provide a low-impedance path for ESD current in the event of an ESD event.

[0041] Since the voltage at node Qs typically follows voltage VLC (which follows the voltage at node Ac1) during transceiver mode, it is understandable that if the circuitry at node Qs is similar to that at node Ac1, the voltage at Qs will closely or even completely follow the voltage at node Ac1, which is controlled. It is for this reason that protection circuit 22 includes transistors T1a and T3a coupled in series between node Nin and ground.

[0042] To protect transistors MN1 and MN2 from the floating voltage at node Qs in transceiver mode, while preventing transistors T1a and T3a from making a substantial contribution to the rectification process, the size of Cq is much smaller than Cp (e.g., 1000 times smaller), and the sizes of transistors T1a and T3a are the same factor (here, 1000) smaller than the sizes of transistors T1 and T3. As a result, the current flowing through transistors T1a and T3a is the same factor (here, 1000) lower than the current flowing through transistors T1 and T3, but the voltage at node Qs is controlled—when voltage Qs would otherwise become negative, it is clamped to ground by transistor T3a, and when voltage Qs would otherwise reach above Vrect, it is forced to reach Vrect through transistor T1a. During an ESD event at node Qs, transistors T1a and T3a provide low-resistance paths to ground and Vrect, thus this design of protection circuit 22 also provides ESD protection.

[0043] During Q-factor measurement mode, the Q-factor measurement enable signal Q_En is asserted, resulting in gate voltages G1 and G2 being deasserted to turn off transistors T1 and T2, while gate voltages G3 and G4 are turned on to turn on transistors T3 and T4. However, since Q_En_B is deasserted, this means that gate voltages G1a and G3a are turned off, turning off transistors G1a and G3a. Therefore, in Q-factor measurement mode, protection circuit 22 becomes transparent. Q-factor measurement is performed as described above.

[0044] In summary, transistors T1a and T3a contribute only 1 / 1000 to the rectification process, while protecting transistors MN1 and MN2 from damage in transceiver mode, being transparent in Q factor measurement mode, and providing electrostatic protection at node Qs.

[0045] In the given example, the dimensions of transistors T1a and T3a are 1 / 1000 of those of transistors T1 and T3, but other size differences can be envisioned, depending on the required ESD protection specifications.

[0046] It should also be noted that although transistor T1 is an n-channel transistor, transistor T1a can be (and in this example is) a p-channel transistor because it is much smaller in size, providing a simple gate drive scheme involving transistor MN3, resistors R3 and R4, and Zener diode Dz.

[0047] While only a limited number of embodiments have been described in this disclosure, those skilled in the art, upon benefiting from this disclosure, will understand that other embodiments can be conceived without departing from the scope of this disclosure. Therefore, the scope of this disclosure should be limited only by the appended claims.

Claims

1. A wireless power system, comprising: A coil having a first terminal and a second terminal; A bridge rectifier has a first input and a second input, the first input and the second input being coupled to a first terminal and a second terminal of the coil, respectively, and the bridge rectifier has an output being coupled to a rectified voltage node; The excitation circuit is coupled to the first input of the bridge rectifier; A protection circuit having a first connection node, the first connection node being coupled to the first terminal of the coil via a capacitor; The protection circuit is configured to operate in Q-factor measurement mode as follows: When the first input of the bridge rectifier is coupled to ground, the first connection node is clamped, and When the first input of the bridge rectifier is coupled to the power supply voltage, the first connection node is connected to the rectified voltage node; The protection circuit described therein is configured to be disabled when in wireless power mode; A transmission gate circuit is coupled between the first connection node and the sensing node of the protection circuit; as well as A sensing circuit is coupled to the sensing node and configured to measure the Q factor of the wireless power system when the protection circuit is in the Q factor measurement mode.

2. The wireless power system according to claim 1, The bridge rectifier mentioned above includes: A first transistor pair and a second transistor pair are coupled in parallel between the rectified voltage node and ground, wherein the first transistor pair includes a first transistor and a third transistor, the first transistor is coupled between the rectified voltage node and the first input of the bridge rectifier, and the third transistor is coupled between the first input of the bridge rectifier and ground; The protection circuit includes: a pair of protection transistors coupled between the rectified voltage node and ground, a tap between the pair of protection transistors coupled to the first connection node of the protection circuit, wherein the pair of protection transistors includes a first transistor and a second transistor, the first transistor being coupled between the rectified voltage node and the first connection node of the protection circuit, and the second transistor being coupled between the first connection node of the protection circuit and ground; and The first transistor in the pair of protection transistors is turned on when the first transistor in the first transistor pair of the bridge rectifier is turned on, and turned off when the first transistor in the first transistor pair of the bridge rectifier is turned off; and the second transistor in the pair of protection transistors is turned on when the third transistor in the first transistor pair of the bridge rectifier is turned on, and turned off when the third transistor in the first transistor pair of the bridge rectifier is turned off.

3. The wireless power system according to claim 1, The bridge rectifier mentioned above includes: A first n-channel transistor is coupled between the rectified voltage node and the first input of the bridge rectifier; A second n-channel transistor is coupled between the rectified voltage node and the second input of the bridge rectifier; The third n-channel transistor is coupled between the first input of the bridge rectifier and ground; as well as The fourth n-channel transistor is coupled between the second input of the bridge rectifier and ground; The protection circuit includes: A p-channel transistor is coupled between the rectified voltage node and the first connection node of the protection circuit, wherein when the protection circuit is in the wireless power mode, the p-channel transistor of the protection circuit is configured to turn on when the first n-channel transistor of the bridge rectifier is turned on, and is configured to turn off when the first n-channel transistor of the bridge rectifier is turned off. as well as An n-channel transistor is coupled between the first connection node of the protection circuit and ground, wherein when the protection circuit is in the wireless power mode, the n-channel transistor of the protection circuit is configured to turn on when the third n-channel transistor of the bridge rectifier is turned on, and is configured to turn off when the third n-channel transistor of the bridge rectifier is turned off, and wherein the n-channel transistor of the protection circuit is configured to turn off when the protection circuit is in the Q factor measurement mode.

4. The wireless power system of claim 3, wherein the first n-channel transistor has a gate, the gate of the first n-channel transistor being coupled to receive a first gate voltage; and wherein the protection circuit further comprises an additional n-channel transistor, a third resistor, and a Zener diode, the additional n-channel transistor having a source, a drain, and a gate, the source of the additional n-channel transistor being coupled to ground, the drain of the additional n-channel transistor being coupled to a second connection node via a fourth resistor, the gate of the additional n-channel transistor being coupled to receive a gate voltage, the gate voltage being the result of performing a logical AND operation between the first gate voltage and a transmission gate enable signal; the third resistor being coupled between the rectified voltage node and the second connection node; the Zener diode having a cathode and an anode, the cathode being coupled to the rectified voltage node, the anode being coupled to the second connection node; wherein the second connection node is coupled to the gate of the p-channel transistor of the protection circuit.

5. The wireless power system of claim 3, wherein the p-channel transistor of the protection circuit has a size equal to a given fraction of the size of the first n-channel transistor of the bridge rectifier; wherein the n-channel transistor of the protection circuit has a size equal to a given fraction of the size of the third n-channel transistor of the bridge rectifier; and wherein the capacitance of the capacitor coupling the first connection node of the protection circuit to the first terminal of the coil is a given fraction of the capacitance of the parasitic capacitance of the coil.

6. The wireless power system of claim 1, wherein the transmission gate circuit includes a pair of transmission gate transistors coupled in series between the first connection node and the sensing node, the pair of transmission gate transistors being configured to: be turned on when the protection circuit is in the Q factor measurement mode, and be turned off when the protection circuit is in the wireless power mode.

7. The wireless power system according to claim 1, further comprising: The first resistor is coupled between the power supply voltage and the sensing node; And a second resistor, which is coupled between the sensing node and ground.

8. The wireless power system according to claim 1, The bridge rectifier mentioned above includes: A first transistor is coupled between the rectified voltage node and the first input of the bridge rectifier; The second transistor is coupled between the rectified voltage node and the second input of the bridge rectifier; The third transistor is coupled between the first input of the bridge rectifier and ground; as well as The fourth transistor is coupled between the second input of the bridge rectifier and ground; The protection circuit includes: A first transistor is coupled between the rectified voltage node and the first connection node of the protection circuit, wherein when the protection circuit is in the wireless power mode, the first transistor of the protection circuit is configured to turn on when the first transistor of the bridge rectifier is turned on, and is configured to turn off when the first transistor of the bridge rectifier is turned off. as well as A second transistor is coupled between the first connection node of the protection circuit and ground, wherein when the protection circuit is in the wireless power mode, the second transistor of the protection circuit is configured to turn on when the third transistor of the bridge rectifier is turned on, and is configured to turn off when the third transistor of the bridge rectifier is turned off, and wherein the second transistor of the protection circuit is configured to turn off when the protection circuit is in the Q factor measurement mode.

9. The wireless power system of claim 8, wherein the first transistor has a gate, the gate of the first transistor being coupled to receive a first gate voltage; and wherein the protection circuit further comprises an additional transistor, a third resistor, and a Zener diode, the additional transistor having a first on terminal, a second on terminal, and a gate, the first on terminal being coupled to ground; The second conducting terminal is coupled to the second connection node via a fourth resistor; the gate of the additional transistor is coupled to receive a gate voltage, the gate voltage being the result of a logical AND operation performed on the first gate voltage and the transmission gate enable signal; the third resistor is coupled between the rectified voltage node and the second connection node; the Zener diode has a cathode and an anode, the cathode being coupled to the rectified voltage node and the anode being coupled to the second connection node; The second connection node is coupled to the gate of the first transistor in the protection circuit.

10. The wireless power system of claim 9, wherein the first transistor of the protection circuit has a size equal to a given fraction of the size of the first transistor of the bridge rectifier; wherein the second transistor of the protection circuit has a size equal to a given fraction of the size of the third transistor of the bridge rectifier; and wherein the capacitance of the capacitor coupling the first connection node of the protection circuit to the first terminal of the coil is a given fraction of the capacitance of the parasitic capacitance of the coil.

11. A method of operating a wireless power system according to any one of claims 1 to 10, the method comprising: In wireless power mode: The time-varying electric field is received at the coil; Operate a bridge rectifier to rectify the AC signal induced in the coil by the time-varying electric field to generate a rectified voltage at the voltage rectification node; When the low-side transistor of the bridge rectifier is coupled to ground, it will be clamped to ground by the first connection node of the coil, which is coupled to the coil through a capacitor; as well as When the high-side transistor of the bridge rectifier is turned on and directly connected to the low-side transistor, the first connection node is connected to the rectified voltage.

12. The method of claim 11, further comprising: In Q-factor measurement mode: Turn off the high-side transistor of the bridge rectifier and turn on the low-side transistor of the bridge rectifier; Turn on the transmission gate transistor to couple the first connection node to the sensing node; Excite the coil; Stop energizing the coil and sense the voltage at the first connection node; as well as The Q factor of the wireless power system is determined based on the voltage sensed at the first connection node.

13. A wireless power system, comprising: First coil terminal node and second coil terminal node; A bridge rectifier has a first input and a second input, the first input and the second input being coupled to a first coil terminal node and a second coil terminal node, respectively, and the bridge rectifier has an output being coupled to a rectified voltage node; The excitation circuit is coupled to the first input of the bridge rectifier; A protection circuit having a first connection node, the first connection node being coupled to the first coil terminal node via a capacitor; The protection circuit is configured to: when in Q-factor measurement mode: When the first input of the bridge rectifier is coupled to ground, the first connection node is clamped, and When the first input of the bridge rectifier is coupled to the power supply voltage, the first connection node is connected to the rectified voltage node; The protection circuit described therein is configured to be disabled when in wireless power mode; as well as A transmission gate circuit is coupled between the first connection node and the sensing node of the protection circuit.

14. The wireless power system according to claim 13, The bridge rectifier mentioned above includes: A first transistor pair and a second transistor pair are coupled in parallel between the rectified voltage node and ground, wherein the first transistor pair includes a first transistor and a third transistor, the first transistor is coupled between the rectified voltage node and the first input of the bridge rectifier, and the third transistor is coupled between the first input of the bridge rectifier and ground; The protection circuit includes: a pair of protection transistors coupled between the rectified voltage node and ground, a tap between the pair of protection transistors coupled to the first connection node of the protection circuit, wherein the pair of protection transistors includes a first transistor and a second transistor, the first transistor being coupled between the rectified voltage node and the first connection node of the protection circuit, and the second transistor being coupled between the first connection node of the protection circuit and ground; and The first transistor in the pair of protection transistors is turned on when the first transistor in the first transistor pair of the bridge rectifier is turned on, and turned off when the first transistor in the first transistor pair is turned off; and the second transistor in the pair of protection transistors is turned on when the third transistor in the first transistor pair of the bridge rectifier is turned on, and turned off when the third transistor in the first transistor pair is turned off.

15. The wireless power system according to claim 13, The bridge rectifier mentioned above includes: A first n-channel transistor is coupled between the rectified voltage node and the first input of the bridge rectifier; A second n-channel transistor is coupled between the rectified voltage node and the second input of the bridge rectifier; The third n-channel transistor is coupled between the first input of the bridge rectifier and ground; as well as The fourth n-channel transistor is coupled between the second input of the bridge rectifier and ground; The protection circuit includes: A p-channel transistor is coupled between the rectified voltage node and the first connection node of the protection circuit, wherein when the protection circuit is in the wireless power mode, the p-channel transistor of the protection circuit is configured to turn on when the first n-channel transistor of the bridge rectifier is turned on, and is configured to turn off when the first n-channel transistor of the bridge rectifier is turned off. as well as An n-channel transistor is coupled between the first connection node of the protection circuit and ground, wherein when the protection circuit is in the wireless power mode, the n-channel transistor of the protection circuit is configured to turn on when the third n-channel transistor of the bridge rectifier is turned on, and is configured to turn off when the third n-channel transistor of the bridge rectifier is turned off, and wherein the n-channel transistor of the protection circuit is configured to turn off when the protection circuit is in the Q factor measurement mode.

16. The wireless power system of claim 15, wherein the first n-channel transistor has a gate, the gate of the first n-channel transistor being coupled to receive a first gate voltage; and wherein the protection circuit further comprises an additional n-channel transistor, a third resistor, and a Zener diode, the additional n-channel transistor having a source, a drain, and a gate, the source of the additional n-channel transistor being coupled to ground, the drain of the additional n-channel transistor being coupled to a second connection node via a fourth resistor, the gate of the additional n-channel transistor being coupled to receive a gate voltage, the gate voltage being the result of performing a logical AND operation between the first gate voltage and a transmission gate enable signal; the third resistor being coupled between the rectified voltage node and the second connection node; the Zener diode having a cathode and an anode, the cathode being coupled to the rectified voltage node, the anode being coupled to the second connection node; wherein the second connection node is coupled to the gate of the p-channel transistor of the protection circuit.

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