IC card regulator

Abstract

This disclosure relates to IC card regulators. According to one embodiment, a linear voltage regulator includes: a first transistor coupled between a first input terminal and an output terminal, the first input terminal being adapted to receive a first voltage and the output terminal being adapted to provide a regulated voltage; a second transistor coupled between a second input terminal and an output terminal, the second input terminal being adapted to receive a second voltage; and an amplifier amplifying the difference between a third voltage proportional to the voltage at the output terminal and a reference voltage, the output of the amplifier being selectively coupled to control terminals of the first transistor and the second transistor, the amplifier being powered by a fourth voltage corresponding to the highest of the first voltage and the second voltage.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to European Patent Application No. 22158957, filed on 25 February 2022, which is incorporated herein by reference. Technical Field

[0003] This invention generally relates to electronic circuits, and more specifically to integrated circuit cards. Background Technology

[0004] Integrated circuit cards, also known as smart cards or IC cards, are widely known. IC cards operate more and more frequently in both contact and contactless modes. Recent developments in IC cards aim to equip them with peripheral systems such as fingerprint sensors, dynamically readable verification codes, and displays. Summary of the Invention

[0005] One embodiment provides a linear voltage regulator comprising: a first transistor between a first input terminal adapted to receive a first voltage and an output terminal adapted to provide an regulated voltage; a second transistor between a second input terminal adapted to receive a second voltage and an output terminal; an amplifier that amplifies the difference between a third voltage proportional to the voltage at the output terminal and a reference voltage, the output of the amplifier being selectively coupled to corresponding control terminals of the first and second transistors, the amplifier being powered by a fourth voltage corresponding to the highest voltage between the first and second voltages.

[0006] According to one embodiment, the amplifier output is coupled to the control terminal of a first transistor via a first switch and to the control terminal of a second transistor via a second switch, the first and second switches being controlled by first and second control signals, respectively.

[0007] According to an embodiment, the control terminal of each of the first and second transistors is pulled up to a fourth voltage.

[0008] According to an embodiment, the third and fourth switches respectively couple the control terminals of the first and second transistors to a fourth voltage, and the third and fourth switches are controlled by the corresponding inverse phases of the first and second control signals.

[0009] According to an embodiment, a voltage divider with regulated voltage provides a third voltage.

[0010] According to one embodiment, the regulator further includes two inputs having respectively coupled (preferably connected) to the first and second input terminals and an output providing a fourth voltage.

[0011] According to an embodiment, the circuit includes a comparator of a first voltage and a second voltage, which controls a switch that selectively couples a first input terminal and a second input terminal to a switch that provides an output of a fourth voltage.

[0012] According to an embodiment, the second voltage is a voltage extracted from an electromagnetic field.

[0013] One embodiment provides an integrated circuit card that includes a regulator.

[0014] According to one embodiment, the card includes: an external contact adapted to receive a first voltage; an antenna adapted to capture an electromagnetic field; and a rectifier adapted to provide a second voltage from the electromagnetic field.

[0015] According to one embodiment, the card also includes a first integrated circuit and an electronic system external to the integrated circuit, the voltage of which is regulated to power the external system. Attached Figure Description

[0016] The foregoing features and advantages, as well as other features and advantages, will be set forth in the following detailed description of embodiments by way of illustration rather than limitation, with reference to the accompanying drawings, in which:

[0017] Figure 1 An embodiment of an integrated circuit card is illustrated schematically;

[0018] Figure 2 An embodiment of the power architecture of a dual-interface integrated circuit card is illustrated schematically and in part.

[0019] Figure 3 An embodiment of a voltage regulator for an integrated circuit card is illustrated schematically and in part.

[0020] Figure 4 Schematic detail shown Figure 3 Embodiments of the regulator; and

[0021] Figure 5 The illustration details Figure 4 An embodiment of a voltage regulator block. Detailed Implementation

[0022] In the various figures, the same features are indicated by the same reference numerals. In particular, common structural and / or functional features in the various embodiments may have the same reference numerals and may have the same structure, dimensions, and material properties.

[0023] For clarity, only the operations and elements used to understand the embodiments described herein have been detailed and described. In particular, the operation of integrated circuit cards or smart cards is not described in detail, and the voltage regulator of this disclosure conforms to the general operation of such cards.

[0024] Unless otherwise stated, when referring to two elements connected together, it means that there is no direct connection between them except for the conductor, and when referring to two elements connected together, it means that the two elements can be connected or they can be coupled through one or more other elements.

[0025] In the following disclosure, unless otherwise stated, when referring to absolute position qualifiers, such as the terms “front,” “back,” “top,” “bottom,” “left,” “right,” etc., or when referring to relative position qualifiers, such as the terms “up,” “down,” “higher,” “lower,” etc., or when referring to orientation qualifiers, such as “horizontal,” “vertical,” etc., the orientation shown in the figure is used.

[0026] Unless otherwise stated, the expressions “about,” “approximately,” “basically,” and “in the order of” indicate within 10%, preferably within 5%.

[0027] Some embodiments of the present invention focus on improving integrated circuit cards. In particular, some embodiments address improvements in the power supply of peripheral devices included in the IC card.

[0028] Figure 1 An embodiment of an integrated circuit card is schematically illustrated. As shown, an integrated circuit card 1, IC card, or smart card using the disclosed embodiment includes: a plastic (or other non-conductive material) card 10; at least one integrated circuit chip 11 (IC chip) embedded in the card 10; a physical conductive contact 13 accessible from one surface of the card 10 and coupled, preferably connected to, the IC chip 11; an antenna 15 (indicated by a dotted line) embedded in the card 10 and coupled, preferably connected to, the IC chip 11 for wireless operation; and an electronic system or circuit 17 (EXT SYS) embedded in the card 10 but outside the chip 11, and coupled to, preferably connected to, the chip 11 via a conductor 19 embedded in the card 10.

[0029] IC chip 11 includes electronic circuitry suitable for the application of card 1. For example, chip 11 includes a microcontroller suitable for operating and controlling other components of card 1 according to the application.

[0030] like Figure 1 As shown, Card 1 is typically designated as a dual-interface smart card. The card has two interfaces: a contact interface for communication with a contact reader and a contactless interface for communication with a wireless reader (NFC, etc.). Depending on whether Card 1 is inserted into a contact reader or is within range of a contactless reader, its electronic circuitry is powered either via the contact interface or via the wireless interface (via the field generated by the contactless reader).

[0031] To enable the operation of card 1 to be compatible with both contact and non-contact power supplies, chip 11 typically includes a voltage regulator capable of supplying power voltage to the remainder of chip 11.

[0032] The increased functionality of IC cards and the growing number of embedded electronic components, such as external (relative to chip 11) systems or circuitry 17, increase the power required for card operation. Both contact and contactless readers are capable of providing this increased power. However, the size of the voltage regulator integrated into the card becomes increasingly important.

[0033] Additionally, dedicated regulators are provided for these external or peripheral circuits 17 because the voltage levels they request may differ from the voltage levels of the main circuit (microcontroller) of chip 11.

[0034] One example of an application is a bank card with a fingerprint sensor. Another example is a bank card with a display showing a changing card verification value (CVV). Yet another example is a card (not necessarily a bank card) with sensors such as fingerprint sensors, temperature sensors, and image sensors. Another example is a card with a display such as a counter value display or an image display. In this application, external circuitry 17 includes sensors such as fingerprint sensors, temperature sensors, CVV displays, counter value displays, and image displays.

[0035] The value of the power supply voltage used by the external embedded system or circuit 17 depends on the application. However, it is desirable to provide a single integrated circuit 11 capable of supplying appropriate voltages to a variety of external circuits 17 in order to increase the market production value of the main integrated circuit 11, which can be used in different applications depending on the nature of the card's external circuits 17.

[0036] Figure 2 An embodiment of the power architecture of a dual-interface integrated circuit card is schematically and partially illustrated. As shown, the dual-interface circuit card 1 includes a voltage regulator 2 (REG) for regulating the voltage VCC provided by a contact reader (not shown) or the voltage VCC_CL extracted from a field generated by a non-contact reader (not shown).

[0037] When card 1 is inserted into the contact reader, DC voltage VCC appears at contact 13 of the card. Figure 1 The two input terminals of the regulator circuit 2 are coupled between the two contacts 21 and 22.

[0038] When card 1 is within range of the contactless reader that generates the electromagnetic field, the oscillation circuit of card 1, including antenna 15 and parallel capacitor 16 (integrated or not integrated in circuit 11), extracts a signal from the field generated by the reader. Terminals 23 and 24 of the oscillation circuit are coupled to, and preferably connected to, rectifier 25, which extracts a DC voltage VCC_CL from the signal present at terminals 23 and 24 of the oscillation circuit. The two inputs of regulator circuit 2 are coupled to, and preferably connected to, the rectified outputs 26 and 27 of rectifier 25. In practice, these outputs are also connected via capacitor Cin.

[0039] When operating in contact mode, the integrated circuit 11 communicates with the contact reader using the other terminals 13 of the card 1.

[0040] When operating in contactless mode, integrated circuit 11 communicates with the contactless reader via antenna 15. For this purpose, the communication circuit (not shown) of circuit 11 is coupled to terminals 23 and 24 of the oscillation circuit.

[0041] Since this disclosure relates to the power supply of the peripheral device 17 of card 1, and more specifically to the regulation of the voltage provided in contact mode or contactless mode, the functional operation of the card in contact mode or contactless mode will not be described in further detail.

[0042] The output 28 of regulator circuit 2 provides a regulated voltage VCC_OUT to the external system 17 of card 1. Optionally, the regulated voltage VCC_OUT is positive relative to ground 29 and is provided by terminal 22 in contact mode or by terminal 27 in non-contact mode. The value of the regulated voltage VCC_OUT depends on the value of the reference voltage VREF provided to regulator 2 by another element (e.g., bandwidth) of integrated circuit 11 (not shown). The value of the regulated voltage VCC_OUT depends on the application and, more specifically, on the type of external circuit 17. As a particular example, the value of the output regulated voltage VCC_OUT can be in the range of 1.4 volts to 2.5 volts, and more than 10 different values ​​can be used within this range depending on the application.

[0043] Figure 3 An embodiment of a voltage regulator for an integrated circuit card is schematically and partially illustrated. As shown, regulator 2 is a linear regulator or a low-dropout (LDO) regulator. The power transistor of regulator 2 couples the corresponding input terminal of the voltage to be regulated to the output terminal that provides the regulated voltage.

[0044] The regulator 2 includes: an output stage 4 comprising two transistors 41 and 45, each transistor having a conductive terminal coupled and selectively connected to a terminal 21 for an applied voltage VCC and a terminal 26 for an applied voltage VCC_CL, respectively, and another conductive terminal coupled and preferably connected to a common output terminal 28 providing an regulated voltage VCC_OUT; and an input stage 3 (input stage) receiving a reference voltage VREF, an regulated output voltage VCC_OUT, and providing analog control signals to the control terminals of transistors 41 or 45 according to the operating mode (contact / non-contact) selected by the digital control signals EN_CL and EN_CNT provided by the microcontroller 12 of circuit 11.

[0045] exist Figure 3 In an exemplary embodiment, transistors 41 and 45 are MOS transistors (preferably PMOS transistors). The respective sources 42 and 46 of transistors 41 and 45 are coupled to, and preferably connected to, terminals 21 and 26. The respective drains 43 and 47 of transistors 41 and 45 are coupled to, and preferably connected to, output terminal 28. The respective gates 44 and 48 of transistors 41 and 45 are coupled to, and preferably connected to, the input stage 3 of the regulator 2. According to the disclosed embodiment, the power transistors 41 and 45 of the regulator 2 share a common input stage 3.

[0046] Figure 4 The illustration details Figure 3 An embodiment of regulator 2. The input stage 3 of regulator 2 includes an error amplifier 31 or gain stage, which amplifies the difference between a feedback voltage VFB, proportional to the regulated output voltage VCC_OUT, and a reference voltage VREF. Amplifier 31 provides an analog signal at output 312 as a function of this difference between voltage VCC_OUT and VREF to control the gate 44 or 48 of transistor 41 or 45. The reference voltage VREF provided by circuit 11 is applied to input 314 of amplifier 31. The feedback voltage VFB, proportional to the value of output voltage VCC_OUT, is provided by feedback voltage divider 33, which receives output voltage VCC_OUT and provides voltage VFB to input 316 of amplifier 31. Figure 4 In the example, voltage divider 33 consists of two resistors R1 and R2 connected in series between output terminal 28 and ground 29, and the midpoint of the series connection forms the output of voltage divider 33 that provides feedback voltage VFB.

[0047] According to one embodiment, the value of the reference voltage VREF is fixed and does not depend on the voltage requested by the external system. Resistors R1 and R2 are then, for example, adjustable resistors, which are finely adjusted according to the application (depending on the value of the power supply voltage of external circuit 17) to select the value of the output voltage VCC_OUT. According to another example, the voltage divider consists of a network of controllable resistors, controlled by microcontroller 12 ( Figure 3 It is configured based on the desired power supply voltage of the external circuit 17.

[0048] According to another embodiment, the value of the reference voltage VREF is provided by the microcontroller 12 of the integrated circuit 11 according to the specific characteristics of the circuit. Resistors R1 and R2 can then have fixed values.

[0049] like Figure 4 As shown, regulator 2 consists of only one feedback resistor chain, which is used for both operating modes.

[0050] To select which transistor 41 or 45 will be controlled by error amplifier 31, switches 51 and 52 are provided between the output 312 of amplifier 31 and the corresponding gates 44 and 48 of transistors 41 and 45. Switch 51 couples terminal 312 to gate 44 of transistor 41, while switch 52 couples terminal 312 to gate 48 of transistor 45. Switch 51 is controlled to be fully on or fully off by an enable signal EN_CL. Switch 52 is controlled to be fully on or fully off by an enable signal EN_CNT. The microcontroller 12 selects which switch 51 or 52 to be turned on based on the selected operating mode (contact or non-contact).

[0051] According to one embodiment, regulator 2, and more specifically, its input stage 3 includes circuit 6 (the larger of VCC and VCC_CL), which selects the maximum or highest voltage between voltages VCC and VCC_CL and provides this maximum voltage as an internal power supply VCC_LDO at output terminal 61 of circuit 6. Capacitor C6 couples terminal 61 to ground 29.

[0052] Error amplifier 31 is powered by voltage VCC_LDO. This ensures the correct bias of the bulk transistors in the gain stage. It also ensures the correct offset of the control signal provided at amplifier output 312.

[0053] Additionally, the bodies of PMOS transistors 41 and 45 are biased by voltage VCC_LDO. This prevents the parasitic diodes of transistors 41 or 45 from conducting, so that they do not operate if the output voltage VCC_OUT is higher than the source voltage of the transistor.

[0054] According to one embodiment, the gate of an inactive transistor 41 or 45 is pulled up to a maximum voltage VCC_LDO between VCC and VCC_CL. This ensures a zero or positive gate-source voltage (Vgs) for the corresponding transistor, i.e., the transistor is in the off state, and therefore the transistor will not leak regardless of the value of its source voltage.

[0055] according to Figure 4 In the illustrated embodiment, the respective gates of transistors 41 and 45 are coupled to the output terminal 61 of circuit 6 via switches 53 and 54, which are controlled by the inversion of signals EN_CNT and EN_CL, respectively. Signal EN_CNT is applied to the control terminal of switch 53 via inverter 55. Signal EN_CL is applied to the control terminal of switch 54 via inverter 56.

[0056] According to another embodiment, the respective gates of transistors 41 and 45 are coupled to terminal 61 via pull-up resistors.

[0057] Figure 5 The illustration details Figure 4 This is one embodiment of circuit 6 of voltage regulator 2. The inputs of comparator 62 are coupled, preferably connected, to terminals 21 and 26, which provide voltages VCC and VCC_CL, respectively. For example, the non-inverting (positive) input (+) of comparator 62 is coupled, preferably connected, to terminal 21, and the inverting (negative) input (-) of comparator 62 is coupled, preferably connected, to terminal 26. In this example, if the contact voltage VCC is higher than the non-contact voltage VCC_CL, the output of comparator 62 is high, and if the non-contact voltage VCC_CL is higher than the contact voltage VCC, the output of comparator 62 is low. Comparator 62 controls two switches 63 and 64, which couple terminals 21 and 26 to output terminal 61, which provides a selected voltage VCC_LDO, respectively. For example, the output of comparator 62 directly controls switch 63 and controls switch 64 via inverter 65.

[0058] The power supply voltage VCC_AUX for comparator 6 is provided by an auxiliary power supply based on the highest voltage between VCC and VCC_CL. For this purpose, terminals 21 and 26 are coupled to the positive power supply terminal of comparator 62 via diodes 66 and 67, respectively. The anodes of diodes 66 and 67 are coupled, preferably, to terminals 21 and 26, respectively. The cathodes of diodes 66 and 67 are coupled to ground via capacitor 68.

[0059] Using an internal voltage VCC_LDO corresponding to the highest voltage between VCC and VCC_CL is particularly useful in contactless system applications. In practice, the value of voltage VCC_CL is variable and can be higher or lower than voltage VCC depending on several factors, such as the distance from the reader, some disturbances in the field generated by the reader, etc. Furthermore, although voltage VCC is only present when the card is inserted into the contact reader, the electromagnetic field can exist anywhere and is generated by antenna 15 (…). Figure 1 )capture.

[0060] Switches 51, 52, 53, 54, 63, and 64, which function as on / off switches, can be made of MOS transistors. These transistors can be much smaller than transistors 41 and 45 because they carry significantly less power. This is especially true for switches 51, 52, 53, and 54. Switches 63 and 64 have slightly higher power than switches 51 to 54 because they should be able to power error amplifier 31. However, this still remains much lower than the power requirements of transistors 41 and 45.

[0061] The advantage of the disclosed embodiments is that, compared to conventional cards that use two different linear regulators, the area occupied by the power regulation system can be reduced.

[0062] Another advantage of the disclosed embodiments is that the shared input stage 3 of regulator 2 for both contact and contactless modes significantly reduces the test time required for the chip. This is especially true for cards that require different output voltage selection.

[0063] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these embodiments can be combined, and other variations will readily conceive of them. In particular, the voltage regulators proposed in this disclosure have been described in detail with reference to examples applied to integrated circuit cards, but are more generally applicable to any wired and wireless devices exhibiting similar problems.

[0064] Finally, based on the functional description provided above, actual implementation of the embodiments and variations described herein is within the capabilities of those skilled in the art. In particular, adapting switches and transistors to the voltage applied to their connection terminals and the current flowing through them, based on the application, is the capability of those skilled in the art.

Claims

1. A linear voltage regulator, comprising: A first transistor is coupled between a first input terminal and an output terminal, the first input terminal being adapted to receive a first voltage, and the output terminal being adapted to provide a regulated voltage; A second transistor is coupled between a second input terminal and the output terminal, the second input terminal being adapted to receive a second voltage; as well as An amplifier amplifies the difference between a third voltage proportional to the regulated voltage at the output terminal and a reference voltage. The output of the amplifier is selectively coupled to the control terminals of the first transistor and the second transistor. The amplifier is powered by a fourth voltage corresponding to the highest of the first voltage and the second voltage. A circuit, the circuit including a comparator configured to compare a first voltage with a second voltage, and the comparator configured to control selective coupling of the first input terminal and the second input terminal to a switch configured to provide the fourth voltage; A first diode is coupled between the first input terminal and the power supply terminal of the comparator; A second diode is coupled between the second input terminal and the power supply terminal of the comparator; as well as A capacitor is coupled between the power supply terminal and the power supply node of the comparator.

2. The regulator according to claim 1, wherein The output of the amplifier is coupled to the control terminal of the first transistor via a first switch, and to the control terminal of the second transistor via a second switch; The first switch is controlled by a first control signal; as well as The second switch is controlled by a second control signal.

3. The regulator of claim 2, wherein the control terminal of the first transistor and the control terminal of the second transistor are configured to be pulled up to the fourth voltage.

4. The regulator according to claim 3, further comprising: A third switch is configured to couple the control terminal of the first transistor to the fourth voltage, wherein the third switch is configured to be controlled by the inverse of the first control signal; as well as A fourth switch is configured to couple the control terminal of the second transistor to the fourth voltage, wherein the fourth switch is configured to be controlled by the inverse of the second control signal.

5. The regulator of claim 1, wherein the voltage divider of the regulated voltage provides the third voltage.

6. The regulator of claim 1, wherein the circuit has inputs coupled to the first input terminal and the second input terminal respectively, and an output configured to provide the fourth voltage.

7. The regulator of claim 1, wherein the second voltage is extracted from an electromagnetic field.

8. An integrated circuit card, comprising the regulator according to claim 1.

9. The integrated circuit card according to claim 8, further comprising: An external contact is coupled to the first input terminal and is adapted to receive the first voltage; Antennas, suitable for capturing electromagnetic fields; as well as A rectifier adapted to provide the second voltage from the electromagnetic field.

10. The integrated circuit card of claim 8, further comprising a first integrated circuit, wherein the regulator is configured to provide the regulated voltage to an electronic system located outside the first integrated circuit.

11. An integrated circuit card system, comprising: Voltage regulator, including: The amplifier has a first input coupled to a reference voltage node and a second input coupled to the output node of the voltage regulator. A first transistor has a first conductive terminal coupled to the output node of the voltage regulator, a second conductive terminal coupled to a first power supply terminal configured to receive a first supply voltage provided by a contact reader, and a control terminal selectively coupled between the output node of the amplifier and a first voltage node configured to provide a disable voltage; and The second transistor has a first conductive terminal coupled to the output node of the voltage regulator, a second conductive terminal coupled to a second power supply terminal configured to receive a second power supply voltage provided by the electromagnetic field of the contactless card reader, and a control terminal selectively coupled between the output node of the amplifier and the first voltage node, the first voltage node being configured to provide a disable voltage. The power selection circuit is configured as follows: When the voltage of the first power supply terminal is higher than the voltage of the second power supply terminal, the first power supply terminal is coupled to the power input of the amplifier via the output node of the power selection circuit; and when the voltage of the second power supply terminal is higher than the voltage of the first power supply terminal, the second power supply terminal is coupled to the power input of the amplifier via the output node of the power selection circuit, wherein the power selection circuit includes: a comparator having an input coupled to the first power supply terminal and an input coupled to the second power supply terminal; a first diode coupled between the first power supply terminal and the power supply terminal of the comparator; a second diode coupled between the second power supply terminal and the power supply terminal of the comparator; and a capacitor coupled between the power supply terminal of the comparator and the power node.

12. The system of claim 11, wherein the power selection circuit further comprises: A first switch is coupled between the first power supply terminal and the output node of the power selection circuit, and the first switch has a control terminal coupled to the output of the comparator. as well as A second switch is coupled between the second power supply terminal and the output node of the power selection circuit. The second switch has a control terminal coupled to the output of the comparator, wherein the switching state of the first switch is opposite to the switching state of the second switch.

13. The system of claim 11, further comprising a switching circuit, the switching circuit comprising: A first switch is coupled between the output node of the power selection circuit and the control terminal of the first transistor; The second switch is coupled between the output node of the power selection circuit and the control terminal of the second transistor; A third switch is coupled between the output node of the amplifier and the control terminal of the first transistor; as well as A fourth switch is coupled between the output node of the amplifier and the control terminal of the first transistor.

14. The system of claim 11, wherein the output node of the voltage regulator is coupled to the second input of the amplifier via a resistive voltage divider.

15. The system of claim 11, further comprising: antenna; as well as A rectifier is coupled to the antenna and the second power supply terminal.

16. The system of claim 15, wherein the antenna includes an LC slot circuit and the rectifier includes a diode.

17. A method of operating an integrated circuit card, the integrated circuit card including a voltage regulator having an amplifier, a first transistor coupled between a first power supply terminal and an output of the voltage regulator, and a second transistor coupled between a second power supply terminal and the output of the voltage regulator, the method comprising: Determining whether the voltage at the first power terminal is greater than the voltage at the second power terminal, the determination includes using a selection circuit, the selection circuit comprising: A comparator is configured to compare the voltage of the first power supply terminal with the voltage of the second power supply terminal, and the comparator is configured to control selective coupling of the first power supply terminal and the second power supply terminal to a switch configured to provide the output with a fourth voltage corresponding to the highest voltage of the voltage of the first power supply terminal and the voltage of the second power supply terminal. A first diode is coupled between the first power supply terminal and the power supply terminal of the comparator; A second diode is coupled between the second power supply terminal and the power supply terminal of the comparator; and A capacitor is coupled between the power supply terminal and the power supply node of the comparator. When the voltage at the first power supply terminal is greater than the voltage at the second power supply terminal, the first power supply terminal is coupled to the power supply node of the amplifier and the control node of the first transistor, and the second transistor is disabled; and When the voltage of the first power supply terminal is not greater than the voltage of the second power supply terminal, the second power supply terminal is coupled to the power supply node of the amplifier and the control node of the second transistor, and the first transistor is disabled.

18. The method of claim 17, further comprising wirelessly receiving power from the antenna via the second power terminal.

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