HK1229032B - Dual frequency hf-uhf identification device - Google Patents

Description

Dual-frequency HF-UHF identification equipment

Technical Field

The present invention relates to dual-band HF-UHF identification devices, and more particularly to such devices comprising a power supply circuit arranged to extract power from at least one captured electromagnetic field. In a first embodiment, the identification device may be a passive device that extracts all required energy from the electromagnetic field provided by at least one external device (a reader/writer or any other RF communication device). In a second embodiment, the identification device may be battery-assisted, i.e., a portion of the energy required for at least part of the device's functionality is stored in the battery.

In particular, the device of the invention forms a contactless electronic token or a contactless smart card.

Background Art

Several dual-frequency RFID integrated circuits have been proposed. Especially for passive devices, a defined power source must be employed, and the corresponding integrated circuits must be designed accordingly. This power source typically includes at least one power generator. With two power generators, one for each voltage induced in the resonant circuit of the HF antenna coil and the other for the voltage induced in the UHF antenna, power management is typically provided, and the integrated circuit is designed for this purpose.

FIG1 shows a prior art dual-frequency HF-UHF identification device, which is a simplified design of the dual-frequency tag described in patent application US2005/0186904. The dual-frequency HF-UHF identification device 2 includes an HF component 4 and a UHF component 6. The HF component 4 is formed by an HF antenna coil 10, a resonant capacitor 8, an HF rectifier 12, and an analog HF front end 14 (AFE_HF). The UHF component 6 is formed by a UHF antenna 16, a UHF rectifier 18, and an analog UHF front end 20 (AFE_UHF). The device 2 also includes a logic unit 22 and a non-volatile memory 24 (NVM). The logic unit 22 is connected to the analog HF front end 14 or the analog UHF front end 20 via a multiplexer (not shown in FIG1 ) arranged in a first part of the logic unit. The HF rectifier is a diode rectifier that rectifies the induced voltage in the resonant circuit formed by the antenna coil 10 and the resonant capacitor 8. The HF rectifier selectively receives positive and negative induced voltages at its two inputs V1a and V1b. The HF rectifier generates a first supply voltage V _HF at its output. In a variant, such an HF rectifier can be associated with a voltage amplifier circuit for generating the first supply voltage. The UHF rectifier is formed by a charge pump connected to two lines of the UHF antenna 16. The UHF rectifier receives positive and negative induced voltages at its two inputs V2a and V2b and is configured to provide a second supply voltage V _UHF at its output.

Furthermore, the device 2 includes a combined power and mode management system formed by a mode detection unit 26 and a switch 30. The mode detection unit senses the induced voltage in the HF resonant circuit (e.g., voltage V1a) and delivers a mode signal DET, the value of which indicates whether the HF antenna coil detects the reception of an HF electromagnetic field within the resonant range of the HF resonant circuit (e.g., 13.56 MHz). The mode signal controls the control gate of the switch 30 via a first control line 31 and the logic unit 22 via a second control line 32. The switch is arranged between the UHF rectifier output and a power supply line 28 providing the supply voltage _Vsup to the electronic circuit. The operation of the power management is as follows:

a) When unit 26 detects at least one predetermined voltage in the HF components of the power generator (particularly an induced voltage in the HF resonant circuit or, alternatively, an induced voltage at the output of the HF rectifier), the output of unit 26 is set to a first logic value (e.g., "1"), and a mode signal DET indicates the presence of an incoming HF electromagnetic field. Switch 30 is configured such that when the mode signal is set to the first logic value, it is opened ("off" position), and the UHF power generator is therefore unavailable, regardless of whether voltage V _UHF is zero. The integrated circuit of device 2 is thus powered solely by the HF components, while the voltage detected by the mode detection unit is at least equal to the predetermined voltage. Furthermore, the logic unit receives the mode signal and activates the HF protocol and associated circuit components; in particular, the multiplexer is placed in a first state in which only the HF demodulated signal is transmitted to the logic unit (no UHF signal is transmitted).

b) When unit 26 does not detect at least one predetermined voltage in the HF components of the power generator, the output of unit 26 is set to a second logic value (e.g., "0"), and mode signal DET indicates the absence of an incoming electromagnetic field. Switch 30 is turned on and then closed, allowing the UHF components of the power generator to power the integrated circuit if an induced voltage is generated in the UHF components. Furthermore, the logic unit receives this mode signal and activates the UHF protocol and associated circuit components. In particular, the multiplexer is placed in a second state in which only the UHF demodulated signal is transmitted to the logic unit (no HF signal is transmitted).

Device 2 is therefore configured to preferentially access the HF field. In a manner similar to that described above, the opposite selection can be made by prioritizing the UHF field. However, to prioritize writing data to the NVM memory, as taught in the aforementioned US patent application, the alternative HF field is preferred. Notably, this document teaches that the voltage generated by the UHF component of the power generator is too low for erasing and programming EEPROM or FLASH memory. Therefore, even if a switch is placed between the HF rectifier output and the power supply terminal _Vsup of the storage capacitor, once a given induced voltage is detected in the HF resonant circuit, the HF mode is selected.

Device 2 has several drawbacks. First, the mode selection allows only HF or UHF communication, not both simultaneously. Furthermore, if a given activity level is detected in the HF range, UHF communication is disabled due to sensitivity reasons, typically a low level, and thus no communication can occur in the UHF range. If UHF communication is already operating, the detection of a given voltage in the HF component will halt such communication. Finally, the power management, conversely, does not allow the HF field provided to Device 2 to contribute to its power supply for UHF communication. This is a significant drawback of Device 2.

Patent application US 2009/0117872 describes a passive device with multiple energy harvesting and communication channels. This document describes a general embodiment in FIG1A , with a more detailed electronic design shown in FIG2A . The passive device includes two antennas, each coupled to two first-order half-wave diode rectifiers arranged in series. To provide DC power to the passive device, the output capacitors of the two rectifiers are connected in series, and a shared capacitor also stores energy from both rectifiers. This implementation is unique. First, it should be noted that the first antenna can supply energy to both output capacitors of the two rectifiers, while the second antenna can supply energy only to the second output capacitor. Furthermore, it is noteworthy that each antenna is coupled to the circuit via an input capacitor connected in series with the antenna. This type of electronic design for multiple energy harvesting presents several challenges. First, capacitor coupling is generally used for most HF frequencies above the typically selected 13.56 MHz, and particularly for the UHF frequency range. However, the type of rectifier taught in US 2009/0117872 is more suitable for LF or HF signals. In fact, it's unreasonable to use such a power generator with an HF signal received via a first antenna and a UHF signal received via a second antenna. The coupling capacitors would be very large and have significant leakage current due to their size. To achieve roughly the same impedance at the inputs of the two rectifiers, the input capacitors for the HF channel would have to be 200 times larger than those for the UHF channel. Consequently, the HF input capacitors would be difficult to integrate into an integrated circuit, requiring excessive space. Furthermore, when the frequencies of the two signals received via the two antennas differ, the described power generator could cause destructive interference, resulting in energy loss.

Other specific embodiments are described in Figures 1B through 11 of US 2009/0117872, but the teachings appear to indicate that these are specific examples with specialized functionality. For example, with reference to the embodiment of Figure 1G , it is stated that the output currents of the two rectifiers must be the same, and with reference to the embodiment of Figure 1H , each of the output voltages of the two RF rectifiers is approximately equal to the input voltage of the power conditioner, i.e., the output voltages of the two RF rectifiers are approximately equal. Most of the time, this situation will not occur for two different signals received via two antennas. Furthermore, one goal of multi-energy harvesting is to be able to harvest energy from one source, the other source, or both, having different generated voltages.

Summary of the Invention

The present invention aims to provide a dual-band HF-UHF RFID integrated circuit and a dual-band HF-UHF identification device comprising such an integrated circuit, which overcomes the drawbacks of the previously described prior art devices and aims to provide such an integrated circuit with a simple and efficient power supply arrangement.

To this end, the present invention relates to a dual-band HF-UHF RFID integrated circuit comprising a power supply having an HF component and a UHF component. The HF component is formed by an HF rectifier, which is intended to be connected to a resonant circuit formed by an HF antenna coil and a resonant capacitor. The UHF component comprises a UHF rectifier, which is formed by a charge pump and is intended to be connected to a UHF antenna. The RFID integrated circuit further comprises a common storage capacitor for both the HF and UHF components of the power supply. Both the HF rectifier output and the UHF rectifier output are continuously connected to the supply terminal of the common storage capacitor. The supply terminal of the common storage capacitor is connected to the output of the HF rectifier via a diode, which is arranged to block current from the supply terminal to the HF rectifier output.

By "continuously connected," it is meant that when both the HF and UHF rectifiers receive at least a useful induced voltage at their respective input terminals, there is no selector switch or other selection device that selects either the HF rectifier or the UHF rectifier as the power generator for the power supply of the device. In other words, there is no failure device that prioritizes one of the HF and UHF rectifiers and prevents the other from powering the electronic device.

A major advantage of the RFID integrated circuit of the present invention is that there is no need to choose between an HF power generator and a UHF power generator for powering the integrated circuit. This means that, regardless of the communication protocol used (HF or UHF), both the incoming HF and UHF fields captured by the HF resonant circuit and the UHF antenna can contribute to the power supply. Notably, the strength of the HF and UHF fields received by the respective antennas can vary as a function of time. The power supply of the present invention allows power to be provided primarily by the HF power generator during a first time interval, and primarily by the UHF power generator during a second time interval following the first time interval. In other scenarios, both the HF and UHF power generators provide sufficient voltage to charge the storage capacitor and power the integrated circuit. In particular, communication over the UHF channel can occur when the RFID integrated circuit is primarily powered by the incoming HF magnetic field captured by the identification device's HF resonant circuit. When communication occurs over the HF channel, the HF power generator typically provides more power than the UHF power generator. However, depending on the HF interrogator and its position relative to the identification device, there are situations in which the UHF power generator may supplement the power supply of the RFID integrated circuit during HF communication. In all cases, the power supply is highly efficient by using all captured electromagnetic fields. Since such a highly efficient power supply is achieved only by simple electronic circuits, it does not increase the cost of the power supply circuit or the power loss.

To block current from the power supply terminal to the HF rectifier output, a diode placed between the HF rectifier output and the power supply terminal of the shared storage capacitor prevents a portion of the power supply current, provided by the UHF power generator, from being dissipated in the HF components of the power supply. This protection is provided to minimize power losses when the RFID integrated circuit is primarily powered by the UHF power generator, particularly in the absence of an HF magnetic field. Because the power generated by the UHF components of the power supply is typically relatively low, this diode is particularly important when the UHF interrogator is located far from the RFID identification device.

According to a preferred variant, a resistor for limiting the current supplied by the HF rectifier is arranged between the output of the HF rectifier and the supply terminal of the common storage capacitor. Furthermore, the supply terminal of the storage capacitor can be further connected to a shunt voltage regulator to regulate the supply voltage _Vsup supplied on the power supply line of the power supply and also limit the voltage level at the output of the UHF power generator. The current-limiting resistor, together with the common storage capacitor, also forms an LF filter. This LF filter helps to further filter any power supply noise that may occur at the _VHF node at the output of the HF rectifier.

According to a particular variant, the supply terminal of the common storage capacitor is directly connected to the output of the UHF rectifier. This feature is also advantageous for the reasons given above. By directly connected, it is meant that there are no electronic components that consume significant power, preferably no electronic components other than the electrical path between the supply terminal of the storage capacitor and the output of the UHF rectifier.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will hereinafter be described in more detail, by way of example and not limitation, with reference to the accompanying drawings, in which:

- FIG1 has been described and schematically shows a dual-frequency identification device in the prior art; and

- Figure 2 shows the power supply of a passive dual-band HF-UHF identification device according to the invention.

DETAILED DESCRIPTION

A preferred embodiment of the present invention will be described with reference to FIG. 2 , which shows the power supply for a dual-band HF-UHF identification device 42, which includes an RFID integrated circuit connected to an HF antenna coil 10 and a UHF antenna 16. The RFID circuit's power supply comprises an HF component 44 and a UHF component 48. The HF component comprises an HF rectifier 12 connected to a resonant circuit formed by the HF antenna 10 and a resonant capacitor 8. This resonant circuit provides selectable positive and negative voltages to the HF rectifier's input terminals V1a and V1b. The HF rectifier's output is connected to the terminals of a smoothing capacitor 46, where it provides a first supply voltage V _HF . In a variant, the HF rectifier is associated with a voltage amplifier circuit to generate the first supply voltage. The UHF component 48 primarily comprises a UHF rectifier 18, formed as a charge pump, connected to two lines of the UHF antenna 16. This UHF rectifier receives positive and negative induced voltages at its two input terminals V2a and V2b and is arranged to provide a second supply voltage V _UHF at its output. According to the present invention, the RFID integrated circuit further comprises a common storage capacitor 50 for the HF part 44 and the UHF part 48 of the power supply of the identification device 42, the HF rectifier output and the UHF rectifier output both being connected serially to the power supply terminal of the common storage capacitor.

On the one hand, the supply terminal of the common storage capacitor 50 is connected to the output of the HF rectifier 12 via a diode 52, which is arranged to block the current from the supply terminal to the HF rectifier output, and on the other hand, the supply terminal of the common storage capacitor 50 is directly connected to the output of the UHF rectifier. Some advantages of this electronic design have been given in the summary of the invention.

According to a particular variant of the invention, the supply terminal of the storage capacitor 50 is further connected to a shunt voltage regulator 56 capable of sinking a shunt current I _Sh in order to regulate the supply voltage V _sup on the supply line 28. Furthermore, a resistor 54 for limiting the current from the HF rectifier is arranged between the output of the HF rectifier and the supply terminal.

The power supply circuit shown in FIG2 can be implemented in various RFID integrated circuits and can be associated with other specific circuits for controlling the power consumption of such circuits, particularly for minimizing their power consumption. In the case of a battery-assisted HF-UHF identification device, the RFID integrated circuit may include a wake-up circuit associated with a listening mode. In certain embodiments, the RFID integrated circuit includes an HF field detector and/or a UHF field detector configured to activate or control certain components of the RFID integrated circuit. Furthermore, means for regulating the supply voltage _Vsup and/or protecting certain components of the RFID integrated circuit, as well as specific voltage boosting means (particularly a voltage amplifier for further increasing the supply voltage), can be provided by those skilled in the art.

Claims (5)

1. A dual-frequency HF-UHF RFID integrated circuit, comprising a power supply having an HF component (44) and a UHF component (48), the HF component (44) being formed by an HF rectifier (12) intended to be connected to a resonant circuit formed by an HF antenna coil (10) and a resonant capacitor (8), the UHF component (48) comprising a UHF rectifier (18) formed by a charge pump and intended to be connected to a UHF antenna, characterized in that the RFID integrated circuit further comprises a storage capacitor (50) common to the HF component and the UHF component of the power supply; wherein the output of the HF rectifier and the output of the UHF rectifier are both continuously connected to the power supply terminal of the storage capacitor; and wherein the power supply terminal of the storage capacitor (50) is connected to the output of the HF rectifier via a diode (52), the diode (52) being arranged to block current from the power supply terminal to the output of the HF rectifier. 2. The RFID integrated circuit according to claim 1, wherein the power supply terminal of the storage capacitor (50) is directly connected to the output of the UHF rectifier (18). 3. The RFID integrated circuit according to claim 1, wherein a resistor (54) for limiting the current provided by the HF rectifier is arranged between the output of the HF rectifier and the power supply terminal. 4. The RFID integrated circuit according to claim 3, wherein the power supply terminal of the storage capacitor (50) is further connected to a parallel voltage regulator (56). 5. A dual-frequency HF-UHF identification device (42), comprising: - The dual-frequency HF-UHF RFID integrated circuit according to claim 1; - A resonant circuit, formed by an HF antenna coil (10) and a resonant capacitor (8), is connected to the HF rectifier (12); and -UHF antenna (16) is connected to the UHF rectifier (18).