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EP-4560527-B1 - RADIO FREQUENCY VOLTAGE LIMITER FOR AN RFID TRANSPONDER

EP4560527B1EP 4560527 B1EP4560527 B1EP 4560527B1EP-4560527-B1

Inventors

  • De La Cruz Marin, Jorge Vicente
  • Zoescher, Lukas
  • MALINOWSKI, Slawomir Rafal

Dates

Publication Date
20260513
Application Date
20241112

Claims (15)

  1. A radio frequency, RF, voltage limiter (20, 30, 40, 50) for a radio frequency identification, RFID, transponder, the RF voltage limiter (20, 30, 40, 50) comprising: an envelope detector (21, 31, 41, 42) having an input coupled to an antenna, the envelope detector (21, 31, 41, 42) configured to track an envelope of a signal received at the antenna, the envelope detector (21, 31, 41, 42) having an output for providing an envelope signal; the radio frequency voltage limiter being characterized in that it further comprises: a peak detector (22, 32, 42, 52) having an input coupled to the output of the envelope detector (21, 31, 41, 42), wherein the peak detector (22, 32, 42, 52) comprises a current mirror for detecting a voltage level of the envelope signal, said current mirror having an input coupled to the output of the envelope detector (21, 31, 41, 42), and an output configured to provide a control signal that has a rising edge that rises with a rising edge of the envelope signal, and the control signal having a falling edge that follows more slowly than a falling edge of the envelope signal; and a shunt circuit (23, 33, 43, 53) coupled to provide an impedance to the antenna in response to the control signal, wherein the impedance decreases with an increasing voltage magnitude of the control signal.
  2. The RF voltage limiter (20, 30, 40, 50) of claim 1, wherein the current mirror comprises: a first transistor having a first current electrode and a control electrode both coupled to receive a reference current, and a second current electrode coupled to the output of the envelope detector (21, 31, 41, 42); a second transistor having a first current electrode, a control electrode coupled to the control electrode of the first transistor, and a second current electrode coupled to provide the control signal to the shunt circuit (23, 33, 43, 53), and wherein the peak detector (22, 32, 42, 52) further comprises a first current source coupled between the first current electrode of the first transistor and a power supply voltage terminal, the first current source for providing the reference current.
  3. The RF voltage limiter (20, 30, 40, 50) of claim 2, further comprising a capacitor coupled between the second current electrode of the second transistor and ground.
  4. The RF voltage limiter (20, 30, 40, 50) of claim 3, further comprising: a second current source having a first terminal coupled to the second current electrode of the second transistor, and a second terminal coupled to a ground terminal; and a third current source having a first terminal coupled to the power supply voltage terminal, and a second terminal coupled to the first current electrode of the second transistor.
  5. The RF voltage limiter (20, 30, 40, 50) of any preceding claim, wherein the envelope detector (21, 31, 41, 42) comprises two cross-coupled charge pump stages.
  6. The RF voltage limiter (20, 30, 40, 50) of claim 5, wherein each of the cross-coupled charge pump stages comprises a pair of cross-coupled P-channel metal-oxide semiconductor transistors, PMOS, and a pair of cross-coupled N-channel metal-oxide semiconductor transistors, NMOS, both pairs capacitively coupled to a first antenna terminal and a second antenna terminal of the RFID transponder.
  7. The RF voltage limiter (20, 30, 40, 50) of any preceding claim, wherein the antenna comprises a first terminal and a second terminal, and the shunt circuit (23, 33, 43, 53) comprises first and second transistors coupled between the first and second antenna terminals, and wherein a control electrode of both the first and second transistors is coupled to receive the control signal.
  8. The RF voltage limiter (20, 30, 40, 50) of any preceding claim, further comprising a switch having a first terminal coupled to the output of the envelope detector (21, 31, 41, 42), and a second terminal coupled to the output of the peak detector (22, 32, 42, 52), the switch configured to selectively bypass the peak detector (22, 32, 42, 52) during a power-up of an integrated circuit of the RFID transponder.
  9. The RF voltage limiter (20, 30, 40, 50) of claim 8, wherein the switch is a transmission gate responsive to a power-on reset signal.
  10. A radio frequency identification, RFID, transponder comprising the RF voltage limiter (20, 30, 40, 50) of any preceding claim.
  11. A method for limiting a radio frequency, RF, voltage at an antenna of a radio frequency identification RFID transponder, the method comprising: tracking, by an envelope detector (21, 31, 41, 42), an envelope of an RF signal at the antenna to produce an envelope signal; detecting, by a peak detector (22, 32, 42, 52) comprising a current mirror, a voltage level of the envelope signal using the current mirror, and providing a control signal, using the current mirror, that has a rising edge that rises with a rising edge of the envelope signal, and the control signal having a falling edge that follows more slowly than a falling edge of the envelope signal; and providing, by a shunt circuit (23, 33, 43, 53), an impedance to the antenna in response to the control signal, wherein the impedance decreases with an increasing voltage magnitude of the control signal.
  12. The method of claim 11, wherein the current mirror comprises: a first transistor having a first current electrode and a control electrode coupled to receive a first reference current, and a second current electrode coupled to the output of the envelope detector (21, 31, 41, 42); and a second transistor having a first current electrode, a control electrode coupled to the control electrode of the first transistor, and a second current electrode coupled to provide the control signal to the shunt circuit (23, 33, 43, 53).
  13. The method of claim 12, wherein the falling edge of the control signal follows the falling edge of the envelope signal more slowing using: a first current source having a first terminal coupled to the second current electrode of the second transistor, and a second terminal coupled to a ground terminal; and a capacitor having a first terminal coupled to the second current electrode of the second transistor, and a second terminal coupled to the ground terminal.
  14. The method of any one of claims 11 to 13, wherein tracking the envelope further comprises using a charge pump to produce the envelope signal.
  15. The method of any one of claims 11 to 14, wherein the shunt circuit (23, 33, 43, 53) comprises first and second transistors coupled between first and second antenna terminals of the antenna, and wherein a control electrode of both the first and second transistors is coupled to receive the control signal.

Description

Background Field This disclosure relates generally to electronic circuits, and more particularly, to a radio frequency (RF) voltage limiter for radio frequency identification (RFID) transponders. Related Art Ultra-high frequency (UHF) RFID transponders, commonly referred to as RFID tags, are widely used to identify objects to which the tags are attached. The most common application examples of RFID tags are retail, supply chain management, shipping services, airline luggage tracking, laundry services, etc. An RFID tag typically includes an antenna and an integrated circuit (IC) (commonly referred to herein as a "chip"). An RFID transponder may communicate inductively with an RFID reader via an electrical, magnetic, or electromagnetic field generated by the RFID reader. In some circumstances, a UHF RFID transponder frontend implementation may experience an overvoltage caused by high levels of received antenna power when receiving an amplitude modulated reader signal. In complementary metal-oxide semiconductor (CMOS) technologies of advanced process nodes, the received high voltage at the transponder frontend may exceed the maximum voltage ratings of the IC, resulting in damage due to overvoltage stress. An RF voltage limiter may be used to avoid overvoltage conditions at the integrated RF frontend at high received antenna power levels. The RF limiter of an RFID tag chip may operate with a high peak detector discharge time to minimize distortions when receiving an amplitude-modulated signal from a reader. Implementing a high peak detector discharge time in the order of several hundred micro seconds (µs) by means of passive components can occupy a large chip area. CN 114 648 084 A describes an RFID tag that comprises: an antenna for receiving a high-frequency signal; a capacitor bank coupled with the antenna; a charge pump coupled with the antenna and configured to convert the high frequency signal into a direct current (DC) signal; an envelope detector to measure a peak voltage of the high frequency signal; and a detector to compare an output of the charge pump to an output of the envelope detector. The RFID tag also includes an impedance tuning circuit coupled with the charge pump and the envelope detector and configured to vary a capacitance of the capacitor bank based on an output of the detector and the envelope detector. US 2023/135571 A1 describes a voltage regulator that includes a shunt transistor and a feedback circuit. The shunt transistor has a first current electrode coupled to a first voltage source terminal, a second current electrode coupled to a second voltage source terminal, a control electrode coupled to receive a reference voltage, and a body electrode. The feedback circuit has an input terminal coupled to the body electrode of the shunt transistor, and an output terminal coupled to the control electrode of the shunt transistor. The voltage regulator is suitable for use in a passive RFID device to protect the device from overvoltage damage. Brief Description of the Drawings The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. FIG. 1 illustrates a block diagram of a differential ultra-high frequency (UHF) RFID frontend in accordance with an embodiment.FIG. 2 illustrates the RF voltage limiter of the UHF RFID frontend of FIG. 1 according to an embodiment.FIG. 3 illustrates the RF voltage limiter of the UHF RFID frontend of FIG. 1 according to another embodiment.FIG. 4 illustrates the RF voltage limiter of the UHF RFID frontend of FIG. 1 according to another embodiment.FIG. 5 illustrates the RF voltage limiter of the UHF RFID frontend of FIG. 1 according to another embodiment.FIG. 6 illustrates various signal waveforms of the RF voltage limiter of FIG. 5.FIG. 7A illustrates RF voltage amplitude versus received antenna power for the RF voltage limiter of FIG. 5.FIG. 7B illustrates modulation depth versus received antenna power for the RF voltage limiter of FIG. 5.FIG. 8 illustrates radio frequency identification (RFID) tag according to an embodiment. Detailed Description Generally, there is provided, a RF voltage limiter for a UHF RFID transponder that includes an envelope detector, a peak detector, and a shunt circuit. The envelope detector provides an envelope signal that tracks a voltage envelope of a signal received at an antenna. The peak detector stage includes a current mirror acting as a rectifying buffer, and a current sink and a small filter capacitor to provide a control signal in response to the envelope signal to control the shunt circuit. The shunt circuit provides an impedance to control the maximum voltage at the antenna in response to the control signal. Use of the RF voltage limiter in a UHF RFID tag provides an area-efficient implementation of a peak detector with