# US 10,770,891 B2 · Protection of an NFC router against overvoltage > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,770,891 B2 - Document ID: US10770891B2 - Status: Granted - Kind: B2 - Application number: 15/842,621 - Filed: 2017-12-14 - Published: 2018-09-13 - Granted: 2020-09-08 - Earliest claimed: 2017-03-10 - Assignees: STMicroelectronics (Rousset) SAS - Applicants: STMicroelectronics (Rousset) SAS - Inventors: Alexandre Tramoni - Web page: https://patentgrep.com/patent/US10770891B2 ## CPC - H02H 9/04: responsive to excess voltage (lightning arrestors H01C7/12, H01C8/04, H01G9/18, H01T) - G06K 7/10009: {sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves} - G06K 7/10148: {the step consisting of dynamically tuning the resonant circuit of the interrogation device that is emitting the interrogation signal, e.g. for impedance matching inside of the interrogation device (for tuning related to loop aerials in general H01Q7/00)} - G06K 19/0715: {the arrangement including means to regulate power transfer to the integrated circuit} - H02H 9/041: {using a short-circuiting device} - H02J 50/10: using inductive coupling - H04B 5/24: Inductive coupling - H04B 5/26: using coils - H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H) - G06K: GRAPHICAL DATA READING (image or video recognition or understanding G06V); PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS - H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY - H04B: TRANSMISSION ## Abstract The invention relates to a device for protecting a near field communication router against possible over-voltages picked up by an antenna. The device includes two voltage-limiter elements between terminals of the antenna and a ground. A circuit detects the presence of an electromagnetic field in the vicinity of an operating frequency of the router, and controls the limiter elements, the limiter elements being active by default. ## Claims ### Claim 1 A device comprising: a first antenna terminal; a second antenna terminal; a ground terminal; a near field communication circuit coupled to the first and second antenna terminals, the near field communication circuit configured to operate at an operating frequency; a first voltage-limiter coupled between the first antenna terminal and the ground terminal; a second voltage-limiter coupled between the second antenna terminal and the ground terminal; and a controller configured to detect, at the first and second antenna terminals, an electromagnetic field having a frequency that corresponds to the operating frequency, and to control the first and second voltage-limiters based upon the detected electromagnetic field, wherein the first and second voltage-limiters are active by default and wherein the controller is configured to deactivate the first and second voltage-limiters after detecting that the frequency corresponds to the operating frequency of the near field communication circuit. ### Claim 2 (depends on 1) The device of claim 1, wherein the first and second voltage-limiters each comprise one or more voltage-limiter components in series with a switch having a control input coupled to an output of the controller. ### Claim 3 (depends on 2) The device of claim 2, wherein the one or more voltage-limiter components comprise diodes. ### Claim 4 (depends on 1) The device of claim 1, wherein the controller comprises: a first circuit for field detection and clock extraction; and a comparator having a first input coupled to the first and a second input coupled to a reference clock generator, the reference clock generator configured to generate a reference frequency corresponding to the operating frequency of the near field communication circuit. ### Claim 5 (depends on 4) The device of claim 4, wherein the comparator is coupled to control the first and second voltage-limiters. ### Claim 6 (depends on 1) The device of claim 1, wherein the controller is powered by a battery. ### Claim 7 (depends on 1) The device of claim 1, wherein the operating frequency of the near field communication circuit is about 13.56 MHz. ### Claim 8 (depends on 1) The device of claim 1, further comprising an antenna coupled to the first and second antenna terminals. ### Claim 9 A device comprising: a first antenna terminal; a second antenna terminal; a ground terminal; a near field communication circuit coupled to the first and second antenna terminals; a first voltage-limiter coupled between the first antenna terminal and the ground terminal; a second voltage-limiter coupled between the second antenna terminal and the ground terminal; a field detector coupled to the first and second antenna terminals; a reference clock generator; and a comparator with a first input coupled to an output of the field detector, a second input coupled to an output of the reference clock generator, and an output coupled to a control input of the first voltage-limiter and to a control input of the second voltage-limiter. ### Claim 10 (depends on 9) The device of claim 9, wherein the first and second voltage-limiters each comprise a voltage-limiter component in series with a switch having a control input coupled to the output of the comparator. ### Claim 11 (depends on 10) The device of claim 10, wherein the first and second voltage-limiters each comprise a plurality of voltage-limiter components in series with the switch. ### Claim 12 (depends on 9) The device of claim 9, wherein the first voltage-limiter comprises a first plurality of diodes coupled in series with a first switch that has a control input coupled to the output of the comparator; and wherein the second voltage-limiter comprises a second plurality of diodes coupled in series with a second switch that has a control input coupled to the output of the comparator. ### Claim 13 (depends on 9) The device of claim 9, further comprising an antenna coupled to the first and second antenna terminals. ### Claim 14 (depends on 13) The device of claim 13, further comprising: a battery coupled to the comparator; a second antenna; and a charger coupled between the second antenna and the battery. ### Claim 15 A near field communication device comprising: an antenna; a near field communication circuit coupled to the antenna, the near field communication circuit configured to operate at a first frequency; a first switch coupled between a first terminal of the antenna and a ground terminal, a second switch coupled between a second terminal of the antenna and the ground terminal; and a controller configured to extract a clock signal from a signal received at the antenna, to compare the extracted clock signal with a reference clock signal to produce a comparison result, and to control the first and second switches based on the comparison result. ### Claim 16 (depends on 15) The near field communication device of claim 15, wherein the first switch comprises a first transistor and the second switch comprises a second transistor. ### Claim 17 (depends on 15) The near field communication device of claim 15, further comprising: a second antenna; a rechargeable battery; and a charger circuit coupled between the rechargeable battery and the second antenna. ### Claim 18 (depends on 15) The near field communication device of claim 15, wherein the controller is configured to turn off the first and second switches when a frequency of the extracted clock signal is equal to a frequency of the reference clock and turn on the first and second switches when the frequency of the extracted clock is not equal to the frequency of the reference clock signal. ### Claim 19 (depends on 15) The near field communication device of claim 15, further comprising: a first diode having an anode coupled to a first terminal of the antenna and a cathode coupled to the first switch; and a second diode having an anode coupled to a second terminal of the antenna and a cathode coupled to the second switch. ### Claim 20 (depends on 15) The near field communication device of claim 15, further comprising a battery coupled to the near field communication circuit. ### Claim 21 A method of overvoltage protection for a contactless communication device, the method comprising: using a voltage limiter to limit a voltage across terminals of an antenna coupled to the contactless communication device; detecting an electromagnetic field having a first frequency, the electromagnetic field being detected at the terminals of the antenna; after detecting the electromagnetic field having the first frequency, turning off the voltage limiter; and while the voltage limiter is off, receiving a signal having the first frequency at the contactless communication device. ### Claim 22 (depends on 21) The method of claim 21, wherein detecting the electromagnetic field having the first frequency comprises: extracting a clock signal from the antenna; and comparing the extracted clock signal with a reference clock signal. ### Claim 23 (depends on 22) The method of claim 22, wherein limiting the voltage across the terminals of the antenna comprises turning on a first switch coupled between a first terminal of the antenna and a ground terminal and turning on a second switch coupled between a second terminal of the antenna and the ground terminal. ### Claim 24 (depends on 23) The method of claim 23, wherein turning off the limiting of the voltage across the terminals of the antenna comprises turning off the first switch and turning off the second switch. ### Claim 25 (depends on 21) The method of claim 21, wherein the first frequency is about 13.56 MHz.