Abstract: We describe an animal entry control system, for example for a cat flap, using RFID (radio frequency identification). The system comprises an RFID reader to register the presence and identification number of a transponder (15) injected under the skin of an animal; and a door (8) mounted on a hinge (10) and controlled by the RFID tag reader. The RFID reader comprises a resonant circuit including a tuning circuit to control the RFID reader such that a drive frequency of the RFID reader matches both a resonant frequency of the RFID reader and a resonant frequency of the transponder. Embodiments of the system are thus tolerant to a degree of detuning, for example from a metallic or magnetic material in the vicinity of the antenna.

Abstract: An RF tag for sending data to a tag reader is described. The tag comprises an antenna to couple to an RF field of the tag reader and first and second resonant circuits, the first comprising a non-linear, adaptive resonator configured to automatically self-tune to a frequency of the RF field, the second a linear resonator. The tag also has a local power store. The tag powers up using the non-linear, adaptive resonator, which can automatically self-tune without an external power supply, and this resonator is used to charge the local power store. Once operational the tag switches to using a linear resonator for communicating with the tag reader.

Abstract: An RFID reader for use in a pet door to control access for a pet bearing an RFID tag or implant. The RFID reader incorporates and is operable in two modes, a learn mode and a normal mode. In learn mode, the reader stores the ID code of an RFID transponder in the vicinity of the reader and also derives additional reader information corresponding to the RFID transponder. In normal mode, the reader compares the ID codes stored in memory to the RFID signal returned from an RFID transponder in the vicinity of said the reader. The RFID reader behavior is at least in part determined by the additional reader information corresponding to said ID codes stored in memory. We also describe a confidence threshold for acceptance of an ID code in learn mode and normal mode. The confidence threshold in normal mode may be less than in learn mode.

Abstract: We describe an animal entry control system, for example for a cat flap, using RFID (radio frequency identification). The system comprises an RFID reader to register the presence and identification number of a transponder (15) injected under the skin of an animal; and a door (8) mounted on a hinge (10) and controlled by the RFID tag reader. The RFID reader comprises a resonant circuit including a tuning circuit to control the RFID reader such that a drive frequency of the RFID reader matches both a resonant frequency of the RFID reader and a resonant frequency of the transponder. Embodiments of the system are thus tolerant to a degree of detuning, for example from a metallic or magnetic material in the vicinity of the antenna.

Abstract: Embodiments of the invention relate to the field of RFID (radio frequency identification). Some particularly preferred embodiments relate to a high-Q, so-called “full duplex” (FDX) RFID Reader. An RFID tag reader, the reader comprising: an electromagnetic (EM) field generator for generating an electromagnetic (EM) field for modulation by said tag, said modulation comprising modulated load of said EM field by said tag; a detector system responsive to fluctuations in strength of said EM field at said reader; a negative feedback system responsive to said detector system to provide a control signal for said EM field generator for controlling said EM field generator to reduce said detected fluctuations; and a demodulator responsive to said control of said EM field to demodulate said EM field modulation by said tag.

Abstract: Embodiments of the invention relate to the field of RFID (radio frequency identification). Some particularly preferred embodiments relate to a high-Q, so-called “full duplex” (FDX) RFID Reader. An RFID tag reader, the reader comprising: an electromagnetic (EM) field generator for generating an electromagnetic (EM) field for modulation by said tag, said modulation comprising modulated load of said EM field by said tag; a detector system responsive to fluctuations in strength of said EM field at said reader; a negative feedback system responsive to said detector system to provide a control signal for said EM field generator for controlling said EM field generator to reduce said detected fluctuations; and a demodulator responsive to said control of said EM field to demodulate said EM field modulation by said tag.

Abstract: We describe RFID tags that incorporate a nonlinear resonator that self-adapts to the driving frequency of a reader. More particularly we describe an RF tag for sending data to a tag reader by modulating energy drawn from an RF field of said tag reader, the tag comprising: an antenna; a resonant circuit coupled to said antenna to resonate at a frequency of said RF field; a local power store to store power extracted from said RF field; a modulation system to modulate one or both of the resonance amplitude and a relative phase of a signal in said resonant circuit with respect to said RF field; and a feedback circuit coupled to said resonant circuit and to said local power store to control one or both of said resonance amplitude and said relative phase to control transients in said resonance amplitude caused by said modulation.

Abstract: Embodiments of the invention relate to the field of RFID (radio frequency identification). Some particularly preferred embodiments relate to a high-Q, so-called “full duplex” (FDX) RFID Reader. An RFID tag reader, the reader comprising: an electromagnetic (em) field generator for generating an electromagnetic (em) field for modulation by said tag, said modulation comprising modulated load of said em field by said tag; a detector system responsive to fluctuations in strength of said em field at said reader; a negative feedback system responsive to said detector system to provide a control signal for said em field generator for controlling said em field generator to reduce said detected fluctuations; and a demodulator responsive to said control of said em field to demodulate said em field modulation by said tag.

Abstract: A circuit block which comprises a non-linear capacitor with two different values of capacitance dependent on a value of a voltage of a resonant signal on the capacitor; a plurality of second capacitors each coupled to a respective switch to enable a said second capacitor to be switched in or out of parallel connection with the nonlinear capacitor; and a tuning control, coupled to the second capacitor switches, and sensing an amplitude of the resonant signal. The tuning control circuit is configured to control the second capacitor switches to successively switch the second capacitors in/out of parallel connection with the non-linear capacitor dependent on the amplitude of the resonant signal until the non-linear capacitor has substantially a single one of two different values, such that in a resonant circuit the circuit block then behaves as a fixed value capacitor.

Abstract: Embodiments of the invention relate to resonant circuits; particularly but not exclusively the embodiments relate to resonant circuits in RPID (radio frequency identification) responsive to a wide frequency range. A controllable electric resonator comprising an inductor coupled to a first capacitor to form a resonant circuit, the resonator further comprising a controllable element, a second capacitor controllable coupled across said first capacitor by said controllable element, and a control device to control said controllable element such that a total effective capacitance of said first and second capacitor varies over a duty cycle of an oscillatory signal on said resonator.

Abstract: Embodiments of the invention relate to the field of RFID interrogators, particularly RFID interrogators that combine low loss with high rates of communication from the interrogator to a tag. Further embodiments relate to the field of active RFID tags and general radio transmitters. We describe a transmitter comprising a resonant circuit and a driver coupled to drive said resonant circuit, wherein said resonant circuit includes a resonance regeneration system such that during amplitude modulation of a resonant signal in said resonant circuit when an amplitude of said resonant signal is reduced energy from said reduction is stored and when said amplitude is increased said stored energy is used to regenerate said resonance signal.

Abstract: Embodiments of the invention relate to the field of RFID interrogators, particularly RFID interrogators that combine low loss with high rates of communication from the interrogator to a tag. We describe a transmitter comprising a resonant circuit and a driver coupled to drive said resonant circuit, wherein said resonant circuit includes a resonance regeneration system such that during amplitude modulation of a resonant signal in said resonant circuit when an amplitude of said resonant signal is reduced energy from said reduction is stored and when said amplitude is increased said stored energy is used to regenerate said resonance signal.

Abstract: A circuit block which comprises a non-linear capacitor with two different values of capacitance dependent on a value of a voltage of a resonant signal on the capacitor; a plurality of second capacitors each coupled to a respective switch to enable a said second capacitor to be switched in or out of parallel connection with the nonlinear capacitor; and a tuning control, coupled to the second capacitor switches, and sensing an amplitude of the resonant signal. The tuning control circuit is configured to control the second capacitor switches to successively switch the second capacitors in/out of parallel connection with the non-linear capacitor dependent on the amplitude of the resonant signal until the non-linear capacitor has substantially a single one of two different values, such that in a resonant circuit the circuit block then behaves as a fixed value capacitor.

Abstract: An RFID reader for use in a pet door to control access for a pet bearing an RFID tag or implant. The RFID reader incorporates and is operable in two modes, a learn mode and a normal mode. In learn mode, the reader stores the ID code of an RFID transponder in the vicinity of the reader and also derives additional reader information corresponding to the RFID transponder. In normal mode, the reader compares the ID codes stored in memory to the RFID signal returned from an RFID transponder in the vicinity of said the reader. The RFID reader behavior is at least in part determined by the additional reader information corresponding to said ID codes stored in memory. We also describe a confidence threshold for acceptance of an ID code in learn mode and normal mode. The confidence threshold in normal mode may be less than in learn mode.

Abstract: Embodiments of the invention relate to the field of RFID interrogators, particularly RFID interrogators that combine low loss with high rates of communication from the interrogator to a tag. Further embodiments relate to the field of active RFID tags and general radio transmitters. We describe a transmitter comprising a resonant circuit and a driver coupled to drive said resonant circuit, wherein said resonant circuit includes a resonance regeneration system such that during amplitude modulation of a resonant signal in said resonant circuit when an amplitude of said resonant signal is reduced energy from said reduction is stored and when said amplitude is increased said stored energy is used to regenerate said resonance signal.

Abstract: We describe RFID tags that incorporate a nonlinear resonator that self-adapts to the driving frequency of a reader. More particularly we describe an RF tag for sending data to a tag reader by modulating energy drawn from an RF field of said tag reader, the tag comprising: an antenna; a resonant circuit coupled to said antenna to resonate at a frequency of said RF field; a local power store to store power extracted from said RF field; a modulation system to modulate one or both of the resonance amplitude and a relative phase of a signal in said resonant circuit with respect to said RF field; and a feedback circuit coupled to said resonant circuit and to said local power store to control one or both of said resonance amplitude and said relative phase to control transients in said resonance amplitude caused by said modulation.

Abstract: Embodiments of the invention relate to the field of RFID interrogators, particularly RFID interrogators that combine low loss with high rates of communication from the interrogator to a tag. We describe a transmitter comprising a resonant circuit and a driver coupled to drive said resonant circuit, wherein said resonant circuit includes a resonance regeneration system such that during amplitude modulation of a resonant signal in said resonant circuit when an amplitude of said resonant signal is reduced energy from said reduction is stored and when said amplitude is increased said stored energy is used to regenerate said resonance signal.