Muting circuit for analog filters in radio frequency identification (RFID) systems
AssigneeAvid Identification Systems, Inc.
InventorsMark Blair, Martin S. H. Ma
Life of this patent
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Abstract
An apparatus, which allows a radio frequency identification (RFID) reader to recover quickly from transient input to its receiving subsystem when transitioning from writing to an RFID transponder to reading its response. In particular, this apparatus is comprised of muting circuits, which both attenuate transients in its receiving subsystem while writing to a transponder, and help the receiving subsystem settle quickly after experiencing such transients.
Claims18
Circuitry for communicating with a radio frequency identification (RFID) transponder, the circuitry comprising:
- an antenna circuit;
- and
- a receiving subsystem coupled with the antenna circuit, wherein the receiving subsystem comprises:
- a detector circuit configured to detect voltages present in the antenna circuit,
- a filter stage comprising a feedback loop, the filter stage configured to output variations of the detected voltages that are caused by transmissions to and from the RFID transponder,
- a microcontroller configured to demodulate the output variations as digital data received from the RFID transponder as part of the communications, and
- a detector muting switch, that includes a pair of cascaded transistors, and that is disposed between the detector circuit and the filter stage to decouple the filter stage from the detector circuit when the detector muting switch is closed, and couple the filter stage with the detector circuit when the detector muting switch is open,
- wherein the microcontroller is configured to:
- maintain the detector muting switch closed during transmissions to the RFID transponder,
- monitor, after an end of transmissions to the RFID transponder, an input of the filter stage to determine whether the detector circuit has settled, and establish a length of a first time interval based on a result of the determination whether the detector circuit has settled, and
- monitor, after the end of the first time interval, an output of the filter stage to determine whether the filter stage has settled, and establish a length of a second time interval based on a result of the determination whether the filter stage has settled.
A method for communicating with a radio frequency identification (RFID) transponder, the method comprising:
- transmitting an RFID reader RF signal from an RFID reader;
- receiving, at an antenna circuit of the RFID reader, a transponder RF signal transmitted by the RFID transponder in response to the RFID reader RF signal;
- detecting, using a detector circuit of the RFID reader, voltages present in the antenna circuit during the transmitting and the receiving;
- after a first time interval since an end of transmitting the RFID reader RF signal, coupling a filter stage to the detector circuit, the filter stage being decoupled from the detector circuit during the transmitting;
- filtering, using the filter stage upon coupling the filter stage to the detector circuit, the detected voltages in the antenna circuit to provide output variations;
- varying a resistance of a feedback loop of the filter stage to decrease resistance of the feedback loop during transmissions from the RFID reader and increase resistance of the feedback loop after a second time interval since the end of the first time interval, the second time interval corresponding to a settling time of the filter stage;
- demodulating the output variations to provide digital data received from the RFID transponder transmitted in the transponder RF signal;
- and
- monitoring, after emitting the RFID reader RF signal, an input of the filter stage to determine whether the detector circuit has settled, and establishing a length of the first time interval based on a result of the determination whether the detector circuit has settled.
Dependencies are inferred from the claim text.