The patent's inventors are El Waffaoui, Rachid (
This patent was filed on
From the background information supplied by the inventors, news correspondents obtained the following quote: "Non-contact communication devices are widely used in a range of applications, such as stock control and inventory management, item tracking, security, and the like. Since a basic function of non-contact communication devices is identification of the device or tag, and radio frequencies are used, this technology is also known as
"Tags may be either passive, or active. An active tag has its own power supply, to power for instance the modulation circuitry. However, providing an on-board power supply is relatively expensive and they are relatively bulky: therefore, passive tags are more widely used. Passive tags do not have their own power supply, but rather extract power from an external source, which is most typically the RF field. Although this invention relates primarily to passive tags, it may also find application in active tags, for instance to avoid or reduce Bit Error Rate (BER) losses under detuned conditions.
"Passive tags, and in particular passive UHF tags, generally have a higher 'read range'--that is to say, the distance between tag and reader over which the tag can communicate--than other tags. However, for all tags, and passive tags in particular, the read range can be affected by environmental factors, which may detune the tag, thus modifying its operating frequency and potentially reducing the received power.
"An RFID tag's performance, assuming constant power consumption in its integrated circuit (IC), depends on the amount of power that can be captured by the antenna and provided to the IC. This in turn depends on impedance matching between the antenna and the IC. Environmental factors such as the presence of metals, liquids or other materials, or the close proximity of further tags, may lead to absorption or parasitic capacitance, which can the result in detuning the tag. Detuning of the tag may also result from the process spread in manufacturing of, for instance, any of the chip, antenna or packaging.
"It has been proposed in U.S. Pat. No. 7,167,090 to provide a feedback tuning circuit, to mitigate the problem of detuning. The tuning circuit alters the impedance of the impedance matching network coupling the antenna to rest of the device, in order to maximise the RF input signal and thereby optimise the performance of a power extraction circuit.
"However, such a circuit is sensitive to noise on the amplitude modulation (AM) signal, variation in transmitter power, and changes in the surrounding environment of the tag."
Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "It is an object of the present invention to provide an alternative non-contact communication device which can be tuned.
"According to a first aspect of the present invention, there is provided a non-contact communication device comprising: an antenna having an antenna impedance and being for receiving an AC signal having a voltage and a current, a main unit comprising a power-extraction unit and a communication unit and having a main unit impedance, a tuning circuit, and a matching network for matching the antenna impedance to the main unit impedance, characterised in that the tuning circuit comprises a phase detector for detecting a phase difference between the voltage and the current and is configured to adjust the impedance of the matching network in dependence on the phase difference.
"Use of a phase detector results in a device which is less sensitive to amplitude modulated noise than known devices, since noise tends to have a more significant impact on the amplitude than the phase of the input RF signal.
"In embodiments, the matching network comprises a capacitor bank for providing a selectable capacitance and the tuning circuit is configured to adjust the impedance of the matching network so as to minimise the quadrature phase error, by selecting the capacitance of the matching network. By quadrature phase error, is meant the amount by which the phases are not in quadrature. For instance, if the first phase leads the second phase by a phase difference of .pi./3, then the out-of-quadrature phase difference is .pi./6, being the difference between .pi./3 and a quadrature phase of .pi./2. The quadrature phase error may also be termed out-of-quadrature phase difference.
"In embodiments the phase detector is a passive phase detector. A passive phase detector does not require the relatively high level of energy typically required by active phase detectors. For active tags this energy may be available, but is unlikely to be available to passive tags, in which the use of a passive phase detector thus may provide a significant advantage.
"In embodiments, the phase detector detects a phase difference between the input voltage and the input current by detecting the phase difference between the input voltage and a coil voltage across a matching coil (L8), which matching coil forms part of the antenna (22)
"In embodiments, the power-extraction unit comprises a first output for providing power to the tuning circuit and a second output for providing power to the communication unit. Thereby, the tuning can operate to match the impedance, under badly detuned conditions, or other conditions where there is not sufficient power available to operate the complete tag.
"In embodiments, the power extraction unit is an RF-to-DC converter and may in particular be a charge pump.
"In embodiments, the first power output has at least one of more stages and a smaller time constant than the second power output. Using more stages for the first output helps to build quickly sufficient voltage under detuning conditions. A smaller time constant helps to speedup the tuning process. Faster response is thereby facilitated, which is beneficial, since a tag should be able to respond to the reader command within a given amount of time.
"In embodiments, the tuning circuit further comprises a quantiser for quantising the output of the phase detectors and for providing an input to a counter, which counter is configured to select the capacitance of the matching network.
"According to another aspect of the present invention, there is provided a method of operating a non-contact communication device, the method comprising: receiving an AC signal at an antenna; extracting power from the AC signal; using at least a part of the extracted power to tune the device by: detecting a phase difference between a voltage and a current of the AC signal in a phase detector, and adjusting a matching network in dependence on the phase.
"In embodiments, adjusting the matching network in dependence on the phase comprises quantising an output of the phase detector, adjusting a counter in response to the quantisation, and selecting the capacitance of a capacitor bank in dependence on the counter.
"In embodiments, the method may further comprise, subsequent to tuning the device, using a further part of the extracted power to power a communication unit.
"These and other aspects of the invention will be apparent from, and elucidated with reference to, the embodiments described hereinafter."
For the URL and additional information on this patent, see: El Waffaoui, Rachid; Manzi, Giuliano. Non-Contact Communication Device and Method of Operating the Same. U.S. Patent Number 8730016, filed
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