Telecommunications – Transmitter and receiver at separate stations
Reexamination Certificate
2000-04-26
2001-05-08
Bost, Dwayne (Department: 2681)
Telecommunications
Transmitter and receiver at separate stations
C455S101000, C455S106000, C340S870030, C340S505000
Reexamination Certificate
active
06229987
ABSTRACT:
TECHNICAL FIELD
The invention relates to wireless communication systems. More particularly, the invention relates to backscatter communication systems.
BACKGROUND OF THE INVENTION
Backscatter communication systems are known in the art. In a backscatter system, one transponder, such as an interrogator, sends out a command to a remote communications device. After the interrogator transmits the command, and is expecting a response, the interrogator switches to a CW mode (continuous wave mode). In the continuous wave mode, the interrogator does not transmit any information. Instead, the interrogator just transmits radiation at a certain frequency. In other words, the signal transmitted by the interrogator is not modulated. After a remote communications device receives a command from the interrogator, the remote communications device processes the command. The remote communications device of the backscatter system modulates the continuous wave by switching between absorbing RF radiation and reflecting RF radiation. For example, the remote communications device alternately reflects or does not reflect the signal from the interrogator to send its reply. Two halves of a dipole antenna can be either shorted together or isolated from each other to modulate the continuous wave.
One example of a backscatter system is described in commonly assigned U.S. patent application Ser. No. 08/705,043, filed Aug. 29, 1996, and incorporated herein by reference. Another example of a backscatter system is described in U.S. Pat. No. 5,649,296 to MacLellan et al. which is also incorporated herein by reference.
In backscatter systems, the reflected backscatter signal can be returned to an interrogator in any phase because the distance between the remote communications device and the interrogator is unknown. Phase is a function of distance. Therefore, an IQ downconverter (e.g., a quadrature downconverter) is included in the interrogator. In an IQ downconverter, the local signal is mixed with the reflected backscatter signal to produce an in phase signal I. The local signal is mixed with the reflected backscatter signal, after either the local signal or the reflected signal is phase shifted 90 degrees, to produce a quadrature signal Q. Depending on the phase of the reflected backscatter signal, when the reflected backscatter signal is mixed with the local signal the result may be a positive voltage, a negative voltage, or no voltage at all. When a periodic signal reaches its peak, a 90 degree phase shifted version of the same signal reaches zero. By mixing at a 90 degrees phase shift as well as mixing the reflected signal without a phase shift, a signal be found for certain somewhere on the I output or Q output, or both. An IQ downconverter is described in U.S. Pat. No. 5,617,060 to Wilson et al., which is incorporated herein by reference.
Circuitry is typically coupled to each of the I and Q signals for various processing steps before the resultant signals are combined into one channel. This can involve duplication of circuitry.
One application for backscatter communications is in wireless electronic identification systems, such as those including radio frequency identification devices. Of course, other applications for backscatter communications exist as well. Most presently available radio frequency identification devices utilize a magnetic coupling system. An identification device is usually provided with a unique identification code in order to distinguish between a number of different devices. Typically, the devices are entirely passive (have no power supply), which results in a small and portable package. However, such identification systems are only capable of operation over a relatively short range, limited by the size of a magnetic field used to supply power to the devices and to communicate with the devices.
Another wireless electronic identification system utilizes a large, board level, active transponder device affixed to an object to be monitored which receives a signal from an interrogator. The device receives the signal, then generates and transmits a responsive signal. The interrogation signal and the responsive signal are typically radio-frequency (RF) signals produced by an RF transmitter circuit. Because active devices have their own power sources, and do not need to be in close proximity to an interrogator or reader to receive power via magnetic coupling. Therefore, active transponder devices tend to be more suitable for applications requiring tracking of something that may not be in close proximity to an interrogator, such as a railway car.
SUMMARY OF THE INVENTION
The invention provides an interrogator for use in a backscatter system. The interrogator includes an antenna configured to receive a backscatter signal. An IQ downconverter is coupled to the antenna and configured to downconvert the backscatter signal to produce I and Q signals. A combiner is coupled to the IQ downconverter and configured to combine the I and Q signals to produce a combined signal. An analog to digital converter is coupled to the combiner and configured to convert the combined signal to a digital signal.
In one aspect of the invention, the combiner is an analog combiner. In another aspect of the invention, the combiner is coupled directly to the IQ downconverter.
Another aspect of the invention provides a system including a wireless communications device. The wireless communications device includes an integrated circuit having a processor. The integrated circuit further includes a memory, a receiver, and a backscatter modulator coupled to the processor. The system further includes an interrogator configured to transmit a command to the wireless communications device and subsequently transmit a continuous wave to the wireless communications device for modulation by the backscatter modulator. The interrogator includes an IQ downconverter configured to receive a modulated backscatter signal from the wireless communications device and to produce I and Q signals. The interrogator further includes a combiner coupled to the downconverter and configured to produce a combined signal.
In one aspect of the invention, the combiner is coupled directly to the downconverter.
Another aspect of the invention provides a method of communications in a backscatter system. The method comprises receiving a backscatter signal. The backscatter signal is downconverted with an IQ downconverter to produce I and Q signals. The I and Q signals are combined to produce a combined signal. The combined signal is converted to a digital signal.
Circuitry coupled to the I signal was duplicated for the Q signal in prior designs. By combining the I and Q signals earlier than in other designs, duplication of circuitry is reduced.
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Greeff Roy
Ovard David K.
Bost Dwayne
Gary Erika A.
Micro)n Technology, Inc.
Wells, St. John, Roberts Gregory & Matkin P.S.
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