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Adjusting parameters associated with transmitter leakageRelated Patent Categories: Telecommunications, Receiver Or Analog Modulated Signal Frequency Converter, Noise Or Interference EliminationAdjusting parameters associated with transmitter leakage description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070249314, Adjusting parameters associated with transmitter leakage. Brief Patent Description - Full Patent Description - Patent Application Claims
CLAIM OF PRIORITY [0001] This application claims priority under 35 USC .sctn.119(e) to U.S. patent application Ser. No. 10/804,198, filed on Mar. 19, 2004, the entire contents of which are hereby incorporated by reference. TECHNICAL FIELD [0002] This invention relates to Radio Frequency (RF) signals and, more particularly, to adjusting parameters associated with transmitter leakage. BACKGROUND [0003] In a known transceiver without signal cancellation, a single antenna is shared by the transmitter portion and receiver portion while simultaneously transmitting and receiving on the same frequency. See FIG. 1. The known transceiver 100 includes a controller 110, a frequency source 120, a transmitter modulator 130, a variable gain amplifier (VGA) 140, a power amplifier (PA) 150, a detector 160, a circulator 170, an antenna 180, an antenna connector 185 and a receiver 190. Controller 110 is a microprocessor. The frequency source 120 is a frequency agile synthesizer. Detector 160 can measure the power output by the transmitter modulator 130. [0004] The output of transmitter modulator 130 is calibrated using an accurate power sensor (not shown) at the antenna connector 185 by adjusting the gain setting of VGA 140, and then storing the gain setting of VGA 140 and the detector reading that produced the desired output power level(s). The transmitter modulator 130 and receiver 190 operate on the same frequency, and thus the performance of receiver 190 is adversely affected by the energy from transmitter modulator 130 that is reflected back from antenna 180, which is non-ideal in its implementation. If all radio frequency (RF) components in the transceiver modulator 130 are precisely 50 ohms, for example, then all energy from transmitter modulator 130 applied to antenna 180 is radiated, and no energy reflects back towards receiver 190. Because an ideal 150-ohm implementation is not realistically achievable, receiver 190 will experience degraded performance due to the energy reflected from the transmitter modulator 130 by antenna 180, relative to the weaker signal sent to receiver 190 detected by the detector. [0005] The signal level reflected back from antenna 180 is, for example, typically between 15 to 25 dB below the signal from the transmitter modulator 130 and radiated by antenna 180. The energy level of the signal reflected back to receiver 190 can be, for example, as high as 100 m W. This can cause signal overload of the sensitive components of receiver 190, resulting in degradation of the sensitivity and range of receiver 190. For the case of a homodyne receiver, this can cause a large direct current (DC) (i.e., 0 Hz) component. SUMMARY [0006] An apparatus comprises a transmitter, a receiver, an antenna and a signal cancellation circuit. The transmitter is configured to send a transmitter signal associated with a frequency. The receiver is associated with the frequency. The antenna is coupled to the transmitter and the receiver. The signal cancellation circuit is coupled to the transmitter, the receiver and the antenna. The signal cancellation circuit is configured to phase shift a first portion of the transmitter signal to produce a phase-shifted signal. The signal cancellation circuit is configured to combine the phase-shifted signal with a second portion of the transmitter signal to produce a combined signal. The second portion of the transmitter signal is associated with a reflection of a third portion of the transmitter signal from the antenna. The first portion, the second portion and the third portion of the transmitter signal are different from each other. [0007] The details of one of more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. DESCRIPTION OF DRAWINGS [0008] FIG. 1 shows a block diagram of a known transceiver. [0009] FIG. 2 shows a block diagram of a transceiver having signal cancellation circuitry, according to an embodiment of the invention. [0010] Like reference symbols in the various drawings indicate like elements. DETAILED DESCRIPTION [0011] In an embodiment of the invention, ''' transceiver having a signal cancellation circuit simultaneously transmits and receives on the same frequency while sharing a single antenna. In particular, a reflected signal from an antenna can be reduced significantly (for example, by 30 dB or more) via a signal cancellation circuit that takes a small amount of the transmitter signal (adjusted in amplitude to be substantially equal in amplitude to the reflected signal), and shifts the phase of the signal such that the phase-shifted signal is 1800 out of phase with the reflected signal. Consequently, when the two signals are combined, a signal having reduced amplitude is produced. Such signal can also be referred to as a "cancelled" signal or can have, for example, significantly reduced amplitude. [0012] FIG. 2 shows a block diagram of a transceiver having a signal cancellation circuit, according to an embodiment of the invention. As shown in FIG. 2, the transceiver 200 includes a controller 210, frequency source 220, transmitter modulator 230, VGA 240, PA 250, detector 260, circulator 270, antenna coupler 285, antenna 280 and receiver 290. Transceiver 200 also includes signal cancellation circuit 300 having coupler 310, variable attenuator 320, phase shifter 330, coupler/combiner 340, detector 350, controller 360, limiter 370 and low noise amplifier (LNA) 380. Each of the components of the signal cancellation circuit 300 is discussed below. [0013] Coupler 310 can be, for example, a directional coupler inserted between the output of PA 250 and circulator 270. Coupler 310 receives signal 402 and sends signals 404 and 406 where signal 404 has a smaller amplitude than the amplitude of signal 406. Signal 404 can used to cancel the reflected signal from the antenna 280 as described below in more detail. [0014] Variable attenuator 320 can be, for example, a variable attenuator used to adjust the amplitude of signal 404 so that the amplitude of the signal 412 substantially corresponds to the amplitude of signal 408 at combiner 340, where signal 408 is reflected from antenna 280. Phase shifter 330 can be, for example, a phase shifter configured to adjust the phase of the signal 41 0 1800 relative to the phase of the signal 408 reflected from antenna 280 and received by coupler 340. [0015] Coupler 340 can be, for example, a signal coupler configured to combine signal. 412 with signal 408 reflected from the antenna. In other words, after variable attenuator 320 adjusts the phase of signal 404 and phase shifter 330 adjusts the phase of signal 410, coupler 340 combines signal 412 with signal 408 received as reflection from antenna 280. [0016] Detector 350 can be, for example, a power detector configured to measure the power of signal 414. Detector 350 provides the detected power of signal 414 to controller 360. Controller 360 is configured to adjust variable attenuator 320 based on the detected power of signal 414. More specifically, controller 360 provides a control signal to variable attenuator 320 so that variable attenuator 320 modifies the amplitude of signal 404 to substantially correspond to t4e amplitude of signal 408. [0017] Controller 360 is also configured to adjust phase shifter 330 based on the detected power of signal 414. More specifically, controller 360 provides a control signal to phase shifter 330 so that the phase of signal 412 is shifted substantially 1800 from signal 408 reflected from the antenna. The output of detector 350 can be minimized, for example, when the amplitude of signals 412 and 408 are substantially equal, and the phase of signals 412 and 408 are substantially 180.degree. relative to each other. [0018] Detector 350 can also be coupled elsewhere within signal cancellation circuit 300. Such alternative locations of detector 350 within signal cancellation circuit 300 can provide an alternative measure of selectivity and sensitivity. Such alternative locations can be, for example, between LNA 380 and receiver 290, or after the mixer (not shown) of the receiver 290. Continue reading about Adjusting parameters associated with transmitter leakage... Full patent description for Adjusting parameters associated with transmitter leakage Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Adjusting parameters associated with transmitter leakage patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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