U.S. patent application number 11/750876 was filed with the patent office on 2007-10-25 for adjusting parameters associated with transmitter leakage.
This patent application is currently assigned to SIRIT TECHNOLOGIES INC.. Invention is credited to Stuart B. Sanders, Richard P. Timmons.
Application Number | 20070249314 11/750876 |
Document ID | / |
Family ID | 34986266 |
Filed Date | 2007-10-25 |
United States Patent
Application |
20070249314 |
Kind Code |
A1 |
Sanders; Stuart B. ; et
al. |
October 25, 2007 |
ADJUSTING PARAMETERS ASSOCIATED WITH TRANSMITTER LEAKAGE
Abstract
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.
Inventors: |
Sanders; Stuart B.; (Cary,
NC) ; Timmons; Richard P.; (Raleigh, NC) |
Correspondence
Address: |
FISH & RICHARDSON P.C.
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
SIRIT TECHNOLOGIES INC.
372 Bay Street, Suite 1100
Toronto
CA
M5H 2W9
|
Family ID: |
34986266 |
Appl. No.: |
11/750876 |
Filed: |
May 18, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10804198 |
Mar 19, 2004 |
|
|
|
11750876 |
May 18, 2007 |
|
|
|
Current U.S.
Class: |
455/296 |
Current CPC
Class: |
H04B 1/525 20130101;
H04B 3/232 20130101 |
Class at
Publication: |
455/296 |
International
Class: |
H04B 1/10 20060101
H04B001/10 |
Claims
1. A method for reducing noise, comprising: sampling, on a receiver
path, Radio Frequency (RF) signal including a signal received from
a transponder and an interference signal, the interference signal
based, at least in part, on an RF transmission signal; dynamically
adjusting a portion of the RF transmission signal based, at least
in part, on the sampled signal; and combining the adjusted portion
of the RF transmission signal into receive path to reduce the
interference signal.
2. The method of claim 1, further comprising splitting, from the RF
transmission signal, the portion of the RF transmission signal.
3. The method of claim 1, wherein dynamically adjusting the portion
of the transmission signal comprises: dynamically adjusting the
amplitude of the portion of the transmission signal based, at least
in part, on the sampled signal; and dynamically adjusting the phase
of the portion of the transmission signal based, at least in part,
on the sampled signal.
4. The method of claim 1, wherein the interference signal includes
a portion of the RF transmission signal reflected by an
antenna.
5. The method of claim 1, a frequency of the RF transmission signal
is substantially the same frequency of the signal received from the
transponder.
6. The method of claim 1, wherein the receive-path signal is
sampled as an RF signal.
7. The method of claim 1, wherein the interference signal is
reduced by at least 30 dB by the adjusted portion of the
transmission signal.
8. The method of claim 1, wherein sampling the RF signal from the
received path comprises determining an amplitude of the
receive-path signal.
9. Method of claim 1, further comprising: dynamically generating
control signals for adjusting the amplitude of the portion of the
RF transmission signal based, at least in part, on the sampled
signal; dynamically generating control signals for adjusting the
phase of the portion of the RF transmission signal based, at least
in part, on the sampled signal; and wherein the amplitude and the
phase of the portion of the RF transmission signal are adjusted in
response to at least the control signals.
10. The method of claim 1, wherein the portion of the RF
transmission signal is dynamically adjusted using a control
loop.
11. An RF reader, comprising: a detector configured to sample, on a
receive path, an Radio Frequency (RF) signal including a signal
received from a transponder and an interference signal, the
interference signal based, at least in part, on a RF transmission
signal; a control element configured to dynamically adjust a
portion of the RF transmission signal based, at least in part, on
the sampled signal; and a coupler configured to combine the
adjusted portion of the RF transmission signal to the receive path
to reduce the interference signal.
12. The RF reader of claim 11, further comprising a coupler
configured to split, from the RF transmission signal, the portion
of the RF transmission signal.
13. The RF reader of claim 11, wherein the control element
comprises: a amplitude element configured to dynamically adjust an
amplitude of the portion of the transmission signal based, at least
in part, on the sampled signal; and a phase element configured to
dynamically adjust a phase of the portion of the transmission
signal based, at least in part, on the sampled signal.
14. The RF reader of claim 11, wherein the amplitude element
comprises a variable attenuator.
15. The RF reader of claim 11, wherein the phase element comprises
a phase shifter.
16. The RF reader of claim 11, wherein the interference signal
includes a portion of the RF transmission signal reflected by an
antenna.
17. The RF reader of claim 11, the frequency of the RF transmission
signal is substantially the same frequency of the signal received
from the transponder.
18. The RF reader of claim 11, wherein the receive-path signal is
sampled as an RF signal.
19. The RF reader of claim 11, wherein the interference signal is
reduced by at least 30 dB by the adjusted portion of the
transmission signal.
20. The RF reader of claim 11, wherein the detector is configured
to determine an amplitude of the receive-path signal.
21. The RF reader of claim 11, further comprising wherein the
control element includes a controller configured to dynamically
generate control signals for adjusting an amplitude and a phase of
the portion of the RF transmission signal based, at least in part,
on the sampled signal, wherein an amplitude and a phase of the
portion of the RF transmission signal are adjusted in response to
at least the control signals.
22. The RF reader of claim 1, wherein the portion of the RF
transmission signal is dynamically adjusted using a control loop.
Description
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.
[0019] Controller 360 can be configured, for example, as a control
loop used to adjust the amplitude and phase of signal 404 so that
signal 414 output by coupler 340 as detected by detector by
detector 350 is minimized. As described above, controller 360
provides control signals to variable attenuator 320 and phase
shifter 330, which adjust the amplitude and phase, respectively, of
signal 404 based on these control signals.
[0020] Limiter 370 receives signal 414 and outputs signal 416.
Limiter 370 is configured to limit the amplitude of signal 414 to
produce signal 416 thereby protecting LNA 380. More specifically,
LNA 8 is configured to amplify signal 416 to improve the
sensitivity performance and range of the receiver 290. Before such
amplification, however, the amplitude of signal 416 provided to LNA
380 is limited by limiter 370 to protect LNA 380 from damage by a
high signal level reflected from the antenna, prior to the
cancellation adjustment I refinement via controller 360.
[0021] Various alternative embodiments are possible. For example,
in one embodiment, the transceiver includes an optional memory
device (not shown). In such an embodiment, the transceiver
detectors (e.g., detectors 260 and 350) can be calibrated based on
the calibrated data stored in the memory device of the transceiver.
By calibrating the transceiver detectors based on the calibration
data, the time it takes to minimize the cancellation by the signal
cancellation circuit can be minimized.
[0022] Similarly, transmitter modulator 230 can be calibrated by
using a power meter (not shown) at antenna connector 285, and by
adjusting VGA 240 until the desired power output from transmitter
modulator 230 is achieved. The setting of VGA 240 and the detected
power of PA 250 can be stored in the optional memory device for
each possible output power setting of transmitter modulator 230.
Finally, with variable attenuator 320 set for maximum attenuation,
a signal can be applied to antenna connector 285 while calibrating
detector 350 over its usable range.
[0023] In another embodiment, a "training" sequence can be
implemented in which variable attenuator 320 is set for maximum
attenuator and detector 350 (previously calibrated) measures the
power level of the reflected signal (e.g., signal 414). Based on
the current power level detected by detector 260, the initial value
of variable attenuator 320 can be approximated to achieve a best
guess of "equal amplitude," and then phase shifter 330 can be
adjusted to minimize the power level of the signal 414 detected by
detector 350. Subsequently, variable attenuator 320 can be fine
tuned to produce a minimum power level of signal 414 detected by
detector 350, and then phase shifter 330 can be fine tuned to
produce a minimum power level of signal 414 detected by detector
350.
[0024] While the invention has been particularly shown and
described with reference to embodiments thereof, it will be
understood by those skilled in the art that various changed in form
and details may be made therein without departing from the spirit
and scope of the invention.
* * * * *