U.S. patent application number 15/404142 was filed with the patent office on 2018-06-21 for method to remove measurement receiver counter intermodulation distortion for transmitter calibration.
The applicant listed for this patent is Futurewei Technologies, Inc.. Invention is credited to Wael Al-Qaq, Hong Jiang, Zhihang Zhang.
Application Number | 20180175945 15/404142 |
Document ID | / |
Family ID | 62554765 |
Filed Date | 2018-06-21 |
United States Patent
Application |
20180175945 |
Kind Code |
A1 |
Jiang; Hong ; et
al. |
June 21, 2018 |
METHOD TO REMOVE MEASUREMENT RECEIVER COUNTER INTERMODULATION
DISTORTION FOR TRANSMITTER CALIBRATION
Abstract
A system, computer readable medium, and method are provided for
calibrating a wireless transmitter. A transceiver that includes a
radio frequency transmitter, a measurement receiver, and a local
oscillator unit may be calibrated by adjusting the duty cycle of
the radio frequency signals generated by the local oscillator unit.
The method for calibrating the wireless transmitter includes the
steps of collecting measurement data corresponding to a number of
pre-defined duty ratio correction factors, calculating estimated
optimum duty ratio correction factors based on the measurement
data, and determining a final optimum duty ratio correction factor
from the estimated optimum duty ratio correction factors. The
pre-defined duty ratio correction factors may be selected to
simplify the calculations for choosing the final optimum duty ratio
correction factor. The wireless transmitter can be calibrated by
configuring the local oscillator unit based on the final optimum
duty ratio correction factor.
Inventors: |
Jiang; Hong; (Kernersville,
NC) ; Zhang; Zhihang; (Cary, NC) ; Al-Qaq;
Wael; (Oak Ridge, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Futurewei Technologies, Inc. |
Plano |
TX |
US |
|
|
Family ID: |
62554765 |
Appl. No.: |
15/404142 |
Filed: |
January 11, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62436363 |
Dec 19, 2016 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H03K 3/017 20130101;
H04B 17/11 20150115; H04B 15/06 20130101; H04L 27/364 20130101;
H04B 1/0475 20130101 |
International
Class: |
H04B 17/11 20060101
H04B017/11; H04L 27/36 20060101 H04L027/36; H03K 3/017 20060101
H03K003/017 |
Claims
1. A method for calibrating a wireless transmitter, comprising:
collecting, via a measurement receiver associated with the wireless
transmitter, measurement data corresponding to a number of
pre-defined duty ratio correction factors; calculating, during a
first iteration, two estimated optimum duty ratio correction
factors based on a first subset of the measurement data;
calculating, during a second iteration, four estimated optimum duty
ratio correction factors based on a second subset of the
measurement data; determining a final optimum duty ratio correction
factor from the six estimated optimum duty ratio correction
factors; and configuring a local oscillator unit associated with
the wireless transmitter based on the final optimum duty ratio
correction factor, wherein a duty ratio correction factor refers to
a parameter that identifies an adjustment to a duty cycle of one or
more radio frequency (RF) signals generated by the local oscillator
unit for the wireless transmitter.
2. The method of claim 1, wherein the number of pre-defined duty
ratio correction factors is four.
3. The method of claim 2, wherein a first pre-defined duty ratio
correction factor, x.sub.1, is equal in magnitude and opposite in
sign to a second pre-defined duty ratio correction factor, x.sub.2
(i.e., x.sub.2=x.sub.1), and a third pre-defined duty ratio
correction factor, x.sub.3, is less than the first pre-defined duty
ratio correction factor, x.sub.1, and greater than a fourth
pre-defined duty ratio correction factor, x.sub.4, which is equal
to zero (i.e., x.sub.1>x.sub.3>x.sub.4=0).
4. The method of claim 1, wherein calculating, during the first
iteration, two estimated optimum duty ratio correction factors
based on the first subset of the measurement data comprises:
calculating a difference between a first measurement vector
associated with a first pre-defined duty ratio correction factor,
x.sub.1, and a second measurement vector associated with a second
pre-defined duty ratio correction factor, x.sub.2; and calculating
a difference between the first measurement vector associated with
the first pre-defined duty ratio correction factor, x.sub.1, and a
third measurement vector associated with a third pre-defined duty
ratio correction factor, x.sub.3.
5. The method of claim 4, wherein calculating, during the second
iteration, four estimated optimum duty ratio correction factors
based on the second subset of the measurement data comprises:
calculating a difference between the first measurement vector
associated with the first pre-defined duty ratio correction factor,
x.sub.1, and a fourth measurement vector associated with a fourth
pre-defined duty ratio correction factor, x.sub.4; and calculating
a difference between the second measurement vector associated with
the second pre-defined duty ratio correction factor, x.sub.2, and
the fourth measurement vector associated with the fourth
pre-defined duty ratio correction factor, x.sub.4.
6. The method of claim 1, wherein determining the final optimum
duty ratio correction factor from the six estimated optimum duty
ratio correction factors comprises: calculating a set of difference
values including: a first difference value between a first
estimated optimum duty ratio correction factor calculated during
the first iteration and a first estimated optimum duty ratio
correction factor calculated during the second iteration (i.e.,
x.sub.0n.sub._.sub.2nd.sub._.sub.p-x.sub.0n.sub._.sub.1st), a
second difference value between the first estimated optimum duty
ratio correction factor calculated during the first iteration and a
second estimated optimum duty ratio correction factor calculated
during the second iteration (i.e.,
x.sub.0n.sub._.sub.2nd.sub._.sub.n-x.sub.0n.sub._.sub.1st), a third
difference value between a second estimated optimum duty ratio
correction factor calculated during the first iteration and a third
estimated optimum duty ratio correction factor calculated during
the second iteration (i.e.,
x.sub.0p.sub._.sub.2nd.sub._.sub.p-x.sub.0p.sub._.sub.1st), and a
fourth difference value between the second estimated optimum duty
ratio correction factor calculated during the first iteration and a
fourth estimated optimum duty ratio correction factor calculated
during the second iteration (i.e.,
x.sub.0p.sub._.sub.2nd.sub._.sub.n-x.sub.0p.sub._.sub.1st); and
determining a minimum absolute difference value based on a
magnitude of the first difference value, a magnitude of the second
difference value, a magnitude of the third difference value, and a
magnitude of the fourth difference value.
7. The method of claim 1, wherein configuring the local oscillator
unit associated with the wireless transmitter based on the final
optimum duty ratio correction factor comprises writing a value of
the final optimum duty ratio correction factor to a register
associated with the local oscillator unit.
8. The method of claim 1, wherein the wireless transmitter, the
local oscillator unit, and the measurement receiver are included in
a transceiver implemented on an integrated circuit.
9. The method of claim 1, wherein the wireless transmitter and the
measurement receiver are configured to operate using in-phase
quadrature (IQ) modulation.
10. A wireless communications system, comprising: a wireless
transmitter; a local oscillator unit configured to provide
radio-frequency signals to the wireless transmitter; a measurement
receiver configured to collect measurement data associated with the
signals transmitted by the wireless transmitter; and logic included
in an integrated circuit, the logic configured to: collect, via the
measurement receiver, measurement data corresponding to a number of
pre-defined duty ratio correction factors, calculate, during a
first iteration, two estimated optimum duty ratio correction
factors based on a first subset of the measurement data, calculate,
during a second iteration, four estimated optimum duty ratio
correction factors based on a second subset of the measurement
data, determine a final optimum duty ratio correction factor from
the six estimated optimum duty ratio correction factors, and
configure the local oscillator unit based on the final optimum duty
ratio correction factor, wherein a duty ratio correction factor
refers to a parameter that identifies an adjustment to a duty cycle
of one or more radio frequency (RF) signals generated by the local
oscillator unit for the wireless transmitter.
11. The system of claim 10, wherein the number of pre-defined duty
ratio correction factors is four.
12. The system of claim 11, wherein a first pre-defined duty ratio
correction factor, x.sub.1, is equal in magnitude and opposite in
sign to a second pre-defined duty ratio correction factor, x.sub.2
(i.e., x.sub.2=x.sub.1), and a third pre-defined duty ratio
correction factor, x.sub.3, is less than the first pre-defined duty
ratio correction factor, x.sub.1, and greater than a fourth
pre-defined duty ratio correction factor, x.sub.4, which is equal
to zero (i.e., x.sub.1>x.sub.3>x.sub.4=0).
13. The system of claim 10, wherein calculating, during the first
iteration, two estimated optimum duty ratio correction factors
based on the first subset of the measurement data comprises:
calculating a difference between a first measurement vector
associated with a first pre-defined duty ratio correction factor,
x.sub.1, and a second measurement vector associated with a second
pre-defined duty ratio correction factor, x.sub.2; and calculating
a difference between the first measurement vector associated with
the first pre-defined duty ratio correction factor, x.sub.1, and a
third measurement vector associated with a third pre-defined duty
ratio correction factor, x.sub.3.
14. The system of claim 13, wherein calculating, during the second
iteration, four estimated optimum duty ratio correction factors
based on the second subset of the measurement data comprises:
calculating a difference between the first measurement vector
associated with the first pre-defined duty ratio correction factor,
x.sub.1, and a fourth measurement vector associated with a fourth
pre-defined duty ratio correction factor, x.sub.4; and calculating
a difference between the second measurement vector associated with
the second pre-defined duty ratio correction factor, x.sub.2, and
the fourth measurement vector associated with the fourth
pre-defined duty ratio correction factor, x.sub.4.
15. The system of claim 10, wherein determining the final optimum
duty ratio correction factor from the six estimated optimum duty
ratio correction factors comprises: calculating a set of difference
values including: a first difference value between a first
estimated optimum duty ratio correction factor calculated during
the first iteration and a first estimated optimum duty ratio
correction factor calculated during the second iteration (i.e.,
x.sub.0n.sub._.sub.2nd.sub._.sub.p-x.sub.0n.sub._.sub.1st), a
second difference value between the first estimated optimum duty
ratio correction factor calculated during the first iteration and a
second estimated optimum duty ratio correction factor calculated
during the second iteration (i.e.,
x.sub.0n.sub._.sub.2nd.sub._.sub.n-x.sub.0n.sub._.sub.1st), a third
difference value between a second estimated optimum duty ratio
correction factor calculated during the first iteration and a third
estimated optimum duty ratio correction factor calculated during
the second iteration (i.e.,
x.sub.0p.sub._.sub.2nd.sub._.sub.p-x.sub.0p.sub._.sub.1st), and a
fourth difference value between the second estimated optimum duty
ratio correction factor calculated during the first iteration and a
fourth estimated optimum duty ratio correction factor calculated
during the second iteration (i.e.,
x.sub.0p.sub._.sub.2nd.sub._.sub.n-x.sub.0p.sub._.sub.1st); and
determining a minimum absolute difference value based on a
magnitude of the first difference value, a magnitude of the second
difference value, a magnitude of the third difference value, and a
magnitude of the fourth difference value.
16. The system of claim 10, wherein configuring the local
oscillator unit associated with the wireless transmitter based on
the final optimum duty ratio correction factor comprises writing a
value of the final optimum duty ratio correction factor to a
register associated with the local oscillator unit.
17. The system of claim 10, wherein the wireless transmitter, the
local oscillator unit, and the measurement receiver are included in
a transceiver implemented on an integrated circuit.
18. The system of claim 17, wherein the logic is implemented as a
plurality of instructions executed by a processor implemented on a
second integrated circuit coupled to the integrated circuit.
19. The system of claim 10, wherein the wireless transmitter and
the measurement receiver are configured to operate using in-phase
quadrature (IQ) modulation.
20. A non-transitory computer-readable media storing computer
instructions for calibrating a wireless transmitter that, when
executed by one or more processors, cause the one or more
processors to perform the steps of: collecting, via a measurement
receiver associated with the wireless transmitter, measurement data
corresponding to a number of pre-defined duty ratio correction
factors; calculating, during a first iteration, two estimated
optimum duty ratio correction factors based on a first subset of
the measurement data; calculating, during a second iteration, four
estimated optimum duty ratio correction factors based on a second
subset of the measurement data; determining a final optimum duty
ratio correction factor from the six estimated optimum duty ratio
correction factors; and configuring a local oscillator unit
associated with the wireless transmitter based on the final optimum
duty ratio correction factor, wherein a duty ratio correction
factor refers to a parameter that identifies an adjustment to a
duty cycle of one or more radio frequency (RF) signals generated by
the local oscillator unit.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 62/436,363 filed Dec. 19, 2016, the entire
contents of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to radio communications, and
more particularly to calibration of radio transmitters.
BACKGROUND
[0003] Radio frequency (RF) communication and, more specifically,
high-speed wireless network communication in cellular baseband
frequencies are ubiquitous in today's consumer electronic devices.
Wireless terminals include not only cellular phones, but other
consumer electronic devices that include chipsets that implement
wireless transmitters and/or receivers. Long-Term Evolution (LTE)
is a standard for high speed wireless communication, and many
chipsets are designed to meet the LTE standard. The counter
inter-modulation (CIM) performance of the wireless terminal
transmitter path is a key parameter for the design of these
devices. In order to achieve a low CIM distortion level,
calibration of the transmitter is often required, especially for a
multi-phase mixer transceiver architecture.
[0004] FIG. 1 illustrates a wireless communications system 100, in
accordance with the prior art. As shown in FIG. 1, the wireless
communications system 100 includes a baseband integrated circuit
and transceiver 110 that includes a transmitter (TX) 120, a local
oscillator 130, and a measurement receiver (MRX) 140. The
transmitter 120 generates an output signal that is coupled to a
power amplifier 160. The power amplifier 160 generates an amplified
signal that is passed through a bandpass filter 170, a coupler 180,
and one or more antenna 190. The coupler 180 couples the signal
output from the bandpass filter 170 to a feedback signal that is
connected to the input of the measurement receiver 140. In effect,
the feedback signal is the same as the filtered, amplified signal
transmitted wirelessly by the antenna 190.
[0005] Calibration of the transmitter 120 is typically performed
using the measurement receiver 140, which is configured to measure
the RF signal generated by the transmitter 120. Analysis of the
measured signal may be performed to determine adjustments for one
or more parameters of the transmitter that affect the CIM
distortion level. One parameter that is often adjusted is a duty
cycle of the RF signals generated by the local oscillator 130 that
feeds an N-phase mixer in the transmitter 120. By varying the one
or more parameters and measuring a CIM distortion level of the
output signal, the measurement receiver 140 may be utilized to
calibrate the transmitter 120 by choosing parameter values that
provide an optimum reduction in CIM distortion in the output
signal.
[0006] Unfortunately, the measurement receiver path may also create
CIM distortion that is added to the CIM distortion from the
transmitter during the analysis. The CIM distortion from the
measurement receiver path may come from various sources including
but not limited to, e.g., power amplifier harmonics mixing with the
measurement receiver local oscillator signal or harmonic distortion
from an analog-to-digital converter (ADC) that converts the
feedback signal to digital samples. The CIM distortion generated
along the measurement receiver path from the coupler 180 to the
measurement receiver 140 can affect the analysis of the feedback
signal such that the parameter values selected during calibration
do not minimize the CIM distortion of the transmitter 120. There
are various work arounds to this issue. For example, the voltage
controlled oscillator clock speed may be increased, but this may
increase power consumption of the system. An additional low pass
filter between the coupler 180 and the measurement receiver 140 may
attenuate certain CIM distortion that negatively affects
calibration, and the design of the measurement receiver may be
ultra linear to minimize CIM distortion from the measurement
receiver, which may be achieved at the cost of more complicated
circuit design. Thus, there is a need for addressing this issue
and/or other issues associated with the prior art.
SUMMARY
[0007] A system, computer readable medium, and method are provided
for calibrating a wireless transmitter. A transceiver that includes
a radio frequency transmitter, a measurement receiver, and a local
oscillator unit may be calibrated by adjusting the duty cycle of
the radio frequency signals generated by the local oscillator unit.
The method for calibrating the wireless transmitter includes the
steps of collecting measurement data corresponding to a number of
pre-defined duty ratio correction factors, calculating estimated
optimum duty ratio correction factors based on the measurement
data, and determining a final optimum duty ratio correction factor
from the estimated optimum duty ratio correction factors. The
pre-defined duty ratio correction factors may be selected to
simplify the calculations for choosing the final optimum duty ratio
correction factor. The wireless transmitter can be calibrated by
configuring the local oscillator unit based on the final optimum
duty ratio correction factor.
[0008] In a first embodiment, the number of pre-defined duty ratio
correction factors is four, referred to as x.sub.1, x.sub.2,
x.sub.3, and x.sub.4.
[0009] In a second embodiment (which may or may not be combined
with the first embodiment), a first pre-defined duty ratio
correction factor, x.sub.1, is equal in magnitude and opposite in
sign to a second pre-defined duty ratio correction factor, x.sub.2,
(i.e., x.sub.2=x.sub.1). In addition, a third pre-defined duty
ratio correction factor, x.sub.3, is less than the first
pre-defined duty ratio correction factor, x.sub.1, and greater than
a fourth pre-defined duty ratio correction factor, x.sub.4, which
is equal to zero (i.e., x.sub.1>x.sub.3>x.sub.4=0).
[0010] In a third embodiment (which may or may not be combined with
the first and/or second embodiments), the two estimated optimum
duty ratio correction factors are calculated by: (1) calculating a
difference between a first measurement vector associated with a
first pre-defined duty ratio correction factor, x.sub.1, and a
second measurement vector associated with a second pre-defined duty
ratio correction factor, x.sub.2; and (2) calculating a difference
between the first measurement vector associated with the first
pre-defined duty ratio correction factor, x.sub.1, and a third
measurement vector associated with a third pre-defined duty ratio
correction factor, x.sub.3.
[0011] In a fourth embodiment (which may or may not be combined
with the first, second, and/or third embodiments), the four
estimated optimum duty ratio correction factors are calculated by:
(1) calculating a difference between the first measurement vector
associated with the first pre-defined duty ratio correction factor,
x.sub.1, and a fourth measurement vector associated with a fourth
pre-defined duty ratio correction factor, x.sub.4; and (2)
calculating a difference between the second measurement vector
associated with the second pre-defined duty ratio correction
factor, x.sub.2, and the fourth measurement vector associated with
the fourth pre-defined duty ratio correction factor, x.sub.4.
[0012] In a fifth embodiment (which may or may not be combined with
the first, second, third, and/or fourth embodiments), determining
the final optimum duty ratio correction factor from the six
estimated optimum duty ratio correction factors comprises
calculating a set of difference values and determining a minimum
absolute difference value based on the magnitudes of the set of
difference values. The difference values include: (1) a first
difference value between a first estimated optimum duty ratio
correction factor calculated during the first iteration and a first
estimated optimum duty ratio correction factor calculated during
the second iteration (i.e.,
x.sub.0n.sub._.sub.2nd.sub._.sub.p-x.sub.0n.sub._.sub.1st); (2) a
second difference value between the first estimated optimum duty
ratio correction factor calculated during the first iteration and a
second estimated optimum duty ratio correction factor calculated
during the second iteration (i.e.,
x.sub.0n.sub._.sub.2nd.sub._.sub.n-x.sub.0n.sub._.sub.1st); (3) a
third difference value between a second estimated optimum duty
ratio correction factor calculated during the first iteration and a
third estimated optimum duty ratio correction factor calculated
during the second iteration (i.e.,
x.sub.0p.sub._.sub.2nd.sub._.sub.p-x.sub.0p.sub._.sub.1st); and (4)
a fourth difference value between the second estimated optimum duty
ratio correction factor calculated during the first iteration and a
fourth estimated optimum duty ratio correction factor calculated
during the second iteration (i.e.,
x.sub.0p.sub._.sub.2nd.sub._.sub.n-x.sub.0p.sub._.sub.1st).
[0013] In a sixth embodiment (which may or may not be combined with
the first, second, third, fourth, and/or fifth embodiments),
configuring the local oscillator unit associated with the wireless
transmitter based on the final optimum duty ratio correction factor
comprises writing a value of the final optimum duty ratio
correction factor to a register associated with the local
oscillator unit.
[0014] In a seventh embodiment (which may or may not be combined
with the first, second, third, fourth, fifth, and/or sixth
embodiments), the wireless transmitter, the local oscillator unit,
and the measurement receiver are included in a transceiver
implemented on an integrated circuit.
[0015] In an eighth embodiment (which may or may not be combined
with the first, second, third, fourth, fifth, sixth, and/or seventh
embodiments), the logic is implemented as a plurality of
instructions executed by a processor implemented on a second
integrated circuit, separate and distinct from the integrated
circuit that includes the wireless transmitter, the local
oscillator unit, and the measurement receiver included within a
transceiver.
[0016] In a ninth embodiment (which may or may not be combined with
the first, second, third, fourth, fifth, sixth, seventh, and/or
eighth embodiments), the wireless transmitter and the measurement
receiver are configured to operate using in-phase quadrature (IQ)
modulation.
[0017] To this end, in some optional embodiments, one or more of
the foregoing features of the aforementioned apparatus, system,
and/or method may afford a more accurate technique for calibrating
a wireless transmitter that, in turn, may enable lower power
consumption of the wireless transmitter device and/or reduce CIM
distortion in the radio frequency signal generated by the device.
It should be noted that the aforementioned potential advantages are
set forth for illustrative purposes only and should not be
construed as limiting in any manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 illustrates a wireless communications system, in
accordance with the prior art;
[0019] FIG. 2 illustrates a wireless communications system, in
accordance with one embodiment;
[0020] FIGS. 3A and 3B illustrate the CIM distortion from the
transmitter path and measurement receiver path, respectively, with
respect to the duty cycle error, in accordance with one
embodiment;
[0021] FIG. 4 is a conceptual diagram of the pre-defined duty ratio
correction factors for simplifying calculations for determining an
optimum duty ratio correction factor, in accordance with one
embodiment;
[0022] FIG. 5 illustrates the functional blocks of the CIM optimum
code estimator unit, in accordance with one embodiment;
[0023] FIG. 6 is a flowchart of a method for calibrating a
transmitter, in accordance with one embodiment; and
[0024] FIG. 7 illustrates a wireless communications system, in
accordance with one embodiment.
DETAILED DESCRIPTION
[0025] Adjusting the duty cycle of the RF signals generated by the
local oscillator unit changes the CIM distortion in the output
signals of the wireless transmitter in a drastic way. However, the
CIM distortion of the signal measured by the measurement receiver
may show very little change when the CIM distortion from the
components of the measurement receiver is the major contributing
source of said CIM distortion. The constant CIM distortion term
from the components of the measurement receiver path (i.e., the
path from the coupler to the measurement receiver) can be
subtracted out of the feedback signal, which means that the CIM
distortion from the components of the transmitter path (i.e., the
components from the transmitter to the coupler) can be measured
more accurately. By measuring the CIM distortion from the
components of the transmitter path more accurately, a more accurate
calibration of the transmitter may be achieved as the duty cycle of
the RF signals generated by the local oscillator unit can be varied
according to the measured CIM distortion from the components of the
transmitter path alone.
[0026] Measurement data may be collected from the measurement
receiver for a number of pre-defined duty ratio correction factors
that identify adjustments to a duty cycle of one or more RF signals
generated by the local oscillator unit. These measurements may be
used to determine an optimum duty ratio correction factor for the
local oscillator unit. It will be appreciated that absolute
differences in the measurement vectors may be relied on because,
for small changes in the duty cycle of the RF signals, the CIM
distortion from the components of the measurement receiver path are
constant and, therefore, will cancel out when the difference of two
separate measurement vectors is calculated. The estimates for the
optimum duty ratio correction factor, therefore, rely predominantly
on the measured CIM distortion from the components of the
transmitter path.
[0027] FIG. 2 illustrates a wireless communications system 200, in
accordance with one embodiment. As shown in FIG. 2, the wireless
communication system 200 includes a baseband integrated circuit
(IC) 210, a transceiver 220, a power amplifier 260, a passband
filter 270, a coupler 280, and an antenna 290. The baseband IC 210
includes a continuous waveform (CW) source 202, a digital front end
(DFE) 204, a pair of digital-to-analog converters (DAC) 252, a CIM
optimum code estimator unit 212, an image correction unit (ICU)
214, a pair of direct current (DC) offset correction (DCOC) units
216, a pair of finite impulse response (FIR) filters 218, and a
pair of analog-to-digital converters (ADC) 254. The transceiver 220
includes a transmitter (TX) 230, a local oscillator (LO) unit 250,
and a measurement receiver (MRX) 240. The transmitter 230 includes
a pair of low-pass filters (LPF) 232, an 8-phase mixer 234, and a
variable gain amplifier (VGA) 236. The measurement receiver 240
includes a passive RC network, a 4-phase mixer 246, a pair of
programmable gain amplifiers (PGA) 244, and a pair of low-pass
filters (LPF) 242. The passive RC network enables the received
feedback signal to be passed through a high-pass filter (HPF), no
filter, or a low-pass filter (LPF) which results in a phase shift
of -45.degree., 0.degree., or +45.degree., respectively. The LO
unit 250 includes a duty ratio adjustment capability. In one
embodiment, the LO unit 250 includes a register that may be written
to specify a duty ratio correction factor that adjusts the duty
ratio of the carrier signals coupled to the N-phase mixers of the
transmitter 230 and the measurement receiver 250.
[0028] The CW source 202 generates discrete intermediate frequency
(IF) (i.e., baseband) waveforms for modulating a signal for
wireless transmission. In one embodiment, the CW source 202 may
generate two waveforms for In-phase Quadrature (I/Q) modulation:
(1) an I waveform; and (2) a Q waveform. These waveforms are passed
to the DFE 204 that may process the waveforms before transmitting
the waveforms to a pair of DACs 252. As shown, the DACs 252
generate a differential current output that is passed to the
transmitter 230 to be transmitted wireless at a particular carrier
frequency. The DAC 252 output is passed through a low-pass filter
232 to attenuate any high-frequency distortion in the analog signal
produced by the components of the baseband IC 210. The filtered
signals are received at the 8-phase mixer 234, which also receives
eight phase-shifted RF signals generated by the LO unit 250. In one
embodiment, each RF signal generated by the LO unit 250 is a fixed
frequency sine wave that is shifted by 45.degree.. The mixer 234
modulates the RF signals at each of the different phases and
combines the signals to produce an outputs signal that is passed
through a VGA 236 to amplify the signal for output to the
components not included in the integrated circuit of the
transceiver 220.
[0029] Similar to the wireless communications system 100 of FIG. 1,
the output signal is passed to a power amplifier 260, a bandpass
filter (BPF) 270, and a coupler 280, and one or more antenna 290. A
feedback signal is routed from the coupler 280 back to an input of
the measurement receiver 240. The feedback signal is passed through
the passive RC network and then to the 4-phase mixer 246. The
feedback signal is mixed with four RF signals from the LO unit 250
to generate differential outputs for I and Q components within the
feedback signal. The differential outputs are passed through the
PGAs 244 and LPFs 242 before being passed to the ADCs 254 of the
baseband IC 210. The I and Q components of the feedback signal are
sampled in a digital domain and passed through the FIR filters 218
and DCOC units 216 before finally being processed by the ICU
214.
[0030] The baseband IC 210 is an integrated circuit in a digital
domain that generates signals for the transmitter 230 and analyzes
signals from the measurement receiver 240 of the transceiver. The
transceiver 220 is an integrated circuit in an analog domain that
generates an RF signal for wireless transmission via the antenna
290 and provides a feedback path for measuring the RF signal.
Although the baseband IC 210 and the transceiver 220 are shown as
separate and distinct ICs in FIG. 2, in alternative embodiments,
the baseband IC 210 and transceiver 220 may be embodied on a single
IC, in a similar manner to the wireless communications system 100
in FIG. 1.
[0031] Many of the components included in communications system
200, and the operation thereof, are well-known in the art. However,
the CIM optimum code estimator unit 212 is a new component that is
configured to determine an optimal duty ratio correction factor
when calibrating the transmitter 230. In one embodiment, the CIM
optimum code estimator unit 212 is a hardware unit configured to
make particular measurements of the feedback signal and determine
the optimum duty ratio correction factor for the LO unit 250. In
another embodiment, the CIM optimum code estimator unit 212 is a
software module that executes instructions configured to make
particular measurements of the feedback signal and determine the
optimum duty ratio correction factor for the LO unit 250.
[0032] The CIM distortion (e.g., 3.sup.rd order intermodulation
products--CIM3, 5.sup.th order intermodulation products--CIM5, etc)
generated by the TX clk (i.e., RF signals from the LO unit 250) in
the 8-phase mixer 234 is strongly dependent of the duty cycle error
of the TX clk due to non-perfect clock harmonics cancellation.
However, the duty cycle error does not vary significantly within
the output signal itself or the output signal harmonics (e.g.,
3*fLO+3*fbb), which means the feedback signal is mostly a fixed
signal, which leads to the CIM distortion from the measurement
receiver path also being fixed while the duty cycle of the RF
signals generated by the LO unit 250 is adjusted. In other words,
duty cycle error in the RF signals generated by the LO unit 250 may
be due to manufacturing defects in the LO unit 250 in the IC of the
transceiver 220, which can be corrected, at least partially, by
adjusting the duty cycle by a duty ratio correction factor.
Adjustment of this duty ratio correction factor significantly
changes the CIM distortion from the TX path, while not
significantly affecting the CIM distortion for the MRX path.
[0033] FIGS. 3A and 3B illustrate the CIM distortion from the TX
path and MRX path, respectively, with respect to the duty cycle
error, in accordance with one embodiment. As shown in FIG. 3A, the
CIM distortion from the TX path is minimized when the duty cycle
error is zero. However, as shown in FIG. 3B, the CIM distortion
from the MRX path is constant and does not vary based on the duty
cycle error. As shown in FIG. 3A, the CIM distortion level of the
TX path may go from approximately -50 dB at duty cycle errors of
approximately 2 percent to approximately -100 dB at duty cycle
errors of 0 percent. In comparison, as shown in FIG. 3B, the CIM
distortion level from the MRX path may be a constant -55 dB, across
a range of duty cycle error of [-2, 2] percent.
[0034] Utilizing the strong/weak dependency characteristics of
different contributors to CIM distortion levels, multiple
measurements can be made to remove the non-TX path contributors so
that the TX path contributors can be measured properly. In order to
remove the non-TX path contributors to CIM distortion, four
measurements must be taken, as shown in Equations 1 through 4:
A.sub.1*e.sup.i.phi.+B*e.sup.i.theta.=M.sub.1*e.sup.i.theta..sup.1
(Eq. 1)
A.sub.2*e.sup.i.phi.+B*e.sup.i.theta.=M.sub.2*e.sup.i.theta..sup.2
(Eq. 2)
A.sub.3*e.sup.i.phi.+B*e.sup.i.theta.=M.sub.3*e.sup.i.theta..sup.3
(Eq. 3)
A.sub.4*e.sup.i.phi.+B*e.sup.i.theta.=M.sub.4*e.sup.i.theta..sup.4
(Eq. 4)
, where A.sub.n*e.sup.i.phi. is the TX clk, non-perfect duty cycle
related CIM3 term, B*e.sup.i.theta. is the combined result of all
other contributors' CIM3 term, and M.sub.n*e.sup.i.theta..sup.n is
the measurement vector. A measurement vector refers to an IQ signal
decoded from the feedback signal measured by the measurement
receiver 240. The coefficient A.sub.n in the TX clk, non-perfect
duty cycle related CIM3 term can be written as:
A.sub.n= {square root over
(a.sup.2*(x.sub.n-x.sub.0).sup.2)}=|a*(x.sub.n-x.sub.0)| (Eq.
5),
where a is a scaling coefficient and x.sub.n is a pre-defined duty
ratio correction factor.
[0035] Assuming that the duty ratio correction factor is small
(i.e., the adjustment of the duty cycle is small), .phi. and
B*e.sup.i.theta. may be approximated as constants. Then, by
combining Equations 1 through 5, Equations 6 through 9 may be
derived:
|(|a*(x.sub.1-x.sub.0)|-|a*(x.sub.2-x.sub.0)|)|=|N.sub.12| (Eq.
6)
|(|a*(x.sub.1-x.sub.0)|-|a*(x.sub.3-x.sub.0)|)|=|N.sub.13| (Eq.
7)
|(|a*(x.sub.1-x.sub.0)|-|a*(x.sub.4-x.sub.0)|)|=|N.sub.14| (Eq.
8)
|(|a*(x.sub.2-x.sub.0)|-|a*(x.sub.4-x.sub.0)|)|=|N.sub.24| (Eq.
9),
where:
|N.sub.12|=|M.sub.1*e.sup.i.theta..sup.1-M.sub.2*e.sup.i.theta..sup.2|
(Eq. 10)
|N.sub.13|=|M.sub.1*e.sup.i.theta..sup.1-M.sub.3*e.sup.i.theta..sup.3|
(Eq. 11)
|N.sub.14|=|M.sub.1*e.sup.i.theta..sup.1-M.sub.4*e.sup.i.theta..sup.4|
(Eq. 12)
|N.sub.24|=|M.sub.2*e.sup.i.theta..sup.2-M.sub.4*e.sup.i.theta..sup.4|
(Eq. 13)
[0036] The solutions to Equations 10-13 may be obtained by
correlating the four measurements collected by the measurement
receiver 240. Furthermore, by carefully selecting the duty ratio
correction factors for x.sub.1, x.sub.2, x.sub.3, and x.sub.4, the
math can be simplified as much as possible.
[0037] FIG. 4 is a conceptual diagram 400 of the pre-defined duty
ratio correction factors for simplifying calculations for
determining an optimum duty ratio correction factor, in accordance
with one embodiment. As shown in FIG. 4, the duty ratio correction
factors x.sub.1 and x.sub.3 are selected to be outside of the chip
variation range with x.sub.1>x.sub.3>0. The functional range
of correcting the duty cycle of the RF signals generated by the LO
unit 250 may be limited to a particular range (e.g., 3 percent). In
other words, if the ideal duty cycle of the RF signals generated by
the LO unit is 50%, then the variation range of the duty cycle may
be limited to between 47% and 53% (or some other defined range) in
order to correct for small defects in manufacturing that cause a
deviation of the duty cycle from the ideal duty cycle. It will be
appreciated that the LO unit 250 may be capable of generating duty
cycles outside of this variation range in order to collect
measurement data, but the actual duty ratio correction factor
utilized for calibrating the transmitter 230 may simply be limited
to this arbitrary range. Having to correct the duty cycle outside
of this range may mean that the chip is out of spec and should be
rejected. Furthermore, it may be pre-defined that the duty ratio
correction factor x.sub.2=-x.sub.1 and the duty ratio correction
factor x.sub.4=0, in order to simplify calculations required during
calibration. The coefficient a and two possible solutions for the
duty ratio correction factors x.sub.0 can be solved from Equations
6 and 7 as:
a = N 13 ( x 1 - x 3 ) ( Eq . 14 ) x 0 p_ 1 st = [ ( x 1 + x 2 ) +
N 12 a ] * 0.5 ( Eq . 15 ) x 0 n_ 1 st = [ ( x 1 + x 2 ) - N 12 a ]
* 0.5 ( Eq . 16 ) ##EQU00001##
[0038] The duty ratio correction factors x.sub.0 represents the
optimum duty ratio correction factor, which may be solved for
iteratively. Equations 15 and 16 can be simplified if
x.sub.2=x.sub.1 because the first terms are equal to zero, such
that:
x 0 p_ 1 st = [ + N 12 a ] * 0.5 ( Eq . 17 ) x 0 n_ 1 st = [ - N 12
a ] * 0.5 ( Eq . 18 ) ##EQU00002##
[0039] Solving Equation 9 under the assumption that x.sub.4=0
yields the following logic. If the optimum duty ratio correction
factor is a negative value (x.sub.0n.sub._.sub.1st), then a second
iteration estimate of the optimum duty ratio correction factor is
given by:
x 0 n_ 2 nd_p = [ x 2 - N 24 a ] * 0.5 ( Eq . 19 ) x 0 n_ 2 nd_n =
[ x 2 - N 24 a ] * 0.5 ( Eq . 20 ) ##EQU00003##
[0040] However, if the optimum duty ration correction factor is a
positive value (x.sub.0p.sub._.sub.1st), then a second iteration
estimate of the optimum duty ratio correction factor is given
by:
x 0 p_ 2 nd_p = [ x 1 - N 14 a ] * 0.5 ( Eq . 21 ) x 0 p_ 2 nd_n =
[ x 1 - N 14 a ] * 0.5 ( Eq . 22 ) ##EQU00004##
[0041] By determining the minimum of the following values:
|x.sub.0n.sub._.sub.2nd.sub._.sub.p-x.sub.0n.sub._.sub.1st|,
|x.sub.0n.sub._.sub.2nd.sub._.sub.n-x.sub.0n.sub._.sub.1st|,
|x.sub.0p.sub._.sub.2nd.sub._.sub.p-x.sub.0P.sub._.sub.1st|, and
|x.sub.0p.sub._.sub.2nd.sub._.sub.n-x.sub.0p.sub._.sub.1st|, the
corresponding second iteration estimate is selected as the optimum
duty ratio correction factor. For example, if the value of
|x.sub.0n.sub._.sub.2nd.sub._.sub.n-x.sub.0n.sub._.sub.1st| is the
minimum value, then the duty ratio correction factor
x.sub.0n.sub._.sub.2nd.sub._.sub.n is the optimum duty ratio
correction factor. The second iteration estimate is used rather
than the first iteration estimate because it tends to yield better
results.
[0042] FIG. 5 illustrates the functional blocks of the CIM optimum
code estimator unit 212, in accordance with one embodiment. The CIM
optimum code estimator unit 212 implements logic for determining
the optimum duty ratio correction factor (i.e., optimum code). In
one embodiment, the logic is implemented in hardware, which
performs the functionality of each of the blocks. In another
embodiment, the logic is implemented in software, executed by a
processor such as a RISC CPU.
[0043] As shown in FIG. 5, the functional blocks of the CIM optimum
code estimator unit 212 include a first block 410 for converting a
reference transmitter signal into a CIM signal. In other words, the
reference transmitter signal is analyzed to determine the CIM
distortion included in the signal. The reference transmitter signal
is received by the CIM optimum code estimator unit 212 from the CW
source 202 and represents a clean transmitter signal before CIM
distortion is added to the signal by the transmitter 230 and the
measurement receiver 240. The functional blocks of the CIM optimum
code estimator unit 212 include a second block 420 for calculating
the four values of Equations 6 through 9. The second block 420
receives the measurement data from the measurement receiver 240,
which has been converted from analog to digital, filtered, and
image corrected. At block 430, the duty ratio correction factors
x.sub.0p.sub._.sub.1st and x.sub.0n.sub._.sub.1st are calculated
using Equations 17 and 18. The second block 420 transmits the
values for |N.sub.12| and a to the third block 430 for solving
these equations. At block 440, the duty ratio correction factors
x.sub.0n.sub._.sub.2nd.sub._.sub.p,
x.sub.0n.sub._.sub.2nd.sub._.sub.n,
x.sub.0p.sub._.sub.2nd.sub._.sub.p, and
x.sub.0p.sub._.sub.2nd.sub._.sub.n are calculated using Equations
19 through 22. The second block 420 transmits the values for
|N.sub.14|, |N.sub.24| and a to the fourth block 440 for solving
these equations. The third block 430 also transmits the values for
the duty ratio correction factors x.sub.0p.sub._.sub.1st and
x.sub.0n.sub._.sub.1st to the fourth block 440. At block 450, an
optimum duty ratio correction factor is determined based on the
comparison of these terms:
|x.sub.0n.sub._.sub.2nd.sub._.sub.p-x.sub.0n.sub._.sub.1st|,
|x.sub.0n.sub._.sub.2nd.sub._.sub.n-x.sub.0n.sub._.sub.1st|,
|x.sub.0p.sub._.sub.2nd.sub._.sub.p-x.sub.0p.sub._.sub.1st|, and
|x.sub.0p.sub._.sub.2nd.sub._.sub.n-x.sub.0p.sub._.sub.1st|. Again,
the minimum value of these terms is used to select the
corresponding 2.sup.nd iteration component of those terms as the
optimum duty ratio correction factor.
[0044] FIG. 6 is a flowchart 600 of a method for calibrating a
transmitter, in accordance with one embodiment. At step 602, the
measurement receiver 240 is utilized to collect measurement data
for four pre-defined duty ratio correction factors (x.sub.1,
x.sub.2, x.sub.3, and x.sub.4). Although the pre-defined duty ratio
correction factors may be arbitrarily selected, calculations may be
simplified by defining the duty ratio correction factors such that
x.sub.2=x.sub.1 and x.sub.4=0. In one embodiment, the CIM optimum
code estimator unit 212 configures the LO unit 250 to use one of
the four pre-defined duty ratio correction factors to generate RF
signals with corrected duty cycles. A known training signal is
transmitted by the transmitter 230 using the corrected RF signals,
and the measurement receiver 240 is utilized to collect a
measurement vector M.sub.n*e.sup.i.theta..sup.n for that duty ratio
correction factor. The process is repeated for the other three
pre-defined duty ratio correction factors to collect all four
measurements.
[0045] At step 604, the measurement data is utilized to estimate
two possible optimum duty ratio correction factors
x.sub.0p.sub._.sub.1st and x.sub.0n.sub._.sub.1st, during a first
iteration. In one embodiment, the CIM optimum code estimator unit
212 estimates the magnitude of vectors |N.sub.12| and |N.sub.13|,
which are defined as a difference between the measurement vectors
corresponding to pairs of pre-defined duty ratio correction factors
x.sub.1, x.sub.2, and x.sub.3, through complex correlation between
a conjugate signal of CIM3 distortion and the vectors N.sub.12 and
N.sub.13.
[0046] At step 606, the measurement data is utilized to estimate
four possible optimum duty ratio correction factors
x.sub.0n.sub._.sub.2nd.sub._.sub.p,
x.sub.0n.sub._.sub.2nd.sub._.sub.n,
x.sub.0p.sub._.sub.2nd.sub._.sub.p, and
x.sub.0p.sub._.sub.2nd.sub._.sub.n, during a second iteration. In
one embodiment, the CIM optimum code estimator unit 212 estimates
the magnitude of vectors |N.sub.14| and |N.sub.24|, which are
defined as a difference between the measurement vectors
corresponding to pairs of pre-defined duty ratio correction factors
x.sub.1, x.sub.2, and x.sub.4, through complex correlation between
a conjugate signal of CIM3 distortion and the vectors N.sub.14 and
N.sub.24.
[0047] At step 608, the CIM optimum code estimator unit 212
determines a final optimum duty ratio correction factor based on
the estimates for the optimum duty ratio correction factors
calculated during steps 604 and 606. In one embodiment, the two
optimum duty ratio correction factors x.sub.0p.sub._.sub.1st and
x.sub.0n.sub._.sub.1st calculated at step 604 are compared to the
four optimum duty ratio correction factors
x.sub.0n.sub._.sub.2nd.sub._.sub.p,
x.sub.0n.sub._.sub.2nd.sub._.sub.n,
x.sub.0p.sub._.sub.2nd.sub._.sub.p, and
x.sub.0p.sub._.sub.2nd.sub._.sub.n calculated during step 606 in
order to determine which optimum duty ratio correction factors
calculated during step 606 is the final optimum duty ratio
correction factor. More specifically, a difference value is
calculated between x.sub.0p.sub._.sub.1st and
x.sub.0p.sub._.sub.2nd.sub._.sub.p as well as between
x.sub.0p.sub._.sub.1st and x.sub.0p.sub._.sub.2nd.sub._.sub.n. A
difference value is also calculated between x.sub.0n.sub._.sub.1st
and x.sub.0n.sub._.sub.2nd.sub._.sub.p as well as between
x.sub.0n.sub._.sub.1st and x.sub.0n.sub._.sub.2nd.sub._.sub.n. The
minimum of these four difference values is determined and a
corresponding term (i.e., one of the optimum duty ratio correction
factors x.sub.0n.sub._.sub.2nd.sub._.sub.p,
x.sub.0n.sub._.sub.2nd.sub._.sub.n,
x.sub.0p.sub._.sub.2nd.sub._.sub.p, and
x.sub.0p.sub._.sub.2nd.sub._.sub.n calculated during step 606
utilized to derive that particular difference value) from the
minimum difference value is selected as the final optimum duty
ratio correction factor.
[0048] At step 610, the CIM optimum code estimator unit 212
configures the LO unit 250 to generate RF signals for the
transmitter 230 with an adjusted duty cycle based on the final
optimum duty ratio correction factor. In one embodiment, the CIM
optimum code estimator unit 212 writes the final optimum duty ratio
correction factor into a register in the LO unit 250. The
transceiver 220 may then be operated in a normal operating mode,
generating RF signals at the LO unit 250 based on the final optimum
duty ratio correction factor. After step 610, the calibration of
the transmitter 230 is complete.
[0049] FIG. 7 illustrates a wireless communications system 700, in
accordance with one embodiment. The system 700 includes logic 710,
a transmitter 730, a receiver 740, and a local oscillator unit 750.
The transmitter 730 provides a means for generating an RF signal to
be transmitted wirelessly via an antenna. The receiver 740 provides
a means for measuring the RF signal transmitted via the antenna to
provide feedback related to the CIM distortion added to the signal
by the transmitter 730. The logic 710 provides a means for
analyzing the feedback signal measured by the receiver 740 to
determine an optimum duty ratio correction factor that specifies an
adjust to a duty cycle of the RF signals generated by the LO unit
750. The wireless communications system 700 may be embodied within
one or more integrated circuits included in a device, such as a
mobile phone, tablet, GPS unit, or other electronic device.
[0050] In one embodiment, the logic 710 collects measurement
vectors related to a number of pre-defined duty ratio correction
factors. The logic 710 calculates a number of estimated optimum
duty ratio correction factors based on the collected measurement
vector and determines a final optimum duty ratio correction factors
based on the estimated optimum duty ratio correction factors.
[0051] It is noted that the techniques described herein, in an
aspect, are embodied in executable instructions stored in a
computer readable medium for use by or in connection with an
instruction execution machine, apparatus, or device, such as a
computer-based or processor-containing machine, apparatus, or
device. It will be appreciated by those skilled in the art that for
some embodiments, other types of computer readable media are
included which may store data that is accessible by a computer,
such as magnetic cassettes, flash memory cards, digital video
disks, Bernoulli cartridges, random access memory (RAM), read-only
memory (ROM), and the like.
[0052] As used here, a "computer-readable medium" includes one or
more of any suitable media for storing the executable instructions
of a computer program such that the instruction execution machine,
system, apparatus, or device may read (or fetch) the instructions
from the computer readable medium and execute the instructions for
carrying out the described methods. Suitable storage formats
include one or more of an electronic, magnetic, optical, and
electromagnetic format. A non-exhaustive list of conventional
exemplary computer readable medium includes: a portable computer
diskette; a RAM; a ROM; an erasable programmable read only memory
(EPROM or flash memory); optical storage devices, including a
portable compact disc (CD), a portable digital video disc (DVD), a
high definition DVD (HD-DVD.TM.), a BLU-RAY disc; and the like.
[0053] It should be understood that the arrangement of components
illustrated in the Figures described are exemplary and that other
arrangements are possible. It should also be understood that the
various system components (and means) defined by the claims,
described below, and illustrated in the various block diagrams
represent logical components in some systems configured according
to the subject matter disclosed herein.
[0054] For example, one or more of these system components (and
means) may be realized, in whole or in part, by at least some of
the components illustrated in the arrangements illustrated in the
described Figures. In addition, while at least one of these
components are implemented at least partially as an electronic
hardware component, and therefore constitutes a machine, the other
components may be implemented in software that when included in an
execution environment constitutes a machine, hardware, or a
combination of software and hardware.
[0055] More particularly, at least one component defined by the
claims is implemented at least partially as an electronic hardware
component, such as an instruction execution machine (e.g., a
processor-based or processor-containing machine) and/or as
specialized circuits or circuitry (e.g., discreet logic gates
interconnected to perform a specialized function). Other components
may be implemented in software, hardware, or a combination of
software and hardware. Moreover, some or all of these other
components may be combined, some may be omitted altogether, and
additional components may be added while still achieving the
functionality described herein. Thus, the subject matter described
herein may be embodied in many different variations, and all such
variations are contemplated to be within the scope of what is
claimed.
[0056] In the description above, the subject matter is described
with reference to acts and symbolic representations of operations
that are performed by one or more devices, unless indicated
otherwise. As such, it will be understood that such acts and
operations, which are at times referred to as being
computer-executed, include the manipulation by the processor of
data in a structured form. This manipulation transforms the data or
maintains it at locations in the memory system of the computer,
which reconfigures or otherwise alters the operation of the device
in a manner well understood by those skilled in the art. The data
is maintained at physical locations of the memory as data
structures that have particular properties defined by the format of
the data. However, while the subject matter is being described in
the foregoing context, it is not meant to be limiting as those of
skill in the art will appreciate that various acts and operations
described hereinafter may also be implemented in hardware.
[0057] To facilitate an understanding of the subject matter
described herein, many aspects are described in terms of sequences
of actions. At least one of these aspects defined by the claims is
performed by an electronic hardware component. For example, it will
be recognized that the various actions may be performed by
specialized circuits or circuitry, by program instructions being
executed by one or more processors, or by a combination of both.
The description herein of any sequence of actions is not intended
to imply that the specific order described for performing that
sequence must be followed. All methods described herein may be
performed in any suitable order unless otherwise indicated herein
or otherwise clearly contradicted by context.
[0058] The use of the terms "a" and "an" and "the" and similar
referents in the context of describing the subject matter
(particularly in the context of the following claims) are to be
construed to cover both the singular and the plural, unless
otherwise indicated herein or clearly contradicted by context.
Recitation of ranges of values herein are merely intended to serve
as a shorthand method of referring individually to each separate
value falling within the range, unless otherwise indicated herein,
and each separate value is incorporated into the specification as
if it were individually recited herein. Furthermore, the foregoing
description is for the purpose of illustration only, and not for
the purpose of limitation, as the scope of protection sought is
defined by the claims as set forth hereinafter together with any
equivalents thereof entitled to. The use of any and all examples,
or exemplary language (e.g., "such as") provided herein, is
intended merely to better illustrate the subject matter and does
not pose a limitation on the scope of the subject matter unless
otherwise claimed. The use of the term "based on" and other like
phrases indicating a condition for bringing about a result, both in
the claims and in the written description, is not intended to
foreclose any other conditions that bring about that result. No
language in the specification should be construed as indicating any
non-claimed element as essential to the practice of the invention
as claimed.
[0059] The embodiments described herein include the one or more
modes known to the inventor for carrying out the claimed subject
matter. It is to be appreciated that variations of those
embodiments will become apparent to those of ordinary skill in the
art upon reading the foregoing description. The inventor expects
skilled artisans to employ such variations as appropriate, and the
inventor intends for the claimed subject matter to be practiced
otherwise than as specifically described herein. Accordingly, this
claimed subject matter includes all modifications and equivalents
of the subject matter recited in the claims appended hereto as
permitted by applicable law. Moreover, any combination of the
above-described elements in all possible variations thereof is
encompassed unless otherwise indicated herein or otherwise clearly
contradicted by context.
* * * * *