U.S. patent application number 11/262424 was filed with the patent office on 2007-05-03 for system and method for efficient upsampled signal processing.
Invention is credited to Daniela Radakovic, Dusan S. Veselinovic.
Application Number | 20070096964 11/262424 |
Document ID | / |
Family ID | 37914141 |
Filed Date | 2007-05-03 |
United States Patent
Application |
20070096964 |
Kind Code |
A1 |
Veselinovic; Dusan S. ; et
al. |
May 3, 2007 |
SYSTEM AND METHOD FOR EFFICIENT UPSAMPLED SIGNAL PROCESSING
Abstract
A system and method for efficiently upsampling and filtering a
signal is provided. The system includes a controller 216 and an
upsampler 202 capable of upsampling a digitized signal. The
upsampler 202 converts a digitized signal having a first sampled
frequency into a digitized signal having a second sampled frequency
by inserting, for example, at least one zero between the samples of
the digitized signal. A plurality of filters 205-208 is coupled to
the upsampler. These filters, which may be band-pass filters, would
be suitable for front end encoding in audio-based applications. The
controller 216 adjusts at least one output of the plurality of the
filters to zero, either by deactivation or forcing the filter to
zero, based upon a predetermined characteristic of the digitized
signal. One example of a predetermined characteristic is a maximum
frequency of interest.
Inventors: |
Veselinovic; Dusan S.;
(Chicago, IL) ; Radakovic; Daniela; (Park Ridge,
IL) |
Correspondence
Address: |
MOTOROLA INC
600 NORTH US HIGHWAY 45
ROOM AS437
LIBERTYVILLE
IL
60048-5343
US
|
Family ID: |
37914141 |
Appl. No.: |
11/262424 |
Filed: |
October 28, 2005 |
Current U.S.
Class: |
341/144 |
Current CPC
Class: |
H03H 17/0621 20130101;
H03H 17/0294 20130101 |
Class at
Publication: |
341/144 |
International
Class: |
H03M 1/66 20060101
H03M001/66 |
Claims
1. A system for processing a digitized signal, comprising: a. a
controller; b. an upsampler capable of upsampling the digitized
signal, wherein the digitized signal is characterized by a
predetermined characteristic, wherein the predetermined
characteristic comprises a maximum frequency of interest; and c. a
plurality of filters coupled to the upsampler, wherein the
controller adjusts at least one filter output selected from the
plurality of filters based upon the predetermined characteristic by
executing an operation selected from the group consisting of
deactivating the at least one filter and setting an output of the
at least one filter to zero.
2. The system of claim 1, wherein the system has no low-pass filter
coupled between the plurality of filters and the upsampler.
3. The system of claim 1, wherein the digitized signal comprises a
series of samples, wherein the upsampler upsamples the digitized
signal by inserting at least one zero between each of the series of
samples.
4. (canceled)
5. (canceled)
6. The system of claim 1, wherein the digitized signal is upsampled
by a factor of M, wherein M is an integer.
7. The system of claim 6, wherein the digitized signal has an
upsampled digitized signal sampling frequency, further wherein the
plurality of filters comprises N filters, wherein each of the
plurality of filters comprises a band-pass filter, wherein the each
of the plurality of filters has a pass bandwidth associated
therewith of the upsampled digitized signal sampling frequency
divided by 2*N.
8. The system of claim 7, further wherein the controller adjusts
outputs of each of the plurality of filters having pass band
frequencies greater than the upsampled digitized signal sampling
frequency divided by M.
9. The system of claim 1, wherein the plurality of filters are
effected in a front end module of a signal encoder.
10. A method of processing a sampled signal, the method comprising
the steps of: a. receiving a sampled signal having a specific
characteristic; b. upsampling the sampled signal; c. delivering an
upsampled, sampled signal to a plurality of band-pass filters; and
d. adjusting an output of at least one band-pass filter selected
from the plurality of band-pass filters based upon the specific
characteristic of the sampled signal, wherein the step of adjusting
an output of at least one band-pass filter comprises an operation
selected from the group consisting of causing the output of at
least one band-pass filter to be zero and deactivating at least one
band-pass filter.
11. The method of claim 10, further comprising the step of omitting
an application of a low-pass filter between the step of upsampling
and the step of delivering.
12. (canceled)
13. The method of claim 10, wherein the sampled signal comprises a
plurality of samples, wherein the step of upsampling comprises
inserting at least one additional sample between each of the
plurality of samples.
14. The method of claim 10, wherein the at least one additional
sample has a zero value.
15. The method of claim 10, wherein the step of upsampling
comprises upsampling by a factor of M by inserting M-1 additional
samples between each of the plurality of samples.
16. The method of claim 10, wherein the specific characteristic
comprises a frequency range of less than a predetermined sampling
frequency.
17. A portable electronic device, comprising: a. a microprocessor;
b. radio frequency circuitry coupled to the microprocessor for
receiving and transmitting electromagnetic signals; c. a signal
processing module comprising: i. a control module; ii. an
upsampling module capable of converting a discrete data stream
having a first sampling frequency associated therewith into a
discrete data stream having a second sampling frequency associated
therewith; iii. a plurality of band-pass filters coupled to the
upsampling module, each of the plurality of band-pass filters
having a unique pass band frequency associated therewith; wherein
the control module executes an operation selected from adjusting at
least one band-pass filter output of the plurality of band-pass
filters to zero based upon a predetermined criterion and
deactivating at least one band-pass filter based upon a
predetermined criterion.
18. The portable electronic device of claim 17, wherein the
upsampling module converts the discrete data stream having a first
sampling frequency associated therewith into the discrete data
stream having a second sampling frequency associated therewith by
inserting zeroes between values in the discrete data stream having
a first sampling frequency associated therewith.
19. The portable electronic device of claim 18, wherein the
portable electronic device comprises a radiotelephone, further
wherein the predetermined criterion comprises a maximum frequency
of interest.
20. The radiotelephone of claim 17, wherein the upsampling module
delivers an output to the plurality of band-pass filters without an
application of a low-pass filter.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] This invention relates generally to a system and method for
efficient upsampling and filtering, and more specifically to a
system and method for upsampling and filtering without the use of a
low-pass filter.
[0003] 2. Background Art
[0004] Digital audio systems rely upon analog to digital converters
for their operation. Analog to digital converters allow a
conventional analog waveform, like acoustic energy for example, to
be sampled and quantized into a data stream of binary numbers. The
conversion from an analog waveform to digital number sequence
allows computers and microprocessors to accurately and reliably
store, recall, transform and reproduce audio sound.
[0005] During this sampling process, the analog wave is effectively
"chopped up" into discrete digital values. The sampling process, by
its very nature, introduces quantization noise into the analog to
digital system, as the formerly smooth analog wave essentially
becomes a piece-wise linear approximation of that wave. In addition
to the quantization noise, a phenomenon known as "aliasing" causes
multiples of the analog wave to appear as duplicate images above
the frequency of interest. These duplicates will compromise the
quality of signal when the discrete digital values are converted
back into an analog wave.
[0006] For example, an audio signal having frequency components
ranging from 0 to 22 kHz must be sampled, in accordance with
Nyquist's Theorem, at a frequency of at least 44 kHz. In addition
to quantization noise, duplicate images will appear at multiples of
the original analog frequencies. A first duplicate appears from 22
kHz to 44 kHz, a second duplicate appears at 44 kHz to 66 kHz, and
so forth.
[0007] To eliminate quantization and oversampling noise, prior art
systems employed very high-order, complex low-pass filters to
eliminate frequency components above the desired frequency. Using
the example in the preceding paragraph, a designer may employ a
fourth or fifth order Chebychev filter to try and eliminate all
frequency components above 22 kHz. The problem with these filters
is not only are they expensive, but they often became unstable and
introduce other forms of noise into the system.
[0008] To rectify these problems, designers have begun using a
process known as oversampling. In oversampling, rather than
sampling the analog signal at twice the maximum frequency of
interest, the system may sample the analog signal at four, eight or
even sixteen times the maximum frequency of interest. Continuing
with the example from above, the 0-22 kHz signal may be sampled at
88 kHz, 176 kHz or 352 kHz. This oversampling causes the duplicate
images to be pushed to higher and higher frequencies. For example,
at 4.times.oversampling, the first image appears at 66-88 kHz,
rather than 22-44 kHz. Additionally, as the oversampling rate
increases, the quantization noise becomes spread across a larger
spectrum, thereby increasing the signal to noise ratio. As a
result, simpler, lower-order low-pass filters may be used to
eliminate the duplicates.
[0009] Designers also realized that a similar process, upsampling,
could be carried out in the digital domain to increase the overall
quality of the signal. The process of upsampling is similar to
oversampling, in that a digital data stream of one frequency is
increased to a higher frequency. In upsampling, the process is
carried out by inserting additional samples between the initial
samples. These additional samples may be either zeroes or
interpolated values between adjoining data points.
[0010] As with oversampling, in conventional upsampling systems an
upsampled data stream is passed through a low-pass filter to remove
any duplicate images introduced by the upsampling process. The
filtered, upsampled data stream may then be passed on to other
signal processing modules, circuits and components.
[0011] The problem with these prior art upsampling systems is that
the low-pass digital filter requires both time and processing power
when in operation. This time and processing power, especially in
the realm of battery-powered, mobile electronics, can come at the
expense of other functions. Additionally, the processing power
required to implement these filters is "multiply and accumulate"
processing power. In the world of microprocessors, performance is
sometimes determined by how many multiply and accumulate (MAC)
operations the processor can perform in one second. As there is a
finite amount of MAC operations that a device may perform, for
every one that must be dedicated to filtering, one less is
available for other functions.
[0012] There is thus a need for an improved upsampling system with
increased efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The accompanying figures, where like reference numerals
refer to identical or functionally similar elements throughout the
separate views and which together with the detailed description
below are incorporated in and form part of the specification, serve
to further illustrate various embodiments and to explain various
principles and advantages all in accordance with the present
invention.
[0014] FIG. 1 illustrates a prior art upsampling system employing a
low-pass filter.
[0015] FIG. 2 illustrates an efficient upsampling system and method
in accordance with the invention.
[0016] FIG. 3 illustrates a method of efficiently upsampling and
filtering in accordance with the invention.
[0017] FIG. 4 illustrates an electronic device having an upsampling
and filtering system in accordance with the invention.
[0018] Skilled artisans will appreciate that elements in the
figures are illustrated for simplicity and clarity and have not
necessarily been drawn to scale. For example, the dimensions of
some of the elements in the figures may be exaggerated relative to
other elements to help to improve understanding of embodiments of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Before describing in detail embodiments that are in
accordance with the present invention, it should be observed that
the embodiments reside primarily in combinations of method steps
and apparatus components related to efficient upsampling, which is
useful in front end encoders. Accordingly, the apparatus components
and method steps have been represented where appropriate by
conventional symbols in the drawings, showing only those specific
details that are pertinent to understanding the embodiments of the
present invention so as not to obscure the disclosure with details
that will be readily apparent to those of ordinary skill in the art
having the benefit of the description herein.
[0020] It will be appreciated that embodiments of the invention
described herein may be comprised of one or more conventional
processors and unique stored program instructions that control the
one or more processors to implement, in conjunction with certain
non-processor circuits, some, most, or all of the functions of
efficient upsampling and filtering described herein. The
non-processor circuits may include, but are not limited to, a radio
receiver, a radio transmitter, signal drivers, clock circuits,
power source circuits, and user input devices. Further, it is
expected that one of ordinary skill, notwithstanding possibly
significant effort and many design choices motivated by, for
example, available time, current technology, and economic
considerations, when guided by the concepts and principles
disclosed herein will be readily capable of generating such
software instructions and programs and ICs with minimal
experimentation.
[0021] A preferred embodiment of the invention is now described in
detail. Referring to the drawings, like numbers indicate like parts
throughout the views. As used in the description herein and
throughout the claims, the following terms take the meanings
explicitly associated herein, unless the context clearly dictates
otherwise: the meaning of "a," "an," and "the" includes plural
reference, the meaning of "in" includes "in" and "on." Further,
relational terms such as first and second, top and bottom, and the
like may be used solely to distinguish one entity or action from
another entity or action without necessarily requiring or implying
any actual such relationship or order between such entities or
actions.
[0022] The present invention offers an efficient method and system
for upsampling and filtering signals. Specifically, the method and
system of this invention allow a signal to be upsampled and
processed without a low-pass filter where a predetermined
characteristic of the signal is known. One application well suited
for the system and method of this invention is an encoder module in
a portable electronic device like a radiotelephone, music player or
video player.
[0023] In one embodiment of the invention a controller works in
conjunction with an upsampler. The upsampler inserts data between
existing samples of an incoming data stream. For instance, if the
incoming sample stream is a sampled audio signal, the upsampler may
upsample by inserting one or more zeroes between each sample of the
sampled audio signal. In so doing, the upsampler increases the
sample frequency of the overall data stream.
[0024] In many applications, predetermined characteristics are
known about the incoming signals. For instance, in a
telephone-based application, not all audible frequencies are
transmitted from one telephone to the next. In conventional
applications like a public switched telephone network for example,
only frequencies ranging from 300 Hz to 3 kHz are transmitted. The
controller of this invention takes advantage of this predetermined
characteristic and adjusts certain post processing operations
accordingly to eliminate the need of any low-pass filtering after
the upsampling stage. The net result is increase overall
efficiency, as both less memory and less multiply and accumulate
commands are required in signal processing. This increased
efficiency leads to longer battery life and more processing power
that may be dedicated to other circuits and modules.
[0025] Turning briefly to FIG. 1, illustrated therein is a
conventional upsampling system 100 that may be employed with an
encoder. The system 100 includes an upsampling module 101 and an
encoder 104. The upsampling module 101 includes an upsampler 102
and a low-pass filter 103. As noted above, when an incoming signal
109 having a sampled frequency of Fs is upsampled, a number of
samples are introduced between each sample in the incoming signal
109. The result is an upsampled signal 110 having an upsampled
frequency Fs'. By way of example, if the sample frequency is 4 kHz,
and two zeroes are inserted between each sample, the upsampled
frequency would be 12 kHz.
[0026] As also noted above, the upsampling causes duplicate images
to appear at frequencies of above the frequency of interest. To
eliminate these aliased images, the low-pass filter 103 is used to
cut out duplicate images above the frequency of interest.
Continuing the example from above, assuming a 4 kHz incoming signal
and an upsampling by 3, the low-pass filter 109 would remove all
duplicate images above 2 kHz. (After upsampling, the upsampled
sample frequency is 12 kHz. Per Nyquist's Theorem, 6 kHz is the
maximum available frequency. Dividing 6 kHz by M, where M=3, yields
2 kHz.)
[0027] In more general terms, for an incoming signal 109 with a
sample frequency Fs, the frequency of interest, staying in
accordance with Nyquist's Theorem, could be no more than 0 to Fs/2.
Normalized, this may be represented as ranging from 0 to .pi.. The
period of the incoming signal may be expressed as 2.pi.. When the
upsampler 102 upsamples by a factor of M, the frequency of interest
gets "compressed" by a factor of M. It is thus periodic with a
period of 2.pi./M. The low-pass filter 103, to effectively
eliminate the images, must remove all frequencies above .pi./M.
[0028] When used in an encoding application, the upsampled,
low-pass filtered signal 111 may then be fed into a bank of
band-pass filters 105-108 for processing, thereby yielding a series
of upsampled, low-pass filtered, band-pass filtered signals
112-115. Systems like that shown in FIG. 1 are often employed in
front-end modules of consumer electronics.
[0029] Turning now to FIG. 2, illustrated therein is a system for
efficient upsampling 200 in accordance with the invention. The
system 200, which may be used for processing a digitized signal and
is suitable for encoder applications, includes a controller 216,
and upsampler 202 and a plurality of filters 205-208 coupled to the
upsampler 202. Each filter 205-208 has a corresponding output
212-215. The modules of the system 200 may be employed or effected
in the front end module of a signal encoder. Alternatively, they
may be disposed in a stand-alone module, or integrated into one
component, like a microprocessor, application specific integrated
circuit (ASIC) or digital signal processor.
[0030] The upsampler 202 is capable of upsampling an incoming
signal 209 by a factor of M. In one embodiment, the upsampling
factor M is an integer. As the incoming signal 209 is a digitized
signal including a series of samples, the upsampler 202 upsamples
by inserting at least one zero between each of the series of
samples, thereby converting the digitized signal sampling frequency
to an "upsampled" digitized signal sampling frequency. It will be
clear to those of ordinary skill in the art having the benefit of
this disclosure that values other than zeroes may be inserted
between each of the series of samples. For example, the average
values of the adjoining samples may be inserted rather than samples
with a zero value.
[0031] For signals characterized by a predetermined characteristic,
like a maximum frequency of interest for example, the controller
216 eliminates the need for a low-pass filter by adjusting at least
one filter output, e.g. output 215 of filter 208 based upon the
predetermined characteristic. As such, no low-pass filter is
coupled between the plurality of filters 205-208 and the upsampler
202.
[0032] For instance, where the predetermined characteristic is a
maximum frequency of interest, the controller 216 may adjust one of
the filters, e.g. filter 208, by either deactivation, i.e. not
running the filter, or by setting it's output 215 to zero. Note
that in one embodiment, each of the plurality of filters 205-208 is
a digital filter that may be implemented mathematically within a
processing component. As such, the "deactivating" may be
deliberately not running that filter within the processing
component, or not applying the filter to the upsampled signal.
Where output values of that filter are required by post processing
circuits, the controller my supply a series of zeroes. It will be
clear to those of ordinary skill in the art that the deactivating
or setting to zero may be done in a variety of ways, but the net
result is the same: the output, if and when required, is zero.
[0033] Taking the telephone example from above, where the
predetermined characteristic of the incoming signal 209 is a
maximum frequency of 3 kHz, the controller assumes that an
upsampled, low-pass filtered signal would cause zeroes to be
forthcoming from some of the plurality of filters 205-208, as
frequencies above the maximum frequency of interest, scaled by the
upsampling factor, would have been eliminated by the low-pass
filter in a conventional system. The invention takes advantage of
this knowledge and eliminates the need for any memory allocation or
multiply and accumulate commands that would be required by a
low-pass filter. The invention does so with the controller 216,
which can set at least one filter, e.g. filter 208, to zero by not
running the filter or forcing its output 215 to be zero.
[0034] Where the plurality of filters 205-208 has N filters, the
number of filters that may be deactivated or set to zero depends
upon the predetermined characteristic. In one embodiment, suitable
for use in an encoder, each of the filters 205-208 is a band-pass
filter having a pass bandwidth associated therewith. In such a
scenario, the pass bandwidth associated with each filter, for the
filters to evenly cover the spectrum, is the upsampled digitized
sampling frequency divided by 2*N. The controller 216 is then be
able to adjust the outputs of the filters having pass band
frequencies greater than the upsampled digitized signal sampling
frequency divided by M by deactivating those filters or setting
their outputs to zero.
[0035] The operation of this system 200, set forth in general
above, is perhaps more easily understood by way of an example. The
following example is illustrative only and is presented to better
explain the operation of the components in the system 200. Presume
for the purposes of this example that the plurality of filters
205-208 is a bank of eight filters, each of which support a
sampling rate of at least 44.1 kHz. Also presume that the input
signal 209 has a sample frequency, Fs, of 11.025 kHz, as may be the
case in an audio application. The upsampler 202 upsamples by
inserting three zeroes between every sample of the incoming signal
209, thereby giving the upsampled signal 210 an upsampled digitized
signal sampling frequency, Fs', of 44.1 kHz. (M equals 4.) Presume
that the input signal 209 has frequency components in the entire
bandwidth, represented normally as extending from -.pi. to
.pi..
[0036] The upsampler 202 begins the process by receiving the
incoming signal 209 and inserting zeroes between each of the
samples. Where the incoming signal 209 has samples represented
x[k], the upsampler output signal 210 may be represented: Z
.function. [ k ] = x .function. [ k ] ##EQU1## where ##EQU1.2## k =
4 * n ##EQU1.3## and ##EQU1.4## n .times. .times. is .times.
.times. an .times. .times. interger , .times. and .times. = 0
.times. .times. otherwise . ##EQU1.5##
[0037] The upsampled signal 210 has a bandwidth of interest that
has now been compressed by M, which in this case is a factor of 4.
As such, the bandwidth is now -.pi./4 to .pi./4. The upsampled
signal 210 also includes aliased duplicate images that fall within
the -.pi. to -.pi./4 and .pi./4 to .pi. bandwidths. With prior art
systems, a "brick wall" low-pass filter, with a pass band of .pi./4
would be needed to remove the duplicates. However, as the
predetermined characteristic is known, specifically a maximum
frequency of interest at .pi./4, the controller 216 is able to
deactivate or otherwise set to zero certain band-pass filters,
thereby eliminating the duplicates.
[0038] As there are eight band-pass filters (represented in FIG. 2
by filters 205-208) being employed, they have the following pass
band frequencies: -.pi./8 to .pi./8; .pi./8 to .pi./4; .pi./4 to
3.pi./8; 3.pi./8 to .pi./2; .pi./2 to 5.pi./8, 5.pi./8 to 3.pi./4
to 7.pi.8; and 7.pi./8 to .pi.. Since the predetermined
characteristic, or maximum frequency of interest is .pi./4, all
filters having pass bands over .pi./4 will be deactivate or set to
zero by the controller 216 in accordance with the invention. In
other words, the filters having the following pass bands will be
set to zero or deactivated: .pi./4 to 3.pi./8; 3.pi./8 to .pi./2;
.pi./2 to 5.pi./8, 5.pi./8 to 3.pi./4 to 7.pi./8; and 7.pi./8 to
.pi.. As noted above, the outputs of these filters may be set to
zero, or in the alternative, as they may be mathematical filters
applied by a processor, they need not even be run or applied to the
upsampled signal 210.
[0039] The lack of a low-pass filter increases efficiency by not
only reducing the number of multiply and accumulate procedures, but
by also reducing the number of operations accessing memory. For the
preceding example, if a conventional low-pass filter would have had
40 taps, it would have required 40 multiply and accumulate commands
in addition to 80 memory access operations to retrieve the samples
and filter tap coefficients. Neglecting memory access operations,
the invention saves at least 40*44100 multiply and accumulate
procedures, which results in a savings of over a million
instructions per second.
[0040] Note that if it is not possible to cause the outputs 212-215
to be forced to zero, the controller 216 may be coupled to a
decoder or synthesis filter bank. The appropriate filters may be
zeroed out at that point, thereby accomplishing the same
effect.
[0041] Any audio component that utilizes an analysis filter bank,
like a plurality of band-pass filters, to separate a signal into
sub-bands, may only support a limited number of sampling
frequencies. As such, the band-pass bandwidths may not correlate
exactly to the maximum frequency of interest as in the preceding
example. In such cases, most audio applications will accommodate a
zeroing of the band-pass filter with a lower cut-off frequency just
below the maximum frequency of interest. For example, if the
maximum frequency of interest was 4 kHz, and the band-pass filters
had band-pass frequencies of 0-3 kHz, 3-6 kHz, 6-9 kHz, the filters
including and beyond the 3-6 kHz filter could be zeroed without
significantly affecting audio performance.
[0042] Turning now to FIG. 3, illustrated therein is a method for
processing a sampled signal in accordance with the invention. At
step 301, a sampled signal having a specific characteristic is
received. At step 302, the sampled signal is upsampled. As the
sampled signal comprises a plurality of samples, the step of
upsampling comprises inserting at least one additional sample
between each of the plurality of samples. For example the step of
upsampling may include upsampling by a factor of M, where M-1
additional samples are inserted between each of the plurality of
samples. As noted above, in one embodiment, the at least one
additional sample is a zero.
[0043] At step 303, shown in dashed line because it is a step of
omission, no low pass filter is applied to the upsampled signal. At
step 304, the upsampled, sampled signal is then delivered to a
plurality of band-pass filters, as would be used to segregate the
signal in an audio encoder application.
[0044] At step 305, an output of at least one band-pass filter is
adjusted based upon a specific characteristic of the upsampled,
sampled signal. In one embodiment, the specific characteristic may
be a frequency range of less than a predetermined sampling
frequency. The step of adjusting an output may include either
causing the output of at least one band-pass filter to be zero or
deactivating at least one of the band-pass filters.
[0045] Turning now to FIG. 4, illustrated therein is one
application for an efficient upsampling system and method in
accordance with the invention. The illustrative embodiment of FIG.
4 is that of an electronic device 400. The electronic device 400
includes a microprocessor 401 that serves as the central brain of
the device 400. The electronic device 400 may be a radiotelephone,
audio player, video player or other device.
[0046] The device 400 also includes an upsampling module 402
capable of converting a discrete data stream having a first
sampling frequency associated therewith, perhaps received and
sampled from radio frequency circuitry coupled to the
microprocessor 401 for receiving and transmitting electromagnetic
signals, into a discrete data stream having a second sampling
frequency associated therewith. The upsampling module 402 converts
the data stream from the first sampled frequency to the second
sampled frequency, in one embodiment, by inserting zeroes between
values in the discrete data stream. As noted above, the upsampling
module 402 may be integrated into the microprocessor 401.
Alternatively, the upsampling module 402 may be effected in a
separate component like a digital signal processor or the front end
of an audio encoder.
[0047] A plurality of band-pass filters 403 are coupled to the
upsampling module 402. Each of the plurality of band-pass filters
403 has a unique pass band frequency associated therewith. A
control module 404 is coupled to the plurality of band-pass
filters. The control module 404 is capable of forcing the outputs
of any of the band-pass filters 403 to zero, either by deactivating
them or by causing them to yield a zero output.
[0048] The control module 404 executes an operation that either
adjusts at least one band-pass filter output to zero based upon a
predetermined criterion or deactivates at least one band-pass
filter based upon a predetermined criterion. The predetermined
criterion, for example, may be a maximum frequency of interest. In
accordance with the invention, this action of the control module
404 allows the upsampling module to deliver its output to the
plurality of band-pass filters 403 without the application of a
low-pass filter, thereby saving memory and processing power.
[0049] In the foregoing specification, specific embodiments of the
present invention have been described. However, one of ordinary
skill in the art appreciates that various modifications and changes
can be made without departing from the scope of the present
invention as set forth in the claims below. Thus, while preferred
embodiments of the invention have been illustrated and described,
it is clear that the invention is not so limited. Numerous
modifications, changes, variations, substitutions, and equivalents
will occur to those skilled in the art without departing from the
spirit and scope of the present invention as defined by the
following claims.
* * * * *