United States Patent (19)
`Bach et al.
`
`US006088,569A
`Patent Number:
`11
`(45) Date of Patent:
`
`6,088,569
`Jul. 11, 2000
`
`54 METHOD AND APPARATUS FOR
`RECEIVING A PLURALITY OF SIGNALS
`HAVING DIFFERENT FREQUENCY
`BANDWIDTHS
`
`75 Inventors: Christopher R. Bach, Elgin; Patrick
`D. Smith, Schaumburg, both of Ill.
`
`73 Assignee: Motorola, Inc., Schaumburg, Ill.
`21 Appl. No.: 09/065,313
`9
`22 Filed:
`Apr. 23, 1998
`(51) Int. Cl." ....................................................... H04H 1/00
`52 U.S. Cl. ................................ 455/3.1; 348/7; 455/207;
`455/249.1; 455/307; 455/313; 455/339;
`s
`s
`455(340
`58) Field of Seth, 45551, 42.3.1. s
`340,350.315.255.249.1313.207,266:
`s - a us - u-as a 1 as
`HoAN7773
`
`56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`5,270,824 12/1993 Dobrovolny ......................... asso
`5,812,928 9/1998 Watson, Jr. et al. ..................... 455/5.1
`5,835,844 11/1998 Stoneback et al. ...................... 455/5.1
`
`5.835,845 11/1998 Niki et al. ................................ 455/5.1
`5,852,772 12/1998 Lampe et al. ........................ 455/226.2
`
`FOREIGN PATENT DOCUMENTS
`2233520 1/1991 United Kingdom ............. HO3D 7/16
`OTHER PUBLICATIONS
`Stephen J. Erst, Tunable crystal filter accepts any frequency,
`MICROWAVES, vol. 17, No. 11, p. 94, Nov., 1978.
`Primary Examiner Andrew I. Faile
`Assistant Examiner Habte Bahgi
`Attorney, Agent, or Firm-Romi N. Bose
`(57)
`ABSTRACT
`A first mixer (306) shifts a first end (208) of a desired signal
`frequency bandwidth (206) of a desired signal (202) to an
`edge (508) of a first filter frequency bandwidth (502) of a
`first filter (312), wherein the first filter frequency bandwidth
`(502) is greater than the desired signal frequency bandwidth
`(206). Signals within a first undesired frequency spectrum
`(504) are attenuated by the first filter (314). A second mixer
`(316) shifts a second end (210) of the desired signal fre
`quency bandwidth (206) to an edge (608) of a second filter
`frequency bandwidth (602) of a second filter (320) to receive
`the desired signal (202).
`17 Claims, 4 Drawing Sheets
`
`
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`
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`
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`92 304 306 312
`
`314
`
`316
`
`BAND-PASS
`FILTER
`
`- - - - - - - - - - - -2.3TT
`
`J20 324
`
`326
`
`DATA
`STREAM
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`U.S. Patent
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`Jul. 11, 2000
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`Sheet 1 of 4
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`6,088,569
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`102
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`122 120
`74-74–
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`RT
`PRIMARY
`STATION 118
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`CABLE
`COMMUNICATION
`NETWORK
`116
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`100 A7 G. 7
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`
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`4
`1N1O
`aa N
`*AAAAAA
`110
`106
`4/NY
`Ea N
`112 E.
`EE
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`4/N108
`432) N
`ya
`Affa
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`200 AZG 2
`
`f(MHz)
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`U.S. Patent
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`Jul. 11, 2000
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`Sheet 2 of 4
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`6,088,569
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`SSV dH-GIN V8I
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`?HIGHJ, TII, H
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`U.S. Patent
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`Jul. 11, 2000
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`Sheet 3 of 4
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`6,088,569
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`IF1
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`f(MHz)
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`S. M.
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`f(MHz)
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`608
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`f(MHz)
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`U.S. Patent
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`Jul. 11, 2000
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`Sheet 4 of 4
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`START
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`RECEIVE UPSTREAM FREQUENCY SPECTRUM h-705
`
`
`
`710
`
`
`
`IS DESIRED
`SIGNAL FREQUENCY
`BANDWIDTH EQUAL TO FIRST
`FILTER FREQUENCY
`BAND WIDTH
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`YES
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`720
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`DETERMINE FIRST
`INTERMEDIATE FREQUENCY
`
`FREQUENCY SHIFT FIRST END OF THE DESIRED
`SIGNAL FREQUENCY BANDWIDTH OF THE DESIRED
`SIGNAL TO THE EDGE OF THE FIRST FILTER
`FREQUENCY BANDWIDTH
`
`
`
`
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`ATTENUATE UNDESIRED SIGNALS WITHIN
`FIRST UNDESIRED FREQUENCY SPECTRUM
`730
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`CENTER DESRED SIGNAL
`FREQUENCY BANDWIDTH
`WITHIN FIRST FILTER
`FREQUENCY BANDWIDTH
`715
`
`735
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`DETERMINE SECOND
`INTERMEDIATE FREQUENCY
`
`FREQUENCY SHIFT SECOND END OF THE DESIRED
`SIGNAL FREQUENCY BANDWIDTH OF THE DESIRED
`SIGNAL TO THE EDGE OF THE SECOND FILTER
`FREQUENCY BANDWIDTH
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`
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`
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`740
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`ATTE
`NUATE UNDESIRED SIGNALS WITHIN
`SECON
`M-742
`D UNDESIRED FREQUENCY SPECTRU
`
`745- DEMODULATE DESIRED SIGNAL
`
`Af7 G. 27
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`1
`METHOD AND APPARATUS FOR
`RECEIVING A PLURALITY OF SIGNALS
`HAVING DIFFERENT FREQUENCY
`BANDWDTHS
`BACKGROUND OF THE INVENTION
`This invention relates generally to receivers and Specifi
`cally to a method, apparatus and System for receiving a
`plurality of Signals having different frequency bandwidths.
`Typical communication Systems involve transmitting and
`receiving Signals that have an approximately fixed frequency
`bandwidth. However, Some Systems allow for Signals having
`different bandwidths. For example, one Such System is being
`proposed by the Multimedia Cable Network System
`(MCNS) consortium for data over cable television commu
`nication in the Data Over Cable Service Interface Specifi
`15
`cation (DOCSIS). The specification proposes a standard for
`data communication that will allow for Signals transmitted in
`the upstream direction (from the subscriber to the head-end
`office) to have one of five different bandwidths. Therefore,
`the receivers at the head-end will be required to have the
`ability to receive signals that may have any one of the five
`frequency bandwidths.
`Typical receivers contain a first mixer that shifts the
`incoming signal to an intermediate frequency (IF) before the
`signal is filtered through an IF filter. The IF filter is typically
`chosen to have a frequency pass band that is slightly wider
`than the incoming Signal. Therefore, in Systems that allow
`transmitted Signals to have one of a variety of frequency
`bandwidths, the IF filter will not be able to effectively filter
`a signal with a bandwidth that is Substantially narrower than
`the bandwidth of the IF filter.
`One attempt at Solving this problem includes using mul
`tiple IF filters having different frequency bandwidths and
`Switching the appropriate IF filter into the receiver circuitry
`in order to receive a particular Signal. However, this attempt
`is expensive and requires additional circuitry. In addition,
`this attempt is inefficient Since it requires a finite time to
`Switch from receiving a signal having one bandwidth to a
`Signal having a different bandwidth.
`Therefore, there exists a need for a method, apparatus, and
`System for efficiently and inexpensively receiving a plurality
`of Signals having different frequency bandwidths.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a block diagram of a communication System in
`accordance with a preferred embodiment of the invention.
`FIG. 2 is a graphical representation of an upstream
`frequency spectrum 200 in accordance with the preferred
`embodiment of the invention.
`FIG. 3 is a block diagram of the receiver 122 in accor
`dance with the preferred embodiment of the invention.
`FIG. 4 is a graphical representation of a frequency spec
`trum 400 at an output of the amplifier 312 in accordance
`with the present invention.
`FIG. 5 is graphical representation of a frequency Spectrum
`500 at the output of the band-pass filter 314 in accordance
`with the preferred embodiment of the invention.
`FIG. 6 is graphical representation of a frequency Spectrum
`600 at an output of the low pass filter 320.
`FIG. 7 is a flow chart of method in accordance with the
`preferred embodiment of the invention.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`The present invention provides a method, apparatus, and
`System for efficiently and inexpensively receiving a signal
`having any one of a plurality of frequency bandwidths.
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`An incoming desired signal is shifted Such that one end of
`a frequency bandwidth of the desired signal is shifted to the
`edge of a filter frequency bandwidth of a first filter. The first
`filter attenuates any undesired signals within a first undes
`ired frequency spectrum (outside the frequency bandwidth
`of the first filter). However, the first filter is designed to have
`a frequency bandwidth slightly wider than the widest pos
`sible signal bandwidth. Therefore, if the desired signal that
`is being received has a bandwidth Significantly narrower
`than the first filter, other undesired signals are still present at
`the output of the first filter.
`In this case, the desired signal is shifted Such that a Second
`end of the desired signal is shifted to the edge of a Second
`filter frequency bandwidth. The second filter attenuates
`undesired Signals within a Second undesired frequency Spec
`trum. These undesired signals are the Signals “missed” by
`the first filter.
`Therefore, the first and second filters are designed to filter
`the widest possible desired signal frequency bandwidth but
`are still used to filter narrower Signals by shifting the desired
`Signal to one edge of a first filter frequency bandwidth and
`then to a edge of a Second filter frequency bandwidth.
`Referring to the figures, FIG. 1 is a block diagram of a
`communication system 100 in accordance with the preferred
`embodiment of the invention. In the preferred embodiment,
`the communication system 100 is a cable television (CATV)
`communication system 100 where a primary station (head
`end) 102 Supplies telephone, data, Video and other Services
`to a plurality of Subscriber premises (104-108). The primary
`station (head end) 102 provides these services by commu
`nicating with a plurality of Secondary Stations (Subscriber
`units)(110-114) through a cable communication network
`116. The communication system 100, however, may be any
`one of many types of wired or wireleSS communication
`Systems including telephony, cellular telephony, Video, two
`way radio, microwave and other communication Systems.
`Preferably, the cable communication network 116 consists
`of hybrid fiber/coaxial cables, splitters, amplifiers and other
`equipment as known in the art. Upstream Signals are defined
`as signals transmitted from the secondary stations 110-114
`to the primary Station 102 through the cable communication
`network 116. Downstream Signals are defined as Signals
`transmitted from the primary station 102 to the secondary
`stations 110-114. The primary station 102 includes at least
`one transceiver 118 that includes a transmitter 120 trans
`mitting downstream signals and a receiver 122 receiving
`upstream signals.
`Various communication methods and protocols are known
`for communicating within cable communication Systems
`and for brevity, only a general Overview is presented.
`Preferably, the communication system 100 utilizes TDM
`techniques with a portion of the available frequency Spec
`trum allocated for downstream Signals and another portion
`allocated for upstream Signals. AS discussed in the back
`ground and as discussed in further detail below, the MCNS
`has proposed a specification allowing for upstream Signals to
`have any one of five frequency bandwidths. Preferably, the
`downstream Signals consist of modulated radio frequency
`(RF) carriers conveying real-time video as well as data,
`telephony, Video telephony and other Services using a
`TDMA protocol.
`FIG. 2 is a graphical representation of an upstream
`frequency spectrum 200 in accordance with the preferred
`embodiment of the invention. A desired signal 202 is trans
`mitted within a plurality of Signals 204 according to the
`protocol of the particular communication system 100. The
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`3
`desired signal 202 has a desired signal frequency bandwidth
`206 having a first end 208 and a second end 210. Preferably,
`the desired signal frequency bandwidth 206 is centered
`around a desired signal frequency (Fs). The desired signal
`202 is a signal transmitted by a secondary station 110 that is
`to be received by the primary station 102. As can be seen in
`FIG. 2, the plurality of signals 204 include signals having
`any one of Several frequency bandwidths. In the preferred
`embodiment, the plurality of Signals 204 may have any one
`of five different frequency bandwidths as defined by the
`MCNS proposed specification.
`Referring now to FIG. 3, FIG. 3 is a block diagram of the
`receiver 122 in accordance with the preferred embodiment
`of the invention. A low pass filter 302 receives the incoming
`upstream frequency spectrum 200 and allows only desired
`System signals (potential desired signals that are part of the
`system protocol) to pass. A variable amplifier 304 adjusts the
`amplitude of the incoming upstream Signals to minimize the
`nonlinearities in the receiver 122. In addition, the variable
`amplifier 304 reduces the requirements of an automatic gain
`control (AGC) loop 322 discussed below.
`The filtered and amplified frequency spectrum is fre
`quency shifted by mixing the desired signal 202 and the
`remaining plurality of Signals 204 with a first local oscillator
`Signal (LO1 Signal) in a first mixer (first frequency shifter)
`306. The LO1 signal is produced by a first local oscillator
`(LO1) 308 and a dual synthesizer 310. A controller 311
`determines the value of the LO1 signal based on the fre
`quency of the desired signal 202, the desired Signal fre
`quency bandwidth 206, and other factors as discussed below
`in reference to FIG. 5. The controller 311 sends a control
`signal to the dual synthesizer 310 to set LO1308 to the
`appropriate frequency. The resulting frequency shifted Sig
`nals are amplified by an amplifier 312 in order to maintain
`an acceptable signal to noise ratio throughout the receiver
`Stages.
`FIG. 4 is a graphical representation of a frequency spec
`trum 400 at an output of the amplifier 312 in accordance
`with the present invention. In the preferred embodiment, the
`desired signal bandwidth 206 is centered around a first
`intermediate frequency (IF1) equal to the difference of the
`frequency values of Fs and LO1. The plurality of signals 204
`are frequency shifted Such that each Signal of the plurality of
`Signals 204 is now at a frequency equal to the difference of
`the original frequency of the particular Signal and LO1.
`Preferably, LO1 is higher in frequency than Fs. However,
`various conversion methods can be used, as known in the art,
`depending on the particular requirements of the communi
`cation system 100.
`Referring again to FIG. 3, the frequency shifted Signals at
`the output of the amplifier 312 are filtered by a band-pass
`filter 314. As will be explained below with reference to FIG.
`5, undesired Signals within a first undesired frequency band
`are attenuated by the band-pass filter 314. The band-pass
`filter 314 is designed to have frequency pass-band slightly
`wider than the frequency bandwidth of Signal having the
`largest frequency bandwidth of the plurality of signals 204.
`A number of the plurality of signals (204) within a frequency
`pass-band of the band-pass filter 314, including the desired
`signal 202, pass through the band-pass filter 314.
`FIG. 5 is graphical representation of a frequency Spectrum
`500 at the output of the band-pass filter 314 in accordance
`with the preferred embodiment of the invention. The desired
`signal 202 and other signals 506 within the pass-band (first
`filter frequency bandwidth) 502 of the band-pass filter 314
`are not significantly effected while Signals outside the pass
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`band 502 (in a first undesired frequency spectrum 504) are
`attenuated. AS can be seen in FIG. 5, the first end 208 of the
`desired signal bandwidth is at an edge 508 of the filter
`frequency bandwidth 502. The controller 311 determines
`IF1 to be such that the first edge 208 of the desired signal at
`the edge of the first filter frequency bandwidth 502 of the
`band-pass filter 314. Factors that are used in determining
`LO1 (and therefore IF1) include the frequency of the desired
`signal 202, the desired signal frequency bandwidth 206, a
`frequency response of the band-pass filter (first filter fre
`quency bandwidth) 502 and other criteria as required by the
`particular communication system 100. If the desired signal
`bandwidth 206 has the widest signal of the plurality of
`signals, the desired signal bandwidth 206 is centered within
`the first filter frequency bandwidth 502.
`Referring again to FIG. 3, the Signals that pass through the
`band-pass filter are frequency shifted by mixing the Signals
`at the output of the band-pass filter with a Second local
`oscillator signal (LO2 signal) in a mixer 316. The LO2
`signal is produced by a second local oscillator (LO2) 318
`and the dual Synthesizer 310 using known techniques. In the
`preferred embodiment, the desired signal bandwidth 206 is
`centered around a second intermediate frequency (IF2) equal
`to the difference of the frequency values of LO2 and IF1.
`The controller 311 sends a control signal to the synthesizer
`310 to set the value of LO2. The controller 311 determines
`LO2 (and therefore IF2) based on the desired signal fre
`quency bandwidth 206, the frequency of the desired signal
`(Fs) 202, and a frequency response of a low pass filter 320.
`AS is discussed below, the controller sets IF2 Such that the
`Second edge 210 is at the edge of a filter frequency band
`width (frequency response) of the low pass filter 320.
`FIG. 6 is graphical representation of a frequency spectrum
`600 at an output of the low pass filter 320. The mixer 316
`shifts the desired signal 202 to a frequency equal to the
`difference between LO2 and IF1. AS is shown in FIG. 6, the
`Second edge 210 of the desired Signal frequency bandwidth
`is at the edge of the filter frequency bandwidth 602. The low
`pass filter 320 attenuates signals 606 inside a second undes
`ired signal frequency spectrum 604. Therefore, the only
`signal present at the output of the low pass filter 320 is the
`desired signal 202.
`Referring again to FIG. 3, an automatic gain control
`(AGC) loop 322 is formed by a variable amplifier 324, a low
`pass filter 326, demodulator back-end 328 and a received
`signal strength indicator (RSSI) 330. The AGC loop 322 is
`designed to maintain the amplitude of the desired signal 202
`at a level required by the demodulator back-end 328 using
`known techniques. A filter 326 further filters the desired
`Signal 202 to obtain greater Selectivity and is preferably
`designed to have a slightly wider frequency response than
`the second filter 320 in order to reduce inter-symbol inter
`ference (ISI) distortion while still protecting the demodula
`tor back-end 328 from nonlinear characteristics of variable
`amplifier 324. A data Stream is produced at an output of the
`demodulator back-end 328 that is further processed by the
`receiver 122 using known techniques.
`FIG. 7 is flow chart of a method in accordance with
`preferred embodiment of the invention. An upstream fre
`quency Spectrum is received at the receiver 122 in a primary
`station 102 at step 705.
`At step 710, the controller 311 determines if the desired
`signal frequency bandwidth 206 is equal to the first filter
`frequency bandwidth 502. In the preferred embodiment, the
`controller determines the desired signal bandwidth 206
`based on the particular subscriber unit 110. As dictated by
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`the MCNS specification, a subscriber can only use one of the
`multiple defined bandwidth possibilities. The method pro
`ceeds to step 715 if the desired signal frequency bandwidth
`is equal to first filter frequency bandwidth 502. Otherwise,
`the method continues at step 720.
`At step 715, the desired signal frequency bandwidth 206
`is centered within the first filter frequency bandwidth 502.
`At step 720, the controller 311 determines the first inter
`mediate frequency based on the desired Signal frequency
`bandwidth 206, the first filter frequency bandwidth 602 and
`the desired Signal frequency.
`At step 725, the first end 208 of the desired signal
`frequency bandwidth 206 of the desired signal 202 is shifted
`to the edge 508 of the first filter frequency bandwidth 502 of
`the first filter 314. As explained above, in the preferred
`embodiment, the desired Signal is frequency shifted by
`mixing the desired signal 202 with the first local oscillator
`(LO1) signal in the first mixer 306. In the preferred
`embodiment, LO1 is higher in frequency than Fs. However,
`other methods of frequency shifting the desired signal to IF1
`may be implemented depending on the particular commu
`nication system 100.
`At step the 730, the first filter 314 attenuates the undesired
`Signals within a first undesired frequency spectrum 504. AS
`explained above, Signals outside the first filter frequency
`bandwidth 502 are attenuated by the first filter 314. The
`desired Signal 202 and Some of the plurality of Signals within
`the first filter frequency bandwidth 502 are not substantially
`effected.
`At step 735, the controller 311 determines the second
`intermediate frequency and the Second local oscillator fre
`quency (LO2) based on the desired signal frequency band
`width 206, the second filter frequency bandwidth 602 and
`the desired Signal frequency.
`At step 740, the second end 210 of the desired signal
`bandwidth 206 is frequency shifted to the edge 608 of the
`second filter frequency bandwidth 602 of the second filter
`320. Preferably, the desired signal 202 is frequency shifted
`by mixing the desired signal 202 with LO2 in the second
`mixer (second frequency shifter) 316 to place the desired
`Signal at IF2.
`At step 742, the second filter 314 attenuates the undesired
`Signals within a Second undesired frequency Spectrum 604.
`If the desired signal bandwidth 206 is less than the first filter
`frequency bandwidth 502, the second filter attenuates undes
`ired signals 606 within the filter bandwidth 502.
`At Step 745, the desired signal is demodulated using
`known techniques.
`Therefore, the receiver 122 can receive any of the plu
`rality of signals (204) efficiently and inexpensively although
`the desired signal 202 may have any one of Several fre
`quency bandwidths. The desired signal 202 is shifted to the
`edge 508 of a first filter 314 to attenuate some of the
`undesired signals. The desired signal 202 is then shifted to
`the edge 608 of a second filter 320 to attenuate the remaining
`undesired signals 606 that were not attenuated by the first
`filter 314.
`We claim:
`1. A method comprising the Steps of:
`shifting a first end of a desired Signal frequency band
`width of a desired signal to an edge of a first filter
`frequency bandwidth of a first filter to determine a first
`undesired Signal that is outside the first filter frequency
`bandwidth, wherein the first filter frequency bandwidth
`is greater than the desired signal frequency bandwidth;
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`attenuating the first undesired signal within a first undes
`ired frequency spectrum; and
`shifting a Second end of the desired signal frequency
`bandwidth to an edge of a Second filter frequency
`bandwidth of a second filter to determine a second
`undesired signal that was not attenuated in the attenu
`ating Step.
`2. A method in accordance with claim 1 further compris
`ing the Step of attenuating the Second undesired signal
`within a Second undesired frequency Spectrum.
`3. A method in accordance with claim 2 wherein the Step
`of Shifting the first end of the desired Signal frequency
`bandwidth comprises mixing the desired signal with a first
`local oscillator Signal.
`4. A method in accordance with claim 3 wherein the step
`of shifting the Second end of the desired signal frequency
`bandwidth comprises mixing the desired Signal with a
`Second local oscillator Signal.
`5. A method comprising the Steps of:
`shifting a first end of a desired Signal frequency band
`width of a desired signal to an edge of a first filter
`frequency bandwidth of a first filter wherein shifting
`the first end of the desired signal frequency bandwidth
`comprises mixing the desired Signal with a first local
`Oscillator Signal, wherein the first filter frequency band
`width is greater than the desired signal frequency
`bandwidth wherein the step of shifting the first end of
`the desired Signal includes shifting the desired Signal to
`place the desired signal at a first intermediate frequency
`equal to the difference of a Second local oscillator
`frequency of the Second local oscillator Signal and a
`desired signal frequency of the desired signal;
`attenuating a first undesired signal within a first undesired
`frequency spectrum;
`shifting a Second end of the desired signal frequency
`bandwidth to an edge of a Second filter frequency
`bandwidth of a second filter wherein shifting the sec
`ond end of the desired signal frequency bandwidth
`comprises mixing the desired signal with a Second local
`Oscillator Signal; and
`attenuating a Second undesired signal within a Second
`undesired frequency Spectrum.
`6. A method in accordance with claim 5 wherein the step
`of Shifting the Second end of the desired Signal includes
`shifting the desired signal to place the desired Signal at
`frequency equal to difference of a Second local oscillator
`frequency of the Second local oscillator Signal and the first
`intermediate frequency.
`7. A method in accordance with claim 6 further compris
`ing the Step of determining the first intermediate frequency
`based on the desired signal frequency bandwidth, the fre
`quency of the desired signal, and the first filter frequency
`bandwidth.
`8. A method in accordance with claim 6 further compris
`ing the Step of determining the Second local oscillator
`frequency based on the desired signal frequency bandwidth,
`the frequency of the desired signal, and the Second filter
`frequency bandwidth.
`9. A method comprising the Steps of:
`mixing a desired Signal with a first local oscillator Signal
`to shift a first end of a desired signal frequency band
`width of the desired signal to an edge of a first filter
`frequency bandwidth of a first filter to determine a first
`undesired Signal that is outside the first filter frequency
`bandwidth, wherein the first filter frequency bandwidth
`is greater than the desired signal frequency bandwidth;
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`attenuating a first undesired signal within a first undesired
`frequency spectrum;
`mixing the desired Signal with a Second local oscillator
`Signal to shift a Second end of the desired Signal
`frequency bandwidth to an edge of a Second filter
`frequency bandwidth of a Second filter to determine a
`Second undesired signal that was not attenuated in the
`attenuating Step; and
`attenuating a Second undesired signal within a Second
`undesired frequency Spectrum.
`10. A method in accordance with claim 9 further com
`prising the Step of receiving a frequency spectrum including
`at least the desired signal, the first undesired frequency
`Spectrum, and the Second undesired frequency Spectrum, the
`frequency Spectrum received from a Subscriber unit through
`a cable communication network.
`11. An apparatus comprising:
`a first filter having a first filter frequency bandwidth
`greater than a desired signal frequency bandwidth of a
`desired signal;
`a first frequency shifter adapted to shifting a first end of
`the desired Signal frequency bandwidth of the desired
`Signal to an edge of the first filter frequency bandwidth
`to determine a first undesired Signal that is outside the
`first filter frequency bandwidth;
`a Second filter having a Second filter frequency bandwidth
`greater than the desired Signal frequency bandwidth;
`and
`a Second frequency shifter coupled between the first filter
`and the Second filter and adapted to shifting a Second
`end of the desired signal frequency bandwidth to an
`edge of the second filter frequency bandwidth filter to
`determine a Second undesired Signal that was not
`determined by the first frequency shifter.
`12. An apparatus in accordance with claim 11 wherein the
`first filter is adapted to attenuating a first undesired signal
`within a first undesired signal Spectrum.
`13. An apparatus in accordance with claim 12 wherein the
`Second filter is adapted to attenuating a Second undesired
`Signal within a Second undesired signal Spectrum.
`14. An apparatus in accordance with claim 11 wherein the
`first filter is a band-pass filter.
`15. An apparatus in accordance with claim 11 wherein the
`Second filter is a low-pass filter.
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`8
`16. An apparatus comprising:
`a first filter having a first filter frequency bandwidth
`greater than a desired signal frequency bandwidth of a
`desired signal;
`a first mixer adapted to mixing a first local oscillator
`Signal with the desired signal to Shift a first end of the
`desired Signal frequency bandwidth of the desired
`Signal to an edge of the first filter frequency bandwidth
`to determine a first undesired Signal that is outside the
`first filter frequency bandwidth;
`a Second filter having a Second filter frequency bandwidth
`greater than the desired Signal frequency bandwidth;
`and
`a second mixer coupled between the first filter and the
`Second filter and adapted to mixing a Second local
`Oscillator Signal with the desired signal to shift a Second
`end of the desired signal frequency bandwidth to an
`edge of the Second filter frequency bandwidth to deter
`mine a Second undesired Signal that was not determined
`by the first frequency mixer.
`17. A System comprising:
`a Subscriber unit adapted to transmitting a desired signal
`having any one of a plurality of frequency bandwidths
`through a communication network;
`a primary cable Station comprising:
`a first filter having a first filter frequency bandwidth
`greater than a desired signal frequency bandwidth of
`the desired signal;
`a first frequency shifter adapted to shifting a first end of
`the desired Signal frequency bandwidth of the desired
`Signal to an edge of the first filter frequency bandwidth
`to determine a first undesired signal that is outside the
`first filter frequency bandwidth;
`a Second filter having a Second filter frequency bandwidth
`greater than the desired Signal frequency bandwidth;
`and
`a Second frequency shifter coupled between the first filter
`and the Second filter and adapted to shifting a Second
`end of the desired signal frequency bandwidth to an
`edge of the Second filter frequency bandwidth to deter
`mine a Second undesired Signal that was not determined
`by the first frequency shifter.
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`k
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`MEDIATEK EX. 1023
`Page 9 of 9
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