a2) United States Patent
`US 7,751,513 B2
`(10) Patent No.:
`Jul. 6, 2010
`(45) Date of Patent:
`Eisenhutet al.
`
`US007751513B2
`
`(54)
`
`SIGNAL PROCESSING METHOD,
`PARTICULARLYIN A RADIO-FREQUENCY
`RECEIVER, AND SIGNAL CONDITIONING
`CIRCUIT
`
`(75)
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`1/1990 Eastmondetal.
`4,893,347 A
`6,009,317 A * 12/1999 Wynn ou... eeeeeeeeeeeees 455/296
`6,608,527 B2
`8/2003 Moloudi etal.
`7,099,641 B2*
`8/2006 Bruckmannetal. ...... 455/232.1
`7,317,894 B2*
`1/2008 Hirose 0... eee eee 455/3.02
`2004/0156450 Al*
`8/2004 Auranen etal.
`............ 375/324
`
`FOREIGN PATENT DOCUMENTS
`
`Inventors: Carsten Eisenhut, Miilheim a.d. Ruhr
`(DE); Jens Kissing, Bonen (DE);
`Giuseppe Li Puma, Bochum (DE);
`Dietolf Seippel, Bottrop (DE); Nenad
`Stevanovic, Bochum (DE)
`
`DE 43 19256 C2—12/1994
`Assignee:
`Infineon Technologies AG, Munich
`(73)
`
`DE 10125909 Al=12/2002
`(DE)
`DE
`10131457 Al
`1/2003
`EP
`1143611 Al
`10/2001
`Subject to any disclaimer, the term of this
`Notice:
`
`WO WO 03/092183 A2—11/2003
`patent is extended or adjusted under 35
`US.C. 154(b) by 259 days.
`
`(21)
`
`Appl. No.: 11/592,423
`
`(22)
`
`Filed:
`
`Nov. 3, 2006
`
`Primary Examiner—Ted M Wang
`(74) Attorney, Agent, or Firm—Eschweiler & Associates,
`LLC
`
`(65)
`
`Prior Publication Data
`
`(57)
`
`ABSTRACT
`
`* cited by examiner
`
`A first signal path having an amplifier and a second signal
`path having an amplifier with adjustable gain factor are pro-
`vided. A signal applied to the first and secondsignal pathsis
`amplified and demodulated on thefirst signal path. Concur-
`rently, the signal is amplified on the second signal path witha
`gain factor, and a powerof the signal amplified by the second
`signal path is determined and used for determining the gain
`factor. A signal conditioning circuithas first and secondsig-
`May 4, 2004
`(DE) wee 10 2004 021 867
`nal paths andafirst and a second operating state. In the first
`operating state, the first signal path is arranged for amplifica-
`Int. Cl.
`tion for a demodulation, and the second signal path is
`arranged for amplification for determination of a powerofthe
`signal present. In the second operating state, one of the two
`signal paths is inactive and the otheris arranged for demodu-
`lating the signal present.
`
`US 2007/0116160 Al
`
`May 24, 2007
`
`Related U.S. Application Data
`
`Continuation of application No. PCT/DE2005/
`000845, filed on May 4, 2005.
`
`Foreign Application Priority Data
`
`(2006.01)
`HO4B 1/10
`US. Ch eee 375/349; 375/316; 375/324;
`375/340; 375/345
`Field of Classification Search ................. 375/349,
`375/316, 324, 340, 345
`See applicationfile for complete search history.
`
`(63)
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`(51)
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`(52)
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`(58)
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`15 Claims, 2 Drawing Sheets
`
`a 100
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` Power
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`Detector
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`INTEL 1023
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`

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`U.S. Patent
`
`Jul. 6, 2010
`
`Sheet 1 of 2
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`US 7,751,513 B2
`
`
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`

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`U.S. Patent
`
`Jul. 6, 2010
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`Sheet 2 of 2
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`US 7,751,513 B2
`
`FIG 3
`
`72
`
`04
`
`a 102
`
`
`
`GFSK
`
`GFSK
`
`|
`
`DOPSK, GFSK, QPSK
`
`AC
`
`PH
`
`GS
`
`PL
`
`200
`
`FIG 4
`
`
`FIG 5
`
`

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`US 7,751,513 B2
`
`1
`SIGNAL PROCESSING METHOD,
`PARTICULARLYIN A RADIO-FREQUENCY
`RECEIVER, AND SIGNAL CONDITIONING
`CIRCUIT
`
`REFERENCE TO RELATED APPLICATIONS
`
`This applicationis a continuation of PCT/DE2005/000845
`filed May 4, 2005 which wasnot published in English, that
`claimsthe benefit ofthe priority date of German Patent Appli-
`cation No. DE 10 2004 021 867.6, filed on May 4, 2004, the
`contents of which both are herein incorporated by reference
`in their entireties.
`
`m 0
`
`FIELD OF THE INVENTION
`
`The invention relates to a method for signal processing,
`particularly in a receiver. The invention further relates to a
`signal conditioning circuit.
`
`20
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`BACKGROUNDOF THE INVENTION
`
`Some modern communication standards have the capabil-
`ity of transmitting information with a variable data rate. One
`example of this is the Bluetooth communication standard. In
`this standard, various types of modulation are provided for
`transmitting various datarates. For a data transmission rate of
`1 Mbit/s, frequency shift keying (GFSK modulation) is used
`as a type of modulation. For medium andhigh data transmis-
`sion rates of 2 to 3 Mbit/s, at/4 DQPSK and 8 DPSK modu-
`lation, respectively, are provided as types of modulation.
`Whereas in pure frequency shift keying, information is only
`transmitted over the time of a zero transition, an amplitude
`and a phase of the signal are changed simultaneously in the
`two 1/4 DQPSK and 8 DPSKtypes of modulation which
`produces different requirements for a receiver.
`FIG. 5 showsa typical block diagram ofa receiver system
`for such a mobile communication standard. The received
`
`signal with a frequency f,,.is amplified in a radio-frequency
`input stage 1 with a low-noise amplifier 12 and converted to
`an intermediate frequencyf,,. by means ofa mixer13. For this
`purpose, the mixer 13 uses a local oscillator signal with the
`frequency f;5. The signal converted to the intermediate fre-
`quencyf;,,1s supplied to a complex channelfilter 2 which is
`arranged as a band-pass filter.
`The filtered signal is amplified in a signal conditioning
`circuit 3 and digitized in a downstream analog/digital con-
`verter. In the signal conditioning circuit 3, the filtered signal
`is amplified up to a level whichis suitable for the subsequent
`analog and digital signal processing. For example, the reso-
`lution of the downstream analog/digital converteris utilized
`by the gain set. The receiver path presented here contains a
`numberofdistributed amplifier stages having, in each case,
`individual gain factors which result ina commongain factor.
`Depending on the mobile radio standard used, the gain
`factors in the individual stages are designed differently for
`optimum reception. For example, in the case of pure fre-
`quency modulation in which frequency shift keying is used,it
`is sufficient to work with limiting amplifier stages since there
`is no information contained in the signal amplitude. ‘The
`amplifier stages can be operated, therefore, in limiting mode.
`Higher-valued modulation methods suchas the 2/4 DQPSK
`and 8 DPSK methoddescribed, however, also use amplitude
`and phase information. The amplification of a signal modu-
`lated with such a modulation method therefore requires a
`linear transfer characteristic of the amplifier stages.
`
`40
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`45
`
`2
`To improve the signal/noise ratio of the received signal
`further, it is suitable to amplify the signal greatly, as far as
`possible before any complex signal processing. However,it is
`importantto note that high inputlevels ofa received signalare
`also amplified linearly so that any amplitude information
`which maybepresentis not corrupted. For this reason, mod-
`ern communication systems use active control of the ampli-
`fication in which, for example, the level of the input signalis
`determined and its amplification is adjusted in dependence
`thereon. The associated power measurement, called RSSI
`(radio signal strength indicator) measurement, allows active
`control.
`
`A particular problem occurs with a mobile radio standard
`which changesthe data rate/type of modulation variably dur-
`ing a transmission. Such an exampleis the new versionofthe
`Bluetooth mobile radio standard which operates in packet
`mode. In this mode, header and packet information, in par-
`ticular, is first transmitted in data packets with a low GFSK
`data rate and GFS modulation and then the payload data are
`transmitted with the same or a medium or higher data rate
`with 2/4 DQPSKor 8 DPSK modulation. It is thus necessary
`to determine the receive level of the received data packet and
`from this to suitably adjust the gain factor in dependence on
`the type ofmodulation ofthe payload data in order to prevent
`amplitude or phaseerrors.
`Accordingly, a need exists for a simplified method for
`determining a suitable gain factor, as well as a corresponding
`signal conditioning circuit and methodofuse thereof.
`
`SUMMARYOF THE INVENTION
`
`The present invention overcomes the limitations of the
`prior art by providing a methodfor signal processing, and a
`signal conditioning circuit and method of using the signal
`conditioning circuit in a simple andefficient manner. Accord-
`ingly, the following presents a simplified summary of the
`invention in order to provide a basic understanding of some
`aspects of the invention. This summary is not an extensive
`overview ofthe invention.It is intendedto neitheridentify key
`orcritical elements ofthe invention nor delineate the scope of
`the invention. Its purpose is to present some concepts of the
`invention in a simplified form as a prelude to the more
`detailed description that is presented later.
`In accordance with one aspect of the present invention a
`method and apparatus are provided, wherein a suitable gain
`factor is determined in a simple manner. According to the
`invention, a first signal path with an amplifier and a second
`signal path with an amplifier are provided. The amplifier of
`the secondsignal path has a controllable gain factor. A signal
`is applied to the first and second signal path, wherein the
`signal is amplified in the first signal path. Concurrently, the
`signal on the secondsignalpathis amplified by the gain factor
`and a powerofthe signal appliedto the secondsignal path is
`determined.
`
`The power determined, for example, can be used for later
`adjustmentof a gain factor. As a result, a demodulation and
`measurementofthe signal level is advantageously carried out
`on two different signal paths. This is advantageous since
`errors during the demodulation, which canbe causedbylevel
`measurement, are thus generally avoided. In particular, an
`optimum gain setting can be found andadjusted on the second
`signal path without demodulation errors occurring due to a
`settling process of the amplifier stages.
`Demodulation, for example, is understood to be signal
`processing which generates digital values fromthe received
`signal. This can include, among other things, the conversion
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`US 7,751,513 B2
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`3
`of the received signal into a baseband,andits separation into
`an in-phase component and a quadrature component.
`In one embodiment, one ofthe two signal paths can also be
`switched off depending on information used as an identifier in
`the data content of the demodulated signal. The subsequent
`received signal can be amplified and processed furthervia the
`one signal path. This, for example, allows the current con-
`sumption of a circuit operating in accordance with this prin-
`ciple to be distinctly lowered because only the amplifier path
`needed for the amplification and the demodulation of the
`signalis active. Further, one of the two signal paths can thus
`be selected in dependence on the type of modulation. In
`addition, an amplifier on the first signal path can be arranged
`in a particularly simple and current-saving manneras a lim-
`iting amplifier having only a few stages via the present inven-
`tion.
`The methodof the present invention can be used particu-
`larly advantageously for receiving signals with a variable data
`rate or type of modulation. The method, for example, can be
`utilized for receiving signals according to the Bluetooth
`mobile radio standard. In this context, a signal, such as a
`Bluetooth signal, is amplified with a gain factor on the second
`signal path and the powerofthe received signal is determined.
`Onthefirst signal path, the signal is amplified and suitably
`demodulated at least partially during the demodulation pro-
`cess.
`
`The determined powerallows a suitable gain factor to be
`set for an optimum amplification at a later time of transmitted
`payload data in the signal, such as in the Bluetooth signal.
`Concurrently, informationused as an identifier about the type
`of modulation of the signal used for the payload data can be
`obtained by the demodulation. In a Bluetooth signal, for
`example, information at the beginning of the signal is advan-
`tageously evaluated for this purpose. One of the two signal
`paths, for example, is switched off in dependence on the
`information obtained.
`
`Ina preferred embodiment, the powerofa signal applied in
`the secondsignal path is determined by converting the signal
`into a value- and time-discrete signal. Subsequently,
`the
`amplitude of the converted signal is determined.
`Tn accordance with another aspect ofthe invention,a signal
`conditioning circuit is provided, wherein the signal condi-
`tioning circuit comprises, apart froma first signal path with a
`first amplifier and a secondsignal path with a second ampli-
`fier with adjustable gain factor, a first and a second operating
`state which can be assumed. Inthefirst operating state which
`can be assumed,thefirst signal path is arranged for amplify-
`ing a signal present and for providing the amplified signal for
`demodulation. In the first operating state which can be
`assumed, the second signal path is also arranged for ampli-
`fying the signal present and for determining a powerof the
`signal present. In the second operating state which can be
`assumedbythe signal conditioning circuit, either the first or
`the secondsignal path is arranged for amplifying the signal
`present and for demodulating the amplified signal. In this
`operating state, the other signal path is arranged for reducing
`acurrent or power consumption.In the second operating state
`which can be assumed,oneofthe two signalpathsis suitably
`inactive, whereasthe other signal path is arranged for ampli-
`fying and for providing the amplified signal in a suitable
`manner for demodulation.
`
`According to one exemplary aspect, the signal condition-
`ing circuit of the invention can be advantageously used for
`determining the level of a received signal, and the measured
`power can be delivered as radio signal strength indicator
`signal (RSSJ)to other signal-processing circuits, such as the
`demodulation device. Due, at least in part, to the parallel
`amplification and provision for demodulation in thefirst oper-
`ating state, it is possible to gain time for the settling of the
`
`4
`individual amplifier stages, thus generally avoiding having to
`change the amplification during the reception of payload data
`and thus any possible loss of data.
`Ina preferred embodiment, the amplifier on the first signal
`path is arranged as a limiting amplifier. In another embodi-
`ment, thefirst signal path contains an analog/digital converter
`for the analog/digital conversion of a signal received and
`amplified via the first amplifier. For example, the analog/
`digital converter can be arranged as a XA(sigmadelta) modu-
`lator.
`In yet another embodiment of the invention, the second
`amplifier has an adjusting input for supplying a signal which
`adjusts the gain factor of the second amplifier. The second
`amplifier is thus arranged as an amplifier which can be pro-
`grammed with its gain factor.
`In accordance with another exemplary aspect of the inven-
`tion, the signal conditioning circuit is arranged for receiving
`and for processing signals coded in accordancewith the Blue-
`tooth mobile radio standard. As an alternative, the signal
`conditioning circuit is arranged for processing signals having
`different types of modulation.
`Thus, according to the invention,thefirst signal path can be
`arranged for receiving and demodulating payload data with
`low data rate and GFSK type of modulation, whereas the
`second signal path can be used for receiving payload data
`with a high data transmissionrate. Thus, during the transmis-
`sion of payload data in one example, only one path is ever
`activated. This reduces the current consumption and the
`power consumption. In addition, in the case of a data trans-
`mission with low data transmissionrate,thefirst signal path is
`used, wherein the current consumption thereof is already
`reduced via the arrangement with a simple amplifier. Since
`the first signal path does not need to determine any data
`relating to the powerofthe signalpresent, it can be configured
`in a correspondingly simple manner. Further, the signal con-
`ditioning circuit can be arrangedas an integrated circuit in a
`single semiconductor body.
`To the accomplishmentof the foregoing andrelated ends,
`the invention comprises
`the features hereinafter
`fully
`described and particularly pointed out in the claims. The
`following description and the annexed drawingsset forth in
`detail certain illustrative embodiments of the invention.
`These embodimentsare indicative, however, of a few of the
`various ways in which the principles of the invention may be
`employed. Other objects, advantages and novel features of
`the invention will become apparent from the following
`detailed description ofthe invention when considered in con-
`junction with the drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 illustrates a block diagram of a signal conditioning
`circuit in accordance with one aspectof the invention.
`FIG. 2 illustrates a block diagram ofa first and second
`signal path in accordance with another aspect of the inven-
`tion.
`
`FIG.3 illustrates a structural overview of a signal packet
`according to the Bluetooth mobile radio standard.
`FIG.4 illustrates an exemplary methodfor signal process-
`ing according to the present invention.
`FIG.5 illustrates a block diagram of a conventional receiv-
`ing path.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`The present invention is directed generally to a method for
`signal processing, and a signal conditioning circuit and
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`US 7,751,513 B2
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`5
`method ofuse thereof. Accordingly, the present invention will
`now be described with reference to the drawings, whereinlike
`reference numerals may be used to refer to like elements
`throughout. It should be understood that the description of
`these aspects are merely illustrative and that they should not
`be interpreted in a limiting sense. In the following descrip-
`tion, for purposes of explanation, numerous specific details
`are set forth in order to provide a thorough understanding of
`the present invention. It will be evident to one skilled in the
`art, however, that the present invention may be practiced
`without these specific details.
`Tn accordance with one exemplary aspect ofthe invention,
`FIG.1 illustrates the signal conditioning circuit 100 on a
`receiving path for Bluetooth signals. An antenna 11 is con-
`nected to the first input ofa mixer 13 via a low-noise amplifier
`12. Via the antenna 11, signals according to the Bluetooth
`mobile radio standard can be received at a frequency fp,
`which are converted to an intermediate frequency f,,. with the
`aid of a local oscillator signal at the frequency f,, in the mixer
`13.
`
`m 0
`
`b 5
`
`20
`
`6
`access code AC, into packet information PH and a synchro-
`nization section GS. The preamble and the synchronization
`section, too, are modulated with a special frequency shift
`keying GFSK (Gaussian Frequency Shift Keying). The actual
`payload data PL are then transmitted with variable data rate
`and data length. The data rate is a result of a type of modula-
`tion. This differs and can change between GFSK, 1/4 DQPSK
`and 8 DPSKperdata packet. The type ofmodulation usedfor
`the payload data and the numberof payload data is coded in
`the preamble. Within one data packet, the payload data uses
`the same type of modulation.
`FIG.2 illustrates an exemplary embodimentofthe first and
`second signal paths 6 and 7 of FIG. 1. Accordingly, compo-
`nents having like function carry like reference symbols. The
`present example comprises a limiting amplifier 64 and a
`linear, gain-programmable amplifier 74.
`The limiting amplifier 64 is a part of the first signal path 6
`and built up of'a few stages in a simple manner. Evaluation or
`determination of RSSIdata is carried outvia the linear ampli-
`fier 74 which formsa part of the second signal path 7. The
`RSSI measurement is made at the beginning of a signal
`presentin order to determine a suitable gain factor as quickly
`as possible. In the case of a Bluetooth signal, the RSSI mea-
`surement is carried out during the transmission of the pre-
`amble. Concurrently, the signal is demodulated.
`For this purpose, the signal on the first signal path 6 is
`amplified by the amplifier 64 and supplied to an analog/
`digital converter 65. In the exemplary embodiment,thelatter
`is arranged as a XA modulator and delivers a sequence of
`binary values at its output.
`In the same manner, the second signal path 7 comprises an
`analog/digital converter 76 which, in the exemplary embodi-
`ment, delivers a parallel digital signal consisting of m bitsat
`the output thereof. This is evaluated in the powerdetector 9
`according to FIG. 1 which then determinesthe level of the
`signal. The powerdetector 9 of FIG. 1 is not shown in FIG. 2
`for reasons of clarity, but controls the gain setting of the
`adjustable amplifier 74 via an n-bit-valued signal at a control
`circuit 75.
`
`subsequentsignal processing.
`Parallel signal processing provides a particularly efficient
`method and simple implementation for adjusting the gain in a
`receiver chain. Further,
`the signal conditioning circuit
`according to the invention provides for the reception and
`demodulation of a radio-frequency signal. Due to the time
`gained in the parallel evaluation of the power measurement
`and the demodulation, amplifiers with greater settling times
`can also be used. Overall, it is thus possible to save power and
`area in the case of an integrated implementation.
`FIG. 4 illustrates an exemplary embodiment of a method
`200 for providing generally simultaneous signal processing
`of a Bluetooth signal during an RSSI measurementof the
`signal. In the present example, for purposesofillustration, the
`
`The output of the mixer 13 is connected to an input 61 and
`71 of a first signal path 6 and a secondsignal path 7, respec-
`tively. The two signal paths 6 and 7 can be individually
`activated or disconnected by a correspondingactivation sig-
`nal at their associated inputs 62 and 72. The signal paths 6 and
`7 can thus both be active, both be disconnected, or one ofthem
`be active and the other be disconnected.
`The twosignal paths 6 and 7, for example, are arranged for
`amplifying a signal presentat the respective inputs 62 and 72,
`and for analog/digital conversion and delivery of the ampli-
`fied and digitized signal at respective outputs 63 and 73. For
`this purpose, for example, the signal paths 6 and 7 each
`comprise at least one amplifier and a analog/digital converter
`following the amplifiers.
`The signal output 73 for the digital signal of the second
`signal path 7, for example, leads to an input of a switch 10.
`The switch 10 can assumeoneof at least two possible states,
`wherein, in a first switching state, the switch connects the
`output 73 to an input 91 of a power detector 9. In a second
`In the case of very high input levels, it may occur that the
`switching state, the switch 10 connects the output 73 of the
`low-noise amplifier 12 at the antenna 11 of FIG. 1 already
`secondsignal path 7 to the input 81 of a demodulation device
`amplifies a received signal, and during this process is driven
`8. Furthermore, the output 63 of the first signal path6 is also
`
`connected to the input 81 of the demodulation device 8. into limiting mode. Asaresult, the received signalis already
`The demodulation device 8 demodulates a digital signal
`overdrivenanddistorted. To prevent this case from occurring,
`presentat its input 81 and generates, from this, the data coded
`it is possible to connect one or more evaluating circuits (not
`in accordance with a type of modulation. Furthermore, the
`shown)directly following the mixer 13 or in parallel with the
`modulation device 8 controls the signal paths 6 and 7 via
`arrangement proposed here. The evaluating circuits can be
`signals at an output 82. The modulation device 8, for example,
`arranged, for example, from simple comparators.
`can thus switch off one of the two signal paths 6 or 7.
`Accordingly, a rapid powerestimation is performedand,if
`The power detector 9 determines the level or the power
`necessary, the gain of the low-noise amplifier 12 at the signal
`from a signal presentat its input 91. The corresponding mea-
`input is reduced to such an extent that the input signal is
`surementis also called RSSI measurement. The detector 9 has
`linearly amplified. The amplification via the input amplifieris
`taken into consideration in the RSSI measurement and the
`an output 92 which is connected to anadjusting input 93 ofthe
`modulation device 8 and input 72 of the secondsignal path 7.
`The signals delivered by the detector 9 can thus be used for
`adjusting the gain on the second signal path 7 and in the
`demodulation device 8. As a result, for example, the demodu-
`lation device is able to correcterrors.
`FIG. 3 illustrates a structure ofa data packet 102 according
`to the Bluetooth mobile radio standard as is received by the
`signal conditioning circuit shown in FIG.1 via its antenna 11.
`The precise specification of the standard is open andtrans-
`parent. The data transmission rate can be increased via new
`extensions such as new types of modulation,as in the present
`case. However,the structure of the data packet 102 remains
`constant over all Bluetooth versions. The data packet 102
`contains a preamble which, in turn, is subdivided into an
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`US 7,751,513 B2
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`7
`circuit 100 of FIG. 1 is used in the method 200, and the
`Bluetooth signal is structured as illustrated in FIG. 3. While
`exemplary methodsare illustrated and described herein as a
`series of acts or events, it will be appreciated that the present
`inventionis notlimited bythe illustrated ordering of such acts
`or events, as some steps may occurin different orders and/or
`concurrently with other steps apart from that shown and
`described herein, in accordance with the invention. In addi-
`tion, not all illustrated steps may be required to implementa
`methodology in accordancewiththe present invention. More-
`over, it will be appreciated that the methods may be imple-
`mented in association with the systems illustrated and
`described herein as well as in association with other systems
`notillustrated.
`
`Tn accordancewith the present invention, in act 202 of FIG.
`4, both thefirst ting path and the second transmitting path are
`active during the reception of the preamble and of the syn-
`chronization section GS, wherein the data contained in the
`preamble and in the synchronization word are modulated
`with frequency shift keying. After conversion to the interme-
`diate frequencyf,,. of FIG. 1, for example, these signals are
`supplied to the limiting signal path 6 andto the signal path 7
`operating with linear amplification.
`In act 204 of FIG. 4, the access code AC and the packet
`information PH ofthe preamble of FIG. 3 are conditioned and
`then processed further on the limiting path 6 of FIG. 1. In
`detail, the signal is amplified by a fixed factor. In the present
`example, itis ofno significance whether the amplifier distorts
`the signal, since no information is coded in the amplitude of
`the preamble. Amongotherthings, the preamble content indi-
`cates whether the subsequent payload data PL are transmitted
`with high or low data transmission rates and what type of
`modulation is needed for demodulation. For a low data trans-
`mission rate of 1 Mbit/s, for example, frequency shift keying
`FSK is used, a data transmission rate of 2 Mbit/s uses 2/4
`QPSK modulation, and the high data transmissionrate of 3
`Mbit/s is achieved with 8 DPSK modulation.
`In the case of a low transmission rate and the frequency
`shift keying used therefor, for example, no amplitude infor-
`mation is needed for error-free demodulation of the payload
`data PL. A limiting amplifier of simple configuration is thus
`adequate for this data transmission rate. In the case of the
`mean or high data rate, the linearity should be taken into
`consideration during amplification in order to prevent data
`losses. Depending on the information about the data trans-
`mission rate contained in the preamble, either the first trans-
`mitting path 6 of FIG. 2 with the limiting amplifier 64 or the
`second transmitting path 7 with the linear amplifier 74 is thus
`selected for receiving the payload data.
`In act 204 ofthe method 200 of FIG. 4, for example, the
`received poweris further concurrently determinedin parallel
`via the second signal path 7 with the linear amplifier 74 of
`FIG.2. In the present example, it is assumedthat the average
`received power remains approximately constant even during
`the payload data signal. The level of the input signal deter-
`minedprovides a gain factor wherein sufficiently good signal
`quality can be achieved with good linearity characteristics.
`The input powerof the signal, for example, is determined at
`the lowest amplification of the linear amplifier 74 and on the
`second signal path 7. This generally ensures linear amplifi-
`cation, whereinat high inputlevels, crosstalk and generation
`of intermodulation products is generally prevented.
`The amplification of the linear amplifier 74 on the second
`signal path 7 can be suitably raised step by step. The optimum
`amplification, for example, is achieved whenthe entire reso-
`lutionof the analog/digital converter 76 following the ampli-
`fier 74 is utilized. Using the parallel signal processing, error-
`
`20
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`25
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`8
`free demodulation of the preamble can be carried out with
`simultaneous or concurrent determinationofthe input level of
`the Bluetooth signal.
`In act 206 of FIG. 4, the signal path not used is switched off
`for the reception of payload data. Accordingly, current is
`saved, while optimum amplification of the received signalis
`further possible.
`Usingthe parallel signal paths reduces the average current
`consumption since linear amplifiers needed for the higher
`transmission rates consume more power than a limiting
`amplifier of simple configuration. At low transmissionrates,
`a simple current-saving amplifier is of advantage and the
`linear amplifier is inactive. However, the linear amplifier can
`be further used for the RSSI measurement whichsaves addi-
`
`tional components for an RSSI measurementin the limiting
`amplifier.
`Accordingly, the present invention provides a method for
`signal processing, and a signal conditioning circuit and
`method of using the signal conditioning circuit in a simple
`and efficient manner. It should be noted that although the
`invention has been shown and described with respect to a
`certain preferred embodiment or embodiments, it is obvious
`that equivalent alterations and modifications will occur to
`others skilled in the art uponthe reading and understanding of
`this specification and the annexed drawings. In particular
`regard to the various functions performed by the above
`described components (assemblies, devices, circuits, etc.),
`the terms (including a reference to a “means”) used to
`describe such components are intended to correspond, unless
`otherwise indicated, to any component which performs the
`specified function of the described component(i.e., that is
`functionally equivalent), even thoughnot structurally equiva-
`lent to the disclosed structure which performsthe function in
`the herein illustrated exemplary embodiments of the inven-
`tion. In addition, while a particular feature of the invention
`may have been disclosed with respect to only one of several
`embodiments, such feature may be combined with one or
`more other features of the other embodiments as may be
`desired and advantageousfor any given orparticular applica-
`tion.
`
`Whatis claimed is:
`
`1. A methodfor signal processing in a receiver, the method
`comprising:
`providing a first signal path and a second signal path,
`wherein the first signal path comprisesa first amplifier,
`and wherein the second signal path comprises a second
`amplifier having a controllable gain factor;
`applying a signal to the first and second signal paths,
`wherein the signal appliedto the first and second signal
`paths is the same signal;
`amplifying the signal on the first signal path, therein defin-
`ing a first amplified signal, and demodulating the first
`amplified signal to generate digital values associated
`with the amplified signal;
`amplifying the signal on the second signal path based on an
`initial gain factor, therein defining a second amplified
`signal;
`digitizing the second amplified signal, therein defining a
`digitized signal having an amplitude associated there-
`with;
`determining a powerof the signal applied to the second
`signal path based on the amplitudeofthe digitized sig-
`nal; and
`controlling the gain factor of the second amplifier based on
`the determined power; and
`
`

`

`US 7,751,513 B2
`
`10
`the switch, whereinthe gain factor of the second ampli-
`fier is controlled based on the determined powerof the
`present signal, and wherein
`ina second operatingstate, one ofthefirst signal path or the
`second signal path is configured for amplifying the
`present signal and for providing the respective first or
`second amplified signal to the demodulation device, and
`the other respective first or second signal path is deacti-
`vated for reducing pow