WO1998013943A1 - Procede et dispositif servant a detecter et a eliminer une modulation indesirable d'emetteur - Google Patents

Procede et dispositif servant a detecter et a eliminer une modulation indesirable d'emetteur Download PDF

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Publication number
WO1998013943A1
WO1998013943A1 PCT/US1997/016974 US9716974W WO9813943A1 WO 1998013943 A1 WO1998013943 A1 WO 1998013943A1 US 9716974 W US9716974 W US 9716974W WO 9813943 A1 WO9813943 A1 WO 9813943A1
Authority
WO
WIPO (PCT)
Prior art keywords
die
phase
amplifier
signal
transmitter
Prior art date
Application number
PCT/US1997/016974
Other languages
English (en)
Other versions
WO1998013943A9 (fr
Inventor
Mark A. Jones
Original Assignee
Ericsson Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ericsson Inc. filed Critical Ericsson Inc.
Priority to AU47372/97A priority Critical patent/AU4737297A/en
Publication of WO1998013943A1 publication Critical patent/WO1998013943A1/fr
Publication of WO1998013943A9 publication Critical patent/WO1998013943A9/fr

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G3/00—Gain control in amplifiers or frequency changers
    • H03G3/20—Automatic control
    • H03G3/30—Automatic control in amplifiers having semiconductor devices
    • H03G3/3036—Automatic control in amplifiers having semiconductor devices in high-frequency amplifiers or in frequency-changers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03C—MODULATION
    • H03C1/00—Amplitude modulation
    • H03C1/02—Details
    • H03C1/06—Modifications of modulator to reduce distortion, e.g. by feedback, and clearly applicable to more than one type of modulator
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/34—Negative-feedback-circuit arrangements with or without positive feedback
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/20—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers
    • H03F3/24—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers of transmitter output stages
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/02—Transmitters
    • H04B1/04—Circuits
    • H04B1/0475—Circuits with means for limiting noise, interference or distortion
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/02—Transmitters
    • H04B1/04—Circuits
    • H04B2001/0408—Circuits with power amplifiers
    • H04B2001/0433—Circuits with power amplifiers with linearisation using feedback

Definitions

  • the present invention address the problem of unwanted radio transmitter modulations that adversely impact radio reception of transmitted information, and in particular, to a method and apparatus for detecting and greatly reducing/eliminating such unwanted transmitter modulation.
  • a radio transmitter In real world radio transmission applications, a radio transmitter is susceptible to a number of external disturbances and influences which ultimately generate unwanted modulations in the transmitted signal, including unwanted phase modulations, frequency modulations, and/or amplitude modulations.
  • the radio transmitter is susceptible to fluctuations in the automobile's electrical system.
  • the automobile's alternating current (AC) alternator is usually unregulated in frequency and amplitude.
  • AC alternating current
  • the actual voltage supplied at the vehicle's battery terminals fluctuates.
  • changes in engine RPM cause periodic power supply fluctuations referred to as "ripple.”
  • These amplitude and/or frequency fluctuations can result in undesirable modulation of the transmitted signal, which when demodulated at the radio receiver, cause an audible "whine.”
  • Fig. 1 is a function block diagram of a vehicular-based mobile radio transmitter which includes a conventional 12 volt alternator battery supply 12.
  • Radio transmitter 10 includes synthesizer/modulator circuitry 14 for generating a modulated signal which is preamplified in exciter 16 and then amplified in power amplifier 18 before being transmitted via an antenna.
  • the automobile power supply system generates unwanted transmitter frequency modulation in the transmitted signal resulting in signal whine at the radio receiver.
  • Prior art methods to minimize alternator whine employ a filter similar to filter 20 shown in Fig. 1 including a series-connected inductor 22 coupled through capacitor 24 to ground.
  • the filter 20 removes some of the undesired components generated by the power supply 12. Some of the undesired modulation frequency components are not blocked by filter 20 causing fluctuations in power supply to the power amplifier 18 which result in the undesired frequency/phase modulations described above.
  • the filter's inductive coil 22 is both large and expensive. Inductor 22 must be large enough in order to handle the large currents generated by power supply 12. In addition, inductor 22 and capacitor 24 must both be of relatively large value (further adding to the filter's size) to effectively filter the lower frequency range in which alternator whine is generated. As result, a filter that achieves acceptable levels of whine reduction is bulky and expensive. It is an object of the present invention to detect and cancel unwanted transmitter modulations accurately and inexpensively.
  • a novel radio transmitter architecture is used to detect and cancel or substantially reduce undesired modulations or other disturbances, e.g., alternator whine, on the transmitted signal.
  • the novel transmitter architecture detects and includes in the feedback signal of a phase-locked loop (PLL) of the radio transmitter a small amount of the transmitted signal being routed to the antenna.
  • PLL phase-locked loop
  • the radio transmitter in accordance with the present invention includes a phase-locked loop which receives an input signal and a feedback signal.
  • An amplifier stage amplifies the output from the phase-locked loop, and an antenna transmits the amplified signal.
  • a signal detector such as a directional coupler detects the transmitted signal and generates the feedback signal. Inclusion of the amplifier stage in the feedback portion of the phase-locked loop compensates for undesirable transmitter modulation introduced at the amplifier stage. In essence, the phase-locked loop modulates the desired modulation of the RF carrier with the information to be transmitted, and at the same time, also rejects undesired modulation. Additional components such as the bulky and expensive filter components described above are not needed.
  • the radio transmitter includes a differencer such as a phase detector which receives an input signal from a frequency or phase modulator as well as the feedback signal to generate a difference or error signal.
  • a loop filter/amplifier couples the output of the phase detector to a voltage-controlled oscillator (VCO) which drives the difference signal to zero.
  • VCO voltage-controlled oscillator
  • the present invention includes the amplifier stage (which may include an exciter and a power amplifier) in the feedback loop.
  • the VCO is controlled to drive the phase difference or error which effectively includes the undesired modulation to zero thereby eliminating or at least substantially reducing the undesired modulation in the transmitted signal.
  • the undesirable modulation may be caused in part by fluctuations in the transmitter power supply.
  • the radio transmitter includes a phase-locked loop frequency synthesizer which receives an input signal and a first feedback signal.
  • An amplifier amplifies the output from the phase-locked loop which is then transmitted via an antenna.
  • a first detector detects the amplified signal and generates the firs sti - O ' ⁇ feedback signal. Inclusion of the amplifier * a * txlthe phase-locked loop compensates for undesired transmitter phase or frequency variations.
  • a second detector detects the amplitude of the transmitted signal. The difference between the detected amplitude and a predetermined power setting is determined to generate a second feedback signal for controlling the gain of the amplifier. The second feedback loop further compensates for undesirable transmitter amplitude modulations.
  • the present invention also provides a method for operating a radio transmitter that includes a phase-locked loop and an amplifier stage which includes a power amplifier.
  • a phase difference between an input signal and a feedback signal is used to drive the phase-locked loop.
  • the transmitted signal is detected and used to generate the feedback signal.
  • including the power amplifier in the phase-locked loop compensates for undesirable transmitter variations, and in particular, undesirable transmitter phase or frequency variations.
  • the amplitude of the transmitted signal may also be detected and compared with a predetermined power setting to generate a second feedback signal for controlling the gain of the power amplifier.
  • the second feedback loop further compensates for undesirable transmitter amplitude variations.
  • Fig. 1 is a function block diagram of a conventional radio transmitter which employs a discrete filter to reduce power supply alternator whine;
  • Fig. 2 is a function block diagram of an example radio transmitter employing the present invention
  • Fig. 3 is a function block diagram of another example embodiment of the present invention.
  • Fig. 4 is a function block diagram of still another example embodiment of the present invention.
  • the present invention may be applied to any radio transmitter application where a disturbance to the radio transmitter generates an undesirable variation/modulation in the transmitted output signal.
  • the present invention may be applied in a radio base station/repeater or omer fixed radio transmitter to eliminate undesirable modulations that might result from a 50/60 Hertz based power supply system providing power to the radio transmitter power amplifier.
  • Another example application of the present invention might be to disturbances to the transmitter other than those generated by a power supply such as radio microphonic disturbances, e.g., a vibrating cooling fan, etc.
  • Audio or data information which is ultimately to be transmitted is input to a frequency or phase modulator 52 to modulate an intermediate frequency (IF) local oscillator signal generated by frequency synthesizer 72.
  • IF intermediate frequency
  • the modulated IF signal is then processed in phase detector 54 along with a loop feedback signal to generate a phase difference or phase error signal.
  • a loop filter 56 which may be for example a high gain amplifier with a controlled frequency response, provides an amplified difference/error signal to a voltage-controlled oscillator (VCO) 58.
  • VCO 58 changes the phase/frequency of its output signal to drive the detected phase error/difference to zero.
  • the VCO output is amplified by an amplifier stage 59 which may include for example an exciter 60 connected to a power amplifier 62.
  • the output of power amplifier 62 is transmitted by way of antenna 64.
  • the power supply to the power amplifier 62 fluctuates or includes some other disturbance, e.g., alternator whine. Such changes in the voltage supply amplitude and frequency ultimately result in undesired frequency or phase modulations in the transmitted signal.
  • a directional coupler 66 detects the transmitted signal output by the power amplifier 62 and feeds that signal to an optional amplitude limiter 68 and downconverter mixer 70 to the phase detector 54 thereby completing die feedback loop/phase-locked loop.
  • Mixer 70 downconverts the detected RF signal using a RF local oscillator signal generated by frequency synthesizer 72. This is done because phase detectors typically are designed for frequencies lower than RF. However, higher frequency phase detectors are available, and if used, would eliminate the need for downconverter mixer 70 in the feedback path.
  • Limiter 68 although optional is nonetheless preferable because it effectively strips the amplitude from the detected transmitted signal leaving only phase information including phase disturbances in the feedback loop. 5
  • the frequency or phase modulator 52 although preferred, is not necessary in the transmitter architecture.
  • the audio or data may be routed directly to the phase detector 54 thereby eliminating the frequency or phase modulator 52 assuming that the phase-locked loop
  • phase-locked loop 10 makes the necessary RF upconversion.
  • the main elements of the phase- locked loop are phase detector 54, loop filter 56 (preferable but not absolutely necessary), voltage-controlled oscillator 58, one or more including power amplifier 62, y- 6> " Bidweciional ⁇ coupler 66, the output of which is coupled back to the phase
  • phase-locked loop as defined above, other advanced types of feedback loops may also be used.
  • a frequency synthesizer may incorporate a phase- locked loop along with other components like frequency dividers, frequency multipliers, etc.
  • the present invention exploits the operation of the negative feedback loop to eliminate (or at least substantially minimize) any disturbance within the loop.
  • the amplifier stage which in the example embodiment in Fig. 2 includes
  • the feedback loop is unable to compensate for disturbances like alternator fluctuations in the power supply to the power amplifier.
  • the loop forces the phase of the feedback signal to match the phase of the input signal, and in that way, eliminates the undesirable phase modulation in the transmitted signal caused by the external disturbance without requiring additional costly and/or bulky filters.
  • the feedback, phase-locked loop bandwidth needs to be greater than the bandwidth of the disturbance which would otherwise result in undesired transmitter modulation.
  • the response time of the loop to eliminate or substantially minimize the error/difference detected by phase detector 54 must be faster than the speed with which the disturbance is changing. Therefore, the highest frequency component of the disturbance, (i.e., the part of the disturbance that is changing most rapidly), should be included within the bandwidth characteristic of the feedback phase-locked loop. Disturbance frequency components which exceed the loop bandwidth will end up as undesired modulations in the transmitted signal.
  • the feedback loop dynamically and immediately cancels or at least substantially cancels unwanted disturbances such as power supply ripple effects in the amplitude of the power amplifier output signal. Both phase and amplitude of the transmitted signal can be detected and controlled to cancel unwanted disturbances like alternator whine.
  • the inventor of the present invention designed the embodiment of Fig. 2 and tested it to observe the achieved reduction in hum and noise at die antenna output. With simulated alternator noise present, the present invention as implemented in the embodiment of Fig. 2 dramatically reduced such hum and noise from approximately -33 dB, which resulted when the power amplifier was not included in the feedback, phase-locked loop, to -57 dB when the power amplifier was included in the feedback, phase-locked loop.
  • Fig. 3 is a simplified diagram showing a synthesizer/phase-locked loop block 74 along with a second feedback loop. Similar to how me phase-locked loop (the first feedback loop) in Fig. 2 detects and cancels unwanted phase disturbance in the power amplifier output, the second feedback loop in Fig. 3 detects and cancels amplitude disturbances in me power amplifier output. Reducing amplitude fluctuations is advantageous when transmitting to a companion receiver which exhibits less than ideal immunity to undesired AM (amplitude modulation) components.
  • AM amplitude modulation
  • the transmitted signal detected by coupler 66 is routed both to limiter 68 as in the embodiment shown in Fig. 2 and also to an RF level detector (e.g., an envelope detector) 74 which detects the amplitude of the transmitted output.
  • the detected amplitude is compared to a predetermined RF power setting in a differential amplifier 76 (for example) which generates a difference signal used to control the gain of exciter 60 to maintain the desired power level.
  • the bandwidth of this second feedback loop should also be greater than the bandwidd of the disturbance.
  • the feedback of the phase-locked loop is the transmitted signal output from the power amplifier rather than the output of the synthesizer/phase-locked loop 74.
  • the second feedback loop may also be connected to control the gain of the power amplifier.
  • Fig. 4 shows another example embodiment of the present invention.
  • the block diagram of Fig. 4 is similar to that shown in Fig. 3 except that limiter 68 is preferably included in the first feedback loop.
  • the limiter 68 is added to the first feedback loop in Fig. 4 for the reasons set forth above with regard to the preferred embodiment illustrated in Fig. 2.
  • the embodiment shown in Fig. 4 may be advantageous when the phase detector is particularly sensitive to input power levels and thus requires constant input levels. In that situation, the limiter 68 evens out the input power thereby improving the performance of the phase detector. With a less sensitive phase detector, however, the limiter may not be necessary, and the embodiment in Fig. 3 may be more appropriate.
  • Both embodiments shown in Figs. 3 and 4 have me additional advantage of dynamically cancelling power supply ripple effects or other disturbances in d e amplitude of the power amplifier output.
  • unwanted phase or frequency disturbances can be detected and compensated for by the first feedback loop and undesired amplitude modulations may be detected and compensated for in the second feedback loop.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Transmitters (AREA)
  • Amplifiers (AREA)

Abstract

Détection et annulation d'une modulation indésirable d'émetteur qui sinon exercerai un effet désagréable au niveau d'une radio recevant le signal émis. L'émetteur radio comprend une boucle à verrouillage de phase recevant un signal d'entrée et un signal de rétroaction. Un étage amplificateur amplifie une sortie depuis la boucle à verrouillage de phase et une antenne transmet le signal amplifié. Un détecteur détecte le signal transmis et génère le signal de rétroaction. L'inclusion de l'étage amplificateur dans la boucle à verrouillage de phase équilibre la modulation indésirable d'émetteur introduite au niveau dudit étage. Un exemple de l'invention s'applique à des systèmes radio basés sur un véhicule, dans lesquels l'émetteur radio est sensible au bruit généré par le système électrique du véhicule et arrivant au récepteur radio sous forme de sifflement. L'invention permet de limiter considérablement ou d'éliminer ce sifflement perçu au niveau du récepteur.
PCT/US1997/016974 1996-09-26 1997-09-24 Procede et dispositif servant a detecter et a eliminer une modulation indesirable d'emetteur WO1998013943A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU47372/97A AU4737297A (en) 1996-09-26 1997-09-24 Method and apparatus for detecting and cancelling unwanted transmitter modulation

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US72133496A 1996-09-26 1996-09-26
US08/721,334 1996-09-26

Publications (2)

Publication Number Publication Date
WO1998013943A1 true WO1998013943A1 (fr) 1998-04-02
WO1998013943A9 WO1998013943A9 (fr) 1998-07-30

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PCT/US1997/016974 WO1998013943A1 (fr) 1996-09-26 1997-09-24 Procede et dispositif servant a detecter et a eliminer une modulation indesirable d'emetteur

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WO (1) WO1998013943A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1017162A2 (fr) * 1998-12-30 2000-07-05 Texas Instruments Incorporated Circuit amplificateur à boucle de contre-réaction négative pour réduire la distortion
WO2001065684A1 (fr) * 2000-03-03 2001-09-07 Siemens Aktiengesellschaft Procede et circuit d'emission destines a produire un signal d'emission

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3831094A (en) * 1973-08-30 1974-08-20 Collins Radio Co Means to prevent coincidental phase modulation in an amplitude modulation transmitter
US4147985A (en) * 1977-07-29 1979-04-03 Rogers Noel A Low level modulation system for a radio transmitter
US5014351A (en) * 1989-06-05 1991-05-07 Motorola, Inc. Method and apparatus for reducing alternator noise
US5511239A (en) * 1993-05-18 1996-04-23 U.S. Philips Corporation Mobile radio system/transmitter with a controllable power amplifier

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3831094A (en) * 1973-08-30 1974-08-20 Collins Radio Co Means to prevent coincidental phase modulation in an amplitude modulation transmitter
US4147985A (en) * 1977-07-29 1979-04-03 Rogers Noel A Low level modulation system for a radio transmitter
US5014351A (en) * 1989-06-05 1991-05-07 Motorola, Inc. Method and apparatus for reducing alternator noise
US5511239A (en) * 1993-05-18 1996-04-23 U.S. Philips Corporation Mobile radio system/transmitter with a controllable power amplifier

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1017162A2 (fr) * 1998-12-30 2000-07-05 Texas Instruments Incorporated Circuit amplificateur à boucle de contre-réaction négative pour réduire la distortion
EP1017162A3 (fr) * 1998-12-30 2003-07-16 Texas Instruments Incorporated Circuit amplificateur à boucle de contre-réaction négative pour réduire la distortion
WO2001065684A1 (fr) * 2000-03-03 2001-09-07 Siemens Aktiengesellschaft Procede et circuit d'emission destines a produire un signal d'emission

Also Published As

Publication number Publication date
AU4737297A (en) 1998-04-17

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