WO2012166060A1 - Procédé et dispositif de pré-distorsion d'amplificateur en bande large non linéaire - Google Patents

Procédé et dispositif de pré-distorsion d'amplificateur en bande large non linéaire Download PDF

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Publication number
WO2012166060A1
WO2012166060A1 PCT/SI2012/000033 SI2012000033W WO2012166060A1 WO 2012166060 A1 WO2012166060 A1 WO 2012166060A1 SI 2012000033 W SI2012000033 W SI 2012000033W WO 2012166060 A1 WO2012166060 A1 WO 2012166060A1
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WO
WIPO (PCT)
Prior art keywords
signal
component
inphase
frequency band
predistorted
Prior art date
Application number
PCT/SI2012/000033
Other languages
English (en)
Inventor
Matjaz BRESKVAR
Rok PIRNAT
Blaz KELBL
Original Assignee
Beyond Devices D.O.O.
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
Priority claimed from SI201100203A external-priority patent/SI23781A/sl
Priority claimed from SI201100208A external-priority patent/SI23782A/sl
Priority claimed from SI201100282A external-priority patent/SI23817A/sl
Application filed by Beyond Devices D.O.O. filed Critical Beyond Devices D.O.O.
Publication of WO2012166060A1 publication Critical patent/WO2012166060A1/fr

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Classifications

    • 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
    • H03F1/32—Modifications of amplifiers to reduce non-linear distortion
    • H03F1/3241—Modifications of amplifiers to reduce non-linear distortion using predistortion circuits
    • H03F1/3294—Acting on the real and imaginary components of the input signal
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/336—A I/Q, i.e. phase quadrature, modulator or demodulator being used in an amplifying circuit

Definitions

  • the presented invention relates to the method for compensation of amplifier nonlinearity, especially in case of wideband signal transmission, as well as to the device based on that method.
  • nonlinear precorrection, nonlinear predistortion with baseband digital predistortion being the most commonly employed.
  • An alternative solution represents frequency selective nonlinear predistortion which is based on the principle of splitting the signal into multiple narrow frequency bands.
  • Each of the bands is independently processed through a circuitry for digital baseband predistortion with complex multiplication and the result combined into a final signal. Since implementing a large number of narrow band signals is technically too complex, a suitable approximation may be achieved by splitting the signal into two frequency bands, an upper frequency band above the carrier frequency and a lower frequency band below the carrier frequency.
  • the Hilbert transform may be used for the purpose of splitting the signal into two frequency bands.
  • the presented solution is based on processing of a baseband modulated signal comprised of an inphase and a quadrature component use of the Hilbert transform is limited.
  • the Hilbert transform does not transfer DC and low frequency components in its basic form suitable for implementation. This property limits its use to systems which lack a DC component in modulated signal (e.g. IEEE 802.1 l g) since generally modulated signals exhibit the highest power spectral density close to the DC component.
  • modulated signal e.g. IEEE 802.1 l g
  • the goal of the invention is to devise a method for nonlinear predistortion of a wideband amplifier to address shortcomings of known solutions as well as to design a device for nonlinear predistortion of a wideband amplifier.
  • the inphase component and quadrature component of an arbitrarily modulated wideband signal are transformed into a real-valued signal at intermediate frequency whereby said real signal is split into an upper band and a lower band signal using filtering.
  • Each band is further split into an inphase and a quadrature component which enables the technique for baseband digital predistortion with complex multiplication to be employed.
  • the baseband signal scaled in amplitude and rotated in phase is converted into a radio signal with an arbitrary carrier frequency using a quadrature mixer and a digital to analog converter.
  • the device for nonlinear predistortion of a wideband amplifier includes a predistortion circuit fed by parallel inphase and quadrature components of an arbitrarily modulated wideband signal.
  • Said predistortion circuit is cascaded with at least one corresponding mixer, followed by an adder, the output of which is further connected to a digital-analog converter.
  • Said converter is cascaded with a signal shaping filter and a high power amplifier.
  • fig. 1 illustrates a device with nonlinear predistortion of the wideband amplifier in accordance with the preferred embodiment of the invention
  • fig. 2 illustrates the predistortion circuit of the device of fig.1
  • the inphase and quadrature component of the arbitrarily modulated signal and their inverse components are fed into a multiplexer which uses sampling frequency to select between input samples.
  • the said inverse components are generated with a -1 multiplier arranged in front of said multiplexer.
  • the multiplexer with the -1 multiplier at the input represents a very straightforward realization of a mixer which simplifies the entire procedure.
  • a sampling frequency of at least four times the highest frequency component of the sampled signal is required to preserve integrity of the predistorted signal in discrete form regardless of the embodiment of the predistortion device.
  • the resulting signal generated from said multiplexer is then split into two equal parallel signals with the first signal fed into a lowpass filter rejecting the upper frequency band and the second signal fed into a highpass filter rejecting the lower frequency band from said signal.
  • the filtered signals generated from each of the said filters are further fed into a lower and upper transmission circuit whereby, according to the presented invention, it is assumed that both transmission circuits are identical and mutually parallel. According to the invention the characteristic of said filters is chosen in such a way that the sum of their amplitude responses in the frequency domain forms unity.
  • the characteristic of the lowpass filter passes signals unmodified in frequency range from the DC component to the fs/4 -fc frequency component where the characteristic of said lowpass filter equals unity (in a strictly mathematical sense) and does not allow signals to pass through a stopband of said filter above the fs/4 + fc frequency component.
  • the transition band between frequencies fs/4 - fc and fs/4 + fc takes the form of a raised cosine in the range between 0 and ⁇ .
  • the characteristic of said highpass filter does not allow a signal to pass through a stopband from DC to fs/4 - fc frequency component and passes signals unmodified above fs/4 +fc where the characteristic of said highpass filter equals unity (in a strictly mathematical sense).
  • the transition band between the frequency components fs/4 - fc and fs/4 + fc takes the form of a raised sine in the range between - ⁇ /2 and ⁇ /2.
  • fs denotes sampling frequency
  • fc denotes the parameter of said filters to adjust the slope of the transition band of said filters.
  • the signal generated from said lowpass filter is split through a demultiplexer in the lower transfer circuit into two signal pairs which consist of a signal and its inverse value generated with -1 multiplier.
  • Each pair of a signal and its inverse value is fed from the demultiplexer into its own interpolation filter which alternately takes samples of a signal and its inverted value every second clock cycle. Consequently, the generated signal from each said interpolation filter represents the inphase and quadrature component of the lower frequency band.
  • a filtered signal generated from said interpolation filter of the upper transfer circuit represents the inphase and quadrature component of the upper frequency band.
  • Each pair of said filtered signals generated from said pair of said interpolation filters is fed into a complex multiplier which simultaneously scales the inphase and quadrature component according to a selected signal from a table stored in a memory which is not mandatorily equal for the upper and the lower frequency band.
  • K2 denotes constants whose product equals the size of each said memory block
  • ind denotes the value which in turn determines how many times the -instantaneous power a of non-predistorted signal needs to be doubled in order not to exceed a predefined threshold in front of a complex multiplier;
  • rem denotes the value dependent on the amplified instantaneous power of a non- predistorted signal.
  • / / denotes the signal generated from the first filter of the lower transfer circuit which represents the inphase component of a lower frequency band signal
  • Iq denotes the signal generated from the second filter of the lower transfer circuit which represents the quadrature component of a lower frequency band signal
  • uqi denotes the signal generated from the second filter of the upper transfer circuit which represents the quadrature component of an upper frequency band signal.
  • a pair of scaled signals generated from said multiplier of each transfer circuit is fed into an adder summing the inphase component of the lower frequency band with the inphase component of the upper frequency band and the quadrature component of the lower frequency band with the quadrature component of the upper frequency band.
  • Each sum of said signals now represents said inphase component and said quadrature component of the predistorted signal which is further fed through the mixer of the device of the preferred embodiment of the invention.
  • the device for predistortion of a nonlinear wideband amplifier includes predistortion circuit 1 which is fed by parallel inphase component 2 and quadrature component 3 of an arbitrarily modulated wideband signal.
  • Said predistortion circuit 1 transforms said components 2, 3 into inphase component 4 and quadrature component 5 of the predistorted signal fed from said circuit 1 through corresponding mixer 6,7 which converts the baseband signal into a radiofrequency signal and further into adder 8.
  • Said components 4, 5 of the predistorted signal are summed in said adder 8 and fed further into a digital-to-analog converter as a single predistorted signal 9.
  • the analog signal generated from said converter 10 is fed into signal shaping filter 11 and high power amplifier 12 transmitting resulting signal 13.
  • the inverse amplitude-amplitude and amplitude-phase characteristic of the upper and lower output signal frequency band (relative to the input signal) of said amplifier 12 is stored in memory 14, 15 of said predistortion circuit.
  • said predistortion circuit 1 includes multiplexer 16 fed by said inphase component 2 and said quadrature component 3 of an arbitrarily modulated signal and their inverse components 2', 3'. Said inverse components 2', 3' are generated with -1 multiplier 17, 18 of each signal 2,3 arranged in front of said multiplexer 16. Said multiplexer 16 selects between said signals 2, 3, 2' and 3' at the input with sampling frequency. Since a predistorted signal occupies a wider frequency band (with regard to the input signal) the sampling frequency of at least four times the highest frequency component of the sampled signal is required to preserve integrity of the predistorted signal in a discrete form regardless of the embodiment of the predistortion device.
  • Resulting signal 19 generated from said multiplexer 16 is split into two equal parallel signals with the first signal fed into lowpass filter 22 which rejects the upper frequency band from said signal 19 and the second signal fed into highpass filter 23 which rejects the lower frequency band from said signal 19.
  • the filtered signal generated from each filter 22, 23 is fed into lower transfer circuit 20 and upper transfer circuit 21 whereby according to the invention it is assumed that both transmission circuits are identical and mutually parallel.
  • the frequency characteristic of said filters 22, 23 is chosen in such a way that the sum of their amplitude responses forms unity.
  • the characteristic of said lowpass filter 22 passes signals unmodified in frequency band range from the DC component to the fs/4 - fc frequency component where the characteristic of said lowpass filter 22 equals unity (in a strictly mathematical sense) and does not allow signals to pass through a stopband of said filter 22 above fs/4 + fc frequency component.
  • the transition band between frequencies fs/4 - fc and fs/4 + fc takes the form of a raised cosine in the range between 0 and ⁇ .
  • the characteristic of said highpass filter 23 does not allow the signal to pass through a stopband from the DC to fs/4 - fc frequency component and passes signals unmodified above fs/4 + fc where the characteristic of said highpass filter 23 equals unity (in a strictly mathematical sense).
  • the transition band between the frequencies fs/4 - fc and fs/4 + fc takes the form of a raised sine in the range between - ⁇ /2 and ⁇ /2.
  • fs denotes sampling frequency
  • fc denotes the parameter of said filter 22, 23 to adjust the slope of the transition band of said filter.
  • said transmission circuit 20 includes demultiplexer 23, cascaded with a pair of parallel interpolation filters 25, 26.
  • the signal generated from lowpass filter 22 is split by said demultiplexer 24 into two signals and through -1 multiplier also their inverse values.
  • said filters 25, 26 alternately take samples of a signal and its inverted value every second clock cycle. Consequently, signal 29 generated from said first filter 25 represents the inphase component of the lower frequency band and signal 30 generated from said second filter 26 represents the quadrature component of the lower frequency band.
  • signal 31 generated from said first filter 25 of the upper transfer circuit -21 represents the inphase component of the upper frequency band and signal 32 generated from said second filter 26 of the upper transfer circuit 21 represents the quadrature component of the upper frequency sideband.
  • Signal pairs 29, 30; 31, 32 generated from each filter pair 25, 26 are fed into complex multiplier 33 which scales the amplitude of the inphase and quadrature component according to the selected signal from the table stored in memory 14, 1 .
  • Ki, K.2 denotes constants whose product equals the size of each said memory block 14,
  • ind denotes the value which in turn determines how many times does the instantaneous power of the non-predistorted signal need to be doubled in order not to exceed a predefined threshold in front of a complex multiplier
  • rem denotes the value dependent on the amplified instantaneous power of non- predistorted signal a.
  • / denotes signal 29 generated from the first filter 25 of lower transfer circuit 20 which represents inphase component 36 of the lower frequency band signal
  • uii denotes signal 31 generated from the first filter 25 of upper transfer circuit 21 which represents inphase component 38 of the upper frequency band signal
  • Iqi denotes signal 30 generated from the second filter 26 of lower transfer circuit 20 which represents quadrature component 37 of the lower frequency band signal
  • uqi denotes signal 32 generated from the second filter 26 of upper transfer circuit 21 which represents quadrature component 39 of the upper frequency band signal.
  • the pairs of scaled signals 36, 37; 38, 39 generated from said multiplier 33 of each transfer circuit 20, 21 are further fed into adder 40, 41, where inphase component 36 of the lower frequency band is added to inphase component 38 of the upper frequency band and quadrature component 37 of the lower frequency band is added to quadrature component 39 of the upper frequency band.
  • adder 40, 41 Inphase component 36 of the lower frequency band is added to inphase component 38 of the upper frequency band and quadrature component 37 of the lower frequency band is added to quadrature component 39 of the upper frequency band.
  • Each sum of each said signal pair 36, 38; 37, 39 represents said inphase component 4 and said quadrature component 5 of the predistorted signal fed through corresponding mixer 6,7 of the preferred embodiment of the invention.
  • the disclosed solution allows for independent dual band adjustment of frequency selective compensation of a high power amplifier's nonlinear characteristic. Its processing does not require feedback from the output and in case of identical table values in both said memory blocks performs equal to digital baseband predistortion with complex multiplication. In this case the inverse characteristic of a high power amplifier can be determined with the same methods as for digital baseband predistortion with complex multiplication. If all values in both tables equal unity the signal traverses the device unmodified.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Transmitters (AREA)
  • Amplifiers (AREA)

Abstract

L'invention concerne un système pour une compensation de fonction de transfert non-linéaire d'amplificateurs haute puissance, notamment dans le cas de la transmission de signaux en bande large. Selon l'invention, le signal d'entrée comprenant une composante en phase et de quadrature d'un signal de bande de base numérique modulé arbitrairement est soumis à une pré-distorsion dans un circuit de pré-distorsion, puis est converti de la bande de base à la bande radiofréquence. Après la conversion numérique-analogique, le signal analogique est ensuite traité avec un filtre de mise en forme et amplifié par un amplificateur haute puissance. La pré-distorsion d'un signal de bande de base complexe repose sur un processus consistant à diviser le signal d'entrée en bandes latérales supérieure et inférieure. Les bandes individuelles sont indépendamment soumises à une pré-distorsion par le biais d'une multiplication complexe par des coefficients stockés dans deux mémoires indépendantes. La sélection du coefficient repose sur la puissance instantanée du signal d'entrée total. Les composantes en phase et de quadrature des bandes latérales supérieure et inférieure sont additionnées par paires en composantes en phase et de quadrature d'un signal de sortie soumis à pré-distorsion.
PCT/SI2012/000033 2011-06-03 2012-06-01 Procédé et dispositif de pré-distorsion d'amplificateur en bande large non linéaire WO2012166060A1 (fr)

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
SIP-201100203 2011-06-03
SI201100203A SI23781A (sl) 2011-06-03 2011-06-03 Naprava za kompenzacijo nelinearnosti širokopasovnega ojačevalnika
SIP-201100208 2011-06-13
SI201100208A SI23782A (sl) 2011-06-13 2011-06-13 Postopek kompenzacije nelinearnosti širokopasovnega ojačevalnika
SI201100282A SI23817A (sl) 2011-07-29 2011-07-29 Postopek samodejne kompenzacije nelinearnih popačenj močnostnega ojačevalnika
SIP-201100282 2011-07-29

Publications (1)

Publication Number Publication Date
WO2012166060A1 true WO2012166060A1 (fr) 2012-12-06

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20020034260A1 (en) * 2000-09-15 2002-03-21 Lg Electronics Inc. Adaptive predistortion transmitter
US20040142667A1 (en) * 2003-01-21 2004-07-22 Lochhead Donald Laird Method of correcting distortion in a power amplifier
US7106806B1 (en) * 1999-06-30 2006-09-12 Andrew Corporation Reducing distortion of signals
WO2008106364A1 (fr) * 2007-02-26 2008-09-04 Harris Corporation Linéarisation d'amplificateurs de puissance rf utilisant un générateur de prédistorsion de sous-bande adaptatif

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7106806B1 (en) * 1999-06-30 2006-09-12 Andrew Corporation Reducing distortion of signals
US20020034260A1 (en) * 2000-09-15 2002-03-21 Lg Electronics Inc. Adaptive predistortion transmitter
US20040142667A1 (en) * 2003-01-21 2004-07-22 Lochhead Donald Laird Method of correcting distortion in a power amplifier
WO2008106364A1 (fr) * 2007-02-26 2008-09-04 Harris Corporation Linéarisation d'amplificateurs de puissance rf utilisant un générateur de prédistorsion de sous-bande adaptatif

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