METHOD FOR PRODUCING AN AMPLIFICATION STAGE FOR A VARIABLE ENVELOPE SIGNAL

Abstract

Disclosed is a method for producing a stage for amplifying the power of a variable envelope signal including at least one amplifier. For each amplifier, a form of ideal variation in average power POUT.sub.L is selected. For each value of each setting parameter and for each average input power value, a value of an optimisation criterion is calculated on the basis of the mathematical expectation of at least one optimisation parameter. An optimum value of each setting parameter is determined and the amplification stage is produced with a number of amplifiers in parallel determined on the basis of an average output power value and with, for each amplifier, matching circuits providing the optimum values of the setting parameters. The invention also relates to an amplification stage produced in this manner.

Claims

1-15. (canceled)

16. Method for producing a stage for amplifying the power of a variable envelope input signal having a predetermined instantaneous power statistical distribution, this amplification stage comprising at least one amplifier (32) and matching circuits (33, 34, 35) determining setting parameters, the value of which influences average power POUT(PIN), phase PM(PIN), and consumption PDC(PIN) transfer functions of the amplification stage, the method comprising: for each amplifier (32), selecting a form of ideal variation in average power POUT.sub.L(PIN) which can be derived at any point and which can be obtained by suitably selecting the matching circuits (33, 34, 35), for each amplifier (32), calculating, for each value of each setting parameter and for each input average power PIN value, a value of an optimisation criterion on the basis of the mathematical expectation of at least one optimisation parameter associated with the average output power of the amplifier, this mathematical expectation being calculated with said instantaneous power statistical distribution of the input signal and from at least said ideal variation in average power POUT.sub.L(PIN), for each amplifier (32), selecting from each value of the optimisation criterion an optimum value of each setting parameter representing an optimisation of the optimisation criterion of the amplifier (32), and determining a corresponding average output power value of the amplifier, producing the amplification stage with a number N of amplifiers (32) in parallel determined on the basis of an average output power value to be provided by the amplification stage and with, for each amplifier (32), matching circuits (33, 34, 35) providing said optimum values of the setting parameters.

17. Method according to claim 16, wherein the optimisation criterion is selected from among the average output power POUTk of the amplifier (32); the consumption PDCk of the amplifier (32); the power dissipated by the amplifier (32); and an amplifier (32) yield determined by the ratio between the average output power POUTk and the consumption PDCk; and combinations thereof.

18. Method according to claim 16, wherein at least one optimisation parameter is selected from among the average output power POUTk of the amplifier (32) and the consumption PDCk of the amplifier (32), each value of the optimisation criterion being calculated on the basis of the mathematical expectation, with the statistical distribution of the input signal, of this optimisation parameter from at least said ideal variation in average power POUT.sub.L(PIN).

19. Method according to claim 16, wherein at least one optimisation parameter is the consumption PDCk of the amplifier (32), the method further comprising: characterising (11) each amplifier (32), using a testbed measuring and recording, for each value of each setting parameter, characteristic variations on the basis of the average input power PIN, of the average power POUTcw(PIN) and of the consumption PDCcw(PIN) from a constant envelope signal applied to the input of the testbed, for each amplifier (32), calculating, for each value of each setting parameter, an ideal variation of the consumption PDC.sub.L(PIN) on the basis of the average input power PIN, from said ideal variation in average power POUT.sub.L(PIN) and said characteristic variations, and wherein each value of the optimisation criterion is determined on the basis of the mathematical expectation, with the statistical distribution of the input signal, of the consumption PDC.sub.L(PIN) obtained from said ideal variation of the consumption PDC.sub.L(PIN) on the basis of the average input power PIN.

20. Method according to claim 19, further comprising a step of characterising each amplifier (32), using a testbed measuring and recording, for each value of each setting parameter, characteristic variations, on the basis of the average input power PIN, of the phase shift PMcw(PIN) of the amplifier (32) from the constant envelope input signal, wherein the matching circuits (33, 34, 35) are selected to obtain a phase shift with a predetermined value, in particular zero.

21. Method according to claim 16, wherein said form of ideal variation in average power POUT.sub.L(PIN) is an affine variation to a greater start of saturation value.

22. Method according to claim 16, wherein the input signal comprises a modulation in accordance with a predetermined modulation scheme.

23. Method according to claim 22, wherein the variable envelope input signal has an instantaneous power probability density of the input signal determined on the basis of the scheme of the modulation of the communication signal.

24. Method according to claim 16, wherein said form of ideal variation in average power POUT.sub.L(PIN) is selected on the basis of a performance criterion of the amplification stage selected from among a signal/noise ratio value and an intermodulation rate.

25. Method according to claim 16, wherein the input signal is a microwave frequency signal.

26. Method according to claim 16, wherein at least one amplifier (32) being a transistor, said setting parameters are selected from the group consisting of at least one biasing voltage and at least one load impedance characteristic.

27. Method according to claim 16, wherein at least one amplifier (32) being a travelling-wave tube, said setting parameters are selected from the group consisting of a beam current, helix voltage and collector voltage.

28. Method according to claim 16, wherein the amplification stage providing a predetermined average output power POUT, for each amplifier (32), an average output power value POUTk of the amplifier (32) is determined for the optimum values of each setting parameter, and wherein the number N of amplifiers in parallel of the amplification stage is selected such that:
?.sub.1.sup.N-1POUTk?POUT??.sub.1.sup.NPOUTk

29. Method according to claim 16, wherein the amplification stage is produced with a plurality of identical amplifiers (32).

30. Stage for amplifying the power of a variable envelope input signal having a predetermined instantaneous power statistical distribution, this amplification stage comprising at least one amplifier (32) and matching circuits (33, 34, 35) determining setting parameters, the value of which influences average power POUT(PIN), phase PM(PIN), and consumption PDC(PIN) transfer functions of the amplification stage, wherein: it comprises, for each amplifier (32), matching circuits (33, 34, 35) providing optimum values of the setting parameters of the amplifier (32), these optimum values being determined from values of an optimisation criterion calculated for each value of each setting parameter, and so as to represent an optimisation of the optimisation criterion of the amplifier (32), the values of the optimisation criterion being calculated on the basis of the mathematical expectation of at least one optimisation parameter associated with the average output power of the amplifier, this mathematical expectation being calculated with said instantaneous power statistical distribution of the input signal and from at least one ideal variation in average power POUT.sub.L(PIN) of the amplifier (32), it comprises a plurality of amplifiers (32) in parallel, the number N of which is determined on the basis of an average output power value to be provided by the amplification stage such that:
?.sub.1.sup.N-1POUTk?POUT??.sub.1.sup.NPOUTk

31. Method according to claim 17, wherein at least one optimisation parameter is selected from among the average output power POUTk of the amplifier (32) and the consumption PDCk of the amplifier (32), each value of the optimisation criterion being calculated on the basis of the mathematical expectation, with the statistical distribution of the input signal, of this optimisation parameter from at least said ideal variation in average power POUT.sub.L(PIN).

32. Method according to claim 17, wherein at least one optimisation parameter is the consumption PDCk of the amplifier (32), the method further comprising: characterising (11) each amplifier (32), using a testbed measuring and recording, for each value of each setting parameter, characteristic variations on the basis of the average input power PIN, of the average power POUTcw(PIN) and of the consumption PDCcw(PIN) from a constant envelope signal applied to the input of the testbed, for each amplifier (32), calculating, for each value of each setting parameter, an ideal variation of the consumption PDC.sub.L(PIN) on the basis of the average input power PIN, from said ideal variation in average power POUT.sub.L(PIN) and said characteristic variations, and wherein each value of the optimisation criterion is determined on the basis of the mathematical expectation, with the statistical distribution of the input signal, of the consumption PDC.sub.L(PIN) obtained from said ideal variation of the consumption PDC.sub.L(PIN) on the basis of the average input power PIN.

33. Method according to claim 18, wherein at least one optimisation parameter is the consumption PDCk of the amplifier (32), the method further comprising: characterising (11) each amplifier (32), using a testbed measuring and recording, for each value of each setting parameter, characteristic variations on the basis of the average input power PIN, of the average power POUTcw(PIN) and of the consumption PDCcw(PIN) from a constant envelope signal applied to the input of the testbed, for each amplifier (32), calculating, for each value of each setting parameter, an ideal variation of the consumption PDC.sub.L(PIN) on the basis of the average input power PIN, from said ideal variation in average power POUT.sub.L(PIN) and said characteristic variations, and wherein each value of the optimisation criterion is determined on the basis of the mathematical expectation, with the statistical distribution of the input signal, of the consumption PDC.sub.L(PIN) obtained from said ideal variation of the consumption PDC.sub.L(PIN) on the basis of the average input power PIN.

34. Method according to claim 16, wherein said form of ideal variation in average power POUT.sub.L(PIN) is an affine variation to a greater start of saturation value.

35. Method according to claim 17, wherein said form of ideal variation in average power POUT.sub.L(PIN) is an affine variation to a greater start of saturation value.

Description

[0048] Other aims, features and advantages of the invention will become apparent upon reading the following description of a non-limiting exemplified embodiment of a method in accordance with the invention and with reference to the attached figures in which:

[0049] FIG. 1 is a logic diagram of the main steps of a method in accordance with one embodiment of the invention,

[0050] FIG. 2 is a schematic diagram illustrating the average output power POUT variations on the basis of the average input power PIN of an amplifier,

[0051] FIG. 3 is a diagram illustrating a matching linearization circuit associated with an amplifier for implementation of a method in accordance with the invention,

[0052] FIGS. 4a to 4c are diagrams illustrating examples of statistical distribution (histograms of the numbers of occurrences of amplitude values) of signals in accordance with three modulation schemes, respective 7 APSK, 16 APSK and 16 QAM,

[0053] FIG. 5 is a diagram illustrating an amplification stage in accordance with the invention produced by a method in accordance with the invention.

[0054] A method for producing an amplification stage shown in FIG. 1 comprises a first step 11 of characterising each amplifier 12 of the amplification stage. In this step 11, an amplifier 32 formed of a field effect transistor is placed in a testbed (not shown) of the type referred to as load pull, for example as described by the publication Caract?risation en puissance aux fr?quences millim?triques de circuits nanom?triques en technologie silicium M. de Matos, E. Kerherv?, H. Lapuyade, J-B. B?gueret, Y. Deval, 10?rnes journees pedagogiques CNFM (CNFM 2008), November 2008, St Malo, France. pp. 111-116. The drain Vd and gate Vg biasing voltage values and the actual value of the load impedance Z and its power factor ? are varied. Using this testbed, for each value of each of these setting parameters Vd, Vg, Z, ?, the characteristics of the variations of the average output power POUTcw(PIN) and of the consumption PDCcw(PIN) of the amplifier as a function of the average power PIN of a constant envelope input signal Scw are measured and recorded.

[0055] An example of a variation of the average power POUTcw(PIN) of the amplifier for a constant envelope input signal is shown in FIG. 2 by a curve of dashed lines. In practice, this variation can be recorded in the form of a table comprising a column of values of the average input power PIN, a column of measured values of the average output power POUTcw and a column of measured values of the consumption PDCcw.

[0056] Furthermore, in this characterising step 11, characteristic variations, on the basis of the average input power PIN, of the phase shift PMcw(PIN) of the amplifier from the constant envelope input signal are likewise measured and recorded in this same table with the testbed for each value of each setting parameter.

[0057] However, it is not possible to optimise the setting of the amplifier from measurements taken with a constant envelope input signal when this amplifier is intended to be used with a variable envelope input signal.

[0058] During the subsequent step 12, a linearization circuit 33 placed upstream of the amplifier 32 and able to provide a form of ideal variation in average output power POUT.sub.L(PIN) which can be derived at any point is selected. In the example in FIG. 2, this ideal variation POUT.sub.L is a variation comprising a first linear portion (affine in reality) to a maximum value POUTmax of saturation of the average output power of the amplifier, with a curved transition which can be derived at any point between the linear portion and the saturation portion. Other examples are possible, and there are numerous matching circuits which allow various forms of ideal variation in average output power of the amplifier to be obtained.

[0059] In particular, this linearization circuit 33 allowing an ideal variation in average output power to be obtained is selected on the basis of a performance criterion which it is desirable to impose on the amplifier, e.g. a value of the signal/noise ratio or of an intermodulation rate at the maximum saturation power, and which is known to be satisfactory for said ideal variation. Thus, in the example shown in FIG. 2, it is known in particular that it is possible to obtain a value of the signal/noise ratio at the saturation power which is e.g. equal to 15 dB by suitably selecting the linearization circuit 33. Therefore, by adopting this linearization circuit 33, it is ensured that the amplifier 32 will provide an output signal which will be in accordance with this performance criterion. Furthermore, the linearization circuit 33 is selected so as to obtain a phase shift of a predetermined value, preferably zero, in the amplified output signal.

[0060] A method for selecting such a linearization circuit 33 is described in French patent application FR1453773. Numerous other known linearization variants can be used in this regard. The characteristics of the electronic circuits allowing the selected variation form to be obtained can be determined in the case of a microwave frequency signal in particular as described by C. W. Park et al., An Independently Controllable AM/AM and AM/PM Predistortion Linearizer for CDMA 2000 Multi-Carrier Applications, IEEE 2001. At lower frequencies, these characteristics can be determined from digital systems, such as equivalence tables (O. Hammi, S. Boumaiza, F. M. Ghannouchi, On the Robustness of Digital Predistortion Function Synthesis and Average Power Tracking for Highly Nonlinear Power Amplifiers, IEEE transactions on microwave theory and techniques, vol. 55, no. 6, June 2007; Nagata Y., Linear amplification technique for digital mobile communications, 39th IEEE Vehicular Technology Conference, May 1989, pp. 159-164; Faulkner M, Mattson T., Yates W., Adaptive linearization using predistortion, 40th of the IEEE Vehicular Technology Conference, May 1990, pp. 35-40).

[0061] As a variant, a parameterizable linearizer circuit can likewise be used, such as the Lintech (US) linearizers in the WAFL series, compatible with the frequency range and average power range provided for the input signal, and for which the variations of the average power and phase shift transfer functions (or profiles) which it produces are predetermined and known for different values of the adjustable parameters of this parameterizable linearizer circuit. A set of parameters of the linearizer circuit is selected such that the average power and phase shift transfer functions produced by this linearizer circuit correspond most closely to the sought-after ideal variation. The choice of a set of adjustable parameters of the linearizer circuit thus allows the selection of an ideal variation in average power POUT.sub.L(PIN) which can be derived at any point. In practice, this ideal variation in average outlet power POUT.sub.L(PIN) is represented by an additional column of the values of the average output power POUT.sub.L in accordance with this ideal variation in the table mentioned above.

[0062] Once the ideal variation in average power POUT.sub.L(PIN) has been selected, it is possible, if the consumption is selected as the optimisation parameter, to recalculate, for each value of each setting parameter, Vg, VD, Z, ?, an ideal variation of the consumption PDC.sub.L(PIN) on the basis of the average input power PIN, from said ideal variation in average power POUT.sub.L(PIN) and said measured variations POUTcw(PIN) and PDCcw(PIN). In fact, the above-mentioned table correlates the values of the measured consumption for the constant envelope signal PDCcw on the basis of the values of the measured output power for the constant envelope signal POUTcw.

[0063] For example, the above-mentioned table is the following:

TABLE-US-00001 Line i, j PIN POUT.sub.cw PDC.sub.cw POUT.sub.L PDC.sub.L 1 0 3 2 2 1 2 2 8 6 5 4 3 4 12 10 7 6 4 6 16 13 10 8 5 8 19 16 12 10 6 10 22 18 15 13 7 12 24 19 18 14 8 14 25 20 20 16 9 16 26 20 23 16 10 18 26 20 25 20 11 20 26 20 26 20

[0064] In order to calculate PDC.sub.L(i) at line i, the following linear interpolation formula is used for example:

PDC.sub.L(i)=POUT.sub.L(i)?[POUTcw(j)?POUTcw(j?1)]/[PDCcw(j)?PDCcw(j?1)]

with j being the selected line such that:

POUTcw(j)?POUT.sub.L(i)?POUTcw(j?1)

[0065] Other forms of interpolation can be selected.

[0066] If the measured values and those representative of the ideal variation are sufficient in number, there will exist, as shown in FIG. 2, a value of j for which:

POUTcw(PIN(j))=POUT.sub.L(PIN(i)),

and PDC.sub.L(PIN(i)) could be taken to equal PDCcw(PIN(j)).

[0067] Then (step 13, FIG. 1), the instantaneous power statistical distribution of the variable envelope input signal to be amplified, which is predetermined, in particular in accordance with the modulation scheme, is used to calculate an optimisation criterion during step 14.

[0068] In fact, it proves to be the case that the signals, such as the communication signals, modulated on one (or more) carrier(s) have an instantaneous power statistical distribution which depends only on the modulation scheme. FIG. 4a thus illustrates the form of histograms of numbers of occurrences of amplitude values of signals modulated in accordance with a 7APSK modulation (modulation of amplitude and phase with 7 symbols); FIG. 4b illustrates the form of histograms of the numbers of occurrences of amplitude values of signals modulated in accordance with a 16APSK modulation (modulation of amplitude and phase with 16 symbols); FIG. 4c illustrates the form of histograms of the numbers of occurrences of amplitude values of signals modulated in accordance with a 16QAM modulation (quadrature modulation of amplitude with 16 symbols). If the modulation scheme, or more generally the instantaneous power statistical distribution of a signal, is known the probability density D.sub.Se (Pi) of the average power of the signal Se on the basis of each value of instantaneous power Pi of the signal Se is known. In practice, this statistical distribution can be in the form of a table of discrete values from which numerical calculations are performed, or of an analytical function or an analytical, e.g. polynomial, approximation of the probability density. Therefore, the mathematical expectation of the average power of such a signal Se can be calculated (by numerical calculation over discrete values or with an analytical function).

[0069] In accordance with the invention, the probability density D.sub.Se(Pi) of the average power of the variable envelope input signal Se to be amplified on the basis of each value of instantaneous power Pi of this variable envelope input signal Se to be amplified is used to calculate, in step 14, the mathematical expectation of at least one optimisation parameter linked with the average power of the amplified output signal, from at least said ideal variation in average power POUT.sub.L(PIN). Advantageously, at least one such optimisation parameter is selected from among the average output power POUTk of the amplifier and the consumption PDCk of the amplifier.

[0070] The choice of each optimisation parameter depends upon the optimisation criterion of the amplifier which it is desired to retain, which itself depends on the application of the amplification stage to be produced.

[0071] For example, in particular for space applications, an electric yield determined by the ratio between the average output power POUTk and the consumption PDCk is preferably used as the optimisation criterion. In this case, the average output power POUTk and the consumption PDCk of the amplifier are thus used as the optimisation parameter. Therefore, in step 14, for each value of each setting parameter Vd, Vg, Z, ?, the mathematical expectation of these optimisation parameters is calculated according to the following formulae:

E.sub.POUT.sub.L[Pi]=?.sub.0.sup.?P.sub.OUT.sub.L(Pi).Math.D.sub.Se(Pi).Math.dPi

E.sub.PDC.sub.L[Pi]=?.sub.0.sup.?PDC.sub.L(Pi).Math.D.sub.Se(Pi).Math.dPi

[0072] And the yield ?:

[00001]$?=\frac{E_{{\mathrm{POUT}}_L}?\left[\mathrm{Pi}\right]}{E_{{\mathrm{PDC}}_L}?\left[\mathrm{Pi}\right]}$

[0073] In practice, these formulae are implemented by statistical formula applications in the tables of values giving D.sub.Se(Pi) and P.sub.OUT.sub.L(Pi) using a spreadsheet. As a variant, a calculation can be made at least for the analytical portion, from an analytical function (or an analytical approximation) of the probability density D.sub.Se(Pi) and an analytical, e.g. polynomial, approximation of P.sub.OUT.sub.L(Pi).

[0074] As a variant, an optimisation criterion other than the yield can be used. For example, only the value of the average output power POUTk can be used as the optimisation criterion, in which case in step 14 only the mathematical expectation of the average output power E.sub.POUT.sub.L[Pi] is calculated. If only the consumption PDCk is used as the optimisation criterion, in step 14 only the mathematical expectation of the consumption E.sub.PDC.sub.L[Pi] is calculated. If only the dissipated power DISSk is used as the optimisation criterion, in step 14 only the mathematical expectation of the dissipated power is calculated:

E.sub.DISS.sub.L[Pi]=E.sub.PDC.sub.L[Pi]?E.sub.POUT.sub.L[Pi]

[0075] It should be noted that each mathematical expectation is calculated from the ideal variation of the corresponding optimisation parameter, i.e. at least from the ideal variation in average power POUT.sub.L(PIN). By thus using an amplifier 32 corrected by matching circuits 33, 34 and 35, such an ideal variation can in fact be used to calculate each mathematical expectation used to calculate an optimisation criterion, whilst ensuring that the amplifier will satisfy predetermined performance criteria linked with the previously made choice of this ideal variation. For example, by using a linearized ideal variation as indicated above, it can be ensured that the amplifier will provide a predetermined signal/noise ratio or intermodulation rate for any value of its average output power.

[0076] At the end of step 14, the different calculations of the optimisation criterion for each value of each setting parameter Vd, Vg, Z, ? are recorded in a table.

[0077] In the subsequent step 15, an optimum combination of the values of setting parameters Vd, Vg, Z, ? is determined from the table of calculated values of the optimisation criterion, in order to optimise this optimisation criterion of the amplifier. Therefore, the optimum combination which provides the highest numerical value ?.sub.max of the yield ? or that which provides the highest numerical value Max[POUTk] of the average output power POUTk or that which provides the lowest numerical value Min[PDCk] of the consumption PDCk is determined e.g. in the table.

[0078] A precise and complete optimisation of the setting of the amplifier is obtained in a simple manner, taking into account the different setting parameters and performance criteria of the amplifier, regardless of what this optimisation criterion is and regardless of what the technology of the amplifier and the corresponding setting parameters are.

[0079] Therefore, such an optimum combination of values of setting parameters of an amplifier can be determined according to the method in accordance with the invention not only for amplifiers formed of field effect transistors (solid-state circuits) but also for travelling-wave tubes, the setting parameters thus typically being the beam current Ik dictated by the voltage VA.sub.0, the helix voltage Vh and the collector voltages Vc1,2,3,4. Steps 11 to 15 can in fact be implemented with these setting parameters.

[0080] Similarly, there is nothing to prevent the selection of any other form of ideal variation than that shown in FIG. 2, in accordance with the required performance criteria. For example, it is possible to provide an over-power zone at the apex of the linearized portion of the ideal variation to increase the average output power close to saturation to a greater extent than this linearized variation. That being said, it is appropriate to select an ideal variation which, on the one hand, can be effected by electronic matching circuits and, on the other hand, corresponds to a physical reality, i.e. does not have any discontinuity and can be derived at any point.

[0081] Once the optimum combination of the setting parameters of each amplifier k has been determined, the value of the average output power POUTk=E.sub.POUT.sub.L[Pi] of the amplifier corresponding to this optimum combination is known, and in step 16 the number N of amplifiers A1, A2, . . . Ak, . . . , AN, to be used in the amplification stage is determined such that the average output power POUT of the amplification stage can be obtained by placing a plurality of amplifiers A1, A2, . . . Ak, . . . , AN in parallel, as shown in FIG. 5, if necessary.

[0082] The number N of amplifiers A1, A2, . . . Ak, . . . , AN in parallel is determined such that:

?.sub.1.sup.N-1POUTk?POUT??.sub.1.sup.NPOUTk

[0083] Preferably, when a plurality of amplifiers in parallel are used to produce the amplification stage, all the amplifiers are identical. However, there is nothing to prevent the use of different amplifiers, but this requires the steps of optimising the setting parameters to be repeated for each amplifier.

[0084] Therefore, in a method in accordance with the invention, given an average output power POUT, at least one performance criterion (e.g. a signal/noise ratio and/or an intermodulation rate), and an instantaneous power statistical distribution, an optimum combination of the setting parameters of each amplifier k, a corresponding value of average output power POUTk=E.sub.POUT.sub.L[Pi] of each amplifier and a number N of amplifiers to be used are determined so as to obtain the average output power POUT of the amplification stage. It should be noted in this regard that the average power of the input signal is not a given constraint but is determined to correspond to the optimum combination of the setting parameters of each amplifier and to the corresponding average output power POUTk.

[0085] As shown in FIG. 3, when field effect transistors are used as amplifiers, the amplification stage comprises, for each amplifier 32, an upstream linearization circuit 33 (allowing in particular an ideal variation of the average output power of the amplifier to be obtained), an output load impedance 34 and a biasing device 35 providing the biasing voltages Vg, Vd of the transistor 32. The linearization circuit 33, the output load impedance 34 and the biasing device 35 are matching circuits of the amplification stage. These matching circuits 33, 34, 35 have fixed characteristics corresponding to the optimum values of the setting parameters and do not depend in particular dynamically on the characteristics of the input signal. Of course, if the amplification stage comprises a plurality of such identical amplifiers 32, it is possible to use a single linearization circuit 33 common to the various amplifiers 32, a single output circuit forming the load impedance 34 for all of the amplifiers 32 and a single biasing circuit 35 providing the various biasing voltages to the various transistors in parallel.

[0086] It should be noted that in a method in accordance with the invention, the optimisation of the setting parameters of each amplifier if favoured over the number of amplifiers possibly used in parallel and over the value of the average output power or that of the average input power. In fact, the inventor was able to show, contrary to the generally accepted principles in this regard according to which it is sufficient to minimise the number of integrated power amplifiers, that it proves to be case that such an optimisation allows in practice an increase in performance such that it largely compensates for the increased cost and/or increased weight possibly brought about by the use of a plurality of amplifiers in parallel, including in applications for on-board systems, in particular for space systems.

[0087] The invention provides a method which is particular simple, sound, reliable and universal for determining the optimum setting parameters of a stage for amplifying the power of variable envelope signals, and in particular communication signals, in particular modulated signals. It goes without saying that the invention can cover numerous variants and applications other than those described above and illustrated in the figures.