Modulators – Phase shift keying modulator or quadrature amplitude modulator
Reexamination Certificate
2003-01-09
2004-12-14
Pascal, Robert (Department: 2817)
Modulators
Phase shift keying modulator or quadrature amplitude modulator
C332S105000
Reexamination Certificate
active
06831526
ABSTRACT:
The invention relates to a method for digitally modulating a periodic carrier signal of high frequency—in particular one which may be in the microwave range (a range of frequencies for which propagation phenomena are not negligible)—with a digital modulation signal generally of lower frequency (that to say less than that of the carrier signal), implemented by a modulator circuit comprising at least one modulation cell—in particular a phase-shift keying modulation cell—intended to receive two digital control signals representing at least a part—in particular a component—of the digital modulation signal. It extends to an electronic modulator circuit designed for implementing such a method.
WO-98.38730 describes an electronic phase-shift keying modulator circuit with distributed structure comprising a distribution line with n phase-shift cells, a plurality of n parallel branches extending from each phase-shift cell and each comprising a switching/modulator circuit, and means for adding in phase the signals coming from the switching/modulator circuits. The number of phase states that can be obtained may be greater than the number of branches when these contain, as the switching/modulator circuit, modulation cells which, in the most elementary embodiment, are cells for modulation by phase-shift keying with two phase states (referred to as BPSK or MDP
2
) which are intended to receive two complementary digital control signals.
The publication BOVEDA et al.: “A 0.7-3 GHZ GAAS QPSK/QAM DIRECT MODULATOR” IEEE JOURNAL OF SOLID-STATE CIRCUITS, Vol. 28, No. 12, 1st Dec. 1993, pp. 1340-1349 also describes other examples of applications of BPSK digital modulation cells for carrying out phase and/or amplitude modulations.
In all the known applications of such cells for BPSK digital modulation with two phase states, as described for example by the publication A. PRIMEROSE et al. “High Bit Rate Four, Phase MMIC Remodulation Demodulator and Modulator” Proceedings of the GAAS 92 European Gallium Arsenide and related III-V Compounds Applications Symposium 27-29, Apr. 1992, NOORDWIJK, the digital control signals applied to these BPSK cells are, by principle, signals with two complementary states I, I.
The points in the Fresnel plane (phase and/or amplitude states) that can be addressed in these known digital modulation methods and circuits are therefore limited to a value such as 2
n
in the case of WO-98.38730.
It has, however, become desirable to be able to increase the number of points in the Fresnel plane (phase and/or amplitude states) for a given circuit structure, in order to improve the performances of the modulation for a given cost price, a given size, a given weight and a given energy consumption.
It is therefore an object of the invention to satisfy this requirement in a simple and economical way. It is a particular object thereof to provide a method and a modulator circuit making it possible to address a large number of points (phase and/or amplitude states) with no loss of consumed power and a low energy consumption, so that this circuit and this method can be adapted and used with numerous types of coding and modulation, in numerous applications.
It is a further object of the invention to provide such a method and such a modulator circuit which are advantageously suited to production in microwave monolithic technology (MMIC)—in particular on gallium arsenide GaAs—with excellent precision.
More particularly, it is an object of the invention to permit a simple choice of the phase and/or amplitude states, and to do so at the very moment of its incorporation into the system (and not during the design or fabrication of the integrated circuit itself).
It is more particularly a further object of the invention to provide such a method and such a modulator circuit which are compatible with the constraints of on-board space systems (small size, excellent reliability, low consumption, etc.).
It is also more particularly an object of the invention to provide such a method and such a modulator circuit which are compatible with high bit rate modulation codings such as MCT, which become advantageous when a large number of phase and/or amplitude states are available.
It is also more particularly an object of the invention to provide such a method and such a modulator circuit which can be adapted to any frequency of carrier signals, in particular in the microwave range.
It is also more particularly an object of the invention to provide such a method and such a modulator circuit which, after production, can accept carrier signals as input whose frequency is fixed but which may also be selected from a wide band (for example from the X band for terrestrial observation telemetry, from the K band of multimedia telecommunication satellites, etc.).
It is a further object of the invention to provide a modulation which does not produce substantial perturbations of the line and of the input signal.
To that end, the invention relates to a method for modulating a carrier signal with a digital modulation signal of lower frequency, implemented by a modulator circuit comprising at least one modulation cell intended to receive two digital control signals representing at least a part of the digital modulation signal, wherein, for at least one value of the digital modulation signal, two digital control signals of equal value are applied to at least one given modulation cell. This modulation cell then delivers, for this value of the digital modulation signal (for which the digital control signals have the same value), a signal, referred to as a modulated elementary signal, which is different in amplitude and/or in phase—in particular which is zero—from that which it delivers when the digital control signals are complementary.
The invention also extends to a circuit designed for implementing the method according to the invention. It therefore also relates to a modulator circuit capable of modulating a carrier signal with a digital modulation signal of lower frequency, comprising at least one modulation cell intended to receive two digital control signals representing at least a part of the digital modulation signal, wherein it is designed so that, for at least one value of the digital modulation signal, at least one given modulation cell receives two digital control signals of equal value.
At least one modulation cell may be of the type with amplitude modulation using a single phase state. Nevertheless, advantageously, and according to the invention, at least one modulation cell is a phase-shift keying modulation cell, the method and the circuit according to the invention carrying out digital modulation at least by phase-shift keying.
Each modulation cell may be a cell for modulation by phase-shift keying of the type with two phase states (referred to as a BPSK or MDP
2
cell)—in particular in opposition—generally having a single amplitude state, but also possibly having two amplitude states. By applying digital control signals of equal value to it, it is given one or two additional phase and/or amplitude state(s). In the event that the phase difference between two states is other than 180°, and/or in the event that the amplitude of the two states is different, the said modulation cell does not deliver the same modulated elementary signal when the digital control signals that it receives are equal to 0 and when they are equal to 1. Two additional states are hence created for this modulation cell. This modulated elementary signal is not necessarily zero when the digital control signals are of equal value (both equal to 0 or to 1).
Preferably, advantageously and according to the invention, at least one modulation cell receiving two digital control signals of equal value for at least one value of the digital modulation signal is nevertheless designed to deliver a signal, referred to as a modulated elementary signal, which is zero for this value of the digital modulation signal.
Advantageously and according to the invention, at least one modulation cell is furthermore designed to deliver a modulated elementary signal with
Boulanger Cyrille
Lalaurie Jean-Claude
Lapierre Luc
Sadowy Jerome
Centre National d'Etudes Spatiales (C.N.E.S.)
Chang Joseph
Pascal Robert
Young & Thompson
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