Modulators – Amplitude modulator – Plural modulation
Patent
1995-12-26
1997-08-19
Grimm, Siegfried H.
Modulators
Amplitude modulator
Plural modulation
332183, 375268, 375300, 455108, H03C 150
Patent
active
056592728
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and a device for amplitude modulation of a signal. It applies particularly to power transmitters known as "solid state" transmitters in the radio frequency field, which are produced on the basis of field-effect or MOSFET-type power transistors.
With the advent of power transistors, which are easy to control and have short switching times making them capable of operating at frequencies from a few hundred kilohertz to one megahertz or more, vacuum-tube transmitters, which are expensive and bulky, requiring very high-voltage power supplies which are difficult to maintain, are tending to be replaced by transmitters the amplifier stages of which use these types of transistors. These transmitters generally consist of elementary power amplifiers or modules assembled in parallel or in series in such a way as to transmit the required power. The usual architecture of these modules is of the H-bridge type, also called "full bridge". Several solutions currently exist for amplitude modulation of the output signal from these transmitters. One is described by the patent application No. 2,567,338 and entitled "Amplifier with amplification stages switchable as a function of the amplitude of the signal to be amplified", filed in France in the name of the Applicant.
This solution is relatively simple to implement and requires no particular management of the operation of the elementary modules. Nevertheless, it requires many chokes and capacitors, dimensioned for sizeable voltages and circuits, as well as transformers with many secondaries, and is therefore an expensive and bulky solution of mediocre efficiency.
Another solution comprising digital management of the modules allows an enhancement of the efficiency but at the cost of great complexity in management of the modules. In this case, the envelope of the transmitted wave is constructed by superposition of the signal supplied by each of the power modules fed with the same voltage E and the operation of which is controlled by the digital part. However, in order to refine the envelope of the signal to be transmitted, it is necessary to use additional power modules fed with a voltage E/2, E/4 . . . E/2.sup.p. This constitutes a major drawback since the elementary modules are no longer all identical, and thus denies the complete interchangeability of these modules. Neither does this allow a mode of operation at degraded or reduced power, since placing at least one module out of circuit, following any malfunction, entails distortion of the transmitted wave in contrast to a solution consisting of interchangeable modules the stopping of one or the other of which entails only a reduction in the transmitted power, while, fairly often in certain particular circumstances, such an operating mode may remain satisfactory for the application.
Moreover, this solution requires many different voltage sources, and the continual switching of the modules generates interfering stray signals. It should be noted, moreover, that the absence of complete interchangeability of the modules entails additional difficulty and cost of maintenance and development.
The object of the invention is to alleviate the abovementioned drawbacks.
To this end, the subject of the invention is a method of amplitude modulation of a signal by a modulation signal characterized in that it consists in breaking down the signal to be modulated into a first and a second signal of the same amplitude and of opposite phases, in phase modulating the first and second signal by the modulation signal and in adding the first and second phase-modulated signals in order to obtain a resultant amplitude-modulated signal.
A further subject of the invention is a device for implementing the abovementioned method.
The main advantages of the invention are that it allows great flexibility in the control of the output power, better precision in the amplitude of the output signal as a function of the modulation signal at the input of the transmitter, and very good overall efficiency. It moreover allows
REFERENCES:
patent: 4319204 (1982-03-01), Weldon et al.
patent: 4331941 (1982-05-01), Kovalick et al.
patent: 4355289 (1982-10-01), Beyer et al.
patent: 5093636 (1992-03-01), Higgins, Jr. et al.
"Thomson-CSF"
Grimm Siegfried H.
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