Amplification circuit for a radio-frequency signal with output supply voltage modulation based on an amplifier output signal measurement

Abstract

An amplification circuit for a radio-frequency signal comprises a transistor power amplifier (100) and a fixed regulated power supply (110) for providing an output supply voltage to the transistors (100). The circuit comprises a modulator (160) regulating the output supply voltage in a continuously variable manner, said modulator being dependent on a detector (150) measuring an output radio-frequency signal of the transistor.

Description

[0001] TITLE: Amplification circuit for radiofrequency signal with modulation of output supply voltage as a function of an amplification output signal measurement

[0002] Technical background

[0003] The invention relates to the field of radio communications, including radio communication as such and the jamming of radio communications. The invention relates more specifically (but not exclusively) to the field of power amplification for transmission by an antenna with solid-state technology circuits, in radio frequency (RF) ranges of the order of MHz up to microwave frequencies, with an instantaneous bandwidth whose ratio between the high frequency and the low frequency is significant with regard to impedance variations - we will speak of a wide band.

[0004] Broadband communication is typically used for military communications and for defensive or offensive jamming.

[0005] Downstream of an amplifier stage (this comprising a transistor or often transistors whose individual output signals are added via combiners to form the amplifier's output signal), the impedances presented to it are variable, linked to the presence of combiners, switches, cables, connecting elements, the antennas themselves (or any other load depending on the use) and parasitic reflectors.

[0006] However, the segments of the frequency range for which the impedance presented is low are of low energy efficiency due to the high nature of the supply voltage required by the frequency segments for which the impedance is the highest. This penalizes the thermal performance, compactness and weight of the amplifier, in particular those of its power supply and its cooling system.

[0007] This has consequences in terms of autonomy between two refuelings for a transmitter powered by a generator in a context of deployment in a mobile terrestrial environment, or in terms of the sizing of this generator and the various cooling systems. We therefore want the amplifier upstream of the transmitting antenna to have the highest possible efficiency.

[0008] These difficulties are typically not encountered in narrowband.

[0009] In wideband, impedance matching at the amplifier output is performed, but this results in a compromise between its performance and operation over the entire band. This situation is aggravated by the nature of the payload, itself wideband and generally resulting from compromises making it imperfectly adapted to all frequencies in the useful band.

[0010] Furthermore, applied to a narrowband situation, for example in mobile telephony of the cellular type, a technique is known for detecting the envelope of the amplifier input signal and modulating the output voltage of the amplification transistors (output terminal called drain or collector depending on the technology) carried out to improve the amplification efficiency. This technique is only interested in the variability of the amplitude of the input signal to optimize the transistor supply voltage. It does not overcome the variability of the impedances presented at the transistor output. However, as soon as the frequencies vary significantly, this variability becomes significant.

[0011] Features of the invention - advantages

[0012] In this context, there remains a need for principles for improving broadband energy efficiency, and associated circuits implementing such principles.

[0013] High power systems typically have a power-regulated output RF signal on the user output continuously for the protection of downstream functions (solid state transceiver switch, other switches, filters, etc.) or for achieving a field mask (typical in electromagnetic compatibility testing). The invention takes advantage of this continuous regulation to compensate for any loss of amplification of the circuit due to the modulation of the transistor supply voltage which is the subject of this document.

[0014] The solution presented here consists of measuring the envelope of the RF signal at the immediate output of a transistor, before the impedance transformation carried out by the adaptation circuits (provided that such an adaptation is used in the circuit concerned, but this is most often the case), and using this information to dynamically bring the output supply voltage of the transistors closer to the envelope of the voltage of the RF signal seen at the immediate output of the transistor. This makes it possible, in an original way, to take into account the impedance of the transmission chain (downstream of the transistors) referred to the terminals of each of the transistors to regulate the supply voltage, and therefore reduce energy losses.

[0015] The voltage measurement, after filtering, is taken as a reference to modulate the supply voltage applied to the drains (or generally to the outputs) of the transistors so that it follows appropriately that of the RF envelope seen at the output of the transistor, which has therefore been measured and is measured continuously. The impedance variability is then dynamically compensated by the modulation of the supply voltage. This compensation is obviously subject to the time constant of the filtering function, insofar as it is used. And the system is stabilized by the continuous regulation of the level of the RF signal seen at the output of the amplifier (after combination of the final stage in the case of several amplification circuits on the last stage), moreover.

[0016] Thus, the invention consists of an amplification circuit for a radiofrequency signal comprising a transistor power amplifier and a regulated power supply for providing a drain voltage (or so-called drain supply voltage, or so-called transistor output supply voltage). These are known concepts.

[0017] But the amplification circuit comprises a modulator, also known, regulating the output supply voltage of each of its transistors, said modulator being dependent on a detector measuring, in an original manner, an output signal of at least one of said transistors.

[0018] In addition to or independently of the known improvement due to the modulation of the supply voltage in accordance with the envelope of the amplifier input signal, monitoring the envelope at the transistor output makes it possible to correct the poor efficiency ranges of a wideband amplifier. This solution thus makes it possible to dynamically correct, as a function of any variation in transmission frequency or as a function of time (in the case of operating modes or other external events), any variation due to the payload and the amplification system itself.

[0019] Improving efficiency in the case of high-power broadband amplifiers allows:

[0020] • optimization of the power available per transistor thanks to the reduction of dissipated power,

[0021] • optimization of the weight and volume of the cooling system,

[0022] • optimizing the weight and volume of AC / DC or DC / DC power supply converters, in addition to adding the circuits necessary for the operation of the output power supply voltage modulation,

[0023] • the energy efficiency of the system.

[0024] All these criteria are critical in the case of embedded systems.

[0025] Optionally and advantageously, the detector can filter and smooth said measurement of an output signal of said transistor to form an output voltage envelope, the modulator regulating the output supply voltage to minimize the difference between said output supply voltage and said output voltage envelope. The fact that the measurement is filtered ensures the stability of the control. Still optionally, the amplification circuit can be of the single-ended type (common mode), but it can also be of the differential type in the context of a push-pull assembly. Thus, the implementation consists of an envelope measurement and detection circuit between drain and source (for the single-ended assembly) - (the source being replaced by the emitter in certain transistor technologies), or alternatively between two drains in the case of a double transistor used in push-pull (0 - 180°).

[0026] In order to reduce the material impact and the overall failure rate of the amplifier, detection can be done on a single transistor with application of the output supply voltage modulation to all the transistors of the same stage. This arrangement is based on the repeatability of the impedance variations of the matching circuits between several transistors of the same amplifier stage.

[0027] And once installed, the circuit generally includes

[0028] - an impedance matching network at the transistor output, according to known principles

[0029] - the original detector according to the invention, measuring an output signal of a transistor, and the measurement filtering circuit,

[0030] - the output supply voltage modulator, taking into account the measurement after filtration.

[0031] It is specified that the signal measurement made by the detector concerns the signal between the transistor and the impedance matching network.

[0032] The invention therefore also relates to the use of an amplification circuit for a radiofrequency signal according to the principles mentioned, of greater interest for a wide frequency band, but not exclusively.

[0033] This use may be for radio communication, or radio communication jamming.

[0034] The invention applies with the use of a continuous wave (CW) or a pulse wave, and any type of modulation.

[0035] List of figures

[0036] Figure 1 shows a first embodiment of the invention.

[0037] Figure 2 shows a second embodiment of the invention.

[0038] Detailed description

[0039] We recall the assembly conventionally used in the prior art for the amplification of a radiofrequency (RF) signal using a transistor amplifier (in a "single-ended" or common mode assembly). We discuss a given transistor in particular.

[0040] A supply voltage or output supply voltage is applied to the transistor assembly. This voltage is sometimes called the drain voltage, and is referenced to ground, to which the transistor is also connected, for example by its source terminal.

[0041] The output supply voltage is generally continuous and sometimes noted VDC and this applied VDC voltage is generally not modulated over time: it is constant.

[0042] An RF input signal, referenced to the source, is applied to an input terminal of the amplifier.

[0043] The RF signal amplified by the amplifier is fed to the output terminal of the transistor or transistors - and is expressed as a voltage relative to ground.

[0044] A two-pole load is connected to the dipole consisting of ground and the output terminal of the transistor or transistors by an impedance matching network to facilitate power transmission.

[0045] The load can be a circuit comprising combiners (to combine the output signals of the transistors of the same stage in an amplifier which, as is often the case, comprises several transistors), switches, filters, coaxial cords and ultimately an antenna, for example. The matching network makes an adaptation between the impedance present between the source and the output of the transistor, noted Z and the impedance of the load brought back to the transistor, noted ZL (which varies according to the frequency of the transmitted signal, the operational modes, and also the environment of the useful system, antenna for example).

[0046] This matching has efficiencies that are better at some frequencies than at others. Energy is lost in the form of heat, particularly at frequencies for which the impedance matching network is not good.

[0047] [Fig. 1] In Figure 1, the invention is also shown in a single-ended, or common mode, embodiment. An input signal S is again applied to the input terminal of an amplifier circuit 100, comprising at least one transistor, and whose source is connected, as previously, to ground. A direct voltage supply 110 (VDC) is available, but this voltage is not applied directly to the output supply terminal of the transistor assembly 100.

[0048] An impedance matching network 120 connects as before the two poles of a load 130 bringing the impedance ZL (dependent on the frequency) to the dipole consisting of the source and the output of the transistor, with impedance noted Z. The load 130 as before can be a circuit comprising combiners, switches, filters, coaxial cords and an antenna and the impedance network 120 makes the adaptation between the impedance Z and the load to present the optimal impedance ZL, with a variable efficiency depending on the frequency. The amplified RF signal S1 develops as a power between the output terminal of the transistor and the source.

[0049] According to the invention, the voltage of the amplified RF signal S1 at the immediate output of the transistor 100 is continuously measured, between the output of the transistor and the source, and, in a drain-source voltage envelope detection module 150, the envelope of this signal is extracted, by using a high-pass filter and smoothing. An instantaneous voltage envelope value is deduced therefrom, which is, in a modulator 160, compared to the current value of the transistor output supply voltage, so as to define a difference, which is used to correct the current output supply voltage of the transistors of the stage to bring this difference back to a predefined setpoint, generally aiming to reduce this difference, within the framework of a control.

[0050] The amplified RF signal therefore develops with an output supply voltage of the transistor which is modulated, which leads to a minimization of the energy lost in the assembly of the transistor, including by taking into account the variations in impedance presented to the transistor at the different frequencies by the load 130 via its matching network 120.

[0051] [Fig. 2] Figure 2 shows an embodiment of the invention based on a differential mode assembly (push-pull).

[0052] An input signal S' is applied to the two input terminals of a double transistor 200, each source of which is also connected to ground. A 210 VDC direct voltage supply is available, but this voltage is not applied directly to the output supply terminals of the double transistor 200 arrangement.

[0053] An impedance matching network 220 connects the two poles of a load 230 bringing the impedance ZL diff (dependent on the frequency) to the dipole consisting of the two output terminals (drains) of the double transistor 200, with an impedance noted Z diff. The load 230 as previously can be a circuit comprising combiners, switches, filters, coaxial cords and an antenna and the impedance network 220 makes the adaptation between the impedance Z diff and the load to present the optimal impedance ZL diff, with a variable efficiency depending on the frequency.

[0054] The amplified RF signal S'1 develops as power between the output terminals of the dual transistor.

[0055] According to the invention, the voltage of the amplified RF signal S'1 is continuously measured at the immediate output of the double transistor 200, between the two output terminals, and, in an envelope detection module 250, the envelope of this signal is extracted, as mentioned in relation to the first embodiment. An instantaneous voltage envelope value is deduced therefrom, which is, in a modulator 260, used to correct the current output supply voltage of the assembly of the double transistor 200 to bring their difference towards a predefined setpoint, generally aiming to reduce this difference, within the framework of a control.

[0056] The amplified RF signal therefore develops with an output supply voltage which is modulated, which leads to a minimization of the energy lost in the double transistor 200, including by taking into account the impedance variations presented to the double transistor 200 at the different frequencies by the load 230 via its matching network 220.

[0057] With previous techniques, whether for a narrowband circuit or a wideband circuit, the impedance variations presented to the amplifier are not taken into account. But here, finely modulating and as close as possible to the output of the transistor (drain-source or emitter-collector), or the outputs of the dual transistor in differential mode (drain-drain or emitter-emitter), the output supply voltage of each transistor makes it possible to obtain the desired energy sobriety.

[0058] The method is based on a servocontrol (in modulators 160 and 260 of figures 1 and 2).

[0059] The process can be implemented analogically, or in a hybrid way, with a part in digital technology.

Claims

CLAIMS 1. Amplification circuit for a radiofrequency signal comprising one or more transistor circuits and a regulated power supply (1 10; 210) for providing an output supply voltage (100; 200) to the transistor, said amplification circuit being characterized in that it comprises a modulator (160; 260) regulating said transistor output supply voltage of the amplification circuits of an amplification stage, said modulator (160; 260) being dependent on a detector (150; 250) measuring for at least one transistor of said amplification stage, a voltage of the envelope of the radiofrequency signal at the output of the transistor (S1, S'1) to minimize the difference between said output supply voltage and said voltage of the envelope of the radiofrequency signal for all the transistors of the same amplification stage.

2. Amplification circuit for RF radiofrequency signal according to claim 1, characterized in that the transistors of the stage are mounted in a single-ended type assembly.

3. Amplification circuit for radiofrequency signal according to claim 1, characterized in that the transistors of the stage are mounted according to a differential type assembly.

4. Amplification circuit for radiofrequency signal according to one of claims 1 to 3, characterized in that it comprises an impedance matching network (120; 220) between said transistor (or multiple transistors) and a load of the circuit, the detector (150; 250) measuring the output voltage between said transistor (or multiple transistors) and the impedance matching network (120; 220).

5. Amplification circuit for radiofrequency signal according to one of claims 1 to 4, characterized in that the detection is carried out on a single transistor (or multiple transistors) with application of the output supply voltage modulation to several transistors (or multiple transistors) of the same amplification stage of the circuit.

6. Use of an amplification circuit according to claim 1 to 5, characterized in that it is carried out for radio communication, or radio communication jamming, or any other application requiring a radio signal.

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