WO2015169909A1

WO2015169909A1 - Radiofrequency amplification system

Info

Publication number: WO2015169909A1
Application number: PCT/EP2015/060085
Authority: WO
Inventors: David Arnaud; Pascal HOPITAL; Nicolas BREANT; Jeremy TASTET
Original assignee: Advanced Wireless Solutions And Services (Aw2S)
Priority date: 2014-05-07
Filing date: 2015-05-07
Publication date: 2015-11-12
Also published as: FR3020905A1

Abstract

The invention relates to a radiofrequency amplification system comprising at least two independent power amplification branches (100a, 100b), each branch being provided with amplification stages (110a, 111a, 110b, 111b) and an outlet isolator circuit (120a, 120b), said system comprising an RF coupling stage (130) of said branches, combining the signals of said branches downstream from the isolator circuits (120a, 120b).

Description

RADIOFREQUENCY AMPLIFICATION SYSTEM

Field of the invention

The present invention relates to a radio frequency amplifier of the type used in mobile telephony and more particularly to a multi-frequency or multi-carrier radio frequency amplifier.

Technological background

Today, the technology known as "MCPA" is a multi-carrier radio amplifiers widely used in the field of mobile wireless networks because of its cost and energy efficiency advantages. However for some uses, the main disadvantage of this system is the unreliability related to the robustness of the amplifier stage. Indeed as several carriers are amplified by one and the same amplifier, when the latter comes to stop working, all the carriers amplified by it come to be affected. Some industries are reluctant to use this technology. To guarantee reliable transmission, they prefer to use a single amplifier per carrier, even if a redundant system is required in the case of critical transmission. The main impacts of this type of system are therefore a high budgetary cost and a high energy cost.

The document WO2006 / 066461 A1 describes an amplifier whose driver and power amplification stages are separated by a combination stage of the driver and isolation signals, which is contrary to the present invention and remains as described in the art. prior to this application. In addition, the coupler stages of this document comprise only a first input 90 ° coupler, this phase shift being transmitted to the output of the amplifier.

Finally, in this document, the power stages are not followed by a hybrid coupler at the amplification output as in the present invention.

The amplifier of the document WO2006 / 066461 A1 does not offer a complete redundancy of the amplification channels and does not allow either to dedicate a channel to the amplification of the carrier signals, the other way to the amplification of the signaling signals. high amplitude to achieve a Doherty type amplification by playing on the polarizations of the stages of each channel is in the event of a failure of one branch, to process the complete signal on the other branch and to deliver ¼ of the power in exit.

Document US201 1/250854 A1 constitutes exactly the example that the present invention seeks to avoid, namely two channels processing the signals of two DAC converters.

In this document, a DSP manages two digital channels each equipped with a digital to analog converter and an amplifier.

Brief description of the invention

The device according to the invention makes it possible to reduce or even remedy these disadvantages, but also to improve the performance of the radio frequency amplifiers.

To do this, the invention proposes a radio frequency amplification system which comprises a signal input supplying at least two independent power amplification branches, each branch being provided with amplification stages and an output isolating circuit and for which an RF coupling stage combines the signals of said branches downstream of the insulator circuits and for which an RF divider coupler 3dB receives the signal to be amplified on one of its input channels and divides this signal in two on its signal channels. quadrature output connected to said amplification branches each provided with successive amplification stages comprising a driver stage and a final stage and each followed by a circulator-type insulator circuit, the quadrature signals leaving said branches being sent to inputs of a coupler Hybrid coupler type RF output where they are re-phased and summed to output to the first output channel of the coupler.

In contrast to WO2006 / 066461 A1, the present invention provides a 90 ° coupler input and a 90 ° output coupler phasing the output signals.

In the present invention a divider coupler receiving a signal to be amplified provides the signal to two separate amplification pathways then recombined.

Preferably, downstream of the RF coupling stage, the amplifier comprises at least one divider stage adapted to provide a signal output and a sampling output.

Advantageously, upstream of the RF coupling stage, each branch comprises at least one divider stage adapted to provide a signal output and a sampling output.

According to a particular embodiment, a coupler stage combines the sampling outputs.

According to a complementary or alternative embodiment, the withdrawal outlets comprise independent and recombinant sampling routes.

According to a particular embodiment, a phase and / or gain adjustment circuit is arranged between the input divider stage and a first amplification stage of at least one of said branches.

The phase and / or gain control circuit is advantageously controlled by a computer so as to optimize the reduction of even-order intermodulation products at the output of the branches.

The signal input of the system of the invention is preferably derived from a computer.

According to a particular embodiment, sampling lanes coming from divider stages at the output of the amplification branches are connected to return loops connected to modules for adding an RF pre-distortion input of said branches. amplification.

Brief description of the drawings Other characteristics and advantages of the invention will become apparent on reading the following description of a nonlimiting exemplary embodiment of the invention with reference to the drawings which represent:

in FIG. 1: a block diagram of an amplification system of the prior art;

in FIG. 2: a block diagram of an amplification system according to a first embodiment of the invention;

in FIG. 3: a block diagram of an amplification system according to FIG. 1 further comprising a sampling circuit;

in FIG. 4: a block diagram of an amplification system according to FIG. 1 comprising branch sampling circuits;

in FIG. 5: a block diagram of an amplification system according to FIG. 4 comprising a phase-shifting circuit and / or an input attenuator on one of the branches;

in FIG. 6: a block diagram of an amplification system according to FIG. 5 comprising a device for selecting the sampling outputs;

in FIG. 7: an application diagram with pre-distortion correction; in FIG. 8: a diagram of a four-way embodiment according to the invention; in FIG. 9: a variant of the diagram of FIG.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention relates to MCPA type power amplifiers (multi-carrier power amplifier).

An example of such an amplifier according to the prior art as shown in Figure 1 generally comprises two to three stages, an optional first amplification stage called according to the English terminology in force in the field "pre-driver" , a second stage called "driver" 1 and a third called "final" 2.

These different stages typically each comprise two transistors 3, 4 for the driver and 5, 6 for the final stage mounted in quadrature in order to improve the linearity of the amplifier.

In some uses such as Doherty type amplifiers, modified class B radio amplifiers, there may be more transistors in the final stage to improve performance. Energy. In addition they are polarized differently, one branch taking charge of the carrier amplification and the other of the peak amplification, and these are sometimes different power transistors.

Still according to FIG. 1, in the case of a correction by digital pre-distortion in real time (digital pre-distortion in English) or in the case of a feedforward type correction according to the English terminology, the output of the final stage is taken by a directional coupler 7 to be analyzed in order to improve the correction of nonlinearities in real time. Then there is an output isolator 8 responsible for isolating the mounting of external disturbances by adding interference rejection that can return from the output. This isolator becomes an element whose linearity is critical because it is excluded from the correction loop.

The present invention proposes to mount the successive amplification stages in separate ways and to include an isolator before recombination instead of leaving it at the output of the assembly after recombination.

The basic principle of the invention is described in FIG. 2. According to this figure, an RF divider coupler 3dB 200 receives the signal to be amplified on one of its input channels E 200a and divides this signal in two on its tracks. in quadrature output 200c, 200d which are connected to amplification channels 100a, 100b each provided with successive amplification stages.

The divider coupler 200 receives on a second input a matched load 201 in a manner known per se.

According to the example, the channel 100a comprises a driver stage 1 10a and a final stage 1 1 1a and the channel 100b comprises a driver stage 1 10b and a final stage 1 1 1b.

Each channel is followed according to a first aspect of the invention by a circulator-type insulator circuit 120a, 120b and the quadrature signals are sent to inputs 130a, 130b of an output coupler 130 of the hybrid coupler type where they are delivered. in phase and summed to output on the first output channel 130c of the coupler to the output S of the amplifier, the second output channel 130d of the coupler to a matched load 131.

A 3 dB RF coupler is a coupler whose output signals are in quadrature. Likewise a hybrid coupler shifts its outputs by 90 °.

In the present invention, between the RF coupler and the hybrid coupler, the amplification channels do not include any other coupler or decoupler in particular between the amplification stages.

Such an arrangement has several advantages.

According to the principle of the invention, in case of failure of one of the transistors of one of the branches, the insulators ensure that the other path can continue to operate correctly.

In case of failure of one of the two channels, the output signal is not suppressed and the amplifier can deliver a quarter of the total power normally supplied by the two channels.

Indeed, the working channel delivers half the power of the amplifier and half of this power is returned by the coupler 130 to the isolator of the failed channel and thus lost while the other half of this power transmitted is transmitted out of the equipment.

Thanks to the assembly of the invention, it is simple to dedicate a channel to the amplification of the carrier signals, the other way to the amplification of the signals of high amplitude to perform a Doherty type amplification by playing on the polarizations of the floors of each lane.

In the case of a digitally controlled amplifier, the operation of the channels can in particular be adapted in real time by the use of polarization means controlled by the digital transmission system and it is thus possible by varying the polarization of the stages. amplification of a system for which the two channels amplify the entire signal to a system for which one channel is dedicated to the amplification of signal peaks, the other channel amplifying the carrier signals or to adapt the polarization to cut a channel in the case of weak signals to be transmitted to reduce the power consumption of the amplifier and improve the ratio signal transmitted on bias current which further reduces the heat dissipation of the amplifier and thus increases its MTBF (average time before failure).

In an embodiment according to FIG. 3, a sampling divider coupler 140 between -10dB and -30dB makes it possible to separate the output S from a sampling output P after the recombination of the signals of the two branches by the coupler 130 disposed after the insulators 120a, 120b of each branch. As for the other couplers, the unused channels 130d and 140b of the couplers 130 and 140 are loaded by suitable loads 131, 141.

The sampling makes it possible to ensure a correction of the signal for example by pre-distortion or to make a real-time measurement of the output.

In the example of FIG. 4, instead of taking the output signal after recombination, the invention provides for sampling by means of directional couplers 150a, 150b, attenuation sampling between 10dB and 30dB on each channel after insulators 120a, 120b. The directional couplers 150a, 150b respectively have signal outputs Sa, Sb and sampling outputs Pa, Pb. The signal outputs Sa, Sb are combined by a coupler stage 155, particularly of the hybrid coupler type 3dB, to give an output signal S while the signals taken at Pa, Pb are combined by a coupler stage 1 60, in particular of the hybrid coupler type 3dB, to give a single sampling output P.

The samples can be processed separately or recombined as shown in FIG. 6, which proposes a mounting for which switches 180a, 180b of analog switch type make it possible to choose between separate sampling outputs Pva, sampling channel A, Pvb, sampling channel B or an output single P sampling by recombination of the two-lane samples at a coupler 1 62.

Samples Pva and Pvb make it possible to observe the channels separately or, in the case of a faulty channel, to observe the channel remaining in operation.

FIG. 5 represents a variant of FIG. 4 for which a phase and / or gain adjusting circuit 170 is incorporated in one of the branches.

This circuit, which can be controlled numerically, makes it possible to refine the adjustment of the quadrature between the channels which makes it possible to balance the channels and to make a first correction of the odd harmonics.

By making sure that it is possible to recover the sample from each channel independently as well as recombinantly as in FIG. 6, it is possible, including the phase and / or gain adjustment 170 continuously set by the system in all the branches minus one. , optimize the phasing and gain and thus ensure better cancellation of even-order intermodulation products.

By extension of this principle, it is possible to create in the case of a linear correction of the linearity, two or more independent chains from the digital to analog conversion to the recombination of the power signal to correct the channels independently but to a much higher cost due to the multiplication of digital analogue conversion chains and the necessary computing power.

Figure 7 corresponds to a system with feedback loop for a pre-distortion type correction.

The DSP 310 adapts the signal BF to send input E of the amplifier by adding a pre-distortion opposite the theoretical distortion of the amplifier.

The feedback loop returns the actual output signal which, once demodulated, is compared to the pure signal to be transmitted. The measured difference is used to adapt the pre-distortion to correct the actual imperfections of the amplifier.

The signal processing circuit 310 called "DSP" can in particular be the combination of a conventional processor or a DSP and an FPGA type component.

The DSP receives the samples of the signal in digital form N. These samples are formatted in the DSP with filtering, crest factor reduction or other algorithms and then pre-distorted by a digital pre-distortion algorithm and sent to the DSP. the digital converter 210.

The converter is followed in a known manner by a filter 215 to reject the images generated by the D / A converter and a modulator 220 which serves to modulate a carrier generated by an oscillator 230 with the signal from the converter.

The modulator is followed by a band pass filter 225, to reject the images generated by the modulator, and possibly a gain control stage 226 which controls the total gain of the amplifier.

Then the signal is split in two in the coupler 200 to be amplified in the separate channels according to the invention. As in FIG. 5, a computer-controlled phase or gain control 170 or DSP 310 is implemented to improve the quadrature between the channels.

As in the previous examples, the channels comprise amplification stages and isolators 120a, 120b before the recombination and sampling couplers.

According to this example, two directional sampling couplers 191 a, 191 b each receive the signal from one channel and distribute it on the one hand to an output coupler 155 and on the other hand in attenuated form to controlled switches 181 a, 181 b discussed below.

In the feedback loop which receives the sampling signal Pr is a filter and / or attenuator 260 a demodulator 240 receiving a carrier generated by an oscillator 250, a second filter 261 and an analog / digital converter 270.

The sampling Pr passes into the band filter and a gain adjustment 260 so that the sampling chain keeps a gain almost constant depending on the temperature.

The sample then passes into a mixer 240 to remove the carrier by means of a frequency coming from the oscillator 250 and then to the antireflection filter 261 before entering the A / D converter 270.

The converter supplies data representing the cleaned and demodulated received low frequency signal from the sampling Pr. These data are supplied to the digital signal processor DSP 310 which will calculate a predistortion of distortion compensation from the amplifier.

This chain has two functions performed by the DSP:

analyzing the output signal to converge the digital pre-distortion (DPD) algorithm so that it optimizes the linearization of the whole,

analyzing the output signal to adjust the gain and phase of the second channel through a second digital-to-analog converter 21 1 and a phase and / or gain adjusting device 170 to best perform quadrature. This can be done by maximizing the power that comes out of the sample or by methods based on the analysis of the signal and its coherence with respect to the input signal of the system.

The DSP can further choose the sample used in order to continue operating in degraded mode. To do this, controlled switches 181a, 181b, 183 are controlled by control outputs C1, C2, C3.

The switches 181a, 181b receive sampling signals Pa, Pb from the directional sampling couplers 191a, 191b at the output of the amplified channels and directing, as a function of control signals C1, C2 emitted by the computer or DSP 310 or these signals to a coupler 195 which recombines the channels Pa, Pb taken in a signal P, or to a three-way switch 183 which, as a function of a control signal C3 emitted by the computer or DSP 310, selects a signal Pr from Pa, Pb and P.

It is also possible by adding a linearity, gain and phase and / or gain control means 170 in each branch to use the Pa and Pb samples to control the parameters of each branch.

Figure 8 corresponds to a two-two recombined four-way embodiment.

At the input, the device comprises a cascade of dividing stages produced by means of hybrid couplers 3dB, a first divider stage 400 supplies two dividing stages 410a, 410b each supplying two channels, a first channel comprising the amplification stages 420a, 421a, 422a and a second channel comprising the amplification stages 420b, 421b, 422b for the divider coupler 410a and a third channel comprising the amplification stages 420c, 421c, 422c and a fourth channel comprising the stages amplifier 420d, 421d, 422d for the divider coupler 410b.

The second and third channels each comprise, according to the example, a phase and / or gain adjusting device 415a, 415b.

The four channels are provided at the output of amplification of circulator type isolators 430a, 430b, 430c, 430d followed by directional sampling couplers 440a, 440b, 440c, 440d separating a signal output Sa, Sb, Se, Sd of an attenuated sampling output Pa, Pb, Pc, Pd.

The outputs Sa, Sb are then combined in a coupler 450a while the outputs Se, Sd are combined in a coupler 450b, the outputs of these two The couplers are then combined in a coupler 470 to provide a single output signal S.

Likewise, the sampling outputs are combined in pairs and then recombined to give a single sampling output p with couplers 460a, 460b and 480.

As in the case of FIG. 8, intermediate samples can be used to control the phase control devices 170a, 170b, linearity and / or gain.

FIG. 9 describes a system for which the sampling channels Pa, Pb coming from the dividing stages 150a, 150b at the output of the amplification channels are used as correction signals for modules 500a, 500b for adding a pre-distortion RF.

To do this, the sampling paths Pa, Pb of the amplification branches are connected to the modules 500a, 500b which adapt the RF pre-distortion necessary for the compensation of the amplification branches.

The sampling output Pa of the amplification branch 100'a is connected to the RF pre-distortion module 500a, the sampling output Pb of the amplification branch 100'b is connected to the predistortion module RF 500b

In this case, the signal enabling the control of the phase control device 170 by the digital system to which the amplifier is connected is taken by means of a sampling coupler 490 after the recombination of the amplification channels by the coupler 155. The sampling coupler 490 has an output channel S and a sampling path P attenuated with respect to the output channel.

The amplifier of the invention which provides a redundancy of the transmission channels is adapted to multi-carrier applications, allows to gain in energy efficiency and offers a more precise management of distortion corrections.

3dB hybrid couplers, -30dB -30dB sampling couplers and other components are chosen to be adapted to the power of the amplifier, the output couplers in particular holding power greater than the input couplers. The invention is not limited to the examples shown and in particular the number of stages of each channel may be different from two or three. Likewise, other types of correction than the pre-distortion correction are possible within the scope of the invention.

Claims

R E V E N D I C A T IO N S

1 - radiofrequency amplification system characterized in that it comprises a signal input supplying at least two independent power amplification branches (100a, 100b), each branch being provided with amplification stages (1 10a, 1 1 1 a, 1 10b, 1 1 1 b) and an output isolating circuit (120a, 120b) and for which an RF coupling stage (130, 155, 470) combines the signals of said branches downstream of the isolating circuits ( 120a, 120b) and for which a 3dB RF splitter coupler (200) receives the signal to be amplified on one of its input channels (200a) and divides this signal in two on its quadrature output channels (200c, 200d). ) connected to said amplification branches (100a, 100b) each provided with successive amplification stages comprising a driver stage (1 10a) and a final stage (1 1 1 a) and each followed by an isolator circuit (120a, 120b ) of the circulator type, the quadrature signals coming out of said branches being sent on entrances es (130a, 130b) of an output coupler (130) hybrid coupler type of RF where they are delivered in phase and summed up to get on the first output channel (130c) of the coupler.

2 - radiofrequency amplification system according to claim 1 wherein downstream of the RF coupling stage the amplifier comprises at least one divider stage (140) adapted to provide a signal output and a sampling output.

3 - radiofrequency amplification system according to claim 1 wherein upstream of the RF coupling stage each branch comprises at least one divider stage (150a, 150b, 191a, 191b, 440a, 440b, 440c, 440d) adapted to provide a signal output and a sample output.

4 - radiofrequency amplification system according to claim 3 wherein a coupler stage (1 60, 195) combines the sampling outputs.

5 - radiofrequency amplification system according to claim 3 wherein the sampling outputs comprise independent sampling channels (151 a, 151 b) as well as recombinant (1 61).

6 - radiofrequency amplification system according to any one of the preceding claims for which a phase control circuit and / or gain (170) is disposed between the input divider stage (200) and a first amplification stage (1 10b) of at least one of said branches (100a, 100b).

7 - radio frequency amplification system according to claim 6 wherein the phase control circuit and / or gain (170) is controlled by a computer 310 so as to optimize the reduction of even order intermodulation products in out of the branches.

8 - radiofrequency amplification system according to any one of the preceding claims for which the signal input is from a computer 310.

9 - radiofrequency amplification system according to any one of the preceding claims for which sampling channels (Pa, Pb) from dividing stages (150a, 150b) at the output of the amplification branches are connected connected return loops modules (500a, 500b) for adding an RF predistortion input of said amplification branches.