FR3091964A1 - Device for generating a modulated signal and associated radiofrequency transmission chain - Google Patents

Abstract

Device for generating a modulated signal and associated radiofrequency transmission chain The invention relates to a device (4) for generating a modulated signal comprising: - a modulator (18), the carrier signal being a radio signal. frequency, the modulating signal being representative of a base signal (A (t)), - a processing unit (14) of the base signal suitable for generating the modulating signal. The basic signal processing block (14) comprises: - a delay (30), the delayed signal (A (t-To)) having a delay (To) with respect to the basic signal, - a convolution unit ( 32) so as to form the Hilbert transform of the delayed signal (B (t-To)), - a phase shifter (34) to phase shift the Hilbert transform of the delayed signal by pi / 2, - a summation module (36) to add the delayed signal and the phase-shifted Hilbert transform so as to generate a complex modulating signal (C (t)). Figure for the abstract: figure 1

Description

Device for generating a modulated signal and associated radio frequency transmission chain

The present invention relates to a device for generating a modulated signal comprising:

- a modulator configured to receive a carrier signal and a modulating signal as input, and configured to generate the modulated signal as output, the carrier signal being a radio-frequency signal, the modulating signal being representative of a base signal, the modulated signal being the carrier signal modulated by the modulating signal,

- a basic signal processing block capable of generating the modulating signal.

The invention also relates to a radio frequency transmission chain.

To generate a modulated signal from a base signal, it is known to carry out a processing of the base signal, then to mount the base signal at radio frequency using a carrier signal, and to amplify using an amplifier.

For example, upscaling is performed in the analog domain, with the analog base signal mixed with an analog carrier signal.

Such a solution does not give complete satisfaction. In particular, an image frequency results from the frequency raising operation. However, it is costly and difficult to selectively suppress this image frequency.

Devices for generating modulated digital signals which implement direct digital synthesis (from the English term “Direct Digital Synthesis”) are also known. In these digital signal generation devices, the frequency increase is performed in the digital domain. However, these digital signal generating devices are limited to certain frequencies which depend on the generator clock. In particular, the range of carrier frequencies that it is possible to generate is limited, because the upscaling from the baseband signal implements a multiple frequency of a working frequency. In addition, they are prone to the generation of spurious spectral lines.

The trend in telecommunications is to work in smaller and smaller cells to exchange larger volumes of data. This results in an increase in frequencies with, for example, 5G bands around 30 GHz and 70 GHz.

To satisfy these constraints, it is known to integrate complex blocks to shape the modulated signal so as to reduce the parasitic spectral lines while preserving the quality of the signal.

However, such blocks are expensive in terms of power consumption.

There is therefore a need for a generator of a modulated signal, of good quality, fast, and consuming little energy.

To this end, the subject of the invention is a device for generating a modulated signal of the aforementioned type in which the basic signal processing block comprises:

- a delay device suitable for generating, from the basic signal, a delayed signal, the delayed signal having a delay with respect to the basic signal,

- a convolution unit suitable for convolving the delayed signal by a convolution signal h(t)=1/(pi*t), so as to form the Hilbert transform of the delayed signal,

- a phase shifter configured to phase-shift the Hilbert transform of the delayed signal by pi/2, and

- a summing module configured to add the delayed signal and the phase-shifted Hilbert transform so as to generate the modulating signal, the modulating signal obtained after the addition being a complex modulating signal.

The device for generating a modulated signal may also include one or more of the following characteristics, taken separately or in any technically possible combination:

- the delay is between 1 ns and 1 µs;

- the complex modulating signal is broken down into two components, each component of the complex modulating signal being injected at the input of the modulator, preferably, one component being the phase of the modulating signal and the other component being the amplitude of the modulating signal;

- the basic signal is a digital signal;

- the processing block comprises at least one logic gate and one transistor, the complex modulating signal being a digital signal;

- the generation device further comprises, for each component of the complex modulating signal, a converter capable of converting said component into an analog signal, the converters being arranged between the output of the processing block and the input of the modulator;

- the generation device further comprises a converter capable of converting the basic signal into an analog signal before it enters the processing block, the processing block comprising at least one capacitor, the complex signal being an analog signal;

- the basic signal is an analog signal, the processing block comprising at least one capacitor, the complex signal being an analog signal;

- the generation device does not include an image rejection filter after the modulator; and

- the modulator is able to receive at input a plurality of synchronized carrier signals, each carrier signal being a radio-frequency signal, and to generate the signal modulated by the modulating signal from the plurality of synchronized carrier signals.

The invention also relates to a radio frequency transmission chain comprising:

- a device for generating a modulated signal as described above, and

- a modulated signal transmission antenna, the generation device being connected at the output to the antenna.

The invention will be better understood on reading the following description, given solely by way of example, and made with reference to the appended drawings, among which:

- [Fig 1] Figure 1 is a diagram of a radio frequency transmission chain according to the invention;

- [Fig 2] Figure 2 is a graph representing the rejection rate obtained as a function of the delay with the transmission chain of Figure 1; and

- [Fig 3] [Fig 4] Figures 3 and 4 illustrate an example of modulated signal obtained with or without the device for generating the transmission chain of Figure 1,

- [Fig 5] [Fig 6] Figures 5 and 6 illustrate an example of modulated signal obtained with or without the device for generating the transmission chain of Figure 1 in multiplexing, and

- [Fig 7] Figure 7 is a diagram of a radio frequency transmission chain according to a variant of the invention.

In the context of the invention, the term "radiofrequency" means any frequency between 3 kHz and 300 GHz.

Figure 1 schematically illustrates a radio frequency transmission chain 1 according to the invention.

The radio frequency transmission chain 1 comprises a source module 2 of a base signal, a generation device 4 of a modulated signal and a transmission antenna 6 of the modulated signal.

The basic signal A(t) contains the information to be transmitted.

The modulated signal is a carrier signal modulated by a modulating signal.

The carrier signal is a radio frequency signal.

The modulating signal C(t) is representative of the basic signal A(t).

The source module 2 is able to generate the basic signal A(t).

In the example shown in Figure 1, the basic signal is an analog signal. We denote this signal A(t).

The source module 2 comprises for example a digital data processing device (not shown) and a converter 10 at the output of the digital data processing device. The basic signal A(t) is obtained at the output of the converter 10.

The digital data processing device is designated by the acronym DSP, coming from “digital signal processing” or DSP in English. The digital data processing device is in particular configured to process a train of digital data received from a device such as a computer, a microphone, or a sensor.

The converter 10 is a digital-analog converter. Such a converter is called, in English, DAC, for Digital to Analog Converter (digital to analog converter). The converter 10 is capable of converting a train of digital data supplied by the digital processing device into an analog signal in baseband.

As a variant, the source module 2 provides the analog base signal directly, without digital processing.

When the basic signal A(t) is represented in the frequency domain, the basic signal comprises components for the positive frequencies and components for the negative frequencies, at the image frequencies of the positive frequencies. The information transported is contained twice in the spectrum of the basic signal A(t).

The generation device 4 of a modulated signal is connected at the input to the source module 2 and at the output to the antenna 6.

The generation device 4 is configured to transmit a modulated radio frequency signal to the antenna 6.

In the example shown, the device 4 for generating a modulated signal comprises a basic signal processing block 14, a generator 16, a modulator 18, and a radio frequency amplifier 20.

The basic signal processing block 14 is able to generate the modulating signal C(t) from the basic signal A(t).

In this embodiment, the processing block 14 is an analog processing block, capable of processing an analog signal.

The basic signal processing block 14 comprises a delay unit 30, a convolution unit 32, a phase shifter 34 and a summing module 36.

The delay 30 is able to generate, from the basic signal A(t), a delayed signal, the delayed signal (A(t-To)) having a delay (To) with respect to the basic signal (A(t-To) ))).

For example, delay 30 is a delay line. For example, the retarder 30 comprises at least one capacitor. Furthermore, the retarder 30 comprises, for example, a resistor or a coil. As a variant or in addition, the retarder 30 comprises a transducer.

For example, the retarder 30 is an analog delay line by propagation or accumulation charge transfer.

The retarder 30 is capable of imposing a delay To independently of the frequency.

The delay To is, for example, between 1 ns and 1 μs.

In a variant, the self-timer 30 includes a delay adjustment module capable of modifying the delay To imposed by the self-timer 30.

The convolution unit 32 is able to convolve the delayed signal (A(t-To)) by a convolution signal h(t)=1/(pi*t), so as to form the Hilbert transform of the delayed signal , denoted (B(t-To).

Thus the Hilbert transform obtained is equal to:

A(t-To) * h(t)=

The Fourier transform denoted H of the convolution signal h(t) is equal to:

Or

w is the angular frequency,

j denotes the imaginary unit,

The Hilbert transform of a function sum is equal to the Hilbert transform sum of each of the functions.

Thus, the passage through the convolution unit 32 has the effect of rotating by +90° each negative frequency component and by −90° each positive frequency component of the signal A(t).

The convolution unit 32 is for example made up of sampled analog operation elements such as the addition and weighting of charges.

Phase shifter 34 is configured to phase shift the Hilbert transform of the delayed signal by pi/2. The signal obtained after phase shift is denoted in complex notation j.B(t-To).

The phase shifter 34 introduces the same phase shift whatever the frequency.

For example, phase shifter 34 includes a capacitor and a resistor. The phase shifter includes synchronized charge transfers to achieve a phase shift.

After the convolution and the phase shift, the negative frequency components of the signal A(t) have thus been phase shifted by 180° and the positive frequency components of the signal A(t) by 0°.

The summing module 36 is configured to add the delayed signal and the phase-shifted Hilbert transform j(B(t-To)) so as to generate the modulating signal C(t).

The modulating signal C(t) obtained after the addition is a complex modulating signal C(t)=A(t-To)+j*B(t-To).

The summing module 36 is for example an addition of charges.

When representing the complex modulating signal C(t) in the frequency domain, the components for negative frequencies have been reduced and the components for positive frequencies have been doubled.

At the output of the processing block 4, the modulating signal C(t), the components of the negative frequencies of the basic signal A(t) have been rejected.

In the ideal case where the elements of the processing block 14 have no defect, the rejection of the negative frequencies is total. However, there is a technological limitation related for example to calculation errors.

The rejection rate is the ratio between the average amplitude of the components for the negative frequencies in the basic signal and the average amplitude of the components for the same negative frequencies in the modulating signal. This rejection is ideally maximum.

The rejection rate is expressed in decibels.

In this embodiment, the complex modulating signal C(t) is an analog signal.

As represented in FIG. 1, the complex modulating signal C(t) is broken down into two components. One component is the phase Arg(C) of the complex modulating signal and the other component is the amplitude of the complex modulating signal │C│.

Generator 16 is a carrier wave generator. For example, generator 16 is capable of generating a carrier wave at the carrier frequency. The carrier frequency is for example between 3 kHz and 300 kHz.

The modulator 18 is connected at the input to the processing block 14 and to the generator 16 and at the output to the radiofrequency amplifier 20.

Modulator 18 is configured to receive a carrier signal and a modulating signal C(t) as input, and configured to generate the modulated signal as output.

In particular, the modulator 18 is configured to receive each component Arg(C), │C│ of the complex modulating signal and to generate the modulated signal at output.

The radiofrequency amplifier 20 is connected at the output to the antenna 6. This amplifier 20 is called "transmission amplifier". It is in particular a power amplifier (“power amplifier” or PA).

The radiofrequency amplifier 20 is capable of amplifying the modulated signal. The amplified modulated signal is then transmitted in the direction of antenna 6.

Antenna 6 is an antenna for transmitting a radiofrequency signal.

Optionally, transmission chain 1 further comprises one or more filters (not shown), inserted between the output of radio frequency amplifier 20 and antenna 6.

Advantageously, the transmission chain 1 does not include an image rejection filter at the output of the modulator 18.

The transmission chain 1 described has many advantages. The invention makes it possible to generate a modulated signal, of good quality, while being fast, and consuming little energy.

Indeed, the components of the signal at negative frequencies are rejected before the rise in frequency. Therefore, upscaling is simpler and there is no interference. This makes it possible to reduce the number of components in the generation device and in the transmission chain.

In addition, such a system allows multi-standard use. It is easily reconfigurable in the event of a change in a communication standard or in the event of the appearance of a new standard.

Advantageously, the delay To is equal to the time necessary for the convolution unit 32 to convolve the delayed signal (A(t-To)) by a convolution signal h(t)=1/(pi*t), so forming the Hilbert transform of the delayed signal (B(t-To)).

Figure 2 illustrates a simulation of the rejection rate obtained as a function of the delay To. This simulation is carried out with a modulation by phase change in quadrature QPSK (acronym for Quadrature phase-shift keying ), and in amplitude modulation in quadrature QAM 4 and QAM 16 (QAM being the acronym for quadrature amplitude modulation ), at 5G frequencies between 1.8 GHz and 3.6 GHz.

Carrier signals are signals corresponding to the 5G standard.

The greater the delay To, the greater the rejection rate obtained.

A delay of 1 ns results in a rejection rate of about 10dB.

Depending on the desired rejection rate, it is possible to choose a greater delay To.

For example, a delay To of 1 µs leads to a rejection rate greater than 70dB. This delay is tolerable in the field of telecommunications and such a rejection rate makes it possible to obtain a modulated signal of high quality.

FIG. 3 represents a modulated signal 40 in a transmission chain not comprising the processing block 14 of transmission chain 1 obtained by simulation. Figure 4 represents the modulated signal 42 in the transmission chain 1, the other parameters being similar to the simulation of Figure 3.

These simulations are performed with a signal modulated by 64 QAM quadrature amplitude modulation with a bandwidth of 20 MHz.

In these simulations, the carrier frequency fo is at 3.6 GHz.

In FIG. 3, the modulated signal 40 presents around the carrier frequency, 2 peaks 44, 46 of the same amplitude respectively for the frequency f corresponding to fo-f1 and to fo+f1 where f is representative of the base signal.

In FIG. 4, the amplitude of the peak 44 of the modulated signal 42 corresponding to the positive frequencies fo-f1 is the same. On the other hand, the amplitude of the peak 46 of the modulated signal 42 corresponding to the negative frequencies fo+f1 has been reduced. The rejection rate 50 obtained is approximately 35 dB.

In a variant, illustrated by FIGS. 5 and 6, the generation device 4 is able to perform multiplexing.

The generator 16 is capable of generating a plurality of synchronized carrier signals, each carrier signal being a radio-frequency signal.

The modulator 18 is able to receive the plurality of synchronized carrier signals as input, and to generate the signal modulated by the modulating signal from the plurality of synchronized carrier signals.

FIG. 5 is similar to FIG. 3, signal 52 having been modulated by 3 carrier signals. FIG. 6 is analogous to FIG. 4, signal 54 having been modulated by 3 carrier signals. For reasons of simplification, a frequency range has been represented.

These simulations are performed with a signal modulated by 64 QAM quadrature amplitude modulation with a bandwidth of 20 MHz with carrier frequency signals of 1.9 GHz, 2, 1 GHz and 3.6 GHz.

The carrier signals are aggregated signals corresponding to the 5G standard.

In FIG. 6, it appears that the rate of rejection of the negative frequencies 56, 58 obtained is substantially the same for the different carriers. The difference between the rejection rates of the negative frequencies 56, 58 obtained for the different carriers is, for example, less than 2 dB and advantageously less than 1 dB.

In a second embodiment not shown, the basic signal A(t) supplied by the source module 2 is a digital signal.

In this embodiment, the generation device 4 further comprises a converter capable of converting the base signal into an analog signal before it enters the processing block. The converter is similar to the converter 10 previously described.

A third embodiment of the invention is represented in FIG. 7. The transmission chain 70 according to the third embodiment differs from the transmission chain 1 according to the first embodiment in that the generation device 72 of the modulated signal includes a processing block 74 capable of processing a digital signal.

In this embodiment, the basic signal A(t) supplied by the source module 2 is a digital signal.

The complex modulating signal C(t) is a digital signal.

Processing block 74 includes, for example, at least one logic gate and one transistor.

The processing block 74 comprises for example a CMOS transistor, an acronym for “Complementary Metal Oxide Semiconductor”, meaning complementary metal oxide semiconductor.

The processing block 74 is advantageously made in the form of a suitably programmed microprocessor. Alternatively, the processing block 74 is implemented as a hardware-configured digital circuit, or a combination of a suitably programmed microprocessor and a digital circuit.

The basic signal processing block 74 comprises a delay unit 76, a convolution unit 78, a phase shifter 80 and a summing module 82.

The delay 76, the convolution unit 78, the phase shifter 80 and the summing module 82 have the same functions as those of the processing block of the transmission chain 1 according to the first embodiment. They differ in that they are suitable for performing their functions in the digital domain. For example, the retarder 76, the convolution unit 78, the phase shifter 80 and the summing module 82 comprise memories and digital calculation units.

Advantageously, the generation device 72 further comprises, for each component of the complex modulating signal Arg(C), │C│, a converter 84, 86 capable of converting said component into an analog signal. Each converter 84, 86 is arranged between the output of the processing block 74 and the input of the modulator 18. The converters are similar to the converter 10 previously described.

The precision of such a transmission chain 70 is greater because the elements of the processing block generally have fewer manufacturing defects.

Claims (11)

Device (4, 72) for generating a modulated signal comprising:
- a modulator (18) configured to receive a carrier signal and a modulating signal as input, and configured to generate the modulated signal as output,
the carrier signal being a radio-frequency signal, the modulating signal being representative of a base signal (A(t)), the modulated signal being the carrier signal modulated by the modulating signal,
- a processing block (14, 74) of the basic signal (A(t)) capable of generating the modulating signal,
characterized in that the basic signal processing block (14, 74) comprises:
- a delay (30, 76) capable of generating, from the basic signal, a delayed signal, the delayed signal (A(t-To)) having a delay (To) with respect to the basic signal (A(t) ),
- a convolution unit (32, 78) suitable for convolving the delayed signal by a convolution signal h(t)=1/(pi*t), so as to form the Hilbert transform of the delayed signal (B(t- To)),
- a phase shifter (34, 80) configured to phase shift the Hilbert transform of the delayed signal by pi/2,
- a summing module (36, 82) configured to add the delayed signal and the phase-shifted Hilbert transform so as to generate the modulating signal, the modulating signal obtained after the addition being a complex modulating signal (C(t)) . Generation device (4, 72) according to claim 1, in which the delay (To) is between 1 ns and 1 µs. Generation device (4, 72) according to claim 1 or 2, in which the complex modulating signal (C(t)) is broken down into two components, each component of the complex modulating signal being injected at the input of the modulator (18) , preferably, one component being the phase of the modulating signal and the other component being the amplitude of the modulating signal. A generating device (4, 72) according to any preceding claim, wherein the base signal is a digital signal. Generation device (72) according to claim 4, in which the processing block comprises at least one logic gate and one transistor, the complex modulating signal being a digital signal. Generation device (72) according to Claim 3 and any one of Claims 4 or 5, further comprising, for each component of the complex modulating signal, a converter (84, 86) able to convert the said component into an analog signal, the converters (84, 86) being arranged between the output of the processing block (74) and the input of the modulator (18). Generation device (4) according to claim 4, further comprising a converter suitable for converting the basic signal into an analog signal before it enters the processing block (14), the processing block (14) comprising at least a capacitor, the complex signal being an analog signal. Generation device (4) according to any one of Claims 1 to 3, in which the basic signal is an analog signal, the processing block (14) comprising at least one capacitor, the complex signal being an analog signal. Generation device (4, 72) according to any one of the preceding claims, in which the generation device (4, 72) does not include an image rejection filter after the modulator (18). Generation device (4, 72) according to any one of the preceding claims, in which the modulator (18) is adapted to receive at input a plurality of synchronized carrier signals, each carrier signal being a radio-frequency signal, and to generating the signal modulated by the modulating signal from the plurality of synchronized carrier signals. Radio frequency transmission chain (1, 70) comprising:
- a device (4, 72) for generating a modulated signal according to any one of the preceding claims, and
- a transmission antenna (6) of the modulated signal, the generation device (4, 72) being connected at the output to the antenna (6).