Enhanced dynamic range radio frequency digitizer

Abstract

High Dynamic Range Radio Frequency Digitizer The invention relates to a radio frequency digitizer (10) comprising a module (12) for dividing the power between: a first branch (14) comprising: - a variable gain application device (16), - a first analog-to-digital converter (18), - a first digital gain application module (20); and a second branch (15) comprising: - an analog combination / coupling module (24) connected, at the output of the power-dividing module, to an analog feedback branch (26) of the digital signal from said first analog-to-digital converter comprising: - a digital-to-analog converter (28); - an analog gain application module (30); - a second analog gain application module (32); - a second analog-to-digital converter (34);- a second module (36) for applying a digital gain, each output of the first and second branches being connected to a digital combination / coupling module (38). Figure for the abbreviation: Figure 1;

Description

Title of the invention: Radiofrequency digitizer with increased dynamics

[0001] The present invention relates to a radiofrequency digitizer capable of digitizing a radiofrequency analog signal.

[0002] Absolute dynamics is an essential characteristic in new generations of digital radio frequency digitizers which are likely to receive signals over a wide input power range.

[0003] Typically, a software radio type digitizer is capable of simultaneously receiving signals having power levels between -120 dBm and +10 dBm corresponding respectively to at least one signal emitted by at least one distant transmitter and to at least one signal emitted by at least one nearby transmitter. The absolute dynamic range is then equal to 130 dB.

[0004] An analog-to-digital converter (ADC) is the central element of this type of digital radio frequency digitizer, and used at sampling frequencies of a few hundred MHz, such an analog-to-digital converter (ADC) generally has an absolute dynamic range of around 80 dB.

[0005] Currently, this difference between the absolute dynamic range of 80 dB of the analog-to-digital converter CAN and that of 130 dB at the input of the digital radio frequency digitizer generally requires designers of digital radio frequency digitizers to implement, upstream of the analog-to-digital converter CAN, an analog automatic gain control system AGC, the role of which is to ensure that the analog-to-digital converter CAN is never saturated. To do this, this device includes a constant mode and an adaptive mode. Thus, the minimum signal level that can be received is expressed according to the following equations: [o°o6j wi +ioiog 10 (B C )

[0007] where 5;. the tangential sensitivity level of the digitizer, kB the Boltzmann constant expressed in mkkgskK'^ -, the temperature in Kelvin K, NF the noise factor, Bc the frequency channel width of the digitizer in Hertz Fz, and this with:

[0008]

[0009] where NFm is the noise factor of the digitizer in the constant mode, A is the attenuation of the adaptive mode, and an increasing function.

[0010] However, the current use of such an analog automatic gain control system AGC does not make it possible to increase the absolute dynamics of the digital radiofrequency digitizer, but only to adapt the level of the strong signal (in terms of power level) to the dynamics accessible by the converter. analog-digital CAN, so that the absolute dynamics of the digital radio frequency digitizer remains limited to 80 dB for example, while an absolute dynamic of 130 dB is required. Furthermore, this solution based on an analog automatic gain control (AGC) system leads to a degradation of the tangential sensitivity of the digitizer by an increase in the noise factor.

[0011] The object of the invention is to overcome the drawbacks of the state of the art by proposing an alternative architecture of the digital radiofrequency digitizer capable of overcoming the current limits associated with the use of an analog automatic gain control (AGC) system. In other words, the present invention aims to propose an alternative architecture of the digital radiofrequency digitizer in order to improve its absolute dynamics and consequently its sensitivity, in order to better correspond to the absolute dynamics of the signals that it is capable of receiving, and this by limiting the associated complexity and hardware cost.

[0012] To this end, the invention proposes a radiofrequency digitizer comprising a module configured to divide the power having an input for receiving an analog stream and two outputs associated respectively with a first branch and a second processing branch distinct from said radiofrequency digitizer, the first branch comprising at least:

[0013] - a device for applying a variable gain whose input is connected to the output of the module configured to divide the power,

[0014] - a first analog-digital converter whose input is connected to the output of the variable gain application device,

[0015] - a first module for applying a digital gain to the generated digital signal at the output of said first analog-digital converter of said first branch;

[0016] said second branch being connected, via a module configured to apply an analog delay, to the associated output of the module configured to divide the power, and comprising:

[0017] - an analog combining / coupling module comprising one output and two entries:

[0018] - a first input being connected to the output of the module configured to divide the power associated with said second branch,

[0019] - a second input being connectable to an analog reinjection branch of the digital signal generated and / or digitally processed at the output of said first analog-digital converter, the analog feedback branch comprising at least:

[0020] - a digital-to-analog converter whose input can be directly connected or indirectly at the output of said first analog-to-digital converter;

[0021] - a first module for applying an analog gain whose input is connected to the output of said digital-to-analog converter;

[0022] - a second module for applying an analog gain whose input is connected at the output of said analog combination / coupling module;

[0023] - a second analog-to-digital converter whose input is connected to the output of the second module applying an analog gain;

[0024] - a second module for applying a digital gain to the digital signal generated at the output of said second analog-digital converter of said second branch,

[0025] the digital output of the first module for applying a digital gain of said first branch and the output of the second module for applying a digital gain of said second branch being connected respectively to two inputs of a digital combination / coupling module suitable for generating the output of said radiofrequency digitizer.

[0026] With such an architecture, the radiofrequency digitizer proposed according to the present invention limits the sensitivity degradation observed according to the state of the art, in particular the state of the art using an analog automatic gain control AGC system. Indeed, the present invention proposes to provide, within the radiofrequency digitizer, a mixed interference cancellation system based on the combination of two analog-to-digital converters CANs and a digital-to-analog converter DAC all three arranged according to said architecture.

[0027] More precisely, to estimate and at least reduce the thermal noise capable of preventing the digitization of low power level signals, the signals desensitized by the first analog-to-digital converter CAN of the first branch can be reinjected in analog, after passing through the digital-to-analog converter CNA of the reinjection branch, and combined / coupled analogically with the initial received signals.

[0028] Thus, the present invention offers the user a dynamic range that is significantly greater than that available in equipment using conventional digitization, particularly in the presence of a received analog stream comprising at least two signals having a high (i.e. greater than a predetermined threshold) power ratio.

[0029] According to particular embodiments, the radiofrequency digitizer comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0030] - the reinjection branch further comprises a third module for applying a digital gain to the digital signal generated at the output of said first analog-digital converter of said first branch, the input of said third module applying a digital gain being connectable via a module configured to apply a digital delay to an output of said first analog-to-digital converter of said first branch, the output of said third module applying a digital gain being connected to the input of the digital-to-analog converter;

[0031] - the device for applying a variable gain corresponds to a control device automatic gain or variable gain amplifier;

[0032] - the device for applying a variable gain comprises a variable attenuator connected at output to a third module for applying a constant analog gain capable of generating the output of said device for applying a variable gain;

[0033] - the variable attenuation value capable of being implemented by said attenuator variable depends on the power of the signals received within said analog input stream of said digitizer, the constant analog gain applied by said third analog gain application module, and the maximum operating power of the first analog-to-digital converter;

[0034] - the first analog-to-digital converter and the second converter analog-digital are of identical resolutions above a predetermined threshold;

[0035] - the digital-to-analog converter has a higher full scale than that associated respectively with the first analog-to-digital converter and the second analog-to-digital converter;

[0036] - the module configured to divide the power is a directional coupler configured to distribute the power differently in said first and second branches, and / or a hybrid coupler configured to reverse the polarity of one of said first and second branches relative to the other;

[0037] - the module configured to divide the power is a power divider configured to distribute power equally in said first and second branches;

[0038] - in the absence of a received analog stream simultaneously comprising a strong signal having a strong power level, above a predetermined power threshold, and a weak signal having a weak power level, below said predetermined power threshold, and when:

[0039] - the module configured to divide the power is a power divider configured to distribute power equally in said first and second branches, and

[0040] - the variable attenuation value capable of being implemented by said attenuator variable is null:

[0041] the reinjection branch is simultaneously disconnected from said first branch and said second branch, and said digital combination / coupling module is capable of generating the output of said radiofrequency digitizer by determining the average of said first and second branches.

[0042] These characteristics and advantages of the invention will appear more clearly on reading the description which follows, given solely by way of non-limiting example, and made with reference to the appended drawings, in which:

[0043] - [Fig.l] [Fig.l] is a schematic representation of the architecture of a nude radiofrequency mezzo-meter according to a first embodiment of the invention;

[0044] - [Fig.2] [Fig.2] is a schematic representation of the architecture of a nude radiofrequency mezzo-meter according to a second embodiment of the invention.

[0045] In the example of [Fig.l], we consider the case where the received analog stream Fi comprises a strong signal Si (i.e. having a strong power level, greater than a predetermined power threshold) and a weak signal S2 (i.e. having a low power level, lower than a predetermined power threshold).

[0046] The radiofrequency digitizer 10 according to the present invention firstly comprises a module 12 configured to divide the power having an input for receiving the analog flow Fi and two outputs associated respectively with a first branch 14 and a second branch 15 of processing distinct from said radiofrequency digitizer 10.

[0047] The first branch 14 comprises at least one device 16 for applying a variable gain, the input of which is connected to the output of the module 12 configured to divide the power, a first analog-digital converter 18, the input of which is connected to the output of the device 16 for applying a variable gain, and a first module 20 for applying a digital gain to the digital signal generated at the output of said first analog-digital converter 18 of said first branch 14. In particular, the first module 20 for applying a digital gain is capable of applying a variable or constant gain.

[0048] Such a first branch 14, according to a particular variant, where the device 16 for applying a variable gain corresponds to an automatic gain control device then corresponds to the conventional architecture of a radiofrequency digitizer mentioned above based on the use of an analog automatic gain control system AGC and then provides, as shown in box 21, a degradation of the sensitivity, the noise level Bi generated at the output of the first analog-digital converter 18 preventing the digitization of the weak signal S2. Indeed, at the output of the first analog-digital converter 18 the strong signal Si is correctly received since conventionally the automatic gain control device 16 makes it possible to avoid its saturation, however, because of the variable attenuation implemented within such a device 16 for applying a variable gain, the weak signal S2 analog stream received Fi is lost by the loss of sensitivity associated with the increase in the noise level Bb

[0049] The second branch 15 is connected, via a module 22 configured to apply an analog delay, to the associated output of the module 12 configured to divide the power. The second branch 15 comprises an analog combining / coupling module 24 comprising one output and two inputs:

[0050] - a first input being connected to the output of the module 12 configured to divide the power associated with said second branch,

[0051] - a second input, connected according to the embodiment of [Fig. 1], to a branch 26 for analog reinjection of the digital signal generated and / or digitally processed at the output of said first analog-digital converter 18.

[0052] In particular, according to the present invention, the analog feedback branch 26 comprises at least one digital-to-analog converter 28 whose input is connectable, directly or indirectly, via a module, not shown, configured to apply a digital delay, to an output of said first analog-to-digital converter 18 of said first branch 14 at the output of said first analog-to-digital converter 18 and a first module 30 for applying an analog gain whose input is connected to the output of said digital-to-analog converter 28. In particular, such a first module 30 for applying an analog gain is capable of applying a variable or constant gain.

[0053] Such a reinjection branch 26 makes it possible to reinject, in analog form via the digital-to-analog converter 28, the digitized signals illustrated in box 21, namely the strong signal Si, the weak signal S2 and advantageously according to the present invention the digital thermal noise level Bi obtained as represented in box 21 at the output of the first analog-to-digital converter 18.

[0054] In addition, the second branch 15 comprises, in addition to the analog combination / coupling module 24, a second analog gain application module 32 whose input is connected to the output of said analog combination / coupling module 24, a second analog-digital converter 34 whose input is connected to the output of the second analog gain application module 32. In particular, such a second analog gain application module 32 is capable of applying a variable or constant gain.

[0055] Such a second branch 15 receives as input to the analog combination / coupling module 24 one of the outputs of the module 12 configured to divide the power, and according to the embodiment of [Fig.l], the analog combination / coupling module 24 is configured to implement a subtraction between these two inputs, namely the one connected, via the module 22 configured to apply an analog delay, to the output of the module 12 configured to divide the power and associated with said second branch 15, and the input corresponding to the output of the reinjection branch 26, which makes it possible to reduce the power level of the received signals as much as possible. At the output of the analog combination / coupling module 24, the signals thus attenuated are processed by the second analog gain application module 32 to apply a predetermined and adapted gain to them in order to pass the second analog-digital converter 34.

[0056] As illustrated by box 35 representing the output of the second analog-digital converter 34, an estimation of the thermal noise level Bi which limited the digitization of the weak signal S2 within the first branch 14 is then advantageously obtained according to the present invention, and moreover, the residue Ri associated with the strong signal Si, the residue R2 associated with the weak signal S2 and the resulting mixed noise level B2 (i.e. mixing the reinjection branch 26 and the second branch 15) and lower than the thermal noise level Bi associated with the first reference branch 14 representative of the state of the art are also obtained. In a manner not shown in this purely explanatory box 35, the resulting total noise would correspond to the sum of the noise levels Bi and B2 (the noise level B2 being substantially lower than the noise level B i).

[0057] The second branch 15 further comprises a second module 36 for applying a digital gain to the digital signal generated at the output of said second analog-digital converter 34 of said second branch 15. In particular, such a second module 36 for applying a digital gain is capable of applying a variable or constant gain.

[0058] Furthermore, according to the architecture of the radiofrequency digitizer proposed according to the present invention, the digital output of the first module for applying a digital gain 20 of said first branch 14 and the output of the second module for applying a digital gain 36 of said second branch 15 are respectively connected to two inputs of a digital combination / coupling module 38 capable of generating the output of said radiofrequency digitizer 10.

[0059] In particular, the digital combination / coupling module 38 is, according to the embodiment of [Fig. 1], suitable for summing the signals coming from the first and second branches 14 and 15 respectively, and the digital gains respectively associated with the first module for applying a digital gain 20 of said first branch 14 and with the second module for applying a digital gain 36 of said second branch 15 are involved in this summation and are configured to subtract and attenuate the thermal noise level Bi which limited the digitization of the weak signal S2 within the first branch 14, so that as illustrated by box 40 only the resulting mixed noise level B2 is applied to the output of the radiofrequency digitizer 10 proposed according to the present invention, allowing the recovery digital operation of the weak signal S2, and therefore a limitation of the desensitization applied by the radiofrequency digitizer according to the present invention.

[0060] In other words, the solution proposed according to this first embodiment of the present invention makes it possible to contain the degradation of sensitivity by carrying out an estimation of the noise level Bi generated by the digitization of the first analog-digital converter 18 and then subtracting it once digitized by the second analog-digital converter 34.

[0061] According to a particular aspect, it should be noted that the combination of the module 22 configured to apply an analog delay, and of the module not shown configured to apply a digital delay and located between the output of said first analog-digital converter 18 and the input of the feedback branch 26, is configured to apply a time synchronization of the branches 14, 15 and 26 of the radiofrequency digitizer according to the present invention. Such a time synchronization allows both a correct estimation of the noise level Bi generated by the digitization of the first analog-digital converter 18 and its correct successive lowering via the digital combination / coupling module 38. In other words, such a time synchronization makes it possible to avoid an increase in the variance of the noise. According to a particular aspect, such a synchronization is at least of the order of the sampling time.

[0062] Various variants or optional additions to this first embodiment are described below.

[0063] In particular, as an optional addition, the reinjection branch 26 further comprises a third module 42 for applying a digital gain to the digital signal generated at the output of said first analog-to-digital converter 18 of said first branch 14, the input of said third module 42 for applying a digital gain being connected via the module, not shown, configured to apply a digital delay to an output of said first analog-to-digital converter 18 of said first branch 14, the output of said third module 42 for applying a digital gain being connected to the input of the digital-to-analog converter 28.In particular, such a third module 42 for applying a digital gain is capable of applying a variable or constant digital gain in order to partially enhance the signals coming from the first analog-digital converter 18, this digital gain applied by the third optional module 42 for applying a digital gain is supplemented by the analog gain applied by the first module 30 for applying an analog gain in order to enhance the signals reinjected via the reinjection branch 26 to the levels of those coming from the module 12 configured to divide the power and intended for the second branch 15 via the module 22 configured to apply an analog delay. Such a third module 42 for applying a digital gain upstream. of the 28 DAC digital-to-analog converter allows in particular to reduce the influence of the noise factor of the 28 DAC digital-to-analog converter.

[0064] As indicated previously according to a first variant, the device 16 for applying a variable gain corresponds to an automatic gain control device or, according to a second variant, corresponds to a variable gain amplifier.

[0065] According to a third variant, the device 16 for applying a corresponding variable gain comprises a variable attenuator 44 connected at the output to a third module 46 for applying a constant analog gain capable of generating the output of said device 16 for applying a variable gain. In particular according to this third variant, the variable attenuation value capable of being implemented by said variable attenuator 46 depends on the power of the signals received S1 and S2 within said analog input stream Fi of said digitizer 10, on the constant analog gain applied by said third module 46 for applying an analog gain, and on the maximum operating power of the first analog-digital converter 18 in order to avoid saturation thereof.

[0066] According to another optional particular aspect, the first analog-to-digital converter 18 and the second analog-to-digital converter 34 have identical resolutions greater than a predetermined threshold, for example a resolution greater than or equal to 14 bits.

[0067] According to another optional particular aspect, the digital-to-analog converter 28 has a higher full scale than that associated respectively with the first analog-to-digital converter 18 and the second analog-to-digital converter 34. In addition, for example, the digital-to-analog converter 28 has a resolution greater than 16 bits.

[0068] With regard to the module 12 configured to divide the power, according to a first optional variant, the module 12 configured to divide the power is a directional coupler configured to distribute the power differently in said first and second branches 14 and 15 respectively, and / or the module 12 configured to divide the power is a hybrid coupler configured to reverse the polarity of one of said first and second branches with respect to the other.

[0069] As an alternative, according to a second optional variant the module configured to divide the power is a power divider configured to distribute the power equally in said first and second branches 14 and 15, which amounts to lowering by 3 dB each of these outputs respectively connected to each of the branches 14 and 15.

[0070] Depending on the first or second variant chosen for the module 12 configured to divide the power, the values ​​of the analog or digital gains of the gain application modules 20, 30, 32, 36 and optionally 42, 44, 46 are adapted to ensure proper operation of the radio frequency digitizer 10.

[0071] [Fig. 2] is a schematic representation of the architecture of a radiofrequency digitizer according to a second embodiment of the invention implemented in particular in the absence of simultaneous reception of both strong and weak signals within the analog stream as was the case in the example illustrated by [Fig. 1]. In other words, the embodiment of [Fig. 2] is implemented in particular in the presence of the received analog stream F2 comprising a single type of signal, for example a weak signal S2 (i.e. having a low power level, lower than a predetermined power threshold).

[0072] Thus, in the absence of a received analog stream simultaneously comprising a strong signal having a strong power level, greater than a predetermined power threshold, and a weak signal having a low power level, lower than said predetermined power threshold, and when:

[0073] - the module 12 configured to divide the power is a power divider configured to distribute power equally in said first and second branches, and

[0074] - the variable attenuation value capable of being implemented by said attenuator optional variable 46 is null:

[0075] the reinjection branch 26 is simultaneously disconnected from said first branch 14 and from said second branch 15, and said digital combination / coupling module 38 is capable of generating the output of said radiofrequency digitizer by determining the average of said first and second branches 14 and 15.

[0076] Furthermore, in this particular case, the first module 20 for applying a digital gain of the first branch 14 and the second module 36 for applying a digital gain of the second branch 15 of [Fig.l] are, in this particular case, identical and correspond to a module 48 for applying a digital gain.

[0077] Indeed, in this particular case of absence of received analog stream comprising simultaneously a strong and weak signal, where the module 12 configured to divide the power is a power divider and where the optional variable attenuator 46 implements a zero attenuation, which corresponds to the realization of three cumulative conditions, the desensitization of 3 dB on the two branches 14 and 15 is not absorbed by the variable attenuation of the optional attenuator 46 which means that the loss of sensitivity at the chain output is also 3 dB.

[0078] To compensate for these 3 dB and thus propose a more conventional architecture with parallel analog-to-digital converters CANs (from the English stackADCs), and this from this particular embodiment of the radiofrequency digitizer architecture described in relation to [Fig.l], the reinjection branch 26 via the digital-to-analog converter CNA is deactivated, as is the action of the analog combining / coupling module 24, so that the two parallel analog-to-digital converters CANs are driven by the same signals and deliver similar outputs illustrated by boxes 50 and 52. Such diversity then makes it possible to theoretically recover 3 dB by averaging implemented by the digital combining / coupling module 38 as illustrated by box 54 of [Fig.2] with a noise level B3 reduced by 3 dB compared to the output noise levels Bi of each analog-to-digital converter illustrated respectively in boxes 50 and 52, which previously in relation to [Fig.l] was suitable for generating the output of said radiofrequency digitizer by summation (or subtraction when the module 12 is a hybrid coupler) of said first and second branches 14 and 15.

[0079] In other words, in the aforementioned particular case, the radiofrequency digitizer architecture according to the present invention and as described in relation to [Fig.l] is suitable for being adapted into a radiofrequency digitizer architecture with parallel CANs, the reinjection branch 26 then being disconnectable. Such an adaptation makes it possible to maintain the sensitivity of the radiofrequency digitizer 10 according to the present invention in the aforementioned particular case.

[0080] Those skilled in the art will understand that the invention is not limited to the embodiments described, nor to the particular examples of the description, the embodiments and variants mentioned above being suitable for being combined with each other to generate new embodiments of the invention.

[0081] It is thus understood in summary that the radiofrequency digitizer 10 according to the present invention using two analog-to-digital converters CANs and a digital-to-analog converter DAC arranged specifically according to the architecture of [Fig.l], makes it possible to reinject in analog the signals desensitized by the first analog-to-digital converter then to subtract them, thanks to the analog combination / coupling module 24, from the initial signals received, to thus estimate the limiting thermal noise preventing the digitization of the weak signals, noise which is subtracted from the signals digitized by the first analog-to-digital converter via the digital combination / coupling module 38 to make the weak signals reappear, and consequently to limit the desensitization of the radiofrequency digitizer 10 (i.e. to reduce the desensitization of the radiofrequency digitizer 10 compared to current techniques of the state of the art).

[0082] Furthermore, according to the aforementioned particular case, such an architecture allows adaptation to an architecture with parallel analog-digital converters (ADCs) in order to maintain sensitivity in the absence of simultaneous reception of strong and weak signals.

[0083] Thus, the present invention offers the user a dynamic range that is significantly greater than that available in equipment using conventional digitization, in particular in the presence of a received analog stream comprising at least two signals having a high (i.e. greater than a predetermined threshold) power ratio, for example a power ratio of the order of 15 dB, making it possible to ensure the digitization of the lower power signal. Thus, compared to the conventional use of an analog automatic gain control (AGC) system, the sensitivity of the digitizer according to the present invention is less degraded, which makes it usable on any analog signal acquisition system or subsystem containing an analog-digital converter, in particular in the context of applications of wideband digitized radiofrequency digitizers, and allows a digital improvement of these systems.

Claims

1. Claims Radiofrequency digitizer (10) comprising a module (12) configured to divide the power having an input for receiving an analog stream and two outputs associated respectively with a first branch (14) and a second branch (15) of processing distinct from said radiofrequency digitizer, the first branch (14) comprising at least: - a device (16) for applying a variable gain, the input of which is connected to the output of the module (12) configured to divide the power, - a first analog-digital converter (18) the input of which is connected to the output of the device (16) for applying a variable gain, - a first module (20) for applying a digital gain to the digital signal generated at the output of said first analog-digital converter (18) of said first branch (14); characterized in that said second branch (15) is connected, via a module (22) configured to apply an analog delay, to the associated output of the module (12) configured to divide the power, and comprises: - an analog combination / coupling module (24) comprising one output and two inputs: - a first input being connected to the output of the module (12) configured to divide the power associated with said second branch, - a second input being connectable to a branch (26) for analog reinjection of the digital signal generated and / or digitally processed at the output of said first analog-digital converter (18), the analog reinjection branch comprising at least: - a digital-analog converter (28) whose input is connectable directly or indirectly to the output of said first analog-digital converter; - a first module (30) for applying an analog gain, the input of which is connected to the output of said digital-to-analog converter (28); - a second module (32) for applying an analog gain, the input of which is connected to the output of said analog combination / coupling module; - a second analog-digital converter (34) whose input is connected to the output of the second gain application module analog; - a second module (36) for applying a digital gain to the digital signal generated at the output of said second analog-digital converter of said second branch, the digital output of the first module (20) for applying a digital gain of said first branch (14) and the output of the second module (36) for applying a digital gain of said second branch (15) being connected respectively to two inputs of a digital combination / coupling module (38) suitable for generating the output of said radiofrequency digitizer (10);the first analog-to-digital converter (18) and the second analog-to-digital converter (34) having identical resolutions greater than a predetermined threshold, the first module for applying a digital gain (20) of said first branch (14) and the second module for applying a digital gain (36) of said second branch (15) intervening in the summation of the signals coming from the first and second branches respectively and being configured to subtract and attenuate the level of thermal noise capable of preventing the digitization of the signals of low power levels.;

2. Radiofrequency digitizer (10) according to claim 1, wherein the feedback branch (26) further comprises a third module (42) for applying a digital gain to the digital signal generated at the output of said first analog-to-digital converter (18) of said first branch (14), the input of said third module (42) for applying a digital gain being connectable via a module configured to apply a digital delay to an output of said first analog-to-digital converter (18) of said first branch, the output of said third module (42) for applying a digital gain being connected to the input of the digital-to-analog converter (28).

3. Radio frequency digitizer (10) according to claim 1 or 2, wherein the device (16) for applying a variable gain corresponds to an automatic gain control device or a variable gain amplifier.

4. Radiofrequency digitizer (10) according to claim 1 or 2, in which the device (16) for applying a variable gain comprises a variable attenuator (44) connected at the output to a third module (46) for applying a constant analog gain capable of generating the output said device (16) for applying a variable gain.

5. Radio frequency digitizer (10) according to claim 4, wherein the variable attenuation value capable of being implemented by said variable attenuator (44) depends on the power of the signals received within said analog input stream of said digitizer (10), the constant analog gain applied by said third analog gain application module (46), and the maximum operating power of the first analog-to-digital converter (18).

6. A radio frequency digitizer (10) according to any preceding claim, wherein the digital-to-analog converter (28) has a higher full scale than that associated with the first analog-to-digital converter (18) and the second analog-to-digital converter (34) respectively.

7. A radio frequency digitizer (10) according to any preceding claim, wherein the module (12) configured to divide the power is a directional coupler configured to distribute the power differently in said first and second branches, and / or a hybrid coupler configured to reverse the polarity of one of said first and second branches relative to the other.

8. A radio frequency digitizer (10) according to any one of claims 1 to 5, wherein the module (12) configured to divide the power is a power divider configured to distribute the power equally in said first and second branches.

9. Radiofrequency digitizer (10) according to claim 4 and claim 8, wherein, in the absence of a received analog stream simultaneously comprising a strong signal having a strong power level, greater than a predetermined power threshold, and a weak signal having a low power level, lower than said predetermined power threshold, and when: - the module (12) configured to divide the power is a power divider configured to distribute the power equally in said first and second branches, and - the variable attenuation value capable of being implemented by said variable attenuator is zero: the reinjection branch (26) is simultaneously disconnected from said first branch (14) and from said second branch (15), and said digital combination / coupling module (38) is capable of generating the output of said radiofrequency digitizer by determining the average of said first and second branches.

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