Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
  • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
  • H03M1/12—Analogue/digital converters
  • H03M1/14—Conversion in steps with each step involving the same or a different conversion means and delivering more than one bit
  • H03M1/16—Conversion in steps with each step involving the same or a different conversion means and delivering more than one bit with scale factor modification, i.e. by changing the amplification between the steps
  • H03M1/164—Conversion in steps with each step involving the same or a different conversion means and delivering more than one bit with scale factor modification, i.e. by changing the amplification between the steps the steps being performed sequentially in series-connected stages
  • H03M1/167—Conversion in steps with each step involving the same or a different conversion means and delivering more than one bit with scale factor modification, i.e. by changing the amplification between the steps the steps being performed sequentially in series-connected stages all stages comprising simultaneous converters
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
  • H03M3/00—Conversion of analogue values to or from differential modulation
  • H03M3/30—Delta-sigma modulation
  • H03M3/39—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators
  • H03M3/412—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators characterised by the number of quantisers and their type and resolution
  • H03M3/414—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators characterised by the number of quantisers and their type and resolution having multiple quantisers arranged in cascaded loops, each of the second and further loops processing the quantisation error of the loop preceding it, i.e. multiple stage noise shaping [MASH] type
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
  • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
  • H03M1/12—Analogue/digital converters
  • H03M1/124—Sampling or signal conditioning arrangements specially adapted for A/D converters
  • H03M1/129—Means for adapting the input signal to the range the converter can handle, e.g. limiting, pre-scaling ; Out-of-range indication
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
  • H03M3/00—Conversion of analogue values to or from differential modulation
  • H03M3/30—Delta-sigma modulation
  • H03M3/458—Analogue/digital converters using delta-sigma modulation as an intermediate step
  • H03M3/478—Means for controlling the correspondence between the range of the input signal and the range of signals the converter can handle; Means for out-of-range indication
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/06—Receivers
  • H04B1/10—Means associated with receiver for limiting or suppressing noise or interference

Definitions

• the present invention relates to a radiofrequency digitizer capable of digitizing an analog radiofrequency signal.
• Absolute dynamics is an essential feature in new generations of digital radio frequency digitizers which are capable of receiving signals over a wide input power range.
• a digitizer of the software radio type, is capable of simultaneously receiving signals having power levels of 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 is then equal to 130 dB.
• An ADC analog-to-digital converter is the central element of this type of digital radio frequency digitizer, and used at sampling frequencies of a few hundred MHz, such an ADC analog-to-digital converter generally has an absolute dynamic range of the order of 80dB.
• this difference between the absolute dynamic of 80 dB of the analog-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 set up, upstream of the analog-digital converter CAN, an analog automatic gain control system AGC, whose role is to ensure that the analog-digital converter CAN is never saturated.
• this device comprises a constant mode and an adaptive mode.
• the minimum signal level that can be received is expressed according to the following equations: r I dBm 10 log 10 (/c s T) + NF ⁇ dB + 10 log 10 (fîc)
• S* the tangential sensitivity level of the digitizer
• k B the Boltzmann constant expressed in m 2 . kg. s ⁇ 2 . K ⁇ 1
• T the temperature in Kelvin K
• NF the noise factor
• B c the channel frequency width of the digitizer in Hertz Hz
• NF const is the noise figure of the digitizer in the constant mode
• A is the attenuation of the adaptive mode
• f ( ) an increasing function
• the object of the invention is to remedy the drawbacks of the state of the art by proposing an alternative architecture of the digital radio frequency digitizer capable of overcoming the current limits associated with the use of an analog AGC automatic gain control system.
• 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 suitable for receiving, and this while limiting the complexity and the associated material cost.
• the invention proposes a radiofrequency digitizer comprising a module configured to divide the power having an analog stream reception input and two outputs associated respectively with a first branch and a second distinct processing branch of said radiofrequency digitizer, the first branch comprising at least:
• a first module for applying a digital gain to the digital signal generated at the output of said first analog-digital converter of said first branch; 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:
• analog feedback 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: - A digital-analog converter whose input can be connected directly or indirectly to the output of said first analog-digital converter;
• 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, the digital output of the first module for applying a digital gain of said first branch and the output of the second digital gain application module of said second branch being respectively connected to two inputs of a digital combination/coupling module able to generate the output of said radio frequency digitizer.
• the radiofrequency digitizer proposed according to the present invention limits the degradation of sensitivity observed according to the state of the art, in particular the state of the art using an analog AGC automatic gain control system.
• the present invention proposes to provide, within the radiofrequency digitizer, a mixed interference cancellation system based on the combination of two analog-digital converters CANs and a digital-analog converter CNA arranged all three according to said architecture.
• the signals desensitized by the first analog-digital converter CAN of the first branch can be reinjected into analog, after passing through the converter digital-to-analog DAC of the feedback branch, and combined/analog-coupled to the initial received signals.
• the present invention offers the user a dynamic much greater than that available in equipment using conventional digitization, in particular in the presence of an analog stream received comprising at least two signals having a strong (i.e. greater than a predetermined threshold) power ratio.
• the radiofrequency digitizer comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations: - the first analog-digital converter and the second analog-digital converter have identical resolutions greater than a predetermined threshold, the first module for applying a digital gain of said first branch and the second module for applying a gain digital of said second branch intervening in the summation of the signals originating respectively from the first and second branches and being configured to subtract and attenuate the level of thermal noise suitable for preventing the digitization of the signals of low power levels;
• the feedback 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 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 of said first branch, the output of said third module for applying a digital gain being connected to the input of the digital-to-analog converter;
• the device for applying a variable gain corresponds to an automatic gain control device or a variable gain amplifier
• the device for applying a variable gain comprises a variable attenuator connected at the output to a third module for applying a constant analog gain capable of generating the output of said device for applying a variable gain;
• variable attenuation value specific to being implemented by said variable attenuator depends on the power of the signals received within said analog input stream of said digitizer, on the constant analog gain applied by said third application module of a analog gain, and the maximum operating power of the first analog-digital converter;
• the first analog-digital converter and the second analog-digital converter have identical resolutions greater than a predetermined threshold
• the digital-analog converter has a higher full scale than that associated respectively with the first analog-digital converter and the second analog-digital converter;
• 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 with respect to the other ;
• the module configured to divide the power is a power divider configured to distribute the power equally in said first and second branches; - in the absence of an analog stream received simultaneously comprising a strong signal presenting a strong power level, higher than a predetermined power threshold, and a weak signal presenting a low power level, lower than said predetermined power threshold, and when:
• the module configured to divide the power is a power divider configured to distribute the power equally in said first and second branches, and
• variable attenuation value capable of being implemented by said variable attenuator is zero: the feedback branch is disconnected simultaneously from said first branch and from said second branch, and said digital combination/coupling module is capable of generating the output of said radio frequency digitizer by determining the average of said first and second branches.
• FIG. 1 is a schematic representation of the architecture of a radio frequency digitizer according to a first embodiment of the invention
• FIG. 2 is a schematic representation of the architecture of a radio frequency digitizer according to a second embodiment of the invention.
• the received analog stream Fi comprises a strong signal Si (i.e. presenting a strong power level, greater than a predetermined power threshold) and a weak signal S2 (i.e. presenting a low power level, below a predetermined power threshold).
• the radiofrequency digitizer 10 firstly comprises a module 12 configured to divide the power having an analog stream reception input F1 and two outputs associated respectively with a first branch 14 and a second processing branch 15 distinct from said radio frequency digitizer 10.
• the first branch 14 comprises at least one device 16 for applying a variable gain whose input is connected to the output of the module 12 configured to divide the power, a first analog-digital converter 18 whose input 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.
• the first module 20 for applying a digital gain is capable of applying a variable or constant gain.
• 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 of such a device 16 for applying a variable gain, the weak analog signal S2 received F1 is lost by the loss of sensitivity associated with the increase in the noise level B1.
• 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 combination/coupling module 24 comprising one output and two inputs:
• the analog feedback branch 26 comprises at least one digital-analog converter 28 whose input can be connected, directly or indirectly, via a module, not shown, configured to apply a digital delay, to a output of said first analog-digital converter 18 of said first branch 14 at the output of said first analog-digital converter 18 and a first module 30 for applying an analog gain whose input is connected to the output of said digital-analog converter 28
• a first module 30 for applying an analog gain is capable of applying a variable or constant gain.
• Such a reinjection branch 26 makes it possible to reinject, in analog form via the digital-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 Bi-digital thermal noise level obtained as represented in box 21 at the output of the first analog-digital converter 18.
• the second branch 15 comprises, in addition to the analog combination/coupling module 24, a second module 32 for applying an analog gain, the input of which 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 module 32 for applying an analog gain.
• a second module 32 for applying an analog gain is capable of applying a variable or constant gain.
• Such a second branch 15 receives at the input of 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. 1, 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 as much as possible the power level of the signals received.
• the signals thus attenuated are processed by the second module 32 for applying an analog gain to apply to them a predetermined and suitable gain in order to pass the second analog-digital converter 34.
• an estimate 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 level B 2 of resulting mixed noise (ie mixing the feedback branch 26 and the second branch 15) and lower than the level of thermal noise B1 associated with the first reference branch 14 representative of the state of the art are also obtained.
• the resulting total noise would correspond to the sum of the noise levels B1 and B 2 (the noise level B 2 being substantially lower than the noise level B1).
• 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.
• a second module 36 for applying a a digital gain is suitable for applying a variable or constant gain.
• 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 combining/coupling module 38 capable of generating the output of said radio frequency digitizer 10.
• the digital combination/coupling module 38 is, according to the embodiment of FIG. application of a digital gain 20 of said first branch 14 and to the second module for applying a digital gain 36 of said second branch 15 intervene in this summation and are configured to subtract and attenuate the level of thermal noise 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 B 2 is applied at the output of the radiofrequency digitizer 10 proposed according to the present invention, allowing the digital recovery of the weak signal S 2 , and therefore a limitation of the desensitization applied by the radiofrequency digitizer according to the present invention.
• the solution proposed according to this first embodiment of the present invention makes it possible to contain the degradation in sensitivity by estimating the noise level B1 generated by the digitization of the first analog-digital converter 18 in order to then subtract it once digitized by the second analog-digital converter 34.
• the combination of the module 22 configured to apply an analog delay, and of the module not shown configured to apply a digital and localized delay between the output of said first analog-digital converter 18 and the input of the reinjection branch 26 is configured to apply a temporal synchronization of the branches 14, 15 and 26 of the radiofrequency digitizer according to the present invention.
• Such time synchronization allows both a correct estimation of the noise level B1 generated by the digitization of the first analog-digital converter 18 and its correct successive lowering via the module 38 of digital combination/coupling.
• a temporal synchronization makes it possible to avoid an increase in the variance of the noise.
• such synchronization is at the very least of the order of the sampling time.
• 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-digital converter 18 of said first branch 14, the input of said third digital gain application module 42 being connected via the module, not shown, configured to apply a digital delay to an output of said first analog-digital converter 18 of said first branch 14, the output of said third application module 42 of a digital gain being connected to the input of the digital-analog converter 28.
• such a third module 42 for applying a digital gain is suitable for applying a variable or constant digital gain in order to partially enhance the signals 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 at the level of those originating 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 digital-analog converter 28 DAC makes it possible in particular to reduce the influence of the noise factor of the digital-analog converter 28 DAC.
• 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.
• 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 application device 16 of varying gain.
• the variable attenuation value specific to being implemented by said variable attenuator 46 depends on the power of the received signals Si and S2 within said analog input stream F1 of said digitizer 10, on the analog gain constant applied by said third module 46 for applying an analog gain, and the maximum operating power of the first analog-digital converter 18 in order to avoid saturation.
• the first analog-digital converter 18 and the second analog-digital converter 34 have identical resolutions greater than a predetermined threshold, for example a resolution greater than or equal to 14 bits.
• the digital-analog converter 28 has a higher full scale than those associated respectively with the first analog-to-digital converter 18 and to the second analog-to-digital converter 34.
• the digital-to-analog converter 28 has a resolution greater than 16 bits.
• 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.
• 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.
• the values of the analog or digital digital gains of the gain application modules 20, 30, 32, 36 and optionally 42, 44, 46 are adapted to ensure proper operation of the radiofrequency digitizer 10.
• 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.
• the embodiment of FIG. 2 is in particular implemented in the presence of the received analog stream F 2 comprising a single type of signal, for example a signal low S 2 (ie having a low power level, lower than a predetermined power threshold).
• 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
• variable attenuation value suitable for being implemented by said optional variable attenuator 46 is zero: the feedback branch 26 is disconnected simultaneously 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.
• 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. this particular case, identical and correspond to a module 48 for applying a digital gain.
• the module 12 configured to divide the power is a power divider and where the optional variable attenuator 46 implements zero attenuation , which corresponds to the fulfillment 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 so that the loss of sensitivity at the output chain is also 3 dB.
• the feedback branch 26 via the digital-to-analog converter CNA is deactivated, as is the action of the module 24 for combining/analog coupling, 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.
• the radio frequency digitizer architecture according to the present invention and as described in relation to FIG. 1 is suitable for being adapted into a radio frequency digitizer architecture with parallel ADCs, the feedback branch 26 being then 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.
• the radio frequency digitizer 10 using two analog-digital converters CANs and a digital-analog converter CNA arranged specifically according to the architecture of FIG. 1, makes it possible to reinject into analog the signals desensitized by the first analog-digital converter then to subtract them, thanks to the analog combination/coupling module 24 24, from the initial signals received, in order to thus estimate the limiting thermal noise preventing the digitization of the weak signals, noise that 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 limit the desensitization of the radiofrequency digitizer 10 (i.e. reduce the desensitization of the radiofrequency digitizer 10 compared to current state-of-the-art techniques of technology).
• such an architecture allows adaptation to an architecture with parallel ADC analog-digital converters (stack ADCs) in order to maintain sensitivity in the absence of simultaneous reception of strong and weak signals.
• the present invention offers the user a dynamic much greater than that available in equipment using conventional digitization, in particular in the presence of an analog stream received comprising at least two signals having a strong (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.
• a strong (i.e. greater than a predetermined threshold) power ratio for example a power ratio of the order of 15 dB

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• Theoretical Computer Science (AREA)
• Circuits Of Receivers In General (AREA)
• Control Of Amplification And Gain Control (AREA)
• Amplifiers (AREA)

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• 2021
  • 2021-10-25 FR FR2111288A patent/FR3128600A1/fr active Pending
• 2022
  • 2022-10-25 EP EP22805883.0A patent/EP4423914A1/de active Pending
  • 2022-10-25 WO PCT/EP2022/079726 patent/WO2023072906A1/fr active Application Filing

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