EP3308465A1 - Procede de synthese d'un bruit analogique, synthetiseur de bruit et chaine de codage utilisant un tel synthetiseur - Google Patents
Procede de synthese d'un bruit analogique, synthetiseur de bruit et chaine de codage utilisant un tel synthetiseurInfo
- Publication number
- EP3308465A1 EP3308465A1 EP16725535.5A EP16725535A EP3308465A1 EP 3308465 A1 EP3308465 A1 EP 3308465A1 EP 16725535 A EP16725535 A EP 16725535A EP 3308465 A1 EP3308465 A1 EP 3308465A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- noise
- analog
- frequency
- digital
- converter
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Ceased
Links
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
- H03M1/06—Continuously compensating for, or preventing, undesired influence of physical parameters
- H03M1/0617—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence
- H03M1/0626—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence by filtering
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
- H03M1/06—Continuously compensating for, or preventing, undesired influence of physical parameters
- H03M1/0614—Continuously compensating for, or preventing, undesired influence of physical parameters of harmonic distortion
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/28—Details of pulse systems
- G01S7/285—Receivers
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/35—Details of non-pulse systems
- G01S7/352—Receivers
-
- 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
Definitions
- the present invention relates to a method of synthesizing an analog noise. It also relates to a high output level noise synthesizer implementing this method. Finally, it relates to a coding chain with very high linearity and very high dynamics using such a synthesizer. It applies in particular for the correction of non-linearity defects present in the analog-to-digital conversion chains.
- a suitable solution consists in coupling to the signal a noise, which makes it possible statistically to limit the periodic passage on the points of non-linearity.
- the power of this noise is large enough to address all the converter codes but it is also essential that this noise can be eliminated after digital acquisition.
- the useful band of the signal to be processed being known, the choice is to inject a power of noise into a band not covering the useful band of the signal so as to easily eliminate the noise by filtering. high or low depending on the frequency positioning of the noise.
- a technical problem to be solved is thus to synthesize an analogue noise in a high but limited frequency band, for example around 350 MHz to +/- 30 MHz, with a relatively high overall power, and this in a volume reduced.
- the noise is generated from a digital-to-analog converter (DAC).
- DAC digital-to-analog converter
- the principle is then to synthesize noise in the digital domain and to convert it to analogue via a DAC.
- this principle it is possible to limit the noise band generated but like any sampled system, it is necessary to filter in analog to limit all the image bands.
- a major disadvantage of this solution with respect to the intended application is that the frequencies used require the use of a very high sampling rate DAC, which requires the generation of an additional external clock and a additional power consumed, and also does not remove the analog amplifier stage.
- An object of the invention is in particular to overcome the aforementioned drawbacks, by allowing noise generation centered around an intermediate or microwave frequency with a frequency band sufficient to effectively linearize the encoders and that with very few components.
- the subject of the invention is a method for synthesizing an analog noise, said method comprising at least the following steps: Generating a pseudo-random noise in the digital domain coded on an N number of bits sampled at a given frequency FH / N;
- the transfer step in the analog domain is followed by an analog filtering step by a bandpass filter.
- the bandwidth of said analog filter is for example centered on half of the sampling frequency of said converter, said bandwidth does not exceed not overlapping the frequency band of said useful signal.
- the filtering step may be followed by a noise amplification step.
- the noise coded on a bit at the output of the multiplexing step is for example centered on a central frequency Fc equal to the half of the sampling frequency of said converter.
- said pseudo-random noise is sampled at a frequency equal to 2/3 of said central frequency Fc.
- the subject of the invention is also an analog noise synthesizer comprising at least the following modules:
- a multiplexer performing in the digital domain the multiplexing of the binary signals produced by each of the N bits at a frequency FH sampling to obtain a noise coded on a bit at said frequency FH;
- a differential transmission interface for transferring the noise thus encoded in the analog domain.
- the differential transmission interface is for example of the LVDS type.
- Said synthesizer comprises, for example, an analog band pass filter at the output of the differential transmission interface.
- Said analog noise being able to be combined with a signal useful at the input of an analog-digital converter the bandwidth of said filter is for example centered on half of the sampling frequency of said converter, said bandwidth not overlapping the frequency band of said useful signal.
- the noise coded on a bit at the output of the multiplexer is for example centered on a central frequency Fc equal to half the frequency sampling of said converter.
- the number N being equal to 4
- said pseudo-random noise is sampled at a frequency equal to 2/3 of said central frequency Fc.
- the pseudo-random noise generation module and the multiplexer are for example made in an FPGA, the differential transmission interface being a differential output of said FPGA.
- the invention also relates to an analog-digital coding string, said string being able to encode a useful signal. It comprises at least: a digital-to-analog converter;
- a combiner combining said useful signal and the noise generated by said synthesizer; the output of said combiner being connected to the input of said converter, so that the combined signal is digitally converted.
- the digitized noise is for example filtered at the output of the converter by a digital filter.
- the said coding chain is particularly suitable for use in a radar reception chain, the said useful signal being a radar reception signal.
- FIG. 1 a representation of an exemplary functional architecture of a noise synthesizer implementing the method according to the invention
- FIG. 2 an exemplary embodiment of a coding chain according to the invention.
- FIG. 1 illustrates the functional architecture of a noise synthesizer implementing the method according to the invention.
- the noise is synthesized on a bit shaped in mixed technology, digital and analog, around a high frequency.
- the digital noise signal is generated in one bit and transferred to the analog domain via a differential interface, and then optimized in the desired frequency band via a filter stage.
- noise 1 is therefore first performed in the digital domain, for example in an FPGA, on the principle of a digital synthesis advantageously coded on a bit, the noise being presented as a succession of binary values sampled at a frequency clock FH.
- the noise generation 1 is carried out by parallelising N low frequency channels, each channel generating a noise clocked at the frequency FH / N. This is equivalent to Generate a 1-bit random sequence from N 1-bit subsampled channels.
- the noise is conformed by digital multiplexing 2 of the N channels giving a noise signal coded on a bit, sampled at the clock frequency FH.
- N is for example equal to 4. It is necessary to understand by consistent noise a noise which is not a white noise but a noise having a given bandwidth, in particular narrow.
- the central frequency of the noise is for example equal to F eC h / 2, F eC h being the sampling frequency of the encoder to be linearized.
- This signal synthesized on a bit is transmitted on a buffer 3, this buffer being a low voltage differential transmission interface, also called LVDS (Low Voting Differential Signal), particularly well suited to very high frequencies, typically several hundred megahertz.
- LVDS Low Voting Differential Signal
- This interface advantageously makes it possible to go from the digital domain to the analog domain without the use of a digital-to-analog converter.
- This interface may advantageously be a differential output of the FPGA in which the digital synthesis is already programmed, which makes it possible not to use an additional component.
- the analog signal at the output of the buffer 3 is then filtered 4 by a band pass filter, the bandwidth of this filter being outside the band of the useful signal with which the noise is intended to be combined.
- the noise can be amplified if necessary.
- FIG. 2 shows an example of an analog-digital coding string according to the invention using a noise synthesizer of the type of that of FIG. 1, applied for example in a radar receiver.
- the useful signal 21 for example a radar reception signal, is combined with the noise signal by means of a combiner 22 before digital conversion by the ADC 23.
- the noise is then filtered downstream of the ADC.
- the noise generation also called "dither" thereafter, is first synthesized digitally.
- the number N of channels is equal to 4.
- a module 1 carries out the generation of a white noise on 4 bits sampled at 2/3 of the central frequency Fc of the desired dither, for example Fc equal to F e ch / 2.
- the module conventionally generates a pseudo-random code by means of a shift register offset looped back on itself and whose initialization value can be parameterized in the mask of the module.
- a brewing function can be added to increase the randomness of the generated code. It is possible to modulate the random signal, that is to say to decrease or increase its amplitude, by adjusting an amplitude parameter.
- This dither function is instantiated twice within the module with different initialization values to generate a noise sampled at 2xFH, ie at 4/3 of the center frequency Fc.
- a function of formatting and concatenation of the different noises is performed.
- the multiplexing of two independent noises and their complemented values makes it possible to maximize the power of the noise around the central frequency Fc, which corresponds to a zone of the spectrum which will be maximized by the analog filtering 4. More precisely, as regards the maximization of the noise in the desired frequency band, it is assumed that this noise must be placed out of band useful, that is to say out-of-band operated by the CAN 23, and it conforms this noise so as to make sure that its contribution in the useful band after sampling remains negligible compared to the noise of the CAN and especially vis-à-vis the noise of the reception chain, in case of radar application for example.
- the noise spectrum is the "spectral complement" of the useful band that one wishes to exploit.
- the digital filtering at the output of the CAN 23 is capable of rejecting the conformed noise, the noise injected at the input of the CAN is eliminated at the output.
- Ni being equal to 0 or 1
- N1, N2, N3, N4, ... Nn clocked at F eC h / 2
- a result of the following form (N1, -N1, N2, -N2, N3, -N3, N4, -N4 ... Nn, -Nn) sampled at F eC h.
- Multiplexer 2 multiplexes the 4-bit coded noise to generate a 1-bit sampled noise at 4xFH, which is 8/3 Fc.
- the signal is then sent to buffer 3 to transfer digitized noise, on a bit, into the analog domain.
- This transfer is advantageously performed by a differential transmission interface, for example according to the LVDS standard.
- This interface may be a differential interface of the FPGA used elsewhere for the dither function or noise generation.
- This has the advantage of using an internal FPGA resource and does not require a specific conversion circuit.
- the 350 mV output level across a 100 ohm resistor which is unique to this standard, provides an output power of -8 dBm once the line impedance has been reduced to 50 ohms.
- This adaptation to 50 ohms is also very simple because the differential interface LVDS works in differential on 100 ohms.
- the digital noise synthesis is optimized to maximize the power around the central frequency selected, for example F eC h / 2, it results at the output of the LVDS interface, that is to say the buffer 3, a power of the order of -10 dBm.
- the following analog filtering 4 may be less constrained.
- Analogue filtering 4 must be sized to ensure that there is no noise residue in the wanted band of the signal to be converted by ADC 23. The difference between the wanted band and the noise band must be so be enough.
- the choice of the central frequency of the noise is optimized and takes advantage of the principles of the sampling which is finally carried out by the CAN.
- the useful band of the signal can not be positioned astride a multiple of the point V2 F eC h, F eC h being as indicated above the sampling frequency of the CAN.
- the noise occupies after conversion by the ADC only half of its initial band, the sampling principle having folded the input signals to 1/2 F eC h, while having the efficiency of the total noise band.
- the bandpass analog filtering is thus added at the output of the differential interface 3 in order to de-correlate the useful band of the noise band.
- An amplifier 5 may be added depending on the full scale of the CAN or the band of the noise is relatively narrow.
- the filtered and possibly amplified noise is combined with the useful signal by the microwave combiner 22, the combined signal being converted into a digital signal by the ADC.
- the noise combined with the digitized signal is then filtered by a digital filter 24.
- the advantage of the consistent noise that is to say with a narrow and controlled bandwidth, is that it can be easily placed out of the useful band signal and therefore simply filtered.
- a simple digital filter 24 which is generally already present at the output of the ADC.
- the invention thus makes it possible to guarantee a complete elimination of the noise in the end contrary to the conventional methods of noise synthesis where the noise occupies the entire sampling band.
- the digital image is subtracted after conversion to digital and the effectiveness of this removal is dependent on the quality of the digital representation of the coded noise which is very difficult to obtain.
- the positioning of the central frequency of the noise at F eC h / 2 thus makes it possible to obtain maximum efficiency in the correction of non-linearity defects of the ADC, and of the encoders in general, while pushing back the frequency band of the noise. as far as possible from the useful band.
- the invention makes it possible to produce a noise generator in a reduced volume, or even zero or almost zero compared to existing equipment.
- an FPGA is already present because used to interface with the CAN. This available FPGA can contain the one-bit digital noise generation function and the LVDS differential interface to switch to the analog domain.
- the invention advantageously makes it possible to dispense with a digital / analog conversion component of the noise. Since the noise signal is coded on a bit, it is advantageously possible to use a differential interface, for example of the LVDS type as has been described. Advantageously, without changing the synthesis principle of the invention, it is possible to increase the noise frequency as the frequency evolution of this type of interface.
- the invention also has another advantage in that it does not require specific processing acquisition output other than the analog filter 4 which limits the noise signal to the useful band to eliminate the noise at the output of the encoder 23. .
- the noise generated according to the invention may be in a location of the spectrum distant from the frequency band of the received signals, and this noise is naturally filtered by the radar reception chain , without the need for additional components or functions.
- the invention advantageously makes it possible to obtain a coding chain with very high linearity and very high dynamics.
- the noise frequency can reach frequencies of the order of 1 GHz.
Abstract
Description
Claims
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR1501203A FR3037456B1 (fr) | 2015-06-10 | 2015-06-10 | Procede de synthese d'un bruit analogique, synthetiseur de bruit et chaine de codage utilisant un tel synthetiseur |
PCT/EP2016/062072 WO2016198269A1 (fr) | 2015-06-10 | 2016-05-27 | Procede de synthese d'un bruit analogique, synthetiseur de bruit et chaine de codage utilisant un tel synthetiseur |
Publications (1)
Publication Number | Publication Date |
---|---|
EP3308465A1 true EP3308465A1 (fr) | 2018-04-18 |
Family
ID=54937116
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP16725535.5A Ceased EP3308465A1 (fr) | 2015-06-10 | 2016-05-27 | Procede de synthese d'un bruit analogique, synthetiseur de bruit et chaine de codage utilisant un tel synthetiseur |
Country Status (4)
Country | Link |
---|---|
US (1) | US10097194B2 (fr) |
EP (1) | EP3308465A1 (fr) |
FR (1) | FR3037456B1 (fr) |
WO (1) | WO2016198269A1 (fr) |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE19514007C1 (de) * | 1995-04-13 | 1996-09-12 | Wandel & Goltermann | Verfahren zur Verbesserung des Klirrverhaltens von Analog-Digitalwandlern |
EP0880235A1 (fr) * | 1996-02-08 | 1998-11-25 | Matsushita Electric Industrial Co., Ltd. | Codeur, decodeur, codeur-decodeur et support d'enregistrement de signal audio large bande |
US6268814B1 (en) * | 2000-03-14 | 2001-07-31 | Lucent Technologies Inc. | Carrier-dependent dithering for analog-to-digital conversion |
US7280764B2 (en) * | 2002-03-01 | 2007-10-09 | Avago Technologies Fiber Ip (Singapore) Pte Ltd | Optical signal multiplexer/demultiplexer employing pseudorandom mode modulation |
TW201015867A (en) * | 2008-10-01 | 2010-04-16 | Ind Tech Res Inst | Frequency synthesizer and method for synthesizing frequency |
-
2015
- 2015-06-10 FR FR1501203A patent/FR3037456B1/fr active Active
-
2016
- 2016-05-27 US US15/574,128 patent/US10097194B2/en active Active
- 2016-05-27 WO PCT/EP2016/062072 patent/WO2016198269A1/fr active Application Filing
- 2016-05-27 EP EP16725535.5A patent/EP3308465A1/fr not_active Ceased
Also Published As
Publication number | Publication date |
---|---|
FR3037456A1 (fr) | 2016-12-16 |
FR3037456B1 (fr) | 2017-06-02 |
WO2016198269A1 (fr) | 2016-12-15 |
US10097194B2 (en) | 2018-10-09 |
US20180152195A1 (en) | 2018-05-31 |
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