GENERATOR OF A FREQUENCY MODULATED RADAR SIGNAL

Abstract

A generator of a frequency modulated radar signal, comprising: a generator of a periodic signal frequency modulated over a part T.sub.ramp of a period T, corresponding to a square signal of which the frequency varies linearly in a first frequency band B.sub.in of central frequency f.sub.in; an oscillator generating a sinusoidal signal of frequency f.sub.c>f.sub.in and comprised in a second frequency band B.sub.amp>B.sub.in and corresponding to the linear variation of the frequency of the radar signal; means coupled to an electrical supply input of the oscillator such that they generate a voltage for supplying the oscillator at the frequency of the frequency modulated periodic signal.

Claims

1. A generator of a frequency modulated radar signal, comprising at least: a device for generating a periodic signal frequency modulated over at least one part T.sub.ramp of a period T, corresponding, over said at least one part T.sub.ramp of the period T, to a square signal of which the frequency varies linearly in a first frequency band B.sub.in of central frequency f.sub.in and of which the amplitude alternates between a first value and a second value different from the first value; an oscillator comprising an electrical supply input coupled to means capable of being controlled by the frequency modulated periodic signal and generating a non-zero voltage for supplying the oscillator only when the amplitude of the frequency modulated periodic signal is equal to the first value or only when the amplitude of the frequency modulated periodic signal is equal to the second value, enabling the oscillator to generate a sinusoidal signal of frequency f.sub.c>f.sub.in and comprised in a second frequency band B.sub.amp>B.sub.in, the second frequency band B.sub.amp corresponding to the linear variation of the frequency of the frequency modulated radar signal intended to be generated.

2. The generator of the frequency modulated radar signal according to claim 1, wherein the device for generating the frequency modulated periodic signal comprises: a device for generating a first periodic signal of period T corresponding, over the part T.sub.ramp of the period T, to a sinusoidal signal of which the frequency varies linearly in the first frequency band B.sub.in; a device for converting the first periodic signal into the frequency modulated periodic signal such that the amplitude of the frequency modulated periodic signal is equal to the first value when the value of the first periodic signal is strictly greater than 0 and is equal to the second value when the value of the first periodic signal is strictly less than 0.

3. The generator of the frequency modulated radar signal according to claim 2, wherein the device for generating the first periodic signal comprises a first voltage controlled oscillator.

4. The generator of the frequency modulated radar signal according claim 2, wherein the device for converting the first periodic signal comprises a frequency locked loop including a ring oscillator.

5. The generator of the frequency modulated radar signal according to claim 1, wherein the device for generating the frequency modulated periodic signal comprises at least one resonator device of which an output is electrically coupled to a phase locked loop, the frequency modulated periodic signal being intended to be obtained at the output of a second voltage controlled oscillator of the phase locked loop.

6. The generator of the frequency modulated radar signal according to claim 1, wherein the frequency modulated periodic signal has a zero value over a second part of the period T different from said at least one part T.sub.ramp.

7. The generator of the frequency modulated radar signal according to claim 1, wherein the second value of the frequency modulated periodic signal is zero.

8. The generator of the frequency modulated radar signal according to claim 1, wherein the value of the first frequency band B.sub.in is comprised between 1% and 2% of the central frequency f.sub.in.

9. The generator of the frequency modulated radar signal according to claim 1, wherein the oscillator is voltage controlled and comprises a free oscillation range including the frequency f.sub.c of which the value is a function of that of a control voltage intended to be applied at the input of this oscillator.

10. The generator of the frequency modulated radar signal according to claim 1, wherein the means capable of being controlled by the frequency modulated periodic signal comprise at least one switch coupled to the electrical supply input of the oscillator or to the output of the oscillator.

11. The generator of the frequency modulated radar signal according to claim 1, further comprising at least one injection locked oscillator intended to receive at the input a signal delivered on the output of the oscillator and to be locked at least periodically at a frequency f.sub.ILO=k.Math.f.sub.in, with k an integer greater than 1, the value of f.sub.ILO being, among the different values multiples of that of f.sub.in, that which is the closest to the value of the frequency f.sub.c.

12. The generator of the frequency modulated radar signal according to claim 1, wherein elements of the generator are produced on an electronic chip.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be better understood on reading the description of exemplary embodiments given for purely indicative purposes and in no way limiting and by referring to the appended drawings in which:

[0043] FIG. 1 shows the temporal variation of the instantaneous frequency of a signal sent by a FMCW type radar;

[0044] FIG. 2 shows the temporal variation of the instantaneous frequency of a FMCW type radar signal having a duty cycle D less than 1;

[0045] FIG. 3 schematically shows a generator of a frequency modulated radar signal according to a first embodiment;

[0046] FIG. 4 schematically shows the first signal x(t) in the temporal domain and in the frequency domain, as well as the evolution in the temporal domain of the instantaneous frequency of this first signal;

[0047] FIG. 5 schematically shows the second signal y(t) in the temporal domain and in the frequency domain, as well as the evolution in the temporal domain of the instantaneous frequency of this second signal y(t);

[0048] FIGS. 6 to 8 show the spectra of the second signal y(t) when the duty cycle of the second signal α.sub.dc is respectively such that α.sub.dc=⅛, α.sub.dc=¼ and α.sub.dc≈1 and less than 1;

[0049] FIG. 9 schematically shows the third signal s(t) in the temporal domain and in the frequency domain, as well as the evolution in the temporal domain of the instantaneous frequency of this third signal s(t);

[0050] FIG. 10 schematically shows the frequency modulated radar signal delivered by the generator, in the temporal domain and in the frequency domain, as well as the evolution in the temporal domain of the instantaneous frequency of this signal;

[0051] FIG. 11 shows the temporal variations of the instantaneous frequency of frequency modulated radar signals of the prior art as well as that of a frequency modulated radar signal delivered at the output of the generator;

[0052] FIG. 12 schematically shows a generator of a frequency modulated radar signal according to a second embodiment.

[0053] Identical, similar or equivalent parts of the different figures described hereafter bear the same numerical references in order to make it easier to go from one figure to the other.

[0054] The different parts shown in the figures are not necessarily represented according to a uniform scale, in order to make the figures more legible.

[0055] The different possibilities (alternatives and embodiments) should be understood as not being mutually exclusive and may be combined with each other.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0056] A generator 100 of a frequency modulated radar signal according to a first embodiment is described below and schematically shown in FIG. 3.

[0057] In this first embodiment, the frequency modulated radar signal generated has a duty cycle D less than 1.

[0058] The generator 100 comprises a device 102 for generating a first periodic signal x(t) of period T corresponding, over the part T.sub.ramp of the period T, to a sinusoidal signal of which the instantaneous frequency varies linearly in a first low frequency band B.sub.in centred on a central frequency f.sub.in. The first signal x(t) linearly modulated in frequency may be expressed by the following equation:

[00003]$x\left(t\right)=\{\begin{array}{c}\sin \left(2\pi \left(f_{\mathrm{in}}^{\prime }t+\alpha t^2\right)\right),\mathrm{for}t\in \left[0,T_{\mathrm{ramp}}\right]\\ 0,\mathrm{for}t.Math.\left[0,T_{\mathrm{ramp}}\right]\end{array}$

[0059] The slope of the ramp formed by the variation of the instantaneous frequency of the signal x(t) over time is characterised by the parameter α=B.sub.in/(2.Math.T.sub.ramp). The frequency f′.sub.in=f.sub.in−α.Math.T.sub.ramp corresponds to the instantaneous frequency of the signal x(t) at the start of the ramp. The first frequency band B.sub.in corresponds to a frequency band of which the values are situated around one to several percent compared to the central frequency f.sub.in, advantageously between around 1% and 2% of f.sub.in. Generally speaking, the value of B.sub.in is advantageously comprised between around several tens of MHz, or for example between 10 MHz and 90 MHz, and the value of f.sub.in is advantageously comprised between around several hundred MHz and several GHz, for example between 100 MHz and 10 GHz. The value of T.sub.ramp is for example less than 250 ns. Moreover, in this first embodiment, the value of T.sub.transitory is less than 10 ns and that of T.sub.stop is greater than or equal to 1 ms.

[0060] FIG. 4 schematically shows the first signal x(t) in the temporal domain (curve designated by the reference 10) and in the frequency domain (spectrum designated by the reference 12), as well as the evolution in the temporal domain of the instantaneous frequency of this first signal x(t) (curve designated by the reference 14, and which includes the ramp formed by the variation of the instantaneous frequency of this first signal during T.sub.ramp). In FIG. 4, the durations T.sub.stop and T.sub.transitory are not shown.

[0061] According to a particular exemplary embodiment, the spectrum of the first signal x(t) is centred on the central frequency f.sub.in=2.16 GHz. The first frequency band B.sub.in of this first signal x(t) is equal to 43.2 MHz, that is to say 0.02.Math.f.sub.in.

[0062] In this first embodiment, the device 102 correspond for example to a voltage controlled oscillator (designated “V.sub.tune” in FIG. 3). The variation of the instantaneous frequency of the first signal x(t) is in this case obtained by varying the amplitude of the control voltage applied at the input of this voltage controlled oscillator.

[0063] An example of control voltage V.sub.tune is shown in FIG. 3. The duration necessary for the signal V.sub.tune to reach the desired voltage level corresponds to the duration T.sub.transitory the signal x(t) has not yet reached the desired frequency during which (which corresponds to the lower limit frequency of the first frequency band B.sub.in). The amplitude of the signal V.sub.tune varies next for the duration T.sub.ramp, which leads to variation of the instantaneous frequency of the first signal x(t) over the whole first frequency band B.sub.in. The value of the control voltage V.sub.tune is next zero over the whole duration T.sub.stop. The values of T.sub.transitory, T.sub.ramp and T.sub.stop are thus parameters defined by the shape of the control signal V.sub.tune and are found in the first signal x(t).

[0064] This first signal x(t) is next converted into a signal intended to serve as envelope signal for a frequency modulation. To do so, the device 100 comprises a device 104 for converting the first periodic signal x(t) into a second periodic and frequency modulated signal, called y(t). The second signal y(t) has an amplitude equal to a first value when the value of the first periodic signal x(t) is strictly greater than 0 and has a second value, different from the first value, when the value of the first periodic signal x(t) is strictly less than 0. The first value may correspond to a high state (for example equal to the value of a supply voltage of the device 100) symbolised for example by the value 1 and the second value may correspond to a low state (for example equal to the value of a reference potential such as that of the earth of the device 100) symbolised for example by the value 0. In this case, the signal y(t) may be such that:

[00004]$y\left(t\right)=\{\begin{array}{c}y=1,x>0\\ y=0,x<0\end{array}$

[0065] The signal y(t) corresponds to a periodic signal and frequency modulated over the part T.sub.ramp of the period T. Over the part T.sub.ramp, the signal y(t) corresponds to a square signal of which the instantaneous frequency varies linearly in the first frequency band B.sub.in and of which the amplitude is equal to the first value or to the second value.

[0066] The second signal y(t) is intended to serve as signal for switching on and for stopping a current source 106 electrically supplying an oscillator 108. The current source 106 controls the phases of starting and stopping the oscillator 108.

[0067] The pulses corresponding to the passages from the second value to the first value of the amplitude of the second signal y(t) form, for the current source 106 and the oscillator 108, start-up times t.sub.start(n) corresponding to a discrete and countable set, for a finite duration ramp. In the general case, these times are given by the relationship:

[00005]$t_{start}\left(n\right)=\frac{f_{\mathrm{in}}^{\prime }{T}_{\mathrm{ramp}}}{B_{in}}\left(-1+\sqrt{1+\frac{B_{in}}{f_{\mathrm{in}}^{\prime }{T}_{\mathrm{ramp}}}\left(2n-1\right)}\right),n\in \mathbb{N}$

[0068] This relationship corresponds to one of the solutions of the ordinary quadratic equation of the phase of the first signal x(t):

αt.sup.2+f′.sub.int−m=0 with m=2n−1 and n∈

[0069] These times make it possible to define the second signal y(t) such that:

[00006]$y\left(t\right)=\underset{n}{\overset{\mathrm{nmax}}{.Math.}}.Math.\left(\frac{t-t_{start}\left(n\right)-T\left(n\right)/2}{T\left(n\right)/2}\right)$

[0070] where Π shows the rectangular function, over the interval T(n)=(t.sub.start(n+1)−t.sub.start(n))/2.

[0071] The value nmax defines the index of the final period of the second signal y(t) in the sequence. This value corresponds to the limit:

nmax=arg max.sub.n∈t.sub.start(n), such that t.sub.start(n)<T.sub.ramp.

[0072] FIG. 5 schematically shows the second signal y(t) in the temporal domain (curve designated by the reference 20) and in the frequency domain (spectrum designated by the reference 22), as well as the evolution in the temporal domain of the instantaneous frequency of this second signal y(t) (curve designated by the reference 24 and which includes the ramp formed by the variation of the instantaneous frequency of this second signal during T.sub.ramp). In FIG. 5, the durations T.sub.stop and T.sub.transitory are not shown.

[0073] The values of T.sub.transitory, T.sub.ramp and T.sub.stop in the first signal x(t) are similar in the second signal y(t).

[0074] The frequency diagram of the second signal y(t) shows that the second signal y(t) includes a continuous signal of fundamental frequency equal to f.sub.in (equal to 2.16 GHz in the particular exemplary embodiment described here), and of which the frequency excursion is in addition greatest in sub-bands centred on whole multiples of the frequency f.sub.in. For example, the 27.sup.th sub-band, called B.sub.in_27 and centred around the frequency 2.16 GHz×27=58.32 GHz, is 27 times wider than the band B.sub.in centred on the frequency f.sub.in, that is to say B.sub.in_27=1.16 GHz. For the 28.sup.th sub-band B.sub.in_28 centred around the frequency 2.16 GHz×28=60.48 GHz, its width is B.sub.in_28=1.20 GHz. Thus, in the spectrum of the second signal y(t), each i.sup.th sub-band B.sub.in_i has a central frequency which is equal to i.Math.f.sub.in and a band width equal to B.sub.in_i=i.Math.B.sub.in, with i an integer greater than or equal to 1.

[0075] The duty cycle, called α.sub.dc, of the second signal y(t) is for example equal to 0.5. In this case, the spectrum of the second signal y(t) corresponds to the following equation:

[00007]$ℱ\left[y\right]\left(f\right)=\underset{n}{\overset{\mathrm{nmax}}{.Math.}}\frac{T\left(n\right)}{2}\sin c\left(\frac{T\left(n\right)}{2}f\right).Math.e^{-j2\pi f\left(t_{start}\left(n\right)+\frac{T\left(n\right)}{4}\right)}$

[0076] When the value of the duty cycle α.sub.dc is different from 0.5, the spectrum of the second signal y(t) corresponds to the following equation:

[00008]$ℱ\left[y\right]\left(f\right)=\underset{n}{\overset{\mathrm{nmax}}{.Math.}}\frac{{\alpha }_{dc}T\left(n\right)}{2}\sin c\left(\frac{{\alpha }_{dc}T\left(n\right)}{2}f\right).Math.e^{-j2\pi f\left(t_{start}\left(n\right)+{\alpha }_{\mathrm{dc}}\frac{T\left(n\right)}{2}\right)}$

[0077] As an example, FIGS. 6 to 8 show the spectra of the second signal y(t) when α.sub.dc is respectively such that α.sub.dc=⅛, α.sub.dc=¼ and α.sub.dc≈1 and less than 1.

[0078] In the first embodiment, the device 104 comprises a frequency locked loop including a ring oscillator. An exemplary embodiment of such a frequency locked loop is given in the document of C.-H. Yen, M. Nasrollahpour, “Low-Power and High-Frequency Ring Oscillator Design in 65 nm CMOS Technology”, 2017 IEEE 12th International Conference on ASIC (ASICON).

[0079] By controlling the electrical supply of the oscillator 108 by the second signal y(t), this oscillator 108 delivers at the output a sinusoidal signal of frequency f.sub.c corresponding to its free oscillation frequency and modulated by the second signal y(t). The value of the frequency f.sub.c is fixed by the value of a control voltage applied at the input of the oscillator 108, and is chosen such that it forms part of a second frequency band B.sub.amp called amplification band and which corresponds to the linear variation of the frequency of the frequency modulated radar signal intended to be generated by the generator 100. Advantageously, the second frequency band B.sub.amp may be comprised between 1 GHz and 3 GHz.

[0080] The signal obtained at the output of the oscillator 108, called third signal s(t), has the particularity of having its phase locked on that of the second signal y(t).

[0081] Such a control of the supply of the oscillator 108 comes down to carrying out an amplification around the frequency f.sub.c and filtering the second signal y(t) in the second frequency band B.sub.amp around the central frequency f.sub.c by the cardinal sine

[00009]$\sin c\left(\frac{f-f_c}{2f_{\mathrm{in}}}\right).$

[0082] The third signal s(t) delivered at the output of the oscillator 108 may be defined by the following equation:

s(t)=Σ.sub.n.sup.nmaxy(t).Math.sin(2πf.sub.c(t−t.sub.start(n))), that is to say

[00010]$s\left(t\right)=\underset{n}{\overset{\mathrm{nmax}}{.Math.}}.Math.\left(\frac{t-t_{s\mathrm{tart}}\left(n\right)-T\left(n\right)/4}{T\left(n\right)/2}\right).Math.\sin \left(2\pi f_c\left(t-t_{start}\left(n\right)\right)\right),$

[0083] The third signal s(t) corresponds to a finite sum of sines windowed with a “rectangular” type function designated by the letter “Π”, of which each rectangular period is defined by T(n)=t.sub.start(n+1)−t.sub.start(n).

[0084] In the above equation, the sine is a real signal being able to be defined such that:

[00011]$\sin \left(2\pi f_c\left(t-t_{start}\left(n\right)\right)\right)=\frac{e^{j2\pi f_c\left(t-t_{st\mathrm{art}}\left(n\right)\right)}-e^{-j2\pi f_c\left(t-t_{start}\left(n\right)\right)}}{2j}$

[0085] Only considering the positive part, the spectrum of the third signal s(t) may be defined by the following equation:

[00012]$ℱ\left[s\right]\left(f\right)=\underset{n}{\overset{\mathrm{nmax}}{.Math.}}\frac{T\left(n\right)}{2}\sin c\left(\frac{T\left(n\right)}{2}\left(f-f_c\right)\right).Math.e^{-j2\pi f\left(t_{st\mathrm{art}}\left(n\right)+T\left(n\right)/4\right)}.Math.e^{j2\pi f_{c}T\left(n\right)/4)}$

[0086] FIG. 9 schematically shows the third signal s(t) in the temporal domain (designated by the reference 30) and in the frequency domain (spectrum designated by the reference 32), as well as the evolution in the temporal domain of the frequency of this signal s(t) (designated by the reference 34 and which corresponds to the ramp formed by the variation of the frequency of this signal over time, this ramp being different to that of the first and second signals x(t) and y(t) due to the fact that the frequency band covered by the third signal s(t) corresponds to the second frequency band B.sub.amp).

[0087] From a frequency point of view, the third signal s(t) has a maximum power at the frequency f.sub.c, and its envelope corresponds to the cardinal sine

[00013]$\sin c\left(\frac{f-f_c}{2f_{in}}\right).$

[0088] The generator 100 also comprises an injection locked oscillator 110, or ILO, receiving at the input the third signal s(t). This ILO 110 filters the third signal s(t) while eliminating the sub-bands adjacent to a band of interest k.Math.B.sub.in, with k an integer greater than 1, and which makes it possible to produce at the output the frequency modulated radar signal called z(t). This filtering is obtained due to the fact that the ILO 110 locks at the ray of the signal s(t) the closest to its free oscillation frequency. The control signal applied on the control input of the ILO 110 makes it possible to position the free oscillation frequency of the ILO 110 close to k.Math.f.sub.in in order to centre the signal delivered by the oscillator 110 exactly on k.Math.f.sub.in during the locking of the ILO 110 on the frequency k.Math.f.sub.in. Returning to the exemplary embodiment described previously, with k=27 and B.sub.in=43.2 MHz, the band k. B.sub.in obtained is equal to 1.16 GHz.

[0089] When the generator 100 comprises such an ILO coupled to the output of the oscillator 108, the value of the frequency f.sub.c of the oscillator 108 is chosen such that it is close to the value of a multiple of the frequency f.sub.in in order that the filtering carried out by the ILO includes the frequency f.sub.c in the main lobe of the template for filtering carried out by the ILO. For example, when f.sub.in=2.16 GHz and when it is desired to obtain a signal in the frequency band corresponding to the 27.sup.th harmonic of f.sub.in, the control voltage applied on the oscillator 108 may be such that the value of the frequency f.sub.c is equal to 60 GHz, which is such that 27f.sub.in<f.sub.c<28f.sub.in.

[0090] In the first embodiment described above, the use of an oscillator to produce the device 102 makes it possible to obtain a rapid start-up, and thus to have a low value of T.sub.transitory, for example less than 10 ns. Due to the fact that the value of T.sub.transitory is low, this first embodiment makes it possible to have an important value for the parameter T.sub.stop, and is thus well suited to maximising the energy saving made by the generator 100.

[0091] FIG. 11 shows on a same diagram the evolutions in the temporal domain of the frequency of frequency modulated radar signals described previously in FIGS. 1 and 2 (bearing respectively the references 40 and 42) as well as that of the frequency modulated radar signal obtained at the output of the generator 100 (reference 44). The radar signal obtained at the output of the generator 100 makes it possible to scan a wide frequency band (referenced B.sub.44) in a very short time (referenced T.sub.ramp44), unlike solutions of the prior art. Thus, the ramp 42, corresponding to that shown in FIG. 1, has an important frequency band B.sub.42 (here similar to the frequency band B.sub.44) but it requires, to be covered by the radar signal, an important duration T.sub.ramp42 much greater than the duration T.sub.ramp44. In addition, the ramp 40, corresponding to that shown in FIG. 2, has a small frequency band B.sub.40 (less than the frequency band B.sub.44) which may be covered with a short duration T.sub.ramp40 (but which is greater than T.sub.ramp44).

[0092] In the first embodiment described above, the second signal y(t) is obtained by firstly generating the first signal x(t), then by transforming the first signal x(t) to obtain the second signal y(t). According to a second embodiment, it is possible that the generator 100 comprises a device making it possible to generate directly the second signal y(t), without generating beforehand the first signal x(t).

[0093] FIG. 12 shows an exemplary embodiment of the generator 100 according to the second embodiment.

[0094] In FIG. 12, the generator 100 comprises a resonator 101 of which an output is electrically coupled to a phase locked loop 103. This loop 103 comprises an oscillator 105 corresponding to a VCO. The loop 103 also comprises a frequency divider 107 capable of dividing the frequency of the signal delivered by the oscillator 105 by a number of which the value is a function of that of a control signal V.sub.mod applied at the input of the frequency divider 107. A periodic signal is obtained at the output of the frequency divider 107 which is next compared to a very stable periodic reference signal of frequency supplied by the resonator 101, for example a quartz resonator. The loop 103 also comprises a phase comparator and a charge pump circuit (PFD+CP) 109 generating a signal of output proportional to the difference in phases between the signal delivered by the resonator 101 and that obtained at the output of the frequency divider 107. A filter 111 is interposed between the output of the charge pump circuit and the input of the oscillator 105. In this loop 103, the linear variation of the instantaneous frequency of the signal delivered at the output of the loop 103 is obtained by varying the division ratio applied by the frequency divider 107 thanks to the variation of amplitude of the control signal V.sub.mod. Another control signal V.sub.mod is applied on the control input of the oscillator 105 in order to stabilise the reaction of the loop 103 to variations in the division ratio.

[0095] The frequency excursion of the PLL may be reduced by an important factor corresponding to the multiplication factor k applied to the frequency f.sub.in. For example, it is sufficient to produce a second signal y(t) with frequency band B.sub.in equal to 43.2 MHz to be able to generate at the output of the ILO 110 a radar signal of which the frequency band B.sub.amp is greater than 1 GHz for values of k≥27. In this case, when the parameter α of the ramp formed by the second signal y(t) is 173 MHz/μs, that of the ramp formed by the radar signal delivered at the output of the ILO 110 correspond to k.Math.173 MHz/μs, i.e. 4.6 GHz/μs when k=27

[0096] The frequency modulated periodic signal y(t) is here obtained at the output of the oscillator 105 of the phase locked loop 103.

[0097] The phase locked loop 103 may be produced as described in the document of Cherniak, D. et al., “A 23-GHz Low-Phase-Noise Digital Bang-Bang PLL for Fast Triangular and Sawtooth Chirp Modulation”, IEEE Journal of Solid-State Circuits, 2018, 53, (12), pp. 3565-3575.

[0098] In this second embodiment, the duration T.sub.transitory is longer than that obtained in the first embodiment, and for example comprised between 1 ms and 2 ms. Conversely, compared to the first embodiment, the linearity of the generator 100 is improved, which makes it possible to maximise the SNR on reception of the radar signal generated.

[0099] According to a third embodiment of the generator 100, which is an alternative of the 2.sup.nd embodiment, the phase locked loop 103 is replaced by a circuit for generating a frequency modulated signal produced as described in the patent application FR 3 100 404 A1. The signal delivered by the resonator 101 is then supplied at the input “CLK_IN” of a device such as described in this patent application. One advantage of this circuit for generating a frequency modulated signal is that it makes it possible to generate frequency ramps much more rapidly (frequency varying more rapidly) and more linearly than circuits based on a phase locked loop. Moreover, the settling time of the signal of such a generation circuit is virtually instantaneous, unlike phase locked loops which always have a non-negligible settling time.

[0100] In the two embodiments described previously, the signal s(t) is obtained at the output of the oscillator 108 thanks to the control of the electrical supply of the oscillator 108 by the second signal y(t).

[0101] In both of the embodiments described previously, the duty cycle α.sub.dc of the second signal y(t) is constant. In an alternative, it is possible to vary the value of this duty cycle periodically, for example at each period T. The values of the duty cycle are for example predefined in a memory, as described for example in the document of C. Jany, “Conception et étude d'une synthèse de fréquence innovante en technologies CMOS avancées pour les applications en bande de fréquence millimétrique” (Design and study of an innovative frequency synthesis using advanced CMOS technologies for millimetric frequency band applications), Science Thesis defended in 2014, chapter 4.

[0102] In the two embodiments described previously, the generator 100 comprises the ILO 110 making it possible to carry out a filtering of the signal s(t) delivered by the oscillator 108 in order that the radar signal generated does not comprise or comprises few components in the band of frequencies other than that in which the ramp varies. In an alternative, it is however possible that the generator 100 does not comprise this ILO 110. In this case, it is possible to choose the value of the duty cycle α.sub.dc of the second signal y(t) as being close to 1 due to the fact that at this value, the spectrum of the second signal y(t) forms secondary bands much more attenuated than the main band of this spectrum (see the spectrum shown in FIG. 8 which corresponds to the case where the duty cycle α.sub.dc of the second signal y(t) is close to 1). This alternative may however be applied even when the duty cycle α.sub.dc of the second signal y(t) is not close to 1. In this case, the radar signal generated by the generator 100 comprises frequency variations in several different frequency bands, which may be advantageous for certain types of multiband radar.

[0103] Generally speaking, the generator 100 makes it possible to obtain the following characteristics: [0104] frequency band B.sub.amp greater than 1 GHz and for example comprised between 1 GHz and 3 GHz; [0105] duration T.sub.ramp comprised between 0.25 μs and 1 μs; [0106] parameter α of the maximum frequency slope greater than 4 GHz/μs; [0107] duration T.sub.transitory less than 10 ns when the generator is produced according to the first embodiment.

[0108] For all the embodiments and alternatives, the generator 100 may be produced in the form of a single electronic chip, corresponding for example to an integrated circuit.