Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
  • H03B15/00—Generation of oscillations using galvano-magnetic devices, e.g. Hall-effect devices, or using superconductivity effects
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/10—Junction-based devices
  • H10N60/12—Josephson-effect devices
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N69/00—Integrated devices, or assemblies of multiple devices, comprising at least one superconducting element covered by group H10N60/00

Definitions

• the present invention relates to a device for reducing phase noise in a signal from a quasi-periodic source.
• phase locked circuits usually used in digital systems (computers or other) do not make it possible to reduce this phase noise in the short term: their action has a stabilizing effect in the long term, to prevent frequency drifts.
• phase noise means the noise corresponding to the noise floor or white noise of the signal frequency spectrum.
• An object of the invention is a device for reducing this phase noise.
• Such a device is particularly interesting in the field of fast digital electronics. It makes it possible in particular to reduce the jitter of the clock signal, which is particularly troublesome in high and very high frequency digital circuits.
• a logical family has developed, using superconducting circuits. It is the logical family RSFQ (English acronym of "Rapid Single Flux Quantum”), based on the use of the quantification of the magnetic flux, and the quantum transfer of flux ⁇ 0 individualized. In this approach, the logical processing of information amounts to manipulating voltage pulses resulting from the passage of flux quanta in current loops.
• the voltage pulse has an amplitude of the order of 2 millivolts on 1 picosecond.
• Each junction is defined by a critical current le and a normal resistance Rn, depending on its geometry and the technology used.
• the propagation / transfer function is ensured by a bias current control of the appropriate junction, which makes it possible to increase or weaken the current passing through the junction, thus allowing the maintenance in the loop or the transfer of the quantum of flux to across the junction, in the next loop.
• RSFQ logic has resulted in many logic circuits such as analog / digital converters, random access memories, signal processing processors calculating fast Fourier transforms, which can operate at very high frequencies.
• the upper operating limit of RSFQ logic elements is given by their critical frequency, depending on their geometry and the technology used (tri-layer, planar ).
• a Josephson transmission line is a line comprising Josephson junctions shunted in parallel, coupled together by superconductive inductors. Such a line allows the propagation of individualized flow quanta (Single Flux Quantum), and therefore serves as a medium for transporting logical information.
• a very short voltage pulse of the order of 2 millivolts on 1 picosecond, which is applied at the input of such a line, propagates along this line by propagation of a quantum of flux ⁇ 0, also called fluxon at through permanent current loops. At the output, this voltage pulse is recovered.
• a sequence of bits representing logical data can thus be modified in the Josephson transmission line, under the effect of the repulsive interaction between the fluxons, which is equivalent to a loss of logical information.
• this loss of information can have serious repercussions: gross loss of information, desynchronization (phase comparator) ...
• the author of the article recommends dimensioning the line so that the temporal separation between two fluxons generated in the line is not less than 3fc "1 , or in the example, at 28.8 ps (saturation value).
• a suitable dimensioning is obtained in particular by playing on the critical current , the normal resistance and the value of the inductances in the definition of the circuit. We can then reduce in operational the effects of the interactions by playing on the bias current of the Josephson junctions.
• the fluxons are organized in the line according to a periodic network.
• the Josephson transmission line it is a one-dimensional periodic network, according to the direction of propagation of the flow quanta. After a certain number of pulses, which correspond to a transient delay, a redistribution of this network is established, with an inter-fluxon distance smoothed around an average value.
• the phenomenon of repulsive interaction between the fluxons associated with the statistics of large numbers leads to a homogeneous redistribution of the fluxons in the network, which results in output of the line by a reduction in the level of white noise of the signal almost periodic.
• phase noise by taking any physical system capable of generating particles having repulsive interactions between them for a distance between particles less than a saturation value of the system (characteristic frequency), such as electrons (quantonic circuits) flow quanta, vortexes, phase noise can be reduced by reorganizing the particle network in the physical system.
• characteristic frequency such as electrons (quantonic circuits) flow quanta, vortexes
• the invention therefore relates to a device for reducing the phase noise of a signal from a quasi-periodic source of fundamental frequency fO.
• this device comprises a physical system of transmission of pulses by transfer of particles, said system being defined to have a characteristic frequency fc defining a range of operating frequency of the device with a low limit linked to said characteristic frequency, such that for the quasi-periodic signal applied at the input, said particles have a repulsive interaction between them, said system providing at output pulses at the fundamental frequency f0.
• the invention also relates to a device for reducing the phase noise of a signal from a quasi-periodic source of fundamental frequency fO.
• it comprises a superconducting circuit with active line for transmitting voltage pulses by transfer of flux quanta ⁇ 0, said circuit being defined to have a characteristic frequency fc such that 0.3fc ⁇ f0 where fO is the fundamental frequency of the quasi-periodic signal (Se) applied as input, and providing as output a pulse signal of voltage of fundamental frequency fO.
• Phase noise reduction can be improved by defining a superconducting circuit with an active line for transmitting voltage pulses such as the flux quanta generated in the circuit under the effect of the application of the quasi-periodic signal s' organize according to a two-dimensional periodic network.
• the interactions between the quanta of flux operate between nearest neighbors according to the two dimensions of the network.
• the invention applies not only to the quanta of fluxes generated in a Josephson transmission line, but more generally to any superconducting circuit with active line for transmitting voltage pulses.
• vortex flow transmission lines Josephson long junction transmission line, Josephson vortex flow, slotted or microbridge line, Abrikosov vortex flow.
• the phase reduction device can also be advantageously used in a frequency multiplier circuit.
• FIG. 1 already described illustrates the spectral density A (Sin) of a signal from a quasi-periodic source
• FIG. 2 shows an electrical diagram of a phase reduction device according to the invention based on a Josephson transmission line comprising a plurality of Josephson junctions
• FIG. 4a schematically represents a periodic network of fluxons generated by a pulse clock signal in the Josephson transmission line
• FIG. 5a represents another embodiment of a phase reduction device comprising two Josephson transmission lines arranged in parallel in the same surface plane and
• FIG. 5b is an illustration of the periodic network of corresponding fluxons
• FIGS. 6a and 6b schematically illustrate two variants of the use of two Josephson transmission lines in parallel in a phase reduction device, in order to improve the efficiency of the correction
• FIG. 7 shows an example of the use of a device for reducing phase noise in a frequency doubling circuit
• FIGS. 8a and 8b represent another exemplary embodiment of a phase reduction device with a Josephson transmission line in a junction technology on a ramp
• FIG. 9a and 9b show two embodiments of a phase noise reduction device, with Josephson long junction transmission line
• - Figures 10a and 10b show a phase noise reduction device with slotted line or microbridge, with vortex flow
• FIG. 11 is an illustration of the periodic network of vortices generated in such a line
• Figure 1 shows the spectral density A (S ⁇ n) of a Sin signal from a quasi-periodic source and applied as a clock signal in a logic system.
• it is sought to reduce the phase noise to N2 / N1 signal ratio by at least a factor of 10, which is of the order of - 115 to -120 dBc for signals from conventional quasi-periodic sources. (oscillators)
• Such a reduction is particularly advantageous in the field of very high frequency electronics and in particular in systems based on RSFQ logic circuits, with high critical temperature superconductor, in which the thermal noise is low. fully of a signal whose short-term noise has been significantly reduced
• phase noise reduction device comprising a superconductive circuit with voltage pulse transmission line, at the input of which the signal Sin to be processed is applied and which outputs a signal Sout, from which the phase noise has been reduced.
• the transmission line is a Josephson transmission line, comprising a plurality of Josephson junctions JJi, JJ 2 , ... JJ 2 oo, represented according to their simplified electrical diagram.
• Josephson junctions are shunted, mounted in parallel, and coupled to each other by superconducting inductors Ls 1 ( Ls 2 , Ls 3 , ... Ls 200.
• a superconductive inductance Ls 0 is also provided at the input, between a signal electrode entrance A and the first junction Josephson JJ-.
• the input signal is applied to the terminals of the line, between two input signal electrodes A and M.
• the output signal Sout is obtained at the line output, between two output signal electrodes, B and M '.
• the electrodes M and M ' are the ground electrodes of the line.
• the junctions are polarized in current Ip, lower than the critical current le of the junctions, so that a loop Bc of permanent current is established in each cell closed by a junction.
• the application of a pulse at the input of such a line increases the current of the junction above the critical current.
• the Josephson effect occurs: a quantum of flux crosses the current loop; a corresponding voltage pulse appears across the junction. The voltage pulse thus propagates in the line, without deformation.
• the characteristics of the line are chosen to obtain a determined characteristic frequency fc.
• This characteristic frequency fc defines a range of operating frequency of the device with a low limit linked to this characteristic frequency: For a quasi-periodic signal applied as an input whose fundamental frequency is included in the operating range thus defined, an interaction is obtained effective repellant, which reduces the white noise floor of this signal. More particularly, the characteristics of the line are chosen to obtain a characteristic frequency fc which checks 0.3fc ⁇ f0. 0.3fc is the lower limit of the operating range of this device.
• the inter-flux distance is less than the line saturation value.
• the phenomenon of repulsive interaction between the flux quanta (fluxons) causes a spatial redistribution of the flux quanta (fluxons) along the line, around an inter-fluxon average value, by smoothing around an average value, corresponding to the average value of the time interval between two pulses.
• the signal has a considerably reduced standard deviation of the time intervals between the pulses. In this way, the short-term noise or phase noise of the input signal is reduced.
• the characteristics of a Josephson transmission line are mainly the values of the inductances, a function of the line length and of the technology, in particular the mutual inductance Lm and of the characteristics of the junctions; critical current le, normal resistance Rn. In order not to complicate the drawing in FIG. 2 too much, these well-known characteristics of Josephson junctions are only shown for the first JJ * junction.
• FIG. 3 a practical example of a phase reduction device according to the invention is given with a superconducting circuit of the Josephson transmission line type comprising a plurality of Josephson junctions, in a planar thin film technology d '' a high critical temperature superconductor (we will use the French acronym of this term, HTC), on a bi-crystal substrate.
• a superconductive film 3 typically a film of a material of the form YBa 2 Cu 3 O n , 6 ⁇ n ⁇ 7, is deposited (epitaxied) on the surface plane of the bi-crystal, straddling the weld line of the bi-crystal substrate, so that a grain 4 joint develops along the weld, under the superconductive film, equivalent to an electrical barrier.
• the film is then engraved according to a scale pattern, each bar of the scale corresponding to a Josephson junction.
• the width w of a bar is of the order of 5 micrometers
• the length I of a bar is of the order of 20 micrometers
• the space h between two bars is of the same order (20
• the film has a width of a few micrometers, for a thickness of a few tenths of a micron, (0.3 ⁇ m for example)
• the substrate has a thickness of a few hundred micrometers, typically 300 to 1000 ⁇ m
• a current source not shown provides a bias current at each of the Josephson junctions, typically of the order of 100 microamps for the technology taken as an example.
• this bias current is applied between two polarization electrodes C and C in current formed on a portion 3 'of the superconductive film 3, shaped (etched) so as to distribute this current along the line, by means of branches of current supply provided in pairs bi, bT, bioo, b ⁇ oo ⁇ arranged on either side of the ladder forming the series of junctions
• a current supply branch b- and its complementary branch bT on the ground line side polarize the two junctions JJ- and JJ 2 by current located on either side of these branches
• the current source is dimensioned to provide a bias current of the order of a few tens of milliamps, for example mple 20 mA, distributed along the line
• the input and output signal electrodes A, M, B, M ' are formed at each end of the film, and on either side of the grain seal 4
• a clock signal of fundamental frequency fO> fc / 3 of the order of 50 to 100 gigolettes and having very offset pulses over time (short-term noise) a Sout signal can be provided at output, the white noise to signal ratio being reduced by a factor of 10, i.e. of the order of -130, -140 dBc (instead
• FIG. 4a schematically represents the network structure of the fluxons generated in such a line, under the effect of a pulse voltage signal applied at the Sin input.
• the line is represented as a channel 5
• the voltage pulses of the signal Sin are injected at one end of this channel, at a clock frequency f0.
• Fluxes flxi, flx 2 , ... flx m are generated in channel 5, which are spatially organized according to a one-dimensional network corresponding to the direction of propagation of the fluxons in the line.
• a spatial redistribution effect occurs by smoothing the inter-fluxon distance around an average value dO, which corresponds to an average value of the time interval between two pulses of the input signal.
• dO average value of the time interval between two pulses of the input signal.
• the standard deviation of the values of the time intervals between the pulses in the output signal is reduced. More precisely, and in relation to FIG. 4b, the phase noise of the signal Sin applied at the input is reflected in this signal by a dispersed time distribution.
• the fluxons generated under the effect of this signal are also spatially dispersed in the line, as shown schematically in Figure 4b.
• the characteristics of the line (f c ) so that the distance between the fluxons generated by the input signal Sin is on average less than the saturation value of the line, there is repulsive interaction between the fluxons more close neighbors.
• these repulsions are indicated by arrows.
• the saturation value corresponds to a time difference of 22 picoseconds.
• the output signal thus has its voltage pulses which are distributed more homogeneously, corresponding to a reduction in the level of phase noise, compared to the signal level at the fundamental frequency f0.
• a transmission line such as that shown in Figure 3
• the spatial separation therefore the interactions, depends on the ratio of the speed of propagation of the fluxons to the frequency of the signal.
• FIGS. 5a and 5b illustrate an alternative embodiment of a phase reduction device with a superconducting circuit with a Josephson transmission line.
• the superconducting circuit comprises two Josephson transmission lines.
• a superconductive film is deposited on zones 3a and 3b, one above each weld, so as to develop a respective grain joint, 4a, 4b.
• the branches of current supplies distributed along the line are wires, typically made of copper, corresponding contact pads 6 being provided on the films.
• Such an embodiment makes it possible to improve the efficiency of the spatial redistribution in the lines, by adding another dimension to the phenomena of interaction between the fluxons.
• an interval of a few microns must be provided.
• the flux flx of a line then undergoes the interactions due to four fluxes: two fluxons flx- and flx 2 on either side of this fluxon flx, on the same line, and two fluxons flx 3 and flx on the other line, located on both sides the bisector 7 of this line passing through the fluxon flx.
• phase shift of ⁇ can be applied in different ways, as shown in Figures 6a and 6b:
• phase shift of ⁇ is applied to the input signal Sin. It is then preferably provided that the signal from the quasi-periodic source 100 is applied to a circuit 101 to be duplicated at the output.
• An exemplary embodiment in RSFQ logic of this splitter circuit 101 is detailed in the figure, by way of a practical example. It provides two phase output signals.
• the phase shift of ⁇ is applied to the output signal
• An interconnection line 102 is then provided to bring the output signal of the first line to the input of the phase shifter of the second line.
• This line is typically produced using a technology of the coplanar, strip, microstrip type and with materials compatible with the technology of the Josephson transmission lines used, or may also be a Josephson transmission line.
• the two Josephson transmission lines may not be precisely aligned on the substrate, the interconnection line 102 can also introduce a delay such that the output signals Sout * and Sou 2 are not perfectly out of phase with ⁇ .
• the interactions between the lines may not be optimal.
• the bias current ip of the junctions is preferably variable, adjustable by junction or groups of junctions.
• FIG. 6c an example of a circuit with three Josephson transmission lines has been illustrated.
• a central line L is provided, receiving the input signal Sin as an input, and two lines Li 2 and Li 3 on both sides, receiving as input a phase shifted signal by ⁇ , which can be the input signal Sin as shown (case of FIG. 6a) or the output signal Souti of the first line (case of the Figure 6b).
• ⁇ can be the input signal Sin as shown (case of FIG. 6a) or the output signal Souti of the first line (case of the Figure 6b).
• each line can then be 045063
• the dimensions are evaluated so that the statistics of large numbers can be applied, to produce the smoothing effect of the desired interfluxon distance.
• the input signal is applied alternately on one line, on the following the phase-shifted input signal (by means of a phase-shifting circuit - FIG. 6a).
• the input signal receives the input signal (Se) and odd rank lines receive the phase shifted input signal.
• the device output signal is output from one of the lines.
• FIG. 7 shows an example of the use of a phase noise reduction device in a frequency doubling circuit.
• the circuit comprises two lines in parallel, the first receiving the input signal Sj n and the other the phase-shifted input signal.
• the first line outputs the Souti signal.
• the other line outputs the signal Sout 2 .
• the two lines are arranged so that the fluxons in the lines interact with each other, reducing phase noise in the short term.
• the two signals at output Souti and Sout 2 thus obtained at output are applied as inputs to a logic circuit RSFQ of confluence (combiner), which provides at output a signal S- 2f o) of double frequency of the input signal Sin, with low phase noise.
• phase noise reduction device can be advantageously used in a frequency doubling circuit, and more generally in a frequency multiplier circuit, by cascading circuits of this type, while maintaining a floor extremely low phase noise.
• FIG. 8a represents another exemplary embodiment of a Josephson transmission line, which can be used in all the variant embodiments of a phase reduction device according to the invention which have just been described.
• Figure 8b can be used in a single line or multiple line structure, but then stacked vertically.
• these two figures 8a and 8b these are lines in ramp junction technology, which is a multilayer SNS technology, acronym for Superconductor-Normal Material or Insulator-Superconductor.
• the normal or insulating material is, for example, non-superconductive PrBaCuO, a material with a structure similar to YBaCuO, compatible with the mesh characteristics of the superconductor.
• a comb shape comprises a first superconductive film 9 (thin layer) deposited on a heterostructure (8) of normal or insulating material deposited on the superconductive base electrode in gray in the figures, on a substrate.
• the teeth of the comb have the shape of a decreasing ramp towards the substrate.
• a thin layer of insulator and a second superconductive film 10 in the form of a comb are deposited on the substrate, the end of the teeth of this comb coming over the end of the teeth of the film 9 as a superconductor of the first comb.
• the junctions JJ-, JJ 2 , ... etc, are thus formed in the plane at the place where the layer 8 of normal or insulating material is thinned, between the two films 9 and 10 of superconductor.
• FIG. 8b is a variant of FIG. 8a in which the second film 10 of superconductor is "folded" over the first film 9, which allows a significant gain in surface area.
• FIG. 9a represents another embodiment of a device for reducing phase noise, with a superconductive circuit with a line of transmission of voltage pulses.
• the transmission line is made by a long Josephson junction.
• Such a junction is typically obtained in a three-layer SIS technology, preferably with a superconductor at low critical temperature: a thin layer 20 of normal (or insulating) material (for example Al 2 0 3 ), forming a barrier between two layers 21 and 22 of superconductor (for example Niobium).
• a bias current i lower than the critical current le of the Josephson long junction is applied between the two layers 21 and 22 of the superconductor.
• the current is preferably distributed along the line as shown in Figure 9b.
• FIGS. 10a and 10b Another embodiment of a phase noise reduction device according to the invention is shown in FIGS. 10a and 10b, corresponding to a type II superconducting circuit, with an active line of transmission with vortex flow from Abrikosov.
• the principle of Abrikosov's vortex flows is succinctly as follows: in the presence of an increasing magnetic field, the superconductor passes into a mixed normal-superconductor state. Currents develop on the surface of the superconductor which tend to screen the magnetic field. The magnetic flux which enters the superconductor is found in the form of field lines grouped on the surface on a disk of a few tens of angstroms of radius.
• the vortex flows are organized "naturally" according to a two-dimensional periodic network with a triangular base.
• the application of an electromagnetic signal as input generates a vortex flux network, which moves in lines L v (FIG. 11) according to this network structure.
• a receiving device any suitable load receives the associated voltage pulses.
• the lines L v correspond to the twin planes.
• the active superconducting circuit comprises (figures
• a slot 14 is made over the entire width of the film, leaving only a microbridge 15 of superconductive film between the two parts 13a and 13b of the film, on either side of the slot. This microbridge has a height less than or equal to the thickness of the film.
• this microbridge has a height e of the order of 0.1 micrometer, for a length L of microbridge, in the direction of the slit, less than a hundred micrometers and a width W, which is also the width of the slit, greater than one hundred micrometers.
• Two polarization electrodes 16 and 17 in direct current i of a few milliamps are provided at each end of the film.
• Two input signal electrodes 18 and 19 are provided at one end of the slot, on each part 13a, 13b of the film on either side of the slot, for applying the alternating input signal Sin, such as it periodically imposes a local magnetic field Be greater than the critical field at the input of the microbridge, so as to generate vortices v at the period of this signal.
• the input signal can be a voltage pulse signal. It is also possible to apply an alternating signal of the sinusoidal type.
• the source of the clock signal (not shown) is adapted in impedance, relative to the impedance of the microbridge (a few tens of ohms).
• Two output signal electrodes 20 and 21 are provided at the other end of the slot, on each part 13a, 13b of the film on either side of the slot, to collect as output the voltage pulses corresponding to the transmission in line of vortices (figure 11).
• each voltage pulse (or each positive peak voltage of the alternating signal) causes the local magnetic field Be at the input of the microbridge to pass over the critical field of the superconducting film causing the nucleation of a collection of vortexes.
• the generation of the vortices is obtained by the modulation of the magnetic field by the clock signal applied at the input.
• the proper polarization of the circuit induces the propagation of the vortices in the desired direction, towards the Sout output of the device.
• a weak continuous magnetic field B for example of the order of twenty milliteslas, oriented properly, so that the vortices are oriented in the same direction. sense, for example by placing a pair of Helmholtz coils on either side of the circuit.
• Such a superconductive circuit can advantageously be used in a frequency doubling stage as indicated above, with another similar circuit associated with a phase shifting circuit, in a frequency multiplication device.
• the transmission line comprises a type II superconductive film in the mixed state, deposited on a crystalline substrate.
• the film is polarized by current at its ends and comprises a slit in the width direction, except at the place of a microbridge, the slit separating the film into two parts.
• the quasi-periodic signal is applied to one end of the slit, between the two parts of the film and the output signal is obtained at the other end of the slit, between the two parts of the film.
• such a superconducting device is immersed in a continuous magnetic field oriented perpendicular to the surface plane of the slot.
• the invention which has just been described thus uses the periodic structure of the network of the flux quantums generated (fluxons, vortex) and the property of repulsive interaction of these flux quantums (comparable to magnetic dipoles) to reduce the noise of phase of a signal from a quasi-periodic source.
• An advantageous use of this device according to the invention makes it possible to provide a multiple frequency signal without degradation of the phase noise.
• the invention applies more particularly in the field of high and very high frequency, in fast electronics systems.
• a device can be used in RSFQ logic circuits.

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