Classifications

• • 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
  • H04B1/69—Spread spectrum techniques
  • H04B1/707—Spread spectrum techniques using direct sequence modulation
  • H04B1/709—Correlator structure
  • H04B1/7093—Matched filter type
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
  • H03H9/46—Filters
  • H03H9/64—Filters using surface acoustic waves
  • H03H9/6406—Filters characterised by a particular frequency characteristic

Definitions

• the present invention relates to a component for differential spread spectrum receiver by direct sequence, a component for differential transceiver spectrum spread by direct sequence and a transceiver spectrum spread by direct sequence.
• the spread spectrum technique has been used for many years in military radiocommunications, essentially because it enables discrete connections, of difficult interception and resistant to interference.
• Two spreading techniques are conventionally used: spread spectrum by frequency hopping and spread spectrum by direct sequence.
• Spreading spectrum by frequency hopping is the technique used for military applications. It consists in changing the radio carrier frequency as often as possible (up to several hundred times per second) according to a law which is known only to friendly receivers. This law, which is managed by one or more pseudo-random sequences, constitutes the link access code.
• This technique requires the use of agile frequency synthesizers. It is therefore expensive and there are only a few applications in the civil field.
• the other technique spreading spectrum by direct sequence (or, for short, ESSD or "Direct Se ⁇ quence Spread Spectrum” (DDSS) in Anglo-Saxon terminology) consists in transforming the signal to be emitted, including the spectral band is Bs, in a signal having the properties of a white noise, whose spectral band is much larger, ie B ⁇ s-
• This spreading operation is carried out by multiplying the message to be transmitted by a sequence pseudo-random formed of bits which can take the values +1 or -1.
• T is the period of the elements of information to be transmitted
• Tc the duration of a binary element of the pseudo-random sequence (also called "chip)
• This processing gain can vary from 10 to several tens of thousands depending on the case, conventional radiocommunication values rarely exceeding 1000.
• the receiver To be able to find the information, the receiver must perform a correlation operation between the message received and an identical pseudo-random sequence to that which was used to carry out the spreading operation. The receiver must therefore know this sequence, which constitutes the access key to the message sent.
• Two independent messages can be transmitted using the same frequency band and two orthogonal sequences, that is to say two sequences having low intercorrelation coefficients.
• a receiver of spread spectrum signals by direct sequence must include a correlator, which delivers on its output a signal SI result of the correlation between the signal received and the spreading sequence used on transmission and a delay line which delivers a signal S2 identical to SI but offset by a duration equal to the period T of the information elements to be transmitted.
• the modulation used is generally differential phase modulation
• the information is carried by the phase difference between the SI signals. and S2. This information is extracted using a multiplier. If the signal at the output of this circuit is positive, SI and S2 are in phase. If it is negative, they are in phase opposition.
• the correlator and the delay line can each be produced in the form of surface acoustic wave devices (SAW abbreviated for "Surface Acoustic Waves"). This is what is described for example in the article by Mohsen KAVEHRAD et al. cited above, ( Figure 4, page 817).
• the correlator is in reality a suitable filter.
• the matched filter or correlator which performs the correlation operation, is composed, like any surface acoustic wave filter, of two surface wave transducers deposited on a piezoelectric material which, in the case of signals modulated in phase, is generally quartz for reasons of temperature stability of the characteristics of the component (central frequency in particular). It is well known that the impulse response of such a device is the product of convolution of the impulse responses of the two transducers; it should be ideally equal to the time reverse of the signal to which the filter must be adapted.
• the transducers are of the "interdigitated combs" type, the electrodes (or fingers) of which may have constant or variable lengths depending on their position. They are produced by depositing aluminum (a few hundred to a few thousand Angstroms thick) on the substrate used. Such components are described and offered in the catalogs of several suppliers of surface wave components.
• transducers than those known conventionally and which are bidirectional. Surface acoustic waves other than those which propagate between the two transducers are attenuated by depositing on the areas located between each transducer and the edge of the substrate which is closest to it, an appropriate material (generally an adhesive). Uncontrolled amplitude and phase signals are thus avoided due to reflections on the edges of the substrate.
• Ie (t), IS] _ (t) and IS2 (t) are called the impulse responses respectively of the input transducer 10 and of the two output transducers 12 and 14, in the embodiment written in this document, we have:
• the object of the present invention is to remedy these drawbacks. To this end, it offers a component which still fulfills, by itself, the double correlation and delay function, but which contains only one transducer adapted to the pseudo-random spreading sequence instead of two and for which the two output transducers are naturally very spaced from each other, which reduces the parasitic capacitance between them.
• the two output transducers have a number of electrodes, alternately connected to two power supply lines.
• the output signal is taken from one of the lines, the other line being connected to ground.
• the length of the transducers is: L ⁇ d (Nl) In the case of making the adapted filter, this length corresponds to the duration of a chip (binary element of the pseudo-random spreading sequence) and one can write, if v is still the propagation speed of the surface acoustic wave on the piezoelectric substrate:
• the input transducer is made up of two lines or electrodes connected, for example, to the signal input and to ground respectively, and groups of interdigitated electrodes connected to the supply electrodes.
• the number of these groups of electrodes corresponds to the number of chips in the pseudorandom spreading sequence.
• the distance separating two consecutive groups is equal to L, the length which the acoustic wave travels during the duration Te.
• These groups of electrodes are polarized according to the spectrum spreading sequence considered. This filter is produced by photolithography from a mask with the spreading sequence used.
• the output transducers are very distant from one another and the parasitic capacitance between transducers is very low. Naturally, in the device of the prior art, one could always offset the output transducers by placing them one above the other, but then the surface of the substrate would be increased and the cost would be equal. ⁇ .
• the parasitic capacitance between transducers is extremely low and the overall performan ⁇ these reception system are improved, in particular vis-à-vis the resistance to radio interference and parasites.
• the spreading sequence, or code determines the shape of a single transducer, namely the input transducer, instead of two (the two output transducers). This is extremely interesting if one wants to make the component programmable, that is to say adaptable to different spreading sequences. In the case of the invention, it will be necessary to program the groups of elementary electrodes of the input transducer whereas, in the prior art, it would be necessary to program twice.
• T M. (L / v)
• the two output signals S] _ (t) and S 2 (t) must verify the relationship the distance separating the two output electrodes must be such that the time taken by the acoustic wave to propagate from one to the other is equal to T. This distance is therefore equal to S + L since
• the component which has just been described has the additional advantage of being able to be very easily transformed into an emitting component.
• a third output transducer identical to the first two and coupled to the input transducer.
• the impulse response in baseband of the channel formed by the input transducer and the first output transducer is equal to the pseudo-random spreading sequence used for the emission reversed in time. If a (t) is this pseudo-random sequence, we can therefore define, for the receiver-transmitter component, three impulse responses seen from the three outputs it presents (two for reception, that is S ⁇ , S, one for l 'emission be S 3 ):
• the third transducer therefore makes it possible to directly generate, at the intermediate frequency, the spread spectrum signal. To do this, simply apply an electrical signal to the input transducer. very short duration pulse similar to a DIRAC pulse. In this case, the output voltage S3 of the third transducer will be worth:
• the present invention therefore also relates to a component for a differential transceiver of spread spectrum signals by direct sequence, this component being characterized in that it comprises:
• an emission channel constituted by the input transducer of the reception component and, moreover, by a third output transducer similar to the other two.
• the present invention also relates to a spread spectrum differential transceiver.
• This transceiver is characterized by the fact that it comprises the transceiver component which has just been defined, this component being used in its transmission channel to produce an intermediate frequency signal with spread spectrum, this component being also used in its reception channel as a frequency signal processing device intermediary capable of correlating with the pseudo-random sequence used on transmission.
• This transceiver is further characterized by the fact that the means of the transmitting channel for transposing the intermediate frequency signal into a radio frequency signal are the same as the means of the receiving channel for transposing the radio frequency signal. as an intermediate frequency signal.
• each of these symbols is associated with a pseudo-random sequence, and, provided that these sequences are weakly correlated with one another, it is possible to decide, at the level of the receiver, between the emission of a "0" or a "1” by carrying out the correlations between the received signal and the two sequences used for transmission.
• This is what the component of the cited document does, which has one input and two outputs, the "0-bit" output realizing the correlation between the input signal and the sequence associated with the bit "0" and the output "1-bit” realizing the correlation between the input signal and the sequence associated with bit "1".
• the originality of the component of the cited document is due to the fact that it uses two reciprocal sequences
• the modulation technique is different.
• the symbols emitted in phase modulate this pseudo-random sequence.
• a bit "0" corresponds to an absence of phase jump between two successive transmitted symbols while a bit "1" corresponds to a phase jump equal to ⁇ between two successive transmitted symbols.
• the component used in the receiver must, in this case, perform two functions which are the operation of correlation between the received message and the sequence used to modulate the data on transmission, and this component must also make it possible to compare the phase of two successive symbols.
• the correlation is carried out by the input electrode and the phase comparison is accessible thanks to the delay of a symbol duration (T) between the two output electrodes.
• the modulation technique used in the invention is called differential phase spread spectrum modulation by direct sequence, which is not the case of the technique of the document cited where the technique used is spread spectrum modulation by direct sequence using orthogonal sequences.
• FIG. 2 shows an exemplary embodiment of a component for a receiver according to the invention
• FIG. 3 shows an exemplary embodiment of a component for a transceiver according to the invention
• FIG. 4 shows part of a spread spectrum transceiver using the component of the invention
• FIG. 5 shows an exemplary embodiment of a programmable component according to the invention
• FIG. 6 shows an exemplary embodiment of a switching circuit
• FIG. 7 shows in perspective the switching circuit with its control connections
• FIG. 8 shows, in top view, the substrate with the input transducer and its output connections
• the component shown in FIG. 2 comprises, on the same substrate 18, an input transducer TRE, and two output transducers, respectively TRS1, TRS2.
• the input transducer comprises two lines or electrodes 20, 21, the first connected to a signal input E, the second connected to ground.
• the output transducers TRS1, TRS2 also include two lines or electrodes, one connected to a signal output, SI and S2 respectively, the other to ground.
• the input transducer is produced in the form of an interdigital comb comprising as many (M) groups of electrodes Gl, ..., GM as there are elements in the pseudo-random sequence .
• M is between a few tens and a few hundred.
• Each group of electrodes has a length (L) corresponding to the duration of a binary element of the pseudo-random sequence.
• the length (S + L) of the input transducer corresponds to the duration (T) of a binary information symbol.
• the output transducers TRS1 and TRS2 they are produced in the form of an interdigital comb with a length L corresponding to the duration (Te) of a binary element of the pseudo-random sequence.
• the component illustrated in FIG. 3 differs from that of FIG. 2 by the presence of a third output transducer, TRS3, placed substantially symmetrically by TRS1 relative to TRE.
• This third output transducer has an electrode connected to an output S3 and another electrode connected to ground. It is identical in structure to the other two output transducers TRSl and TRS2.
• the TRE-TRS3 assembly constitutes a transmission channel, while the TRE-TRS1-TRS2 assembly constitutes a reception channel.
• FIG. 4 illustrates part of a transceiver according to the invention.
• This circuit comprises a radio frequency stage E (RF), an intermediate frequency stage E (FI), and, between the two, frequency transposition means TF.
• RF radio frequency stage
• FI intermediate frequency stage
• TF frequency transposition means
• This device comprises six switches, referenced from II to 16, with two positions E or R.
• Position E corresponds to an operation in transmission and activates means constituting a "transmission channel”.
• Position R corresponds to an operation in reception and activates means constituting a "reception channel”.
• the transceiver of FIG. 4 generally comprises:
• a radiofrequency amplifier 102 2 a radiofrequency amplifier 102 2 , a bandpass filter 104 and a transmitting antenna 100,
• a reception antenna which is merged with the transmitting antenna 100 and a radiofrequency planner 102_, means for transposing the radiofrequency signal into an intermediate frequency signal, these means being precisely the means 110, 112 of the transmission channel for transposing the signal at intermediate frequency into a radio frequency signal,
• an intermediate frequency signal processing device comprising means capable of correlating the intermediate frequency signal with the pseudo-random sequence used on transmission, these means being constituted by the reception channel of the component 80.
• a complete circuit also includes means for demodulating and processing the demodulated signal which are not shown in FIG. 4 because they are well known to those skilled in the art. These means restore the information D used on transmission.
• the differential transceiver of FIG. 4 is characterized in particular by the fact that it comprises the transceiver component which has been described above with respect to FIG. 3. This component, referenced 80, is used in its path d 'TRE-TRS3 transmission to produce the intermediate frequency spread spectrum signal and, in its reception path TRE, TRS2, TRS2, as an intermediate frequency signal processing device capable of correlating with the sequence pseudo-random used on the broadcast.
• a first switch II is provided for connecting the antenna 100 either to the reception amplifier 102] _, or to the transmission amplifier 102 2 .
• a second switch 12 is also provided for connecting, in synchronism with the first, either the amplifier of reception 102] _, ie the transmission amplifier 102 to the common means 110, 112 for signal transposition.
• a bandpass filter 104 can be provided just after the amplifier 102 2 .
• the transceiver further comprises:
• a third switch 13 connecting the input of said amplifier 114 either to the common frequency transposition means 110, 112, or to the transmission channel TR3, F3 of the component 80,
• a fourth switch 14 for synchronously connecting with the third switch 13, the output of the band pass filter 116, either to the reception channel TRI, FI, TR2, F2, or to the common means of frequency transposition 110, 112
• An automatic gain control circuit 118 is also provided for adjusting the gain of the amplifier 114 from the received signal.
• the structure shown in FIG. 4 clearly shows the use of several sub-assemblies, both on transmission and on reception.
• the portion of the receive mode transmission mode is done through the switches II to 15. These switches may be diode switches, from 'so that the transition from one mode to another is done quickly.
• all the switches are in the receive position (R).
• transmit mode the gain of amplifier 114 is fixed and preset using a potentiometer 120. We can consider using this gain control input of amplifier 114 to adjust the transmit power either using calibrated voltages, or using an automatic gain control loop whose input setpoint would be the signal strength emitted by the antenna.
• the signal supplied by the antenna is amplified by 102 ⁇ and filtered by 106 whose band is equal to or greater than Bes.
• the signal at the output of the mixer 112 is filtered by 106, amplified by 102 2 then filtered again by 104 before being transmitted by the antenna 100.
• the filter 104 is necessary to avoid any secondary lobe which could be produced by the non-linearities in the amplifier 102 2 .
• the mixer 112 operates in down-converter in reception mode, that is to say that the signal present at the input is mixed with the signal of the local oscillator and that the frequency of the signal supplied at intermediate frequency is the difference in frequencies between the frequency of the local oscillator and the radio frequency, the intermediate frequency being less than the frequency of the local oscillator and at the radio frequency, the frequency FI being lower than the OL and RF frequencies.
• the intermediate frequency stage operates as follows in reception mode.
• the signal at intermediate frequency at output of 112 is amplified by 114 then filtered by 116, the band of which is greater than Bes, before being injected at the input of the component 80, the detailed operation of which has been described above.
• the gain control circuit 118 automatically adjusts the gain 114 so that the power of the intermediate frequency signal at the reception input of the filtered component is constant.
• the signal is applied to the input E of the transducer TRE of the component 80.
• the two outputs SI and S2 of the component are identical to within a delay, the value of this delay being T, duration of the binary symbol transmitted, as already indicated .
• the switches II to 15 are in position E.
• the component of the invention is made programmable, that is to say that its conformation can be controlled at will as a function of the spreading sequence used.
• the component of the invention remains composed of interdigitated comb-shaped electrodes, these electrodes or fingers being connected to common electrodes, themselves connected either to a general signal input, or to a point brought to a reference potential. (e.g. mass).
• the electrode groups are all identical and are separated from each other.
• Each group includes a first series of electrodes all connected to a first common electrode and a second series of electrodes interposed with the first and all connected to a second common electrode.
• the component further comprises electronic means for programmable switching capable of connecting the first common electrode of each group either to the general signal input, or to a point brought to a reference potential (for example ground). Simultaneously, these switching means connect the second common electrode of the same group either to the point brought to the reference potential or to the general signal input.
• each group of electrodes can be shaped as desired, to correspond to a +1 bit or to a -1 bit. All the groups of electrodes can therefore be adapted to any pseudo-random sequence.
• Programmable surface acoustic wave filters are described in the article by E.J. STAPPLES et al. entitled “A Review of Device Technology for Programmable Surface-Wave Filters", published in the journal IEEE Transactions on Microwave Theory and Techniques, vol. MIT 21, n ° 4, April 1973, pp. 279-287.
• the switching means are combined in a circuit and the connections between this circuit and the groups of electrodes are made using conductive microbeads.
• the component represented in FIG. 5 comprises a substrate 30 on which are deposited groups of electrodes G1, ..., G5 all identical and separate from each other. If Figure 5 shows five such groups, it should be understood, as already pointed out, that in reality there may be many more.
• the component of FIG. 5 further comprises, like that of FIG. 2, two output transducers TRS1, TRS2.
• the signal input is via input E.
• the reference potential which in this case is the mass, is available at the point marked Pref.
• Each group of electrodes for example the first, (Gl), comprises a first series of electrodes or fingers dl, all connected to the first common electrode El and a second series of electrodes or fingers dl ', interposed with the first dl, and all connected to the second common electrode El '.
• the component comprises switching means constituted by as many first switches SW1, SW2, ... as there are groups of electrodes, each of these switches being connected to the first common electrode El, E2, ' ... of the electrode group to which it corresponds.
• SW1 is connected to El.
• Each switch is able to connect this first common electrode (for example El) to one or the other of two connection lines Ls, Lref connected respectively to the general signal input E and at least Pref brought to ground.
• the switching means comprise, symmetrically, as many second switches SW1 ', SW2', ... as there are groups of electrodes, each second switch being connected to the second common electrode El ', E2', ... of a particular group of electrodes. For example, SW1 'is connected to El'. Each second switch is able to connect this second common electrode El ', E2', ... to that of the two said lines
• the connections between the common electrodes El, E2, ..., El ', E2', ... and the switches SW1, SW2, ..., SW1 ', SW2', ... preferably take place at using various conductive pads.
• the first common electrode E1, E2, ... of each group of electrodes is connected to a first connection pad PI, P2, ... arranged on the substrate 30.
• the component thus comprises a first row of first connection pads PI, P2, ... aligned along the first common electrodes El, £ __, ...
• the second common electrode E1 ', E2', ... of each group of electrodes is connected to a second connection pad PI ', P2', ... arranged on the substrate 30.
• the component thus comprises a second row of first connection pads PI ', P2', ... aligned along the second common electrodes El ', E2', ...
• the switches SW1, SW2, ..., SW1 ', SW2', ... are not produced on the substrate but are combined in a switching circuit physically separate from the substrate.
• FIG. 6 schematically represents such a switching circuit. It includes a shift register 40 to an input 42 of programming data
• This register comprises as many cells as there are groups of electrodes in the input transducer, that is to say M. It includes as many outputs SI, ..., SM.
• the circuit also includes a latch circuit 46
• This circuit includes as many registers as there are cells in the shift register 40, ie again M.
• the switching circuit comprises a switching assembly 50 comprising a first set of first switches SW1, ... at two positions, these first switches being in number equal to the number M of electrode groups, and a second set of second switches SW1 ', .. in the same number.
• Each first switch SW1, ... of the first set is connected to a first output pad pi, p2, ... while each second switch SW1 ', ... is connected to a second output pad pi', p2 ' , ...
• circuit 50 two lines not shown (but which correspond to the lines Ls and Lref in FIG. 3) respectively connect the two pads of the same switch either at the signal input E or at the point Pref brought to the potential reference.
• the operation of this circuit is as follows.
• the shift register 40 is loaded with a sequence of binary data corresponding to the desired pseudo-random sequence. This sequence is introduced by input 42 at the rate of the clock applied at 44.
• each bit thereof is loaded into the corresponding register of circuit 46.
• This bit then controls the two associated switches, in a complementary manner. For example, a bit 1 will place the switch SW1 on the pad connected to the signal input and, in a complementary manner, the switch SW1 'on the pad connected to ground. The stud output pi will therefore be connected to the signal input and the pin pi 'to ground.
• circuits 40, 46, 50 are combined in an integrated circuit 60 arranged on a substrate 62.
• the output pads of the circuit 60 are distributed on each side of the circuit with a first row formed by the pads pi, p2, ... and a second row formed by the pads pi ', p2', ...
• the surface acoustic wave transducer will be made so that its dimensions agree with those of the circuit of FIG. 7. This is what is shown in FIG. 8 where we see that the input transducer TRE is registered in a frame 62 ′ which corresponds to the substrate 62 in FIG. 7.
• connection pads PI, P2, ... are in geometrical agreement with the output pads pi, p2, ... of the switching circuit, as well as the pads pi ', p2', ... are in agreement with the output pads pi ', p2', ...
• these means can be conductive microbeads Bl, ..., Bl ', ... These microbeads allow extremely short connections to be made with very low resistance, inductance and capacitance values. In addition, automatic mounting is possible.
• the fingers of the various surface acoustic wave components can be cut to the desired length, by laser machining.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)
• Transceivers (AREA)

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• 1993
  • 1993-07-06 FR FR9308272A patent/FR2707441B1/fr not_active Expired - Fee Related
• 1994
  • 1994-07-05 WO PCT/FR1994/000827 patent/WO1995002285A1/fr not_active Application Discontinuation
  • 1994-07-05 CA CA002143433A patent/CA2143433A1/en not_active Abandoned
  • 1994-07-05 EP EP94921685A patent/EP0658292A1/de not_active Withdrawn
  • 1994-07-05 JP JP7503858A patent/JPH08501672A/ja active Pending

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