Radio system for data transmission with a passive terminal station.

p0001The present invention relates generally to radio communications proximity. More particularly, the invention relates to a data transmission system by radio microwaves between a central station and a passive end not comprising own microwave source and operative in response fashion.

p0002Such a radio system used to exchange information between short a privileged point or central station and one or more passive ends or terminal stations which have to remain very simple design to meet the constraints of cost and space. This type of radio system has many applications, for example in: - Remote data collection systems such as a system of record of domestic meters interrogator mobile radio, - Access management or pointing systems with code numbers stored in remote interrogation of individual access cards or score, - For road or railway signaling systems, - Automatic sorting systems for example postal packages, - Automatic billing systems for card payments at contactless chip - Etc ...

p0003Several radio systems in a passive end are known in the prior art. In general, such as in a coded responder card disclosed by the FR-A-2527870, it is uses an amplitude modulation to transmit data in the transmission direction from the passive to the one end it central station. A microwave incident emitted by the central station is received by the passive end which modulates in amplitude by data to transmit the microwave incident received or one of its harmonics before retransmitting to the central station. The passive end draws power from the incident microwave. A recovery and filter circuit is generally expected to produce a DC voltage supply from the received incident microwave.

p0004Microwave modulated re-emitted by the passive end to the central station is low power because of the low energy efficiency in receiving the microwave incident and the energy taken to power the passive end and consecutively such radio system necessarily has a limited scope. Furthermore, the amplitude modulation has a low noise immunity compared to a frequency or phase modulation which does not favor the system range in the prior art.

p0005A solution to improve the range of a radio system at one end passive, for example to replace the amplitude modulation of the microwave re-emitted by a two-state modulation phase having a better noise immunity. However, this solution presents problems of implementation because the passive end should remain very simple and it n'est therefore not possible to use phase modulators known design too complex.

p0006The present invention aims to provide a data transmission radio system in a passive end wherein a modulation with two phase states is implemented for the transmission direction passive end - central station. The passive end or terminal station of a radio system according to the invention is extremely simple and compact.

p0007To this end, the radio system according to the invention is as defined by claim 1.

p0008According to an alternative embodiment allowing a more efficient detection of the first data signal from the first microwave, the terminal station is equipped with quadratic detecting means. These means of detection quadratic comprises a transistor to effect field having a first electrode connected to a ground reference of the station terminal, a second electrode connected to a short-circuit reflector and a third electrode receiving the first microwave to produce the second electrode a signal representative of the first microwave square and detecting a DC component of said representative signal of the first data signal.

p0009Preferably the central station is as defined in claim 5.

p0010The invention will be better understood on reading the following description of several preferred embodiments of the radio system of the invention with reference to the corresponding accompanying drawings in which:<ul><li>- Fig. 1 is a block diagram of the data transmission radio system in a passive end according to the invention;</li><li>- Fig. 2 shows an embodiment in microstrip technology of an antenna and microwave mixers included in a central station of the radio system according to the invention;</li><li>- Figs. 3 and 4 show respectively the schematic diagram and an embodiment in microstrip technology of a quadratic detector amplitude included in a terminal station of the radio system according to the invention;</li><li>- Fig. 5 is a block diagram of a microwave switch included in the terminal station;</li><li>- Fig. 6 shows an embodiment in microstrip technology of contactless smart card equipped with a terminal station of a radio system according to the invention;</li><li>- Fig. 7 is a schematic diagram of a microwave mixer included in the central station;</li><li>- Fig. 8 is a block diagram of a phase detector included in the central station; and</li><li>- Fig. 9 shows a logic diagram relating to the operation of a circuit control logic included in the detector phase Fig.8 to recover a data signal transmitted by the terminal station from a dynamic selection of a signal demodulating among four demodulation signals available.</li></ul>

p0011Referring to Fig. 1, the radio data transmission system according to the invention allows to alternately transmit serial data digital signals D12 and D21 between two remote units U1 and U2 data processing. The units U1 and U2 are respectively connected to a central station 1 and a terminal station 2 of the system. Central and terminal stations 1 and 2 constitute a radio equipment for transmitting data associated with the units U1 and U2. The unit U1 and the central station 1 is for example included in a public phone contactless payment card. The unit U2 and the terminal station 2 in this case are included in a payment card contactless card type chip.

p0012Signal transmission data D12 and D21 alternately to the central station 1 to the terminal station 2 and inversely called respectively to a modulation amplitude and a modulation with two phase states 0 and π of the same microwave P frequency F issued by the central station 1. periods of transmission data of the unit U1 to the unit U2 and vice versa are alternately assigned to the data processing units U1 and U2. During periods of data transmission assigned to them, the units U1 and U2 respectively transmit the D12 and D21 data signals. XON and XOFF characters reserved worn by D12 and D21 data signals are exchanged between the units U1 and U2 to learn about the beginning and end of a data transmission period.

p0013During periods of data transmission of the unit U1 to the unit U2, the central station 2 transmits eg rectilinear horizontal polarization H, a microwave PA frequency F which is amplitude modulated by the data signal D12 . During periods of data transmission unit U2 towards unit U1, the central station 1 transmits straight horizontal polarization H microwave unmodulated microwave P. The P is detected by an antenna of the terminal station 2 and is modulated in two phase states 0 and π by the data signal D21 to generate a microwave phase modulated frequency F PP retransmitted to the central station 1 in rectilinear cross polarization, ç'est ie in in this example rectilinear vertical polarization V. the modulated microwaves PA and PP are respectively demodulated in the terminal stations 2 and core 1 in order to recover the data signals D12 and D21.

p0014The central station 1 comprises a local oscillator microwave 10, an amplitude modulator 11, a microwave antenna 12, and demodulating means synchronous phase constituted by four mixers 13a-13d and a phase detector 14.

p0015The local oscillator 10 generates a microwave signal OL of frequency F for example equal to 2.45 GHz. The LO signal is applied to a first input of the amplitude modulator 11. A second input of modulator 11 receives the data D12 of the signal transmitted by the unit U1.

p0016During the data transmission periods from unit U1 towards unit U2, the signal D12 is active and the modulator 11 outputs a modulated microwave signal OLA corresponding to the microwave signal OL amplitude modulated by the signal D12. The signal modulated microwave OLA is applied to access horizontal polarization of the antenna 12 and transmits it in response microwave PA corresponding horizontally polarized.

p0017During periods of data transmission unit U2 towards unit U1, the signal D12 is inactive and the modulator 11 outputs the signal microwave OL. The signal OL is applied to access to horizontal polarization antenna 12 and it emits in response to corresponding microwave P.

p0018The microwave antenna 12 is a planar antenna with 2n square patterns printed form, where n is an integer greater than or equal to 1. In the embodiment shown in Fig. 1, n is chosen equal to 2 and the antenna 12 includes four units 12a to 12d. Referring also to Fig. 2, the antenna 12 is supported by a plate of double-sided printed circuit board 123. On a front face, besides the antenna patterns 12a to 12d, the plate holder 123 also mixers 13a to 13d. A conductive back side of the plate 123 is connected to a reference mass and form a reflector R1 screen. Each pattern 12a to 12d is a square having sides of dimension equal to λ / 2, where λ is the wavelength corresponding to the frequency F of the microwave signal OL. To form the planar microwave antenna 12, the four units 12a to 12d are disposed respectively at four corners of a square surface dxd so that the sides of the antenna units are parallel and perpendicular to the sides of square surface dxd, where is a characteristic dimension of the antenna 12 fixed in known manner to obtain a desired radiation diagram. A pattern antenna, for example 12a, 2 includes access to vertical polarization and V0A Vπa located respectively at the centers of two parallel first sides of the antenna pattern 12a, and two access polarization and horizontal H0A Hπa located respectively at centers 2 second sides parallel pattern antenna 12a. A microwave signal applied to a polarization access to vertical or horizontal antenna pattern of a square product issuing a microwave corresponding polarized vertically or horizontally, respectively, and vice versa a microwave vertically polarized or horizontally received by the antenna pattern produces a microwave signal corresponding to the two access to vertical or horizontal polarization of the antenna pattern, respectively. Two microwave signals detected respectively to the two polarization access to vertical or horizontal pattern of a square antenna and corresponding to the same microwave received are out of phase by π and reciprocally the same signal microwave applied successively to both access to vertical or horizontal polarization produces two microwave polarization corresponding phase-shifted by π between them.

p0019As shown in Fig. 2, the signals microwave OLA and OL are provided access to horizontal polarization Hπa, H0B, h0C and Hπd of the antenna 12 through microstrip adaptation and phase 120b, 120c, 120a and 120d. The microwave signals received at access Hπa and HΠd and corresponding to the signal OLA or OL are phase shifted by π relative to the signals received microwave corresponding to the access H0B and h0C and the antenna 12 emits the corresponding microwave PA or P horizontally polarized to the terminal station 2.

p0020Referring to Fig. 1, the terminal station 2 includes an antenna 20, a circuit rectification and filtering 21, an amplitude detector 22, and a switch microwave 23.

p0021The antenna 20 is composed of a single printed pattern square identical to printed patterns 12a to 12d of the antenna 12 of the central station 1.

p0022During periods of data transmission of the unit U1 to the unit U2, the antenna 20 receives the microwave PA amplitude modulated by the signal D12 and outputs in response the signals microwave matching of phase π between them SA₂ and SA (π) ₂ respectively by access to horizontal polarization and H0 Hπ. ₂ signals SA and SA (π) ₂ are respectively applied to an input 230 of the switch 23 and input circuits 21 and 22. During periods of transmission of data of the unit U2 to the unit U1, the antenna 20 receives the microwave P and delivers the response signals corresponding microwave out of phase π between them ₂ SP and SP (π) ₂ respectively by the access H0 and Hπ. ₂ signals SP and SP (π) ₂ are the same as the signals SA ₂ and SA (π) ₂ respectively applied to the input 230 of the switch 23 and input circuits 21 and 22.

p0023The circuit rectification and filtering circuitry 21 is a classic example of the type with a diode rectifier and a filtering capacity. Circuit 21 produces a VA DC supply voltage by rectification and filtering. The voltage VA is supplied to the unit U2 to supply all or part of the circuitry of the unit U2, and possibly the amplitude detector 22. A battery electric miniature B is provided if needed to provide the unit U2 a DC voltage supply additional VAa.

p0024During periods of transmission of the unit U1 to the unit U2, the detector 22 recovers the data signal D12 by direct detection of the signal amplitude. The data signal D12 supplied by the detector 22 is supplied to the data processing unit U2.

p0025According to a first embodiment of a transmission system according to the invention short-range detector 22 of the terminal station 2 is formed vector using a diode detector operating in nonlinear regime.

p0026In a second embodiment of the system more efficient transmission according to the invention, the detector 22 is realized using a field effect transistor (FET) operating in multiplier for a quadratic detection of the data signal D12. In this case the supply voltage VA is supplied to the detector 22 for biasing a gate of the FET transistor.

p0027Referring to Fig. 3, a detector 22 for said second embodiment of the transmission system according to the invention comprises essentially a transistor FET, 220.

p0028The signal microwave SA (π) ₂, is supplied through a capacitor 221 connecting to a gate 220G of the transistor 220 and to a first terminal of a coil 222. A second terminal of the coil 222 receives the voltage supply VA and is connected to a ground reference of the station terminal 2 via a decoupling capacitor 223. the voltage VA is here a bias voltage negative to polarize so as adequate the gate 220G of the transistor 220. a source 220S of the transistor 220 is connected to ground. A drain 220D of the transistor 220 is connected to a first terminal of a coil 224, and a short-circuit reflection 225. A second terminal of the coil 224 is connected to ground through a decoupling capacitor 226. During the periods of data transmission of the unit U1 to the unit U2, the signal SA (π) ₂ applied to the gate 220G also appears on the drain 220D of the transistor 220 and propagates to the short circuit 225. signal AG ( π) ₂ is reflected by the short-circuit 225 and returns to the drain 220D. The transistor 220 operates multiplier and produces the signal (SA (π) ₂) ². The signal (SA (π) ₂) ² has a DC component proportional to the amplitude of the signal (SA (π) ₂) ² and representative of the data signal D12. This DC component representative of the signal D12 is detected to the second terminal of the coil 224 and is supplied to the data processing unit U2.

p0029A practical embodiment corresponding technology microstrip detector amplitude 22 described with reference to Fig. 3 is shown by way of example in Fig. 4. The coils 222 and 224 are formed substantially by microstrip lengths adequate same references 222 and 224. The short-circuit reflection 225 is formed using a capacitor having a first terminal connected to the drain 220D of the transistor 220 through a microstrip of appropriate length and a second terminal connected to ground. T metallized holes are provided on either side of legs connecting the source 220S of the transistor 220.

p0030Referring to Fig. 1, during periods of data transmissions from the unit U2 towards unit U1, U2 unit delivers the signal data D21 to be transmitted to the unit U1 via the stations 2 and 1. The signal is applied to D21 a first control input 231a of switch 23 and to an input of a logic inverter I. the inverter I generates a signal of data<o>D21</o> complementary to the signal D21. The signal<o>D21</o> is applied to a second control input 231b of the switch 23.

p0031A block diagram of the microwave switch 23 is shown in FIG. 5, the switch 23 is preferably a switch integrated for example as a switch microwave broadband marketed by TACHONICS CORPORATION under reference TCSW-0401. First and second outputs 232a and 232b of the switch 23 are respectively connected to the first and second access to vertical polarization Vπ and V0 of the antenna 20. When the data signal D21 is a logical state "0", the entry 230 is connected to the output 232b of the switch 23 and the signal SP microwave ₂ provided by access H0 of the antenna 20 is applied to the access V0 of the antenna 20 which emits in response the corresponding microwave PP with a relative phase equal to 0. When the data signal D21 is at a logic state "1", the input 230 is connected to the output 232a of the switch 23 and the signal SP microwave ₂ is applied to the access Vπ of the antenna 20 which emits in response microwave PP corresponding with a relative phase equal to π. Microwave PP is thus modulated with two phase states 0 and π by the signal D21.

p0032Referring to Fig. 6, the terminal station 2 and the processing unit data U2 are included in a smart card 202 shown approximately to a scale 3/4. A front face of the card 202 supports the antenna 20 and the various circuits of the station 2 and the unit U2. The circuits of the station 2 and of the unit U2 are in the form of chips whose connection tabs are welded to the microstrips of the plate 202. The locations on the map 202 of circuits 21 and 22 of the station 2, and the unit U2 are shown in dashed lines. A screen reflector R2 located on a rear face of the card 202 is connected to the ground reference of the terminal station 2. To be integrated in the smart card 202, the amplitude detector 22 shown in FIGS. 1, 3 and 4 is made in a more compact than that shown by way of example in Fig. 4.

p0033Referring to Fig. 1, the microwave PP transmitted by the antenna 20 of the terminal station 2 is received in the central station 1 by 2n = 4 units 12a to 12d of the antenna 12. The 2n = 4 units 12a, 12b, 12c and 12d deliver in response to receipt of the corresponding microwave PP microwave signals A, B, C and D respectively by the access vertically polarized V0A, V0B, Vπc Vπd and the antenna 12. the signals A to D are applied to first inputs of mixers 13a and 13d respectively. The signals A to D are phase-shifted in pairs of ± π / 2 or ± π modulo 2π. Second inputs of the mixers 13a to 13d receive signals from local oscillator OLa Old respectively. Local oscillator signals from OLa, OLB, OLC and OLd are issued respectively by the access to horizontal polarization H0A, Hπb, Hπc and H0d antenna 12 and are derived from the signal OL supplied to antenna patterns 12a to 12d by the local oscillator 10 through the amplitude modulator 11. the signals are phase shifted in Old OLa pairs of 0 or ± π modulo 2π. The signals A to D and OLa to OLd are expressed by the equalities: A U = cos (ωt + ψ + θ) B = U cos (ωt + ψ + θ 3 π / 2) C = U cos (ωt + ψ + θ + π), and D = U cos (πt + ψ + θ + π / 2), and OLa V = cos (ωt) OLB V = cos (ωt + π) OLC V = cos (ωt), and OLd V = cos (ωt + π) where U and V are respectively the magnitudes of the microwave A to B signals and local oscillator signals OLa Old, and where ω ψ and represent respectively the angular frequency corresponding to the frequency F of the LO signal and a random phase shift introduced by the radio transmission between the stations 1 and 2, and where θ = 0 or π represents the D21 data state signal of the function phase of the microwave PP modulated at two 0 and π phase states.

p0034The mixers 13a to 13d deliver as output respectively four signal demodulation low frequency SMa to SMd derivatives product signals A.OLa, B.OLb, C.OLc and D.OLd made by the mixers 13a to 13d. Signals SMa to SMd are provided to phase detector 14 so that the detector 14 recovers the data signal D21 from the signals SMa to SMd. The signals SMa to SMd are expressed by the equalities follows: SMa UV = cos (θ + ψ) SMB = UV cos (ψ + θ + π / 2) SMc UV = cos (ψ + θ + π) SMd UV = cos (ψ + θ 3 π / 2).

p0035The equations above show that the signals SMa to SMd depend according to trigonometrical functions sine or cosine of the phase state θ = 0 or π of the microwave PP and random phase shift ψ.

p0036The mixers 13a to 13d have structures and operations like. The mixer 13a is shown in detail in Fig. 7; it essentially comprises a field effect transistor (FET) 130a operating in nonlinear regime. A drain of the transistor 130a is connected to the access V0A pattern corresponding antenna 12a and to a first terminal of a coil 131a. A second terminal of the coil 131a is connected to ground through a decoupling capacitor 132a. A source of the transistor 130a is connected to the ground reference of the station unit 1 '. A gate of transistor 130a is connected to the access H0A pattern antenna 12a through a connecting capacitor 133a, and the first terminals a resistance 134a and a coil 135a. A second terminal of the resistor 134a is connected to ground. A second terminal of the coil 135a is connected to ground through a decoupling capacitor 136a.

p0037The signals A and OLa are applied respectively to the drain and the gate of transistor 130a. The gate of transistor 130a is biased by a negative bias voltage VP applied to the second terminal of the coil 135a. The signal SMa is produced at the second terminal of the coil 131a.

p0038Practical realization in microstrip technology of the mixer 13a, and mixer 13b to 13c, is shown in FIG. 2. microstrip 131a and 135a perform the same references coils 131a and 135a. The microstrip 133a capacitively couples the gate of the transistor 130a access H0A pattern antenna 12a and carries the ability to link same reference 133a.

p0039Referring to Fig. 8, the phase detector 14 comprises essentially amplifier input 140, two subtractors 141a to 141b analog, an analog multiplexer with four inputs 142, an exclusive OR gate having two inputs 143, two detectors module 144a and 144b, four comparators 145a to 145d, and a circuit control logic 146.

p0040The SMa and SMB signals are applied through the input amplificatuers 140 respectively to direct inputs + subtractors 141a and 141b. The signals SMc and SMd are applied through the amplifier input 140 respectively to inputs reversed - subtractors 141a and 141b. The subtractors 141a and 141b deliver output signals X and Y represent differences signals ADM, MSC and SMB-SMd and respectively expressed by the following equations: X = SMa-SMc UV = [cos (θ + ψ) - cos (θ + ψ + π)] = 2.UV cos (θ + ψ), and Y = SMB-SMd UV = [cos (θ + ψ + π / 2) - cos (θ + ψ 3 π / 2)] = 2.UVsin (ψ + θ)

p0041The signals X and Y are respectively supplied to first and third inputs of the multiplexer 143. signal -X and -Y represent differences SMc-SMa and SMd-SMB signals are produced from the X and Y signals by inverting amplifiers 147a and 147b and are provided to second and fourth inputs of the multiplexer 142 respectively. One of the signals S X, X, Y and-Y is chosen by means of a selection word MS provided by circuit control logic 146 and applied to input selection of multiplexer 142. The SELECT signal S is supplied to a + direct input of the comparator 145a whose inverse input is connected to the reference ground. The comparator 145a constitutes a sign detector delivering a logic state "0" when the sign of the signal S is positive and a logic state "1" in the opposite case. The comparator 145a outputs the data signal D21.

p0042The comparators 145b, 145c and the exclusive OR gate 143 have the function of generating a signal SIG (XY) representative of the sign of the product of the signals XY

p0043Direct input + of the comparators 145b and 145c respectively receive the signals X and Y inputs inverse - the comparators 145b and 145c are connected to the ground reference. The comparator 145b outputs a signal SIG (X) representative of the sign of the signal X. The comparator 145c outputs a signal SIG (Y) representative of the sign of the signal Y. The signal SIG (X) or SIG (Y) is in a logic state "0" when the sign of the signal corresponding X or Y is positive and a logic state "1" in the opposite case.

p0044Signals SIG (X) and SIG (Y) are respectively applied to first and second inputs of gate 143 and gate 143 outputs a signal SIG (XY) representative of the sign of the product of the signals XY signal SIG (XY ) is a logic state "0" when the sign of the product XY is positive and a logic state "1" in the opposite case where the sign of the product XY is negative. The signal SIG (XY) is applied to a first input of the control logic circuit 146.

p0045Detectors module 144a and 144b receive as input the signals X and Y, and output the modules [X] and [Y] of these signals, respectively. The 144a and 144b detectors are for example constituted by a double precision rectifier circuits alternations. Modules [X] and [Y] are respectively supplied to inputs direct and reverse + - of the comparator 145d. The comparator 145d outputs a signal SIG [X] - [Y]) representative of the sign of the difference modules [X] - [Y]. The [X] signal SIG - [Y]) is applied to a second input of the logic control circuit 146.

p0046The control logic circuit 146 sends a dynamic selection of the signal S from the signals X, -X, Y, -Y in order to allow a correct and optimum recovery of the data signal D21 and irrespective of random variations in phase due to the transmission radio and may introduce errors decision on the signal D21. From the signals SIG [X] - [Y] and SIG (XY) the circuit 146 detects the signals X and Y which has a higher modulus and sign changes of the signals X and Y due to random variations of the phase shift. The modulus of the SELECT signal [S] is set equal to the greater of modules [X] and [Y]. The sign S allocated to the SELECT signal depends on the detected sign changes of the X and Y signals from the signal SIG (XY).

p0047The diagram shown in Fig. 8 specifies the SELECT signal X = S, S = -X, Y = S or S = -Y in function module Information [X]> [Y] and [X] <[Y] and XY sign conditions> 0 and XY <0 detected from the signals SIG ([X] - [Y]) and SIG (XY) respectively.

p0048To demonstrate the proper interpretation to make this diagram, it is assumed for example an initial state during transmission where [X]> [Y] is the condition module detected; the signal S or X = S = -X is then SELECT. In case the condition [X] <[Y] is then detected if the signal S = X is the signal SELECT at the initial state then the new condition [X] <[Y] leads to the selection of the signal S = Y in the case where the sign condition XY> 0 is also detected, and causes the selection signal S = -Y where this is provided XY <0 is detected. If the signal S = X-is the signal SELECT to the initial state then the new condition [X] <[Y] leads to the selection signal S = Y-where the sign condition XY> 0 is also detected and causes the selection signal S = Y where ç'est condition XY <0 is detected. The skilled person easily interpret this diagram for an initial state during transmission where [X] <[Y] is the condition module detected.