ITTO20070566A1 - FRONT-END ARCHITECTURE TO RADIOFREQUENCES FOR A POSITIONING AND METHOD RECEIVER TO RECEIVE A FIRST AND A SECOND BAND OF FREQUENCY OF A SATELLITE SIGNAL - Google Patents

Description

"RADIOFREQUENCY FRONT-END ARCHITECTURE FOR A POSITIONING RECEIVER AND METHOD FOR SIMULTANEOUSLY RECEIVING A FIRST AND A SECOND FREQUENCY BAND OF A SATELLITE SIGNAL"

SUMMARY

A front-end architecture (1,1 ') for simultaneously receiving a first and a second satellite signal of a satellite positioning system and a relative method is described, the architecture comprising: conversion means for converting a radio frequency signal into an intermediate frequency signal, in which the conversion means (3) comprise a fixed frequency local oscillator (31), and extraction means (23,28) for extracting the first and second satellite signals from the intermediate frequency signal, wherein the extraction means (23,28) are operable at a sampling frequency which is a function of an oscillation frequency generated by the local oscillator (31) and which is such as to allow the undersampling of the intermediate frequency signal.

DESCRIPTION

The present invention relates to the field of multiband satellite receivers.

More particularly, the present invention relates to a radio frequency front-end architecture for reconfigurable multi-band and multi-channel satellite receivers and a method for simultaneously receiving a first and a second frequency band of a satellite signal.

After having represented a valid tool in the military field, having become indispensable in the field of meteorological forecasting and Earth observation, having changed the world of research and that of communications, the satellite is about to become a strategic ally for mobility and security. daily.

In fact, increasingly complex satellite systems will allow, in the near future, to travel and move more quickly and safely.

Satellite positioning systems, however, are not a very recent invention; although originally born to satisfy only war and research needs such as the US satellite system Gps ("Global Positioning System") or the lesser known Russian satellite system Glonass ("Globalnaya Navigate ionnay a Sputnikova Sistema" or "Global Navigation Satellite System ") also used for rescue at sea.

A system conceived, on the other hand, mainly for civil use will be the European Galileo positioning satellite system.

The Galileo system has a greater availability of bands than the current GPS system. In fact, the GPS system transmits only the so-called LI band (at about 1.5 GHz) for civil applications and the so-called L2 band (at about 1.2 GHz) for military applications. However, the modernization of the GPS system provides for the creation of additional civil bands such as L5 and L2c. In Galileo there are currently four bands: E5a (1176.45 MHz), E5b (1207.14 MHz), E5 (1191.795 MHz), E6 (1278.75 MHz) and El-Ll (1575.42 MHz). Although some of the frequency bands of the Galileo system coincide with those of the GPS system, they are designed so as not to interfere with the signals of the GPS system.

To take full advantage of the additional signals introduced by the Galileo system and GPS, the future positioning receivers will have to operate in multiband mode.

However, each additional frequency band requires additional hardware inside the receiver, with a consequent increase in the cost of the receiver itself, a cost that proves unbearable especially when the receiver is intended for low-cost civil applications.

Also, since it is impractical to design a receiver capable of receiving all possible frequency bands, the receiver designer must also choose which frequency bands to let the receiver receive.

The problem therefore arises of designing a dynamically reconfigurable multiband receiver, at minimum cost and with the least possible circuit complexity.

Some solutions to this problem have been proposed.

For example, the United States patent application US 7,035,613 relates to a multiband receiver, capable of receiving simultaneously the signals L1 and L2 of a GPS system, or even just one of the two signals. The receiver comprises a fixed phase loop, or PLL, locking circuit and the related voltage controlled oscillator, or VCO, is configured to obtain a low power configuration with the frequency dividers for the second mixing stage. conventional and whole type. While, on the one hand, this circuit arrangement requires low power for the operation of the receiver, on the other hand, it does not make the circuit suitable for selecting signals other than L1 and L2 in a reconfigurable manner.

For example, the international patent application WO 2006/086118 describes a multiband positioning receiver capable of simultaneously receiving two satellite signals such as L1 / E2 and L2, L5 / L5a and L2, L1 / E2 and E5b, L5 / E5a and E5b . However, this type of receiver is not able to receive all the possible satellite signals of the positioning systems since, for example, due to the way its architecture is conceived, it is not able to obtain the E5 frequency band and therefore precludes the use. of types of modulations that require this band, such as the modulation called "Alt-BOC".

The purpose of the present invention is therefore to indicate a radiofrequency front-end architecture for a positioning receiver and a method for simultaneously receiving two frequency bands of a satellite positioning system, capable of receiving any pair of signals from a any satellite positioning system.

A further object of the present invention is to indicate a radio frequency front-end architecture for a positioning receiver and a method for simultaneously receiving two frequency bands of a satellite positioning system, which allow to realize a receiver of minimum circuit complexity. and therefore low cost.

A further object of the present invention is to indicate a radiofrequency front-end architecture for a positioning receiver and a method for simultaneously receiving two frequency bands of a satellite positioning system, which allow to realize a highly integrable receiver for mass production in consumer applications.

These and other objects of the invention are achieved with the method and the system as claimed in the attached claims which form an integral part of the present description.

The aforementioned purposes will become clearer from the detailed description of the method and system according to the invention, with particular reference to the attached Figures in which:

Figures 1 and 2 represent respectively a block diagram of a first and a second embodiment of a radio frequency front-end architecture according to the invention for a positioning receiver; - Figure 3 represents a frequency plan relating to the two types of embodiment of the radio frequency front-end architecture of Figures 1 and 2.

With reference to Figure 1, a block diagram of a first embodiment of a radio frequency front-end architecture 1 according to the invention is represented.

In said first embodiment, the front-end architecture 1 comprises a first circuit chain 2 for receiving a first radiofrequency signal, for example of the type L2, E6, E5a, E5b or E5, and a second circuit chain 4 for receiving the Ll / El signal.

This first embodiment foresees to always receive the signal Ll / El, which is a signal used for civil applications, and which can always be used to fast fix the position and be used by the other bands to make a fixing starting from a point already known. The choice of receiving Ll / El is advantageous since the other satellite signals have wider frequency bands than the Ll / El signal.

The first circuit chain 2 comprises the following components in cascade:

- a first antenna 5 for receiving a radio frequency signal;

- a first radio frequency filter 7, for example of the SAW ("surface acoustic wave") type, variable according to a first selected frequency band, for example L2, E5, E5a, E5b or E6;

- a first low noise amplifier 9 for amplifying the output signal from the first filter 7;

- a second radio frequency filter 11, for example of the SAW type, which varies according to the first frequency band selected, to reject the image signal;

- a first active mixer stage 13,15 comprising a first radio frequency gain amplifier 13 and a first mixer 15 which mixes the output signal from the first gain amplifier 13 with a signal generated by a local oscillator 31 at fixed frequency;

- a first signal amplifier 17 for amplifying the output signal from the first mixer 15;

- a first intermediate frequency filter 19 IFi, for example of the SAW type, variable according to the first frequency band selected and suitable for carrying out the channel selection;

- a first automatic gain control amplifier (AGC) 21 for amplifying the output signal from the first IFI intermediate frequency filter 19, and

- a first analog-to-digital converter 23 (ADC) with selectable sampling frequency and controlled by an integer frequency divider 40 of variable type.

The second circuit chain 4 comprises the following components in cascade:

- a second antenna 6 for receiving a radio frequency signal;

- a first fixed radio frequency filter 8, for example of the SAW type, for filtering a second selected frequency band, for example L1;

- a second low noise amplifier 10 for amplifying the output signal from the first filter 8;

- a second fixed radiofrequency filter 12, for example of the SAW type, to reject the image signal;

- a second active mixer stage 14, 16 comprising a second radio frequency gain amplifier 14 and a second mixer 16 which mixes the output signal from the second gain amplifier 14 with a signal generated by the local oscillator 31 at fixed frequency;

- a first filter 18 with fixed intermediate frequency IFI, for example of the SAW type, for filtering the output signal from the second mixer 16;

- a third mixer 20 which mixes the output signal from the first fixed intermediate frequency IFI filter 18 with a fixed frequency signal generated by the local oscillator 31 which is treated by a first fixed frequency divider 32;

- a second signal amplifier 22 for amplifying the output signal from the third mixer 20;

- a second filter 24 at fixed intermediate frequency IFi, for example of the SAW type, and adapted to carry out the selection of the channel;

- a second amplifier 26 with automatic gain control (AGC) for amplifying the output signal from the second fixed intermediate frequency filter 24, and

- a second analog-to-digital converter 28 (ADC) with selectable sampling frequency and controlled by a second fixed frequency divider 38.

The local oscillator 31 comprises a phase-locked loop circuit 36, or PLL, controlled by an oscillator 34, preferably of the compensated type and in particular a TCXO ("Temperature Controlled Xstall Oscillator"). The PLL 36 generates a control signal for a voltage controlled oscillator 30, or VCO.

The front-end architecture 1 is also connected to a demodulation block 42, in which the output signals from the first circuit chain 2 and from the second circuit chain 4 are processed to bring the demodulated signals into the baseband and process them appropriately to extract the information. useful from said signals.

The synchronization of the demodulation block 42 with the front-end architecture 1 is ensured by the fact that the demodulation block 42 provides an input SYS CLK which receives the signal generated by the compensated oscillator 34.

By means of the front-end architecture 1 it is possible to tune the desired frequency bands only by acting on the sampling frequency of the first analog-digital converter 23; this is possible by operating on the integer frequency divider 40. In this way, the signal supplied by the local oscillator 31 to the mixers 15, 16 is at a fixed frequency for all tunable frequency bands.

The different frequency bands obtainable on the first circuit chain 2 can be selected by varying the filters of the variable type 7, 11 and 19, which are preferably of the switchable LC type or, as previously mentioned, of the SAW type.

The choice of a front-end architecture 1, in which one circuit chain is dedicated to receiving only the LI signal and the other circuit chain is dedicated to receiving one of the other satellite signals, is also dictated by integration needs on the silicon in CMOS technology.

In fact, in CMOS technology, a low noise amplifier is not a broadband amplifier, as for example in SiGe or GaAs technology, but a low noise amplifier with a passband centered on the desired band and usually very narrow.

Therefore, the fact of using a circuit chain only for the signal L1 allows to integrate the low noise amplifier 10 and the subsequent components of the second circuit chain 4 (with the exception of the filters 8, 12 and 18 which are typically very selective in frequency of the Surface Acoustic Wave type and therefore cannot be integrated on silicon) in a chip, since the frequency band of the LI signal is known a priori.

Therefore, receiving L1 with a suitable circuit chain, the other signals to be received and converted at the bottom of the first circuit chain 2 have a frequency range very close to each other being included between 1176.45 MHz of the signal E5a and 1278.75 MHz of the signal E6. As mentioned before, a narrow frequency range is a necessary requirement for the design and integration of a low-noise amplifier in CMOS technology. Consequently, also the low noise amplifier 9 and the subsequent circuit components of the first circuit chain 2 (with the exception of filters 7 and 11 which are typically very frequency selective of the Surface Acoustic Wave type and therefore cannot be integrated on silicon) are integrable in said chip.

A pushed integration of the front-end architecture 1 is certainly advantageous for the production of low-cost and high-consumption satellite signal receivers which comprise said architecture 1.

With reference to Figure 2, a second embodiment of a front-end architecture 1 'according to the invention is represented in which a first circuit portion 3 of Figure 1 is replaced by a second circuit portion 3' of Figure 2, while all the other circuit components are unchanged with respect to Figure 1.

In said second embodiment, the front-end architecture 1 'comprises an initial portion in which the two satellite signals to be received simultaneously are filtered on a single circuit chain instead of two as in the case of Figure 1.

The second circuit portion 3 'of Figure 2 comprises:

- a third multiband antenna 51 for receiving radio frequency signals;

- a first broadband amplifier 53 for amplifying the signal received by the third antenna 51;

- a first bandpass filter 55 which filters the output signal from the first broadband amplifier 53 to extract two frequency bands RF1 and RF2; - an active mixer stage comprising a first buffer amplifier 57 and a second mixer 59 which is the mixer 16 of Figure 1;

- a second buffer amplifier 61 which divides the output signal from the second mixer 59 into two channels, of which a first channel is reconnected, by means of a further amplifier 63, to the first signal amplifier 17 of the first circuit chain 2 and a second channel it is reconnected to the third filter 18, through a further amplifier 65, of the second circuit chain 4.

With reference to Figure 3, a table is shown comprising a frequency plan used by the front-end architecture 1,1 'according to the invention.

In the columns of the table of Fig. 3 the following fields can be highlighted, from left to right:

- "Satellite": indicates the type of satellite, GPS or Galileo;

- "Band": indicates the frequency band of the satellite signal to be converted downwards, for example Ll / El, L2, E5, E5a, E5b or E6;

- "Carrier": indicates the carrier frequency, expressed in MHz, of the frequency band of the respective signal;

- "TXCO": indicates the fixed oscillation frequency, expressed in MHz, of the compensated oscillator 34;

- "MDd": indicates the fixed frequency, expressed in MHz, of the signal generated by the VCO 30;

- IF1 ": indicates the frequency of the output signal from mixers 15 and 16, expressed in MHz, obtained by subtracting the fixed frequency indicated in the" MDd "column from the carrier frequency;

- "Sample divider": indicates the integer number of the divisor 32 by which the fixed frequency, expressed in MHz, of the signal generated by the VCO 30 is divided;

- "MIX2": indicates the fixed frequency, expressed in MHz, resulting from dividing the frequency indicated in the "MDd" column with the whole number indicated in the "Sample Divisor" column;

- "IF2": indicates the fixed frequency, expressed in MHz, of the output signal from mixer 20 and corresponding to the difference between the frequency of the value in the "IF1" column and that of the "MIX2" field;

- "Freq. Sub-sampling": hereinafter also called Fs, it indicates a possible sub-sampling frequency at which the first analog-digital converter 23 or the second analog-digital converter 28 is operated to obtain one of the satellite signals L2 , E5, E5a, E5b, E6 or Ll / El;

- "BW": indicates the bandwidth of the satellite signal indicated in the second column;

- "Comments": indicates whether the signal is converted directly or through a two-stage conversion.

The table of Figure 3 highlights the fact that the analog-digital converter 23 is operated at a sampling frequency which is a function of the local oscillator 31 such as to allow the undersampling of the intermediate frequency signal.

The subsampling frequency is chosen in such a way as to satisfy two conditions:

a) IF1 - n <■> Fs> BW / 2, where n is an integer greater than 1, so that the replica of the sampled signal is placed in a positive half plane, and therefore does not generate an "aliasing" effect , that is, of superposition of spectra;

b) 0 <2 <■> (IF1 - n - Fs BW / 2) <Fs, in order to satisfy the Nyquist theorem according to which a signal, to be sampled, must have a band less than or at most equal to half of the sampling rate .

From the above description the characteristics of the present invention are therefore clear, as well as its advantages.

A first advantage is that the front-end architecture 1,1 'according to the present invention allows to simultaneously receive any combination of satellite signals from the GPS and Galileo systems.

A further advantage of the front-end architecture 1,1 'according to the present invention is that it is possible to receive both the E5 and E5a and E5b signals. One of the advantages of getting the E5 signal is that the E5 signal is used in the "Alt-BOC" modulation types.

A further advantage of the front-end architecture 1,1 'is that it is necessary to reconfigure a single radio frequency filter and a single intermediate frequency filter to tune the frequency band. In principle, a fully reconfigurable multiband receiver is possible simply by adding a chain of electronically interchangeable parallel filters centered on the frequencies of interest.

A further advantage of the front-end architecture 1 according to the invention is given by the fact that it is possible to integrate it pushed on chip in CMOS technology, so as to be able to produce positioning receivers at low cost and high consumption.

A further advantage of the front-end architecture 1,1 'according to the invention is that it is a superheterodyne architecture and therefore does not require image rejection mixers, thus allowing to process the signal at intermediate frequencies in the 'around 100 MHz: this allows for better signal processing than architectures that descend to very low intermediate frequencies.

A further advantage of the front-end architecture according to the invention is that the fact of dedicating a circuit chain to receive the L1 signal requires only one analog-to-digital converter with configurable sampling frequency for the other signals, the other analog converter digital being sampled in a fixed manner to receive the signal L1.

A further advantage of the front-end architecture according to the present invention is that it does not use fractional dividers to obtain the required frequency bands, thus reducing the spurious frequencies, and consequently the crosstalk.

There are numerous possible variants to the radiofrequency front-end architecture for a positioning receiver and to the method for simultaneously receiving a first and a second frequency band of a satellite signal described as an example, without departing from the novelty principles inherent in the inventive idea, just as it is clear that in its practical implementation the forms of the illustrated details may be different, and the same may be replaced with technically equivalent elements.

For example, instead of dedicating a circuit chain to receive the L1 signal and the other circuit chain to receive one of the other possible signals, it is possible to dedicate a circuit chain to receive one of the signals E2, E5, E5a, E5b or E6, and the other circuit chain to the remaining signals.

For example, the described front-end architecture can also receive other satellite signals that could be added in the near future to the Galileo satellite positioning system or other similar satellite positioning systems.

Therefore it is easy to understand that the present invention is not limited to a radio frequency front-end architecture for a positioning receiver and to a method for simultaneously receiving a first and a second frequency band of a satellite signal previously described, but it is passable of various modifications, improvements, replacements of parts and equivalent elements without however departing from the idea of the invention, as it is better specified in the following claims.

Claims (20)

CLAIMS 1. Front-end architecture (Ι, Ι ') to simultaneously receive a first and a second satellite signal of a positioning satellite system, said architecture comprising: - conversion means for converting a radiofrequency signal into an intermediate frequency signal, said conversion means (3) comprising a fixed frequency local oscillator (31); - extraction means (23,28) for extracting said first and said second satellite signals from said intermediate frequency signal, characterized in that said extraction means (23,28) are operable at a sampling frequency which is a function of an oscillation frequency generated by said local oscillator (31) and which is such as to allow the sub-sampling of said signal at intermediate. 2. Front-end architecture according to claim 1, characterized in that said extraction means (23,28) comprise a first (23) and a second (28) analog-digital converter to extract respectively said first and said second satellite signal , said first analog-to-digital converter (23) being operable by means of a variable-type integer frequency divider (40), and said second analog-digital converter (28) being operable by means of a fixed-type integer frequency divider (38). 3. Front-end architecture according to claim 1, characterized in that said local oscillator (31) comprises an oscillator (34), preferably of the compensated type (TXCO), a phase-locked loop circuit (36) and an oscillator voltage controlled (30). 4. Front-end architecture according to claim 1, characterized in that it comprises at least one variable type radio frequency filter (7,11; 55) and at least one variable type intermediate frequency filter (19) to select a frequency band of said first satellite signal. 5. Front-end architecture according to claim 4, characterized in that said at least one variable type radiofrequency filter (7,11; 55) and at least one variable type intermediate frequency filter (19) are LC filters. 6. Front-end architecture according to claim 4, characterized in that said at least one radio frequency filter (7,11; 55) of the variable type and at least one intermediate frequency filter (19) of the variable type are SAW filters. Front-end architecture according to claim 1, characterized in that said conversion means further comprise a first mixer (15,16) which mixes said radiofrequency signal with a fixed frequency signal supplied by said local oscillator (31). 8. Front-end architecture according to claim 7, characterized in that said conversion means comprise a second mixer (20) which mixes the output signal from said first mixer (15,16) with said fixed frequency signal supplied by said local oscillator (31) divided by an integer frequency divider (32) of the fixed type. Front-end architecture according to claim 7 or 8, characterized in that it further comprises a single antenna (51) and a broadband amplifier (53) for receiving said first and said second satellite signals. 10. Front-end architecture according to claim 7 or 8, characterized in that it comprises a first circuit chain (2) and a second circuit chain (4) for treating respectively a first radiofrequency signal and a second radiofrequency signal received respectively by a first (5) and a second antenna (6). Front-end architecture according to claim 10, characterized in that a first mixer (15) is arranged on said second circuit chain (4) and said radiofrequency signal is said second radiofrequency signal, and that a second mixer is provided (16) on said first circuit chain (2) which mixes said first radiofrequency signal with said fixed frequency signal supplied by said local oscillator (31). Front-end architecture according to one or more of the preceding claims, characterized in that a demodulation block (42) is provided downstream of said architecture, in which the signals called first and second satellite signals are processed to bring said signals into base band and suitably process them in order to extract useful information from said signals. 13. Front-end architecture according to one or more of the preceding claims, characterized in that said first satellite signal is one of the signals L2, E5, E5a, E5b, E6 and said second satellite signal is the L1 signal. 14. Front-end architecture according to one or more of the preceding claims, characterized in that it can be integrated into a single chip, preferably in CMOS technology. Receiver comprising a front-end architecture according to one of claims 1 to 14. 16. Method for simultaneously receiving a first and a second satellite signal of a satellite positioning system, said method including the steps of: - converting a radiofrequency signal into an intermediate frequency signal by means of conversion means, said conversion means comprising a local oscillator (31) with a fixed frequency; - extracting said first and said second satellite signals from said intermediate frequency signal by means of extraction means (23,28), said method being characterized by operating said extraction means (23,28) at a sampling frequency which is a function of said local oscillator (31) and which is such as to allow the undersampling of said intermediate frequency signal. Method according to claim 16, characterized in that said extraction means (23,28) are operated at a sampling frequency which is a fraction of the frequency of the signal generated by said local oscillator (31). 18. Method according to claim 16, characterized in that said first satellite signal can be selected from a plurality of tunable satellite signals by varying at least one radio frequency filter and an intermediate frequency filter. 19. Method according to claim 16, characterized in that said sampling frequency is chosen in such a way as to satisfy the Nyquist theorem and not to generate an "aliasing" effect. 20. Front-end architecture, receiver and method for simultaneously receiving a first and a second satellite signal of a positioning satellite system according to the innovative teachings of the present description and the annexed drawings which show examples of preferred and advantageous execution of said front architecture -end, receiver and method.