EP1580834B1 - System and method of dynamic control of the band-width of an antenna, associated telephone - Google Patents

Description

GENERAL TECHNICAL FIELD

The present invention relates to a technique for dynamically controlling the width of the bandwidth of an antenna.

More specifically, it relates to the control of the bandwidth width of an antenna of a mobile phone.

STATE OF THE ART

Currently, antennas used in mobile phones suffer from miniaturization and the diversity of functions integrated in them. The space available for the antennas is reduced.

The direct consequence of reducing the available space for the antenna in a mobile phone is a decrease in antenna performance and bandwidth.

Faced with this problem, different strategies are currently being implemented by mobile phone manufacturers.

First, one can design a small mobile phone and be satisfied with poor phone performance.

For example, the losses of the antenna of a mobile for which the volume of the antenna is restricted are typically at the end of the GSM band ("Global System for Mobile Communications" or global system of mobile communications) of 2 dB, and losses at the end of the DCS band ("Digital Communication System") and PCS ("Personal Communications Services") between 1.7 dB and 3 dB. These losses are relatively large and the central resonant frequency of the antenna of a telephone is chosen so as to find a compromise between the transmission losses and the losses in reception.

Second, we can give up designing a mobile as small as the consumer wants to focus on the performance of the antenna.

It is clear that these first two strategies are not satisfactory.

Thirdly, we can develop complex switching systems either within the antenna or on its mass access in the case of antennas with mass feedback - such as patch antennas, "PIFA (Plane Inverted F Antenna)" etc.

An example of a known switching system within the antenna is shown schematically on the figure 1 .

Two switching elements, for example in the form of impedances L, are placed between two radiating surfaces 1 and 2 of an antenna of a mobile telephone. Depending on the frequency of use of the antenna, the impedances L connect or not the two radiating surfaces 1 and 2 and thus switch within the antenna. Other switching elements are of course known, and combine capacitors and / or diodes with inductances.

Such switching systems within the antenna, however, are not satisfactory.

Indeed, they are generators of losses, beyond the complexity introduced by the addition of components within the antenna. Due to the presence of a strong current on the periphery of the surface of the antenna, the quality factor Q of the components is essential. For example, for use in the GSM band, the gain of the switching system of the figure 1 is -3 dBiso for an impedance L equal to 10 nh and having a quality factor Q of 80, while the gain is -4 dBiso for an impedance L equal to 10 nh and having a quality factor Q of 50.

Known switching systems on ground returns, on patch antennas, for example, have the same disadvantages as the switching systems within the antenna. They introduce significant losses.

Complex systems for adapting the impedance of the antenna to its RX and TX transmission channels can also be developed. The principle of impedance switching is widely known for frequency tuning an antenna.

An example of a known impedance matching system is shown schematically on the figure 2 .

Such a system thus comprises a transmitting / receiving antenna 3 connected to a transmitter / receiver module 4 in which all the digital and radio elements of a telephone are present.

The module 4 thus comprises a reception channel output RX of a GSM band, an output of a GSM TX transmission line, and for example an output of a reception channel RX of a DCS band and an output of TX DCS transmission chain. Other bands can of course be provided in addition to the band or in replacement of the DCS band, such as a PCS band for example.

Switching means 41 controlled by control means 42 make it possible to switch between impedance matching circuits. Thus, an RX GSM impedance matching circuit 43 is connected between the switching means 41 and the output 47, a GSM TX impedance matching circuit 44 is connected between the switching means 41 and the output 48, an RX DCS impedance matching circuit 45 is connected between the switching means 41 and the output 49, and a TX DCS impedance matching circuit 46 is connected between the switching means 41 and the output 50. shows it figure 4 all these means are included in the transceiver module 4.

It is thus possible to globally adapt the antenna to the RX or TX channel of each GSM and DCS band for example.

Such a switching system however has many disadvantages.

Indeed, if one wants to be able to test the RF performance of the RF device in point 5, it is necessary that the output impedance of the module 4 is substantially equal to 50 Ω at this point.

However, with such a system, there is no point at 50 Ω that is common to all frequency bands. This lack of common point at 50 Ω poses the following problems.

It is difficult, if not impossible, to insert at the transceiver module 4 a connector for access to an external antenna.

It is difficult to define a single point of control in manufacturing and in revenue controls for operators receiving manufactured mobile phones. It is necessary to perform many calibrations for these checks.

It is difficult, if not impossible, for the manufacturers of complete transmitter / receiver modules comprising a baseband and a radio frequency band to manufacture standard modules independent of the application of the customers.

It is difficult, if not impossible, for manufacturers of front end modules comprising a power amplifier and a switching module to manufacture standard modules that are independent of the application of the customers.

It is difficult to adapt the transceiver module 4 from one mobile phone to the other. Module 4, in particular the front module, depends on the antenna 3 used.

In addition, the switching means 41 are generally characterized at 50 Ω as well, which also introduces losses in the gain of the antenna 3.

The documents JP-A-409331206 and US Patent 5923297 disclose systems and methods of the state of the art.

PRESENTATION OF THE INVENTION

The invention proposes to overcome at least one of the disadvantages of the prior art.

One of the aims of the invention is to propose a technique for controlling the bandwidth of an antenna which allows a reduction in the dimensions of the antenna while retaining acceptable performances in terms of efficiency and bandwidth.

One of the aims of the invention is to propose a technique for controlling the bandwidth of an antenna which makes it possible to adapt the impedances on the reception and transmission channels RX and TX when the characteristic of the antenna is too far from 50 Ω.

One of the aims of the invention is to propose a technique for controlling the bandwidth of an antenna which makes it possible to have a point at 50 Ω which is common to all the frequency bands.

In particular, one of the aims of the invention is to propose a technique for controlling the bandwidth of an antenna which makes it possible to insert a connector for an access to the standard transmitter / receiver module comprising a baseband and a radio frequency band. to an external antenna.

One of the aims of the invention is also to propose a technique for controlling the bandwidth of an antenna that makes it possible to define a single control point in the manufacture and during the recipe checks at the operators

It is also an object of the invention to provide an antenna bandwidth control technique which allows manufacturers of complete transmitter / receiver modules having a baseband and a radio frequency band to make independent standard modules. customer application and / or front end manufacturers including a power amplifier and a switch module to manufacture standard modules independent of the customer application.

One of the aims of the invention is to propose a bandwidth control technique that makes it possible to adapt a transmitter / receiver module comprising a baseband and a radio frequency band from one mobile telephone to the other.

For this purpose, the invention proposes a system according to claim 1.

Preferred embodiments are presented in the subclaims.

The invention also relates to a telephone and a method of implementing the system.

The invention particularly has the advantage of extending the bandwidth of the antenna of a mobile phone in multiband configuration.

PRESENTATION OF FIGURES

• la figure 1, déjà commentée, représente schématiquement un exemple d'un système connu de commutation au sein d'une antenne d'un téléphone mobile ;
• la figure 2, déjà commentée, représente schématiquement un exemple d'un système connu de commutation permettant une adaptation d'impédance ;
• la figure 3 montre un schéma de principe ;
• les figures 4A et 4B représentent schématiquement deux états d'un système de commutation d'impédance ;
• la figure 5 représente le diagramme des pertes de l'antenne en fonction des fréquences ;
• la figure 6 montre un premier exemple schématique possible d'un système de commutation ;
• les figures 7A à 7B montrent plusieurs choix possibles pour l'impédance Z d'adaptation ;
• la figure 8 montre schématiquement un exemple possible complet d'un commutateur comportant un système de commutation ; et
• la figure 9 montre une variante de la figure 8 dans laquelle l'impédance Z est variable et commandée par les moyens de commande.

Other features, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the appended drawings in which:

• the figure 1 , already commented, schematically represents an example of a known system of switching within an antenna of a mobile phone;
• the figure 2 , already commented, schematically represents an example of a known switching system for impedance matching;
• the figure 3 shows a schematic diagram;
• the Figures 4A and 4B schematically represent two states of an impedance switching system;
• the figure 5 represents the pattern of antenna losses as a function of frequencies;
• the figure 6 shows a first possible schematic example of a switching system;
• the Figures 7A to 7B show several possible choices for the adaptation impedance Z;
• the figure 8 schematically shows a complete possible example of a switch having a switching system; and
• the figure 9 shows a variant of the figure 8 wherein the impedance Z is variable and controlled by the control means.

Similar elements carry identical numerical references.

DETAILED DESCRIPTION OF THE INVENTION

The figure 3 shows a schematic diagram. The inventor has realized that by associating a relatively simple impedance switching system 6 directly in series with the attack point B of a multiband antenna 3 (in the driven domain) and at the output A of a transmitter / receiver module 4, it was possible to extend the bandwidth of the antenna 3.

The principle is simple and makes it possible to extend the bandwidth of a multiband antenna 3 from an antenna having characteristics of insufficient bandwidth for a given application.

The switching system 6 placed between points A and B makes it possible to switch between at least two band modes. Each band mode corresponds to a state corresponding to the series connection of an impedance between said antenna 3 and said module 4.

The first band mode is shown schematically at the Figure 4A . In this configuration, the impedance between the points A and B is zero and the frequency-dependent losses diagram is for example that in solid line on the figure 5 .

The second band mode is shown schematically at the Figure 4B . In this configuration, the impedance between points A and B is equal to an adaptation impedance Z and the frequency loss diagram is that in dashed lines on the figure 5 . The loss diagram is shifted in the frequency domain (frequency shifting phenomenon). It is thus possible to improve the performance of the antenna 3 as a function of the frequency of use.

The impedance Z varies as a function of the frequency of use of the antenna 3. Thus, the impedance Z is equal to a first value Z ₁ for the equal frequency value f ₁ and Z is a second value Z ₂ for the value of equal frequency f ₂ .

The figure 6 shows a first possible schematic example of a switching system 6.

The system 6 is thus mainly composed of an active switching element 61 that can be switched on or off between the module 4 and the antenna 3, the passive impedance Z being composed, for its part, of an inductor 62 mounted in a series of a capacitor 63, the inductor 62 and the capacitor 63 being connected in parallel with the active element 61 at the points A and B.

Advantageously, the active element is an active diode 61.

Preferably, the active diode 61 is of the PIN diode type (semiconductor configuration: P-layer - intrinsic layer - n-layer). Thus, in the off state, the diode 61 is equivalent to a capacitance of 0.2 pF in parallel with a resistance of 10 kΩ. It thus materializes an approximate infinite impedance. In the on state, the diode 61 is equivalent to a resistance of 0.3 Ω in series with an inductance of 0.4 nh. It thus materializes an approximate short circuit.

Of course, the active diode 61 may be replaced by any other device capable of switching between a short circuit and an open circuit for signals of the type considered.

In particular, the diode 61 may be replaced by a field effect transistor, or a miniature electromechanical switch in MEMS technology ("micro-electronic mechanical system").

Table 1 gives examples of digital applications for values of the impedance Z _A of the antenna 3 for a GSM band on the RX chain in the case of the figure 6 , the diode 61 being busy. It is recalled that the TOS is the Stationary Wave Rate of the antenna and characterizes the distance of the characteristic of the antenna from the ideal value of 50 Ω. The closer the TOS is to -∞, the better the antenna is. Table 1 Frequency f (MHz) Impedance Z _A TOS (dB) Losses (dB) 925 27 Ω + 2.3 nh -9.4 0.5 948 20 Ω + 6.5 nh -4.26 2 960 21 Ω + 8.8 nh -3.3 2.7

If we place, in the diagram of the figure 6 , a capacity 63 of 4.3 pF in series of the antenna 3, the 6.5 nh inductive element of the antenna 3 is compensated. To this end, the capacitor 63 is placed in series with the antenna 3 by putting the diode 61 in the off state and putting an inductance 62 of negligible value. We counteract the parasitic impedance of the antenna 3 and we obtain the results of Table 2. Table 2 Frequency f (MHz) Impedance Z _A TOS (dB) Losses (dB) 925 27 Ω + 6.7 pF -7.3 0.88 948 20 Ω -7.3 0.88 960 21 Ω + 2.2 nh -6.95 0.88

We will therefore work with a diode 61 in the on state for the frequencies around 925 MHz to obtain the good results of the first line of Table 1, and work with a diode in the off state around 948 MHz and 960 MHz to obtain the results of the last two rows of Table 2. There is thus a use of the antenna 3 which is optimized as a function of frequency.

The above developments apply to a single band. For the case of an antenna 3 having several resonant frequencies, the choice of Z is of course different from what is represented in FIG. figure 6 . It takes into account in particular the presence of the diode 61 and its equivalent electrical diagram.

The Figures 7A to 7E show several possible choices for Z, the choice being made according to the different bands.

The Figure 7A represents a capacitance in parallel with an inductance connected in series with a capacitance, the Figure 7B represents a series inductance with a capacitance, the Figure 7C represents an inductance connected in parallel with a capacitance, the mounting being in series with an inductor, the Figure 7D represents a series inductance with a capacitance and the figure 7E represents an inductance connected in parallel with a capacitance. Table 3 shows the equivalent electrical characteristics of each Z as a function of the usage band. Table 3 schemes Behavior of Z for the GSM band Behavior of Z for the DCS / PCS band Figure 7A C ₁ C ₂ Figure 7B L ₁ L ₂ (L ₁ <L ₂ ) Figure 7C L ₁ L ₂ (L ₁ > L ₂ ) Figure 7D C ₁ L ₂ Figure 7E L ₁ C ₂

It is thus sought that the impedance Z, as a function of the frequencies, is equivalent to a capacitance when the antenna 3 comprises a parasitic inductive element and that Z is equivalent to an inductance when the antenna 3 comprises a parasitic capacitive element. Z compensates as well always the parasitic behavior of the antenna 3 for a given frequency, so that the TOS and the losses are the lowest possible.

The width of the bandwidth of the antenna is thus dynamically controlled.

The figure 8 schematically shows a complete possible example of a switch having a switching system 6.

The system 6 is connected, as on the figures 3 and 6 for example, between the transmitter / receiver module 4 and the antenna 3. The connection between the system 6 and the module 4 is embodied by the point 5, which is the common point at 50 Ω of all the frequency bands. The connection between the system 6 and the antenna 3 is materialized as for it by the pole 8.

The telephone further comprises means 7 forming a central processor defining the switching strategy of the active element 61, preferably the active diode 61, in communication. The means 7 thus comprise memory means able to store a switching program of the active diode 61 and microprocessor means for implementing the program.

The switching strategy of the active diode 61 is thus predefined in the switching program and depends on the frequency and the communication cycle (transmission phase, reception or monitoring). The connection between the system 6 and the means 7 is effected by a pole referenced by 9.

The means 7 also control, through a link 68, means 41 for switching the different channels (RX, TX and monitoring) of the different GSM / DCS / PCS bands of the telephone. The means 41 for switching the different channels are similar to the means referenced 41 on the figure 1 . The control of the band switching means 41 is performed in synchronism with the control of the switching system 6 of the active diode 61.

The system 6 is also connected to the mass of the telephone thanks to the pole 10.

As previously, the impedance Z and the active diode 61 are connected in parallel with each other between the points A and B. The point A is connected to the point 5 and the point B is connected to the point 8.

A capacitor 66 is connected between the pole 10 and a terminal 67 internal to the system 6. A control resistor 65 is connected between the point 67 and the pole 9.

A choke inductor 64 is connected between point 67 and point A.

If according to the switching program, the diode 61 is still on TX and the diode is locked in RX, then the control voltage of the diode arriving at the pole 9 is 3 V for the on state and 0 V for the blocked state. There is indeed no harmonic generated.

On the other hand, the switching program can set that the active diode 61 can be locked in TX as well. In this case, there is a risk of creating harmonics. Therefore, the control voltage arriving at the pole 9 is this time 3 V for the on state and -20 / -30 V for the off state. This avoids the creation of harmonics.

The control signal may also be a control current.

The control signal arriving at the pole 9 thus controls the opening or closing of the diode 61 according to the frequency of use and the communication cycle (TX transmission, RX reception or monitoring). The command is thus dynamic.

The switching of the diode 61 from one state to another takes place during the phases of radio inactivity of the telephone, and in a very short time (of the order of a few tens of microseconds) according to the predefined strategy in the means 7.

With such a system, it is possible to obtain losses of the order of 0.1 dB only (because of the control inductance and the resistance of the diode), whereas switching systems within the antenna present at the same time. better losses of 1.2 dB.

The above developments apply to a phone with a single antenna. We can of course extend the invention to a telephone having more than one antenna. It is thus possible to provide another antenna dedicated to the UMTS ("Universal Mobile Telecommunication System" or Universal Mobile Communication System), for example in parallel with the already described antenna dedicated to GSM, DCS, PCS.

The foregoing developments also apply to active Z inductance.

The figure 9 shows a possible embodiment of a switch according to the invention. The device is similar to that of the figure 8 and items are not included for clarity. The difference in the embodiment of the figure 9 compared to the example of the figure 8 is that the impedance Z is variable. The value of the impedance Z is set by the control means 7 by means of a link 69. The means 7 thus control the value of the impedance Z at the same time as the state of the active diode 61 for optimized use of the the antenna.

The invention has the advantage of allowing dynamic control of the bandwidth of the antenna through a simple device.

Claims (7)

1. A system for controlling the width of the pass-band of an antenna (3) of a mobile telephone comprising a transmission/reception module (4) and an impedance switching system (6) comprising an active switching element (61) that is capable of switching between at least two switching states, wherein the switching system (6) is controlled by dynamic control means (7) comprising memory means that are capable of storing a program for switching the switching system (6) and means forming a microprocessor that allows for implementing the program, wherein a passing or blocked state of the active element (61) is controlled by the dynamic control means (7), wherein said active element (61) is mounted in parallel to an adapting impedance (Z), each switching state corresponding to the connection in series of an impedance between said antenna (3) and said module (4), wherein the active element (61) is an active diode and the adapting impedance (Z) is a variable impedance, a value of which is controlled by the dynamic control means (7).
2. The system according to claim 1, wherein the active element (61) is capable of switching between a first state, in which the antenna (3) is directly connected to the module (4), and a second state, in which the adapting impedance (Z) is connected in series between said antenna (3) and said module (4).
3. The system according to claim 1 or 2, wherein the switching system (6) comprises at least one pole for connecting to the ground of the telephone, a pole for connecting to the antenna (3), a pole for connecting to the transmission/reception module (4) and a pole for connecting to the dynamic control means (7) that is capable of receiving a control voltage or current.
4. The system according to one of claims 1 to 3, wherein the module (4) comprises multiband switching means (41).
5. The system according to claim 4, wherein the multiband switching means (41) are controlled by the dynamic switching means (7).
6. A mobile telephone comprising at least one antenna (3) and a transmission/reception module (4), wherein it comprises at least one control system according to one of claims 1 to 5.
7. A method for controlling the width of the pass-band of an antenna (3) of a mobile telephone comprising a transmission/reception module (4), comprising a step of dynamically controlling an impedance switching system (6) comprising an active switching element (61) by dynamic control means (7) comprising memory means that are capable of storing a program for switching the switching system (6) and means forming a microprocessor that allows for implementing the program, in order to switch said switching system (6) between at least two switching states, wherein a passing or blocked state of the active element (61) is controlled by the dynamic control means (7), wherein said active element (61) is mounted in parallel to an adapting impedance (Z), said method further comprising a step of controlling means (41) for multiband switching of the module (4) in synchronism with the switching system (6), each switching state corresponding to the connection in series of an impedance between said antenna (3) and said module (4), and a step of controlling, by the dynamic control means (7), a value of the adapting impedance (Z), which is a variable impedance.

Images