WO2002097983A1

WO2002097983A1 - Power varying circuit, radio transmitter, radio terminal and method for varying the power of signals

Info

Publication number: WO2002097983A1
Application number: PCT/EP2001/006170
Authority: WO
Inventors: Petri Nyberg
Original assignee: Nokia Inc
Current assignee: Nokia Inc
Priority date: 2001-05-31
Filing date: 2001-05-31
Publication date: 2002-12-05
Anticipated expiration: 2003-11-30

Abstract

The invention relates to a power varying circuit. In order to be able to provide an improved performance of such a circuit it is proposed that by employing a switch (10), a received signal can be forwarded either to a first signal path (11) amplifying signals passing through with a first amplification factor or to a second signal path (12) amplifying signals passing through with a second amplification factor. Coupling means (6) to which an output of said first signal path (11) and an output of said second signal path (12) are connected couple at least a portion of signal leaving said first signal path (11) to an output terminal RF_OUT and couple a portion of signals leaving said second signal path (12) to said output terminal RF_OUT. The invention equally relates to a radio transmitter, to a radio terminal and to a corresponding method.

Description

Power varying circuit, radio transmitter, radio terminal and method for varying the power of signals

FIELD OF THE INVENTION

The invention relates to a power varying circuit, to a radio transmitter and to a radio terminal. The invention equally relates to a method for detecting the power of signals.

BACKGROUND OF THE INVENTION

Power varying circuits for radio transmitters can be employed e.g. in radio terminals for controlling the output power of signals that are to be transmitted by the radio transmitter within a predetermined dynamic range.

The power range required for the output power of signals can be rather high for some applications, while the requirements for the accuracy of the output power level are increasing. There are some applications for radio terminals operating at microwave or at millimetre wave frequencies that require a dynamic range of more than 40 dB for the output power level. Such a wide dynamic range is on the one hand hard to realise at millimetre wave frequencies and on the other hand difficult to control. For illustration, figure 1 schematically shows a conventional radio transmitter including a power varying circuit. The depicted transmitter comprises an IQ (in-phase, quadrature) mixer 1, with two inputs for IQ-components of signals and another input connected to a local oscillator 2. The output of the IQ mixer 1 is connected via amplifying stages 3 to the input of a power varying circuit which is indicated in the picture with a rectangle of dashed lines. The output of the power varying circuit forms at the same time the output RF_OUT of the complete radio transmitter, which can be connected e.g. to an antenna via a duplex filter.

Between the input and the output of the power varying circuit, a voltage controlled variable attenuator 4 and power amplifiers 5 are arranged in a cascade connection. A directional coupler 6 associated to the connection between the power amplifiers 5 and the output of the power varying circuit, forms in addition a coupling link to the input of a detection diode 7. The output of the detection diode 7 in turn is connected to the input of an automatic level control circuit 8. Another input of the control circuit 8 is connected to a reference power value source 9, while the output of the control circuit 8 has a controlling access to the voltage controlled variable attenuator 4.

IQ-components of a signal that is to be transmitted by the radio transmitter of figure 1 are fed to the IQ mixer 1, in which the components are mixed and upconverted into a high- frequency signal having the frequency that is to be used for transmission according to the frequency provided by the local oscillator 2.

The high-frequency signal output by the IQ-mixer 1 is first amplified by the amplifying stages 3. The voltage controlled variable attenuator 4 then attenuates or amplifies the high- frequency signal according to a voltage currently applied to its control input. In a subsequent step, the signal output by the voltage controlled variable attenuator 4 is further amplified with a fixed factor by the power amplifiers 5. The high-frequency signal leaving the power amplifiers 5 is then fed to the antenna connected to the output RF_OUT of the radio transmitter for transmission as radio signal.

A portion of the high-frequency signal fed to the antenna is moreover coupled by the directional coupler 6 to the detector diode 7. More specifically, the coupler 6 provides a signal to the diode 7 which signal has a power that is reduced by the coupling factor of the coupler 6 compared to the power of the signal output by the power amplifiers 5 and fed to the transmission antenna. The detector diode 7 receives this portion of the high-frequency signal and outputs a voltage indicative of the power of the received signal and thereby, with the coupling factor known, indicative of the power of the transmitted signal.

The automatic level control circuit 8 can now compare the voltage output by the detector diode 7 with a value received from the reference power value source 9 as reference power value. This reference value represents the power that is presently desired as transmission power for the signals that are transmitted by the antenna. The coupling factor of the coupler 6 is either taken into account in the reference power value source 9 when producing the reference value or in the automatic level control circuit 8 in the comparison. In case there is a deviation between the measured power value and the reference power value, the automatic level control circuit 8 adjusts the attenuation factor applied by the voltage controlled variable attenuator 4 to the received high-frequency signals by changing the voltage applied to the control input of the voltage controlled variable attenuator 4.

In such a radio transmitter, the dynamic range of more than 40 dB required is hard to realise at millimetre wave frequencies for several reasons .

Since the linearity of voltage controlled variable attenuators realised with MMIC (monolithic microwave integrated circuit) technology is poor, they have to be arranged close to the IQ-mixer in the transmit chain. Such a placement, however, raises the noise floor of the output spectrum of the transmitter at low output power levels.

Moreover, typical PHEMT (pseudo-morphic high electron mobility transistor) MMIC processes have a low gain at 40 GHz. The nominal gain per amplifier stage is only 6.5 dB, while at the same time, there is a lot of gain variations in the order of +1.5 dB per stage due to process and temperature effects that cannot be compensated by biasing. If a total gain of e.g. 40 dB is needed in the transmitter after the IQ mixer in order to achieve the required maximum output power level, then at least 9 to 11 amplifier stages are needed when taking into account losses in voltage controlled variable attenuators, chip to package interfaces, etc. The total gain of the amplifiers can vary from 45 to 72 dB. This means, more than 25 dB extra dynamic range are needed just to cancel the tolerances of the gains of the amplifiers.

Voltage controlled variable attenuators with a dynamic range of more than 40 dB are moreover hard to realise in anyhow with MMICs due to limited isolation. Also the minimum loss of high dynamic range voltage controlled variable attenuators is in the order of 3 dB and therewith relatively high.

Voltage controlled variable attenuators could be substituted by step attenuators, which are digitally controlled and have typically a better linearity than voltage variable attenuators. High linearity step attenuators could even be arranged after the power amplifiers in order to reduce the noise floor of the output spectrum. But at this position, the minimum losses of step attenuators, which are in the order of 2 to 5 dB, would cause a significant power loss. The power amplifier should be made bigger thus causing increased DC-power consumption and possibly thermal problems . Finally, experience shows that the dynamic range of a detector circuit is limited to about 30 dB, when a detector diode is employed which is integrated into the chip with the power amplifiers and using signal conditioning circuitry. Therefore also an exact control of a wide dynamic range of e.g. 40 dB is difficult.

The US patent 5,530,923 describes a dual mode transmitter circuit with an architecture similar to the architecture of the transmitter of figure 1. More specifically, a signal that is to be transmitted passes through a controllable amplifier and a power amplifier. The control amplifier is controlled by control means receiving an indication of the power of the presently transmitted signals via a coupler. In this document, it is moreover proposed to arrange a bypass signal path in parallel to the power amplifiers and to provide switches at the input and at the output of the power amplifiers and the bypass signal path. The switches are controlled by a mode control unit in a way that digital signals pass through the power amplifier, while analogue signals bypass the power amplifier. Behind the second switch, signals are fed to an antenna and coupled out as described with reference to figure 1.

When employing such a transmitter for transmitting signals with a wide dynamic power range, some of the mentioned problems can be avoided. In the circuit proposed in the document, however, a detector employed for detecting the respective power of transmitted signals would still have to operate in a large dynamic range, if the output power of the signals varies within a wide range. Moreover, each switch employed increases the loss in signal strength.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a power varying circuit, a radio transmitter, a radio terminal and a method for varying the power of signals with an improved performance .

This object is reached according to the invention with a power varying circuit comprising a first signal path amplifying signals passing through with a first amplification factor, and a second signal path amplifying signals passing through with a second amplification factor. The power varying circuit of the invention further comprises a switch for forwarding signals input to said power varying circuit to an input of either said first or said second signal path. Moreover, it comprises coupling means to which an output of said first signal path and an output of said second signal path are connected, said coupling means coupling at least a portion of signals leaving said first signal path to an output terminal and coupling a portion of signals leaving said second signal path to said output terminal .

The object is equally reached with a radio transmitter comprising such a power varying circuit and with a radio terminal comprising a radio transmitter with such a power varying circuit . Finally, the object is reached according to the invention with a method for varying the power of signals. In a first step of this method, signals are received by a power varying circuit. The received signals are then forwarded to a first signal path or to a second signal path of said power varying circuit, wherein said first signal path amplifies signals passing through with a first amplification factor and wherein said second signal path amplifies signals passing through with a second amplification factor. At least a portion of the signals leaving the first signal path are then coupled to an output terminal. A portion of the signals leaving the second signal path are equally coupled to said output terminal .

The invention proceeds from the idea that a power varying circuit topology can be designed to include different ways of providing signals to an output terminal . To this end, two different signal paths are included in the power varying circuit, which provide a different amplification or attenuation. A switch can forward signals that are to be transmitted to a selected one of these signal paths. The different ways of providing the signal power to the output terminal are realised by the coupling means, which feed at least a portion of the signals leaving the first signal path to the output terminal and which feed a portion of the signals leaving the second signal path to the output terminal. The size of the portion can be selected by providing a suitable coupling factor of the coupling means. The signals leaving the first signal path are preferably fed essentially entirely to the output terminal .

The power varying circuit has the advantage that a low noise floor can be achieved also at low output power levels. At the same time, no components resulting in extra losses after the power amplifier are introduced, like the second switch proposed in the above mentioned US patent.

The solution of the invention therefore improves the performance of the power varying circuit and reduces its costs .

Preferred embodiments of the invention become apparent from the subclaims .

In a first preferred embodiment of the power varying circuit, the power varying circuit moreover comprises power detecting means. The coupling means, which are e.g. a directional coupler, then couple a portion of signals leaving the first signal path and at least a portion of signals leaving the second signal path to the power detecting means. The signals leaving the two signal paths are thus provided to the power detecting means just in an opposite way as to the output terminal. I.e., the coupling means feed at least a portion of the signals leaving the second signal path to the power detecting means, preferably essentially the entire signals, and feed a portion of the signals leaving the first signal path to the power detecting means. The power detecting means then detect the power of received signals. The detected power corresponds to the power of the signals currently coupled to the output terminal, when the respective coupling factor is taken into account. The features of this embodiment can equally be applied to the radio transmitter, the radio terminal and the method of the invention.

The main advantage of this preferred embodiment is that it allows a good power detection accuracy over the whole dynamic range with power detecting means having a range considerably below the power range of the transmitted signals. To this end, signals that are to be transmitted with a high power are simply fed to the first signal path and signals that are to be transmitted with a low power are fed to the second signal path.

The power detecting means can be a normal on-chip or off- chip detector diode, which may also be integrated in or connected to a chopper power detection circuit.

In a further preferred embodiment, the second signal path does not include any components but simply serves for bypassing the at least one power amplifier in the first signal path. In this case, the amplification factor applied by the second signal path to signals passing through is essentially equal to one. It is possible, however, to include in this signal path any desired components, including amplifiers or attenuators. It only has to be ensured that the total amplification applied to signals passing through the second signal path is below the total amplification applied to signals passing through the first signal path.

In an equally preferred embodiment, the power varying circuit includes an adjustable gain device arranged between the input of the power varying circuit and the switch used for forwarding signals either to the first or the second signal path. The gain device is used for applying a variable gain to signals input to said power varying circuit before forwarding said signals to said switch. The gain device can be for example an adjustable attenuator, but also an adjustable amplifier.

Moreover, control means, in particular in form of an automatic level control circuit, can be provided as part of the power varying circuit. An output of the control means is thus connected to an adjustment input of said adjustable gain device .

The control means control the adjustable gain device based on the detected output power level of the power varying device and/or a control (CTRL) input information. The control input information can be any suitable kind of information. It can be for example an analogue voltage signal in proportion to the wanted output power level or a digital signal or a mixture of analogue and digital control signals. The control input information can moreover indicate e.g. a desired output power level or a desired change of the output power level . The latter kind of control input information can also come from a receiving radio end, like a base station.

The control means evaluates the information received at its input or inputs and adjusts the gain applied to signals by the gain device accordingly via its output .

Advantageously, at least one input of such control means is connected to power detection means providing information indicative of the power level at the output terminal. In this case, the control means can e.g. compare the current power with a reference power and adjust the gain in a way that the current power approaches the reference power.

In a further preferred embodiment, the power varying circuit comprises selection means . The selection means can be realised similar to the control means. That is, the selection means advantageously receive as input a detected output power level of the power varying circuit and/or a control (CTRL) input information. An output of such selection means is connected to a control input of the switch of the power varying circuit. This enables the selection means to cause the switch to forward received signals to the first signal path for a high power mode and to the second signal path for a low power mode.

The mode is selected in the selection means based on information received. This information can indicate in particular the current power of signals output by the power varying circuit. The high power mode can then be selected whenever the current power of the transmitted signals exceed a predetermined power level, and the low power mode can be selected whenever the current power of the transmitted signals is below the predetermined power level.

Advantageously, an output power level information is provided to the selection means by power detection means connected to an output of the coupling means for detecting the power of signals leaving said first signal path or said second signal path via said coupling means.

Preferably, the control means and the selection means are realised by a single unit. Moreover, the detecting means may be integrated in the control means, the selection means or the combined control and selection means.

In time division multiplex systems (TDD) , the state of the gain device and the switch most likely have to be freezed during the transmit burst, the settings of gain device and switch being done before or after the transmit burst. Therefore, also a control input information indicating that the state of the switch and gain device settings has to be freezed should be available to be input to the control means and/or selection means . When this information is fed to the control means and/or the selection means, a power information received by the control means and/or selection means is not able to change the current settings.

Preferably, the at least one power amplifier in the first signal path is switched off, whenever signals are forwarded to the second signal path. This way, a low DC power consumption is achieved at low output power levels, which also improves the reliability of the power control.

In a preferred embodiment of the invention, a part or the entire topology of the power varying circuit is integrated into a single MMIC chip.

The discontinuity in the power control according to the invention will usually not be critical. In a PMP radio terminal, for example, a wide range will only be needed during installation. After installation, the output power level should be at least less than 20 dBm. Moreover, the operating mode of PMP terminals is FDMA/TDD (frequency division multiple access / time division duplex) . Therefore, the output power mode can be switched between transmission bursts so that the switching will have no effect on the accuracy of the output power.

The invention is particularly suited for an employment with PMP radio terminals. It can be used, however, with any application transmitting radio signals with varying powers.

BRIEF DESCRIPTION OF THE FIGURES

In the following, the invention is explained in more detail with reference to drawings, of which

Fig. 1 shows a conventional radio transmitter; and Fig. 2 shows an embodiment of a power varying circuit for a radio transmitter according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 has already been described with reference to the background of the invention.

Figure 2 shows an embodiment of a power varying circuit according to the invention. The power varying circuit forms e.g. part of a radio transmitter of a PMP radio terminal and is used for adjusting the output power of radio frequency signals that are to be transmitted by the radio terminal.

The power varying circuit comprises a voltage controlled variable attenuator 4, the input of which constitutes the input RF_IN of the power varying circuit. The output of the voltage controlled variable attenuator 4 is connected via a switch 10 either to a first signal path 11 or to a second signal path 12. The branches of the switch 10 to the signal paths 11, 12 should be of a non-reflective type. The first signal path 11 includes power amplifiers 5 with a total gain of 12 dB. The second signal path 12 does not include any components .

The output of the first signal path 11 and of the second signal path 12 respectively are connected to different inputs of a directional coupler 6 with a coupling factor of 12 dB. A first output of the coupler 6 is connected to an output terminal RF_OUT. This output terminal RF_OUT is connected to an antenna of the radio terminal, which is not included in the figure. Possibly, the output terminal RF_0UT is connected to the antenna via a duplex filter enabling a common use of the antenna for reception and transmission of signals .

A second output of the coupler 6 is connected to detecting means 7. These detecting means 7 include a chopper power detection circuit connected to a power detection diode with a dynamic range of 30 dB. In the figure, the detecting means 7 are represented by the detection diode.

The output of the detecting means 7 are connected to the input of an automatic level control circuit 8. A further input is connected to a reference power value source not shown in figure 2. A first output of the automatic level control circuit 8 is connected to a control input of the switch 10 and a second output is connected to a control input of the voltage controlled variable attenuator 4.

The power varying circuit of figure 2 functions as follows:

High-frequency signals that are to be transmitted by the radio terminal are input via the input RF_IN of the power varying circuit to the voltage controlled variable attenuator 4. These high-frequency signals are formed in the radio transmitter as described with reference to figure 1 by an IQ mixer 1 and amplifying stages 3. The voltage controlled variable attenuator 4 amplifies or attenuates the received high-frequency signals according to a voltage applied presently to its control input. The high-frequency signals are then forwarded by the switch 10 to either the first or the second signal path 11, 12, depending on the current state of the switch 10, which in turn depends on a signal applied to the control input of the switch 10. In the situation presented in figure 2, the switch 10 is connecting the variable attenuator 4 to the second signal path 12, therefore received radio signals are currently forwarded to this second signal path 12.

Signals forwarded to the first signal path 11 are amplified by the power amplifiers 5 in this first signal path 11. The thus amplified high-frequency signals are then forwarded via the directional coupler 6 to the output terminal for transmission. In addition, the directional coupler 6 provides signals of a power of 12 dB less then the power of the signals leaving the first signal path 12 to the detecting means 7. In case the coupler 6 works essentially lossless, the signals forwarded from the first signal path 11 to the output terminal of the power varying circuit are barely influenced by the coupler 6.

Signals forwarded to the second signal path 12 are provided directly via the directional coupler 6 to the detecting means 7. Additionally, the directional coupler 6 provides signals of a power of 12 dB less then the power of the signals leaving the second signal path 12 to the output terminal of the power varying circuit. Again, in case the coupler 6 works essentially lossless, the signals forwarded from the second signal path 12 to the detecting means 7 circuit are barely influenced by the coupler 6.

The power amplifiers 5 in the first signal path 11 are switched off whenever the received high-frequency signals are being forwarded to the second signal path 12, in order to save DC power. They are moreover balanced in order to maintain good return losses for the directional coupler 6 in both positions of the switch 10.

In the detecting means 7, the signals received from either the first or the second signal path 11, 12 are passed on via the chopper power detection circuit to the detecting diode. The detecting diode transforms the power of received signals into a voltage indicative of this power. However, since the basic voltage varies depending on the tolerances of the diode and on changes in temperature, the chopper power detection circuit is used for switching the provision of signals to the detector diode on and off. Thereby, the diode is able to provide always a relative voltage, i.e. the difference between the voltage resulting at present when no radio frequency signal is applied to the diode and the voltage resulting when the power of the current signal is applied to the diode. Such a relative voltage is much more accurate than an absolute voitage, since it is essentially independent of component tolerances and changes in temperature . The voltage output by the detecting means 7 is provided to the input of the automatic level control circuit 8. Here, the voltage is compared to a reference voltage, the used reference voltage taking into account the present state of the switch 10 and the coupling factor of the directional coupler 6. In case there is a deviation in either direction, the first output of the automatic level control circuit 8 is used for outputting a voltage which is provided to the control input of the voltage controlled variable attenuator 4 for adjusting the attenuation applied to incoming radio frequency signals accordingly. More specifically, the attenuation applied by the voltage controlled variable attenuator 4 is reduced when the measured power is below a reference power, and increased when the measured power is above a reference power, the respective powers being represented by respective voltages.

In addition, the automatic level control circuit 8 decides whether currently low power signals or high power signals are being transmitted. Whenever high power signals are transmitted, the second output of the automatic level control 8 is set to a value that switches the switch 10 from the second signal path 12 to the first signal path 11 or that keeps the switch 10 in this state. Whenever low power signals are transmitted, the second output of the automatic level control 8 is set to a value that switches the switch 10 from the first signal path 11 to the second signal path 12 or that keeps the switch 10 in this state. Therefore, the power varying circuit of figure 2 divides the dynamic range of the output power of signals into a high power range and a low power range. For the high power range, the transmitted signals are fed to the first signal path 11 and only a small portion of the signals is coupled to the detecting means 7. For the low power range, in contrast, the power amplifiers 5 in the first signal path 11 are bypassed by forwarding received radio signals to the second signal path 12, and basically the entire power of signals leaving the second signal path 12 is fed to the detecting means 7, while only a small portion of the signals is coupled to the radio frequency output terminal for transmission.

In this embodiment of a power varying circuit, the dynamic range of about 30 dB of the detector diode in the detecting means 7 suffices for detecting the power of signal with a dynamic range of output power of more than 40 dB. This means that a wide range of output power of transmitted signals can be detected accurately with detecting means of a considerably lower dynamic range.

Claims

C l a i m s

1. Power varying circuit comprising: a first signal path (11) amplifying signals passing through with a first amplification factor; a second signal path (12) amplifying signals passing through with a second amplification factor; a switch (10) for forwarding signals (RF_IN) input to said* power varying circuit to an input of either said first or said second signal path (11,12); and coupling means (6) to which an output of said first signal path (11) and an output of said second signal path (12) are connected, said coupling means (6) coupling at least a portion of signals leaving said first signal path (11) to an output terminal (RF_0UT) and coupling a portion of signals leaving said second signal path (12) to said output terminal (RF_OUT) .

2. Power varying circuit according to claim 1 further comprising power detecting means (7) , wherein said coupling means (6) couple a portion of signals leaving said first signal path (11) to said power detecting means (7) , and wherein said coupling means (6) further couple at least a portion of signals leaving said second signal path (12) to said power detecting means (7) , said power detecting means (7) detecting the power of signals received via said coupling means (6) .

3. Power varying circuit according to claim 1 or 2 , wherein the second amplification factor is essentially equal to one.

4. Power varying circuit according to one of the preceding claims, further comprising an adjustable gain device (4) arranged between the input of the power varying circuit and said switch (10) for applying a variable gain to signals input to said power varying circuit before forwarding said signals to said switch (10) , the adjustable gain device (4) being adjusted by a control signal .

5. Power varying circuit according to claim 4, further comprising control means (8) , an input of said control means (8) being connected to power detection means (7) providing information indicative of the power level at said output terminal (RF_0UT) , and an output of said control means (8) being connected to a control input of said adjustable gain device (4) , said control means (8) being designed for adjusting the gain applied by said adjustable gain device (4) via said control input of said adjustable gain device (4) based on information received at the input of said control means (8) .

6. Power varying circuit according to claim 5, wherein said power detecting means (7) are connected to an output of said coupling means (6) for detecting the power of signals received from said first signal path (11) or from said second signal path (12) via said coupling means (6) , said control means (8) being designed for adjusting the gain applied by said adjustable gain device (4) based on the power of signals leaving one of said signal paths (11,12) detected by said power detecting means (7) compared to a power level setting control signal (9) .

Power varying circuit according to one of the preceding claims, further comprising selection means (8) , an output of said selection means (8) being connected to a control input of said switch (10) , and an input of said selection means (8) being connected to means (7) providing information indicative of the signal path (11,12) to which the switch is to forward signals currently received by the power varying circuit, said selection means (8) switching said switch (10) via said control input of said switch (10) to forwarding received signals to said first signal path (11) or to said second signal path (12) , based on information received via said input of said control means (8) .

Power varying circuit according to claim 7, wherein the input of said selection means (8) is connected to the output of power detecting means (7) connected to an output of said coupling means (6) for detecting the power of signals leaving said first signal path (11) or said second signal path (12) via said coupling means (6) , said selection means (8) switching the switch (10) to forwarding signals by the power varying circuit to the first signal path (11) in case the power of signals detected by said power detecting means (7) is above a predetermined power level and for switching the switch (10) to forwarding received signals to the second signal path (12) in case the power of signals detected by the power detecting means (7) is below a predetermined level .

9. Power varying circuit according to one of the preceding claims, wherein at least two of the first signal path (11) , the second signal path (12) , the switch (10) , the coupling means (6) and power detecting means (7) are integrated into a single chip.

10. Power varying circuit according to one of the preceding claims, wherein said coupling means (6) are a directional coupler.

11. Radio transmitter comprising a power varying circuit according to one of the preceding claims .

12. Radio terminal comprising a radio transmitter with a power varying circuit according to one of claims 1 to 10.

13. Method for varying the power of signals comprising: receiving signals by a power varying circuit; forwarding said received signals to a first signal path (11) or to a second signal path (12) of said power varying circuit, wherein said first signal path (11) amplifies signals passing through with a first amplification factor and wherein said second signal path (12) amplifies signals passing through with a second amplification factor; coupling at least a portion of signals leaving said first signal path (11) to an output terminal

(RF_OUT) ; and coupling a portion of signals leaving said second signal path (12) to said output terminal (RF_OUT) .

14. Method according to claim 13, further comprising coupling a portion of signals leaving said first signal path (11) to power detecting means (7) and coupling at least a portion of signals leaving said second signal path (12) to said power detecting means (7) , said power detecting means (7) detecting the power of the signals coupled to said power detecting means (7) .

15. Method according to claim 13 or 14, wherein said second signal path has an amplifying factor of essentially one.

16. Method according to one of claims 13 to 15, wherein received signals are forwarded to said first signal path (11) , in case the power of the signals coupled to said output terminal (RF_0UT) lies above a predetermined power value and forwarded to said second signal path (12) , in case the power of signals coupled to said output terminal (RF_0UT) lies below a predetermined power value.

17. Method according to one of claims 13 to 16, further comprising applying a variable gain to the received signals by an adjustable gain device (4) before forwarding them to either said first signal path (11) or said second signal path (12) , the adjustable gain device (4) being adjusted by a control signal.

18. Method according to claim 17, wherein the gain device is adjusted by a control signal which is determined based on the power of signals coupled to said output terminal (RF_OUT) compared to a power level setting control signal (9)

19. Method according to one of claims 13 to 18, wherein said signals coupled to said output terminal (RF_OUT) are transmitted by an antenna.

20. Method according to one of claims 13 to 18, wherein said coupling is done by a directional coupler.