WO1995015618A1

WO1995015618A1 - Bridging amplifier arrangement for a group of receivers

Info

Publication number: WO1995015618A1
Application number: PCT/FI1994/000545
Authority: WO
Inventors: Tapani KÄRKI
Original assignee: Nokia Telecommunications Oy
Priority date: 1993-12-01
Filing date: 1994-12-01
Publication date: 1995-06-08
Also published as: FI97178B; FI97178C; AU1110995A; FI935382A0; FI935382A

Abstract

The object of the present invention is a bridging amplifier arrangement for a group of receivers comprising an antenna means (10), a matching means (3) for connecting the antenna means to an amplifier means (4), and means (8) for feeding signals obtained from the output of the amplifier means into a receiver unit belonging to the group of receivers. To provide an arrangement with which optimum sensitivity is achieved during the normal traffic operation without that the accuracy of the antenna measurements is impaired, the arrangement comprises a control unit (9) arranged to change the state of the matching means (3) between two alternative input matching states. During the normal traffic operation of the receivers, the control unit (9) sets the matching means (3) to a state where the input match of the antenna means (10) is a noise match, and for the duration of the testing of the antenna means (10), the control unit (9) sets the matching means (3) to a state where the input match of the antenna means (10) is a complex conjugate match.

Description

Bridging amplifier arrangement for a group of receivers

The object of the invention is a bridging amp¬ lifier arrangement for a group of receivers comprising an antenna means, a matching means for connecting the antenna means to an amplifier means, and means for feed¬ ing signals obtained from the output of the amplifier means into a receiver unit belonging to the group of receivers. In particular, the invention relates to a base station of a cellular radio system comprising one common antenna by which a receiver or receivers of the base station receive signals transmitted by active radio transmitters located within the coverage area of the base station. The signals received by the antenna are fed into different receivers through a bridging ampli¬ fier of the base station.

Here input matching means that the impedance of the antenna and the impedance of a pre-amplifier are matched to each other to create optimum conditions for feeding signals into either direction, whereby the losses of power are minimized. Two contradictory requirements are set for input matching of a bridging amplifier at a base station. For antenna measurements carried out as the operation of the base station is tested, the input match must be a 'gain match', i.e. a complex conjugate match with respect to the pre¬ amplifier. During the normal traffic operation, on the other hand, a first stage input match should be a 'noise match' to optimize the noise figure (sensitivity) of the receiver. Noise matching and complex conjugate matching are described in greater detail e.g. in Microwave transistor amplifiers by Gozales Guillermo, Prentice- Hall, Inc., New Jersey, USA, 1984, ISBN: 0-13-581646-7. In one known solution, the above requirements have been observed by compromising on the requirements. This solution, however, leads to uncertain - sometimes even erroneous - antenna measurements. During the normal traffic operation at the base station, on the other hand, the compromise leads to a situation where a noise match is not optimal, which impairs the sensitivity of the receiver.

In another known solution, the signal path of a bridging amplifier is divided into two parallel branches at the input, transistor amplifier stages being arranged in both branches. The attenuation (3 to 4 dB) caused by the branching unit thus improves the match visible to the input connector in antenna measurement, although it has been possible to implement some kind of noise match at the inputs of parallel pre-amplifiers. The drawback of this known solution is that the noise figure of the amplifiers connected in parallel is even in theory about 1.5 dB worse than that of one such amplifier. This is due to the fact that the payload signal is attenuated at the input branching unit by at least 3 dB but the noise is not attenuated, the back¬ ground noise being on a level of 174 dBm/Hz even after the branching unit. In addition, the noise signals generated at the inputs of the parallel amplifiers sum up at least to some extent, which impairs the sensitivity of the chain of receivers by about 1 to 1.5 dB.

The object of the present invention is to elim- inate the above problems, and to provide a bridging amplifier arrangement with which an optimum noise figure (sensitivity) for a pre-amplifier is achieved during the normal traffic operation at the base station and by which optimum accuracy of the antenna measurement carried out as the operation of the base station is tested can be maintained. These objectives are achieved with the bridging amplifier arrangement of the inven¬ tion, the arrangement being characterized in that it comprises a control unit arranged to change the state of the matching means between two alternative input matching states; that during the normal traffic opera¬ tion of the receivers the control unit sets the matching means to a state where the input match of the antenna means is a noise match; and that for the duration of the testing of the antenna means, the control unit sets the matching means to a state where the input match of the antenna means is a complex conjugate match.

The basic idea of the invention is that the input matching circuit of the bridging amplifier is rendered modifiable so that for the duration of the antenna measurement the input matching circuit is set to a state where the input matching circuit is optimal in respect of antenna measurements, i.e. to a state where complex conjugate matching is realized. During the traffic operation, on the other hand, the input matching circuit is set to a state where it is optimal with respect to noise (sensitivity). Thus the major advantage of the arrangement according to the invention is that no compromise is needed on the requirements set for input matching of the bridging amplifier, since the state of the input matching circuit can be changed by the control unit contained in the arrangement to achieve the optimum characteristics needed.

One advantageous embodiment of the arrangement according to the invention is characterized in that the group of receivers is part of a base station of a cellu¬ lar radio system, advantageously of a GSM system.

In the following the invention will be de¬ scribed in greater detail by means of a first advantage- ous embodiment with reference to the attached figure showing a block diagram of one advantageous embodiment of the bridging amplifier arrangement according to the invention.

The bridging amplifier arrangement shown in the figure can be e.g. a bridging amplifier arrangement of a base station of the GSM system. The structure and operation of the GSM system are described e.g. in The GSM system for mobile communications by M. Mouly & M-B Pautet, Palaisean, France, 1992, ISBN: 2-9507190-0-7, and so they are not described in greater detail herein.

Signals received by an antenna 10 of the base station are fed through an antenna connection 1 and a filter 2 into the bridging amplifier shown in the figure. To the output of the filter is connected an input matching circuit 3 by which the impedance of the antenna of the base station and the impedance of a pre¬ amplifier 4 are matched to each other so that the sensitivity of the receivers at the base station are optimal during the normal traffic operation at the base station. The match between the pre-amplifier 4 and the antenna 10 of the base station must then be a noise match.

Between the matching circuit 3 and the pre¬ amplifier 4 is arranged a switch 5 by which the signals received by the antenna of the base station are con¬ ducted to either pre-amplifier 4 or 7. Pre-amplifiers 4 and 7 are identical in type. Two amplifiers are needed so that the operation of the base station is not inter¬ rupted even if one amplifier malfunctions. Only one of the pre-amplifiers 4 and 7 is used at a time, the other standing by for a malfunction.

The inputs of the amplifiers 4 and 7 are con¬ nected to switch 5, which is identical to switch 6 in type. In the event of a malfunction, switches 5 and 6 are controlled by a control unit (not shown in the figure) contained in the base station.

The output of switch 6 is connected to branch means 8, by which the received signals are branched from the bridging amplifier to receivers RX 1 to 4 contained in the base stations.

As the operation of the base station is tested, the matching circuit 3 is set to a testing state for the duration of the antenna measurements. The match between the antenna of the base station and pre-amplifier 4 is then a 'gain match' , i.e. a complex conjugate match.

The matching circuit 3 is set to a testing state by feeding a control signal from a control unit 9 contained in the base station into the matching circuit 3. The signal fed through an output 13 of the control unit 9 shown in the figure has a voltage of either 0 V or 0.7 V, depending on whether a complex conjugate match or a noise match is to be provided.

The matching circuit 3 comprises a matching means 11 which is either grounded or not grounded at its one end, whereby it either exists or does not exist from the viewpoint of an RF signal fed between the filter 2 and pre-amplifier 4, i.e. the state of the antenna match varies. In the figure, the grounding of the matching means 11 affected by the control unit 9 - is implemented by a PIN diode 12, the current passing through the diode being e.g. 0 mA or 15 mA, depending on the effect of the control unit 9.

It is to be understood that the above descrip- tion and the accompanying figures are only intended to illustrate one advantageous embodiment of the arrange¬ ment according to the invention without limiting the invention thereto. Thus the arrangement according to the invention can also be utilized in other ways than in the base stations of a cellular radio system, although above the invention is described primarily in connection with base stations. The advantageous embodiments of the arrangement according to the invention can thus vary within the scope of the attached claims.

Claims

1. A bridging amplifier arrangement for a group of receivers comprising an antenna means (10), a match- ing means (3) for connecting the antenna means to an amplifier means (4), and means (8) for feeding signals obtained from the output of the amplifier means into a receiver unit belonging to the group of receivers, c h a r a c t e r i z e d in that the arrangement comprises a control unit

(9) arranged to change the state of the matching means (3) between two alternative input matching states, that during the normal traffic operation of the receivers, the control unit (9) sets the matching means (3) to a state where the input match of the antenna means (10) is a noise match, and that for the duration of the testing of the antenna means (10), the control unit (9) sets the match¬ ing means (3) to a state where the input match of the antenna means (10) is a complex conjugate match.

2. The arrangement according to claim 1, c h a r a c t e r i z e d in that the group of receivers is part of a base station of a cellular radio system, advantageously of a GSM system.