Abstract:
There is described an RF integrated circuit receiver structure. The structure comprises a receiver channel; a selectable amplification stage associated with the receiver channel; and a selectable diversity channel associated with the receiver channel. There is therefore provided a modular reconfigurable RFIC receiver architecture.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority of European Patent Application No. 99302632.7, which was filed on Apr. 1, 1999. 
     FIELD OF THE INVENTION 
     The present invention relates to an RF receiver on a single integrated circuit chip, and particularly but not exclusively to such a receiver for use in the base station of a mobile communications system. 
     BACKGROUND TO THE INVENTION 
     The analogue part of a mobile communications base station comprises radio frequency (RF) and IF circuitry. The RF circuitry is currently realised using discrete electronic components. In the interests of minimising circuit size and reducing costs, there is presently a drive toward the implementation of RF circuitry on integrated circuits (ICs). 
     The system architecture and RF IC requirements for different types of base station are significantly different, and this has led to the provision of integrated circuits implementing the RF circuitry for the different types of base station which can be used exclusively in the different types of applications. 
     For example, a base station for a macro-cellular mobile communications system requires a diversity channel, but may not necessarily require a low noise amplifier in the receiver channel. For a micro-cellular mobile communications system, a low noise amplifier and a diversity channel are usually required. For a pico-cellular system, neither a low noise amplifier nor a diversity channel is usually required. 
     Designing of RF IC receivers for all possible base station classes is thus costly and time consuming. 
     It is therefore an object of the present invention to provide an improved RF IC receiver. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided an RF integrated circuit receiver structure comprising: a receiver channel; a selectable amplification stage associated with the receiver channel; and a selectable diversity channel associated with the receiver channel. 
     Thus there is proposed a general purpose, modular, radio frequency integrated circuit receiver architecture, which enables the system architecture to be configured differently around a single RF IC, to realise the functionality required for different base station applications. 
     For example, the amplification stage may be not selected, and the diversity channel may be selected, when the receiver channel is used in a base station of a macro-cellular mobile communications system. 
     In a further example the amplification stage may be selected and the diversity channel may be selected when the receiver channel is for use in a base station of a micro-cellular mobile communications system. 
     In a further example the amplification stage may not be selected and the diversity channel may not be selected when the receiver channel is for use in a base station of a pico-cellular mobile communications system. 
     The amplification stage is preferably a low noise amplifier. 
     The receiver channel may include a driver amplifier, a mixer, and an IF amplifier. 
     The elements of the receiver channel may be interconnected off-chip in accordance with the application of the receiver channel. 
     The diversity channel may comprise a driver amplifier, a mixer and an IF amplifier. 
     The elements of the diversity channel may be interconnected off-chip in accordance with the application of the receiver channel. 
     The invention will now be described by way of non-limiting example with reference to the attached drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an implementation of an RF IC according to an exemplary embodiment of the present invention; 
     FIG. 2 illustrates the RF IC of FIG. 1 configured for use in a macro-cellular base station; 
     FIG. 3 illustrates the RF IC of FIG. 1 configured for use in a micro-cellular base station; and 
     FIG. 4 illustrates the RF IC of FIG. 1 configured for use in a pico-cellular base station. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     FIG. 1 shows a schematic representation of a radio frequency (RF) integrated circuit (IC)  2  according to the present invention. The RF IC includes a receiver channel generally designated by reference numeral  3 , a diversity channel generally designated by reference numeral  5 , a low noise amplifier  14  associated with the receiver channel  3 , and a low noise amplifier  12  associated with the diversity channel  5 . 
     In this preferred implementation the receiver channel  3  includes a driver amplifier  6 , a mixer  8 , and an IF amplifier  10 . The diversity channel  5  preferably includes a driver amplifier  14 , a mixer  16  and an IF amplifier  18 . However, it will be appreciated that the implementation of the receiver channel and diversity channel may vary beyond that shown in FIG.  1 . 
     In the arrangement of FIG. 1 the output of the mixer  8  is connected to the input of the IF amplifier  10  on-chip. The interconnection of the other components of the receiver channel are determined by off-chip connections in accordance with the application of the RF IC. Also in the arrangement of FIG. 1 the output of the mixer  16  is connected to the input of the IF amplifier  18  on-chip. The interconnection of the other components of the diversity channel are similarly determined by off-chip connections in accordance with the application of the RF IC. 
     The RF IC in this preferred implementation also includes a local oscillator buffer  22  which is provided to receive a locally generated oscillator signal from off-chip. The output of the local oscillator buffer  22  forms an input to a local oscillator splitter  20 , which in turn provides outputs to the two mixers  8  and  16 . The inputs to the mixers  8  and  16  from the local oscillator splitter  20  provide the reference frequency for heterodyning the received signal. Although in the preferred implementation the RF IC includes the local oscillator buffer and local oscillator splitter, it will be appreciate that these components are not essential, and the reference inputs to the mixers may be provided directly from off-chip. 
     The low noise amplifiers  12  and  14  and the diversity channel  5  of FIG. 1 are selectively connected in combination with the receiver channel  3  by off-chip connections, such that in accordance with the invention, the RF IC of FIG. 1 can be used in a number of different applications. Three advantageous selections of the functionality provided by the RF IC  2  are discussed hereinbelow with reference to FIGS. 2 to  4 , but it will be appreciated that the RF IC has applications beyond these three specific examples. Referring to FIG. 2, there is shown the selection of the diversity channel and low noise amplifier associated with the receiver channel when the RF IC is used as part of a receiver structure in the base station of a macro-cellular mobile communications structure. In the implementation of a macro-cellular base station considered herein, there is no requirement for a low noise amplifier in the receiver channel, since it is assumed that the implementation provides a low noise amplifier elsewhere in the system arrangement, for example in the antenna mast. The on-chip low noise amplifier is therefore not required and hence is not selected. It is envisaged that in alternative arrangements of a macrocellular system, the low-noise amplifier may not be provided elsewhere in the system and the on-chip low noise amplifier would therefore need to be used. 
     A diversity channel is required in the macro-cellular structure, and the diversity channel  5  is therefore selected. FIG. 2 also shows an example of the off-chip connections of the receiver channel and the diversity channel, and the interconnection of the essential components of the respective channels. 
     The driver amplifier  6  of the receiver channel receives the RF input signal from the receiver antenna on line  24  as its input. An off-chip image rejection filter  26  receives on its input line  28  the output of the driver amplifier  6 . The output of the image rejection filter  26  on line  32  forms an input to a 3 dB splitter  34 . The splitter  34  has two outputs on lines  30  and  36 . The output on line  30  forms the off-chip input to the mixer  8 . The output on line  36  forms the diversity output, as discussed further hereinbelow. The output of the receiver channel is provided on lines  38  from the RF IC. 
     The diversity input signal to the diversity channel  5  may be provided, in a preferable implementation, from a receiver or diversity channel off-chip tuned to a different frequency. Thus the RF IC  2  may be tuned to a first frequency and a second RF IC may be tuned to a second frequency. The second RF IC may receive an input signal on the main receiver channel  3  from a second antenna. The diversity output on line  36  of the first RF IC may be connected to one of the diversity inputs of the second RF IC, and the diversity output on the equivalent line  36  of the second RF IC may be connected to the one of the input lines  44  and  48  of the first RF IC. In such an arrangement the first RF IC tuned to the first frequency can select between the signals from the first and second antennas by selecting either the output of the receiver channel  3  on lines  38 , or the output of the diversity channel on lines  42 . Similarly the second RF IC tuned to the second frequency may select between the signals from the first and second antennas. 
     In an alternative arrangement the diversity input on either line  44  or  46  may be provided directly from a second antenna. In this arrangement the RF IC provides for selection between antennas by selection of one of the outputs on either lines  38  or  42 . In this case both channels of the RF IC are tuned to the same frequency. 
     The RF input signal from the diversity antenna provides an input either on line  44  to the driver amplifier  14 , or on line  46  to the mixer  48 . If the driver amplifier is required, then the output of the driver amplifier on line  48  provides an input to the mixer on line  46 . The output of the diversity channel is provided on lines  42  from the RF IC. 
     Referring to FIG. 3, there is shown the selection of the diversity channel and low noise amplifier associated with the receiver channel when the RF IC is used as part of a receiver structure in the base station of a micro-cellular mobile communications structure. In such an implementation, there is a requirement for a low noise amplifier in the receiver channel, and therefore the low noise amplifier is selected. A diversity channel is required, and the diversity channel  5  is therefore also selected. FIG. 3 also shows an example of the off-chip connections of the receiver channel and the diversity channel in this example implementation, and the interconnection of the essential components of the respective channels. 
     The low noise amplifier  4  receives the RF input signal from the receiver antenna on line  24  as its input. The off-chip image rejection filter  26  receives on its input line  28  the output of the low noise amplifier  4 . The output of the image rejection filter  26  on line  32  forms an input to the driver amplifier  6 . The output of the driver amplifier forms the input on line  32  to the 3dB splitter  34 . The splitter  34  has two outputs on lines  30  and  36  as before. The output on line  30  forms the off-chip input to the mixer  8 . 
     The output of the receiver channel is provided on lines  38  from the RF IC. Once again, the RF input signal from the diversity antenna provides an input either on line  44  to the driver amplifier  14 , or on line  46  to the mixer  48 . If the driver amplifier is required, then the output of the driver amplifier on line  48  provides the input to the mixer on line  46 . The output of the diversity channel is provided on the lines  42  from the RF IC. 
     Referring to FIG. 4, there is shown the selection of the diversity channel and low noise amplifier associated with the receiver channel when the RF IC is used as part of a receiver structure in the base station of a pico-cellular mobile communications structure. In such an implementation, there is no requirement for a low noise amplifier in the receiver channel, and therefore the low noise amplifier is not selected. A diversity channel is also not required, and the diversity channel  5  is therefore also not selected. FIG. 4 also shows an example of the off-chip connections of the receiver channel, and the interconnection of the essential components of the receiver channel. 
     The driver amplifier  6  of the receiver channel receives the RF input signal from the receiver antenna on line  24  as its input. The off-chip image rejection filter  26  receives on its input line  28  the output of the driver amplifier  6 . The output of the image rejection filter  26  on line  32  forms the off-chip input to the mixer  8 . The output of the receiver channel is provided on lines  38  from the RF IC. 
     The low noise amplifier  12  is not used in any of the example implementations given above. However, its presence provides for extra flexibility and future system options. For example, the diversity channel  5  may be used as a receiver channel for a different antenna to that associated with the receiver channel  3 , and the low noise amplifier  12  may form an input stage of such receiver channel. In such an arrangement the RF IC  2  provides two receiver channels at a common frequency, for two antennas. 
     The use of the general purpose, modular, base station receiver RF IC as described hereinabove provides a more comprehensive overall solution than current solutions allow, and gives base station system designers greater flexibility. The RF IC allows a single integrated circuit to meet the receiver requirements for three classes of base station, and has applications beyond. 
     Those elements of the RF IC not required for a particular application may be not selected by power not being supplied to them.