Abstract:
In a circuit arrangement and method for testing a radio receiving system, the circuit arrangement includes multiple antennas, an antenna selector switch for the antennas, a receiver, and a diversity processor that controls the antenna selector switch. A diagnostic processor has an output terminal connected to a control input of the diversity processor, which provides at its output terminal, a signal that prevents the diversity processor from performing any further switching operations.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a circuit arrangement and a method for testing a diversity switching system. 
     BACKGROUND INFORMATION 
     Diversity antenna switching systems are described, for example, in European Published Patent Application No. 0 201 977. The system is essentially a single component having antenna switches and a TEA6101 diversity processor with a TDA1596 IF demodulator, both from Philips. The diversity processor detects receiving disturbances by evaluating an IF signal supplied from the radio, subsequently using the antenna switch to switch over to another antenna, the signal quality of which, in turn, is tested, etc. 
     This system does not make it possible to easily activate specific antennas for testing, i.e., to connect them to the radio input terminal. 
     A circuit arrangement that achieves this object is described in German Published Patent Application No. 195 13 872. The following is a description of this circuit arrangement, with reference to FIG.  1 . Switching between (for example) four antennas  1 ,  2 ,  3  and  4  is accomplished by providing an antenna switch  5 , which is controlled by a diversity processor  6 . Control signals which are generated by a demodulator  10 , and which demodulator  10  derives from the IF signal provided by a receiver (radio)  8  having one or more speakers  9 , are present at diversity processor  6 . 
     A converter  51 , which is controlled by a control unit, e.g., radio  8 , is provided to continuously activate specific antennas. To do this, the control unit generates a digital signal that is transmitted to converter  51 , for example, via the antenna cable with separating filter  52 , or via the IF line used to control the diversity system. Converter  51  uses electronic switches to select one of, for example, four antennas  1 ,  2 ,  3  or  4 . However, because diversity processor  6  is not deactivated during testing of the selected antenna, its switching pulses may interfere with the incoming signal. 
     The procedure described in German Published Patent Application No. 195 13 872 has the advantage that it is relatively easy to implement. Nevertheless, it has the disadvantage that it can test only the function of the antennas, but not the function of the diversity processor itself, and the diversity processor remains in operation while the function of an antenna is being tested. 
     The express reference made to the above-mentioned publications and to the product description of the above-mentioned circuits also applies to all details and technical objects not described in greater detail here. 
     SUMMARY 
     It is an object of the present invention to provide a circuit arrangement and a method for testing a diversity switching system that may be used to test not only the function of the antennas, but also that of the diversity processor itself. 
     In particular, the circuit arrangement according to the present invention prevents the processor from generating, during diagnosis, switching signals that interfere with the function test. 
     According to the present invention, a diagnostic processor is provided, which has an output terminal connected to a control input of the diversity processor and which provides, at its output terminal, a signal that prevents the diversity processor from performing any further switching operations. 
     In particular, use may be made of a characteristic of conventional diversity processors, such as the Philips TEA6101 circuit. This diversity processor may, for example, interrupt switching to another antenna when a stop signal is supplied to its control input. 
     The diagnostic processor provided according to the present invention generates the stop signal at the exact moment when it determines that the selected antenna has been activated by the diversity processor. Diagnosis is not accomplished by using an additional control unit for the antenna switch, according to the present invention, but rather the diversity processor is suitably controlled so that it continuously activates the selected antenna independently of the antenna signal at the moment. 
     For clarity, it should be noted that the use of the term “processor” does not imply that this circuit needs to be a microprocessor or microcontroller. “Hard-wired” circuits may also be used instead of processors of this type. 
     The circuit arrangement according to the present invention may be used, for example, to perform diagnosis as follows: 
     1. A frequency at which a relatively weak signal is received is first set at the radio. This is necessary because the diversity processor switches to the antenna only within the receiving level range at which noise may be heard in the speaker. 
     2. The number of the antenna to be set is entered at the radio either subsequently or beforehand. The radio transmits this value to the diagnostic processor. 
     3. Existing receiving signal fluctuations, or fluctuations that are produced, for example, by touching the antenna, cause the diversity processor to switch to another antenna. If the diagnostic processor determines that the desired antenna is set using a comparator, for example it sets the stop signal for the diversity processor. The achievement of this state is transmitted back to the radio and displayed there. 
     4. Switching to another antenna is an indication that the diversity processor is in proper working order. The antenna itself may then be tested, for example, by performing an audio test. 
     If a more thorough test of the system is necessary, for example for final inspection during manufacturing, conventional test signals may be used to test both the diversity switching threshold and the antenna function. 
     The directional characteristics of the individual antennas may also be tested by disconnecting the antenna cable from the radio input and supplying the antenna output signal to a measuring receiver. 
     According to a further example embodiment, it is possible to use special switching actions to cause the system to switch to the next antenna during diagnosis. This may be accomplished, for example, by briefly deactivating all antennas and thereby triggering switchover by the diversity processor. This action is most easily performed directly at the antenna switch at the concentration point of the switching diodes. 
     It is also possible to use the demodulator level signal to evaluate the antenna receiving level more precisely. In the range relevant for diversity operation, the magnitude of this signal is largely proportional to the receiving level and may therefore be compared to a reference signal during the test. 
     According to a further example embodiment, a test unit produced specifically for the intended purpose may be used instead of the radio as the control unit for the diagnostic processor. 
     Without limiting its scope and nature, the present invention is described below, by way of example, on the basis of embodiments with reference to the drawing, to which express reference is made for the purpose of describing all details according to the present invention that are not explained in greater detail in the text. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a four-antenna diversity system with diagnostic function according to the related art. 
     FIG. 2 is a schematic view of an example embodiment of a four-antenna diversity system according to the present invention, having a diagnostic function. 
     FIG. 3 a  is a schematic view of a first example embodiment of a diagnostic processor according to the present invention. 
     FIG. 3 b  is a schematic view of a second example embodiment of a diagnostic processor having the ability to deactivate all antennas simultaneously. 
     FIG. 3 c  is a schematic view of a third example embodiment of a diagnostic processor having the ability to evaluated the IF signal level. 
     FIG. 3 d  is a schematic view of a further example embodiment of the diagnostic processor with the ability to deactivate all antennas simultaneously and to evaluate the IF signal level. 
     FIG. 4 is a schematic view of an example embodiment of an antenna switch with the ability to deactivate all antennas simultaneously. 
     FIG. 5 is a schematic view of a four-antenna diversity system with diagnostic function and transmission of the test signals over the IF line. 
    
    
     DETAILED DESCRIPTION 
     In the Figures, the same reference numbers always refer to the same parts, making it unnecessary to introduce these parts repeatedly in the explanation of further figures. 
     FIG. 2 is a block diagram of an example embodiment of an antenna diversity system having diagnostic function. Four antennas  1  through  4  are connected to an antenna switch  5 , which is controlled by a diversity processor  6  and which “switches” the signal of a particular antenna to its output terminal according to the control function. The output signal of antenna switch  5  present at this output terminal (RF signal) is supplied to a radio  8  having at least one speaker  9 , which may be used, among other things, to perform an acoustic evaluation. 
     According to the present invention, a diagnostic processor  7  is provided, the function of which is described below. 
     Diagnostic processor  7  has input terminals for the four switching lines (in the example embodiment illustrated) for antenna switch  5 , one input/output terminal for the digital test signals and one further (optional) input terminal, the function of which is explained below. 
     The IF signal generated by receiver  8  is supplied to a demodulator  10  over a coaxial cable. Demodulator  10  internally generates, from the IF signal, the level and audio signals, which are sent to diversity processor  6 . The level signal, which is also supplied to the other input terminal of diagnostic processor  7 , is a DC signal proportional to the IF signal level and enables the receiving level to be evaluated. The audio signal is the modulation content of the radio signal. 
     Diagnostic processor  7  may also have an output terminal at which is present a signal that may be used to deactivate all antennas. 
     The operation of diagnostic processor  7  provided according to the present invention is explained in greater detail below with reference to FIGS. 3 a  to  3   d . The same reference numbers refer to the same parts as in FIG.  2  and do not need to be described again. 
     FIG. 3 a  illustrates a first example embodiment of diagnostic processor  7 : 
     The four antenna switching lines (in the example embodiment illustrated) are routed to a comparing element  71 . The comparison input terminals of comparing element  71  are connected to a register  72  which stores the number of antenna  1 ,  2 ,  3  or  4  to be set for the diagnosis. The number of the antenna is transmitted from radio  8  to comparison input terminals of register  72  via an interface  73 . Interface  73  also provides a diagnosis enabling signal, which, together with the output signal of comparing element  71 , is present at an AND element  74  in the form of an input signal, the output signal of which is present, in the form of a stop signal, at the control input terminal of diversity processor  6 . 
     FIG. 3 b  illustrates a modification of the example embodiment illustrated in FIG. 3 a , in which interface  73  has an output terminal at which a signal is present which may be used to deactivate all antennas  1  . . .  4 . This feature, which may be used when switching to the next antenna, must not or may not be triggered by a poor-quality incoming signal, but rather exclusively by the control unit at a specific point in time. 
     According to the example embodiment illustrated in FIG. 3 c , not only the test signals generated by radio  8 , but also the output signal of a window comparator  75 , which compares the level signal to a reference voltage U ref , is present at the interface. This characteristic may be used to test the diversity system in the automobile manufacturer&#39;s facilities during vehicle production, using defined frequency-modulated RF test signals. 
     FIG. 3 d  illustrates an example embodiment that has the same characteristics as the example embodiments illustrated in FIGS. 3 b  and  3   c.    
     It is possible to extend the illustrated circuit to more or fewer than four antennas at any time. 
     FIG. 4 illustrates an example embodiment of an antenna switch  5 , which enables all antennas to be deactivated simultaneously. Without limiting the overall configuration, illustrated antenna switch  5  has two inputs  53  and  54  that are connected to a radio output terminal  57  as a function of switching signals present at terminals  55  and  56 . Reference number  58  identifies a deactivation input terminal. When a control signal with zero potential is present at terminal  58 , circuit point  59  becomes connected to plus voltage +Ub due to the deactivated transistor, so that the switching diodes may no longer conduct current, and a signal is no longer present at terminal  57 . This arrangement makes it possible to deactivate all antennas with a single signal. 
     FIG. 5 illustrates a modification of the example embodiment illustrated in FIG. 2, in which the test signals are routed via the IF cable to simplify the wiring. This arrangement enables the two diplexers on,,the radio and processor sides, of which only diplexer  710  on the processor side is illustrated in FIG. 5, to couple in and out. The diplexer on the radio side is not illustrated because it is located inside the radio. It is not practical to use the RF antenna cable for this purpose because the latter may need to be removed from the radio, for example, to measure the antenna directional diagrams. The antenna cable is then connected to a measuring receiver. If it is still necessary to control the antenna or activate a particular antenna under these circumstances, the control signals may be transmitted from the radio to the diversity circuit over a cable other than the RF signal cable.