Abstract:
The present invention relates to a high-speed interface for radio systems, in particular to a synchronous serial digital interface for car radio. In an its embodiment the synchronous serial digital interface for at least dual radio receiver systems comprises a master device and a slave device; the dual radio receiver systems having an intermediate frequency; the master device and the slave device exchange data in bi-directional manner on at least one communication channel; the master device and the slave device have a unique bit clock; the master device supply a synchronization signal to the slave device the synchronization signal has a frequency spectrum with an amplitude at the intermediate frequency lower than the amplitude of other frequencies.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application is based upon and claims priority from prior European Patent Application No. 02425547.3, filed on Sep. 2, 2002 the entire disclosure of which is herein incorporated by reference.  
         FIELD OF THE INVENTION  
         [0002]    The present invention generally relates to a high-speed interface for radio systems, in particular to a synchronous serial digital interface for car radios.  
         BACKGROUND OF THE INVENTION  
         [0003]    In radio applications the electromagnetic interference is a very important issue.  
           [0004]    Further, very high scale integration includes embedding many functions on CMOS technology in smaller and smaller chip areas. In order to cover a wide range of different customer requirements, while minimizing the number of dedicated chips required, device manufacturers have adopted a modular approach. For example, a radio system operated with low power analog signals from antennas and turner front-ends.  
           [0005]    Literature for radio systems provides a wide variety of digital interfaces to reduce as much as possible electromagnetic emission. This literature for radio systems, although useful for reducing electromagnetic emission, does not address the electromagnetic emission problems with dual or multi tuner radio receivers where switching noise contributes significantly to performance degradation.  
           [0006]    Accordingly, a need exists to overcome the problems with the prior art and to provide a system for reducing the electromagnetic emissions in multi tuner radio receivers.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides a system to overcome the problems with the prior art and provides a high-speed interface for radio systems and in particular for car radio systems.  
           [0008]    The present invention includes a synchronous serial digital interface for multi radio receiver systems comprising a master device and a slave device. The multi radio receiver systems have an intermediate frequency. The master device and the slave device exchange data in bi-directional manner on at least one communication channel. The master device and the slave device have a unique bit clock. The master device supplies a synchronization signal to the slave device. The synchronization signal has frequency spectrum with an amplitude at the intermediate frequency lower than the amplitude at the other frequencies.  
           [0009]    Furthermore according to the present invention, an antenna diversity system for radio systems includes a synchronous serial digital interface according to claim 1.  
           [0010]    The present invention provides an interface compatible with systems combining low emission, high speed, and high data transfer efficiency. The characteristic of the present invention provides very low electro-magnetic emission, resulting in a very quiet interface. The present invention can easily and be freely integrated in multi tuner radio components while reducing noise when high rate data transfer operates.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0011]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings in which:  
         [0012]    [0012]FIG. 1 shows a block scheme of a dual radio receiver system according to the present invention;  
         [0013]    [0013]FIG. 2 shows the timing diagram of the transfer data; and  
         [0014]    [0014]FIG. 3 shows chip comprising an interface according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    It should be understood that these embodiments are only examples of the many advantageous uses of the innovative teachings herein. In general, statements made in the specification of the present application do not necessarily limit any of the various claimed inventions. Moreover, some statements may apply to some inventive features but not to others. In general, unless otherwise indicated, singular elements may be in the plural and vice versa with no loss of generality.  
         [0016]    The dual radio receiver system shown in FIG. 1, include two antennas  10  and  11  connected respectively to two turner front end  12  and  13 , which from antennas  10  and  11  takes the RF (radio frequency) and convert it to IF (intermediate frequency) of 10.7 MHz.  
         [0017]    The IF signals, coming from the turner front end  12  and  13  are supplied respectively to two digital signal processors (DSP)  14  and  15 .  
         [0018]    The digital signal processors  14  and  15  communicate between them by means of two synchronous serial digital interfaces  16  and  17  (respectively), according to present invention. The digital interface  16  is to be considered as a master and the digital interface  17  is to be considered as a slave. They use a single clock signal generated by the same crystal quartz  18 . The master digital interface  16  supply to the slave digital interface  17  a synchronization signal  19 , and the digital interfaces  16  and  17  exchange their data in bi-directional way by means of the signals  20 . The whole system has only one audio output  21 .  
         [0019]    To enhance the quality of FM stations, tuner diversity can be adopted, giving an impressive improvement to the reception even in adverse environments, where multi-path and fading effects are dominants, as well as suppressing strong adjacent channels.  
         [0020]    According to the present invention two sets of turner front end  12  and  13  and digital signal processors  14  and  15  are connected together, to implement an antenna diversity system.  
         [0021]    Signals coming from separate antennas are processed in each device, and then are exchanged between them by means of the digital interfaces  16  and  17 . In this case with a proper algorithm is possible enhances quality of reception. The converted IF signals are gathered into the Master device which first analyse field strength of each of them: the one with insufficient field strength is dropped, and the other chosen; else, if both have significant strength, a proper amplitude and phase correction is performed before sum them up. That leads to an antennas beam forming, which is typically used in Radio Base Band Stations.  
         [0022]    On the other hand the data exchange is at very high rate, very close to IF and FM bandwidth, hence the request to reduce as much as possible radiation from the digital interfaces  16  and  17  is raised. The digital interfaces  16  and  17  do not exchange a high-speed clock, but only a synchronization signal  19  is used to permits data rebuild in the slave interface.  
         [0023]    The data rate is, in the present case, 1/256 the crystal frequency, i.e. 74.1 MHz/256=289.45 kHz. Word length is 16 bits, and 2 words are transmitted and/or received at a time, which leads to a bit rate for each channel of 289.45 kHz*16*2=9.2625 Mbit/sec. The synchronization signal synchronises the digital interfaces  16  and  17  on its rising edge. Whereas in slave mode the synchronization signal is received and extracted to internally initialise the blocks and send synchronously back the slave data stream.  
         [0024]    Master interface  16  does not need send bit clock to slave, since both interfaces run off same crystal so instantly they are at the exactly same frequency, and slave only needs to recover the proper phase, to latch data in. The same clock phase is used by the slave to send out its own data.  
         [0025]    Referring now to FIG. 2, the master interface  16  sends data Mi with a bit clock Ck running at 9.2625 MHz, and a synchronization signal MSynch with a rising edge (the synchronization will be on the slave chip upon the rising edge of it) at the synchronization rate Fs or period T 0 . At the rising edge of the synchronization signal start the transmission of data from the master interface  16  toward the slave interface  17 .  
         [0026]    The duty cycle D=τ/T 0  of the synchronization signal MSynch can be adjusted among different values, at which the interference around the IF frequency (10.7 MHz) is minimised.  
         [0027]    The slave interface  17  is such that the master interface  16  can capture the slave Si bit at the rising edge of the master bit clock Ck just after the one which has previously generated the master Mi bit.  
         [0028]    Data line has the maximum frequency of 9.26 MHz/2=4.63 MHz, when transmitting or receiving a sequence of 101010 . . . , in general it can be assumed data sequence being random, thus spreading its frequency spectrum over the band.  
         [0029]    The synchronization signal gives the start of the frame, and the serial interface uses one on its edges to extract the synchronization and to recover from serial to parallel format the data upon reception. One choice of the synchronization signal is a square wave with a duty cycle D=τ/T 0 , where T 0  is the period and τ is the time where the synchronization signal is on.  
         [0030]    The Fourier series expansion of a generic periodic function with period T 0  is:  
               F        (   t   )       =       A   0     +     ∑       A   n          cos        (     2                 π                 n        t     T   0         )           +     ∑       B   n          cos        (     2                 π                 n        t     T   0         )                       where               A   0     =       1     T   0              ∫       -     T   0       /   2         T   0     /   2              F        (   t   )                          t                         A   n     =       1     T   0              ∫       -     T   0       /   2         T   0     /   2              F        (   t   )            cos        (     2                 π                 n        t     T   0         )                          t                         B   n     =       1     T   0              ∫       -     T   0       /   2         T   0     /   2              F        (   t   )            sin        (     2                 π                 n        t     T   0         )                          t                                       
 
         [0031]    So where F(t) is a square wave with duty cycle D=τ/T 0  we have:  
         [0032]    A 0 =τ/T 0 =D  
         A   n     =           2                 π       T   0              sin        (     π                 n        τ     T   0         )         π                 n        τ     T   0             =     2      D          sin        (     π                 n                 D     )         π                 n                 D                                 
 
         [0033]    B n =0  
         [0034]    Being T 0 =1/289.45 KHz, the 37 th  harmonics, that is 289.45 KHz*37=10.7095 MHz, falls inside the IF bandwidth (10.7 MHz). So, the 37 th  coefficient of the Fourier series must be 0 or close to it, which leads to sin(πnD)=0 or 37*πn*D=k*π, or 37*D=k where k is any whole number. Hence we have to choose D=k/37. Being our time resolution 1/74.1 MHz we have D=δ/256, with δ any integer number within the range 0&lt;δ&lt;256. The best we can have is δ=83, which leads A 37 /A 0 =2 sin (37*π*83/256)/(37*π), that is about −73 dB. Therefore, a preferable value for τ is τ=D*T 0 =δ/256 *T 0 =(83/256)*(1/289.45 KHz).  
         [0035]    It is important to note that other values have been advantageously shown to provide good rejection at the interfering harmonic, for example value of D comprised between D=75/256 and D=90/256.  
         [0036]    The rejection can be easily further reduced by increasing T 0  by a multiple M of it, for example 10 times, so that we have to consider the 37*M harmonic.  
         [0037]    Alternatively, for a even better spreading of noise coming from harmonics of synchronization signal, the duty cycle can be changed on the fly with a pseudo-random numeric sequence, thus giving more reduction to in-band interference. This can be easily performed by varying the value of δ from 1 to 127: a counter from 0 to 255 and a comparator with variable threshold originated of the synchronization signal; by varying the threshold with a pseudo random sequence of numbers from 1 to 127, for example stored in a look-up table, the duty cycle δ/D is modulated, and harmonics peak level reduced, thus whitening the noise due to radiation.  
         [0038]    Referring now to FIG. 3, the interface can be partitioned in two main modules: the synchronization signal manager  30 , and the channel management blocks  31 ,  32 ,  33 . It also contains the control status register (not shown), responsible for the set-up configuration of synchronization and channel blocks.  
         [0039]    In this specification the channel management blocks  31 ,  32 ,  33  are three, but can be any number, i.e. many blocks of the same kind can be placed more than once, provided the control status register contains enough bits for proper set-up configuration and data.  
         [0040]    There are  2  main configurations of the interface, mutually exclusive.  
         [0041]    The master one: in this case the interface is responsible for synchronization signal generation MSynch, and gives the proper duty cycle shaping.  
         [0042]    The slave one: in this case the interface is responsible for recovery of the synchronization from the reception of master synchronization signal MSynch, and it also synchronises all the channel blocks of the slave. It can also be used for the slave interface synchronization.  
         [0043]    When in master mode a down-up counter counting from 0 to 255 by 1 step and clocked at 74.1 MHz provides the basic waveform for the MSynch signal to be output as master to the slave. It is then shaped with an offset, selectable from external by a register in the range 1 to 127, of which resulting MSB is the Msynch (as aforesaid); the duty cycle is D=offset/256. The offset should be set as described above. Internally the data are handled in parallel, thus a parallel to serial in transmit mode, and serial to parallel in receive mode conversions are needed. The 8 bit counter overflow is the load signal for the parallel to serial or serial to parallel conversion in the channel management block, which performs the conversion, and send/receive data to/from the electrical interface.  
         [0044]    When in slave mode the clock divide by 8 samples the incoming MSynch (from external master) with four 90 degrees off phase clocks at 9.26 MHz frequency. It defines the window, where the MSynch has its rising edge. The clock phase selector selects one out of the four phases (clk 0 , clk 90 , clk 180 , clk 270 ), to be used as slave clock in the channel managers (PhasedClk). It also provides a synchronization pulse at 74.1 MHz to synchronise the 8 bit counter, and in turn the load operation, as well as a slave synchronization to be used elsewhere in the slave interface (for instance to resynchronise the slave interface to the master one). The interface also has a reset from outside and needs a 74.1 MHz system clock. A start signal is also available to synchronization the interface when in master mode.  
         [0045]    The synchronization signal manager  30  has the one shot feature which enables the MSynch out just once in a 32 bit data frame upon request. This is to have the quietest environment possible, where the synchronization between the two interfaces is done just once for example at the very beginning, or upon request by software.  
         [0046]    Here the serial in/out data are handled, together with the parallel to serial and serial to parallel interface. The write and read operation to data registers can be done either from digital signal processors or to/from an hardware block, hooked up to it.  
         [0047]    Even in channel management block there are two main configurations of the channel.  
         [0048]    The transmitter one: parallel data are read from digital signal processors or other block, and properly loaded into the 32 bit register to be sent out serially at 9.26 MHz rate.  
         [0049]    The receiver one: the 32 bit register serially reads in data from master, with proper re-phased 9.26 MHz, then transferred to the digital signal processors register for parallel read from outside  
         [0050]    The 32 bit register is essentially a mono directional 32 bit shift register, which can be up-loaded either from parallel bus (from DSP registers for instance) or from serial line (Dataln in our case), hooked up to the first bit, or can download its contents to parallel registers or to the serial out line (DataOut).  
         [0051]    The signals of the interface, according to the present invention, are the followings.  
         [0052]    Inputs.  
         [0053]    Clock: system clock at 74.1 MHz.  
         [0054]    Resetn: main reset of all the sequential circuitry. Active Low.  
         [0055]    Start: for resynchronization of all counters and internal synchronization signals.  
         [0056]    MSynch: in Slave mode, synchronization signal from external Master interface.  
         [0057]    HW 0 _ 0 ,_ 1 ,_ 2 : data input to last 16 bit of sent/received serial data of respectively Channel Management Blocks  0 ,  1 ,  2 .  
         [0058]    HW 1 _ 0 ,_ 1 ,_ 2 : data input to first 16 bit of sent/received serial data of respectively Channel Management Blocks  0 ,  1 ,  2 .  
         [0059]    Dataln 0 ,  1 ,  2 : serial data in receiver mode.  
         [0060]    Outputs.  
         [0061]    PhasedClk: phased clock output, to be used externally as signal (e.g. test purposes).  
         [0062]    Slave Synch: 1 pulse at 74.1 MHz frequency, to be used as external synchronization in Slave mode.  
         [0063]    Master Synch: synchronization output signal when in master mode, with duty cycle controllable.  
         [0064]    SynchPadEnCtrl: controls direction of the synchronization output. High impedance when in slave mode, output when in master mode.  
         [0065]    DataOut 0 ,  1 , 2 : serial data out in transmitter mode.  
         [0066]    PadEnCtrl 0 ,  1 ,  2 : gives direction to the InOut serial data pad, High impedance when in receiver mode, output when in transmitter mode.  
         [0067]    Registers.  
         [0068]    DSPIF: data address interface (in/out) to the DSP core, for communication to it.  
         [0069]    Master/Slave Selection: bit which selects between Master (High) and Slave (Low). At reset it is Low (Slave).  
         [0070]    Offset: 7 bit value, which gives the offset for Master Synch output duty cycle. At reset equals 0.  
         [0071]    OneShot: when enabled, and in Master Mode the Master Synch is applied once in a data frame.  
         [0072]    TxRx 0 ,  1 ,  2 : for each block  1  bit select for transmitter (High), receiver (Low) mode. At reset is Low (Receiver).  
         [0073]    HwSwMode 0 ,  1 ,  2 : for each block  1  bit select for up/download from to either DSP (Low) or Hw block (High). At reset it is Low (DSP).  
         [0074]    Preferably, the interface according to the present invention, as disclosed in FIG. 3, is carried out in a single chip.  
         [0075]    The number of channels can be extended, since each channel management block is fully independent of each other. In a dual antenna diversity system, the typical configuration is with master having two receiving channels (generally IF in phase and quadrature signals), and one transmitting channel, which is used for instructing the slave device.  
         [0076]    Although a specific embodiment of the invention has been disclosed, it will be understood by those having skill in the art that changes can be made to this specific embodiment without departing from the spirit and scope of the invention. The scope of the invention is not to be restricted, therefore, to the specific embodiment, and it is intended that the appended claims cover any and all such applications, modifications, and embodiments within the scope of the present invention.