Abstract:
A radio front end utilizes at least one band pass filter to pass only the appropriate frequency band. Once the desired frequency band has been isolated it is converted to a digital format in an analog to digital converter and a digital signal processing device interprets the signal.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application No. 60/851,809 filed Oct. 13, 2006. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    The present application relates to a radio front end for filtering incoming radio waves for an automotive AM/FM receiver unit. 
         [0003]    A typical analog AM/FM receiver unit for use in automobiles currently consists of several stages. In the first stage an antenna receives a signal and sends it to an amplifier. In the amplifier the signal strength is adjusted to an amplitude that the remaining stages can use. No changes are made to the content of the signal in the initial amplification stage. The initial signal received by the antenna contains all the signals broadcast in the frequency ranges that the antenna is capable of receiving. 
         [0004]    After being amplified the signal is sent to a “tracked RF filter.” The tracked RF filter is a filtering component that filters the signal based on what frequency the radio is set to receive. If a passenger wishes to listen to 98.5 FM then the tracked RF filter would be adjusted to center its filtering on 98.5 MHz, for example. The tracked RF filter then strips the signal of other frequencies and allows only the selected frequency to pass. After being passed through the filter, the signal is sent to a mixer. In the mixer, the signal is modified until it is a preset frequency. This modification does not significantly change the information that is encoded in the signal; however it does change the frequency from a transmission frequency (for example 98.5 MHz) to a new frequency (for example 10.7 MHz) that the remainder of the components are capable of utilizing. 
         [0005]    After the mixer the signal is sent to a second filter. This filter is used to remove static from the signal. Then the signal is sent to a final amplifier where it is again adjusted to ensure it is at a level that the remaining components can handle, and finally it is sent to a demodulator. The demodulator interprets the signal and converts it to an analog audio signal which is sent to the speakers. 
         [0006]    Digital receivers currently used in the art utilize an almost identical process as the process described above with the exception of the last step. In a standard digital receiver the demodulator is replaced with an analog to digital converter and a digital signal is sent to a digital device that interprets the signal and outputs an audio signal to the speakers. 
         [0007]    Both the analog and the digital designs run into problems with complexity in properly aligning the tracked RF filter. If the tracked RF filter is improperly aligned the resulting signal can have a bleed from other radio stations, static, or any number of other problems associated with the final sound. Additionally the design and implementation of a tracked RF filter is difficult and complex. 
         [0008]    Another problem arises as a result of the tracked RF filter in that while it removes some frequencies other than the desired frequency, it also introduces noise at other frequencies into the system. This noise becomes attached to the signal and travels through the remaining components. Once the noise has become attached to the signal it cannot be removed without the introduction of another filter into the system. 
         [0009]    Still another problem that arises from the use of the tracked RF filter is that due to technological limitations on the tracked RF filter, only one station may be received at a time for each tuner. Because the tracked RF filter is adjusted to specifically tune into the selected frequency, any other signals are removed before the signal is passed to the next stage. This results in a necessity for multiple tuners if a person desires to record one station while listening to another, or perform any other activity involving multiple radio stations. 
       SUMMARY OF THE INVENTION 
       [0010]    A radio front end uses an antenna, a filter that can pass a radio frequency band while stripping other frequencies, and an analog to digital converter to create a digital radio signal. This signal is interpreted in a digital signal processing unit. 
         [0011]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  illustrates a block diagram of an embodiment of a radio front end. 
           [0013]      FIG. 2  illustrates a block diagram of a second embodiment of a radio front end. 
           [0014]      FIG. 3  illustrates a block diagram of a third embodiment of a radio front end. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]    Referring to  FIG. 1 , an example radio front end  100  receives a signal through an antenna  110 . The signal is simultaneously sent to two parallel filters  120 ,  130 . The first filter is an FM frequency band filter  120 , and the second filter is an AM frequency band filter  130 . The FM frequency band filter  120  will pass a range of frequencies  125  from 87 MHz to 108 MHz, and the AM frequency band filter  130  will pass a range of frequencies  135  from 520 KHz to 1710 KHz. The ranges  125 ,  135  are examples only, and in practice the AM frequency band and the FM frequency band could encompass any range of frequencies. For the purposes of this application “FM frequency band” and “AM frequency band” should be interpreted to include any two differentiated radio frequency bands. After passing through the FM frequency band filter  120  the signal is passed to an input  142  of a selector  140 . Likewise after passing through the AM frequency band filter  130  the signal is passed to an input  144  of the selector  140 . The selector  140  is capable of switching between input  142  or  144  and passing the selected input to the next stage in the radio front end  100 . After the selector  140  the selected signal is passed to an analog to digital converter  150 . The analog to digital converter  150  converts the analog signal it receives into a digital signal  155  which is readable by the digital signal processor (DSP)  160 . Once received by the DSP  160  the desired radio frequencies are pulled out and converted into sound signals  180  and sent to speakers so a person can listen to them. 
         [0016]    Referring to  FIG. 2 , another example radio front end  205  does not include a selector  140  and instead utilizes a first analog to digital converter  250  to convert the signal from a FM frequency band filter  210 , and a second analog to digital converter  260  to convert the signal from an AM frequency band filter  220 . A first amplifier  230  and a second amplifier  240  increase or decrease the signal strength to put it in a form that the analog to digital converters  250 ,  260  are capable of converting. The analog to digital converters change the input signals into digital signals  255 ,  265 . 
         [0017]    Upon exiting the analog to digital converters  250 ,  260  the signals  255 ,  265  are sent to the DSP  270  where the digital signals  255 ,  265  are processed and a sound signal  280  is ultimately output. Both the FM band signal and the AM band signal are sent to the DSP  270  where the DSP  270  determines which signal to read and utilize. Because both the FM band signal  125  and the AM band signal  135  are sent to the DSP  270  a user may listen to a signal on the FM band and simultaneously record a signal on the AM band, or perform any other use requiring the simultaneous interpretation of both the AM and FM frequency bands. 
         [0018]    Referring to  FIG. 3 , another example radio front end  300  includes two signal amplifiers  340 ,  350  between the band pass filters  320 , and  330  and the selector  360 . The amplifiers  340 ,  350  adjust the strength of the signals  125 ,  135  to put it at a level desired for processing by the analog to digital converter  370  and the DSP  380 . 
         [0019]    Although several embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.