Abstract:
A system and method of injecting audio content into a radio system is provided. The method includes the steps of receiving in a radio receiver a first RF signal from an antenna and processing the signal at a select frequency within a radio frequency band. The method also includes the step of providing audio content from an auxiliary device. The method also includes the step of modulating the audio content from the auxiliary device and replicating the modulated signal to generate a replicated RF signal at the multiple frequencies within the radio frequency band. The method further includes the step of injecting the replicated RF signal into the radio receiver.

Description:
TECHNICAL FIELD 
       [0001]    The present invention generally relates to audio radios, and more particularly relates to the injection of audio content from an auxiliary device to a radio receiver. 
       BACKGROUND OF THE INVENTION 
       [0002]    Automotive vehicle AM/FM radios are generally configured to receive broadcast radio frequency (RF) signals that are processed at a user selected radio frequency to acquire and play audio content. For example, a listener may select frequency modulated (FM) RF signals in the radio frequency band ranging from about 88.1 to 107.9 MHz, typically selectable at 200 kHz increments. Auxiliary sources of audio content may be available and may be configured to communicate with the vehicle radio to allow for multiple sources of audio content to be played by the vehicle radio. 
         [0003]    Conventional methods for injecting an RF signal containing audio content into an existing car radio system  110  generally employ an FM modulator  124  associated with an auxiliary device  122  as shown in  FIG. 1 . According to one method, the FM modulator  124  outputs an FM modulated RF signal  130  at a predetermined single FM frequency W C  to a switch  120 . The switch  120  interrupts the connection from the antenna  118  and its received RF FM signal  132  to the car radio receiver  112  and injects the RF FM signal  130  at predetermined FM frequency W C . However, this approach generally requires the user to select the appropriate FM station frequency W C  prior to use. 
         [0004]    According to another conventional approach, a method detects LO signal leakage from the radio, generally between the radio receiver and the antenna, and determines from the signal leakage which FM frequency station the user is listening to. This method then modulates the audio content at the determined frequency W C  to inject the audio content in an RF signal  130  into the radio by switching the connection from the antenna received RF signal  132  to the RF signal  130  applied to the radio receiver  112  via the switch  120 . However, the method of detecting LO signal leakage generally requires sufficient LO signal leakage from the radio to be detected, which typically is not available on many modern day radios. Additionally, this conventional method typically requires the installed radio to have standard RF tuner frequencies. 
         [0005]    Accordingly, it is therefore desirable to provide for a system and method of injecting audio content into a radio that does not require user selection of a specific radio frequency or detection of leakage signal from the radio. In particular, it is desirable to provide for a vehicle radio system that allows for an auxiliary audio source to inject audio content into the radio in a manner that is easy to use and reliable. 
       SUMMARY OF THE INVENTION 
       [0006]    In accordance with the teachings of the present invention, a system and method of injecting audio content into a radio is provided. According to one aspect of the present invention, a method of injecting audio signal content into a radio receiver is provided. The method includes the steps of receiving in a radio receiver a first RF signal from a first source, wherein the radio receiver processes the first RF signal at a select frequency within a radio frequency band. The method also includes the step of providing audio content from a second auxiliary source. The method includes the steps of modulating the audio content from the second auxiliary device to generate a modulated signal and replicating the modulated signal to generate a replicated second RF signal at multiple frequencies within the radio frequency band. The method further includes the step of injecting the replicated RF signal into the radio receiver. 
         [0007]    According to another aspect of the present invention, an audio system is provided that receives injected audio signal content and injects the audio signal content into a radio. The audio system includes a radio receiver for receiving first RF signals at frequencies in a radio frequency band and processing the signals at a select frequency. The audio system also includes a switch coupled to the radio receiver for selecting an input signal to the radio receiver. The system has a first RF signal source coupled to the switch for providing a first RF signal at a select frequency in the radio frequency band and a second auxiliary RF signal source for injecting audio content into the radio receiver. The method further includes a modulator for modulating the audio content to generate a modulated signal and a signal replicator for generating a replicated second RF signal containing the modulated audio content at multiple frequencies within the radio frequency band for input to the second input of the switch, wherein the switch inputs the replicated second RF signal to the radio receiver. 
         [0008]    Accordingly, the system and method advantageously injects audio content into a radio receiver without requiring user selection of a specific radio frequency or detection of a leakage signal from the radio. The system and method are easy to use and reliable to inject audio content from an auxiliary source into the radio. 
         [0009]    These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0011]      FIG. 1  is a block diagram illustrating a conventional audio radio system employing an auxiliary device and FM modulator; 
           [0012]      FIG. 2  is a block diagram illustrating an audio radio system employing an auxiliary device and FM modulator and replicator, according to one embodiment of the present invention; 
           [0013]      FIG. 3  is a block diagram illustrating the FM modulator and replicator in  FIG. 2 , according to a first embodiment of the present invention; 
           [0014]      FIG. 4  is a block diagram illustrating the FM modulator and replicator in  FIG. 2 , according to a second embodiment of the present invention; 
           [0015]      FIG. 5  is a graph illustrating a baseband signal in the time domain without applying the pulse train switch; 
           [0016]      FIG. 6  is a graph illustrating an FM time signal in the frequency domain without the pulse train switch applied; 
           [0017]      FIG. 7  is a graph illustrating the FM time signal with the pulse train switch applied; 
           [0018]      FIG. 8  is a graph illustrating the FM signal in the frequency domain with the pulse train switch applied; and 
           [0019]      FIG. 9  is a graph illustrating one example of the replicated audio signal throughout the entire FM radio bandwidth. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    Referring now to  FIG. 2 , an audio radio system  10  is illustrated that receives audio content in a first RF signal from a first RF source, shown as an antenna  18 . The radio system  10  also receives injected audio signal content from a second RF source, shown as an auxiliary device  22 , according to one embodiment of the present invention. The audio radio system  10  is shown employing a car radio receiver  12  having a tuner  14 , such as an FM tuner. The FM tuner  14  may be tuned to any RF FM frequency W C  such as the standard FM frequencies broadcast between about 88 and 108 MHz, centered in slots at 200 kHz increments, such as 88.1 MHz, 88.3 MHz, 88.5 MHz, . . . 107.5 MHz, 107.7 MHz and 107.9 MHz. While the car radio receiver  12  is shown as an FM radio receiver, it should be appreciated that the audio radio system  10  may employ other radio receivers, such as an AM receiver configured with a tuner to receive AM frequency signals, without departing from the teachings of the present invention. 
         [0021]    The car radio receiver  12  is shown having an input  16  for receiving a selected signal from switch  20 . Switch  20  has a first input for receiving a first RF signal  32  from antenna  18  and a second input for receiving a second RF signal  30  that is generally processed as the output of the auxiliary device  22 . The switch  20  is controlled in response to a switch control signal  28  received from the auxiliary device  22  to select one of RF signals  30  and  32  as the input  16  to the radio receiver  12 . When the auxiliary device  22  is to inject audio content into radio receiver  12 , switch control signal  28  causes switch  20  to switch the input  16  to receive signal  30  instead of signal  32 . 
         [0022]    The auxiliary device  22  may include any of a number of audio content sources such as a cell phone, a CD player, a satellite radio, or other devices that may be employed to inject audio content such as audio sound and/or data to the car radio receiver  12 . The auxiliary device  22  may be wired into switch  20  using conventional coaxial audio cables or other wire connections, or may employ wireless signal communication. The auxiliary device  22  may be mounted within a vehicle or may be a portable device brought on board the vehicle. The auxiliary device  22  operates as an additional source of audio content that is input to the radio receiver  12  for broadcast or display to one or more users within the vehicle. 
         [0023]    The audio radio system  10  includes an FM modulator  24  which may be separate from or integrated within the auxiliary device  22 . The FM modulator  24  receives the audio content output from the auxiliary device  22  and modulates the audio content in an FM signal, according to one embodiment. The modulator  24  outputs the modulated output signal to a replicator  26 . The replicator  26  may be a stand alone device or may be integrated with the FM modulator  24 . The replicator  26  and FM modulator  24  may be integrated together such as on an application specific integrated circuit (ASIC). The replicator  26  outputs the modulated RF signal containing the audio content to be injected at all selectable FM radio frequency selections as RF signal  30 . 
         [0024]    The FM modulator  24  and replicator  26  are further illustrated in  FIG. 3 , according to a first embodiment of the present invention. The FM modulator  24  is shown receiving a digital input signal containing the audio content from the auxiliary device  22  and providing a modulated output analog signal. The audio input signal containing audio content may be transmitted as streamed data. In this embodiment, the FM modulator  24  has a digital-to-analog (D/A) converter  36  for converting the digital input signal to an analog signal. However, it should be appreciated that the FM modulator  24  may alternatively receive an analog input signal and provide a modulated analog output signal, without requiring use of the digital-to-analog converter  36 . Additionally, it should be appreciated that the FM modulator  24  may receive either an analog or digital audio input signal and provide a digital output signal according to other embodiments. 
         [0025]    The analog output signal from FM modulator  24  is input to a pulse train switch  40  which also receives a pulse train signal from a pulse train generator  38 . The pulse train generator  38  generates a periodic signal pulsed at a frequency of approximately 200 kHz, according to one example. The pulsed signal closes the switch  40  to ground out the analog input signal at a periodic rate of 200 kHz. The pulse train switch  40  essentially inserts grounded signals or zeros into the analog input signal. This in effect creates a broad spectrum due to harmonics. The pulse train switched output of switch  40  is amplified by an amplifier  42 . The amplified signal is then filtered by bandpass filter  46  having a pass band in the FM radio frequency band of about 88 to 108 MHz. 
         [0026]    The filtered and amplified modulated FM signal is output as the RF signal  30 . The output RF signal  30  provides the audio content at all FM radio frequencies W C  as an input to switch  20  which, when switched by auxiliary device  22 , is input to the car radio receiver  12 . In effect, the output RF signal  30  provides the audio content centered at all possible FM frequency slots (selections) such that the FM radio receiver  12  receives and processes the output RF signal  30  and its audio content no matter what frequency selection the tuner  14  is set at. 
         [0027]    The FM modulator  24  and replicator  26  may be implemented on an ASIC  50  as shown in  FIG. 4  according to a second embodiment of the present invention. According to this embodiment, the audio input signal is input to a baseband FM modulator  24 . The FM modulator  24  generates a baseband (low frequency) RF FM signal. The output of the FM modulator  24  is transformed from a time domain signal to a frequency domain signal by performing a fast Fourier transform (FFT)  52 . In the frequency domain, the output of the fast Fourier transform  52  is replicated by a replicate frequency generator  54  which essentially copies the modulated RF signal at each incremental frequency slot of 200 kHz throughout the FM radio frequency bandwidth. The replicated RF signal in the frequency domain is then converted back to the time domain with an inverse fast Fourier transform (IFFT)  56 . The replicated RF signal in the time domain is then converted to an analog RF signal with a digital-to-analog (D/A) converter  58 . The analog RF output signal of the D/A converter  58  is then up mixed by up mixer  60  and amplified by amplifier  62 . The amplified RF signal is filtered by bandpass filter  64  to pass the FM frequency band and outputs the output RF signal  30  centered at all FM frequency selections (e.g., 88.1 MHz, 88.3 MHz, 88.5 MHz, 88.7 MHz, etc.) as discussed above. 
         [0028]    The magnitude of each FM signal slot can be individually controlled, if desired. In one embodiment, the data can be upsampled by zero insertion, which is equivalent to mixing with an impulse train. The impulse train may be considered the simplest signal with the desired spectral properties. This can be implemented in the D/A converter  58  using short return to zero pulses. More general mixing signals can be used, but the more enhanced speed may require a digital signal processor (DSP) or other ASIC. 
         [0029]    Referring to  FIG. 5 , one example of the FM time signal  70  is illustrated without the pulse train switching which essentially is the output of the FM modulator  24 . The modulated signal  70  has a sinusoidal waveform and an FM signal amplitude from −1.0 to +1.0 v. In  FIG. 6 , the output of the FM modulator  24  is shown transformed to the frequency domain having signal  72  without the pulse train switching. In effect, this would be equivalent to the output of the fast Fourier transform  52  in  FIG. 4 . 
         [0030]    In  FIG. 7 , the FM time signal  74  is illustrated with the pulse train switching applied. This is equivalent to the time domain signal that is input to the amplifier  42  in  FIG. 3  after the pulse train switching. Referring to  FIG. 8 , the replicated FM signal in the frequency domain is illustrated having signal spikes  74  at 200 kHz increments. The spikes  76  are essentially mirrored about the low points between signal peaks which essentially is the output of switch  40 . According to the second embodiment, the waveform shown in  FIG. 8  would be the identical peak signal  76  at 200 kHz increments in that the waveform is copied at every 200 kHz increment by the replicate frequency generator  54 . 
         [0031]    Referring to  FIG. 9 , the theoretical 20 MHz frequency index is shown for the entire FM frequency band with the pulse train switching providing a plurality of peak signals  76  within the 20 MHz FM radio frequency bandwidth  78  ranging from about 88 MHz to 108 MHz. As seen, the resulting waveform provides the broadcast of audio content at each selectable FM frequency selection within the entire bandwidth  78  ranging from about 88 MHz to 108 MHz such that the radio receiver acquires the injected audio content from the auxiliary device and is able to process and play the audio content without requiring user intervention to select a frequency. 
         [0032]    Accordingly, the audio radio system  10  and method advantageously provide for the injection of audio content from an auxiliary device  22  into a radio receiver  12  in a manner that does not require user intervention to select the radio frequency and is easy to use. 
         [0033]    It will be understood by those who practice the invention and those skilled in the art, that various modifications and improvements may be made to the invention without departing from the spirit of the disclosed concept. The scope of protection afforded is to be determined by the claims and by the breadth of interpretation allowed by law.