Abstract:
A receiving system for audio processing includes a first demodulation unit and a second demodulation unit. The first demodulation unit is utilized for receiving an audio signal and generating a first demodulated audio signal. The second demodulation unit is utilized for selectively receiving the audio signal or the first demodulated audio signal according to a setting of a television audio system which the receiving system is applied, and generating a second demodulated audio signal.

Description:
BACKGROUND 
       [0001]    The invention relates to receiving systems and methods for TV audio processing, and more particularly, to a receiving system complying with multiple audio standards and related method thereof. Audio stereo signal standards for TV broadcasts include Zweikanalton, also known as German Stereo or A2 Stereo, Near Instantaneous Companded Audio Multiplex (NICAM), and Multichannel Television Sound (MTS), which is also known at the BTSC standard. Standards such as Zweikanalton and NICAM rely on two separate FM carriers. The second FM carrier of Zweikanalton, for example, is transmitted on a frequency 242 kHz higher than the main FM carrier. It can carry either a completely separate audio program, or be used for stereo sound transmission. In the latter case, the first FM carrier carries L+R for compatibility, while the second carrier carries 2*R. The second carrier also contains a control tone to indicate whether the transmission is stereo or dual sound. Absence of this tone is interpreted as a monaural transmission. A receiver capable of receiving and processing signals of such two-carrier system has two sets of audio signal processing hardware for processing signals carried by the two carrier concurrently. 
         [0002]    The MTS signal is transmitted at a designated carrier frequency as part of the composite broadcast television video. The MTS signal comprises two or more channels, a first channel, which is the main channel formed as the sum of the left and right audio signals, and can be detected by both monophonic TV receivers and stereo receivers. A second channel is formed as the difference between the left and right audio signals, and is detectable only by stereo receivers. A SAP channel is used to provide a Supplemental Audio Program (SAP) such as a second language, for example Chinese. 
         [0003]    The MTS receiver performs two steps of demodulation, first FM (frequency modulation) demodulation, follows by AM (amplitude modulation) demodulation for stereo audio input, or FM demodulation for dual audio input. For example, an FM demodulator circuit demodulates a stereo signal and removes the FM carrier to output a composite audio signal. The composite audio signal is then coupled to a signal processing circuit that separates the various audio channels with AM demodulation. Corresponding audio signals L and R can thus be output for reproduction by the television speakers. 
         [0004]    Vendors can hold the edge over their rivals if a solution complying with different audio standards is provided. An instinct way to satisfy different TV audio standards, say MTS and Zweikanalton, is to equip receivers with parallel audio signal processing hardware. When receiving audio channels from a Zweikanalton system, the receiver demodulates signals carried by two carriers with two audio signal processing hardware concurrently, and when receiving audio channels from a MTS system, only one signal processing hardware is occupied. 
         [0005]    Please refer to the receiving system illustrated in  FIG. 1 , which is capable of receiving audio channels from a Zweikanalton system or a MTS system. The two sets of audio signal processing hardware of the receiving system in  FIG. 1  operate to process audio signals carried by two carriers concurrently if it is working with the NICAM system. One of the signal processing hardware is unused if the receiving system is working with the MTS system. 
       SUMMARY  
       [0006]    According to one embodiment of the present invention, a receiving system for audio processing includes a first demodulation unit and a second demodulation unit. The first demodulation unit is utilized for receiving a modulated audio signal and generating a first demodulated audio signal. The second demodulation unit is utilized for selectively receiving the modulated audio signal or the first demodulated audio signal according to a setting of a television audio system which the receiving system is applied, and generating a second demodulated audio signal. 
         [0007]    According to another embodiment of the present invention, a receiving method for audio processing comprises: receiving an audio signal and generating a first demodulated audio signal; and selectively receiving the audio signal or the first demodulated audio signal according to a setting of a television audio system, and generating a second demodulated audio signal. 
         [0008]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a related art receiving system capable of receiving audio channels from a Zweikanalton system and a MTS system. 
           [0010]      FIG. 2  is a diagram illustrating a receiving system capable of receiving audio channels from the Zweikanalton system and the MTS system according to a first embodiment of the present invention. 
           [0011]      FIG. 3  is a diagram illustrating a receiving system capable of receiving audio channels from the Zweikanalton system and the MTS system according to a second embodiment of the present invention. 
           [0012]      FIG. 4  is a diagram illustrating a receiving system capable of receiving audio channels from the Zweikanalton system and the MTS system according to a third embodiment of the present invention. 
           [0013]      FIG. 5  illustrates a hardware configuration of the FIR filters shown in  FIG. 4  and related circuits. 
       
    
    
     DETAILED DESCRIPTION  
       [0014]    Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ” The terms “couple” and “couples” are intended to mean either an indirect or a direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
         [0015]      FIG. 2  is a diagram illustrating a receiving system  200  capable of receiving audio channels from the Zweikanalton system and the MTS system according to a first embodiment of the present invention. As shown in  FIG. 2 , the receiving system  200  includes an analog-to-digital converter  210 , a first demodulation unit  220 , a second demodulation unit  230 , a base-band processing unit  240 , and a multiplexer  250 . The first demodulation unit  220  includes a quadrature mix  222 , a filter  224 , a down sample rate converter  226 , and a buffer  228 . The second demodulation unit  230  includes a quadrature mix  232 , a filter  234 , a down sample rate converter  236 , and a buffer  238 . 
         [0016]    When the receiving system  200  is set to receive audio signals from the Zweikanalton system, the audio signal generated from the analog-to-digital converter  210  is inputted into the first and second demodulation units  220  and  230 , and the first and second demodulation units  220  and  230  respectively demodulate audio signals carried by two carriers concurrently. On the other hand, when the receiving system  200  is set to receive audio signals from the MTS system, the audio signal from the analog-to-digital converter  210  is only inputted into the first demodulation unit  220  to be performed FM demodulation. The first demodulation unit  220  demodulates the audio signal and removes the FM carrier to output a FM-demodulated or a partially demodulated audio signal. Then, the FM-demodulated or the partially demodulated audio signal is inputted into the base-band processing unit  240  and the second demodulation unit  230 . The second demodulation unit  230  performs AM demodulation on the FM-demodulated audio signal to output an AM-demodulated audio signal. Finally, the base-band processing unit  240  synchronizes the FM-demodulated audio signal and the AM-demodulated audio signal, and output these two demodulated audio signals for further operations. 
         [0017]    In the detail operations of the first demodulation unit  220 , the audio signal is performed quadrature mixing operation by the quadrature mix  222 , and then being filtered out frequency component at double carrier frequency by the filter  224 . After that, the down sample rate converter  226  converts a sample rate of a filtered audio signal from the filter  224 . Then a converted audio signal from the down sample rate converter  226  is stored into the buffer  228 . Additionally, the operations of the quadrature mix  232 , the filter  234 , the down sample rate converter  236  and the buffer  238  in the second demodulation unit  230  are respectively the same as corresponding components in the first demodulation unit  220 . Therefore, further description is omitted here. 
         [0018]    It is noted that, in the above description, the first and second demodulation units  220  and  230  respectively perform FM demodulation and AM demodulation. However, when the audio signal in the MTS system is modulated by two FM modulations, the second demodulation unit  230  performs another FM demodulation on the FM-demodulated audio signal generated from the first demodulation unit  220 . 
         [0019]    In addition, the base-band processing unit  240  can be implemented by hardware, software, or the combination. Besides, in the receiving system  200 , the base-band processing unit  240 , the down sample rate converters  226  and  236 , and the buffers  228  and  238  are optional devices. That is, in other embodiments of the present invention, the receiving system can function well without these optional devices. 
         [0020]      FIG. 3  is a diagram illustrating a receiving system  300  capable of receiving audio channels from the Zweikanalton system and the MTS system according to a second embodiment of the present invention. As shown in  FIG. 3 , the receiving system  300  includes an analog-to-digital converter  310 , a first demodulation unit  320 , a second demodulation unit  330 , a DSP (digital signal processing) processor  340 , a multiplexer  350 , and a storage device  360 . The first demodulation unit  320  includes a quadrature mix  322 , a filter  324 , a down sample rate converter  326 , and a buffer  328 . The second demodulation unit  330  includes a quadrature mix  332 , a filter  334 , a down sample rate converter  336 , and a buffer  338 . 
         [0021]    When the receiving system  300  is set to receive audio channels from the Zweikanalton system, the audio signal generated from the analog-to-digital converter  310  is inputted into the first and second demodulation units  320  and  330 , and the first and second demodulation units  320  and  330  respectively demodulate audio signals carried by two carriers concurrently. On the other hand, when the receiving system  300  is set to receive audio channels from the MTS system, the audio signal from the analog-to-digital converter  310  is only inputted into the first demodulation unit  320  to be performed FM demodulation. The first demodulation unit  320  performs FM demodulation on the audio signal to output a FM-demodulated or a partially demodulated audio signal. Then the FM-demodulated or the partially demodulated audio signal is processed by the DSP processor  340 , and a processed audio signal from the DSP processor  340  is stored into the storage device  360 . After that, the processed audio signal is inputted into the second demodulation unit  330  to be performed AM demodulation or another FM demodulation, and the second demodulation unit  330  outputs an AM-demodulated audio signal (or another FM-demodulated signal) to the DSP processor  340 . Finally, the DSP processor  340  synchronizes the FM-demodulated audio signal and the AM-demodulated audio signal, and output these two demodulated audio signals for further operations. In addition, the detailed operations in the first and second demodulation unit  320  and  330  are respectively the same as the first and second demodulation unit  220  and  230  shown in  FIG. 2 . Therefore, further descriptions are omitted here. 
         [0022]    It is noted that, in the receiving system  300 , the storage device  360  is an optional device. That is, the storage device  360  can be removed without influencing the functions of the receiving system  300 . Besides, the buffer  328  or the buffer  338  can be served as the storage device  360 , for storing the processed audio signal from the DSP processor  340 . 
         [0023]    It is noted that, in the receiving system  300 , the down sample rate converters  326  and  336 , and the buffers  328  and  338  are optional devices. That is, in other embodiments of the present invention, the receiving system  300  can function well without these optional devices. 
         [0024]      FIG. 4  is a diagram illustrating a receiving system  400  capable of receiving audio channels from the Zweikanalton system and the MTS system according to a third embodiment of the present invention. As shown in  FIG. 4 , the receiving system  400  includes an analog-to-digital converter  410 , a first demodulation unit  420 , a second demodulation unit  430 , a timing recovery  429 , and a DSP processor  440 . The first demodulation unit  420  includes a quadrature mix  422 , a CIC (cascaded integrator-comb) filter  423 , two FIR (finite impulse response) filters  424 , two down sample rate converters  426 , and a buffer  428 . The second demodulation unit  430  includes a quadrature mix  432 , a CIC filter  433 , two FIR filters  434 , two down sample rate converter  436 , and a buffer  438 . 
         [0025]    When the receiving system  400  is set to receive audio channels from the Zweikanalton system, the audio signal generated from the analog-to-digital converter  410  is inputted into the first and second demodulation units  420  and  430 , and the first and second demodulation units  420  and  430  respectively demodulate audio signals carried by two carriers concurrently. On the other hand, when the receiving system  400  is set to receive audio channels from the MTS system, the audio signal from the analog-to-digital converter  410  is only inputted into the first demodulation unit  420  to be performed FM demodulation. The first demodulation unit  420  performs FM demodulation on the audio signal to output a FM-demodulated or partially demodulated audio signal. Then the FM-demodulated or partially demodulated audio signal is processed by the DSP processor  440 , and a processed audio signal from the DSP processor  440  is stored into the buffer  438 . After that, the processed audio signal is inputted into the FIR filters  434  to filter out frequency components at double carrier frequency and to be performed AM demodulation or another FM demodulation. Additionally, the operations of the second demodulation unit  430  is similar to the operations of the second demodulation unit  330  shown in  FIG. 3 , therefore, the operations of the quadrature mix  432 , the CIC filter  433  and the down sample rate converters  436  are omitted here. Besides, in the receiving system  400 , the FIR filters  434  generate a phase error feedback to the quadrature mix  432  for phase correction, that is, phases of two carrier signals (sin ω n  and cos ω n ) generated from the quadrature mix  432  are adjusted based on the phase error feedback from the FIR filters  434 . 
         [0026]    It is noted that, in the receiving system  400 , the down sample rate converters  426  and  436 , the buffers  428  and  438 , and the timing recovery  429  are optional devices. That is, in other embodiments of the present invention, the receiving system  300  can function well without these optional devices. 
         [0027]    Please refer to  FIG. 5 .  FIG. 5  illustrates a hardware configuration of the filters  436  and related circuits. As shown in  FIG. 5 , the processed audio signal generated from the DSP processor  440  is respectively multiplied by the carrier signals sin ω n  and the cos ω n  generated from the quadrature mix  432  by the multipliers  502  and  504 . Then the filters  436  generate two filtered audio signals according to two multiplied signal from the multiplier  502  and  504 . Then the multiplier  506  multiplies the two filtered audio signals to generate the phase error feedback. The hardware configuration shown in  FIG. 5  can accelerate the AM demodulation or another FM demodulation in MTS system. 
         [0028]    Briefly summarized, when the receiving system is designed for both the Zweikanalton system and the MTS system, the receiving system required two demodulation units for respectively demodulate two carriers concurrently in the Zweikanalton system. However, when the receiving system is set to be used in the MTS system, only one demodulation unit is required to perform two level demodulations (FM/FM or FM/AM) on the audio signal, and another demodulation unit is unused. In the present invention, the FM demodulation is processed by the first demodulation unit, and the AM demodulation (or another FM demodulation) is processed by the second demodulation unit (original unused demodulation unit). Therefore, the original unused second demodulation unit is now used to perform AM demodulation, a loading of a firmware in the receiving system is lower, and the audio signal demodulation is accelerated. 
         [0029]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.