Patent Publication Number: US-2007121961-A1

Title: POP noise processing circuit structure applying to panel display apparatus

Description:
FIELD OF THE INVENTION  
      The present invention relates to a POP noise processing circuit structure of an output apparatus, and in particularly, to a POP noise process circuit structure comprising a POP noise process unit in order to remove the POP noise produced from the ON-OFF mode or mute mode of the POP noise processing circuit structure.  
     BACKGROUND OF THE INVENTION  
      The liquid crystal display (LCD) flat panel display is an interesting product of the optoelectronic industry. The products related to LCD display are popular and widespread in our daily life. The LCD applications will be introduced in the near future as the coming of digital information era and familiarization of human with digital display apparatus. LCD TVs have the advantages of big size, flat panel, less occupancy, low radiation and high resolution for being the most suitable display apparatus in digital homes. However, there exists a problem of low quality of audio performance in LCD display apparatus. This problem is further described as followings.  
      In  FIG. 1 , it is a block diagram of an output apparatus in the prior art. The output apparatus  10  can be a flat panel display apparatus or an LCD TV. The output apparatus  10  comprises at least one first processing unit (First PU)  11 , one second processing unit (Second PU), one operational amplifier processing unit (OP PU)  13  and one speaker  14  wherein the first processing unit  11  provides an audio signal into the operational amplifier processing unit  13  and the audio signal is further amplified by the operational amplifier processing unit  13 ; the second processing unit  12  provides a mute sound signal into the operational amplifier processing unit  13 ; and the operational amplifier processing unit  13  transmits processed audio signal into the speaker  14 . Moreover, the first processing unit  11  can be an audio signal processing unit, and the second processing unit  12  can be a microcontroller or a video processing unit.  
      In  FIG. 2 , it is an application diagram of an output apparatus in the prior art. The output apparatus  10  can be a flat panel display apparatus or an LCD TV.  FIG. 2  further illustrates the audio signal  111  including one high voltage pulse  19 . Referring to the output apparatus  10  in  FIG. 2 , while the first processing unit  11  and second processing unit  12  are in a mute mode or shutdown mode, there is a POP noise from the speaker  14  at the time the switch  18  is in the shutdown (OFF). The transmission speed of mute signal  121  of the second processing unit  12  to the operational amplifier processing unit  13  is slower than that of the audio signal  111  of the first processing unit  11  and causes a high voltage pulse  19  of audio signal  111  directly amplified by the operational amplifier processing unit  13  in the mute mode or at the time the system is shutdown. Thus, an undesirable audio signal  131  is received and outputted by the speaker  14  deteriorating the audio quality.  
      People can only respond to the audio signal whose frequency is from 20 Hz to 20K Hz. Neither audio signal with pulse period less than 50 ms, nor audio signal with frequency larger than 20K Hz can be heard by the ears of human. If the high voltage pulse  19 , created as the first processing unit  11  in  FIG. 2  is in the mute mode or at the time of shutdown, has a frequency less than 20 Hz or larger than 20K Hz, the POP noise can be ignored by the ears of human. Limited by the properties of the first processing unit  11  in the prior art, the high voltage pulse  19 , created as the first processing unit  11  is in the mute mode or at the time of shutdown, is transmitted into the operational amplifier processing unit  13  and amplified as a POP noise sound within the frequency range noticeable to the ears of human.  
      It is an object of the present invention to provide a POP noise processing circuit structure for eliminating the POP noise of the output apparatus and having improved qualities.  
     SUMMARY OF THE INVENTION  
      The present invention provides a POP noise processing circuit structure for an output apparatus which can be a flat panel display apparatus or an LCD TV. The POP noise processing circuit structure can solve the problem of POP noise. The POP noise is an audio signal, amplified by the speaker, comprising a high voltage pulse produced by the output apparatus while the output apparatus is in the mute mode or at the time of turning off. Before the operational amplifier processing unit receives a mute signal, the high voltage pulse from the first processing unit is accepted by the operational amplifier processing unit and amplified by the speaker and causes POP noise sounds.  
      Therefore, the present invention provides a POP noise processing circuit structure not only comprising a first processing unit, a second processing unit, an operational amplifier processing unit and a speaker, but also a POP noise process unit coupling and between the second processing unit and the operational amplifier processing unit.  
      The features of the POP noise process unit can make the operational amplifier processing unit to receive the mute signal at the time earlier than that of outputting of the audio signal from the first processing unit. Thus, after receiving the mute signal at first, the undesirable audio signal from the first processing unit will be ignored by the operational amplifier processing unit. By this way, the POP noise sounds can be ignored.  
      For that reason, the POP noise process unit of the present invention manipulates the original mute signal received from the output apparatus and sends the manipulated mute signal to the operational amplifier processing unit at the time earlier than that of the arrival of the POP noise signal from the first processing unit. The operational amplifier processing unit processes the coming signals and enters the mute mode without the POP noise sounds created by the speaker in the mute mode or at the time of shutdown.  
      The features and advantages of the present invention are further disclosed and illustrated with the detail descriptions of preferred embodiments and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram of an output apparatus in the prior art;  
       FIG. 2  is an application diagram of an output apparatus in the prior art;  
       FIG. 3  is a block diagram of an output apparatus according to the present invention;  
       FIG. 4  is an application diagram of an output apparatus according to the present invention; and  
       FIG. 5  is a block diagram of a POP processing unit (POP PU) of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      In  FIG. 3 , it is a block diagram of an output apparatus according to the present invention. The output apparatus  10  can be a flat panel display apparatus or an LCD TV. Referring to  FIG. 3 , the output apparatus  10  comprises a first processing unit  11 , a second processing unit  12 , an operational amplifier processing unit  13 , a speaker  14  and a POP noise process unit (POP PU)  21  coupling and between the second processing unit  12  and the operational amplifier processing unit  13 . The POP noise process unit  21  not only integrates the signals transmitted from the second processing unit  12 , but also outputs a mute signal manipulated by the POP noise process unit  21  into the operational amplifier processing unit  13 . The first processing unit  11  transmits a signal into the operational amplifier processing unit  13  which amplifies signals received. Moreover, the first processing unit  11  can be an audio processing unit and the second processing unit  12  can be a microcontroller or a video processing unit.  
       FIG. 4  is an application diagram of an output apparatus according to the present invention. The output apparatus  10  can be a flat panel display apparatus or an LCD TV.  FIG. 4  illustrates more signals in the system described in  FIG. 3  wherein the signals comprises a system mute signal  121 , an audio testing signal  211  and a video mute control signal  212 . The first processing unit  11  can be an audio processing unit providing decode functions for external audio signals  112 . The second processing unit  12  can be a video processing unit or a microcontroller providing decode functions for external video signals  113 , too. While the first processing unit  11  and the second processing unit  12  are in the mute mode or at the time of shutdown, an audio signal  111  including a high voltage pulse  19  is produced by the first processing unit  11 . Meanwhile, the POP noise process unit  21  manipulates the system mute signal  121  from the second processing unit  12 , audio testing signal  211  and mute control signal  212  of video system, and then sends a manipulated mute signal  213  into the operational amplifier processing unit  13 . With circuit designs of the POP noise process unit  21  according to the present invention, the manipulated mute signal  213  arrives at the operational amplifier processing unit  13  earlier than the audio signal  111  from the first processing unit  11  does. Thus, the audio signal  111  from the first processing unit  11  will not be amplified by the operational amplifier processing unit  13  and not be transmitted into the speaker  14  in the form of an amplified audio signal  131 . The POP noise signal is blocked according to the present invention.  
      More detailed descriptions about the POP processing unit in  FIG. 4  of the present invention are illustrated in  FIG. 5 . A POP noise process unit  21  in the embodiment of  FIG. 5  comprises a pair of carbon film fixed resistors  311 ,  312  forming a voltage divider circuit  31 ; an OR logic gate circuit  32 ; a NAND logic gate circuit  33 ; an inverter logic gate circuit  34 ; a first supply voltage  15 ; a second supply voltage  16 ; and a common ground  17 . The voltage divider circuit  31  comprising a carbon film fixed resistor  311  and a carbon film fixed resistor  312  wherein the carbon film fixed resistor  311  connects the carbon film fixed resistor  312  with a metal material of good conductivity and the voltage divider circuit  31  is supplied with the second supply voltage  16  and grounded with the common ground  17 . A divided voltage point  161  is obtained from the voltage divider circuit  31  and then used as the supply voltage of the inverter logic gate circuit  34 .  
      In  FIG. 5 , the input terminals  321 ,  322  of the OR logic gate circuit  32  couple with the audio testing signal  211  and the mute control signal  212  of video system from the second processing unit  12 . Moreover, the output terminal  323  of the OR logic gate circuit  32  connects to the input terminal  331  of the NAND logic gate circuit  33 . The input terminal  332  of the NAND logic gate circuit  33  connects to the system mute signal  121  outputted from the second processing unit  12 . Moreover, the output terminal  333  of the NAND logic gate circuit  33  connects to the input terminal  341  of the inverter logic gate circuit  34 . Furthermore, the output terminal  342  of the inverter logic circuit  34  connects to the mute signal  213  of the operational amplifier processing unit  13 .  
      In addition,  FIG. 5  also illustrates the arrival time to the operational amplifier processing unit  13  of the mute signal  213  is earlier than that of the audio signal  19  while the output apparatus  10  is in the mute mode or at the time of shutdown. The POP noise process unit  21  utilizes that the turning off time of the second supply voltage  16  is earlier than that of the first supply voltage  15 , and the voltage divider circuit  31  of the POP noise process unit  21  couples with the second supply voltage  16  to send the mute signal at the time before the audio signal arrives the operational amplifier processing unit  13 .  
      Although the features and advantages of the embodiments according to the preferred invention are disclosed, it is not limited to the embodiments described above, but encompasses any and all modifications and changes within the spirit and scope of the following claims.