Patent Publication Number: US-2007121016-A1

Title: Audio/video switch circuit using and I2C bus

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an audio/video switch circuit and, more particularly, to an audio/video switch circuit using an inter integrated circuit (I 2 C) bus.  
      2. Description of Related Art  
       FIG. 1  is a functional block diagram that demonstrates the conventional method of switching multiple audio/video signals, in which the circuit comprises multiple audio/video signal sources  10 , a plurality of video switches  11 ,  12 , an audio switch  13 , a microcontroller unit (MCU)  14 , a video decoder  15  and an audio integrated circuit  16 . The video switches  11 ,  12  are electrically connected to the MCU  14 . The audio switch  13  is electrically connected to the MCU  14 , in which the video switches  11 ,  12  and the audio switch  13  are electrically connected to the input/output pins of the MCU  14 . Also, the video switches  11 ,  12  are electrically connected to the video decoder  15 , and the audio switch  13  is electrically connected to the audio integrated circuit  16 .  
      The video switches  11 ,  12  and the audio switch  13  are configured to receive multiple audio/video signal sources  10 . The MCU  14  controls the switch by both the video switches  11 ,  12  and the audio switch  13  through the input/output pins, such that the video signal that are intended to be outputted can pass through one of the video switches  11 ,  12  and be outputted to the video decoder  15  for decoding.  
      However, the above method requires several video switches  11 ,  12  and at least one audio switch  13  and that those video switches  11 ,  12  and the audio switch  13  take up too many input/output pins of the MCU  14 , thus complicating the hardware design and the layout of the circuitry.  
      Therefore, it is desirable to come up with an improved audio/video switch circuit to overcome the aforementioned problems.  
     SUMMARY OF THE INVENTION  
      One of the objectives of the present invention is to provide an audio/video switch circuit using an I 2 C bus, such that the number of input/output pins of an MCU to be used can be significantly reduced.  
      The other objective of the present invention is to provide an audio/video switch circuit using an I 2 C bus, such that the number of video switches and audio switches can be significantly reduced.  
      To achieve the objectives, the present invention provides an audio/video switch circuit controlled by an I 2 C bus. The audio/video switch circuit comprises a video decoder, an audio integrated circuit, an audio/video switch unit and an MCU. The aforementioned audio/video switch unit, which is configured to receive multiple audio/video input signals, includes a plurality of video signals and at least one audio signal and is electrically connected to the video decoder and the audio integrated circuit respectively. The MCU is electrically connected to the audio/video switch unit through an I 2 C bus, such that one of the audio/video input signals could be outputted, by switching the audio/video switch unit, to the video decoder and the audio integrated circuit.  
      Within the aforementioned audio/video switch circuit controlled by the I 2 C bus, the audio/video switch unit further comprises five input ports and two output ports. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a functional block diagram illustrating the prior art for the switch of multiple audio/video signals.  
       FIG. 2  is a functional block diagram illustrating a preferred embodiment according to the present invention.  
       FIG. 3  is a clock diagram showing an I 2 C bus basic operation. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The audio/video switch circuit using an I2C bus can be used in a digital television or any video devices.  
      The preferred embodiment of the present invention is illustrated in  FIG. 2  of a functional block diagram, in which the embodiment includes an MCU  21 , an audio/video switch unit  22 , a video decoder  23  and an audio integrated circuit  24 .  
      The MCU  21  is electrically connected to the audio/video switch unit  22  through an I2C bus  25 . The audio/video switch unit  22  is electrically connected to the video decoder  23  and the audio integrated circuit  24  respectively.  
      The audio/video switch unit  22  is configured to receive a plurality of audio/video signal sources  20 , wherein each audio/video signal  20  can include either a video signal and an audio signal concurrently, one single video signal or one single audio signal.  
      The MCU  21  controls the switch of the audio/video switch unit  22  through its connection to the input/output pins of the I 2 C bus  25 . Since the space occupied by the I 2 C bus  25  is rather small whilst the I 2 C bus  25  being able to be parallel connected to multiple controlled modules (e.g. the audio/video switch unit  22 ), the overall complication involved within the design in terms of the hardware and the circuitry layout, as well as the space occupied on the circuit board, can be significantly reduced. Besides, the MCU  21  is electrically connected to the audio/video switch unit through the I 2 C bus  25 ; therefore, the input/output pins of the MCU  21  occupied can be effectively reduced, allowing more input/output pins of the MCU  21  to become available for other uses.  
      The aforementioned I 2 C bus  25  further comprises a serial data line (SDA), which is configured to transmit address signals, and a serial clock line (SCL), which is configured to transmit control signals, for providing the switch of the audio/video switch unit  22  that is determined in accordance to the address signals and the control signals.  
       FIG. 3  is the clock diagram showing the basic operation of the I 2 C bus  25 . Referring to FIG. 2  and  FIG. 3  together, the MCU  21  uses the SCL line to control the transmitting direction of the I 2 C bus  25  and also uses the SCL line to set up both START and STOP conditions: As the voltage of the SCL sets at HIGH, if the voltage of the SDA line changes from HIGH to LOW, it indicates a START condition. As the voltage of the SCL line sets at HIGH, if, on the other hand, the voltage of SDA line changes from LOW to HIGH, then it indicates STOP condition. During the period when the voltage of the SCL line is LOW, the status of the SDA can be altered.  
      The MCU  21  of the present invention is configured to control the switch by the audio/video switch unit  22  using the I 2 C bus  25 . For further details regarding the switch by the audio/video switch unit  22 , please continue referring to  FIG. 2 .  
      In the present invention, the audio/video switch unit  22  further comprises a plurality of internal switch units  221 ,  222 ,  223 ,  224 ,  225  and  226 , wherein the internal switch units  221 ,  222 ,  223 ,  224  and  225  are configured to individually receive video signals from the audio/video signal source  20 . The internal switch unit  226  is configured to receive audio signals from the audio/video signal source  20 . In this embodiment the audio/video switch unit  22  includes a total of five input ports and two output ports, in which the first output port  227  of the audio/video switch unit  22  is electrically connected to the video decoder  23 , and the second output port  228  of the audio/video switch unit  22  is electrically connected to the audio integrated circuit. In other embodiments the number of input ports and output ports of the audio/video switch unit  22  can be adjusted according to each different demand in practice.  
      The MCU  21  can receive a remote control signal from a user, for which the MCU  21  outputs a switch signal with respect to the remote control signal. The switch signal is then sent to the audio/video switch unit  22  by the MCU  22  through the I 2 C bus  25 , such that one of the audio/video input signals is outputted, through the switching of the audio/video switch unit  22 , to the video decoder  23  and the audio integrated circuit  24  respectively.  
      Therefore, to output a video display with its corresponding sound, a remote control can be used to output a control signal that is related to the intended video display and sound to the MCU  21 , such that the desired graphics and sounds can be outputted using the MCU  21  and through the switch of the audio/video switch unit  22 , and those undesired graphics and sounds can be blocked also with the MCU  21  and through the switch of the audio/video switch unit  22 .  
      From above it is known that the present invention uses an audio/video signal unit to receive a plurality of audio/video signals. The audio/video switch unit is electrically connected to an MCU through an I 2 C bus, such that the MCU, via the I 2 C bus, can send out the switch signal to the audio/video switch unit in order to control the switch of that unit and output the desired graphics and/or sounds.  
      Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed.