Abstract:
An apparatus and method for masking interference noise contained in a signal source. According to the present invention, the apparatus comprises: a pseudo random binary sequence generator for generating a digital dither signal; a scrambler for receiving an offset signal and generating a dithered offset signal by scrambling the offset signal with the digital dither signal; a digital-to-analog converter for converting the dithered offset signal into an analog dithered offset signal; a summing device for generating a dithered image signal in response to the analog dithered offset signal and the analog image signal; and an analog-to-digital converter for converting the dithered image signal into the digital image signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the priority benefits of U.S. provisional application titled “APPARATUS AND METHOD FOR MASKING INTERFERENCE NOISE CONTAINED IN SIGNAL SOURCE” filed on Sep. 24, 2002, Ser. No. 60/412,792. All disclosure of this application is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to signal processing technology. More particularly, the present invention relates to an apparatus and method for masking interference noise contained in a signal source. 
   2. Description of the Prior Art 
   Currently, most personal computers utilize graphics cards that convert digital signals into RGB analog signals to be transmitted to a display device, such as a liquid crystal display (LCD), through a cable. The display device comprises an analog-to-digital converter (ADC) to convert the RGB analog signals into digital signals for displaying graphics or image. However, the RGB analog signals may suffer from interference noise, such as patterned or moving noise, which may be amplified during analog-to-digital conversion to cause “wave noise” on the display device. This may bring ripple or other visual effect to users&#39; notice and thus significantly degrade display quality. 
   SUMMARY OF THE INVENTION 
   It is therefore an objective of the present invention to provide an apparatus and method for masking interference noise in a signal source by means of dithering approach. 
   For attaining the above objective, the present invention provides an apparatus for converting an analog image signal into a digital image signal. The apparatus comprises: a pseudo random binary sequence generator for generating a digital dither signal; a digital-to-analog converter for converting the digital dither signal into an analog dither signal; a summing device for generating a dithered image signal in response to the analog dither signal and the analog image signal; and an analog-to-digital converter for converting the dithered image signal into the digital image signal. 
   In addition, the present invention provides an apparatus for converting an analog image signal into a digital image signal. The apparatus comprises: a pseudo random binary sequence generator for generating a digital dither signal; a scrambler for receiving an offset signal and generating a dithered offset signal by scrambling the offset signal with the digital dither signal; a digital-to-analog converter for converting the dithered offset signal into an analog dithered offset signal; a summing device for generating a dithered image signal in response to the analog dithered offset signal and the analog image signal; and an analog-to-digital converter for converting the dithered image signal into the digital image signal. 
   Moreover, the present invention provides a method for converting an analog image signal into a digital image signal. The method comprises the following steps of: (a) generating a digital dither signal; (b) converting the digital dither signal into an analog dither signal; (c) adding the analog image signal with the analog dither signal to generate a dithered image signal; and (d) converting the dithered image signal into the digital image signal. 
   Furthermore, the present invention provides a method for converting an analog image signal into a digital image signal. The method comprising the following steps of: (a) generating a digital dither signal; (b) scrambling an offset signal with the digital dither signal to generate a dithered offset signal; (c) converting the dithered offset signal into an analog dithered offset signal; (d) adding the analog image signal with the analog dithered offset signal to generate a dithered image signal; and (e) converting the dithered image signal into the digital image signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and form part of the specification in which like numerals designate like parts, illustrate preferred embodiments of the present invention and together with the description, serve to explain the principles of the invention. In the drawings: 
       FIG. 1  schematically depicts a block diagram of a circuit  1  in accordance with one preferred embodiment of the present invention; 
       FIG. 2  schematically depicts a block diagram of a circuit  2  in accordance with another preferred embodiment of the present invention; and 
       FIG. 3  schematically depicts a block diagram of a circuit  3  in accordance with one another preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific preferred embodiments in which the invention may be practiced. The preferred embodiments are described in sufficient detail to enable these skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims. 
   Referring to  FIG. 1 , a block diagram of a circuit  1  in accordance with one preferred embodiment of the present invention is schematically illustrated. The circuit  1  can be used in a digital display, such as a liquid display (LCD), and integrated in a display controller of the digital display, preferably. The circuit  1  is used to receive an analog image signal Vin and convert the analog image signal Vin into a digital image signal Dout through analog-to-digital conversion. It should be understood that the term “image signal” can represent any image signal, graphics signal, or video signal in the following description. 
   As shown in  FIG. 1 , the circuit  1  comprises a PRBS generator  10 , a digital-to-analog converter (DAC)  12 , a summing device  14 , and an analog-to-digital converter (ADC)  16 . The analog image signal Vin is received and processed by the circuit  1  so as to generate the digital image signal Dout. The analog image signal Vin can be provided by a computer host, a video cassette player, a VCD player, a DVD player or the like. However, the analog image signal Vin transmitted from various signal sources may suffer from interference noise, such as patterned or moving noise. The interference noise may be amplified during analog-to-digital conversion due to large quantizing gain of small noise signal. Accordingly, the digital image signal converted from the analog Dout bears the interference noise and causes wave noise on the digital display. 
   According to the present invention, the PRBS generator  10  is employed to generate a digital dither signal  11 . Therefore, the digital dither signal  11  generated by the PRBS generator  10  is provided with pseudo random binary sequence (PRBS), which are semi-random sequences in the sense that they appear random within the sequence length, fulfilling the needs of randomness, but the entire sequence repeats indefinitely. The detailed circuit of the PRBS generator can be referred to R. N. Mutagi, “Pseudo Noise Sequences for Engineers,”  Electronics  &amp;  Communication Engineering Journal , April 1996, pp. 79–87, which is incorporated herein by reference. In the application of the LCD controller, the pseudo-random sequences length is larger than the total pixel number of a image frame. 
   The DAC  12  is electrically connected to the PRBS generator  10  and the summing device  14 . The DAC  12  is used to convert the digital dither signal  11  into a random-like dither signal  13  in analog form to be received by the summing device  14 . Therefore, the analog dither signal  13  is incorporated with the analog image signal Vin at the summing device  14 . Because the digital dither signal  11  provided with semi-random characteristic, the interference noise contained in the analog image signal Vin can be masked by adding the analog dither signal  13  so as to generate a masked image signal  15  by the summing device  12 . The masked signal  15  is thereafter applied to the ADC  16  for further processing. 
   The ADC  16  receives the masked image signal  15  and converts the masked signal  15  into the corresponding digital image signal Dout. Because the interference noise has been masked by adding the analog image signal Vin with the analog dither signal  13 , the digital image signal Dout converted from the masked image signal  15  has reduced interference noise. 
   Referring to  FIG. 2 , a block diagram of a circuit  2  in accordance with another preferred embodiment of the present invention is schematically illustrated. In  FIG. 2 , the circuit  2  comprises a PRBS generator  20 , an adder  22 , an offset digital-to-analog converter (offset DAC)  25 , a summing device  27  and an analog-to-digital converter (ADC)  29 . The offset DAC  25  is preexisting in the display controller to process an offset signal OFFSET  23 . In this embodiment, the offset DAC  25  is used to process offset and dither in low cost manner. 
   The offset signal  23  is generated by a microprocessor, which is responsive to brightness adjustment made by the user. As an example, the offset signal  23  is provided with 8 bits, OFFSET[ 7 : 0 ]. The adder  22  is used to add the offset signal  23  with a digital dither signal  21  generated by the PRBS generator  20 , and generate a dithered offset signal  24 . 
   The offset DAC  25  is used to convert the dithered offset signal  24  into a random-like dithered offset signal  26  in analog form to be received by the summing device  27 . Therefore, the analog dithered offset signal  26  can be incorporated with the analog image signal Vin at the summing device  27 . Because the digital dither signal  21  provided with semi-random characteristic, the interference noise contained in the analog image signal Vin can be masked by adding the analog dithered offset signal  26  so as to generate a masked image signal  28  by the summing device  27 . The masked signal  28  is thereafter applied to the ADC  29  for further processing. 
   The ADC  29  receives the masked image signal  28  and converts the masked signal  328  into the corresponding digital image signal Dout. Because the interference noise has been masked by adding the analog image signal Vin with the analog dithered offset signal  26 , the digital image signal Dout converted from the masked image signal  28  has reduced interference noise. 
   Referring to  FIG. 3 , a block diagram of a circuit  3  in accordance with one another preferred embodiment of the present invention is schematically illustrated. In  FIG. 3 , the circuit  3  comprises a PRBS generator  30 , a scrambler  32 , an offset digital-to-analog converter (offset DAC)  36 , a summing device  38  and an analog-to-digital converter (ADC)  40 . The offset DAC  36  is preexisting in the display controller to process an offset signal OFFSET. In this embodiment, the offset DAC  36  is used to process offset and dither in low cost manner. 
   The offset signal OFFSET is generated by a microprocessor, which is responsive to brightness adjustment made by the user. As an example, the offset signal OFFSET is provided with 8 bits, OFFSET[ 7 : 0 ], wherein one LSB or two LSBs can be applied to the scrambler  32  to be scrambled with a digital dither signal  31  generated by the PRBS generator  20 . As shown in  FIG. 3 , two LSBs OFFSET[ 1 : 0 ] are employed to scramble with the digital dither signal  31  at the scrambler  32  so as to generate a dither-incorporated signal  33 , which is designated as DO[ 1 : 0 ]. The dither-incorporated signal DO[ 1 : 0 ]  33  and the OFFSET[ 7 : 2 ] are converged to form a dithered offset signal  35 , which can be designated as DO[ 7 : 0 ]. 
   The offset DAC  36  is used to convert the dithered offset signal  35  into a random-like dithered offset signal  37  in analog form to be received by the summing device  38 . Therefore, the analog dithered offset signal  37  can be incorporated with the analog image signal Vin at the summing device  38 . Because the digital dither signal  31  provided with semi-random characteristic, the interference noise contained in the analog image signal Vin can be masked by adding the analog dithered offset signal  37  so as to generate a masked image signal  39  by the summing device  38 . The masked signal  39  is thereafter applied to the ADC  40  for further processing. 
   The ADC  40  receives the masked image signal  39  and converts the masked signal  39  into the corresponding digital image signal Dout. Because the interference noise has been masked by adding the analog image signal Vin with the analog dithered offset signal  37 , the digital image signal Dout converted from the masked image signal  39  has reduced interference noise. In addition, the circuit as depicted in  FIG. 3  can solve nonlinear DAC problem by restricting PRBS effect to LSB only. 
   Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.