Abstract:
Disclosed is a video display an auto-convergence error in a projection television receiver (TV) capable of preventing generation of an error when an auto-convergence is performed. The apparatus includes a screen for displaying an image signal, first to eighth sensing units having first and second optical sensors for sensing a pattern displayed on the screen, first and second amplifying units for receiving and amplifying sensed values sensed by the first to fourth sensing units and the fifth to eighth sensing units with predetermined multiple amplification factors, first and second comparators for receiving and comparing amplified values outputted from the first and second amplifying units, an inverter for inverting output values of the first and second comparators, an operation unit for AND-gating the outputs of the amplifying units and outputs of the inverter, and a microcomputer for receiving an output of the operation unit, judging a degree of convergence correction, and outputting a corresponding control signal.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to a video display appliance, and more particularly, to an apparatus for preventing an auto-convergence error in a projection television receiver (TV) which prevents generation of an error when an auto-convergence is performed.  
         [0003]     2. Description of the Related Art  
         [0004]     Generally, diverse types of video display appliances including a small-sized analog television receiver (TV) to a large-sized projection TV of more than 60 inches have been provided to consumers.  
         [0005]     A conventional apparatus for transmitting/receiving digital video data, as shown in  FIG. 1 , includes a transmitter part  100  which includes a video processor  102  and a digital-to-analog (DA) converter  104 , and a receiver part  106  which includes an analog-to-digital (AD) converter  108  and a video processor  110 .  
         [0006]     A projection TV is an appliance which displays an image on a screen by projecting R, G, B colors on the screen using R, G, B Braun tubes, and its sensitivity items are W/U (White Uniformity), B/U (Bright Uniformity), convergence, focus, distortion, etc.  
         [0007]     The convergence is to gather R (Red), G (Green), B (Blue) beams emitted from electron guns onto one spot on a screen by a magnetic field of a deflection yoke. If the electron beams are not properly deflected due to an abnormal operation of the deflection yoke or an influence of a magnetic field, a mis-convergence is generated, which deteriorates the color balance. That is, if the convergence is normally performed and the R, G, B beams accurately converge on a spot, an image of a white color is displayed. If a mis-convergence is generated, lines having colors of R, G, B may appear near by the image of the white color, and this deteriorates the picture quality.  
         [0008]     Accordingly, in order to clearly display the image of the white color, the R, G, B beams should be gathered onto one spot, which is called an auto-convergence.  
         [0009]     According to this auto-convergence, a specific pattern is produced on the screen, the degree of mis-convergence is detected using an optical sensor, and this mis-convergence is collected.  
         [0010]     Hereinafter, a conventional convergence control apparatus for a projection TV will be explained with reference to the accompanying drawings.  
         [0011]      FIG. 1  is a block diagram illustrating the construction of a conventional convergence control apparatus in a projection TV.  FIG. 2  is a view showing a sensing method for an optical sensor according to the movement of a measurement pattern, and  FIG. 3  is a waveform diagram illustrating an output waveform of an optical sensor according to the movement of the measurement pattern.  
         [0012]     The conventional convergence control apparatus in a projection TV, as shown in  FIG. 1 , includes a screen  10  for displaying an image signal, first to eighth sensing units  11  to  18  mounted in a specified area of the screen  10 , an amplifying unit  20  for receiving and amplifying sensed values outputted from the first to eighth sensing units  11  to  18  with a predetermined amplification factor, a comparing unit  30  for receiving amplified values outputted from the amplifying unit  20  through inverting (−) terminals and non-inverting (+) terminals and comparing the inputted amplified values, an inverter  40  for inverting the output value of the comparing unit  30 , a D-type flip-flop  50  for latching an output value of the inverter  40 , and a microcomputer  60  for receiving data through the D-type flip-flop  50  and outputting a control signal for a convergence control.  
         [0013]     The first, third, fifth and seventh sensing units  11 ,  13 ,  15  and  17  among the first to eighth sensing units are positioned in the middle parts of borders of the screen  10 , and the second, fourth, sixth and eighth sensing units are positioned at the corners of the screen  10 , respectively. Also, the sensing units  11  to  18  are classified into a first group composed of the first to fourth sensing units  11  to  14  and a second group composed of the fifth to eighth sensing units  15  to  18 , and each of the first to eighth sensing units  11  to  18  includes first and second optical sensors A and B as shown in  FIG. 2 .  
         [0014]     The amplifying unit  20  includes a first amplifying unit  21  for receiving and amplifying the sensed values outputted through the first optical sensors A and the second optical sensors B of the first to fourth sensing units  11  to  14 , and a second amplifying unit  22  for receiving and amplifying the sensed values outputted through the first optical sensors A and the second optical sensors B of the fifth to eighth sensing units  15  to  18 .  
         [0015]     Here, the first amplifying unit  21  includes a first amplifier  21   a  for receiving and amplifying values sensed through the first optical sensors A of the first to fourth sensing units  11  to  14 , and a second amplifier  21   b  for receiving and amplifying values sensed through the second optical sensors B of the first to fourth sensing units  11  to  14 . The second amplifying unit  22  includes a third amplifier  22   a  for receiving and amplifying values sensed through the first optical sensors A of the fifth to eighth sensing units  15  to  18 , and a fourth amplifier  22   b  for receiving and amplifying values sensed through the second optical sensors B of the fifth to eighth sensing units  15  to  18 .  
         [0016]     The comparing unit  30  includes a first comparator  31  for receiving and comparing output values of the first and second amplifiers  21   a  and  21   b,  and a second comparator  32  for receiving and comparing output values of the third and fourth amplifiers  22   a  and  22   b.    
         [0017]     The operation of the conventional convergence control apparatus for a projection TV will now be explained.  
         [0018]     If an auto-convergence control mode is selected, the position of a pattern is sensed through the first to eighth sensing units  11  to  18 . The sensed values outputted through the first optical sensors A of the first to eighth sensing units  11  to  18  are inputted to the second and fourth amplifiers  21   b  and  22   b,  and the sensed values outputted through the second optical sensors B of the first to eighth sensing units  11  to  18  are inputted to the first and third amplifiers  21   a  and  22  the amplification factor of which is twice the amplification factor of the second and fourth amplifiers  21   b  and  22   b.    
         [0019]     The amplified value b 1  outputted through the first amplifier  21   a  is inputted to the inverting (−) terminal of the first comparator  31 , and the amplified value al outputted through the second amplifier  21   b  is inputted to the non-inverting (+) terminal of the first comparator  31 , so that a compared value c 1  is outputted from the first comparator  31 . Also, the amplified value b 2  outputted through the third amplifier  22   a  is inputted to the inverting (−) terminal of the second comparator  32 , and the amplified value a 2  outputted through the fourth amplifier  22   b  is inputted to the non-inverting (+) terminal of the second comparator  32 , so that a compared value c 2  is outputted from the second comparator  31 .  
         [0020]     The output values of the first and second comparators  31  and  32  are AND-gated, and then inputted to the inverter  40 . The inverted value outputted through the inverter  40  is latched in the D-type flip-flop  50 , and then inputted to the microcomputer  60 .  
         [0021]     Here, the sensing method according to the movement of the measurement pattern performed through the first to eighth sensing units  11  and  18  will be explained with reference to  FIGS. 2 and 3 .  
         [0022]     If the pattern moves downwards in the case that the measurement pattern is red (or green or blue), the third sensing unit  13  performs the sensing process. As shown in  FIG. 2 , when the pattern is at a first sensing point t 1 , the pattern falls on neither of the first and second optical sensors A and B, and no light is sensed by both the first and second optical sensors A and B. In this case, low-level signals are applied to the first and second amplifiers  21   a  and  21   b,  and this causes low-level signals to be outputted from the first and second amplifiers  21   a  and  12   b  as shown in  FIG. 3 .  
         [0023]     The low-level signals outputted from the first and second amplifiers  21   a  and  21   b  are inputted to the non-inverting (+) terminal and the inverting (−) terminal of the first comparator  31 , and the first comparator  31  outputs a high-level signal. This is because several pull-up resistors are connected to the non-inverting (+) terminal of the first comparator  31 .  
         [0024]     Also, as shown in  FIG. 2 , if the pattern moves further and reaches a second sensing point t 2 , ½ of the pattern falls on the first optical sensor A, but no pattern falls on the second optical sensor B and no light is sensed by the second optical sensor B. In this case, the output value of the second amplifier  21   b  is larger than the output value of the first amplifier  21   a,  and thus the first comparator  31  continuously outputs a high-level signal.  
         [0025]     If the pattern moves further and reaches a third sensing point t 3 , the pattern falls on the first optical sensor A in full, but ½ of the pattern falls on the second optical sensor B. In this case, the output value of the second amplifier  21   b,  which has received the sensed value of the first optical sensor A, becomes twice the output value of the first amplifier  21   a,  which has received the sensed value of the second optical sensor B (i.e., A=2B). However, since the amplification factor of the first amplifier  21   a  is twice the amplification factor of the second amplifier  21   b,  the output value of the first amplifier  21   a  is equal to the output value of the second amplifier  21   b,  and thus the first comparator  31  outputs a low-level signal thereafter.  
         [0026]     In the same manner, the second comparator  32  outputs a low-level signal. The outputs of the first and second comparators  31  and  32  are AND-gated, and this AND-gated signal is inverted into a high-level signal through the inverter  40 . This inverted high-level signal is inputted to the D-type flip-flop  50  as its clock so that the D-type flip-flop latches data, and then inputted to the microcomputer  60 .  
         [0027]     The microcomputer  60  judges the time point where its port goes from a low level to a high level as the third set position t 3 , judges the degree of the mis-convergence by measuring the distance from the initial position of the pattern to the third set position t 3 , and outputs a corresponding collection control signal.  
         [0028]     The conventional auto-convergence error preventing apparatus in a projection TV, however, has the following problems:  
         [0029]     First, if it is assumed that the pattern falls on the second set position t 2  while the pattern is moved in order for any one of the optical sensing units mounted on the border of the screen to search for the third set position t 3 , the output of the comparator must be the high-level signal. However, if a surrounding light is inputted to other optical sensing units, the outputs of the corresponding comparators are varied, and this may cause the microcomputer to misrecognize the set position.  
         [0030]     Second, if an external light is inputted to other sensing units besides the sensing unit subject to sensing, it affects the present sensing position, and it is difficult to measure the position accurately.  
         [0031]     Third, as it is difficult to measure the position accurately, the convergence cannot be accurately controlled which deteriorates the picture quality.  
       SUMMARY OF THE INVENTION  
       [0032]     The present invention is directed to an apparatus for preventing an auto-convergence error in a projection TV that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
         [0033]     It is an object of the present invention to provide an apparatus for preventing an auto-convergence error in a projection TV which can prevent in advance a sensing error that may be generated in a conventional auto-convergence control apparatus and provide a clear image of a high picture quality.  
         [0034]     To achieve these objects and other advantages in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided an apparatus for preventing an auto-convergence error in a projection television receiver (TV) provided with a screen for displaying an image signal and first to eighth sensing units having first and second optical sensors for sensing a pattern displayed on the screen, the apparatus comprising first and second amplifying units for receiving and amplifying sensed values sensed by the first to fourth sensing units and the fifth to eighth sensing units with predetermined multiple amplification factors, first and second comparators for receiving and comparing amplified values outputted from the first and second amplifying units, an inverter for inverting output values of the first and second comparators, an operation unit for AND-gating the outputs of the amplifying units and outputs of the inverter, and a microcomputer for receiving an output of the operation unit, judging a degree of convergence correction, and outputting a corresponding control signal.  
         [0035]     Preferably, the operation unit comprises an XOR operation unit for receiving and XOR-gating signals inputted to non-inverting (+) terminals of the first and second comparators, and an AND gate for receiving and AND-gating an output of the XOR operation unit and the output of the inverter.  
         [0036]     In another aspect of the present invention, there is provided an apparatus for preventing an auto-convergence error in a projection television receiver (TV) provided with a screen for displaying an image signal and first to eighth sensing units having first and second optical sensors for sensing a pattern displayed on the screen, the apparatus comprising a first amplifying unit for receiving and amplifying sensed values outputted through first optical sensors provided in the first to fourth sensing units and sensed values outputted through second optical sensors provided in the first to fourth sensing units, a second amplifying unit for receiving and amplifying sensed values outputted through first optical sensors provided in the fifth to eighth sensing units and sensed values outputted through second optical sensors provided in the fifth to eighth sensing units, a comparing unit for receiving and comparing amplified values outputted from the first and second amplifying units, an inverter for inverting output values of the comparing unit, a first operation unit for receiving and operating output values from all output terminals of the first and second amplifying units, a second operation unit for receiving and operating output values of the first operation unit and the inverter, and a microcomputer for outputting a control signal for a convergence control in accordance with an output of the second operation unit.  
         [0037]     Preferably, the first amplifying unit comprises second, fourth, sixth and eighth amplifiers for receiving and amplifying the sensed values outputted through the first optical sensors in the first to fourth sensing units, and first, third, fifth and seventh amplifiers for receiving and amplifying the sensed values outputted through the second optical sensors in the first to fourth sensing units.  
         [0038]     Preferably, the second amplifying unit comprises 10 th , 12 th , 14 th  and 16 th  amplifiers for receiving and amplifying the sensed values outputted through the first optical sensors in the fifth to eighth sensing units, and 9 th , 11 th , 13 th  and 15 th  amplifiers for receiving and amplifying the sensed values outputted through the second optical sensors in the fifth to eighth sensing units.  
         [0039]     Preferably, the first operation unit receives and XOR-gates all the output values of the first and second amplifying units.  
         [0040]     Preferably, the second operation unit comprises an AND gate for receiving and AND-gating the output values of the first operation unit and the inverter, and a D-type flip-flop for receiving an output of the AND gate, as its clock signal, and latching data.  
         [0041]     In still another aspect of the present invention, there is provided an apparatus for preventing an auto-convergence error in a projection television receiver (TV) provided with a screen for displaying an image signal and first to eighth sensing units having first and second optical sensors for sensing a pattern displayed on the screen, the apparatus comprising a first amplifying unit for receiving and amplifying sensed values outputted through first optical sensors provided in the first to fourth sensing units and sensed values outputted through second optical sensors provided in the first to fourth sensing units, a second amplifying unit for receiving and amplifying sensed values outputted through first optical sensors provided in the fifth to eighth sensing units and sensed values outputted through second optical sensors provided in the fifth to eighth sensing units, first and second comparing units for receiving and comparing the sensed values of the first to eighth sensing units which are outputted from the first and second amplifying units, first and second inverter units for receiving and inverting all output values of the first and second comparing units, first and second latch units for receiving outputs of the first and second inverter units and latching data, and a microcomputer for receiving outputs of the first and second latch units and outputting a control signal for a convergence control.  
         [0042]     Preferably, the first comparing unit comprises first to fourth comparators for receiving and comparing the sensed values of the first to fourth sensing units which are amplified through the first amplifying unit, and the second comparing unit comprises fifth to eighth comparators for receiving and comparing the sensed values of the fifth to eighth sensing units which are amplified through the second amplifying unit,  
         [0043]     Preferably, the first inverter unit comprises first to fourth inverters for inverting the outputs of the first comparing unit, and the second inverter unit comprises fifth to eighth inverters for inverting the outputs of the second comparing unit.  
         [0044]     Preferably, the first latch unit comprises first to fourth D-type flip-flops for latching the output values of the first inverter unit, and the second latch unit comprises fifth to eighth D-type flip-flops for latching the output values of the second inverter unit.  
         [0045]     Preferably, the microcomputer receives all the outputs of the latch units through its different ports, and outputs the control signal for the corresponding convergence control.  
         [0046]     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0047]     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
         [0048]      FIG. 1  is a block diagram illustrating the construction of a conventional convergence control apparatus in a projection TV;  
         [0049]      FIG. 2  is a view explaining a sensing method of an optical sensor according to the movement of a measurement pattern;  
         [0050]      FIG. 3  is a waveform diagram illustrating an output waveform of an optical sensor according to the movement of the measurement pattern;  
         [0051]      FIG. 4  is a block diagram illustrating the construction of an auto-convergence error preventing apparatus in a projection TV according to the present invention;  
         [0052]      FIG. 5  is a block diagram illustrating the construction of an auto-convergence error preventing apparatus in a projection TV according to a first embodiment of the present invention; and  
         [0053]      FIG. 6  is a block diagram illustrating the construction of an auto-convergence error preventing apparatus in a projection TV according to a second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0054]     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or similar parts.  
         [0055]     Hereinafter, the construction and operation of the apparatus for preventing an auto-convergence error in a projection TV according to the present invention will be explained in detail with reference to the accompanying drawings.  
         [0056]      FIG. 4  is a block diagram illustrating the construction of an auto-convergence error preventing apparatus in a projection TV according to the present invention.  FIG. 5  is a block diagram illustrating the construction of an auto-convergence error preventing apparatus in a projection TV according to a first embodiment of the present invention, and  FIG. 6  is a block diagram illustrating the construction of an auto-convergence error preventing apparatus in a projection TV according to a second embodiment of the present invention.  
         [0057]     The auto-convergence error preventing apparatus in a projection TV according to the present invention, as shown in  FIG. 4 , includes a screen  100  for displaying an image signal, first to eighth sensing units  101  to  108 , mounted in a predetermined area of the screen  100 , for sensing a pattern displayed on the screen  100 , an amplifying unit  110  for amplifying sensed values outputted through the first to eighth sensing units  101  to  108 , a comparing unit  120  for receiving and comparing amplified values outputted from the amplifying unit  110 , a first operation unit  130  for receiving and operating the signals inputted to non-inverting terminals of the comparing unit  120 , an inverter  140  for inverting outputs of the comparing unit  120 , a second operation unit  150  for receiving and AND-gating an output of the first operation unit  130  and an output of the inverter  140 , a D-type flip-flop  160  for receiving an output of the second operation unit  150  as its clock and latching data, and a microcomputer  170  for outputting a control signal for a convergence control in accordance with the output value of the D-type flip-flop  160 .  
         [0058]     Here, each of the first to eighth sensing units  101  to  108 , as shown in  FIG. 4 , is provided with first and second optical sensors A and B mounted on different positions. Also, the first to eighth sensing units  101  to  108  are classified into a first group composed of the first to fourth sensing units  101  to  104  and a second group composed of the fifth to eighth sensing units  105  to  108 .  
         [0059]     The amplifying unit  110  includes a first amplifying unit  111  for receiving and amplifying the sensed values outputted through the first and second optical sensors A and B of the first to fourth sensing units  110  to  104 , and a second amplifying unit  112  for receiving and amplifying the sensed values outputted through the first and second optical sensors A and B of the fifth to eighth sensing units  105  to  108 .  
         [0060]     The first amplifying unit  111  includes a first amplifier  111   a  for receiving and amplifying the sensed values outputted through the second optical sensors B of the first to fourth sensing units  101  to  104 , and a second amplifier  112   b  for receiving and amplifying the sensed values outputted through the first optical sensors A of the first to fourth sensing units  101  to  104 .  
         [0061]     The second amplifying unit  1   12  includes a third amplifier  112   a  for receiving and amplifying the sensed values outputted through the second optical sensors B of the fifth to eighth sensing units  105  to  108 , and a fourth amplifier  112   b  for receiving and amplifying the sensed values outputted through the first optical sensors A of the fifth to eighth sensing units  105  to  188 .  
         [0062]     The comparing unit  120  includes a first comparator  121  for receiving and comparing output values of the first and second amplifiers  111   a  and  112   b,  and a second comparator  32  for receiving and comparing output values of the third and fourth amplifiers  112   a  and  112   b.    
         [0063]     The operation of the auto-convergence error preventing apparatus in a projection TV according to the present invention will now be explained with reference to the sensing method using the first and second optical sensors according to the movement of the pattern as illustrated in  FIG. 2 .  
         [0064]     As shown in  FIG. 2 , if it is assumed that the pattern falls on the second set position t 2  while the pattern is moved in order to search for the third set position t 3  preset through the third sensing unit  103 , the output of the fourth amplifier  112   b  is higher than the output of the third amplifier  112   a  even if an external light is inputted to the eighth sensing unit  108 , and thus the second comparator  122  outputs a high-level signal. At this time, the output of the first amplifier  111   a  is equal to the output of the second amplifier  111   b,  and the first comparator  121  outputs a low-level signal.  
         [0065]     Accordingly, the inverter  140  receives and inverts the low-level signal, which is a result of AND-gating the outputs of the first and second comparators  121  and  122 , into a high-level signal, and the first operation unit  130  receives and XOR-gates the output value of the second amplifier  111   b  of the first amplifying unit  111  and the output value of the fourth amplifier  112   b  of the second amplifying unit  112 .  
         [0066]     At this time, the results of the XOR-gating are shown in Table 1 below.  
                                     TABLE 1                                       XOR Truth Table                Input   Output                       00   0           01   1           10   1           11   0                      
 
         [0067]     If the inputs of the first operation unit  130  are identical with each other, a low-level signal is outputted from the first operation unit  130 , while if the inputs are different from each other, a high-level signal is outputted from the first operation unit  130 .  
         [0068]     Accordingly, the first operation unit  130 , which has received high-level signals outputted from the second amplifier  111   b  and the fourth amplifier  112   b,  outputs a low-level signal, and the second operation unit  150  AND-gates the low-level signal from the first operation unit  130  and the high-level signal outputted from the inverter  140  to output a low-level signal to the D-type flip-flop  160 .  
         [0069]     Consequently, the microcomputer  170  cannot receive the information as described above. Accordingly, even if an external light is inputted to other sensing units besides the sensing unit subject to sensing, the error generation is prevented in advance, and thus more accurate convergence control can be made.  
       First Embodiment  
       [0070]     The auto-convergence error preventing apparatus in a projection TV according to the first embodiment of the present invention, as shown in  FIG. 5 , includes a screen  200  for displaying an image signal, first to eighth sensing units  201  to  208 , mounted in a predetermined area of the screen  200 , for sensing a pattern displayed on the screen  200 , an amplifying unit  210  for amplifying sensed values outputted through the first to eighth sensing units  201  to  208 , a comparing unit  220  for receiving and comparing amplified values outputted from the amplifying unit  210 , a first operation unit  231  for receiving and AND-gating all output values of the comparing unit  220 , a second operation unit  230  for receiving and operating the signals inputted to non-inverting terminals of the comparing unit  210 , an inverter  240  for inverting outputs of the comparing unit  220 , a third operation unit  250  for receiving and AND-gating an output of the second operation unit  230  and an output of the inverter  240 , a D-type flip-flop  260  for receiving an output of the third operation unit  250  as its clock input and latching data, and a microcomputer  270  for outputting a control signal for a convergence control in accordance with an output value of the D-type flip-flop  260 .  
         [0071]     Here, the amplifying unit  210  includes a first amplifying unit  211  for receiving and amplifying sensed values outputted through first optical sensors A provided in the first to fourth sensing units  201  to  204  and sensed values outputted through second optical sensors B provided in the first to fourth sensing units  201  to  204 , and a second amplifying unit  212  for receiving and amplifying sensed values outputted through first optical sensors A provided in the fifth to eighth sensing units  205  to  208  and sensed values outputted through second optical sensors B provided in the fifth to eighth sensing units  205  to  208 .  
         [0072]     The first amplifying unit  211  includes second, fourth, sixth and eighth amplifiers  211   b,    211   d,    211   f  and  211   h  for receiving and amplifying the sensed values outputted through the first optical sensors A provided in the first to fourth sensing units  201  to  204 , and first, third, fifth and seventh amplifiers  211   a,    211   c,    211   e  and  211   g  for receiving and amplifying the sensed values outputted through the second optical sensors B provided in the first to fourth sensing units  201  to  204 .  
         [0073]     The second amplifying unit  212  includes 10 th , 12 th , 14 th  and 16 th  amplifiers  212   b,    212   d,    212   f  and  212   h  for receiving and amplifying the sensed values outputted through the first optical sensors A provided in the fifth to eighth sensing units  205  to  208 , and 9 th , 11 th , 14 th  and 15 th  amplifiers  212   a,    212   c,    212   e  and  212   g  for receiving and amplifying the sensed values outputted through the second optical sensors B provided in the fifth to eighth sensing units  205  to  208 .  
         [0074]     The comparing unit  220  includes a first comparing unit  221  for comparing output values of the first amplifying unit  211 , and a second comparing unit  222  for comparing output values of the second amplifying unit  212 .  
         [0075]     The first comparing unit  221  includes a first comparator  221   a  for receiving and comparing output values of the first and second amplifiers  211   a  and  211   b,  a second comparator  221   b  for receiving and outputting values of the third and fourth amplifiers  211   c  and  211   d,  a third comparator  221   c  for receiving and comparing output values of the fourth and sixth amplifiers  211   e  and  211   f,  and a fourth comparator  221   d  for receiving and comparing output values of the seventh and eighth amplifiers  211   g  and  211   h.    
         [0076]     The second comparing units  222  includes a fifth comparator  222   a  for receiving and comparing output values of the 9 th  and 10 th  amplifiers  212   a  and  212   b,  a sixth comparator  222   b  for receiving and outputting values of the 11 th  and 12 th  amplifiers  212   c  and  212   d,  a seventh comparator  222   c  for receiving and comparing output values of the 13 th  and 14 th  amplifiers  212   e  and  212   f,  and an eighth comparator  222   d  for receiving and comparing output values of the 15 th  and 16 th  amplifiers  212   g  and  212   h.    
         [0077]     Also, the first operation unit  231  receives and AND-gates all outputs of the comparing unit  220 , and the second operation unit  230  receives and XOR-gates all outputs of the first to eighth comparators  221   a  to  221   d  and  222   a  to  222   d.  The inverter  240  receives and inverts an AND-gated output value outputted from the second operation unit  230 , and the third operation unit  250  receives and AND-gates an output of the second operation unit  230  and an output of the inverter.  
         [0078]     As described above, in the first embodiment of the present invention, the first to eighth comparators  221   a  to  221   d  and  222   a  to  222   d  are connected to the first to eighth sensing units  201  and  208 , respectively, and the second operation unit  230  receives and XOR-gates the signals inputted to the non-inverting (+) terminals of the first to eighth comparators  21   a  to  21   d  and  222   a  to  222   d.    
         [0079]     At this time, the operation results of the second operation unit are shown in Table 2 below.  
                                                   TABLE 2                                       Truth Values                Input   Output                            00000001   1           00000010   1           00000100   1           00001000   1           00010000   1           00100000   1           01000000   1           10000000   1           Others   0                      
 
         [0080]     As shown in Table 2, if only one of the signals inputted to the second operation unit  230  is a high-level signal, the second operation unit  230  outputs a high-level signal, while if plural signals inputted to the second operation unit  230  are high-level signals, the second operation unit  230  outputs a low-level signal.  
         [0081]     In the first embodiment of the present invention, the first to 16 th  amplifiers  21  a to  211   h  and  212   a  to  212   h  and the first to eighth comparators  221   a  to  221   d  and  222   a  to  222   d  are provided in association with the first to eighth sensing units  201  to  208 , and the second operation unit  230  XOR-gates the sensed values of the first optical sensors A of the first to eighth sensing unit  201  to  208 , which are inputted to the non-inverting terminals of the first to eighth comparators  221   a  to  221   d  and  222   a  to  222   d.  Accordingly, even if the external light is inputted to other sensing units besides the sensing unit subject to sensing, the error can be intercepted through the second operation unit  230  and the third operation unit  250 .  
       Second Embodiment  
       [0082]     The auto-convergence error preventing apparatus in a projection TV according to the second embodiment of the present invention will be explained. In explaining the second embodiment, the same reference numerals are used for the same elements in  FIG. 5 .  
         [0083]     The auto-convergence error preventing apparatus in a projection TV according to the second embodiment of the present invention, as shown in  FIG. 5 , includes a screen  200  for displaying an image signal, first to eighth sensing units  201  to  208 , mounted in a predetermined area of the screen  200 , for sensing a pattern displayed on the screen  200 , an amplifying unit  210  for amplifying sensed values outputted through the first to eighth sensing units  201  to  208 , a comparing unit  220  for receiving and comparing amplified values outputted from the amplifying unit  210 , an inverter unit  280  for inverting outputs of the comparing unit  220 , a latch unit  290  for receiving outputs of the inverter unit  280  as its clock inputs and latching data, and a microcomputer  270  for outputting a control signal for a convergence control in accordance with output values of the latch unit  290 .  
         [0084]     Here, the amplifying unit  210  includes a first amplifying unit  211  for receiving and amplifying sensed values outputted through first optical sensors A provided in the first to fourth sensing units  201  to  204  and sensed values outputted through second optical sensors B provided in the first to fourth sensing units  201  to  204 , and a second amplifying unit  212  for receiving and amplifying sensed values outputted through first optical sensors A provided in the fifth to eighth sensing units  205  to  208  and sensed values outputted through second optical sensors B provided in the fifth to eighth sensing units  205  to  208 .  
         [0085]     The first amplifying unit  211  includes second, fourth, sixth and eighth amplifiers  211   b,    211   d,    211   f  and  211   h  for receiving and amplifying the sensed values outputted through the first optical sensors A provided in the first to fourth sensing units  201  to  204 , and first, third, fifth and seventh amplifiers  211   a,    211   c,    211   e  and  211   g  for receiving and amplifying the sensed values outputted through the second optical sensors B provided in the first to fourth sensing units  201  to  204 .  
         [0086]     The second amplifying unit  212  includes 10 th , 12 th , 14 th  and 16 th  amplifiers  212   b,    212   d,    212   f  and  212   h  for receiving and amplifying the sensed values outputted through the first optical sensors A provided in the fifth to eighth sensing units  205  to  208 , and 9 th , 11 th , 13 th  and 15 th  amplifiers  212   a,    212   c,    212   e  and  212   g  for receiving and amplifying the sensed values outputted through the second optical sensors B provided in the fifth to eighth sensing units  205  to  208 .  
         [0087]     The comparing unit  220  includes a first comparing unit  221  for comparing output values of the first amplifying unit  211 , and a second comparing unit  222  for comparing output values of the second amplifying unit  212 .  
         [0088]     The first comparing unit  221  includes a first comparator  221   a  for receiving and comparing output values of the first and second amplifiers  211   a  and  211   b,  a second comparator  221   b  for receiving and outputting values of the third and fourth amplifiers  211   c  and  211   d,  a third comparator  221   c  for receiving and comparing output values of the fourth and sixth amplifiers  211   e  and  211   f,  and a fourth comparator  221   d  for receiving and comparing output values of the seventh and eighth amplifiers  211   g  and  211   h.    
         [0089]     The second comparing units  222  includes a fifth comparator  222   a  for receiving and comparing output values of the 9 th  and 10 th  amplifiers  212   a  and  212   b,  a sixth comparator  222   b  for receiving and outputting values of the 11 th  and 12 th  amplifiers  212   c  and  212   d,  a seventh comparator  222   c  for receiving and comparing output values of the 13 th  and 14 th  amplifiers  212   e  and  212   f,  and an eighth comparator  222   d  for receiving and comparing output values of the 15 th  and 16 th  amplifiers  212   g  and  212   h.    
         [0090]     The inverter unit  280  includes first to fourth inverters  281   a  to  281   d  for receiving and inverting outputs of the first to fourth comparators  221   a  to  221   b,  and fifth to eighth inverters  282   a  to  282   d  for receiving and inverting outputs of the fifth to eighth comparators  222   a  to  222   d.    
         [0091]     The latch unit  290  includes first to eighth D-type flip-flops  291   a  to  291   d  and  292   a  to  292   d  for receiving outputs of the first to eighth inverters  281   a  to  281   d  and  282   a  to  282   d  as their clock inputs, and latching data.  
         [0092]     The microcomputer  270  receives output signals of the first to eighth D-type flip-flops  291   a  to  291   d  and  292   a  to  292   d  through its different ports, and outputs the control signal for controlling the corresponding convergence.  
         [0093]     In the second embodiment of the present invention, unlike the first embodiment, the first to eighth inverters  281   a  to  281   d  and  282   a  to  282   d  and the first to eighth D-type flip-flops  291   a  to  291   d  and  292   a  to  292   d  are provided in association with the first to eighth comparators  221   a  to  221   d  and  222   a  to  222   d,  instead of the XOR operation unit and the AND gates provided in the first embodiment. Thus, the microcomputer  270  does not receive the signal through one port, but receives the signals through its first to eighth ports.  
         [0094]     Accordingly, since the microcomputer  270  recognizes in advance the sensing unit subject to sensing, it performs a convergence control only by taking the signal of the corresponding port from the signals inputted through the first to eighth ports. Thus, even if any signal is inputted through any other port due to the external light, the microcomputer  270  ignores this signal.  
         [0095]     As described above, the auto-convergence error preventing apparatus in a projection TV according to the present invention has the following effects:  
         [0096]     First, even if the sensing unit subject to sensing operates due to an external light, in detecting the degree of mis-convergence using a control pattern when the auto-convergence is performed, the sensed signal is intercepted or ignored so that the microcomputer cannot recognize the sensed signal, and thus the degree of mis-convergence can be detected more accurately.  
         [0097]     Second, by detecting the degree of mis-convergence more accurately as described above, a clear image of a high picture quality can be provided.  
         [0098]     Third, as the clear image of a high picture quality is provided, a user&#39;s satisfaction with the product and the reliability thereof can be improved.  
         [0099]     The forgoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.