A column electrode driving circuit for a display apparatus

Abstract: An improved column electrode driving circuit can drive a matrix type display apparatus without necessitating digital signals transmitted between partial column electrode driving circuits. Each of the partial column electrode driving circuits is allocated with a number. In each of the partial column electrode driving circuits, shift register shifts a sample signal to sequentially output it from a plurality of outputs. At each time when a predetermined number of clock pulses have been counted, a count signal is produced. When the shift direction is set to the right direction, a signal indicating the allocated number is produced. When the shift direction is set to the left direction, a signal indicating a number which is obtained by subtracting the allocated number from a specified number is produced. When this number and the clock pulse count number satisfy a predetermined relationship, the sample signal is output.

Description: BACKGROUND OF THE INVENTION 1. Field of the invention: This invention relates to a column electrode driving circuit for a display apparatus, and more particularly to a column electrode driving circuit for a matrix type display apparatus. 2. Description of the prior art: As a typical example of a matrix type display device, a matrix type liquid crystal display (LCD) apparatus is shown in Figure 6. The LCD apparatus of Figure 6 comprises an LCD panel 61 having: a plurality of row electrodes 61a which are disposed on a substrate parallel to one another; and a plurality of column electrodes 61b which intersect the row electrodes 61a . A pair of a picture element (pixel) electrode 61c and a thin film transistor (TFT) 61d which functions as a switching element is disposed at each crossing of the row electrodes 61a and the column electrodes 61b . The LCD panel 61 is driven by a row electrode driving circuit 62 and column electrode driving circuit 63 . The row electrode driving circuit 62 produces scanning pulses which are in turn supplied to the row electrodes 61a to sequentially turn on each row of the switching transistors 61d . The column electrode driving circuit 63 produces voltage signals which are applied to the pixel electrodes 61c through the column electrodes 61b . A control circuit 64 controls the operations of the row electrode driving circuit 62 and the column electrode driving circuit 63 . As shown in Figure 7, the column electrode driving circuit 63 comprises a shift register circuit 71 , a sample-hold circuit 72 , and a buffer circuit 73 . The shift register circuit 71 shifts a sample signal D in accordance with clock pulses  and sequentially outputs the sample signal to lines q₁ , q₂ , ···, q n . The sample-hold circuit 72 samples and holds a video signal V in accordance with sample signals output to the lines q₁ , q₂ , ···, q n . The buffer circuit 73 simultaneously outputs the voltage signals held in the sample holding circuit 72 to the column electrodes 61b , as voltage signals Q₁ , Q₂ , ···, Q n , at the time when an output timing signal T is input. The operation of the column electrode driving circuit 63 will be described with reference to Figure 8. After the input of the sample signal D , sample signals are sequentially output to the lines q₁ , q₂ , ···, q j , ··· from the shift register circuit 71 . The sample-hold circuit 72 samples instantaneous voltages V i1 , ···, V ij , ··· of the video signal V in accordance with these sample signals. At the time when the sampling of one row has been completed, the output timing signal T is input, and the buffer circuit 73 operates. If the number of the column electrodes 61b to be driven is large, the column electrode driving circuit 63 is usually composed of a plurality of partial column electrode driving circuits 90 each corresponding to a portion of the column electrodes 61b , as shown in Figure 9. Each of the partial column electrode driving circuits 90 is integrated in one LSI chip, and provided with a shift register circuit 91 , a sample holding circuit 92 , and a buffer circuit 93 . The shift register circuit 91 , sample holding circuit 92 and buffer circuit 93 may have the same structure as the shift register circuit 71 , sample holding circuit 72 and buffer circuit 73 , respectively, except that the number of column electrodes to drive is different. It is necessary for the shift register circuits 91 in all of the partial column electrode driving circuits 90 , as a whole, to continuously perform sampling and holding operations as a single shift register circuit. Therefore the output of the final step of the shift register circuit 91 in each partial column electrode driving circuit 90 is supplied to the shift register circuit 91 in the next partial column electrode driving circuit 90 . In the above mentioned column electrode driving circuit 63 , digital signals and analog signals mixedly exist, and therefore noise from the digital signals which are mixed with the analog signal becomes a problem. When such a driving circuit is applied to a display apparatus in a small sized television display device, in addition to a direct effect via power lines and signal lines etc., high frequency noise radiated into the air is picked up by an antenna of the device, causing disturbance in the displayed image. Furthermore, at the instant when the level of the digital signals changes, currents of a comparatively large amount flow, and as a result, a linear disturbance synchronized with the change in the digital signal level is generated on the display of the display apparatus. With respect to disturbance in the image caused by a digital signal, counter measures can be considered such as that digital signals, which undergo changes in level, are used as little as possible within the column electrode drive circuit during the period when sampling is performed, or that a circuit for eliminating the high frequency components of the signal is provided in a location as close as possible to the supply terminal of the digital signal for the column electrode driving circuit. However, in such a column electrode driving circuit wherein a plurality of LSIs are connected in a cascade, the level of digital signals transmitted between the LSIs changes during the sampling operation, thereby causing the image disturbance. Furthermore, since LSIs are usually mounted in a high density, there are many cases where it is impossible to carry out effective noise countermeasures in the vicinity of the LSIs. SUMMARY OF THE INVENTION The column electrode driving circuit of this invention, as defined by claim 1, comprises: a plurality of partial column electrode driving circuits which respectively drive groups of column electrodes of said display apparatus, each partial column electrode driving circuit being allocated a number; each partial column electrode driving circuit comprising: count means for counting clock pulses, and for producing a count signal upon each count of a predetermined number of the clock pulses; sample signal output means for outputting a sample signal when a predetermined relationship is satisfied between the number of count signals produced by said count means and said allocated number; shift register means for receiving said sample signal and shifting the same to sequentially output said sample signal from a plurality of outputs; and sample-hold means for sampling and holding an input video signal in accordance with said sequentially outputted sample signal; characterised by: the direction of shift provided by said shift register means being changeable in accordance with a shift direction control signal; switch means for, when said shift direction is set to a first direction, producing a signal indicating said allocated number, and for, when said shift direction is set to a second direction which is opposite to said first direction, producing a signal indicating a number which is obtained by subtracting said allocated number from a specified number; and said sample signal output means receiving said signal output from said switch means. The features of the preamble of claim 1 are disclosed in combination in EP-A-0 319 661. The dependent claims 2 to 5 define preferred features of the invention. Thus, the invention disclosed herein makes possible the objectives of: (1) providing a column electrode driving circuit which can drive a display apparatus without impairing the display quality; (2) providing a column electrode driving circuit which can drive a display apparatus without requiring digital signals transmitted between partial column electrode driving circuits; (3) providing a column electrode driving circuit which can drive a display apparatus without producing noise caused by digital signals transmitted between partial electrode driving circuits; and (4) providing a column electrode driving circuit in which the sequence of driving column electrodes in a display apparatus can be easily reversed. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram illustrating a partial column electrode driving circuit used in a column electrode driving circuit according to the invention. Figure 2 is a block diagram illustrating the column electrode driving circuit according to the invention. Figures 3 and 4 are timing charts illustrating the operation of the column electrode driving circuit of Figure 2. Figure 5 is a circuit diagram of the partial column electrode driving circuit of Figure 1. Figures 6 to 9 relate to prior art. Figure 6 diagrammatically illustrates an LCD apparatus. Figure 7 is a block diagram illustrating a column electrode driving circuit 63 of the apparatus of Figure 6. Figure 8 is a timing chart illustrating the operation of the column electrode driving circuit of Figure 7. Figure 9 is a block diagram illustrating partial column electrode driving circuits 90 which may be used in the circuit 63 of Figure 6. DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 2 illustrates a column electrode driving circuit according to the invention. The circuit of Figure 2 can drive the LCD apparatus shown in Figure 6, and comprises four partial column electrode driving circuits 10 , each of which corresponds to k number of column electrodes in the LCD apparatus. The number of partial column electrode driving circuits 10 , and the number of column electrodes which correspond to one of the partial column electrode driving circuit 10 are not restricted to the above and can be selected arbitrarily. Each of the partial column electrode driving circuits 10 is integrated into one LSI chip, and includes a shift register circuit 11 , a sample-hold circuit 12, a buffer circuit 13 and a shift register control circuit 14. Clock pulses  and shift direction control signal R/L are commonly supplied to the shift register circuits 11 and shift register control circuits 14 in all of the partial column electrode driving circuits 10 . A start signal S is further supplied to the shift register control circuits 14 . Furthermore, a video signal V and an output timing signal T are input respectively to the sample-hold circuits 12 and buffer circuits 13 in the partial column electrode driving circuits 10 . Figure 1 shows one of the partial column electrode driving circuits 10 in more detail. The sample-hold circuit 12 and buffer circuit 13 are constructed in the same manner as those used in the prior art. The shift register circuit 11 is structured so that the shift direction reverses in response to the shift direction control signal R/L . When the shift direction control signal R/L is right (R), the shifting operation toward the right (normal shifting) is performed, and the sample signals are sequentially output from the lines q₁ , q₂ , ···, in this order. When the shift direction control signal R/L is left (L), the shifting operation toward the left (reverse shifting) is performed, and the sample signals are sequentially output from the lines q k , q k-1 , ···, in this order. In the prior art, the sample signal D which is input to the shift register circuit 11 is supplied from outside of the partial column electrode driving circuit 10 . By contrast, in this embodiment, the sample signal D is generated by the shift register control circuit 14 . The shift register control circuit 14 comprises a count circuit 15 , a timing selection circuit 16 , and a switching circuit 17 . The count circuit 15 supplies a count signal C to the timing selection circuit 16 immediately after receiving the start signal S , and every time k clock pulses  (k is the number of steps in the shift register circuit 11 ) are counted after the input of the start signal S . The switching circuit 17 supplies externally established data ℓ, when the shift direction control signal R/L is R, and data (n - 1 - ℓ ), when the shift direction control signal R/L is L, to the timing selection circuit 16 . Here, n is the total number of the partial column electrode driving circuits 10 , and in this embodiment n = 4. As shown in Figure 2, ℓ is a value assigned to each of the partial column electrode driving circuits 10 , based upon the arrangement order in which the partial column electrode driving circuits 10 are disposed. Data supplied from the switching circuit 17 to the timing selection circuit 16 is indicated by ℓ′ in Figure 1. In other words, when the shift direction control signal R/L is R, ℓ′ = ℓ , and when the shift direction control signal R/L is L, ℓ′ = (n - 1 - ℓ ). The timing selection circuit 16 outputs the sample signal D to the shift register circuit 11 when the number of count signals C which have been input is equal to ℓ′. The operation of this embodiment will be described with reference to Figure 3 which is the timing chart for a case in which the shift direction control signal R/L is R. Immediately after receiving the start signal S ((b) of Figure 3) which directs the commencement of the sampling operation, the count circuit 15 generates one count signal C ((c) of Figure 3). Following this, one count signal C is generated every time k number of clock pulses  ((a) of Figure 3) are input. The time interval t k for generating the count signal C is equal to the period of time required for shifting the sample signal D through all of the steps of the shift register circuit 11 . In (d) to (g) of Figure 3, subscripts 0 to 3 are added to the sample signal D in accordance with the values (0 to 3) of the data ℓ which are assigned to the partial column electrode driving circuits 10 , in the same way as in Figure 2. As seen from the above description, according to this embodiment, the shift register control circuit 14 can generate the sample signal D which is directed to the shift register circuit 11 within the same partial column electrode driving circuit 10 , with proper timing based upon the data ℓ. In this embodiment, the sample signals D₁ , D₂ and D₃ are generated with the same timing as the digital signals transmitted between partial column electrode driving circuits in the prior art. Therefore, the digital signals which are transmitted between the partial column electrode driving circuits in a column electrode driving circuit of the prior art are not necessary, and thus it is possible to avoid image disturbance due to noise from the digital signals. Moreover, the level of the start signal S changes outside of the sampling period, and the start signal S can be generated outside of the LSI which contains the partial column electrode driving circuit 10 . Hence, it is possible to easily add a circuit as a noise countermeasure, so that the start signal S does not become a source of image disturbance. Figure 4 illustrates the operation of this embodiment in the case where the shift direction control signal R/L is L. When R/L = L, the generation sequence of the sample signals D₀ through D₃ is opposite to that in the case where R/L = R, as is shown in (d) to (g) of Figure 4. Furthermore, although not illustrated, the direction in which the sample signal D is shifted by the shift register circuit 11 within the partial column electrode driving circuit 10 is also opposite to that in the case where R/L = R. A circuit diagram of the shift register control circuit 14 is shown in Figure 5. In the shift register control circuit 14 shown in Figure 5, the value k is set to 64 , data ℓ is expressed with two bits (ℓ₁, ℓ₀). When the shift direction control signal R/L is R, it has the value of "0", and When the shift direction control signal R/L is L, it has the value of "1". The count signal C which is generated immediately after the input of the start signal S is output from a D flip-flop 152 . A 1/64 counter 151 counts the clock pulses . When the output of the 1/64 counter 151 changes from 63 (= 111111) to 0 (=000000), the count signal C is output from an OR gate 154 as the count signal C . The count signal C which is output from the OR gate 154 is counted by a 1/4 counter 161 . When the count signal C is output from the D flip-flop 152 or the OR gate 154 , it is determined by the combination of NOR gates 162 - 165 whether or not the data ℓ′ expressed by two bits (ℓ′₁, ℓ′₀) and supplied from the switching circuit 17 coincide with the output of the 1/4 counter 161 . If yes, the sample signal D is output from an OR gate 166 . According to this invention, it is not necessary to produce digital signals between partial column electrode driving circuits. In the column electrode driving circuit of the invention, therefore, image disturbance due to noises resulting from digital signals can be eliminated. Furthermore, in the column electrode driving circuit of the invention, the sequence of driving column electrodes in a display apparatus can be easily reversed by controlling the shift direction control signal.

Claims: A column electrode driving circuit for a display apparatus, comprising: a plurality of partial column electrode driving circuits (10) which respectively drive groups of column electrodes of said display apparatus, each partial column electrode driving circuit being allocated a number (ℓ); each partial column electrode driving circuit (10) comprising: count means (15) for counting clock pulses, and for producing a count signal (C) upon each count of a predetermined number of the clock pulses; sample signal output means (16) for outputting a sample signal (D) when a predetermined relationship is satisfied between the number of count signals (C) produced by said count means (15) and said allocated number (ℓ); shift register means (11) for receiving said sample signal (D) and shifting the same to sequentially output said sample signal (q₁ to q k ) from a plurality of outputs; and sample-hold means (12) for sampling and holding an input video signal (V) in accordance with said sequentially outputted sample signal; characterised by: the direction of shift provided by said shift register means (11) being changeable in accordance with a shift direction control signal (R/L); switch means (17) for, when said shift direction is set to a first direction, producing a signal (ℓ′) indicating said allocated number (ℓ), and for, when said shift direction is set to a second direction which is opposite to said first direction, producing a signal (ℓ′) indicating a number (n-1-ℓ) which is obtained by subtracting said allocated number (ℓ) from a specified number (n-1); and said sample signal output means (16) receiving said signal output from said switch means (17). A column electrode driving circuit according to claim 1, wherein said predetermined number of clock pulses is equal to the number of steps of said shift register means (11). A column electrode driving circuit according to claim 1 or claim 2, wherein said allocated number (ℓ) of each partial column electrode driving circuit (10) corresponds to the position of the partial column electrode driving circuit with respect to the other partial column electrode driving circuits. A column electrode driving circuit according to any of claims 1 to 3, wherein said specified number (n-1) relates to the number (n) of said partial column electrode driving circuits (10). A matrix-type liquid crystal display apparatus comprising a column electrode driving circuit (63) according to any preceding claim.

Inventors: KAWAGUCHI TAKAFUMI, TAKEDA MAKOTO, TAKEDA SHIRO, KAWAGUCHI, TAKAFUMI, TAKEDA, MAKOTO, TAKEDA, SHIRO
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1990
Main classification: G09G3
IPC codes: G09G3