JP2008192491A - Lamp drive control device and method as well as signal processing circuit and liquid crystal backlight driving device built into this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method effective for realizing improvement of picture quality and reduction of power consumption by backlight control. <P>SOLUTION: A lamp current detected for each lighting block BL1 to BL4 through a detection resistor is inputted in a backlight control part 16 consisting of a digital circuit, and, after being A/D converted at a digitalizing part 58 for each block, is compared with a control target value by a comparator part 60. Error informations obtained as a result are integrated at a loop filter 62, and integration results are processed at a driving pulse generating part 56 to have driving pulses generated for driving each lighting block BL1 to BL4 with. The driving pulses are outputted from output ports P1 to P4 through a driver 22 into each lighting block BL1 to BL4, and lighting control of the lamps is carried out by a bridge circuit based on the driver outputs. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lamp drive control device and method, a signal processing circuit incorporated therein, and a liquid crystal backlight drive device, and more particularly to an effective technique for improving image quality and reducing power consumption.

  As a technique for improving the moving image performance of a liquid crystal display typified by a liquid crystal TV, a technique for dividing a light source of a liquid crystal backlight into a plurality of blocks and controlling the lighting timing for each of the divided blocks has been studied. This technique is described in Patent Document 1, for example.

  This Patent Document 1 shows a configuration in which backlights 32 to 35 divided into four blocks are independently driven by drive circuits 28 to 31 as described in FIG. 1 of the same document. .

  On the other hand, as a technique for reducing power consumption of a liquid crystal display, an APL-AGC (Average Picture Level Automatic Gain Control) technique for controlling the brightness of a backlight according to the average brightness of an image is known. This technique is described in Patent Documents 2 to 5, for example.

  These documents describe effective methods of backlight control linked to video scenes, but in order to realize these methods in actual products, they are changed to image processing circuits composed of LSIs. Therefore, it is difficult to cope with variations in the image processing LSI because the correspondence varies depending on the configuration and control method of the backlight drive unit.

  In addition, in order to further reduce power consumption, it is necessary to upgrade the backlight control method itself and combine various backlight control methods one after another, which is a large-scale image processing circuit that requires enormous development costs. It is difficult to meticulously respond within the company.

In addition, when the control is divided into a plurality of blocks, if the conventional analog control means is used, the current balance accuracy between the blocks is difficult, and the control circuit scale is proportional to the number of blocks divided. There was a problem that the cost increased as much as that. In addition, carrier synchronization and interlock control between blocks have become complicated, and a separate digital control circuit is required exclusively for interlock control.
JP 2005-99367 A JP 2002-156951 A JP 2002-258401 A JP 2002-357810 A JP 2004-059661 A

  Therefore, the present invention provides an effective technique for realizing image quality improvement and power consumption reduction by backlight control.

  In order to achieve the above object, according to a first aspect of the present invention, there is provided a lamp drive control device for controlling drive of a lamp, wherein means for detecting a waveform of a current flowing through the lamp is compared with a reference signal. And means for generating a pulse waveform and means for performing digital processing based on the pulse waveform.

  According to a second aspect of the present invention, in the first aspect of the present invention, the detection means further comprises means for weakly smoothing the detected current waveform.

  According to a third aspect of the present invention, in the first aspect of the invention, the detection means further comprises means for averaging a predetermined value or more of the detected current waveform.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, a constant value is used for the reference signal.

  The invention according to claim 5 is the invention according to claim 1, further comprising means for generating a basic timing of control and means for generating a triangular wave synchronized with the basic timing, and is synchronized with the basic timing. The triangular wave is used as the reference signal.

  The invention according to claim 6 is the invention according to claim 1, wherein the synchronization of the basic timing includes synchronization of the basic timing to a double frequency.

  According to a seventh aspect of the present invention, in the first aspect of the present invention, means for generating a basic timing of control, means for generating a triangular wave synchronized with the basic timing, and a tip of the triangular wave in a pointed shape. And a correcting means, wherein the triangular wave having the peak is used as the reference signal.

  The invention according to claim 8 is the invention according to claim 1, further comprising means for changing the reference signal to vary the target current.

  The invention described in claim 9 is characterized in that, in the invention described in claim 1, there is provided means for varying the target current by changing the target value of the duty of the pulse waveform.

  According to a tenth aspect of the present invention, in the lamp driving control method for controlling driving of a lamp, a step of detecting a current waveform flowing through the lamp and a pulse waveform generated by comparing the detected waveform with a reference signal. And a step of performing digital processing based on the pulse waveform.

  According to an eleventh aspect of the present invention, in a signal processing circuit incorporated in a lamp drive control device for controlling drive of a lamp, means for detecting a current waveform flowing through the lamp, and comparing the detected waveform with a reference signal Thus, a means for generating a pulse waveform and a means for performing digital processing based on the pulse waveform are provided.

  According to a twelfth aspect of the present invention, in the control device for controlling the lamp provided in the liquid crystal backlight, means for detecting a current waveform flowing through the lamp, and comparing the detected waveform with a reference signal. It comprises means for generating a pulse waveform and means for performing digital processing based on the pulse waveform.

  The invention as set forth in claim 13 is a lamp drive control device for controlling drive of a lamp, wherein means for AD converting a current waveform flowing through the lamp, and the digital signal after the AD conversion is converted into one carrier cycle or half carrier cycle. It is characterized by comprising means for averaging all or part of the waveform for one period or half period every time, and means for performing digital processing based on the averaged value.

  According to the first aspect of the invention, since the AC lamp current waveform is converted into a PWM waveform having a pulse width corresponding to the current value, the A / D is obtained by digitally counting the pulse width with a high frequency clock. The amount of lamp current can be quantified with an inexpensive circuit configuration without using an expensive circuit configuration like a converter.

  According to the second aspect of the present invention, since the detection is performed by weak averaging that leaves a large ripple in the instantaneous waveform of the AC lamp current, the smoothing filter is compared with the case of peak detection or complete smoothing averaging. The delay due to the current can be suppressed to a very small level, and the high-speed response can be achieved, the influence of the leakage current of the current on the stray capacitance can be reduced, and good control characteristics can be obtained.

  According to the third aspect of the present invention, since only the portion of the lamp current waveform that is equal to or greater than the predetermined value is to be detected, control that is more faithful to brightness is possible.

  According to the fourth aspect of the present invention, since the detected current waveform close to the weakly averaged triangular wave and the reference having a constant value are used, a PWM waveform with less fluctuation elements that do not disturb the relative phase relationship can be obtained. .

  Further, according to the fifth aspect of the present invention, since a triangular wave synchronized with the basic timing of the control for generating the carrier of the driving current is used as the reference signal, it is possible to obtain a PWM waveform with a stable relative phase relationship and less fluctuation. .

  Further, according to the invention described in claim 6, since the triangular wave synchronized with the carrier double frequency timing of the drive current is used as the reference signal, the relative phase relationship between the full-wave rectified drive current and the same frequency is particularly stable, In addition, a PWM waveform with good linearity can be obtained.

  According to the seventh aspect of the present invention, since the triangular wave having a peak shape is used as the reference signal, the dullness of the peak of the waveform close to the triangular wave on the detection waveform side is compensated, so that linearity with a wide dynamic range is achieved. A good PWM waveform can be obtained.

  According to the eighth aspect of the invention, the target current can be varied by changing the reference signal.

  According to the ninth aspect of the invention, the target current can be varied by changing the target duty of the obtained PWM waveform.

  According to the thirteenth aspect of the present invention, the waveform of the AC lamp current is left as it is or after the waveform after full-wave rectification is digitized through a high-speed AD converter, and then one cycle of the waveform, that is, one cycle or half cycle of the carrier. In addition, the average of all or part of the waveform can be obtained to obtain a numerical value corresponding to the average current amount, and control by digital processing can be performed in the same manner as in the methods described in claims 1 and 2.

  As described above, according to the present invention, improvement in image quality and reduction in power consumption by backlight control can be expected with an inexpensive configuration.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments described below, and can be modified as appropriate.

  FIG. 1 is a conceptual diagram showing a configuration of a liquid crystal backlight driving device according to an embodiment of the present invention. As shown in FIG. 2A, the present liquid crystal backlight drive device controls the lighting blocks BL1 to BL4 that are separately arranged as backlight light sources on the back surface of the liquid crystal panel 10 and the lighting blocks that are separately arranged. The backlight control unit 16 is configured.

  In FIG. 4A, an image processing unit 14 performs predetermined image processing based on a video signal VD input at a predetermined frame period, and as a result, a signal for driving the liquid crystal panel 10 is transmitted to the liquid crystal driving unit 12. And outputs a signal for controlling the lighting blocks BL1 to BL4 to the backlight control unit 16.

  The liquid crystal drive unit 12 controls the orientation of the liquid crystal elements constituting the liquid crystal panel 10 based on the output signal of the image processing unit 14 to set the color and gradation of each pixel constituting the display video, and The light control unit 16 controls the light amount and lighting state of the corresponding display area and the ON / OFF state of the backlight by controlling the light amount and lighting state of the lighting blocks BL1 to BL4 based on the output signal of the image processing unit 14.

  Here, the lighting blocks BL1 to BL4 are divided into four blocks along the liquid crystal scanning direction, and the backlight control unit 16 controls the lighting state of the lighting block corresponding to the liquid crystal region driven by the liquid crystal driving unit 12. Thus, for example, pseudo impulse drive type moving image improvement is performed by sequentially lighting the backlight while avoiding the transition timing of the liquid crystal.

  Each of the divided lighting blocks includes a lamp L1 serving as a light source, as exemplified by the lighting block BL1 in FIG. 5B, and this lamp includes a bridge circuit composed of switching elements Q1 to Q4. Driven by the transformer TR1.

  Here, the bridge circuit is configured by a switching portion on the positive current side (iP) composed of switching elements Q1 and Q4 and a switching portion on the negative current side (iN) composed of switching elements Q3 and Q2. As indicated by dotted lines iP and iN in the figure, the positive half cycle current iP flows in the direction of the switching element Q1, the transformer TR1, and the switching element Q4, and the negative half cycle current iN is supplied to the switching element Q3, the transformer It flows in the direction of TR1 and switching element Q2, and as a result, an alternating current is supplied to the lamp serving as a load. This operation is the same in each of the lighting blocks BL1 to BL4.

  FIG. 2 is a circuit block diagram showing the overall configuration of the liquid crystal backlight driving device shown in FIG. As shown in the figure, in this apparatus, an analog circuit unit 100 including a bridge circuit and a lighting block is controlled by a backlight control unit 16.

  The bridge circuit that drives the lighting block BL1 includes a pair of switching elements Q1 and Q2 driven by the control signal S1-1 and a pair of switching elements Q3 and Q4 driven by the control signal S1-2. The other lighting blocks BL2, BL3, and BL4 are similarly configured.

  The backlight controller 16 includes ports P1 to P1 corresponding to the bridge circuit control signals S1-1, S1-2, S2-1, S2-2, S3-1, S3-2, S4-1, and S4-2. P4 is provided, and a signal for controlling each pair of switching elements is output from these ports.

  Further, the lighting blocks BL1 to BL4 are provided with resistors R1 to R4 for detecting currents flowing through the lamps L1 to L4, and the detected current values are applied to the corresponding ports P1 to P4 of the backlight control unit 16. Entered. Based on the input current value, dimming control is performed for each lighting block.

  FIG. 3 is a circuit diagram and a timing chart showing an operation example of the bridge circuit shown in FIG. As shown in FIG. 5A, when the control inputs to the switching elements Q1 to Q4 constituting the bridge circuit are A to D, the amount of power supplied to the load LOAD by the relative relationship of the control signals of these A to D. Is determined.

  That is, as shown in FIG. 4B, a switching waveform of A to D is generated based on the output PWM signal synchronized with the carrier timing indicated by “Timing” in the figure, and the period when the control signal A is ON. A current in the positive direction is supplied to the load LOAD, and a current in the negative direction is supplied to the load LOAD while the control signal C is ON.

  The amount of power supplied to the load LOAD is controlled by the duty of the output PWM waveform. When supplying large power to the load LOAD, the duty of the output PWM waveform is increased, and when supplying small power to the load LOAD, the output PWM Reduce the waveform duty.

  Such control of the power supply amount is performed for each lighting block based on the current value detected for each lighting block, thereby adjusting the luminance balance between the lighting blocks and lighting blocks corresponding to the video scene. It is possible to perform scene control in which the luminance is changed every time.

  FIG. 4 is a circuit diagram and timing chart showing another operation example of the bridge circuit shown in FIG. As shown in FIG. 5A, when the control inputs to the switching elements Q1 to Q4 constituting the bridge circuit are A to D, the amount of power supplied to the load LOAD by the relative relationship of the control signals of these A to D. Is determined.

  That is, as shown in FIGS. 5B and 5C, the switching duty of the control signals A to D is set as a constant condition, and the ON states of the control signals A and B are complementarily switched. The ON state is switched complementarily, and the current in the positive direction is supplied to the load LOAD by the overlap of the control signals A and D, and the current in the negative direction is supplied to the load LOAD by the overlap of the control signals B and C.

  That is, the amount of power supplied to the load LOAD can be controlled by changing the phase of the control signal C and D pair with respect to the control signal A and B pair. When supplying a large amount of power to the load LOAD, it is only necessary to increase the overlap between both pairs, as shown in FIG. 5B. When supplying a small amount of power to the load LOAD, as shown in FIG. In addition, the overlap between both pairs may be reduced.

  Such control of the power supply amount is performed for each lighting block based on the current value detected for each lighting block, thereby adjusting the luminance balance between the lighting blocks and for each lighting block according to the video scene. Scene control for changing the brightness can be performed.

  FIG. 5 is a circuit block diagram showing a control configuration of the liquid crystal backlight driving device shown in FIG. As shown in the figure, the lighting blocks BL1 to BL4 provided in the analog circuit unit 100 are supplied with DC power from the power circuit 20, and this DC current is switched and boosted by a bridge circuit to generate high-voltage AC. Is done.

  Here, the backlight control unit 16 is configured by a digital circuit, and the lamp current detected via the detection resistor for each of the lighting blocks BL1 to BL4 is input to the backlight control unit 16 from the input ports P1 to P4. .

  The input lamp current information is A / D converted by the digitizing unit 58 for each lighting block, and then compared with the control target value by the comparing unit 60, and error information obtained as a result is output by the loop filter 62. Integration is performed, and the integration result is processed by the drive pulse generator 56 to generate drive pulses for driving the lighting blocks BL1 to BL4.

  These drive pulses are output from the output ports P1 to P4 to the lighting blocks BL1 to BL4 via the driver 22, and lamp lighting control is performed by the bridge circuit based on the driver output.

  The digitizing unit 58 and the drive pulse generating unit 56 are supplied with carrier timing that is a basic signal for waveform generation generated by the timing generating unit 310, and uses this carrier timing to perform A / D by the digitizing unit 58. Conversion and drive pulse generation by the drive pulse generator 56 are performed.

  The data digitized by the digitizing unit 58 is output to a parameter detecting unit 52 that detects parameters such as lamp impedance for each lighting block, and the protection operation by the protection circuit 50 based on the detected parameters. The activation control of the lamp is performed by the activation control unit 54.

  As the protection operation by the protection circuit 50, the power supply circuit 20 is shut off, the drive pulse duty is reduced, the start-up control is stopped, and the like according to the degree of protection determined from the detected parameters.

  FIG. 6 is a circuit block diagram illustrating a configuration example of the digitizing unit and the comparing unit illustrated in FIG. In the figure, only the lighting block BL1 is shown, but the other lighting blocks are similarly configured. As shown in the figure, the lamp current information of the lighting block is detected by the detection unit 220, and the result is strongly smoothed or weakly smoothed by the smoothing average RC filter 230, and the result is converted to a reference triangular wave by the comparator 240. The comparison is made and the result is output as a detection PWM signal.

  The detected PWM signal is counted by the input pulse width count circuit 322, the difference from the target value is calculated by the subtraction circuit 324, and the result is nonlinearly processed by the nonlinear characteristic adding unit 326 to generate an input error signal. Is done.

  FIG. 7 is a circuit block diagram showing a first example for generating a detection PWM signal. The example shown in the figure is an example of a case where a detection PWM signal is generated by full-wave rectification and strong smooth averaging of the lamp current detected via the detection resistor R1 and comparing it with a reference triangular wave.

  Here, the detection unit 220 includes a full-wave rectification circuit 222 and a clip circuit 224, and the clip circuit shapes the vicinity of the zero value of the rectified waveform.

  The smoothing average RC filter 230 is composed of an RC charging / discharging circuit having a strong smoothing averaging characteristic, that is, a long discharge time constant, and the reference triangular wave generator 250 is composed of an RC circuit that smoothes a reference pulse signal. When a reference pulse such as a carrier timing or a current offset PWM signal is input to the RC circuit, a triangular wave synchronized with the carrier is generated.

  The smoothed average signal and the reference triangular wave are compared by the comparator 240, and a detection PWM signal in which lamp current information is expressed as a pulse signal is generated.

  Note that the target current may be variable by changing the reference signal input to the comparator 240. For example, when the carrier timing is used as the reference pulse input to the reference triangular wave generation unit 250 in the figure, the target current may be made variable by changing the duty of the carrier timing, and a current offset is separately added to the reference pulse. PWM is supplied to add DC by the long time constant smoothing filter 252, or the reference pulse itself is a triangular wave with a high-speed 1-bit modulation offset, a high-speed pulse density modulation PDM or the like, and a reference triangular wave having a predetermined offset and waveform. The target current may be made variable by changing the initial load value of the input pulse width counter 322 in FIG. 6 or changing the target value supplied to the subtracting circuit 324 in FIG. The current may be variable.

  FIG. 8 is a waveform timing chart showing the A / D conversion operation according to the first example for generating the detection PWM signal. As shown in FIG. 6A, the lamp current detected by the detection resistor becomes an AC waveform indicated by a solid line, and this waveform is full-wave rectified to become a rectified waveform shown in FIG.

  Thereafter, as shown in FIG. 6C, the vicinity of zero of the rectified waveform is clipped, and the waveform (thin solid line) is subjected to strong smooth averaging to generate a pseudo-triangular wave (dark solid line) with a small amplitude. .

  On the other hand, as shown in FIG. 5E, the reference triangular wave (dark solid line) synchronized with the carrier timing is compared with the strong smoothed average waveform (thin solid line) to generate the PWM pulse waveform shown in FIG. Is done.

  FIG. 9 is a circuit block diagram illustrating a second example of generating the detection PWM signal. As shown in the figure, when the transformer TR1 is composed of a two-output type twin transformer and two lamps L1-1 and L1-2 are connected to one transformer, resistors R1-1 and R1- 2 may be configured to perform pseudo full-wave rectification using the half-wave rectifier circuit 221 by utilizing the fact that the polarity of the waveform detected at 2 is reversed.

  Here, the detection unit 220 includes a half-wave rectification circuit 222 and a clip circuit 224, and the clip circuit shapes the vicinity of the zero value of the rectified waveform.

  The smoothing average RC filter 230 is configured by an RC charging / discharging circuit having a weak smoothing averaging characteristic, that is, a short discharge time constant, and the reference triangular wave generation unit 250 is configured by an RC circuit that smoothes a reference pulse signal. When a reference pulse is input to this RC circuit, a triangular wave synchronized with the carrier is generated.

  The smoothed average signal and the reference triangular wave are compared by the comparator 240, and a detection PWM signal in which lamp current information is expressed as a pulse signal is generated.

  FIG. 10 is a waveform timing chart showing the A / D conversion operation according to the second example for generating the detection PWM signal. As shown in FIG. 6A, the lamp currents having different polarities indicated by the solid line and the dotted line are detected, and these are half-wave rectified and synthesized by the diode OR to form the rectified waveform shown in FIG. .

  Thereafter, as shown in FIG. 6C, the vicinity of zero of the rectified waveform is clipped, and the waveform (thin solid line) is weakly smoothed and a pseudo triangular wave (dark solid line) having a small amplitude is generated. .

  On the other hand, as shown in (e) of the figure, the reference triangular wave (dark solid line) synchronized with the carrier timing is compared with the weakly smoothed average waveform (thin solid line) to generate the detected PWM waveform shown in (f) of FIG. Is done.

  FIG. 11 is a circuit block diagram illustrating a third example of generating a detection PWM signal. The example shown in the figure is an example in which a constant value is used as a reference for the comparator 240, and the others are the same as those in the second example.

  FIG. 12 is a waveform timing chart showing an A / D conversion operation according to the third example for generating the detection PWM signal. In the case of this example, as shown in (e) of the figure, a constant value reference (dark solid line) is compared with a weakly smoothed average waveform (thin solid line), and the PWM pulse waveform shown in (f) of FIG. Generated. Others are the same as the above-mentioned 2nd example.

  FIG. 13 is a circuit block diagram showing a fourth example for generating a detection PWM signal. The example shown in the figure is an example in which the detected PWM signal is generated by full-wave rectifying and weakly smoothing the lamp current detected via the detection resistor R1 and comparing it with a constant reference. Others are the same as those in the first example.

  FIG. 14 is a waveform timing chart showing an A / D conversion operation according to a fourth example for generating a detection PWM signal. In the case of this example, as shown in (d) to (f) of the figure, the weakly smoothed average signal is compared with a certain reference value to generate a detection PWM signal. Others are the same as the above-mentioned first example.

  FIG. 15 is a circuit block diagram showing a fifth example for generating a detection PWM signal. The example shown in the figure is an example in which a double frequency reference pulse is supplied to the reference triangular wave generation filter 250 to generate a double frequency triangular wave, and the others are the same as the fourth example described above.

  FIG. 16 is a waveform timing chart showing an A / D conversion operation according to a fifth example for generating a detection PWM signal. In the case of this example, as shown in (e) of the figure, the double-frequency triangular wave reference (dark solid line) is compared with the weakly smoothed average waveform (thin solid line), and the PWM pulse waveform shown in (f) of FIG. Generated. Others are the same as the above-mentioned 4th example.

  FIG. 17 is a circuit block diagram illustrating a sixth example of generating a detection PWM signal. In this example, as shown in FIG. 15A, an edge enhancement waveform is adapted to the double frequency triangular wave generation unit 251 in FIG. In this case, as shown in FIG. 6B, the portion where the weak smooth average waveform is actually rounded can be absorbed by a triangular wave having a peak shape to which the edge enhancement waveform is applied. Others are the same as the above-mentioned 5th example.

  FIG. 18 is a circuit block diagram showing a sixth example in which an average current value is obtained after high-speed AD conversion of a current waveform directly without generating a detection PWM signal. In the case of this example, as shown in the figure, the A / D converter 360 performs AD conversion as it is after the current waveform is converted into a voltage with a high-speed sampling clock having a frequency eight times that of the carrier.

  Then, three samples in the middle of each half cycle of the waveform are acquired by flip-flops 362-1 and 362-2, and the result of digital addition by the adder 363 is converted into an absolute value by the absolute value calculation circuit 364, and then the average value calculation is performed. By the flip-flop 366, re-sampling is performed again at twice the frequency of the carrier, that is, with an operation sampling clock every half cycle, and a numerical average current value other than the vicinity of the zero cross every half cycle is obtained. Thereafter, it is input to the comparison circuit 60 of FIG. 5 and the same processing as described above is performed.

  FIG. 19 is a timing chart showing processing timing of the circuit block shown in FIG. As shown in FIGS. 4A and 4B, in the A / D converter of this example, sampling is performed four times in a half cycle of the current carrier frequency. However, as shown in FIG. The total value of the three sample outputs is resampled once every half cycle, that is, once every four samples, and the waveform within one cycle is shown in FIG. The average output of “b + c + d” and “f + g + h” excluding e and i in the vicinity of the zero cross is obtained.

  FIG. 20 is a conceptual diagram illustrating an example of nonlinear characteristics loaded by the nonlinear characteristic addition circuit 326 illustrated in FIG. As shown in the figure, the PWM duty indicated on the horizontal axis is determined in accordance with the error output value indicated on the vertical axis. Here, the solid line area indicated by “x2” in the figure is a characteristic for quickly starting up with a double gain until reaching near the steady state, and the negative error steady range of the solid line area indicated by “x1” in the figure. Is a characteristic for switching to a steady gain in the vicinity of the steady value, and the positive error steady range in the solid line region indicated by “x1” in the figure is a characteristic that is secured large so as not to jump over the steady range at a stretch. There is a solid line region indicated by “x8” in the figure, which is a characteristic for rapidly suppressing a dangerous overcurrent in the case of an electric shock or the like by increasing the gain by 8 times.

  FIG. 21 is a circuit block diagram showing a configuration of the loop filter shown in FIG. In the figure, only the lighting block BL1 is shown, but the other lighting blocks are similarly configured. As shown in the figure, the loop filter 62 includes an adder circuit 332, an output clip circuit 334, and a flip-flop 336, and an integration process of the input error signal nonlinearly processed by the loop filter is performed, and closed loop control is performed. A signal is generated.

  FIG. 22 is a circuit block diagram showing a configuration example in the case where the soft start / stop control is independently performed for each block by the single current common control for one block.

  FIG. 23 is a circuit block diagram showing a configuration of input error generation unit 342 shown in FIG. As shown in the figure, the rectified current waveform integrated through the maximum value selection / full-wave rectifier circuit of each block lamp current is weakly smoothed and then converted into detection PWM by a comparator. The detected PWM is digitized by a pulse width counter, subtracted from the target value, added with nonlinear characteristics, and then output as an input error signal. These configurations and operations are performed in the same manner as in FIG.

  The input error signal generated as described above is integrated by the loop filter 62 shown in FIG. 22 to generate a control signal by a closed loop in a steady state.

  The steady control signal is output to the soft waveform generators 350-1 to 350-4 provided for each lighting block in the drive pulse generator 56, and soft start / stop waveforms are generated by the respective soft waveform generators. After that, it is output to the pulse conversion units 370-1 to 370-4 as an output amplitude signal. At this time, a steady achievement signal indicating the achievement state to the steady state is output to the NOR circuit 344 by the soft waveform generation units 350-1 to 350-4, and is output to the loop filter 62 as an unsteady signal.

  The output amplitude signal of each lighting block is converted into a pulse signal by pulse conversion units 370-1 to 370-4, and output as a drive PWM signal of each lighting block from the backlight control unit 16 shown in FIG. 5. The light is output from the ports P1 to P4 to the lighting blocks BL1 to BL4 via the driver 22.

  24 is a circuit block diagram showing a configuration of the loop filter shown in FIG. As shown in the figure, the loop filter 62 includes an adder circuit 332, an output clip circuit 334, a flip-flop 336, and an AND circuit 338, and an integration process of the input error signal is performed by this loop filter.

  The signal output from the AND circuit 338 to the flip-flop 336 is output as a hold signal for preventing an increase in output due to the open loop in the non-steady state, and the signal output from the output clip circuit 346 to the AND circuit 348 is positive. In this case, the rising direction of the steady control value is indicated. Note that this AND circuit is not necessarily required, and the flip-flop 336 may be held unconditionally during non-stationary conditions.

  FIG. 25 is a conceptual diagram showing a configuration of the soft start / stop waveform generation unit shown in FIG. In the figure, only the lighting block BL1 is shown, but the other lighting blocks are similarly configured. As shown in the figure, the loop filter output signal generated for each lighting block is output to the comparison circuits 354 and 355 and the selection circuit 356, and the output amplitude indicating the PWM duty is selected according to the steady achievement state. A signal is generated.

  Here, based on a signal indicating the vicinity of zero or the vicinity of the steady value output from the comparison circuit 354, a plurality of slope values are selected by the slope value selection circuit 351, and these slope values are turned on / off of the lighting block by the polarity selection circuit 352. The polarity based on the OFF signal is applied, and the result is added to the integration loop by the adder circuit 353 to generate a forced curve.

  FIG. 26 is a timing chart showing an example of a soft start / stop waveform. FIG. 11A shows an ON / OFF signal of the lighting block BL1, FIG. 10B shows a voltage waveform of the output amplitude selected by the slope value selection unit 351 in FIG. 25, and FIG. Indicates the timing corresponding to the slope near the zero value and the slope near the steady value, FIG. 6D shows the timing when the lighting block BL1 reaches the steady state, and FIG. 4E shows the lighting block BL2. (F) of FIG. 25 shows the voltage waveform of the output amplitude selected by the slope value selection unit 351 of FIG. 25, and (g) of FIG. 25 shows that the lighting block BL1 or BL2 is in a steady state. Shows the timing to achieve.

  The control feature shown in the figure is as follows: First, the output slew rate at start / stop is forcibly limited in a closed loop, and the up and down curves are forcibly made while always controlling. There is a method of smoothly switching between / OFF.

  In this method, in the control configuration shown in FIG. 5, that is, in the configuration in which an error is detected with respect to the target current in a steady state and the output of this error component is automatically controlled via a loop filter, FIG. In accordance with the ON / OFF control input of each lighting block shown, a forcible curve for output control of rising at ON and falling at OFF as shown by a broken line in FIG. 26B is generated. The forced curve is generated by the slope value selection unit 351, the polarity selection unit 352, and the addition circuit 353 shown in FIG.

  Here, when the generated forced curve is going to exceed the automatic control value indicated by the “closed loop steady value” in FIG. 26B when the generated forced curve is increased by the comparison circuit 354 shown in FIG. 25, the selection circuit in FIG. In 356, the output on the automatic control side (“steady control signal by closed loop” in the figure) is selected and used, and the value is also used as the current value for forced curve output at the next moment.

  Further, when it is going to descend on the forced curve, it is forcibly lowered from the automatic control value, and the forced curve output is selectively output in a range smaller than the automatic control value. When it falls and falls below zero or other predetermined value, it clips to that predetermined value and outputs that value.

  While the forced curve is being selected and output, the automatic control output is held so that the automatic control value does not rise excessively due to an open loop. As a result, the automatic control and the forced slope curve at the end of the start can be shifted with high accuracy and the noise can be reduced.

  In addition to the above, it is also effective to make the sound gentler by reducing the slope immediately after start / stop or immediately before start / stop completion. For example, when the forced curve is near the automatic control value or near the lower limit, the up and down curves may be gently configured by selecting a gentler slope value. As a result, the switching between the steady value and the lower limit value is smoothed, the high frequency component of the current amount change is suppressed, and the noise is further reduced.

  Further, the control by the forced curve at the start / stop is performed by multi-channel control independent of each lighting block, so that ON / OFF control can be independently performed at an arbitrary timing with a small circuit.

  For example, as shown in FIG. 22, the steady-state current value of each lighting block is controlled by a common steady-state automatic control circuit, and each lighting block is independently turned ON / OFF and the output rises and falls by start / stop. When the steady control output is selected for any one of the common control targets, the control loop is enabled without holding, and the steady control is held when all channels are out of the steady control output selection state. Put it in a state. This makes it possible to inexpensively perform automatic control and generate independent start / stop slope curves with a set of steady automatic control circuits regardless of the state of each channel.

  FIG. 27 is a timing chart showing another example of the soft start / stop waveform. FIG. 4A shows an ON / OFF signal of the lighting block BL1, and FIGS. 4B to 4D show examples of soft start / stop control for the ON / OFF signal.

  Fig. 2 (b) shows an example in which the low voltage output range in which no current flows through the lamp at the start / stop is an example in which the output of the voltage is increased and decreased at a steep slope to shorten the time until the lighting time. The slope from the zero point shown in the figure to the switching threshold voltage slightly lower than the discharge start voltage is a corresponding portion.

  FIG. 4C shows an example in which the lamp is put on standby at a low voltage in a range where no current flows through the lamp, and the time until the start of lighting at the start is shortened and the noise is reduced.

  Fig. 6D shows a standby start signal that is slightly ahead of the ON / OFF signal as shown in Fig. 8E. The standby voltage in the range where no current flows through the lamp is standby in advance, and the time required for starting is shortened. This is an example of reducing unnecessary power consumption when the light is turned off due to the current flowing in the stray capacitance during standby and the switching loss of the bridge circuit while achieving quietness.

  According to the present invention, since more advanced backlight control is possible, application to a large liquid crystal display that requires high image quality and reduced power consumption is expected.

It is a conceptual diagram which shows the structure of the liquid crystal backlight drive device which concerns on embodiment of this invention. FIG. 2 is a circuit block diagram showing an overall configuration of the liquid crystal backlight driving device shown in FIG. 1. FIG. 3 is a circuit diagram and a timing chart showing an operation example of the bridge circuit shown in FIG. 2. FIG. 6 is a circuit diagram and a timing chart showing another operation example of the bridge circuit shown in FIG. 2. FIG. 2 is a circuit block diagram illustrating a control configuration of the liquid crystal backlight driving device illustrated in FIG. 1. FIG. 6 is a circuit block diagram illustrating a configuration example of a quantification unit and a comparison unit illustrated in FIG. 5. It is a circuit block diagram which shows the 1st example which produces | generates a detection PWM signal. It is a waveform timing chart which shows the A / D conversion operation | movement which concerns on the 1st example which produces | generates a detection PWM signal. It is a circuit block diagram which shows the 2nd example which produces | generates a detection PWM signal. It is a waveform timing chart which shows the A / D conversion operation | movement which concerns on the 2nd example which produces | generates a detection PWM signal. It is a circuit block diagram which shows the 3rd example which produces | generates a detection PWM signal. It is a waveform timing chart which shows the A / D conversion operation | movement which concerns on the 3rd example which produces | generates a detection PWM signal. It is a circuit block diagram which shows the 4th example which produces | generates a detection PWM signal. It is a waveform timing chart which shows the A / D conversion operation | movement which concerns on the 4th example which produces | generates a detection PWM signal. It is a circuit block diagram which shows the 5th example which produces | generates a detection PWM signal. It is a waveform timing chart which shows the A / D conversion operation | movement which concerns on the 5th example which produces | generates a detection PWM signal. It is a circuit block diagram which shows the 6th example which produces | generates a detection PWM signal. FIG. 10 is a circuit block diagram illustrating a sixth example in a case where an average current value is obtained after high-speed AD conversion of a current waveform directly without generating a detection PWM signal. FIG. 19 is a timing chart showing processing timing of the circuit block shown in FIG. 18. FIG. It is a conceptual diagram which shows the example of the nonlinear characteristic loaded with the nonlinear characteristic addition circuit 326 shown in FIG. FIG. 6 is a circuit block diagram illustrating a configuration of the loop filter illustrated in FIG. 5. It is a circuit block diagram which shows the structural example in the case of performing soft start / stop control independently for every block by 1 block common single current control. FIG. 23 is a circuit block diagram illustrating a configuration of an input error generation unit 342 illustrated in FIG. 22. It is a circuit block diagram which shows the structure of the loop filter shown in FIG. It is a conceptual diagram which shows the structure of the soft start / stop waveform generation part shown in FIG. It is a timing chart which shows the example of a soft start / stop waveform. It is a timing chart which shows the other example of a soft start / stop waveform.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Liquid crystal panel, 12 ... Liquid crystal drive part, 14 ... Image processing part, 16 ... Backlight control part, 20 ... Power supply circuit, 22 ... Driver, 50 ... Protection circuit, 52 ... Parameter detection part, 54 ... Start-up control part, 56 ... Driving pulse generation unit, 58 ... Digitization unit, 60 ... Comparison unit, 62 ... Loop filter, 70 ... Timing generation unit, 100 ... Analog circuit unit, 220 ... Detection unit, 221 ... Half-wave rectification circuit, 222 ... All Wave rectifier circuit, 224 ... Clip circuit, 230 ... Smooth averaging RC filter, 240 ... Comparator, 250 ... Reference triangular wave generation filter, 300 ... Digital circuit part, 320 ... Input counter, 322 ... Input pulse width count part, 324 ... Subtraction , 326... Nonlinear characteristic adding unit, 330... Loop filter, 332... Adding unit, 334. Flop, 340, maximum value selection circuit, 344, NOR circuit, 348, AND circuit, 350, soft waveform generation unit, 351, gradient value selection unit, 352, polarity selection unit, 353, addition circuit, 354, comparison circuit, 355 ... Comparison circuit 356... Selection circuit 357... Register circuit 360... A / D converter 362. Part

Claims (13)

In a lamp drive control device that performs drive control of a lamp,
Means for detecting a current waveform flowing in the lamp;
Means for generating a pulse waveform by comparing the detected waveform with a reference signal;
And a means for performing digital processing based on the pulse waveform.   2. The lamp drive control device according to claim 1, wherein the detection means further comprises means for weakly smoothing the detected current waveform.   2. The lamp drive control device according to claim 1, wherein the detection means further comprises means for averaging a predetermined value or more of the detected current waveform.   2. The lamp drive control device according to claim 1, wherein a constant value is used for the reference signal. Means for generating the basic timing of control;
Means for generating a triangular wave synchronized with the basic timing,
2. The lamp drive control device according to claim 1, wherein a triangular wave synchronized with the basic timing is used as the reference signal.   6. The lamp drive control device according to claim 5, wherein the synchronization of the basic timing includes synchronization of the basic timing to a double frequency. Means for generating the basic timing of control;
Means for generating a triangular wave synchronized with the basic timing;
Means for correcting the tip of the triangular wave to a pointed shape,
2. The lamp drive control device according to claim 1, wherein a triangular wave having the peak is used as the reference signal.   2. The lamp drive control device according to claim 1, further comprising means for changing the target current by changing the reference signal.   2. The lamp drive control device according to claim 1, further comprising means for changing the target current by changing a target value of the duty of the pulse waveform. In a lamp drive control method for performing drive control of a lamp,
Detecting a current waveform flowing in the lamp;
Generating a pulse waveform by comparing the detected waveform with a reference signal;
And a step of performing digital processing based on the pulse waveform. In a signal processing circuit incorporated in a lamp drive control device that performs drive control of a lamp,
Means for detecting a current waveform flowing in the lamp;
Means for generating a pulse waveform by comparing the detected waveform with a reference signal;
And a means for performing digital processing based on the pulse waveform. In the control device that controls the lamp provided in the liquid crystal backlight,
Means for detecting a current waveform flowing in the lamp;
Means for generating a pulse waveform by comparing the detected waveform with a reference signal;
Means for performing digital processing based on the pulse waveform. In a lamp drive control device that performs drive control of a lamp,
Means for AD converting a current waveform flowing in the lamp;
Means for averaging all or a part of the waveform of one or half period of the digital signal after AD conversion every one carrier period or half carrier period;
And a means for performing digital processing based on the averaged value.

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