KR0166624B1 - Flicker component measuring apparatus - Google Patents

Abstract

A flicker component measuring apparatus for measuring a flicker component of a selected frequency of a liquid crystal display, comprising: photoelectric conversion means for converting a luminance of a display screen of the liquid crystal display into an analog signal; Filter means for filtering an analog signal to output a filtered signal having a selected frequency component; And signal conversion means for converting the filtered signal into a digital signal.

Description

Flicker Component Measuring Device

1 is a block diagram showing the configuration of a flicker component measuring apparatus according to an embodiment of the present invention.

2A, 2B, and 2C are diagrams for explaining the principle of flicker generation in a liquid crystal display device.

3 is a schematic view showing the configuration of a conventional apparatus for measuring flicker components included in a signal output from a liquid crystal display.

4 is a view showing a waveform of an analog signal output from a conventional flicker component measuring apparatus.

5 is a block diagram illustrating a flicker component detector constituting a flicker component measuring apparatus in the embodiment of the present invention.

6 is a block diagram for explaining a band pass filter constituting the flicker component measuring apparatus in the embodiment of the present invention.

7 is a block diagram illustrating an A / D converter constituting the flicker component measuring apparatus in the embodiment of the present invention.

8 shows an example of an operating waveform of the A / D converter.

9 is a graph showing the characteristic correlations between the present invention and the prior art, comparing measurements of flicker levels.

10 is a graph showing the temperature characteristics of the flicker level in comparison with the present invention.

11a and 11b show details of a switched capacitor filter.

* Explanation of symbols for main parts of the drawings

1: liquid crystal display 101: flicker component measuring device

2: light receiver 3: backlight device

4: illuminometer 5: flicker component detector

7: Signal Conditioner (Amplifier) 8: 1/3 OCT Bandpass Filter

9: AC / DC converter 10: Ripple cancellation filter

11: A / D converter 13: Frequency measuring device

14: switched capacitor filter (SCF) 15: low pass filter

16: clock generator

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flicker component measuring apparatus, and more particularly, to a device for measuring a difference in a counter voltage applied to a counter electrode of a display panel of a liquid crystal display and flicker generated in the liquid crystal display panel.

First, the generation principle of flicker in the liquid crystal display device will be described.

One exemplary method for driving a full-line panel in a liquid crystal display device is an interlace driving method similar to the method used in the conventional CRT. In the case of the NTSC system, a vertical resolution of approximately 300 to 350 TV copies is obtained using a conventional CRT. On the other hand, in the interlace driving method, the resolution of 480 TV copies can be obtained in principle using a full-line LCD (that is, having 480 scan lines).

On the other hand, the LCD panel may be driven by an AC drive, that is, a driving method for inverting the polarity of the voltage applied to the liquid crystal in order to prevent polarization of the liquid crystal.

As shown in FIG. 2C, in the interlace driving method in which a signal voltage having a different polarity is applied to each pixel every 1/60 second, the polarity of the voltage applied to each pixel electrode is changed to a frequency of 60 Hz. In this case, the counter voltage is adjusted to an intermediate level between the maximum level of the positive signal voltage and the minimum level of the negative signal voltage.

In the LCD panel, the signal voltage applied to the odd scan line and the signal voltage applied to the even scan line are different from each other as shown by comparing the solid line and the dotted line in FIG. 2C, wherein the odd scan line And even scan lines are adjacent to each other. Therefore, when the counter voltage is adjusted to the center of the signal voltage applied to the odd-numbered scan line indicated by the solid line, the counter voltage is from the center of the signal voltage of the even-numbered scan line indicated by the dotted line due to the characteristics of the driving circuit of the scan electrode. Is offset.

Accordingly, in the pixel corresponding to the scanning line to which the signal voltage indicated by the dotted line is applied; As shown in FIG. 2A, the difference voltage B with respect to the counter voltage in the odd-numbered field (hereinafter referred to as odd field), and the even-numbered field (hereinafter referred to as even field) as shown in FIG. 2B. ), The difference voltage C with respect to the counter voltage becomes different due to the shift of the counter voltage. If the voltages of the same polarity applied every 1/30 second have different difference voltages with respect to the opposite voltages, as indicated by voltage B (odd field) and voltage C (even field), flicker occurs and the display is stained. do.

Other examples of the method for driving a full-line panel include a non-interlaced driving method and a double speed driving method in which one line is scanned in a half horizontal period. In either of these methods, when the applied signal voltage is shifted from the opposite voltage, flicker, that is, flicker generated per one pixel unit or flicker generated per one scan line unit, is generated. For example, flicker occurs when a direct current voltage is applied to the liquid crystal; If the polarity is switched fast enough, no change will be noticed in the observer's eye and flicker will not appear. Nevertheless, flicker continues to occur.

In the conventional method of measuring flicker, as described in Japanese Patent Laid-Open No. 5-323379, the counter voltage is adjusted to an optimum value based on data obtained by the luminance meter. In this case, the data obtained by the luminance meter is not processed but is output therefrom. Flicker can be measured on the same principle using the value 1x read from the light receiving portion of the luminance meter.

3 is a schematic view showing the configuration of a conventional flicker component measuring apparatus. The flicker component measuring device 201 for measuring flicker components included in a signal output from the liquid crystal display device (liquid crystal display panel) 1 includes a light receiving unit 2 and a liquid crystal display device which are disposed to face the liquid crystal display device 1. The illuminometer 4 for measuring the illuminance of (1) is included. The illuminometer 4 outputs an analog signal obtained by the photoelectric conversion performed by the light receiving unit 2. This analog signal is input to the oscilloscope. Behind the liquid crystal display device 1, a backlight device 3 for emitting light for uniformly irradiating the liquid crystal display device 1 is arranged. Of course, in the flicker component measuring apparatus configured as described above, the illuminometer described in Japanese Patent Application Laid-open No. 5-323379 may be used instead of the illuminometer 4.

Next, a description will be given of an inspection process of the flicker component. While the liquid crystal display device 1 is in the ON state, the light receiving portion 2 of the illuminometer 4 is positioned opposite to the liquid crystal display screen, and the analog output from the illuminometer 4 is performed. The waveform of the signal is displayed on the oscilloscope as shown in FIG. While the waveform is displayed on the oscilloscope, the deviation from a constant frequency component is checked at the analog level.

At present, deviations such as line flicker are adjusted using an inspection method in which the inspector observes the adjustment visually through a magnifying glass or the like.

As described above, in order to measure the change in illuminance on the display screen using a conventional flicker component measuring device, the liquid crystal display device 1 is in the ON state and the light receiving portion 2 of the illuminometer 4 is disposed opposite the display screen. do. Therefore, the waveform corresponding to the measured illuminance change is not a pure sinusoidal wave, but a sinusoidal wave (high frequency noise, etc.) of various frequencies as shown in FIG. 4.

Therefore, the signal waveform displayed on the oscilloscope contains noise and becomes difficult to read. Due to such difficulties. An error of reading by the inspector is caused and the inspector cannot accurately determine whether the product is accepted or not. As a result, when the product is inspected for the flicker component, the time required for the inspection and the quality of the product that has passed the inspection are not constant.

In order to solve the above problem, a method of processing an analog synthesized waveform by a fast Fourier transform (FFT) operation may be used. However, general purpose FFT analyzers are expensive. Developing a new FFT analyzer for a specific application requires a lot of effort and expense to develop software such as A / D conversion and GP-IB (program for access to external devices).

In addition to how FFT operations are used, a higher order filtering process may be used to simply extract the selected frequency components included in the output from the illuminometer. In this case, however, data obtained by performing A / D conversion of the analog signal output from the illuminometer must be processed by a digital filter. This method requires a digital oscilloscope or the like, which adds considerable cost to the development of the flicker component measuring device.

The flicker component measuring apparatus for measuring the flicker component included in the signal output from the liquid crystal display of the present invention outputs a photoelectric converter for converting the brightness of the display screen of the liquid crystal display into an analog signal and a signal having a selected frequency component. A filter for filtering the analog signal to: and a signal converter for converting the filtered signal into a digital signal.

In one embodiment of the present invention, the photoelectric converter includes a light receiving unit arranged to face the display screen, and the photoelectric conversion means outputs the analog signal to the filter means.

In one embodiment of the present invention, the flicker component measuring apparatus further comprises an amplifier for receiving and amplifying the analog signal and outputting the amplified signal to the filter means.

In one embodiment of the present invention, the filter may change the frequency bandwidth of the analog signal filtered by the filter means, based on the signal output from the frequency measuring device.

In one embodiment of the present invention, the signal converter; An AC-DC converter for converting the filtered signal into an effective signal corresponding to the effective value of the filtered signal; And a ripple remover for removing a ripple overlapping the effective signal. And an A-D converter for converting the signal output from the ripple canceller into a digital signal.

In one embodiment of the present invention, the flicker component measuring device further includes a display device for displaying a digital signal.

According to the present invention, the deviation of the luminance on the display screen of the liquid crystal display device is measured. From the analog signal obtained therefrom, only selected frequency components are taken out as measurement results. Next, the frequency component extracted as a measurement result is converted into a digital signal. As a result, digital measurement on the flicker component included in the signal of the desired frequency can be performed. By displaying the digital signal digitally, a read error by the inspector and a confusion in the pass / fail decision of the inspector can be prevented.

When the deviation of the luminance on the display screen of the liquid crystal display device is measured, the luminance meter and illuminometer used in the conventional apparatus can be used.

Further, only the designated frequency is taken out from the analog signal obtained by the above adjustment, and then A-D conversion is performed. Therefore, an expensive general purpose FFT analyzer or the like for performing fast Fourier transform operation on the analog composite waveform is unnecessary. In addition, in the filtering process for extracting the selected frequency components, the filtering can be performed at the analog level instead of using the digital filter required when the filtering process is performed on the AD-converted data. And cost can be reduced.

Accordingly, the present invention provides a flicker component measuring apparatus capable of measuring flicker components using instruments used in conventional apparatuses, whereby a read error by the inspector and a confusion in the pass / fail determination of the inspector can be prevented. Can be. In addition, the effort and cost required for the development of the flicker component measuring apparatus can be reduced.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram showing the configuration of a flicker component measuring apparatus according to an embodiment of the present invention. 5 is a block diagram showing the configuration of the flicker component detector of the flicker component measuring apparatus shown in FIG.

In FIG. 1, the flicker component measuring device 101 for measuring the flicker component included in the signal output from the liquid crystal display device (liquid crystal display panel) 1 is located near the display screen of the liquid crystal display device 1. An illuminometer 4 for measuring the illuminance of the display screen of the liquid crystal display device 1 and the illuminometer 4 based on the arranged light receiving unit 2, an analog signal obtained by photoelectric conversion performed by the light receiving unit 2 And a flicker component detector (5) for receiving an analog signal outputted from the < RTI ID = 0.0 > 1 < / RTI > The flicker component measuring apparatus 101 is provided with a driving device (not shown) for electrically driving the liquid crystal display device 1. The light receiving portion 2 is connected to the illuminometer 4 via an extension cable 2a. Behind the liquid crystal display device 1, a backlight device 3 for emitting light for uniformly irradiating the liquid crystal display device 1 is arranged.

Next, the flicker component detector 5 will be described in detail. An example of the configuration for extracting a frequency signal of 30 Hz from the analog signal output from the illuminometer 4 will be described.

The flicker component detector 5 shown in FIG. 5 is described sequentially from its input side.

Since the analog signal (AC component) input from the light receiving unit 2 through the illuminometer 4 is at a low level, it is difficult to determine whether to sum / negative products such as a liquid crystal display device. Thus, at the first stage of the flicker component detector 5, an amplifier is provided as the signal conditioner 7. The gain of the amplifier 7 is set to 10 times. Thus, for example, a signal of about 6 mV can be amplified so that a signal of 60 mV can be output from the amplifier 7. When the signal is amplified 10 times, the clock noise contained in the signal output from the illuminometer 4 is also amplified. As described later, when the switched capacitor filter is provided to the flicker component detector 5, the maximum gain of the amplifier 7 is 10 times. If the signal output from the illuminometer 4 is sufficiently large, the flicker component detector 5 does not need to be provided with the signal conditioner 7.

Next, the configuration of the 1/3 OCT (abbreviated octave) bandpass filter 8 will be described. 6 is a block diagram showing the configuration of a 1/3 OCT bandpass filter 8. FIG. The 1/3 OCT band pass filter 8 extracts only a specified frequency component from the analog signal output from the amplifier 7.

The bandpass filter may be formed as an active filter, but a filter having a high Q value has a high order, and a high precision capacitor and a resistor are required to provide a filter having a high Q value. In one embodiment of the invention, a switched capacitor filter (hereinafter referred to as SCF) 14 is used for the bandpass filter 8.

The SCF 14 includes a plurality of capacitors and a plurality of resistors. In general, the signal and frequency bands that pass through the filter may vary depending on the combination of capacitor and resistor. This SCF 14 can be realized with an IC. For example, a plurality of capacitors are formed in one substrate, and the capacitance of the capacitors does not change. The center frequency of the signal passing through the SCF 14 is changed by changing the resistance of the resistor.

11A is an equivalent circuit diagram of the SCF 14. The resistance of the resistor shown in FIG. 11A is controlled in accordance with the clock signal generated by the clock generator 16. The frequency of the clock signal is determined in accordance with the instruction output from the frequency measuring device 13. As shown in FIG. 11B, the resistance of the resistor can be conducted by turning the switch SW ON / OFF in accordance with the clock signal output from the clock generator 16. FIG. Accordingly, the frequency band of the signal passing through the SCF 14 can be changed with high precision.

Therefore, by using the bandpass filter described above, any frequency component can be taken out. Further, in the flicker component measuring apparatus according to the present invention, the characteristics of the SCF 14 are measured before the adjustment is made to accurately adjust the bandwidth and the center frequency, and each flicker component is measured according to the characteristic of the clock signal frequency measured. The frequency of the clock signal is determined for the measuring device.

The signal output from the SCF 14 has a waveform sampled by the switch SW. This sampled signal has switching noise. The low pass filter 15 removes switching noise superimposed on the signal output from the SCF 14. When the signal output from the SCF 14 contains almost no high frequency components, the 1/3 band pass filter 8 does not need the low pass filter 15. In order to maintain the characteristics of the SCF 14, a clock signal is counted by a frequency counter (frequency measuring device) 13 to control the 1/3 band pass filter 8.

When the frequency counter is included in the flicker component measuring apparatus, the clock signal may be counted in the flicker component measuring apparatus. Thus, an external measuring device such as a frequency counter is unnecessary.

Next, the AC / DC converter 9 and the ripple cancellation filter 10 will be described. The AC / DC converter 9 is connected to the output terminal of the band pass filter, and the ripple cancellation filter 10 is connected to the output terminal of the AC / DC converter 9. The bandpass filter 8 extracts a frequency signal of 30 Hz from the analog signal output from the illuminometer 4 by filtering. The AC / DC converter 9 receives a signal having a frequency of 30 Hz, and converts the signal into an analog signal of DC level, which is an effective value of a binary. The ripple cancellation filter 10 removes the ripple of the frequency of 30 Hz from the signal obtained by the AC / DC converter 9, and removes the fluctuation of the input signal of the A / D converter 11. However, the ripple cancellation filter 10 has a drawback that the response speed of the circuit including the filter 10 becomes slow. Since the ripple cancellation filter is used in this embodiment, the response speed can be shortened to 1 second or less. When the ripple cancellation filter is not used, the response speed can be 1 second or less (not shown).

Next, the A / D converter 11 will be described.

7 is a circuit configuration diagram of the A / B converter 11. The A / D converter 11 converts the analog signal output from the ripple cancellation filter 10 into a digital value, which is displayed by the LED display device 12. The A / D converter 11 is an integrator 21 for integrating the analog signal output from the ripple cancellation filter 10, and a second for comparing the level of the analog signal output from the ripple cancellation filter 10 with a ground level. A first comparator 22a and a second comparator 22b for comparing the level of the signal output from the integrator 21 with the level of the voltage Vc. One of the input terminals of the comparator 21a included in the integrator 21 is connected to the V1 input terminal 17, which is connected via an integrating resistor 19 having a resistance value R1 and a switch 25a. An analog signal output from the cancellation filter 10 is received. The VR1 input terminal 18a and the VR2 input terminal 18b for receiving the first and second reference voltages are connected to one terminal of the integrating resistor 19 via switches 25b and 25c, respectively.

An integral capacitor 20b having a capacitor C2 is connected between one of the input terminals of the comparator 21a and the output terminal. The integrating capacitor 20a and the second integrating switch 26b each having a capacitor C1 are connected to the integrating capacitor 20b on a bottle-by-bottle basis. The first integrating switch 26a is connected between the connection point of the integrating capacitor 20a and the second integrating switch 26b and ground. The switches 25a to 25c and the integrator 21 are controlled by an A / D control LSI 23 driven by a clock pulse sent from the clock oscillator 24a. The outputs of the first comparator 22a and the second comparator 22b are processed by the A / D control LSI 23.

The A / D converter 11 configured as described above operates as follows. After the input voltage V1 is integrated for a predetermined period by the integrating capacitors 20a and 20b, the input voltage V1 and the first reference voltage VR1 of reverse polarity are integrated. After the signal output from the integrator 21 is reduced to an appropriate level, the first integrating capacitor 20a and the electric charge are transmitted to the second integrating capacitor 20b by opening and closing the integrating switches 26a and 26b. As a result, the signal output from the integrator 21 is greatly increased by (Cl + C2) / C2 times.

The operation of the switches 26a and 26b will be described below. The input voltage is integrated by the integrating capacitors 20a and 20b, in which case the switch 26a is turned off and the switch 26b is turned on. Next, switch 26a is turned on, and switch 26b is turned off. As a result, the charge of the capacitor 20a is transferred to the capacitor 20b. If the capacitor C2 of the capacitor 20b is smaller than the capacitor C1 of the capacitor 20a, the voltage is increased proportionally according to the relationship of V = Q / C; For example, if the capacitor C2 is 1/10 of the capacitor C1, the voltage is increased by 10 times. Therefore, the signal output from the integrator 21 increases. In this way, the opening and closing of the switches 26a and 26b terminate the transfer of electric charges.

When the transfer of charge is completed, the integration switches 26a and 26b open to cut off the first integration capacitor 20a. Next, the second reference voltage VR2 is integrated. The A / D control LSI 23 detects whether the signal output from the integrator 21 has reached an initial level, for example, the level 500 as shown in FIG. When the signal output from the integrator 21 reaches an initial level, for example, level 500, A / D conversion is terminated.

8 shows the operation waveform of the signal output from the integrator 21. FIG. When the integral period of the input voltage V1 is T1, the integral period of the first reference voltage VR1 is TR1, the integral period of the second reference voltage VR2 is TR2, and the integral resistance is R1 or less, the integral capacitor ( The amount of charge Q accumulated in Cl + C2) is expressed by the following equation.

Q = (V1 / R1) T1 .... (1)

The amount of charge Q1 released in the period TR1 is expressed by the following equation.

Q1 = (VR1 / R1) TR1 .... (2)

The amount of charge Q2 released in the period TR2 is expressed by the following equation.

Q2 = (VR2 / R1) TR2 .... (3)

Since Q = Q1 + Q2, V1 can be represented by the following equation.

V1 =-((VR1TR1 + VR2TR2) / T1) .... (4)

The input voltage is obtained by equation (4) by calculating the clock pulse generated by the clock oscillator 24a during the periods TR1 and TR2, and multiplying the value TR1 + TR2 obtained by the calculation with the weights VR1 and VR2 of the reference voltage, respectively. Can lose.

In principle, since the integral period TR1 does not depend on the characteristics of the comparator, the value V1 can be obtained at a sufficient speed. Further, in the integration period TR2, the signal output from the integrator 21 is greatly expanded to (C1 + C2) / C2 times. As a result, the input voltage can be easily detected with high accuracy.

Next, the operation of the flicker component measuring apparatus according to the present invention will be described. The center frequency of the bandpass filter 8 of the flicker component detector 5 is determined by the clock signal generated by the clock generator 16 to determine the frequency of the flicker component to be measured. Next, the liquid crystal display device 1 is driven, and the backlight device 3 is turned on. Accordingly, the flicker component included in the signal output from the liquid crystal display in the display state is measured.

At this time, light is incident on the light receiving portion 2 from the display screen of the liquid crystal display device 1 and photoelectrically converted into an analog signal by the light receiving portion 2. The analog signal is then output from the illuminometer 4 to be transmitted to the flicker component detector 5. The analog signal input from the illuminometer 4 to the flicker component detector 5 is amplified by the signal conditioner 7 at a predetermined amplification factor and then input to the bandpass filter 8. The band pass filter 8 extracts only a predetermined frequency component from the analog signal. The AC signal output from the band pass filter 8 is converted into a signal having a DC level which is an effective value (direct current signal) of the jeans by the AC / DC converter 9. Next, the ripple component of the constant frequency superimposed on the DC signal is removed by the ripple cancellation filter 10.

The A / D converter 11 performs A / D conversion of the signal output from the ripple cancellation filter 10, and outputs the digital signal according to the LED display device 12 as a result. Displayed digitally on device 12. The signal output from the 1/3 OCT bandpass filter 8 is displayed on the LED display 12 through the AC / DC converter 9, the ripple cancellation filter 10, and the A / D converter 11.

In general, when the flicker of the NTSC system is measured, the signal and center frequency output from the 1/3 OCT bandpass filter 8 are selected to be 30 Hz. Other examples are as follows; When the opposing voltage is adjusted, the center frequency is selected as the frequency having a horizontal period. When the DC component of the voltage of the video signal is adjusted, the center frequency is selected as the frequency having the vertical period. When flicker of the PAL method is measured, the center frequency is selected to 25 Hz. In this case, the 1/3 OCT bandpass filter 8 can select any frequency component. Therefore, the noise component included in the signal output from the illuminometer 4 can be cut by the 1/3 OCT bandpass filter 8.

Next, the flicker component measuring apparatus and the conventional apparatus of the present invention are compared with the obtained data.

9 is a graph showing the characteristics of the flicker component measuring apparatus. For example, looking at the relationship between analog measurement (prior device) and digital measurement (an embodiment of the present invention), the value obtained by analog measurement is 20 mV, while the value obtained by digital measurement is 10. Thus, the adjustment level can be set to ten. 10 is a graph showing the characteristics between the temperature and the flicker component. Conventionally, inspection is performed on the surface of a panel by the analog measurement at the temperature of 60 degreeC. The value obtained by digital measurement varies linearly from a temperature of 30 ° C. to a temperature of 70 ° C. Therefore, in the digital measurement of this invention, when inspection is performed at normal temperature (25 degreeC), the judgment level can set the minimum digital display value at 1.7, and can select good or bad goods.

9 and 10, reference numeral 24 denotes a measurement module (serial NO.ER45301-009) and reference numeral 25 denotes a measurement module (serial NO.ER45047-054).

As described above, according to the present invention, the flicker level of the required frequency is processed to the analog level by the amplifier 7 and the bandpass filter 8, and then converted into a digital value to be displayed. Conventionally, analog values are obtained using the above apparatus, and inspection is performed based on the analog values thus obtained. Therefore, the inspection criteria are visually ambiguous, resulting in an ambiguous measurement error or pass / fail determination. By digitalizing the measurement, this problem can be solved. As a result, the time required for inspection and measurement can be shortened, and inspection can be performed accurately. Further, by combining the flicker component measuring apparatus according to the present invention with a personal computer or the like, the inspection can be automatically performed. By digitizing the measurement, a display device can be constructed based on the digital multimeter.

When performing the inspection, an illuminometer and a luminance meter used for the inspection of the flicker and the measurement of the counter voltage for the conventional liquid crystal display device can be used for the digital measurement. Therefore, a significant improvement of equipment is not necessary. For this reason, the time and cost required for inspection can be reduced.

In the past, when criteria for good and defective products were determined, a sample showing the minimum pass quality was employed as the pass criterion. It is difficult to make a sum / negative determination with such a criterion. By digitizing the measured value of the flicker component, the criteria for sum / negative determination are easily determined, and the quality is uniform.

As described above, in the flicker component measuring apparatus according to the present invention, only a predetermined frequency component is taken out from the analog signal obtained by measuring the luminance change of the liquid crystal display panel. Next, the frequency component extracted as a measurement result is converted into a digital signal so that the flicker component of the required frequency can be measured digitally. As a result, the digital signal is displayed digitally, whereby the read error by the inspector and the ambiguity of the sum / sub decision of the inspector can be prevented.

In addition, when the luminance variation of the liquid crystal display panel is measured, the luminance meter and illuminometer used in the conventional apparatus can be used. In addition, only a specified frequency component is extracted from the analog signal obtained by the measurement, and A / D conversion is performed therefor. Therefore, an expensive general purpose FFT analyzer for performing a fast Fourier transform operation on the analog composite waveform becomes unnecessary. In the filtering process for extracting the selected frequency component, Instead of using the digital filter required when the filtering process is done on A-D converted data, the filtering can be done at the analog level. As a result, the effort and cost required for the development of the measuring device can be reduced.

Those skilled in the art will appreciate that various modifications may be made without departing from the scope and spirit of the invention. Accordingly, the appended claims should not be limited to the foregoing description but should be construed broadly.

Claims (6)

A flicker component measuring apparatus for measuring a flicker component of a selected frequency of a liquid crystal display, comprising: photoelectric conversion means for converting brightness of a display screen of the liquid crystal display into an analog signal; Filter means for filtering the analog signal to output a filtered signal having a selected frequency component; And signal conversion means for converting the filtered signal into a digital signal. The flicker component measuring apparatus according to claim 1, wherein the photoelectric conversion means includes a light receiving portion arranged to face the display screen, and the photoelectric conversion means outputs the analog signal to the filter means. The apparatus of claim 1, further comprising amplifying means for receiving and amplifying the analog signal and outputting the amplified signal to a filter means. 2. An apparatus according to claim 1, wherein said filter means is capable of changing the frequency bandwidth of an analog signal to be filtered by said filter means. 2. The apparatus of claim 1, wherein the signal conversion means; An AC-DC converter for converting the filtered signal into an effective signal corresponding to the effective value of the filtered signal; A ripple remover for removing a ripple overlapping the effective signal; And an A-D converter for converting the signal output from the ripple canceller into a digital signal. 2. An apparatus for measuring flicker component according to claim 1, further comprising display means for displaying a digital signal.