JPS63189830A - Method and device for driving plzt optical shutter array - Google Patents

Abstract

PURPOSE:To attain an accurate gradation control with a simple circuit constitution by impressing a voltage to be impressed to a PLZT with a pulse signal and changing its period/duty in accordance with an image level. CONSTITUTION:A pulse signal having a period shorter than that of one-unit subscanning controlled at its period/duty in accordance with the density level of an image is formed. Since the quantity of light to be transmitted through the PLZT is determined by a voltage value to be impressed in a subscanning period, the integrating value of the quantity of transmitted light in the subscanning period can be changed by changing the duty. The quantity of transmitted light in the subscanning period can be changed also by changing the pulse period. In order to surely execute gradation control, the period of the pulse should be shorter than that of subscanning. A pulse signal whose frequency and duty are simultaneously changed can be also used. Thus, the gradation control can be attained by forming the pulse signal and impressing the pulse signal to each pixel of a PLZT optical shutter array.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method and device for driving a PLZT optical shutter array, and more specifically to a method and apparatus for driving a PLZT optical shutter array, which can control the gradation of the PLZT optical shutter array. The present invention relates to a driving method and device.

(Background of the invention) PLZT is an electro-optic ceramic that has high transmittance and good electro-optic effect characteristics, and its manufacturing method is as follows, for example. It is synthesized by optical reaction, and after mixing these benzene solutions in a predetermined composition ratio, hydrolyzing and drying the resulting precipitate, the resulting powder is hot-pressed into a sintered body.Here So, what is the electro-optic effect?PLZ
It refers to current dyeing in which birefringence (6 points) changes in response to the electric field (E) applied to T. Here, birefringence Δn means PLZT
Difference in refractive index n2- when a difference occurs between the refractive index n1 of light vibrating in the parallel direction and the refractive index n2 of light vibrating in the perpendicular direction in the electric field E in the area where the electric field E acts on the electric field E. n 1
means. When the relationship between the electric field E and the birefringence Δn is linear as shown in FIG. This relationship is called the second-order electro-optic effect or Kerr (K, err) effect.

Here, we will explain how to represent PLZT types.

The following formula is usually used as the composition formula of PLZT.

(Pb + -X, 1ax) (Zry, Tiz
) s-fo3 The composition shown in the above formula is abbreviated as PLZ
It is written as T(x/V/Z). An example of PLZT having a primary electro-optic effect is PLZT (12/4
0/60) and has a second-order electro-optic effect.
For example, there is PLZT (9/65/35).

Using the electro-optic effect, by changing the magnitude of the electric field applied to PLZT, the weight of transmitted light can be changed, and it can be used as an optical modulator or optical shutter. FIG. 8 is a conceptual diagram of an optical shutter/VA converter using PLZT.

Light emitted from a light source 1 that emits unpolarized light passes through a first polarizing plate 2 having a polarization direction of 45° with respect to the horizontal axis.
Only the light component L1 having a vibration direction of 45° with respect to the horizontal axis is passed through, and enters the PLZT3 to which an electric field set at an angle of 45° with the polarization direction of the polarizing plate 2 is applied. Here, PLZT3 is PLzT(9/65/35)t'al with a second-order electro-optic effect. P L Z
T 3 k: Lt D An electric field is applied from the control circuit 4, and this electric field can be varied.

The light L2 that has passed through the PLZT3 is 45
The light enters the second polarizing plate 5 set in the direction of .degree., and the light transmitted through the polarizing plate 5 becomes output light.

As is clear from the figure, the first polarizing plate 2 and the second polarizing plate 5 are arranged so that the angle difference in their polarization directions is 90''. indicates the direction of vibration of light.

With this configuration, from the control circuit 4 to the PLZT3
When no voltage is applied to PLZT, PLZT is an optically isotropic medium, and there is no change in the polarization state of light passing through PLZT3. The same light as Ll passes through PLZT3 as it is. Therefore, the photographing direction of the light L+ and the polarization direction of the second polarizing plate 5 form an angle of 90°, and the light cannot pass through the second polarizing plate 5. On the other hand, when a voltage is applied to the PLZT 3 from the control circuit 4, the PLZT acts like a uniaxial optical crystal and produces birefringence. Here, when the applied voltage is set to a half-wavelength voltage, the polarization direction of the light L2 after passing through the PLZT3 is rotated by 90 degrees, and becomes the same direction as the polarization direction of the second polarizing plate 5, so that the light becomes the second polarized light with low loss. Board 5
(light shutter operation). On the other hand, PLZT3
When the applied voltage is set to a voltage other than the half-wavelength voltage, the birefringence Δn changes according to the value of the applied voltage, changing the optical layer of the output light (light modulation operation).

The light modulation operation described above can be used as is to control the gradation of an input image. In other words, in the case of a bright image, the PL is
By controlling the birefringence of ZT3 and controlling the birefringence of PLZT3 so that in the case of a dark image, the light passing through the second polarizing plate 5 is reduced, the light output having gradation characteristics can be changed to the second polarized light. 1q can be removed from board 5.

By the way, there are two types of gradation control methods as shown below.

■Change the voltage value applied to PLZT (applying time is constant).

■Change the application time within the sub-scanning period (applied voltage is constant).

Here, the sub-scanning period refers to the period from one scan line of an image to the next scan line.

(Problem to be solved by the invention) In the first method, the voltage value is changed for each pixel and the PLZT
The circuit becomes complicated.

On the other hand, in the case of the second method, if the recording material is not stopped each time when spacing the recording material continuously, area gradation will occur, and the blank area will become large at low m degrees, leading to a decrease in image quality. I'll be there.

The present invention has been made in view of these points, and
The purpose is to realize a driving method and apparatus for a PLZT optical shutter array that has a simple configuration and can perform accurate gradation.

<Means for Solving the Problems> A first invention for solving the above-mentioned problems is a method for driving a PLZT optical shutter array that controls the gradation of each pixel of a PLZT optical shutter array consisting of a large number of pixels for light modulation. , the period and/or change depending on the density level of the image.
Alternatively, the present invention is characterized in that a pulse signal having a period shorter than one unit sub-scanning period with adjusted duty is created and the pulse signal is applied to the pixels. The second invention is a PLZT optical shutter array driver 1FJl device that controls the gradation of a PLZT optical shutter array consisting of a large number of pixels for light modulation for each pixel, and the period and/or duty of the PLZT optical shutter array is controlled according to the density level of the image. Adjusted 1
The present invention is characterized in that a pulse signal having a period shorter than the unit D1 scanning period is created and the pulse signal is applied to the pixels.

(Operation) The voltage to be applied to the PLZT is applied as a pulse signal, and the period and/or duty is changed according to the 11 degree level of the image.

(Example) FIG. 1 is a 70-chip diagram showing an example of the method of the present invention.

Step (2) Create a pulse signal with a period shorter than one unit sub-scanning period whose period and/or duty is set by the WA clause according to the density level of the image.

Our technology involves changing the voltage value applied to PLZT,
We adopted a method of changing the application time within the sub-scanning period, but the applied voltage is a pulse signal, and this pulse signal is used as a PLZ
Even if T is applied, the amount of transmitted light of the input light can be changed in the same way. That is, since the amount of transmitted light of PLZT is determined by the integral value of the applied voltage within the sub-scanning period, the integral value of the amount of transmitted light within the sub-scanning period can be changed by changing the duty. Also, the pulse period is p t-zT
Since the transmitted light intensity depends on the pulse period in the region around the hydrogen ion response time, the amount of transmitted light within the sub-scanning period can be changed by changing the pulse period (frequency).

FIG. 2 is a diagram showing an example of a created pulse signal. (A) shows a pulse signal whose period is changed every sub-scanning period. PLZT responds to changes in applied voltage with a certain delay time. For example, when a step voltage is applied, the time required for the transmitted light m to rise from 10% to 90% amplitude of the final value is 20 to 100 μs.

On the other hand, the falling time is 10 μs or less. Therefore, if the frequency of the applied pulse is increased, the amplitude of the amount of light transmitted through the PLZT becomes extremely small as shown in (b), and if the frequency of the applied pulse is decreased, the amplitude of the transmitted light m of the PLZT will be reduced accordingly. The amplitude gradually increases as shown in (b). Therefore, the integral value of the transmitted light m within the sub-scanning period becomes smaller as the frequency of the applied pulse becomes higher, and becomes larger as the frequency becomes lower. By utilizing this phenomenon, the gradation of the output light passing through the polarizing plate 5 can be controlled. In other words,
This method can be said to be a gradation control method that takes advantage of the fact that PLZT has a finite response time. Therefore, tone control can be performed by lowering the pulse frequency when the image density is low (bright) and increasing the pulse frequency when the image density is high (dark). Note that since PLZT is capacitive, when a resistive component is connected to the PLZT element due to the circuit configuration, it has a response time specific to the circuit configuration, so by changing the period of the applied pulse in the region around the response time. , the gradation control as described above becomes possible.

(C) shows a pulse signal whose duty is changed every sub-scanning period. By increasing the pulse duty, it is possible to increase the integral value of the amount of transmitted light within the sub-scanning period, and therefore, by increasing the transmitted light a, the output light passing through the second polarizing plate 5 at Rffl shown in FIG. 8 is increased. be able to. Conversely, if the duty of the pulse is lowered, the integral value of the transmitted light m within the sub-scanning period can be reduced, and therefore the amount of transmitted light can be reduced and the output light passing through the second polarizing plate 5 can be reduced. In this case, unlike the case of frequency control described above, the integral value of the applied pulse itself becomes a problem.

Therefore, tone control can be performed by increasing the pulse duty when the image density is low (bright) and by decreasing the pulse duty when the image density is high (dark).

In (d), the number of pulses within the sub-scanning period is changed. In order to perform gradation control reliably, the period of the applied pulses must be shorter than Tl, as shown by the first period T1.

In (e), the frequency is the same for each sub-scanning period, but the pulse amplitude is changed.

Although not shown in FIG. 2, it is also possible to use a pulse signal whose frequency and duty are changed at the same time.

In the example shown in FIG. 2, a pulse having amplitudes in both positive and negative directions is shown as a pulse applied to the PLZT, but it does not necessarily have to have amplitudes in both polarities. Unipolar pulses having amplitude only in the positive direction or in the negative direction may be used. However, PLZT has a phenomenon in which the change in birefringence is difficult to completely return to its original state even when the electric field is reduced, that is, hysteresis. Therefore, the floor HQ@11 control characteristics are improved by using bipolar pulses rather than by using unipolar pulses.

Step ■ Apply the pulse signal created in step ■ to the pixels.

In step (2), a pulse signal whose period and/or duty is adjusted according to the image density is created and applied to each pixel of the PLZT optical shutter array, thereby creating a pulse signal that passes through the second polarizing plate 5 (see FIG. 8). You can change the number of times and control the gradation.

According to the present invention, since the frequency of the applied pulse or the duty of the applied pulse is changed, the circuit configuration is simplified and accurate gradation control can be performed.

FIG. 3 is a configuration diagram showing an embodiment of the apparatus of the present invention. In the figure, 11 is a pixel clock generator that generates a pixel clock, 12 is an N frequency divider that divides the pixel clock output from the pixel clock generator 11 by 1/N, and 13 also receives the pixel clock as a synchronization clock. It is an image data generator.

The image data generator 13 is a television camera.

Various types such as COD are possible. The clock frequency-divided by the N frequency divider 13 becomes the reference clock.

A counter controller 14 counts the reference clock and outputs a counter value, as well as a positive/negative switching signal and a fade-out timing signal. 15
R uses the output of the image data generator 13 and the output of the counter controller 14 as input data (address), and the receiver outputs a value corresponding to the input data as serial data.
It's OM. 16 is a pixel clock shift clock, R
This is a shift register that receives the output (serial data) of the OM15 as input data and converts the serial data into N-bit parallel data.

17 is a fade-out signal generator that generates a fade-out signal in response to a fade-out timing signal from the counter controller 14; 18 is a signal generator of positive and negative polarity;
FtWA is connected to the amplifier, which receives the output of the fade-out signal generator 17 as a gain control signal, and generates both positive and negative voltages. One is amp 1
A switch 20 receives the positive and negative voltages of 8 and selects one or none of these voltages by a positive/negative switching signal from the counter controller 14, which is sent via the switch 19. This is a PLZT optical shutter array that receives a pulse signal as an applied voltage and N-bit data from a shift register 16 as a pixel select signal.

It is assumed that the PLZT optical shutter array 2o is composed of N vixenos 1. The operation of the apparatus configured as described above will be explained below with reference to the timing chart of FIG.

The pixel clock generator 11 generates a pixel clock as shown in FIG. 4(a). The N frequency divider 12 divides the pixel clock by 1/N and generates a reference clock as shown in (b). The reference clock enters counter controller 14. The counter controller 14 is equipped with a counter that is reset after counting up to 16 clocks and starts counting 16 clocks again, and the counter value changes from 0 to 15 in synchronization with the reference clock as shown in (d). changes up to. At the same time, the counter controller 14 generates a positive/negative switching signal as shown in (c). In the example shown in the figure, the first period is positive and the ninth period is negative.

On the other hand, the pixel clock is also given to the image data generator 13, and the image data generator 13 outputs image data synchronized with the pixel clock. Data corresponding to the density of input image data is written in the ROM 15 in advance.
Data as shown in (e) is output in synchronization with the counter value output from the counter controller 14. In other words, the output of ROM15 is PL within one period of the reference clock.
This is a control signal for turning on or turning off the voltage applied to the ZT. This ROM data output is shift register 1
6, and the shift register 16 converts the ROM output (serial data) into N-bit parallel data in synchronization with the pixel clock and latches it.
/off data is provided to the corresponding pixel of the PLZT optical shutter array 20.

A positive/negative switching signal from the counter controller 14 is applied to a switch 19, which first applies a positive voltage and then applies a negative voltage to the PLZT optical shutter array 20. The switch 19 receives the positive/negative switching signal to create a state in which neither the positive nor negative voltages are connected, and creates an O voltage when switching from positive to negative, thereby causing the PLZT optical shock array 20 to operate. ing. The applied voltage is turned on and off according to the N-bit output of the shift register 16, and as a result, voltages of both positive and negative polarities as shown in (see below) are applied to the PLZT optical shutter array 20, and gradation control is performed. be exposed.

FIGS. 4(g) and 4(h) are diagrams showing other examples of the PLZT applied signal, and show how the duty of the pulse changes depending on the degree level of the image data. The l1ffl level increases in the order of (H), (E), and (G).

By repeating the above-described operations, PLZT tone control within the sub-scanning period is performed. FIG. 5 is a macroscopic view of the timing chart shown in FIG. 4. The sub-scanning period consists of a transmission period during which gradation control is performed by applying a pulse signal to the PLZT, and a hysteresis interval during which hysteresis remaining in the PLZT is removed. The applied signals shown in (f) to (h) of FIG. 4 are shown during the transmission period.

At the end of the transmission period, counter controller 14 sends a timing signal to fadeout signal generator 17, which provides a signal to amplifier 18 that decreases the gain over time. Amplifier 1
8 outputs a positive P4 voltage whose amplitude decreases over time, and a bipolar pulse for hysteresis cancellation as shown in FIG. 5 is applied to PLZT during the hysteresis cancellation period.

This erases the previous history and enables accurate gradation control. In addition, when performing such hysteresis cancellation, PLZ
If the optical signal incident on T is left as it is, the optical signal will pass through even during the hysteresis cancellation period, so it is necessary to turn off the optical signal during this period or put a shutter in front of the PLZT to prevent the optical signal from passing through. There is.

FIG. 6 is a diagram showing a modification of the drive pulse during the transmission period. This shows that the pulse period was changed corresponding to three cases of high, medium, and low transmittance. In the example shown in the figure, there is no O voltage in the drive pulse (PLZT application signal), and either a positive voltage or a negative voltage is applied. In this way, binary control (three-value control in the case of Figures 2, 4, and 5)
Therefore, control becomes easy.

(Effects of the Invention) As explained in detail above, according to the present invention, P L
By applying the voltage to ZT as a pulse signal and changing its period and/or duty according to the image level, the circuit configuration is simple and accurate 1 m control can be performed. A method and apparatus for driving a PLZT optical shutter array can be realized.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing an embodiment of the method of the present invention;
Fig. 2 is a diagram showing an example of the created pulse signal, Fig. 3 is a block diagram showing an embodiment of the device of the present invention, Fig. m4 and Fig. 5 are timing charts showing the operation of each part, and Fig. 6 is A diagram showing a modified example of the drive pulse during the transmission period, FIG. 7 is P
FIG. 8, which is a diagram showing the relationship between electric field E and birefringence of LZT, is a conceptual diagram of an optical shutter/modulator using PLZT. 1... Light source 2, 5... Polarizing plate 3...
PLZT 4...Control circuit 11...
- Pixel clock generator 12...N frequency divider 13... Image data generator 14... Counter controller 15... ROM 16... Shift register 17... Fade out signal generator 18...・Amplifier 19...Switch 20...
・PLZT optical shutter array patent applicant Roku Konishi Photo Industry Co., Ltd. Representative Patent attorney Fuji Ishima

Claims (5)

[Claims] (1) In a PLZT optical shutter array driving method that controls the gradation of a PLZT optical shutter array consisting of a large number of light modulating pixels for each pixel, one unit whose period and/or duty is adjusted according to the density level of the image A method for driving a PLZT optical shutter array, characterized in that a pulse signal having a period shorter than a sub-scanning period is created and the pulse signal is applied to pixels. (2) The method for driving a PL ZT optical shutter array according to claim 1, wherein the pulse signal has an amplitude in at least one of both positive and negative directions. (3) The method for driving a PLZT optical shutter array according to claim 1, wherein the pulse signal is a binary pulse signal that takes only two values of a positive polarity voltage and a negative polarity voltage. (4) The PL according to claim 1, characterized in that a hysteresis cancellation period is provided in the latter half of the one unit sub-scanning period in which a pulse having a high frequency and both phase amplitudes is applied.
Driving method of ZT optical shutter array. (5) In a PLZT optical shutter array driving device that controls the gradation of a PLZT optical shutter array consisting of a large number of light modulating pixels for each pixel, one unit whose period and/or duty is adjusted according to the density level of the image A driving device for a PLZT optical shutter array, characterized in that it is configured to create a pulse signal with a period shorter than the sub-scanning period and apply the pulse signal to pixels.