JPS63141026A - Liquid crystal optical phase filter driving device - Google Patents

Abstract

PURPOSE:To always obtain a MODULATION TRANSFER FUNCTION MTF which is invariably stable even when the temperature drops by constituting such a circuit that the value of a driving voltage has a negative coefficient to the temperature. CONSTITUTION:A rectangular wave outputted by an oscillator 15 is made into a constant-voltage rectangular wave by a voltage correcting circuit 16 and outputted. A temperature compensating amplifier 17 outputs a temperature- corrected voltage by a thermistor 19 with a negative resistance temperature coefficient and the voltage is applied to a liquid crystal optical phase filter 4. If the ambient temperature is low and the viscosity of liquid crystal is high at this time, a higher voltage than usual is applied, and as the temperature rises, the applied voltage is made lower. Consequently, the MTF is held invariable constant regardless of variation in the ambient temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical phase filter that reduces the sharpness of an image formed state, and in particular to a drive device for an optical phase filter using a liquid crystal. It is useful for

[Summary of the Disclosure] This specification and drawings describe a driving device for a liquid crystal optical phase filter in which a circuit is configured such that the value of the driving voltage has a negative coefficient with respect to temperature, so that when the temperature decreases, However, the present invention discloses a technology for creating a drive device that can always obtain a stable MTF.

[Prior Art] Conventionally, an optical phase filter as shown in FIG. 2 has been used as a means for reducing the sharpness of an image formed by a lens or the like. In FIG. 2, 1 is an optical phase filter, 2 is a glass substrate, and 3 is a phase portion formed into a transparent circular convex portion made of silicon oxide or the like. The optical phase filter l is generally called a soft focus filter, is attached to the front surface of a camera lens, etc., and serves to reduce the sharpness of an image. As a result, a photograph with a soft depiction can be obtained, and the photograph becomes psychologically desirable.

Next, the characteristics of the above-mentioned optical phase filter will be explained.

The sharpness of the image when the optical phase filter l shown in Fig. 2 is placed on the pupil plane of the imaging optical system, that is, the MTF (Modulat
The behavior of ion Transfer Function has already been analyzed. Now, assuming that the phase difference of the phase sections 3 shown in FIG. 2 is δ and that the phase sections 3 are randomly arranged, the MTF becomes a curve shown in FIG. 3. In other words, a part A-B where the randomness correlation decreases and a part B-C where the randomness correlation is constant and only the pupil aperture correlation works are connected at the break point B. There is. If the coordinates of this breaking point B are (Fb, Wb) as shown in Figure 3, then Fbmi a/(f・in) ・・・・・・・・・・・・
・・・・・・・・・・・・(1) Mb= lAo+Aδ・
exp(-ikδ)12,', AO+Aδ=1
・・・・・・・・・・・・・・・・・・(2) k・δ=
It is given by (2π/in)In-1)d = (3). Here, a is the average diameter of the phase section 3, f is the focal length of the imaging lens, λ is the wavelength of light, ^δ is the ratio of the total area of the phase section 3 to the total area of the optical phase filter 1, A
O is the ratio of the total area other than the phase section 3 to the total area of the optical phase filter l, n is the refractive index of the phase section 3, and d is the phase section 3
is the geometric thickness of Note that the phase difference δ is the phase difference between the light transmitted through the phase portion 3 and the other portions.

According to the above equations (1) to (3), the phase difference δ and the ratio Ao
, Aδ, b, point distance f, diameter a, and wavelength input can be arbitrarily determined to determine the break point B.

Therefore, if Ao=Aδ=0.5, Mb==
cos2 (kδ/2) ・・・・・・・・・・・・
...(4), now 5 phase difference δ = 0.5 people, = o,
When sX550[n+*1, >ITF value Mb of corner point B changes with respect to wavelength input as shown in FIG. In addition, enter.

is the green wavelength.

When the phase difference δ=0.59, the optical phase filter l can reduce the MTF value almost in the entire visible light region. That is, by attaching such an optical phase filter l to a camera, it is possible to always obtain photographs with soft depictions.

However, since camera lenses do not always provide soft depictions, but sometimes provide sharp depictions, the optical phase filter l has been attached or removed depending on the situation. However, there are cases where it is desired to quickly switch between soft depiction and sharp depiction, and in such cases it is difficult to quickly attach and detach the conventional optical phase filter l.

Therefore, the present applicant proposed a liquid crystal optical phase filter having a cell structure in which liquid crystal is sandwiched in Japanese Patent Laid-Open No. 59-228622-3. According to this liquid crystal optical phase filter, since the arrangement of liquid crystal molecules changes depending on the applied voltage value, it is possible to switch between a soft image and a sharp image without replacing the filter.

[Problems to be solved by the invention] However, since the viscosity of liquid crystal changes depending on the temperature,
There is a problem in that even if the same voltage is applied, it becomes difficult to operate, especially at low temperatures. This will be explained below with reference to the drawings.

Figure 5 shows a conventional liquid crystal optical phase filter.
FIG. 5(A) is a sectional view of the liquid crystal optical phase filter, and FIG. 5(B) is a plan view thereof. In FIG. 5(A), 4
5.6 is a liquid crystal optical phase filter, 5.6 is a glass substrate, and a transparent electrode 7.8 is formed on the surface of the glass substrate 5.6. As shown in FIG. 5(B), the transparent electrode 7 is an electrode in which circular openings 7a are randomly formed, and 7b is a non-opening. Further, 8 is a transparent electrode that is uniform over the entire surface, 9 is a liquid crystal layer made of nematic liquid crystal with positive dielectric anisotropy, and d is the thickness of the liquid crystal layer.

FIG. 6 is a diagram schematically showing a cross section of liquid crystal molecules of the liquid crystal optical phase filter. Liquid crystal molecules exhibit a refractive index of ne for light polarized in the direction of their long axis, and a refractive index of no for light polarized in the direction of their short axis.

Therefore, liquid crystal molecules are optically represented as a rotating body with a long axis of 2ne and a short axis of 2no. In FIG. 6, 10 indicates a liquid crystal molecule in the case of no electric field, that is, an applied voltage O, and 10θ indicates a liquid crystal molecule with a voltage applied and its long sleeve facing the direction of the electric field due to its dielectric anisotropy. , the liquid crystal molecule lO is in the device rotated by θ°, and if light is incident from the X-axis direction, the components of this incident light are:
It can be considered to be divided into two polarization components: the X-axis direction and the Y-axis direction (direction perpendicular to the paper) perpendicular to the X-axis. These two components are each in equal amounts in the case of natural light.

Here, regarding the polarization component in the Y-axis direction, as is clear from FIG. 6, even if the liquid crystal molecules 10 rotate and become 100, the refractive index is always nQ. On the other hand, the polarization direction in the X-axis direction changes with the rotation of the liquid crystal molecules, and the refractive index no at this time is obtained as the value at the point where it intersects with the X-axis. That is, the projection of no onto the X' axis and Z/axis rotated by θ from the X and Z axes is expressed as χ0. If zθ, the cross section is an ellipse, so n02=χ02+zθ2. It is expressed as s:n0=zO/nθ, and as the liquid crystal molecules rotate, the refractive index becomes n@(0
=0) to no (θ=90°). FIG. 7 shows a specific example of such a change in refractive index for a nematic liquid crystal ZLI-1694 (ne"1.633゜nO
-1,503) when using liquid crystal molecule rotation angle (horizontal axis) and refractive index for polarized light in the long axis direction of liquid crystal molecules (vertical axis)
It expresses the relationship between

58 schematically represents the change in the liquid crystal molecule arrangement of the liquid crystal optical phase filter shown in FIG. 12 is the incident light, 13 and 14 are the outgoing lights, a and b are the polarization directions (directions relative to the plane of the paper), and d is the thickness of the liquid crystal layer 9. Transparent electrode 7.8
When no voltage is applied between the liquid crystal molecules 10 of the liquid crystal layer 9
is uniformly horizontal (homogeneous array) to the boundary surface 11 as shown in FIG. 8(B). At this time, the incident light 12 is natural light ( (non-polarized light), due to the birefringence of the liquid crystal layer 9, the emitted light 14 is n e in the extraordinary ray +41 parallel to the liquid crystal molecules 10 + n in the ordinary ray 142 perpendicular to the liquid crystal molecules 10.

The light beam passes through a medium with a refractive index of . However, since the two orthogonal polarization components do not interfere with each other and are uniform over the entire surface, no change in MTF occurs.

On the other hand, when a voltage is applied between the transparent electrodes 7 and 8, liquid crystal molecules l between the non-opening portion 7b of the transparent electrode 7 and the transparent electrode 8
Only O rotates with respect to the boundary surface 11 as shown in Figure 8 (A),
At its maximum, it is vertical (homeotropic alignment), and the polarization direction a of the incident light 12 becomes a light ray 131 that has passed through a medium with a refractive index of no shown in FIG. Further, the polarization direction is the same as the polarization direction perpendicular to the liquid crystal molecules in FIG. 8(B), resulting in a light ray 132 that has passed through a medium with a refractive index of no.

That is, when a voltage is applied, the light beams at the aperture 7a and the non-aperture 7b of the transparent electrode 7 are 131 . . . ned
, 132 ... nod, 141 ... ne
d.

142...-nod phase difference is received. Regarding the component of the polarization direction S of the incident light 12, both 132 and 142 above are n, regardless of the location of the voltage. d, there is no phase difference δ of the emitted light.On the other hand, the component in the polarization direction a varies depending on the presence or absence of voltage.

That is, the phase difference δ of the emitted light is δ=lne−n01·d from the above 131.141.

When such a liquid crystal optical phase member is placed near the pupil position of the imaging lens, the break point shown in FIG.
).

However, in equation (2), when using the liquid crystal optical phase filter according to the present invention, 50% of the incident light acts on the non-phase part, and the remaining 50% acts on the phase part and the non-phase part due to the voltage. do. That is, the area of the light beams of the emitted light beams 131, 132, and 142 corresponds to the area ratio AO of the out-of-phase portion, and the area of the light beam 141 corresponds to the surface MAδ of the phase portion. Furthermore, in equation (3), when the liquid crystal optical phase filter according to the present invention is used, the phase difference is 2 π k・δ= −or In e−n Oid −・・−C5
).

The aforementioned rotation angle θ of the liquid crystal molecules is inversely proportional to the strength of the electric field and the ease of movement of the molecules, that is, the viscosity.

Therefore, when the viscosity of liquid crystal increases, molecules become difficult to move, and the same rotation angle cannot be obtained even with the same electric field strength.
As a result, the MTF changes each time. As described above, the viscosity of liquid crystal increases as the temperature decreases, so conventional liquid crystal optical phase filters have been disadvantageous when the ambient temperature is low.

It is an object of the present invention to provide a driving device for a liquid crystal optical phase filter that eliminates the drawbacks of the conventional example and provides a stable MTF at all times even when the temperature decreases.

[Means for Solving the Problems] Means for solving the above problems will be explained using FIG. 1 corresponding to the embodiment. A liquid crystal optical phase filter driving device characterized by comprising a voltage correction circuit 16 that outputs the voltage as a rectangular wave between 0 and IV, and a temperature correction amplifier 17 equipped with a thermistor 19 that outputs a negative temperature coefficient of resistance. be.

[Operation] The rectangular wave output from the oscillator 15 is output as a constant voltage rectangular wave in the voltage correction circuit 16. In the temperature correction amplifier 17 , a temperature-corrected voltage is outputted by a thermistor 19 having a negative temperature coefficient of resistance, and is applied to the liquid crystal optical phase filter 4 . At this time, when the ambient temperature is low and the viscosity of the liquid crystal is high, a voltage larger than usual is applied, and on the other hand, as the temperature becomes higher, the applied voltage becomes smaller. Therefore, regardless of changes in ambient temperature, the NTF
can be kept constant.

[Embodiment] FIG. 1 is a configuration diagram of a drive circuit showing an embodiment of the present invention. In FIG. 1, 15 is an oscillator, which includes a switch 18, an inverter 20, a resistor 101, and a capacitor 201.
It is composed of 16 is a voltage correction circuit, which includes a Zener diode 21, an operational amplifier 301, a resistor 102.
It is composed of a capacitor 103. 17 is a temperature compensation amplifier, which includes a thermistor 19 having a negative temperature coefficient of resistance.
, an operational amplifier 302, and resistors 104, 105, and 106. 4 is the liquid crystal optical phase filter mentioned above.

Next, the operation of the L wiring circuit will be explained.

First, when the switch 18 is turned on, the potential between the two inverters 20 composed of C-MOS is changed to the resistor 101,
Due to the time constant determined by the capacitor 201, the signal is output as a rectangular wave. In the voltage correction circuit 16, an operational amplifier 301 with a gain (voltage gain) of 1 is connected to a 2-Ead eight resistor 18.
Since the Zener diode 21 is connected in parallel with the Zener diode 2, a constant potential rectangular wave determined by the dark value voltage of the Zener diode 21 is output. Note that since the gain is 1, the voltage determined by the Zener diode 21 needs to be lower than the input voltage. Therefore, when m is higher than the input voltage, +i? An amplifier may be used in the j stage. Temperature compensation amplifier 1
7, the feedback resistor 105 of the operational amplifier 302
A thermistor 19 having a negative temperature coefficient of resistance is connected in parallel with. The gain G of the operational amplifier 302 is determined by the resistance of the thermistor 19 being TH, and the feedback resistance 105 being TH.
．． Each resistance value of 106 is R4.

If it is R5.

It is expressed as R5+TH G=□ (6). Therefore, if the resistance of the thermistor 19 decreases, the gain G also decreases, and the voltage decreases. on the other hand,
As the resistance of the thermistor 19 increases, the gain G also increases and the voltage increases. That is, the temperature correction amplifier 17 obtains a gain proportional to the resistance of the thermistor 19. As is clear from equation (6), the applied voltage is R
It is composed of a bias voltage based on 5/R4 and a temperature correction voltage based on T H/Ra, and they act in the same way. The voltage corrected for temperature in this way is applied to the liquid crystal optical phase filter 4.

Figure 9 shows how the applied voltage (vertical axis) to obtain a constant MTF corresponds to the temperature (horizontal axis) in a liquid crystal optical phase filter that uses Merck ZLI-1694 as the liquid crystal and has two liquid crystal layers with a thickness d = 12 μm. This is a temperature-corrected voltage curve expressed as follows.

Now, connect resistor 1 so that the output of oscillator 15 is I KHz.
01, when the capacitor 201 is set, a rectangular wave varying between OV and 5V is output. This rectangular wave is converted into OV and l by a Zener diode 21 in the voltage correction circuit 16.
It is corrected and output as a rectangular wave between . If the voltage shown in FIG. 9 is applied to the liquid crystal optical phase filter 4, it is possible to always obtain a constant MTF against temperature changes. 2XD-5 manufactured by Denshi was used. The change in resistance value with respect to temperature change at this time is shown in Fig. 1θ. Also, resistance 104 = 10 KΩ, resistance 105 = 31 KΩ
Then, the output voltage of the temperature compensation amplifier 17 is the 11th
The temperature-corrected voltage curve (
It was possible to make it almost the same as the broken line b) in Fig. 11.

That is, according to the present invention, even if the temperature at which the liquid crystal optical phase filter 4 is used changes, it is possible to always obtain a constant MTF simply by turning on the switch 18 of the oscillator 15.

In this embodiment, a fixed resistor is used as the feedback resistor 105 of the temperature compensation amplifier 17 shown in FIG. 1, but by making it a variable resistor, the temperature compensation characteristics of the voltage applied to the liquid crystal optical phase filter 4 can be maintained. You can arbitrarily change the MTF value while keeping the value unchanged.

Furthermore, although a thermistor 19 with a negative temperature coefficient is used, a thermistor with a positive temperature coefficient may also be used. In this case, the same effect can be obtained by connecting the thermistor in series with the resistor 104. I can do it.

[Effects of the Invention] As explained above, according to the present invention, a thermistor having a negative temperature coefficient of resistance is connected in series with a feedback resistor to configure a circuit such that the output voltage has a negative temperature coefficient. By doing so, a desired MTF can always be obtained even if the ambient temperature changes, which is extremely useful in practice.

[Brief explanation of the drawing]

Figure 1 is a circuit configuration diagram showing an embodiment of the present invention, Figure 2 is a perspective view of a conventional optical phase filter, and Figure 3 is its MT.
Figure 4 is a characteristic diagram of a conventional optical phase filter, Figures 5 (A) and (B) are a cross-sectional view and a plan view of a liquid crystal optical phase filter, respectively, and Figure 6 is a cross-section of liquid crystal molecules. 7 is a diagram showing the relationship between the rotation angle of liquid crystal molecules and the refractive index, and FIG. 8 is a schematic diagram showing changes in the alignment of liquid crystal molecules.
Figure 9 is a temperature compensation voltage curve of a liquid crystal optical phase filter, Figure 10 is a characteristic diagram of a thermistor with a negative temperature coefficient of resistance,
FIG. 11 is a characteristic diagram of the drive device according to the present invention. l: optical phase filter, 4: liquid crystal optical phase filter, 7.8: transparent electrode, 7a: opening, 7b = non-opening part, 9: liquid crystal layer, 10: liquid crystal molecule, 15:
Oscillator, 16: Voltage correction circuit, 17: Temperature correction amplifier, 19: Thermistor, 21: Zener diode.ぢ [Come Light Character Lee π -O -eye Filter Ritsu 47 Shellfish diagram Figure 2 MTF Nino 4J Show 2 Fig. 300 500 600 [NRR +] Subsection, U.S. Ue -Ei Filter F1 Sumita Dai 4Figure 4;
) (B) ) Explanation of the old filter Figure 5 Formula for the cross section of the crystal molecule; Fig. 6 □ Liquid crystal valve rotation angle The effect is to open the door to moxibustion.
ne) ”141(n″)(A)
(B) Circle showing changes in crystal molecular arrangement Σ Figure 8 Temperature correction voltage ffEtf 3 lines Figure 9 Characteristics of thermistor 4 Figure 10

Claims (2)

[Claims] (1) A liquid crystal optical phase filter comprising an oscillator, a voltage correction circuit that corrects the output of the oscillator to a first voltage, and a temperature correction amplifier equipped with a thermistor having a negative temperature coefficient of resistance. Drive device. (2) The temperature compensation amplifier amplifies the first voltage to a second voltage and outputs a composite voltage with a temperature-compensated third voltage. 2. The liquid crystal optical phase filter driving device according to 2.