Liquid-crystal light-amount adjusting device, method of driving liquid-crystal light-amount adjusting device, and camera including the liquid-crystal light-amount adjusting device

• US 20080074532A1
• Filed: 10/05/2007
• Published: 03/27/2008
• Est. Priority Date: 12/18/2001
• Status: Active Grant

• Current Assignee: Toshifumi Takaoka
• Original Assignee: Toshifumi Takaoka
• Inventors: Takaoka, Toshifumi
• Granted Patent: US 7,394,498 B2
• Time in Patent Office: Days
• US Class Current: 348/362
• CPC Class Codes: G02F 1/13306 Circuit arrangements or driving methods for the control of single liquid crystal cells G02F1/132, G02F1/133382 take precedence
• CPC Class Codes: G02F 2203/60 Temperature independent
• CPC Class Codes: H04N 23/60 Control of cameras or camera modules
• CPC Class Codes: H04N 23/75 by influencing optical camera components

Abstract

A liquid-crystal light-amount adjusting device in which the effective power of driving pulses for acceleration is optimized to improve response characteristics of optical transmittance, a method of driving the apparatus, and a camera including the apparatus. The liquid-crystal light-amount adjusting device according to the present invention includes a driving-pulse generating circuit (16) for generating driving pulses having pulsed voltages, a liquid-crystal light-amount adjusting unit (12) for changing the optical transmittance of a liquid crystal according to pulse shapes of the driving pulses, and a microcomputer (19) for controlling frequencies and duty ratios of the driving pulses. The microcomputer (19) exercises control so that the driving-pulse generating circuit (16) generates driving pulses including driving pulses for acceleration, having a pulse shape with a first frequency and a first duty ratio, and driving pulses for dimming, having a pulse shape with a second frequency that is different from the first frequency and a second duty ratio that is different from the first duty ratio.

Claims

1. A liquid-crystal light-amount adjusting device comprising:

a driving-pulse generating circuit for generating driving pulses having pulsed voltages;

a liquid-crystal light-amount adjusting unit, to which the driving pulses are supplied, for changing an optical transmittance of a liquid crystal according to pulse shapes of the driving pulses;

a control circuit for controlling frequencies and duty ratios of the driving pulses; and

a temperature detecting circuit for detecting an ambient temperature of the liquid-crystal light-amount adjusting unit and outputting a result of detection to the control circuit, the control circuit changing the frequencies of the driving pulses in accordance with the ambient temperature,

wherein the control circuit exercises control so that the driving-pulse generating circuit generates driving pulses for acceleration for a first applying time, having a pulse shape with a first frequency and a first duty ratio, and driving pulses for dimming for a second applying time, having a pulse shape with a second frequency that is different from the first frequency and a second duty ratio that is different from the first duty ratio,

wherein the first frequency and the first duty ratio and the first applying time are based upon the driving pulses for dimming and the second applying time is determined from the first applying time,

wherein the number of pulses in the driving pulses for acceleration is an integer multiple of one period in the first applying time and the number of pulses in the driving pulses for dimming is an integer multiple of one period in the second applying time.

2. A liquid-crystal light-amount adjusting device according to claim 1, comprising:

a storage circuit for storing an association table defining association of an optical transmittance with driving pulses for acceleration and driving pulses for dimming for achieving the optical transmittance,

wherein the control circuit exercises control so that the driving-pulse generating circuit, by referring to the association table, generates driving pulses with which a desired optical transmittance is achieved.

3. A method of driving a liquid-crystal light-amount adjusting device, comprising:

acceleration driving pulses, having a frequency that is different from a frequency of driving pulses having a pulse shape in accordance with a desired optical transmittance, are supplied to the liquid crystal;

dimming driving pulses, having a pulse shape in accordance with the desired optical transmittance, are supplied to the liquid crystal;

changing an optical transmittance of the liquid-crystal in accordance with the pulse shapes of the acceleration driving pulses and dimming driving pulses supplied to the liquid crystal;

detecting an ambient temperature of the liquid-crystal light-amount adjusting unit; and

changing the respective frequencies of the acceleration driving pulses and the dimming driving pulses in accordance with the ambient temperature,

wherein a frequency, a pulse amplitude, a duty ratio, and a first applying time of the acceleration driving pulses are based on the dimming driving pulses and a second applying time of the dimming driving pulses is determined from the first applying time,

wherein the number of pulses in the acceleration driving pulses is an integer multiple of one period in the first applying time and the number of pulses in the dimming driving pulses is an integer multiple of one period in the second applying time.

4. A camera comprising:

an optical system for focusing light coming from a target on an imaging surface;

a liquid-crystal light-amount adjusting unit for adjusting an amount of the light that reaches the imaging surface, by changing an optical transmittance of a liquid crystal;

a driving-pulse generating circuit for generating driving pulses having pulsed voltages, the driving pulses being supplied to the liquid crystal to change the optical transmittance; and

a control circuit for controlling frequencies and duty ratios of the driving pulses;

a temperature detecting circuit for detecting an ambient temperature of the liquid-crystal light-amount adjusting unit and outputting a result of detection to the control circuit, the control circuit changing the frequencies of the driving pulses in accordance with the ambient temperature,

wherein the control circuit exercises control so that the driving-pulse generating circuit generates driving pulses for acceleration for a first applying time, having a first frequency and a first duty ratio, and driving pulses for dimming for a second applying time, having a second frequency that is different from the first frequency and a second duty ratio that is different from the first duty ratio,

wherein the first frequency and the first duty ratio and the first applying time are based upon the driving pulses for dimming and the second applying time is determined from the first applying time,

wherein the number of pulses in the driving pulses for acceleration is an integer multiple of one period in the first applying time and the number of pulses in the driving pulses for dimming is an integer multiple of one period in the second applying time.

5. A camera comprising:

an optical system for focusing light coming from a target on an imaging surface;

a liquid-crystal light-amount adjusting unit for adjusting an amount of the light that reaches the imaging surface, by changing an optical transmittance of a liquid crystal;

a driving-pulse generating circuit for generating driving pulses having pulsed voltages, the driving pulses being supplied to the liquid crystal to change the optical transmittance;

a control circuit for controlling a frequency and a duty ratio of the driving pulses;

wherein the control circuit changes the frequency of the driving pulses during-imaging for one screen into a first applying time of driving pulses for acceleration and a second applying time for driving pulses for dimming; and

a temperature detecting circuit for detecting an ambient temperature of the liquid-crystal light-amount adjusting unit and outputting a result of detection to the control circuit, the control circuit changing the frequencies of the driving pulses in accordance with the ambient temperature,

wherein a first frequency and a first duty ratio and the first applying time of the driving pulses of accelerations are based upon the driving pulses for dimming and the second applying time is determined from the first applying time,

wherein the number of pulses in the driving pulses for acceleration is an integer multiple of one period in the first applying time and the number of pulses in the driving pulses for dimming is an integer multiple of one period in the second applying time.

6. A camera according to claim 5, wherein an imaging time for one screen is a sum of the first applying time and the second applying time.