Method and apparatus for driving liquid-crystal optical-modulation device
View Patent ↗For statically driving a liquid-crystal optical-modulation device, an alternating electric field produced by a drive signal is applied to a liquid crystal included therein. In a first period in which the alternating electric field has a first polarity, the drive signal is pulse-width modulated based on a first ON-voltage and a first OFF-voltage. In a second period in which the alternating electric field has a second polarity, the drive signal is pulse-width modulated based on a second ON-voltage and a second OFF-voltage.
1. A method of statically driving a liquid-crystal optical-modulation device by applying an alternating electric field to a liquid crystal that is included in the liquid-crystal optical-modulation device and sandwiched by a common electrode and a segment electrode, the alternating electric field being produced by a drive signal that is pulse-width modulated based on modulation data, wherein
the drive signal is a difference between a common signal and a segment signal that are applied to the common electrode and the segment electrode, respectively,
in a first period in which the alternating electric field has a first polarity, the drive signal has a first ON-voltage and a first OFF-voltage, and in a second period in which the alternating electric field has a second polarity, the drive signal has a second ON-voltage and a second OFF-voltage that respectively differ from the first ON-voltage and the first OFF-voltage
the absolute value of the first OFF-voltage and the absolute value of the second OFF-voltage are equal to an absolute value of a bias voltage that is a minimum voltage for changing a phase of light passing through the liquid crystal,
a duration of the first ON-voltage and a duration of the second ON-voltage vary according to a phase shift amount of the light,
the segment signal is a binary signal having a first segment voltage and a second segment voltage, and
the common signal is a binary signal having a first common voltage higher than the first segment voltage by the bias voltage and a second common voltage lower than the second segment voltage by the bias voltage.
2. The method according to claim 1 , wherein
a polarity of the first ON-voltage is opposite to a polarity of the second ON-voltage,
an absolute value of the first ON-voltage is equal to an absolute value of the second ON-voltage,
a polarity of the first OFF-voltage is opposite to a polarity of the second OFF-voltage,
an absolute value of the first OFF-voltage is equal to an absolute value of the second OFF-voltage,
the polarity of the first ON-voltage is equal to the polarity of the first OFF-voltage, and
the polarity of the second ON-voltage is equal to the polarity of the second OFF-voltage.
3. An apparatus for statically driving a liquid-crystal optical-modulation device by applying an alternating electric field to a liquid crystal that is included in the liquid-crystal optical-modulation device and sandwiched by a common electrode and a segment electrode, the alternating electric field being produced by a drive signal that is pulse-width modulated based on modulation data, the apparatus comprising:
a segment driving circuit that generates, based on the modulation data, a segment signal to be applied to the segment electrode;
a common driving circuit that generates, based on a polarity signal, a common signal to be applied to the common electrode;
a control circuit that provides a clock signal for timing control of pulse width modulation to the segment driving circuit, and provides the polarity signal to the common driving circuit; and
an analog power-source circuit that includes
a first direct-current power source that provides a first direct-current voltage for voltage amplification to the segment driving circuit,
a second direct-current power source that provides a second direct-current voltage for voltage amplification to the common driving circuit, the second direct-current voltage being higher than the first direct-current voltage by a bias voltage, and
a third direct-current power source that provides a third direct-current voltage for voltage amplification to the common driving circuit, the third direct-current voltage being lower than the first direct-current voltage by the bias voltage.
4. The apparatus according to claim 3 , wherein the second direct-current power source and the third direct-current power source are a variable power source.
5. The apparatus according to claim 3 , wherein the second direct-current power source and the third direct-current power source change the bias voltage based on a correction signal for correcting a variation due to a characteristic change of the liquid crystal so as to cancel the variation.