Polarizing modulator for an electronic stereoscopic display
View Patent ↗A polarizing modulator for use in an electronic stereoscopic display system having a sequentially scanning display includes a plurality of liquid crystal segments arranged contiguously in a direction of the sequential scan. The liquid crystal material used in each segment has its phase shift tuned to eliminate the perception of a visible line between segments. In a preferred embodiment, the phase shift is tuned by applying a bias voltage to the liquid crystal in its low state.
1. In an electronic stereoscopic display system of the type wherein images are sequentially scanned across an electronic display, wherein the display, a polarizing sheet and a modulator are held in juxtaposition and observed by a user with polarizing eyewear, wherein the modulator includes a plurality of segments each having liquid crystal material and arranged contiguously in a direction of the sequential scan, and wherein each segment is selectively driven in correspondence with the scan by applying and removing a drive voltage to drive the liquid crystal to a high state and a low state, respectively, wherein the improvement comprises tuning the phase shift of each liquid crystal to eliminate the perception of visible lines between the segments.
2. An electronic stereoscopic display system as in claim 1 , wherein the phase shift is tuned by applying a bias voltage to drive the liquid crystal in its low state.
3. An electronic stereoscopic display system as in claim 1 , wherein the phase shift is tuned by selecting a liquid crystal material having a different birefringence.
4. An electronic stereoscopic display system as in claim 1 , wherein the phase shift is tuned by adjusting a gap thickness of the liquid crystal material.
5. An electronic stereoscopic display system as in claim 2 , wherein each segment is driven with the drive voltage to its high state in synchrony with the scan for a selected eye.
6. An electronic stereoscopic display system as in claim 5 , wherein each segment is driven with the bias voltage to its low state in synchrony with the scan for a non-selected eye.
7. An electronic stereoscopic display system as in claim 1 , wherein the bias voltage is a proportional fraction of the drive voltage.
8. A polarizing modulator for an electronic stereoscopic display system having a sequentially scanning display, comprising:
a plurality of segments each containing liquid crystal material and arranged contiguously in a direction of the sequential scan, and
driving circuitry coupled to each segment and adapted to drive each segment to a high state with a drive voltage and to a low state with a bias voltage such that an optical artifact creating a perception of visible lines between the segments is eliminated.
9. A polarizing modulator as in claim 8 , wherein each segment is driven with the drive voltage to its high state in synchrony with the scan for a selected eye and wherein each segment is driven with the bias voltage to its low state in synchrony with the scan for a non-selected eye.
10. An electronic stereoscopic display system as in claim 8 , wherein the bias voltage is a proportional fraction of the drive voltage.
11. An electronic stereoscopic display system as in claim 8 , further comprising a circuit adapted for varying the bias voltage.
12. A drive circuit for a modulator in an electronic stereoscopic display system having a sequentially scanning display, wherein the modulator includes a plurality of segments each containing liquid crystal material and arranged contiguously in a direction of the sequential scan, comprising:
a plurality of amplifiers each coupled to drive a respective segment, and
a plurality of multiplexors each coupled to a respective amplifier and each selecting one of four voltages to provide to the amplifier in response to two control inputs from a controller, said four voltages being a drive voltage of positive polarity, a drive voltage of negative polarity, a bias voltage of positive polarity and a bias voltage of negative polarity,
said controller comprising:
a circuit receiving a scan signal from the display system, wherein the scan signal is in a high state when one image perspective is visible and a low state when another image perspective is visible,
an oscillating crystal, and
a circuit calculating timing and generating said two control inputs based on the transition of the scan signal between high and low states, wherein a first of the control inputs is set to one state to select a drive voltage and another state to select a bias voltage, and wherein a second of the control inputs is set to one state to select a positive polarity and to another state to select a negative polarity.
13. A drive circuit as in claim 12 wherein the timing calculating circuit defines a field time as the length of time between transitions of the scan signal, a blanking time as a fraction of the field time and a segment time as a fraction of the field time, and wherein the control inputs are generated to drive each segment in correspondence with the sequential scan for each image perspective.
14. A drive circuit as in claim 13 , wherein the modulator includes five segments, and wherein the blanking time is defined as 1/16 of the field time and the segment time is defined as 3/16 of the field time, and wherein the control inputs are generated to drive each segment in correspondence with the sequential scan for each perspective image.
15. A drive circuit as in claim 14 , wherein the control inputs are generated to drive each segment just prior to the corresponding sequential scan for each perspective image.
16. A drive circuit as in claim 15 , wherein the control inputs are generated to drive each segment approximately two milliseconds prior to the corresponding sequential scan for each perspective image.