Laser display with improved brightness control
A laser display system 100 is configured to increase the dynamic range of a laser diode by modulating an operating current applied to the laser diode based on a desired sequence of brightness levels and a temperature of the laser diode. In some embodiments, a measuring circuit measures a voltage of the laser diode at a given current, which indirectly indicates the temperature of the laser diode, thus obviating the need for a direct measurement of temperature. In addition, in some embodiments, the measuring circuit identifies a threshold current of the laser diode based on a range of current values at which values of the current multiplied by the derivative of the voltage against the current vary relatively rapidly. By compensating for temperature effects and identifying the threshold current, a driver of the laser diode more precisely controls light output of the laser diode across an increased dynamic range.
1 . A method comprising:
measuring a first voltage of a laser at a first current of the laser of a display system;
measuring a second voltage of the laser at a second current of the laser at a time after measuring the first current of the laser;
generating a sequence of currents of the laser based on a target sequence of brightness levels of the laser, the second current, and the second voltage; and
modulating an operating current of the laser based on the sequence of currents,
the measuring of the first voltage and the measuring of the second voltage being suspended when the laser is not emitting.
2 . The method of claim 1 , wherein modulating the operating current of the laser comprises:
maintaining a difference between an actual sequence of brightness levels output by the laser and the target sequence of brightness levels of the laser below a predetermined threshold.
3 . The method of claim 2 , wherein the difference comprises a largest relative difference between a desired radiometric brightness level and an actual radiometric brightness level in a sequence of brightness levels.
4 . The method of claim 3 , wherein the predetermined threshold is less than 20%.
5 . The method of claim 1 , wherein the time is a predetermined time is less than 100 ms after measuring the first current of the laser.
6 . The method of claim 1 , further comprising:
deriving a first temperature of the laser from the first current and the first voltage;
generating the sequence of currents based on the first temperature; and
storing a light output versus current curve for the laser at the first temperature.
7 . The method of claim 6 , further comprising:
deriving a second temperature of the laser from the current and the second voltage;
generating the sequence of currents based on the second temperature; and
storing a light output versus current curve for the laser at the second temperature.
8 . The method of claim 1 , wherein the time is based on a brightness level of the laser.
9 . The method of claim 1 , wherein the measuring of the first voltage and the measuring of the second voltage occur when a sequence of brightness levels exceeds a predetermined brightness.
10 . A system comprising:
a display comprising a laser;
a circuit configured to measure a voltage at the laser at a current; and
a driver configured to:
generate a sequence of currents of the laser based on a target sequence of brightness levels of the laser, the current, and the voltage;
maintain a difference between an actual sequence of brightness levels output by the laser and the target sequence of brightness levels of the laser below a threshold of 20%, the brightness levels being photometric brightness levels; and
modulate an operating current of the laser based on the sequence of currents.
11 . The system of claim 10 , wherein the current is a first current, the voltage is a first voltage, the circuit is further to:
measure a second current of the laser at a predetermined time after measuring the first current of the laser; and
measure a second voltage of the laser at the second current, and wherein generating the sequence of currents of the laser is based on the target sequence of brightness levels of the laser, the second current, and the second voltage.
12 . The system of claim 11 , wherein the predetermined time is less than 100 ms after measuring the first current of the laser.
13 . The system of claim 11 , wherein the predetermined time is based on the target sequence of brightness levels.
14 . The system of claim 10 , wherein the current is a first current, the voltage is a first voltage, the driver is to:
derive a first temperature of the laser from the first current and the first voltage;
generate the sequence of currents based on the first temperature; and
store a light output versus current curve for the laser at the first temperature.
15 . The system of claim 14 , wherein the current is a first current, the voltage is a first voltage, the driver is to:
derive a second temperature of the laser from a second current and a second voltage;
generate the sequence of currents based on the second temperature; and
store a light output versus current curve for the laser at the second temperature.
16 . The system of claim 10 , wherein the actual sequence of brightness levels include perceived brightness levels.
17 . The system of claim 10 , wherein a predetermined relationship between the voltage, the current, and the actual sequence of brightness levels are interpolated to facilitate the difference being below the threshold.
18 . A non-transitory computer-readable medium including instructions that, when executed, are configured to cause at least one processor to perform a method, the method comprising:
measuring a first voltage of a diode at a first current of a diode of a display system;
measuring a second voltage of the diode at a second current of the diode at a time after measuring the first current of the diode; generating a sequence of currents of the diode based on a target sequence of brightness levels of the diode, the second current, and the second voltage; and
modulating an operating current of the diode based on the sequence of currents,
the measuring of the first voltage and the measuring of the second voltage being suspended when the diode is not emitting.
19 . The non-transitory computer-readable medium of claim 18 ,
wherein modulating the operating current of the diode comprises:
maintaining a difference between an actual sequence of brightness levels output by the diode and the target sequence of brightness levels of the diode below a predetermined threshold.
20 . The non-transitory computer-readable medium of claim 19 ,
wherein the difference comprises a largest relative difference between a desired radiometric brightness level and an actual radiometric brightness level in a sequence of brightness levels.
21 . The non-transitory computer-readable medium of claim 18 , further comprising:
providing the second current of the diode at a predetermined time after measuring the first current of the diode; and
measuring the second voltage of the diode at the second current, wherein generating the sequence of currents of the diode is based on the target sequence of brightness levels of the diode, the second current, and the second voltage.
22 . The non-transitory computer-readable medium of claim 18 , wherein the diode emits stimulated emission.
23 . The non-transitory computer-readable medium of claim 18 , wherein the diode emits spontaneous emission.