Light source system
View Patent ↗The present disclosure relates to a light source system suitable for use in a time of flight camera. The light source system includes a light source, such as a laser, and a driver arranged to supply a drive current to the light source to turn the light source on to emit light. The driver includes two transistors coupled to the light source in series, such that when both transistors are turned on, a drive circuit is completed, current flows and the light source turns on. A very short pulse of light emission may be achieved efficiently by switching one of the transistors to the on-state to complete the drive circuit and a short time later turning off the other transistor in order to break the drive circuit. In this way, a pulse of light in the order of less than 1 nanosecond or less than 500 picoseconds may be achieved.
1 . A laser light source system comprising:
a laser light source;
a first transistor device coupled to the laser light source;
a second transistor device coupled to the first transistor device; and
a controller arranged to control a state of the first transistor device and a state of the second transistor device, wherein the controller is configured to control a pulse emission of light from the laser light source by:
a) switching on the first transistor device whilst the second transistor device is in an off-state;
b) after switching on the first transistor device, turning on the laser light source by switching on the second transistor device such that both the first transistor device and second transistor device are in an on-state; and
c) after switching on the second transistor device, turning off the laser light source by switching off the first transistor device.
2 . The laser light source system of claim 1 , wherein the controller is configured to turn off the laser light source by switching off the first transistor device whilst the second transistor device is still in the on-state.
3 . The laser light source system of claim 2 , further configured to:
d) after switching off the first transistor device, resetting the laser light source system by switching off the second transistor device such that the first transistor device and the second transistor device are both in the off-state.
4 . The laser light source system of claim 1 , wherein the controller is configured to:
generate a first control signal for controlling the state of the first transistor device; and
generate a second control signal for controlling the state of the second transistor device, wherein
the controller is configured to control a duration of the pulse emission of light from the laser light source by setting a time difference between a change in the second control signal causing the second transistor device to turn on and a change in the first control signal causing the first transistor device to turn off.
5 . The laser light source system of claim 1 , wherein the controller is configured to control the laser light source to emit a laser light pulse with a duration of less than 1 nanosecond.
6 . The laser light source system of claim 1 , further comprising:
a discharge transistor coupled to the laser light source and arranged to create a discharge path approximately at a time of switching off the first transistor device, so as to discharge parasitic charge associated with the laser light source.
7 . The laser light source system of claim 1 , further comprising:
a first driver comprising:
an input coupled to the controller to receive a first control signal for the first transistor device; and
an output coupled to a control terminal of the first transistor device to output a buffered first control signal to the control terminal of the first transistor device.
8 . The laser light source system of claim 7 , wherein switching on the first transistor device comprises setting the first control signal to a voltage that causes the buffered first control signal to turn on the first transistor device, and
wherein turning off the first transistor device comprises setting the first control signal to a voltage that causes the buffered first control signal to turn off the first transistor device.
9 . The laser light source system of claim 1 , further comprising:
a second driver comprising:
an input coupled to the controller to receive a second control signal for the second transistor device; and
an output coupled to a control terminal of the second transistor device to output a buffered second control signal to the control terminal of the second transistor device.
10 . The laser light source system of claim 9 , wherein switching on the second transistor device comprises setting the second control signal to a voltage that causes the buffered second control signal to turn on the second transistor device.
11 . The laser light source system of claim 1 , wherein switching on the first transistor device comprises:
pre-charging the first transistor device by applying a turn-on voltage to a control terminal of the first transistor device to charge a capacitance associated with the control terminal of the first transistor device, and
removing the turn-on voltage applied to the control terminal of the first transistor device such that the first transistor device is held in the on-state by the capacitance associated with the control terminal of the first transistor device.
12 . The laser light source system of claim 11 , wherein the capacitance associated with the control terminal of the first transistor device is a parasitic capacitance of the first transistor device.
13 . A laser light source controller for coupling to a laser driver circuit that comprises at least a first transistor, a second transistor and a laser light source, wherein the laser light source controller is configured to:
output a first control signal for controlling the first transistor; and
output a second control signal for controlling a second transistor, wherein the first transistor, second transistor and laser light source are arranged in series,
wherein the laser light source controller is configured to control a pulse emission of light from the laser light source by:
a) setting the first transistor to a conducting state using the first control signal whilst the second transistor is in a non-conducting state;
b) after setting the first transistor to the conducting state, turning on the laser light source by setting the second transistor to a conducting state using the second control signal such that both the first transistor and second transistor are conducting; and
c) after setting the second transistor to the conducting state, turning off the laser light source by setting the first transistor to a non-conducting state.
14 . The laser light source controller of claim 13 , wherein the first control signal is for switching the first transistor from the non-conducting state to the conducting state, and wherein the laser light source controller is further configured to:
output a third control signal for switching the first transistor from the conducting state to the non-conducting state, wherein the laser light source controller is configured to set the first transistor to the non-conducting state using the third control signal.
15 . The laser light source controller of claim 13 , wherein the first control signal is for switching the first transistor from the non-conducting state to the conducting state, and for switching the first transistor from the conducting state to the non-conducting state.
16 . The laser light source controller of claim 13 , further configured to control a time difference between setting the second transistor to the conducting state and setting the first transistor to the non-conducting state based on a target light emission duration.
17 . A laser light source controller configured for controlling a pulse of light from a laser light source, wherein the laser light source controller is configured to:
set a first transistor coupled in series with the laser light source to a conducting state whilst a second transistor coupled in series with the laser light source is in a non-conducting state;
turn on the laser light source by setting the second transistor to a conducting state such that both the first transistor and second transistor are conducting; and
turn off laser light source by setting the first transistor to a non-conducting state.
18 . The laser light source controller of claim 17 , further configured to:
after setting the first transistor to a non-conducting state, set the second transistor to a non-conducting state such that the first transistor and the second transistor are both in the non-conducting state.
19 . The laser light source controller of claim 17 , wherein a duration of the pulse of light from the laser light source is set by a time difference between setting the second transistor to the conducting state and setting the first transistor to the non-conducting state.
20 . The laser light source controller of claim 17 , wherein the laser light source controller is configured to output at least a first control signal for controlling a state of the first transistor and output at least a second control signal for controlling a state of the second transistor.