# US 2021/0242661 A1 · Light source system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0242661 A1 - Document ID: US20210242661A1 - Status: Published application - Kind: A1 - Application number: 17/080,629 - Filed: 2020-10-26 - Published: 2021-08-05 - Earliest claimed: 2020-02-03 - Assignees: Analog Devices International Unlimited Company - Applicants: Analog Devices International Unlimited Company - Inventors: Jonathan Ephraim David Hurwitz; David Neil - Web page: https://patentgrep.com/patent/US20210242661A1 ## CPC - H01S 5/0428: {for applying pulses to the laser} - H05B 47/105: in response to determined parameters - H01S 5/0239: Combinations of electrical or optical elements - H01S 5/042: Electrical excitation {; Circuits therefor (monolithically integrated laser drive components H01S5/0261)} - H03K 17/6871: {the output circuit comprising more than one controlled field-effect transistor} - H05B 45/12: using optical feedback - G01S 7/484: Transmitters - H01S 5/02345: Wire-bonding - H01S 5/06216: {Pulse modulation or generation} - H01S 5/183: having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] - H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL - H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL - H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M) - G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES ## Abstract 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. ## Claims ### Claim 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 laser light source, wherein the first transistor device and second transistor device are arranged such that when both the first transistor device and the second transistor device are in an on-state, a laser drive circuit is complete and a laser drive current flows through the laser light source; and a controller arranged to control a state of the first switch and a state of the second switch, 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. ### Claim 2 (depends on 1) 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. ### Claim 3 (depends on 2) 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. ### Claim 4 (depends on 1) The laser light source system of claim 1, wherein switching on the first transistor comprises: pre-charging the first transistor by applying a turn-on voltage to a control terminal of the first transistor to charge a capacitance associated with the control terminal of the first transistor, and removing the turn-on voltage applied to the control terminal of the first transistor such that the first transistor is held in the on-state by the capacitance associated with the control terminal of the first transistor. ### Claim 5 (depends on 4) The laser light source system of claim 4, wherein the capacitance associated with the control terminal of the first transistor is a parasitic capacitance of the first transistor. ### Claim 6 (depends on 4) The laser light source system of claim 4, wherein the laser light source system further comprises a pre-charge transistor for controlling the application of the turn-on voltage to the control terminal of the first transistor, and wherein the controller is configured to apply the turn-on voltage and remove the turn-on voltage by controlling the state of the pre-charge transistor. ### Claim 7 (depends on 4) The laser light source system of claim 4, wherein switching off the first transistor comprises discharging the capacitance associated with the control terminal of the first transistor. ### Claim 8 (depends on 7) The laser light source system of claim 7, further comprising a turn-off transistor for controlling the discharge of the capacitance associated with the control terminal of the first transistor, and wherein the controller is configured to discharge the capacitance associated with the control terminal of the first transistor by controlling the state of the turn-off transistor using a turn-off control signal. ### Claim 9 (depends on 8) The laser light source system of claim 8, further comprising a cascode transistor in the capacitance discharge path. ### Claim 10 (depends on 4) The laser light source system of claim 4, wherein a magnitude of the turn-on voltage is greater than a magnitude of a laser drive voltage used to supply the laser drive current. ### Claim 11 (depends on 4) The laser light source system of claim 4, further comprising a bootstrap capacitor, wherein a first plate of the bootstrap capacitor is coupled to the control terminal of the first transistor and a second plate of the bootstrap capacitor is coupled to the controller, and wherein the controller is further configured to apply, prior to switching on the second transistor device, a bootstrap voltage to the second plate of the bootstrap capacitor to increase a magnitude of a voltage at the control terminal of the first transistor to be greater than a magnitude of the turn-on voltage. ### Claim 12 (depends on 1) 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; and generate a second control signal for controlling the state of the second transistor, 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 to turn on and a change in the first control signal causing the first transistor to turn off. ### Claim 13 (depends on 1) The laser light source system of claim 1, wherein the controller is configured to control the laser light source to emit the laser light pulse with a duration of less than 1 nanosecond. ### Claim 14 (depends on 1) 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 the time of switching off the first transistor device, so as to discharge parasitic charge associated with the laser light source. ### Claim 15 A laser light source controller for coupling to a laser driver circuit that comprises 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 to a second transistor that is coupled to the laser light source, wherein the first transistor, second transistor and laser light source are arranged in series such that when both the first transistor and second transistor are conducting, the laser light source turns on, 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 device 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 device and second transistor device 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. ### Claim 16 (depends on 15) The laser light source controller of claim 15, 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. ### Claim 17 (depends on 15) The laser light source controller of claim 15, 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. ### Claim 18 A method for controlling a pulse of emission of light from a laser light source comprising: setting 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; turning 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 turning off laser light source by setting the first transistor to a non-conducting state. ### Claim 19 (depends on 18) The method of claim 18, further comprising: after setting the first transistor to a non-conducting state, setting the second transistor to a non-conducting state such that the first transistor and the second transistor are both in the non-conducting state. ### Claim 20 (depends on 18) The method of claim 18, wherein a duration of the pulse emission 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.