POWER EFFICIENT LASER DIODE DRIVER CIRCUIT AND METHOD

• US 20150130903A1
• Filed: 11/12/2013
• Published: 05/14/2015
• Est. Priority Date: 11/12/2013
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Thompson, Barry, Wurster, Stefan, Prather, Lawrence A., Snow, Dane, McCauley, Richard
• Granted Patent: US 9,769,459 B2
• Time in Patent Office: Days
• US Class Current: 348/46
• CPC Class Codes: A63F 13/213 comprising photodetecting means, e.g. cameras, photodiodes or infrared cells A63F13/219, A63F13/655 take precedence
• CPC Class Codes: G06V 40/23 Recognition of whole body movements, e.g. for sport training
• CPC Class Codes: H01S 5/042 Electrical excitation ; Circuits therefor monolithically integrated laser drive components H01S5/0261
• CPC Class Codes: H01S 5/0427 for applying modulation to the laser
• CPC Class Codes: H01S 5/0651 Mode control
• CPC Class Codes: H01S 5/06808 by monitoring the electrical laser parameters, e.g. voltage or current
• CPC Class Codes: H01S 5/06825 Protecting the laser, e.g. during switch-on/off, detection of malfunctioning or degradation
• CPC Class Codes: H04N 13/254 in combination with electromagnetic radiation sources for illuminating objects

Abstract

A voltage mode laser diode driver selectively turns on and off a laser diode. An output stage has an output node configured to be connected to one of the terminals of the laser diode. Depending upon implementation, an active swing controller drives the output stage in a manner that substantially prevents inductive kickback from causing the output node voltage to swinging above the voltage level at the voltage output of the power supply, or swing below ground. The output stage provides a discharge path around the laser diode to shunt current associated with the inductive kickback, and substantially eliminates ringing on the output node of the output stage while the laser diode is off. A power supply controller adjusts the voltage level of the voltage output of the power supply so that current through the laser diode when on and emitting light is substantially equal to a predetermined desired current.

Claims

1. A voltage mode laser diode driver for selectively turning on and off a laser diode, wherein the laser diode has an anode terminal and a cathode terminal, and wherein the voltage mode laser diode driver is powered by a power supply having a voltage output, the voltage mode laser diode driver comprising:

an output stage including an output node configured to be connected to one of the terminals of the laser diode; and

an active swing controller configured to drive the output stage in dependence on a modulation signal;

wherein the output stage, under control of the active swing controller,

selectively pulls a voltage level of the output node of the output stage towards a first voltage level, in response to which the laser diode is turned on and emits light, and

selectively pulls the output node of the output stage towards a second voltage level, in response to which the laser diode is turned off and does not emit light; and

wherein the active swing controller drives the output stage in a manner that substantially prevents inductive kickback, which occurs in response to the laser diode being turned from on to off, from causing the voltage level at the output node of the output stage swinging past the second voltage level.

2. The voltage mode laser diode driver of claim 1, wherein:

the cathode terminal of the laser diode is connected to ground;

the anode terminal of the laser diode is connected to the output node of the output stage;

the first voltage level is a voltage level at the voltage output of the power supply;

the second voltage level is ground;

the output stage, under control of the active swing controller,

selectively pulls the voltage level of the output node of the output stage towards the voltage level at the voltage output of the power supply, in response to which the laser diode is turned on and emits light, and

selectively pulls the output node of the output stage towards ground, in response to which the laser diode is turned off and does not emit light; and

wherein the active swing controller drives the output stage in a manner that substantially prevents inductive kickback, which occurs in response to the laser diode being turned from on to off, from causing the voltage level at the output node of the output stage from swinging below ground.

3. The voltage mode laser diode driver of claim 1, wherein:

the cathode terminal of the laser diode is connected to the output node of the output stage;

the anode terminal of the laser diode is connected to the voltage output of the power supply;

the first voltage level is ground;

the second voltage level is a voltage level at the voltage output of the power supply;

the output stage, under control of the active swing controller,

selectively pulls the voltage level of the output node of the output stage towards ground, in response to which the laser diode is turned on and emits light, and

selectively pulls the output node of the output stage towards the voltage level at the voltage output of the power supply, in response to which the laser diode is turned off and does not emit light; and

wherein the active swing controller drives the output stage in a manner that substantially prevents inductive kickback, which occurs in response to the laser diode being turned from on to off, from causing the voltage level at the output node of the output stage from swinging above the voltage level at the voltage output of the power supply.

4. The voltage mode laser driver of claim 1, wherein:

the output stage comprises

an NMOS transistor including a gate, a source connected to ground, and a drain connected to the output node of the output stage; and

a PMOS transistor including a gate, a source connected to the voltage output of the power supply, and a drain connected to the drain of the NMOS transistor;

the active swing controller drives the gates of the NMOS transistor and the PMOS transistor of the output stage in dependence on the modulation signal;

when the NMOS transistor is turned on and the PMOS transistor is turned off, a current flows from the voltage output of the power supply through the laser diode and through the NMOS transistor to ground, which causes the laser diode to turn on and emit light; and

when the NMOS transistor is turned off and the PMOS transistor is turned on, substantially no current flows through the laser diode, the NMOS transistor and the PMOS transistor.

5. The voltage mode laser diode driver of claim 4, wherein:

the PMOS transistor of the output stage provides a discharge path around the laser diode to shunt a current associated with the inductive kickback that occurs in response to the laser diode being turned from on to off; and

the PMOS transistor of the output stage also provides impedance matching that substantially eliminates ringing on the output node of the output stage while the NMOS transistor of the laser diode is off.

6. The voltage mode laser diode driver of claim 4, wherein the active swing controller comprises:

a strong PMOS transistor that selectively pulls up a voltage level at the gate of the NMOS transistor of the output stage towards the voltage level of the voltage output of the power supply, in response to which the NMOS transistor is turned from off to on and the laser diode is turned from off to on and emits light;

a weak NMOS transistor that selectively pulls down the voltage level at the gate of the NMOS transistor of the output stage towards ground, in response to which the NMOS transistor is turned from on to off and the laser diode is turned from on to off and stops emitting light; and

a further PMOS transistor that selectively connects the gate and the drain of the NMOS transistor of the output stage, and thereby selectively diode connects the NMOS transistor of the output stage, when the NMOS transistor of the output stage is turned from on to off;

wherein a rate at which the strong PMOS transistor pulls up the voltage level at the gate of the NMOS transistor of the output stage is faster than a rate at which the weak NMOS transistor pulls down the voltage level at the gate of the NMOS transistor of the output stage, which causes the laser diode to turn on faster than it is turns off.

7. The voltage mode laser diode driver of claim 1, further comprising:

a pre-driver that receives a high frequency periodic differential signal that transitions between ground and a high voltage level that is different than the voltage level of the voltage output of the power supply, and voltage shifts the received high frequency periodic differential signal to a high frequency periodic differential signal that transitions between ground and the voltage level of the voltage output of the power supply;

wherein the high frequency periodic differential signal that transitions between ground and the voltage level of the voltage output of the power supply comprises the modulation signal in dependence on which the active swing controller drives the output stage.

8. The voltage mode laser diode driver of claim 1, further comprising:

a power supply controller that adjusts the voltage level of the voltage output of the power supply so that the current that flows through the laser diode when the laser diode is turned on and emitting light is substantially equal to a predetermined desired current.

9. The voltage mode laser diode driver of claim 8, wherein the power supply controller produces a feedback signal that is provided to the power supply in order to adjust the voltage level of the voltage output of the power supply in dependence a drain-to-source voltage of a transistor of the output stage while the laser diode is turned on, said drain-to-source voltage of the transistor of the output stage being indicative of an actual laser diode current while the laser diode is on and emitting light.

10. The voltage mode laser diode driver of claim 8, wherein:

the power supply controller produces a feedback signal that is used to adjust the voltage level of the voltage output of the power supply; and

the feedback signal is produced in dependence on a difference between a first drain-to-source voltage of a transistor of the output stage, and a second drain-to-source voltage of a reference transistor, the first drain-to-source voltage being indicative of an actual laser diode current while the laser diode is on and emitting light, and the second drain-to-source voltage being indicative of a predetermined desired laser diode current.

11. For use by a voltage mode laser diode driver powered by a power supply having a voltage output, a method for driving a laser diode having an anode terminal and a cathode terminal, the method comprising:

selectively pulling a voltage level at a one of the terminals of the laser diode towards a first voltage level, in response to which a current flows through the laser diode causing the laser diode to turn on and emit light, the current being dependent on a voltage level at the voltage output of the power supply;

selectively pulling the voltage level at the one of the terminals of the laser diode towards a second voltage level, in response to which current stops flowing through the laser diode causing the laser diode to turn off and not emit light; and

adjusting the voltage level of the voltage output of the power supply so that the current that flows through the laser diode when the laser diode is turned on and emitting light is substantially equal to a predetermined desired current.

12. The method of claim 11, wherein

the laser diode driver includes an output stage having an output node to which the one of the terminals of the laser diode is connected, and

the adjusting the voltage level of the voltage output of the power supply, so that the current that flows through the laser diode when the laser diode is turned on and emitting light is substantially equal to a predetermined desired current, comprises:

producing a feedback signal that is provided to the power supply in order to adjust the voltage level of the voltage output of the power supply in dependence a drain-to-source voltage of a transistor of the output stage while the laser diode is turned on, said drain-to-source voltage of the transistor of the output stage being indicative of an actual laser diode current while the laser diode is on and emitting light.

13. The method of claim 11, wherein

the laser diode driver includes an output stage having an output node to which the one of the terminals of the laser diode is connected, and

the adjusting the voltage level of the voltage output of the power supply, so that the current that flows through the laser diode when the laser diode is turned on and emitting light is substantially equal to a predetermined desired current, comprises:

producing a feedback signal in dependence on a difference between a first drain-to-source voltage of a transistor of the output stage, and a second drain-to-source voltage of a reference transistor, the first drain-to-source voltage being indicative of an actual laser diode current while the laser diode is on and emitting light, and the second drain-to-source voltage being indicative of a predetermined desired laser diode current; and

using the feedback signal to adjust the voltage level of the voltage output of the power supply.

14. The method of claim 11, wherein the laser diode driver includes an output stage having an output node to which the one of the terminals of the laser diode is connected, and wherein the method further comprises:

substantially preventing inductive kickback, which occurs in response to the laser diode being turned from on to off, from causing the voltage level at the one of the terminals of the laser diode, that is connected to the output node of the output stage, from swinging past the second voltage level.

15. The method of claim 11, wherein the laser diode driver includes an output stage having an output node to which the one of the terminals of the laser diode is connected, and wherein the method further comprises:

providing a discharge path around the laser diode to shunt current associate with inductive kickback that occurs in response to the laser diode being turned from on to off; and

providing impedance matching that substantially eliminates ringing on the one of the terminals of the laser diode, that is connected to the output node of the output stage, while the laser diode is off.

16. A depth camera system, comprising:

a power supply including a voltage output;

a laser diode including an anode terminal and a cathode terminal;

a laser diode driver that

selectively causes a current to flow from the voltage output of the power supply through the laser diode, which causes the laser diode to turn on and emit light, and

selectively causes substantially no current to flow from the voltage output of the power supply through the laser diode, which causes the laser diode to turn off and not emit light; and

an image pixel detector that detects light originating from the laser diode that has reflected off an object and is incident of the image pixel detector.

17. The system of claim 16, wherein the laser diode driver includes a power supply controller that adjusts the voltage level of the voltage output of the power supply so that the current that flows through the laser diode when the laser diode is turned on and emitting light is substantially equal to a predetermined desired current.

18. The system of claim 16, wherein the laser diode driver includes:

an output stage having an output node configured to be connected to one of the terminals of the laser diode; and

an active swing controller drives the output stage;

wherein the output stage, under control of the active swing controller,

selectively pulls a voltage level of the output node of the output stage towards a first voltage level, in response to which the laser diode is turned on and emits light, and

selectively pulls the output node of the output stage towards a second voltage level, in response to which the laser diode is turned off and does not emit light; and

wherein the active swing controller drives the output stage in a manner that substantially prevents inductive kickback, which occurs in response to the laser diode being turned from on to off, from causing the voltage level at the output node of the output stage swinging past the second voltage level.

19. The system of claim 18, wherein the laser diode driver includes an output stage having an output node to which one of the terminals of the laser diode is connected, wherein the output stage provides:

a discharge path around the laser diode to shunt a current associated with the inductive kickback that occurs in response to the laser diode being turned from on to off; and

impedance matching that substantially eliminates ringing on the one of the terminals of the laser diode, that is connected to the output node of the output stage, while the laser diode is off.

20. The system of claim 16, further comprising:

one or more processors that produce depth images in dependence on outputs of the image pixel detector;

wherein the one or more processors update an application based on the depth images.