Light Source Driving Circuitry for Electronic Devices

• US 20170264076A1
• Filed: 03/11/2016
• Published: 09/14/2017
• Est. Priority Date: 03/11/2016
• Status: Active Application

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Moyer, Todd K., Peterson, Jonathan R.
• Granted Patent: US 10,260,940 B2
• Time in Patent Office: Days
• CPC Class Codes: G01J 1/32 adapted for automatic variation of the measured or reference value regulation of light intensity G05D25/00
• CPC Class Codes: G01J 1/46 using a capacitor
• CPC Class Codes: H01S 5/0428 for applying pulses to the laser
• CPC Class Codes: H01S 5/06808 by monitoring the electrical laser parameters, e.g. voltage or current
• CPC Class Codes: H05B 47/13 by using passive infrared detectors
• CPC Class Codes: Y02B 20/40 Control techniques providing energy savings, e.g. smart controller or presence detection

Abstract

An electronic device may have control circuitry and input-output components. The input-output components may include audio components, sensors, and other devices. A proximity sensor may supply the control circuitry with proximity sensor data. The control circuitry may adjust the audio components or take other suitable action in response to proximity sensor readings from the proximity sensor. The proximity sensor may have a light source such as an infrared laser diode and a light detector that measures a reflected portion of infrared light pulses emitted by the infrared laser diode. The control circuitry may include circuitry for safely producing pulses of emitted light with the light source. This circuitry may include a signal generator that produces ramped pulses, a differentiator that differentiates the ramped pulses to produce differentiated pulses, and an output driver that produces current pulses for the light source based on the differentiated pulses.

Claims

1. Circuitry, comprising:

a signal generator that produces ramped pulses;

a differentiator that differentiates the ramped pulses to produce differentiated pulses;

a light source; and

an output driver circuit that receives the differentiated pulses and that supplies corresponding signal pulses to the light source.

2. The circuitry defined in claim 1 wherein the output driver comprises a transistor having a gate that receives the differentiated pulses.

3. The circuitry defined in claim 2 wherein the signal generator includes an operational amplifier having an output.

4. The circuitry defined in claim 3 wherein the differentiator comprises a capacitor that is coupled in series between the output of the operational amplifier and the gate of the transistor.

5. The circuitry defined in claim 4 further comprising:

a switch between the output of the operational amplifier and the capacitor; and

control circuitry that controls the switch to produce the ramped pulses.

6. The circuitry defined in claim 5 wherein the light source comprises an infrared laser diode that produces infrared light at an output power and wherein the control circuitry controls the switch to produce the ramped pulses to control the output power.

7. The circuitry defined in claim 6 further comprising:

a light-based proximity sensor that includes the infrared laser diode and that includes a light detector that measures infrared light from the infrared laser diode that has reflected from an object.

8. The circuitry defined in claim 1 further comprising:

control circuitry, wherein the signal generator includes a digital-to-analog converter controlled by a control signal from the control circuitry.

9. The circuitry defined in claim 8 wherein the digital-to-analog converter comprises:

a first terminal coupled to a positive power supply;

a second terminal coupled to ground;

a capacitor; and

a switch that is controlled by the control signal and that is configured to alternately couple the first terminal and the second terminal to the capacitor.

10. The circuitry defined in claim 9 wherein the output driver circuit comprises a transistor, wherein the light source comprises a diode, and wherein the circuitry further comprises a resistor coupled in series with the transistor and the diode.

11. The circuitry defined in claim 10 further comprising a signal path coupled between the resistor and a node, wherein the capacitor of the digital-to-analog converter is coupled to the node, and wherein the signal generator includes an operational amplifier that receives signals from the node.

12. The circuitry defined in claim 11 further comprising an additional switch that is controlled by the control circuitry, wherein the additional switch is interposed between the differentiator and an output of the operational amplifier.

13. The circuitry defined in claim 12 further comprising:

an additional capacitor coupled between the output of the operational amplifier and the node; and

a further switch coupled between the output of the operation amplifier and the node in parallel with the additional capacitor.

14. The circuitry defined in claim 1 wherein the signal generator comprises an operational amplifier having an output, the circuitry further comprising:

a switch coupled between the output and the differentiator.

15. A method, comprising:

supplying signal pulses to a differentiator;

with the differentiator, differentiating the signal pulses to produce differentiated pulses; and

with an output driver circuit, supplying drive signal pulses to a light source in response to receiving the differentiated pulses.

16. The method defined in claim 15 wherein the light source emits pulses of infrared light in response to the drive signal pulses, wherein the light source forms part of a light-based proximity sensor having a light detector, and wherein the method further comprises:

measuring reflected portions of the pulses of infrared light with the light detector to produce proximity sensor data.

17. An electronic device, comprising:

a proximity sensor having a light source that is controlled by current pulses to produce pulses of infrared light and having a light detector that measures reflected portions of the pulses of infrared light to produce proximity sensor readings; and

control circuitry coupled to the proximity sensor, wherein the control circuitry includes;

a signal generator that produces signal pulses;

a differentiator that differentiates the signal pulses to produce differentiated signal pulses; and

an output driver circuit that receives the differentiated signal pulses and that supplies the current pulses to the light source based on the differentiated signal pulses.

18. The electronic device defined in claim 17 wherein the signal generator comprises:

an operational amplifier; and

a switch coupled between the operational amplifier and the differentiator.

19. The electronic device defined in claim 18 wherein the output driver circuit includes a transistor having a gate that receives the differentiated signal pulses.

20. The electronic device defined in claim 19 further comprising a capacitor coupled between an output of the operational amplifier and an input of the operational amplifier.