Analog limit on digitally set pulse widths

• US 9,887,537 B2
• Filed: 06/30/2015
• Issued: 02/06/2018
• Est. Priority Date: 06/30/2015
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Inventors: Wyland, David C., Mehta, Agustya Ruchir
• Primary Examiner(s): Nguyen, Danny
• Application Number:
  US14/755,877
• Publication Number:
  US 20170005465A1
• Time in Patent Office: 952 Days
• Field of Search: 361 56, 361 911, 361111
• CPC Class Codes: G01S 7/484 Transmitters
• CPC Class Codes: G06F 3/011 Arrangements for interaction with the human body, e.g. for user immersion in virtual reality blind teaching G09B21/00
• CPC Class Codes: H01S 5/0014 Measuring characteristics or properties thereof measuring techniques per se G01J, G01K, G01N, G01R
• CPC Class Codes: H01S 5/0428 for applying pulses to the laser
• CPC Class Codes: H02H 9/04 responsive to excess voltage lightning arrestors H01C7/12, H01C8/04, H01G9/18, H01T
• CPC Class Codes: H03K 17/08122 in field-effect transistor switches
• CPC Class Codes: H03K 2017/0806 against excessive temperature

Abstract

A power switching device (e.g., a power MOSFET) drives relatively large surges of pulsed power through a laser emitter of a Time of Flight (TOF) determining system where both the power switching device and laser emitter are closely packed on a printed circuit board having further closely packed and temperature sensitive other components. Waveforms of pulse trains that control the power switching device are programmably defined and thus may include pulse durations that are unduly large or spacing between pulses that are unduly small such that overheating may occur. A pulse duration limiting circuit is provided having an analog integrator configured to integrate over time, the programmably defined pulses and a voltage triggered clamping device coupled to an output of the analog integrator. The voltage triggered clamping device has a predetermined threshold voltage at and above which it is switched from a relatively low transconductances mode to a substantially higher transconductances mode. The voltage triggered clamping device is coupled to a current supplying circuit branch of the system, the current supplying circuit branch being one that has an ability to supply current for switching on the power switching device.

Claims

1. A method using analog processing for limiting risk of overheating of circuit components due to digitally set pulse widths, the method comprising:

integrating over time and with analog integration circuitry, digitally defined pulses that cause a turning on and off of surges of current through a load and a corresponding current switching device; and

applying an output of the analog integration circuitry to a voltage triggered clamping device, the voltage triggered clamping device having a predetermined threshold voltage at and above which it is switches from being in a first transconductance range to being in a second transconductance range, where transconductances of the second transconductance are substantially larger than corresponding ones of the first transconductance range, the voltage triggered clamping device being coupled to a current supplying circuit branch that has an ability to supply current for switching on said current switching device;

wherein if the voltage triggered clamping device is in the first transconductance range, it does not significantly interfere with the ability of the current supplying circuit branch to supply current for switching on the current switching device; and

wherein if the voltage triggered clamping device is in the second transconductance range, it removes a substantial amount of current from the current supplying circuit branch and thereby significantly impedes the ability of the current supplying circuit branch to supply current for switching on the current switching device.

2. The method of claim 1 wherein the voltage triggered clamping device includes a junction type semiconductive device whose voltage to current transconductance characteristic curve has a knee at the predetermined threshold voltage whereby the junction type semiconductive device exhibits a first set of one or more transconductance slopes if driven below the predetermined threshold voltage and a second set of one or more substantially larger, second transconductance slopes if driven at or above the predetermined threshold voltage.

3. The method of claim 2 wherein the second set of one or more transconductance slopes of the junction type semiconductive device corresponding to it being driven above the predetermined threshold voltage are each at least ten times (10×

) corresponding ones of the first set of one or more transconductance slopes.

4. The method of claim 2 wherein the second set of one or more transconductance slopes of the junction type semiconductive device corresponding to it being driven above the predetermined threshold voltage are each at least hundred times (100×

) corresponding ones of the first set of one or more transconductance slopes.

5. The method of claim 2 wherein the junction type semiconductive device includes a first bipolar junction transistor (BJT).

6. The method of claim 5 wherein the current supplying circuit branch includes a base-to-emitter branch of a second bipolar junction transistor (BJT).

7. The method of claim 6 wherein the current supplying circuit branch includes a source-to-drain branch of a field effect device that supplies drive current to the base-to-emitter branch of the second BJT.

8. The method of claim 7 wherein the field effect device is configure to exhibit a relatively large drain-to-source voltage drop while the voltage triggered clamping device is in the second transconductance range and to exhibit a substantially smaller drain-to-source voltage drop while the voltage triggered clamping device is in the first transconductance range.

9. The method of claim 1 wherein the voltage triggered clamping device is additionally coupled to an inductive circuit that is configured to switch off the current switching device in response to the voltage triggered clamping device switching from its first to its second transconductance range.

10. A pulse duration limiting circuit comprising:

an analog integrator configured to integrate over time, digitally defined pulses that cause episodic turning on and off of surges of current through a load and a corresponding current switching device of a power outputting system; and

a voltage triggered clamping device coupled to an output of the analog integrator, the voltage triggered clamping device having a predetermined threshold voltage at and above which it is switches from being in a first transconductance range to being in a second transconductance range, where transconductances of the second transconductance are substantially larger than corresponding ones of the first transconductance range,

wherein the voltage triggered clamping device is coupled to a current supplying circuit branch of the system, the current supplying circuit branch being one that has an ability to supply current for switching on the switching device of the power outputting system;

wherein if the voltage triggered clamping device is in its first transconductance range, it does not significantly interfere with the ability of the current supplying circuit branch to supply current for switching on the switching device of the power outputting system; and

wherein if the voltage triggered clamping device is in its second transconductance range, it removes a substantial amount of current from the current supplying circuit branch and thereby significantly impedes the ability of the current supplying circuit branch to supply current for switching on the switching device of the power outputting system.

11. The circuit of claim 10 wherein:

the voltage triggered clamping device includes a junction type semiconductive device whose voltage to current transconductance characteristic curve has a knee at the predetermined threshold voltage whereby the junction type semiconductive device exhibits a first set of one or more transconductance slopes if driven below the predetermined threshold voltage and a second set of one or more substantially larger, second transconductance slopes if driven at or above the predetermined threshold voltage.

12. The circuit of claim 11 wherein the second set of one or more transconductance slopes of the junction type semiconductive device corresponding to it being driven above the predetermined threshold voltage are each at least ten times (10×

) corresponding ones of the first set of one or more transconductance slopes.

13. The circuit of claim 11 wherein the junction type semiconductive device includes a first bipolar junction transistor (BJT).

14. The circuit of claim 13 wherein the current supplying circuit branch includes a base-to-emitter branch of a second bipolar junction transistor (BJT).

15. The circuit of claim 14 wherein the current supplying circuit branch includes a source-to-drain branch of a field effect device that supplies drive current to the base-to-emitter branch of the second BJT.

16. A time of photonic flight (TOF) determining system comprising:

a plurality of light emitters respectively configured to output respective bursts of photonic pulses for reflection from objects disposed within a predetermined range of distances;

a plurality of emitter drivers connected to corresponding ones of the light emitters and respectively configured to output corresponding pulses of current for driving the light emitters and thus causing the light emitters to output their respective bursts of photonic pulses;

one or more pulse train generating circuits, each being digitally programmable to output a programmably defined waveform of spaced apart pulses having respective, programmably defined pulse widths;

a plurality of pulse duration limiting circuits operatively coupled to corresponding ones of the emitter drivers, where each emitter driver has a respective current supplying circuit branch having an ability to supply a control current for switching on a power switching device of the emitter driver;

wherein one or more of the pulse duration limiting circuits respectively comprises;

an analog integrator configured to integrate over time, the programmably defined pulses of a corresponding one of the pulse train generating circuits; and

a voltage triggered clamping device coupled to an output of the analog integrator, the voltage triggered clamping device having a predetermined threshold voltage at and above which it is switched from a first transconductance mode to a second transconductance mode, transconductances of the second transconductance mode being substantially greater than corresponding transconductances of the first transconductance mode,

wherein the voltage triggered clamping device is coupled to the respective current supplying circuit branch of a corresponding one of the emitter drivers;

wherein if the voltage triggered clamping device is in its first transconductance mode, it does not significantly interfere with the ability of the respective current supplying circuit branch to supply current for switching on the power switching device of the corresponding emitter driver; and

wherein if the voltage triggered clamping device is in its second transconductance mode, it removes current from the respective current supplying circuit branch and thereby significantly impedes the ability of the current supplying circuit branch to supply current for switching on the power switching device of the corresponding emitter driver.

17. The TOF determining system of claim 16 and further comprising:

a printed circuit board on which are mounted at least two of the light emitters, their corresponding emitter drivers, their corresponding plurality of pulse duration limiting circuits and one or more of the pulse train generating circuits.

18. The TOF determining system of claim 17 wherein:

the voltage triggered clamping device of at least one of the pulse duration limiting circuits includes a junction type semiconductive device whose voltage to current transconductance characteristic curve has a knee at the predetermined threshold voltage whereby the junction type semiconductive device exhibits one or more relatively small transconductance slopes if driven below the predetermined threshold voltage and one or more substantially larger transconductance slopes if driven at or above the predetermined threshold voltage.

19. The TOF determining system of claim 18 wherein:

the one or more transconductance slopes of the junction type semiconductive device of the at least one of the pulse duration limiting circuits, while driven above the predetermined threshold voltage are each at least a hundred times (100×

) respective transconductance slopes of the junction type semiconductive device while driven below the predetermined threshold voltage.

20. The TOF determining system of claim 19 wherein:

the junction type semiconductive device includes a bipolar junction transistor (BJT).