Using light pulses to implement auto-focus in a digital camera

1. A method for implementing auto-focus by a camera comprising:

transmitting light pulses at a first frequency;

receiving return signals corresponding to the transmitted light pulses, the return signals reflected from objects from different distances;

sampling electrical signals corresponding to the return signals at a second frequency that is lower than the first frequency;

identifying a signal level from the sampled electrical signals that exceeds a threshold level and corresponds to a quickest return time, the quickest return time being a time for receiving the return signals from a closest subject for which there is significant signal strength; and

effecting a setting of a camera lens focus distance based on a one of the sampled electrical signals corresponding to the identified signal level.

2. The method of claim 1 , wherein the light pulses comprise infrared light.

3. The method of claim 1 , further comprising:

digitizing the sampled electrical signals;

determining a focus distance responsive to the digitized electrical signals; and

focusing a camera lens responsive to the determined focus distance.

4. The method of claim 1 , wherein the light pulses are transmitted by a plurality of light transmitters.

5. The method of claim 1 , wherein the light pulses are transmitted by a light transmitter that is responsive to electrical pulses received by the light transmitter from a pulse generator.

6. The method of claim 5 , wherein the electrical pulses are amplified by a driver prior to being received by the light transmitter.

7. The method of claim 5 , wherein the light transmitter comprises a light emitting diode (LED).

8. The method of claim 1 , wherein the electrical signals are sampled by a sampler that is responsive to electrical pulses received by the sampler from a pulse generator.

9. The method of claim 8 , wherein the electrical signals are amplified prior to being sampled by the sampler.

10. The method of claim 1 , wherein the return signals are detected by a photo-diode configured to convert the return signals into the electrical signals.

11. A camera comprising:

a light transmitter configured to transmit light pulses at a first frequency;

a light receiver configured to receive return signals corresponding to the light pulses transmitted by the light transmitter, the return signals reflected from objects from different distances;

a sampler configured to sample a plurality of electrical signals corresponding to the return signals received by the light receiver, wherein the sampler is configured to sample the plurality of electrical signals at a second frequency that is lower than the first frequency; and

a processor configured to:

identify a signal level from the plurality of sampled electrical signals that exceeds a threshold level and corresponds to a quickest return time, the quickest return time being a time for receiving the return signals from a closest subject and the threshold level corresponding to a predefined significant signal strength; and

effect a setting of a camera lens focus distance based on a one of the plurality of sampled electrical signals corresponding to the identified signal level.

12. The camera of claim 11 , wherein the light pulses and the corresponding return signals comprise infrared light.

13. The camera of claim 11 , further comprising:

an analog to digital (A/D) converter configured to digitize the sampled electrical signals; and

wherein the processor configured is configured to determine the focus distance based on the digitized electrical signals.

14. The camera of claim 13 , wherein the processor is configured to effect the setting by enabling a camera lens to be positioned at a focus location that is responsive to the determined focus distance.

15. The camera of claim 11 , wherein the light transmitter is responsive to electrical pulses received by the light transmitter from a pulse generator, and wherein the electrical pulses are output by the pulse generator at the first frequency.

16. The camera of claim 15 , wherein the electrical pulses are amplified by a driver prior to being received by the light transmitter.

17. The camera of claim 15 , wherein the light transmitter comprises a light emitting diode (LED).

18. The camera of claim 11 , wherein the sampler is responsive to electrical pulses received by the sampler from a pulse generator, wherein the electrical pulses are output by the pulse generator at the second frequency.

19. The camera of claim 18 , wherein the electrical signals are amplified prior to being sampled by the sampler.

20. The camera of claim 11 , wherein the light receiver comprises a photo-diode configured to convert the return signals into the electrical signals.

21. A system for implementing auto-focus, the system comprising:

means for receiving return signals corresponding to light pulses transmitted at a first frequency, the return signals reflected from objects from different distances;

means for sampling electrical signals corresponding to the return signals at a second frequency that is lower than the first frequency; and

means for identifying a signal level from the sampled electrical signals that exceeds a threshold level of a predefined significant signal strength and corresponds to a quickest return time for receiving the return signals from a closest subject; and

means for effecting a setting of a camera lens focus distance based on a one of the sampled electrical signals corresponding to the identified signal level.

22. The system of claim 21 , wherein the light pulses comprise infrared light.

23. The system of claim 21 , further comprising:

means for digitizing the sampled electrical signals; and

wherein the means for effecting further comprises means for determining the focus distance responsive to the digitized electrical signals.

24. The system of claim 23 , further comprising:

means for focusing a camera lens responsive to the determined focus distance.

25. The system of claim 21 , further comprising means for transmitting the light pulses.

26. The system of claim 25 , further comprising means for driving the means for transmitting.

27. The system of claim 26 , further comprising means for generating a pulse that is provided to the means for driving.

28. The system of claim 21 , wherein the means for sampling is responsive to electrical pulses provided by a pulse generator.

29. The system of claim 28 , further comprising means for amplifying the electrical pulses provided by the pulse generator.

30. The system of claim 21 , wherein the means for receiving comprises a photo-diode.

31. A method for implementing auto-focus in a camera, comprising:

generating an output pulse having a first frequency;

amplifying the output pulse to genefrequency an amplified output pulse having the first frequency;

emitting a light pulse responsive to the amplified output pulse, the light pulse having a frequency that is substantially equal to the first frequency;

detecting reflections corresponding to the light pulse;

generating a composite reflection signal corresponding to the detected reflections, the detected reflections from objects from different distances;

amplifying the composite reflection signal;

generating a sampling pulse having a second frequency that is lower than the first frequency;

sampling the amplified composite reflection signal responsive to the sampling pulse at a frequency that is substantially equal to the frequency of the sampling pulse to genefrequency a sampled signal;

converting the sampled composite signal into a corresponding digital composite signal;

identifying a signal level from one of the signals of the digital composite signal that exceeds a threshold level of a predefined significant signal strength and corresponds to a quickest return time for receiving the return signals from a closest subject and the threshold level; and

effecting a setting of a camera lens focus distance based on a one of the signals of the digital composite signal corresponding to the identified signal level.

32. The method of claim 31 , further comprising:

determining a focus position for a camera lens responsive to the digital composite signal.

33. A method for implementing auto-focus in a camera, comprising:

transmitting light pulses at a pre-determined output frequency and receiving the corresponding reflections, the light pulses repeating at a frequency sufficiently high to successively sample a composite return signal over many pulse cycles;

sampling the reflections at a sampling frequency that is lower than the output frequency, the reflection from a single subject in a field of an emitter and detector being a pulse delayed by travel time required for a pulse to reach a subject and then return to the detector;

digitizing and analyzing the sampled signals to determine a desired focus distance, the desired focus distance corresponding to the closest subject for which there is a significant signal strength.

34. The method of claim 33 wherein the light pulses are from an infra-red (IR) light-emitting diode (LED) configured to emit IR light pulses.

35. The method of claim 34 wherein the LED is pulsed at a high frequency from about 1 to 10 MHz and the duration of each of the IR pulses is narrow between about 1 and 10 ns to enable a high level of accuracy.