Optical sensor device

• US 8,125,620 B2
• Filed: 10/17/2008
• Issued: 02/28/2012
• Est. Priority Date: 10/18/2007
• Status: Active Grant

• Current Assignee: Garmin Switzerland GmbH (Garmin Limited)
• Original Assignee: PulsedLight, LLC
• Inventors: Lewis, Robert Alden
• Primary Examiner(s): ALSOMIRI, ISAM A
• Application Number:
  US12/288,305
• Publication Number:
  US 20100026984A1
• Time in Patent Office: 1,229 Days
• Field of Search: 356/4.01, 356/5.01, 356/5.07, 356/5.08, 356/5.15, 356/28
• US Class Current: 356/5.01
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 17/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 7/4811 common to transmitter and receiver
• CPC Class Codes: G01S 7/491 Details of non-pulse systems
• CPC Class Codes: G01S 7/4915 Time delay measurement, e.g. operational details for pixel components signal extraction and conditioning G01S7/493; Phase measurement
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

A method and apparatus for the acquisition of repetitive signals in a sensing device comprising a transmitter, a receiver and an object. The transmitter repetitively emits a modulated electro-magnetic signal into a transmission medium, with the emitted signal interacting with the object producing a counter propagating return signal. The return signal may contain properties that reflect all, or a portion, of the initial signal or may be correlated with said signal through a process of absorption and reemission, in which reflected signal characteristics are governed by the object'"'"'s physical material characteristic. The return signal is detected and converted into digital signals by a receiver via a reception channel through the use of edge transitions rather than logic levels from one or more comparator outputs to reconstruct the return signal waveform. A several waveform acquisition and reconstruction methods are disclosed for use with an edge sampling detection apparatus. When directed towards the time-of-flight distance measurement the invention also discloses a useful method to provide optical feedback using a moving waveguide.

Claims

1. A sensing device configured to synchronously emit one or more modulated electro-magnetic signals into a transmission channel to produce a receive signal based on an interaction of the emitted signal with an object, the sensing device comprising:

a detector to convert said electromagnetic signal into an electrical signal; and

a signal sampler to convert the signal into binary logic states at successive sample points based on a detection reference;

an edge detector to detect a positive or negative edge transition at a sample point based on the previous and present logic state of the signal sampler, wherein said edge detector uses at least 2 consecutive signal samples to determine edge state;

a summing element to accumulate the number of rising and falling edges associated with a given sample point; and

a signal reconstruction module configured to use the difference between the number of rising and falling edges at sample points to estimate a signal slope.

2. The device according to claim 1, wherein the signal sampler includes a signal comparator and a clocked serial to parallel converter.

3. The device according to claim 2, wherein the serial to parallel convertor comprises a tapped delay line and associated sampling latches.

4. The device according to claim 3, further comprising a clocked data synchronizer situated prior to the tapped delay line to sample the comparator output roughly 180 degrees out of phase to the nominal sampling interval.

5. The device according to claim 3, wherein the tapped delay line comprises at least two parallel delay lines coupled to inverted and non-inverted signal comparator outputs.

6. The device according to claim 5, where the states of associated taps of the delay line are configured to be decoded to cancel the effect of asymmetric propagation delays on the effective sample points of rising and falling edge transitions.

7. The device according to claim 1, wherein said summing element includes a series of adders and a memory.

8. The device according to claim 7, wherein the number of required adders is reduced by alternatively processing rising and falling edges with skipped edge data passed forward to the next summing cycle using a bit storage pipeline.

9. The device according to claim 1, wherein the edge difference is normalized based on a sum of rising and falling edges to produce a transfer function with a value between minus one and plus one.

10. The device according to claim 9, wherein if the normalized slope estimate of the transfer function exceeds a value in the range of +/−

0.9 to 0.95 the signal slope is based on the sum of rising and falling edges multiplied by a large signal scale factor.

11. The device according to claim 10, wherein the large signal scaling factor is based on the mean of the slope transfer function divided by the corresponding sum of the rising and falling edges at points bordering the large signal transition.

12. The device according to claim 11, wherein the border between the small signal and large signal is based on normalized transfer function values in the range of +/−

0.8 to 0.95.

13. The device according to claim 1, wherein the detection reference is adjustable.

14. The device according to claim 13, wherein the detection reference is configured to be swept through the signal envelope.

15. The device according to claim 14, wherein the detection reference sweep is based on measured signal strength.

16. The device according to claim 1, wherein the signal reconstruction module further comprises:

a past edge sum register to store previous edge sum values; and

a present edge sum register to store present edge sum value values; and

a detection reference storage register to store the last threshold value; and

an acquisition status flag register to disable the continued updating of the past and present edge sum registers; and

a comparison device to determine when a present sum is less than the pass sum value to inhibit additional updates of associated edge storage and detection reference registers; and

a signal estimator configured to provide signal amplitude estimate, wherein the signal amplitude is based on a interpolated threshold level; and

a detection reference generator.

17. The device according to claim 16, wherein the interpolation calculation is based on the last stored detection threshold level and the edge sum value divided by the difference in the past and present edge sum values.

18. The device according to claim 17, wherein the output of the detection reference generator is configured to follow a ramp waveform.

19. The device according to claim 1, wherein the signal reconstruction module is configured to convert the slope into an amplitude value.