Dual mode adaptive threshold architecture for 3-D ladar FPA

• US 6,522,396 B1
• Filed: 01/08/2002
• Issued: 02/18/2003
• Est. Priority Date: 01/08/2002
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Halmos, Maurice J.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): ANDREA, BRIAN K
• Application Number:
  US10/040,214
• Time in Patent Office: 406 Days
• Field of Search: 356/4-1-, 356/141.1, 382/103, 382/106
• 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 17/894 3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
• CPC Class Codes: G01S 7/481 Constructional features, e.g. arrangements of optical elements
• CPC Class Codes: G01S 7/4873 by deriving and controlling a threshold value

Abstract

An integrated detector and signal processor (31) for ladar focal plane arrays (30) which internally compensates for variations in detector gain, noise, and aerosol backscatter. The invention (31) is comprised of a detector element (42) for receiving an input signal, a circuit (72) for generating a threshold based on the RMS noise level of the input signal, and a circuit (74) determining when the input signal is above that threshold. The detector element (42) is physically located in the interior of the detector array (30), while the signal processing circuitry (50) is located on the periphery of the array (30). In the preferred embodiment, the signal processor (31) also includes a circuit (56) for sampling the input signal and a circuit (58) storing multiple samples, allowing for multiple returns to be detected. In the preferred embodiment, the signal processor (31) can be operated in two modes: self triggered and externally triggered (range-gate mode). In the self triggered mode, the detector continually monitors and samples the incoming signal until a return is detected (by the thresholding circuit). In the range-gate mode, the detector stops sampling when it receives a signal from an external source. Once the data has been acquired, readout electronics (66) output the stored samples along with the stored “stopped” time code to an external computer (26).

Claims

1. An integrated detector and signal processor for ladar focal plane arrays comprising:

first means for receiving an input signal wherein said first means is located in an interior of said array;

second means for generating an adaptive threshold setting based on a characteristic of said input signal; and

third means for detecting when said input signal is above said threshold,

wherein said second and third means are located on a periphery of said array.

2. The invention of claim 1 wherein said threshold is set to a multiple of the RMS (root mean square) noise amplitude of said input signal.

3. The invention of claim 2 wherein said second means includes an RMS sensor and an amplifier.

4. The invention of claim 3 wherein said RMS sensor includes a rectifier and a low pass filter.

5. The invention of claim 3 wherein said amplifier can be varied to adjust for low or high sensitivity.

6. The invention of claim 1 wherein said third means is a comparator.

7. The invention of claim 1 wherein said signal processor further includes means for storing a time code corresponding to the time when said third means detects that said input signal is above said threshold.

8. The invention of claim 1 wherein said signal processor further includes fourth means for sampling said input signal.

9. The invention of claim 8 wherein said fourth means is a Sample and Hold circuit.

10. The invention of claim 8 wherein said signal processor further includes fifth means for storing multiple samples of said input signal.

11. The invention of claim 10 wherein said fifth means includes a data storage pipeline.

12. The invention of claim 8 wherein said sampling stops a predetermined period after said third means detects that said input signal is above said threshold.

13. The invention of claim 8 wherein said signal processor further includes means for operating in an alternate mode wherein said sampling stops upon receiving a signal from an external source.

14. The invention of claim 10 wherein said signal processor further includes means for outputting said samples to an external computer a predetermined period after said third means detects that said input signal is above said threshold.

15. The invention of claim 1 wherein said signal processor further includes means for converting said input signal to a voltage signal wherein said means is located in an interior of said array.

16. The invention of claim 15 wherein said means for converting said input signal to a voltage signal is a trans-impedance preamplifier.

17. A method for internal bias adjustment of detectors in a ladar focal plane array including the steps of:

receiving an input signal using a detector element located in an interior of said array;

generating an adaptive threshold setting based on a characteristic of said input signal; and

detecting when said input signal is above said threshold, wherein said threshold generation and detection is implemented through electronics located on a periphery of said array.