Circuit and method for preventing laser jamming of night vision goggles

• US 5,747,792 A
• Filed: 08/30/1996
• Issued: 05/05/1998
• Est. Priority Date: 08/30/1996
• Status: Expired due to Fees

• Current Assignee: Douglas Limited
• Original Assignee: Mcdonnell Douglas Corporation (The Boeing Co.)
• Inventors: Kintz, Kevin G., Rogers, Mark D.
• Primary Examiner(s): Westin, Edward P.
• Assistant Examiner(s): PYO, KEVIN K
• Application Number:
  US08/697,875
• Time in Patent Office: 613 Days
• Field of Search: 250/214 VT, 250/214 AL, 250/214 R, 313/523, 313/529, 313/537, 315/158, 315/159
• US Class Current: 250/214.0VT
• CPC Class Codes: G01S 7/495 Counter-measures or counter-counter-measures using electronic or electro-optical means

Abstract

A method for preventing laser jamming of night vision goggles having a gated image intensifier device and a display for displaying an intensified image of a scene. The method includes the steps of detecting laser pulses from a jamming laser source and producing respective electrical pulses in response thereto, and gating off the gated image intensifier device in synchronism with the electrical pulses in order to thereby prevent the laser pulses from affecting the intensified image of the scene displayed by the display. The step of gating off the gated image intensifier device is preferably carried out by using a phase locked loop to produce a PLL output signal synchronized with the laser pulses, conditioning the PLL output signal to produce a conditioned PLL output signal, comparing the conditioned PLL output signal with a prescribed reference voltage to generate a comparator output signal having a first level when the PLL output signal is greater than a prescribed reference voltage, and a second level when the PLL output signal is not greater than the prescribed reference voltage, generating a pulse train in response to the comparator output signal, and applying the pulse train to the gated intensifier device. The step of detecting laser pulses from the jamming laser source is preferably carried out by using a photodetector device to detect the laser pulses and to produce rounded electrical pulses corresponding to the detected laser pulses, and squaring the rounded electrical pulses to produce the electrical pulses, wherein the electrical pulses comprise square electrical pulses. Also disclosed is a circuit for implementing the above-described method for preventing laser jamming of night vision goggles.

Claims

1. A method for preventing laser jamming of night vision goggles having a gated image intensifier device and a display for displaying an intensified image of a scene, including the steps of:

detecting laser pulses, wherein the gating step includes the sub-steps of;

using a phase locked loop to produce a PLL output signal synchronized with said laser pulses;

comparing said PLL output signal with a prescribed reference voltage to generate a comparator output signal having a first level when said PLL output signal is greater than said prescribed reference voltage, and a second level when said PLL output signal is not greater than said prescribed reference voltage; and

,

applying said comparator output signal to said gated image intensifier device.

2. The method as set forth in claim 1, wherein said PLL output signal comprises a square wave having a 50% duty cycle.

7. The method as set forth in claim 1, wherein said prescribed reference voltage is adjustable.

3. A method for preventing laser jamming of night vision goggles having a gated image intensifier device and a display for displaying an intensified image of a scene, including the steps of:

detecting laser pulses and producing respective electrical pulses in response thereto; and

,

gating off the gated image intensifier device in synchronism with said electrical pulses in order to thereby prevent said laser pulses from affecting the intensified image of the scene displayed by the display, wherein the gating step includes the sub-steps of;

using a phase locked loop to produce a PLL output signal synchronized with said electrical pulses;

conditioning said PLL output signal to produce a conditioned PLL output signal;

comparing said conditioned PLL output signal with a prescribed reference voltage to generate a comparator output signal having a first level when said PLL output signal is greater than said prescribed reference voltage, and a second level when said PLL output signal is not greater than said prescribed reference voltage;

generating a pulse train in response to said comparator output signal; and

,

applying said pulse train to said gated image intensifier device.

4. The method as set forth in claim 3, wherein the detecting step includes the sub-steps of:

using a photodetector device to detect said laser pulses and to produce rounded electrical pulses corresponding to the detected laser pulses; and

,

squaring said rounded electrical pulses to produce said electrical pulses, wherein said electrical pulses comprise square electrical pulses.

5. The method as set forth in claim 4, wherein the conditioning sub-step is carried out using a low-pass filter, to thereby convert said square electrical pulses into said conditioned PLL output signal, wherein said conditioned PLL output signal comprises an RC charge/decay wave.

6. The method as set forth in claim 5, wherein the sub-step of generating a pulse train comprises the sub-steps of:

using a spike pulse generator circuit to produce spike pulses coincident with transitions of said comparator output signal from said second level to said first level; and

,

producing said pulse train in response to said spike pulses.

8. The method as set forth in claim 5, wherein said prescribed reference voltage is adjustable.

9. A circuit for preventing laser jamming of night vision goggles having a gated image intensifier device and a display for displaying an intensified image of a scene, including:

means for detecting laser pulses and producing respective electrical pulses in response thereto; and

,

means for gating off the gated image intensifier device in synchronism with said electrical pulses in order to thereby prevent said laser pulses from affecting the intensified image of the scene displayed by the display, wherein the gating means includes;

a phase locked loop for producing a PLL output signal synchronized with said laser pulses;

means for comparing said PLL output signal with a prescribed reference voltage to generate a comparator output signal having a first level when said PLL output signal is greater than said prescribed reference voltage, and a second level when said PLL output signal is not greater than said prescribed reference voltage; and

,

means for applying said comparator output signal to said gated image intensifier device.

10. The circuit as set forth in claim 9, wherein said PLL output signal comprises a square wave having a 50% duty cycle.

11. A circuit for preventing laser jamming of night vision goggles having a gated image intensifier device and a display for displaying an intensified image of a scene, including:

means for detecting laser pulses and producing respective electrical pulses in response thereto; and

,

means for gating off the gated image intensifier device in synchronism with said electrical pulses in order to thereby prevent said laser pulses from affecting the intensified image of the scene displayed by the display, wherein the gating means includes;

a phase locked loop for producing a PLL output signal synchronized with said laser pulses;

means for conditioning said PLL output signal to produce a conditioned PLL output signal;

means for comparing said conditioned PLL output signal with a prescribed reference voltage to generate a comparator output signal having a first level when said conditioned PLL output signal is greater than said prescribed reference voltage, and a second level when said conditioned PLL output signal is not greater than said prescribed reference voltage;

means for generating a pulse train in response to said comparator output signl; and

,

means for applying said pulse train to said gated image intensifier device.

12. The circuit as set forth in claim 11, wherein said detecting means includes:

a photodetector device to detect said laser pulses and to produce rounded electrical pulses corresponding to the detected laser pulses; and

,

means for squaring said rounded electrical pulses to produce said electrical pulses, wherein said electrical pulses comprise square electrical pulses.

13. The circuit as set forth in claim 12, wherein:

said squaring means comprises a one-shot; and

,

said conditioning means comprises a low-pass filter.

14. The circuit as set forth in claim 13, wherein said prescribed reference voltage is adjustable.

15. A circuit for preventing laser jamming of night vision goggles having a gated image intensifier device and a display for displaying an intensified image of a scene, including:

a first circuit for detecting laser pulses and producing respective electrical pulses in response thereto; and

,

a second circuit for gating off the gated image intensifier device in synchronism with said electrical pulses in order to thereby prevent said laser pulses from affecting the intensified image of the scene displayed by the display, wherein said second circuit includes;

a phase locked loop for producing a PLL output signal synchronized with said laser pulses;

a comparator circuit for comparing said PLL output signal with a prescribed reference voltage to generate a comparator output signal having a first level when said PLL output signal is greater than said prescribed reference voltage, and a second level when said PLL output signal is not greater than said prescribed reference voltage; and

,

means for applying said comparator output signal to said gated image intensifier device.

16. The circuit as set forth in claim 15, wherein said PLL output signal comprises a square wave having a 50% duty cycle.

17. A circuit for preventing laser jamming of night vision goggles having a gated image intensifier device and a display for displaying an intensified image of a scene, including:

means for detecting laser pulses and producing respective electrical pulses in response thereto; and

,

means for gating off the gated image intensifier device in synchronism with said electrical pulses in order to thereby prevent said laser pulses from affecting the intensified image of the scene displayed by the display, wherein said second circuit includes;

a phase locked loop to produce a PLL output signal synchronized with said electrical pulses;

a conditioning circuit for conditioning said PLL output signal to produce a conditioned PLL output signal;

a comparator circuit for comparing said conditioned PLL output signal with a prescribed reference voltage to generate a comparator output signal having a first level when said conditioned PLL output signal is greater than said prescribed reference voltage, and a second level when said conditioned PLL output signal is not greater than said prescribed reference voltage;

a pulse train generator circuit for generating a pulse train in response to said comparator output signal; and

,

means for applying said pulse train to said gated image intensifier device.