LOW-POWER SURVEILLANCE SENSOR

DESCRIPTION

Field of the Invention

[Para 1 ] The present invention generally relates to image sensors, and more particularly to a low-power image sensor that may be used for surveillance and other applications.

Background of the Invention

[Para 2] Image sensors are used in a wide variety of applications. One application is perimeter and/or area surveillance. This application often requires image sensors to operate continuously to monitor the desired perimeter and/or area. In some cases, the positioning of the sensors is at locations without immediate access to a power supply making it desirable for the image sensor to be able to operate solely on battery power.

Summary of the Invention

[Para 3] The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.

[Para 4] The present invention provides for a system and a method of operating imaging sensors in a lower power manner. In one illustrative embodiment, an image sensor system includes a sensor controller coupled to a sensor array. The sensor controller may be adapted to read at least some of the sensor array pixels, and provide an output.

[Para 5] In some illustrative embodiments, at least a portion of the sensor controller has a higher power state, which is active when reading the at least part of the sensor array, and a lower power state, which is active between read operations. In one illustrative embodiment, the sensor controller may read at least some of the sensor array pixels at a reduced frame rate. A comparator may be provided for comparing at least some of the sensor array pixels of two or more pixel frames. A change detector may be coupled to the comparator for detecting a change between the two or more pixel frames.

[Para 6] When a change is detected by the change detector, the frame rate may be increased to capture more scene information. Thus, in some cases, the imaging sensor may be operated in a "trip wire" type mode, which may reduce operating power dramatically during periods of inactivity in the field of view, yet produce more detailed imagery relatively immediately when desired.

[Para 7] In some embodiments, the sensor array may also have a lower power and a higher power operating mode. The sensor array may be in the higher power operating mode during read operations, and in the lower power operating mode between successive read operations. This may also reduce the power consumption of the sensor. In some cases, such as when the sensor array is an infrared (IR) bolometer array, the sensor array may be continuously operated so that the sensor array remains thermally stable. However, this is not required in all embodiments.

[Para 8] In some cases, some read operations of the sensor array may read out every "nth" pixel of the sensor array, where "n" is an integer greater than one. For example, only a fraction of the pixels may be read out during periods of inactivity, and in some cases at a reduced frame rate. More pixels may be read out (e.g. every pixel), and in some cases at an increased frame rate, when a change is detected in the scene. This may also help reduce the power consumption of the image sensor.

Brief Description of the Drawings

[Para 9] Figure 1 is a schematic diagram of an illustrative low-power sensing system;

[Para 10] Figure 2 is a schematic diagram of an illustrative low-power sensing system including an infrared bolometer array;

[Para 1 1 ] Figure 3 is a schematic diagram of an illustrative low-power sensing system including an infrared bolometer array;

[Para 1 2] Figure 4 is a schematic diagram of an illustrative lower-power sensing system including an array of visible light sensors (e.g. Charge- Coupled Device or CCD);

[Para 13] Figure 5 is a diagram of a process of operating a low-power sensing system;

[Para 14] Figure 6 is a diagram of another process of operating a low-power sensing system; and

[Para 1 5] Figure 7 is a diagram of an alternative process of operating a low- power sensing system.

Detailed Description of the Drawings

[Para 16] The following description should be read with reference to the drawings wherein like reference numerals indicate like elements throughout the several views. The detailed description and drawings show several embodiments which are meant to be illustrative of the claimed invention.

[Para 17] Figure 1 is a schematic diagram of an illustrative sensing system. The illustrative sensing system includes a sensor array 18 and a controller 10. The illustrative controller 10 includes a sensor controller 12, a comparator 14, and a change detector 16. It is contemplated that the controller 10 may be implemented in software, hardware, or a combination thereof. In some cases, the controller 10 may activate a portion of the sensor array 8 while leaving the remaining sensors 9 inactive to reduce the power consumption of the sensor array 18. In other cases, the entire sensor array may be continuously active so that the sensor array remains thermally stable. This may be particularly useful

when, for example, the sensor array is an infrared (IR) microbolometer sensor array. However, this is not required in all embodiments. The sensor array 18 may be, but is not limited to, an infrared (IR) bolometer array, a visible light sensor array (e.g. Charge-Coupled Device (CCD)), or any other suitable sensor array as desired.

[Para 1 8] In the illustrative embodiment, the sensor array 1 8 produces pixel frames at a selectable rate. In a typical real time application, a single frame may take 1 /30th of a second, however, the time for one frame may be more or less. The sensor controller 1 2 is coupled to the sensor array 1 8 via an interface 1 5. The sensor controller 12 is adapted to read at least some of the sensor array 18 pixels and provide an output 1 7. In some embodiments, at least a portion of the sensor controller 1 2 has a higher power state, which is active when reading the sensor array 1 8, and a lower power state or "sleep" state between successive readings. The sensor controller 12 reads the sensor array 1 8 pixels and produces a pixel frame. The sensor controller 1 2 is in the lower power state for a time between reading successive pixel frames. For example, if the sensor array operates at a single frame per second, which may be 1 /30 second, and the sensor controller 12 is in a sleep state between each reading, the power consumed is approximately 1 /30 of a conventional image sensor operating at 30 frames per second. However, the embodiment is not limited to one frame per second, but may be any other number of frames per second whereby the power reduction would be adjusted accordingly.

[Para 19] Alternatively, or in addition, in some illustrative embodiments, every nth pixel of the sensor array 1 8 can be read out by the sensor controller 12, also reducing the power consumption of the sensor. By reducing the number of pixels read out by the sensor controller 12 to every nth pixel, the total number of pixels read may be reduced by n ² . Also, the time required to read the array is reduced by n ² , which when the sensor controller 1 2 is in a sleep state between successive reads of the sensor array, may reduce the power consumed by the sensor controller 12.

[Para 20] For example, if every 6th pixel is read, the number of pixels read out is reduced by a factor of 36, and the time required to read the sensor array

1 8 is 1 /36 of the full array read time, thus reducing the power of the sensor controller 1 2 by a factor of about 36. In some cases, the use of a decreased frame rate and only reading every nth pixel may be used together or separate, as desired. If both are used, for example, one frame per second is read and every 6th pixel is read, the total power is reduced by about 1 000 times relative to a conventional image sensor that reads every pixel at 30 frames per second.

[Para 21 ] In the illustrative embodiment, the comparator 14 may be used for comparing the sensor array pixels of two or more pixel frames. The change detector 16 may be coupled to the comparator 14, and may be used for detecting a change between the two or more pixel frames. For the change detector 16 to detect a change in the pixel frames, the change between the two or more pixel frames may exceed a certain threshold value. The threshold value may be any suitable threshold value, depending on the application. If the threshold value is exceeded, the frame rate of the sensor array 1 8 may be increased. In some cases, the increase is the maximum frame rate of the sensor array 1 8, but may be any desired frame rate. Also, all of the pixels may be read. Thus, the system can be low-power, but when needed, it can switch to a higher power state to more fully monitor the scene.

[Para 22] Figure 2 is a schematic diagram of an illustrative lower-power sensing system including an array of sensors 20. Each sensor 20 may be sensitive to visible, infrared or some other wavelength of radiation, as desired. In one illustrative embodiment, each sensor 20 is an infrared sensor known as a bolometer. An infrared bolometer 20 is a thermal radiation detector that operates by absorbing incident infrared radiation, converting the absorbed energy into heat and then indicating the resulting temperature change by a change in electrical resistance or the like. In some cases, a read-out integrated circuit (ROIC) 22 may be provided to help read out the sensor values from the array of sensors. For example, ROIC 22 may sequentially measure a resistance of the individual bolometers 20 in the array in a relatively short time. As noted above, the bolometer array 20 may be coupled to the controller 10 via interface 1 5.

[Para 23] Figure 3 is a schematic diagram of an illustrative lower-power bolometer array. In some cases, the bolometer array may include thin film resistors 27 with a relatively high temperature coefficient. One terminal of the thin film resistor 27 may be connected to a power supply voltage 24. The other terminal of the thin film resistor 27 may be connected to a corresponding row read line through a column select switch. In operation, the sensor elements 27 that are in a selected row are read in succession from a first sensor element 27a to a last sensor element 27b before the sensor elements 27 in the next row are read. To accomplish this, a row select circuit 25 selects a row and a column select circuit 23 sequentially activates each column. Once all the sensor elements 27 in a row are read, a next row is selected by the row select circuit 25. Then the column select circuit 23 again sequentially activates each column. This is continued until each row is read in the bolometer array 20. In another case, the sensor elements 27 may be activated so that each sensor element 27 in a diagonal is read. More generally, any arrangement of sensor elements 27 or readout sequence or method of activating sensor elements 27 may be used, as desired.

[Para 24] In some cases every nth sensor may be read. To accomplish this, and in one illustrative embodiment, the row select circuit 25 may select a row and the column select circuit 23 may sequentially active every nth sensor element 27 in the row. Once every nth sensor element 27 is read, the row select circuit 25 may select the next row. Then the column select circuit 23 again may sequentially activate every nth sensor element 27 in the row. This is continued until every row is read in the bolometer array 20.

[Para 25] Alternatively, the row select circuit 25 may select a row and the column select circuit 23 may sequentially activate every sensor element 27 in the row. Once every sensor element 27 is read, the row select circuit 25 may select the nth row. Then the column select circuit 23 again reads out every sensor element 27 in the row. Then the row select circuit 25 selects the next nth row. This is continued until every nth row is read in the bolometer array 20. These are just a few examples. It is contemplated, however, that every

nth row may be read, every nth column may be read, or any other combination of activating the row and column sensor elements 27 may be used, as desired.

[Para 26] Figure 4 is a schematic diagram of an illustrative lower-power visible sensing system including a Charge-Coupled Device (CCD). The CCD 30 includes an array of photo sensors 32. In many cases, the photo sensors 32 are connected to vertical registers 36, which are connected to a horizontal register 34. The output of the CCD 30 is sent to the controller 10 via interface 1 5.

[Para 27] Figure 5 is a flow diagram of an illustrative method of operating a sensing system. Initially, and as shown at block 50, the sensor array 1 8 may operate at a lower frame rate. In the illustrative embodiment, the sensor controller 1 2 has a higher power state and a lower power state. The sensor controller 1 2 operates in the higher power state when reading the sensor array 1 8. For example, the frame rate could be one frame per second. In some cases, a single frame may be 1 /30th of a second. Thus, the sensor controller 1 2 may operate only 1 /30th of the time relative to real time operation. As such, the power needed to operate the sensor controller 1 2 may be approximately 1 /30 of the power needed to operate at real time rates.

[Para 28] After each frame is read by the sensor controller 12, the comparator 14 may compare the current frame to one or more previous frames. The change detector 1 6 then may detect a difference in the frames found by the comparator 14. If the change is not greater than a predetermined threshold value, then the sensor array 1 8 continues to operate at the lower frame rate. If the change detected is greater than the predetermined threshold value 52, the sensor array 1 8 may increase the frame rate 54. In some cases, the sensor array operates at the increased frame rate for a predetermined period of time, until the change detector does not detect a change greater than a threshold value, or for some other period of time, as desired. The sensor array may then return back to the lower frame rate, if desired.

[Para 29] Figure 6 is a flow diagram of another illustrative method of operating a sensing system. In this method, the sensor array 1 8 reads out only every nth pixel 60, where "n" is an integer greater than one. For example,

if the sensor array reads out every 6th pixel, horizontally and vertically, the time needed for the sensor controller 12 to read the sensor array 1 8 is reduced by a factor of 36, and the power dissipated by the sensor controller 1 2 may be reduce to about 1 /36th of the power dissipated when all pixels are read out. Similar to the previous method, a comparator 14 may compare successive frames of the sensor array 1 8, and the change detector 1 6 may detect a change in the pixel frames. If the change is not greater than a predetermined threshold value, the sensor array 18 may continue to read out every nth pixel for each frame. If the change is greater than the predetermined threshold value 62, the sensor array 1 8 may read out more pixels 64, such as every pixel, to increase the resolution of the image produced by the sensor system. The sensor array 1 8 may continue to read out every pixel for a predetermined time period, until the change detector 16 detects a change not greater than a predetermined threshold value, or some other time as desired. Then the sensor array 1 8 may return to read out every nth pixel. The method of Figure 6 may be used in conjunction with the method described with reference to Figure 5, if desired.

[Para 30] Figure 7 is a flow diagram of another illustrative method of operating a sensing system. In this illustrative method, a lower-power sensor array 1 8 is used. In some cases, the sensor array 1 8 is an infrared bolometer array 20 using a low-power ROIC 22 design. The sensor array 1 8 is operated continuously at the full frame rate 70, so the sensor array 18 has a constant power state and is thus thermally stable. This can be important in infrared bolometer applications, since IR bolomoters are measuring relatively small heat signatures.

[Para 31 ] Also, at least part of the controller 10 may be in a lower power state

72. In the illustrative embodiment, the controller 1 0 is operated intermittently

73, at predetermined times 74, in response to a stimulus 75, or by any other means as desired. When the controller 10 is operated, it operates in a higher power state 76. At the expiration of the time or stimulus 78, the controller 10 returns to the lower power state 72. For example, the controller 10 may operate only three times per second to accept three pixel frames from the

sensor array 1 8, and is in a lower power state between readings. Thus, the power dissipated by the image sensor may be reduced.

[Para 32] Having thus described the preferred embodiments of the present invention, those of skill in the art will readily appreciate that yet other embodiments may be made and used within the scope of the claims hereto attached. Numerous advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respect, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the invention. The invention's scope is, of course, defined in the language in which the appended claims are expressed.