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.
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.
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.
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.
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.
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.
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.
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.
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.
In the illustrative embodiment, the sensor array 18 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 12 is coupled to the sensor array 18 via an interface 15. The sensor controller 12 is adapted to read at least some of the sensor array 18 pixels and provide an output 17. In some embodiments, at least a portion of the sensor controller 12 has a higher power state, which is active when reading the sensor array 18, and a lower power state or “sleep” state between successive readings. The sensor controller 12 reads the sensor array 18 pixels and produces a pixel frame. The sensor controller 12 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.
Alternatively, or in addition, in some illustrative embodiments, every nth pixel of the sensor array 18 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 n2. Also, the time required to read the array is reduced by n2, which when the sensor controller 12 is in a sleep state between successive reads of the sensor array, may reduce the power consumed by the sensor controller 12.
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 18 is 1/36 of the full array read time, thus reducing the power of the sensor controller 12 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 1000 times relative to a conventional image sensor that reads every pixel at 30 frames per second.
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 18 may be increased. In some cases, the increase is the maximum frame rate of the sensor array 18, 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.
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.
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.
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 16 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 18 continues to operate at the lower frame rate. If the change detected is greater than the predetermined threshold value 52, the sensor array 18 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.
Also, at least part of the controller 10 may be in a lower power state 72. In the illustrative embodiment, the controller 10 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 18, and is in a lower power state between readings. Thus, the power dissipated by the image sensor may be reduced.
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.