Image sensor including real-time automatic exposure control and swallowable pill including the same
View Patent ↗An imager and a method for real-time, non-destructive monitoring of light incident on imager pixels during their exposure to light. Real-time or present pixel signals, which are indicative of present illumination on the pixels, are compared to a reference signal during the exposure. Adjustments, if necessary, are made to programmable parameters such as gain and/or exposure time to automatically control the imager's exposure to the light. In a preferred exemplary embodiment, only a selected number of pixels are monitored for exposure control as opposed to monitoring the entire pixel array.
1. An image sensor comprising:
an array of pixels comprising a plurality of rows and columns;
a plurality of comparison circuits, each comparison circuit receiving a reference signal value and being coupled to a respective column, each comparison circuit comparing a pixel signal value to the reference signal value and having an output that indicates if the pixel signal value is greater than the reference signal value;
a first circuit connected to and counting a number of outputs from the comparison circuits that indicate the pixel signal value is greater than the reference signal value, said first circuit outputting the number of outputs; and
a logic circuit that receives the number of outputs from the first circuit, wherein during an exposure period said logic circuit compares the number received from the first circuit to a predetermined number of pixels that may have a pixel signal value greater than the reference signal value and, if the number received from the first circuit is greater than the predetermined number of pixels and a current exposure time is less than a maximum exposure time, the logic circuit adjusts automatic exposure control parameters for a remaining portion of the exposure period by setting a readout gain of the image sensor to a minimum gain value and adjusting the reference signal value to a value of a full scale pixel signal.
2. The image sensor of claim 1 , wherein said first circuit comprises:
a collection circuit connected to receive the outputs from all of the comparison cicuits; and
a counter connected to the collection circuit, said counter counting the results from the connection circuit and generating the number of outputs.
3. The image sensor of claim 1 , further comprising a reference generator for generating and outputting the reference signal value to the comparison circuits.
4. The image sensor of claim 3 , wherein said reference generator generates the reference signal value based on a mean reset value.
5. The image sensor of claim 3 , further comprising:
a plurality of first switches, each first switch having a first state connecting a first input of a respective comparison circuit to a pixel signal from a respective column, each switch having a second state connecting the first input of the respective comparison circuit to the reference signal, each comparison circuit having a first output for outputting a comparison result based on the first input;
a plurality of second switches, each second switch having a first state connecting a second input of a respective comparison circuit to the reference signal, each switch having a second state connecting the second input of the respective comparison circuit to a pixel signal from a respective column, each comparison circuit having a second output for outputting a comparison result based on the second input; and
a plurality of third switches for outputting the first output from the comparison circuits to the first circuit in a first state, and for outputting the second output from the comparison circuits to the first circuit in a second state.
6. A swallowable pill comprising:
an image sensor, said image sensor comprising:
an array of pixels comprising a plurality of rows and columns;
a plurality of comparison circuits, each comparison circuit receiving a reference signal value and being coupled to a respective column, each comparison circuit comparing a pixel signal value to the reference signal value and having an output that indicates if the pixel signal value is greater than the reference signal value;
a first circuit connected to and counting a number of outputs from the comparison circuits that indicate the pixel signal value is greater than the reference signal value, said first circuit outputting the number of outputs; and
a logic circuit that receives the number of outputs from the first circuit , wherein during an exposure period said logic circuit compares the number received from the first circuit to a predetermined number of pixels that may have a pixel signal value greater than the reference signal value and, if the number received from the first circuit is greater than the predetermined number of pixels and a current exposure time is less than a maximum exposure time, the logic circuit adjusts automatic exposure control parameters for a remaining portion of the exposure period by setting a readout gain of the image sensor to a minimum gain value and adjusting the reference signal value to a value of a full scale pixel signal.
7. An image sensor comprising:
an array of pixels comprising a plurality of rows and columns;
a plurality of comparison circuits, each comparison circuit receiving a reference signal value and being coupled to a respective column, each comparison circuit comparing a pixel signal value to the reference signal value and having an output that indicates if the pixel signal value is greater than the reference signal value;
a first circuit connected to and counting a number of outputs from the comparison circuits that indicate the pixel signal value is greater than the reference signal value, said first circuit outputting the number of outputs; and
a logic circuit that receives the number of outputs from the first circuit, wherein during an exposure period said logic circuit compares the number received from the first circuit to a predetermined number of pixels that may have a pixel signal value greater than the reference signal value and, if the number received from the first circuit is greater than the predetermined number of pixels and a current exposure time is within a predetermined time interval, the logic circuit adjusts automatic exposure control parameters for a remaining portion of the exposure period by setting a readout gain to a gain value between a maximum gain value and a minimum gain value and setting the reference signal value to a value of a full scale pixel signal divided by the readout gain value set to be between the maximum gain and the minimum gain value.
8. The image sensor of claim 7 , wherein said first circuit comprises:
a collection circuit connected to receive the outputs from all of the comparison circuits; and
a counter connected to the collection circuit, said counter counting the results from the connection circuit and generating the number of outputs.
9. The image sensor of claim 7 , further comprising a reference generator for generating and outputting the reference signal value to the comparison circuits.
10. The image sensor of claim 9 , wherein said reference generator generates the reference signal value based on a mean reset value.
11. The image sensor of claim 9 , further comprising:
a plurality of first switches, each first switch having a first state connecting a first input of a respective comparison circuit to a pixel signal from a respective column, each switch having a second state connecting the first input of the respective comparison circuit to the reference signal, each comparison circuit having a first output for outputting a comparison result based on the first input;
a plurality of second switches, each second switch having a first state connecting a second input of a respective comparison circuit to the reference signal, each switch having a second state connecting the second input of the respective comparison circuit to a pixel signal from a respective column, each comparison circuit having a second output for outputting a comparison result based on the second input; and
a plurality of third switches for outputting the first output from the comparison circuits to the first circuit in a first state, and for outputting the second output from the comparators to the first circuit in a second state.
12. A swallowable pill comprising:
an image sensor, said image sensor comprising:
an array of pixels comprising a plurality of rows and columns;
a plurality of comparison circuits, each comparison circuit receiving a reference signal value and being coupled to a respective column, each comparison circuit comparing a pixel signal value to the reference signal value and having an output that indicates if the pixel signal value is greater than the reference signal value;
a first circuit connected to and counting a number of outputs from the comparison circuits that indicate the pixel signal value is greater than the reference signal value, said first circuit outputting the number of outputs; and
a logic circuit that receives the number of outputs from the first circuit, wherein during an exposure period said logic circuit compares the number received from the first circuit to a predetermined number of pixels that may have a pixel signal value greater than the reference signal value and, if the number received from the first circuit is greater than the predetermined number of pixels and a current exposure time is within a predetermined time interval, the logic circuit adjusts automatic exposure control parameters for a remaining portion of the exposure period by setting a readout gain to a gain value between a maximum gain value and a minimum gain value and setting the reference signal value to a value of a full scale pixel signal divided by the readout gain value set to be between the maximum gain and the minimum gain value.