Read-out circuitry for an image sensor
View Patent ↗An array of image sensing elements is arranged in rows and columns. A readout circuit for each column includes a circuit configured to receive a column select signal. A memory stores data indicative of a voltage of an image sensing element which is being read. An analog to digital conversion circuit provides an output to the memory to control the storing of data. The output is dependent on the voltage of the image sensing element. Power control circuitry operates to disable, at least partially, the analog to digital conversion circuit when the column has not been selected.
1. A readout circuit for a column of an array of image sensing elements arranged in rows and columns, comprising:
a circuit configured to receive a column select signal;
a memory configured to store data indicative of a voltage of an image sensing element which is being read;
an analog to digital conversion circuit configured to provide an output to said memory to control the storing of said data, said output being dependent on said voltage of said image sensing element; and
a power control circuit configured to disable, at least partially, said analog to digital conversion circuit in dependence upon said column select signal and a row style signal.
2. The readout circuit as claimed in claim 1 , wherein said power control circuit is configured to receive said column select signal.
3. The readout circuit as claimed in claim 2 , wherein said power control circuit is configured in dependence on the value of the column select signal to provide either an enable output or a disable output.
4. The readout circuit as claimed in claim 3 , wherein said analog to digital conversion circuit is configured to receive said enable or disable output from said power control circuit.
5. The readout circuit as claimed in claim 4 , wherein said analog to digital conversion circuit comprises a comparator which is configured to be disabled by said disable output from power control circuit when said column has not been selected.
6. The readout circuit as claimed in claim 4 , wherein said analog to digital conversion circuit comprises a sample and hold circuit which is configured to be disabled by said disable output from power control circuit when said column has not been selected.
7. The readout circuit as claimed in claim 1 , wherein said memory comprises a plurality of memory elements.
8. The readout circuit as claimed in claim 7 , wherein said memory elements are configured to be clocked by an output of said analog to digital conversion circuit.
9. The readout circuit as claimed in claim 7 , wherein said memory elements include an input circuit configured to provide a low data input to said memory element when said column is not enabled.
10. The readout circuit as claimed in claim 1 , wherein said power control circuit comprises at least one memory element.
11. The readout circuit as claimed in claim 10 , wherein said at least one power control circuit memory element comprises a clock input configured to receive a column decoding output, a data input configured to receive a column enable signal and an output, said output being provided to said analog to digital conversion circuit.
12. The readout circuit as claimed in claim 11 , wherein said power control circuit memory element output is configured to enable or disable said at least part of said analog to digital conversion circuit.
13. The readout circuit as claimed in claim 10 , wherein said at least one power control circuit memory element comprises an enable input.
14. The readout circuit as claimed in claim 13 , wherein said power control circuit memory element enable input is tied to an enable logic level.
15. The readout circuit as claimed in claim 13 , wherein said power control circuit memory element enable input is configured to receive said row style signal.
16. The readout circuit as claimed in claim 15 , further comprising at least two power control circuit memory elements, wherein different ones of said memory elements receive different row style signals.
17. The readout circuitry as claimed in claim 16 , wherein first logic is provided such that a clock input is provided to said at least one power control circuit memory element only if a column is enabled and the row style signal is enabled.
18. The readout circuit as claimed in claim 17 , wherein said first logic comprises an AND gate.
19. The readout circuit as claimed in claim 16 , comprising second logic configured to receive said row style signal and row style information stored in said power control circuit memory elements and if there is a match to enable said analog to digital conversion circuit.
20. The readout circuit as claimed in claim 7 , wherein at least one memory element comprises a SRAM element.
21. The readout circuit as claimed in claim 1 , wherein said data indicative of a voltage comprises a count value.
22. An image sensor, comprising:
an array of image sensing elements arranged in rows and columns; and
a read out circuit for each column, wherein each read out circuit comprises:
a circuit configured to receive a column select signal;
a memory configured to store data indicative of a voltage of an image sensing element which is being read;
an analog to digital conversion circuit configured to provide an output to said memory to control the storing of said data, said output being dependent on said voltage of said image sensing element; and
a power control circuit configured to disable, at least partially, said analog to digital conversion circuit in dependence upon said column select signal and a row style signal that indicates a pattern of image sensing elements in a row for read out.
23. The image sense of claim 22 implemented as an integrated circuit.