Imaging array with enhanced event detection
First Claim
Patent Images
1. An imaging device comprising an array of pixels in which, for each pixel, there is provided:
- a sensor which is sensitive to a variable quantity to be imaged and for outputting a signal representative of the variation in said quantity during a monitoring period;
a comparator having a first input and a second input;
a connection for connecting the output of said sensor to said first input in such a way that said comparator continuously monitors said output signal; and
a connection for applying a reference voltage to said second input;
said comparator being such as to change its output state at the point in time at which the amplitude of said output signal crosses said reference voltage level,wherein each pixel further comprises a hit flag generator which is operable to generate a flag signal indicative of whether, during the monitoring period, the output state of said comparator changes, and readout circuitry which is operable to read the contents of a memory unit during a read period, following the monitoring period, only if the hit flag generator indicates that the output state of the comparator changed during the monitoring period.
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Abstract
An imaging device comprising an array of pixels fabricated using a microelectronic technology such as CMOS is disclosed. The imaging device provides information regarding rapid increases in incident radiation. The sensor is sensitive to a variable quantity to be imaged, such as visible or non-visible radiation, and a signal representative of the quantity is output. The quantity is measured over a monitoring period, and the timing of the incidence may also be output.
52 Citations
19 Claims
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1. An imaging device comprising an array of pixels in which, for each pixel, there is provided:
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a sensor which is sensitive to a variable quantity to be imaged and for outputting a signal representative of the variation in said quantity during a monitoring period; a comparator having a first input and a second input; a connection for connecting the output of said sensor to said first input in such a way that said comparator continuously monitors said output signal; and a connection for applying a reference voltage to said second input; said comparator being such as to change its output state at the point in time at which the amplitude of said output signal crosses said reference voltage level, wherein each pixel further comprises a hit flag generator which is operable to generate a flag signal indicative of whether, during the monitoring period, the output state of said comparator changes, and readout circuitry which is operable to read the contents of a memory unit during a read period, following the monitoring period, only if the hit flag generator indicates that the output state of the comparator changed during the monitoring period. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. An imaging device comprising an array of pixels in which, for each pixel, there is provided:
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a sensor which is sensitive to a variable quantity to be imaged and for outputting a signal representative of the variation in said quantity during a monitoring period; a comparator having a first input and a second input; a connection for connecting the output of said sensor to said first input in such a way that said comparator continuously monitors said output signal; and a connection for applying a reference voltage to said second input; said comparator being such as to change its output state at the point in time at which the amplitude of said output signal crosses said reference voltage level, wherein each pixel comprises a plurality of memory units, wherein the output of the comparator is connected to a multi-way switch which is operable to connect the output of the comparator to one of said memory units at a time, and wherein a reset unit is provided for resetting the output of said sensor after a change of state of the comparator output so that a further change of the output state of the comparator within the monitoring period can be detected, said multi-way switch being controlled in such a way as to store timing information relating to each change of the output state of the comparator within the monitoring period in a separate one of said memory units.
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14. An imaging device comprising an array of pixels in which, for each pixel, there is provided:
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a sensor which is sensitive to a variable quantity to be imaged and for outputting a signal representative of the variation in said quantity during a monitoring period; a comparator having a first input and a second input; a connection for connecting the output of said sensor to said first input in such a way that said comparator continuously monitors said output signal; and a connection for applying a reference voltage to said second input; said comparator being such as to change its output state at the point in time at which the amplitude of said output signal crosses said reference voltage level, wherein each pixel further comprises amplitude measurement circuitry for measuring the amplitude of the output signal from the sensor at the point in time at which the amplitude of the output signal crosses said reference voltage level, and a memory unit for storing a value representative of the amplitude of the output signal from the sensor, and wherein each pixel further includes a switching circuitry means associated with said comparator for causing said comparator to operate in one of two modes; a) a “
timing”
mode in which said reference voltage level is constant and said second input to the comparator is connected to receive said reference voltage level, and said output is connected to said memory unit;
orb) an “
amplitude”
mode in which said second input to the comparator is connected to receive a ramp voltage to cause the comparator to operate as a ramp ADC, and said output is connected to said memory unitand a control unit for switching the comparator to “
timing”
mode at the beginning of the monitoring period, and switching to “
amplitude”
mode in the event that the comparator output changes state, thus enabling the analogue value of the amplitude to be stored as a digital value, by means of the ADC action of the comparator, in said memory unit. - View Dependent Claims (15, 16)
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17. An imaging device comprising an array of pixels in which, for each pixel, there is provided:
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a sensor which is sensitive to a variable quantity to be imaged and for outputting a signal representative of the variation in said quantity during a monitoring period; a comparator having a first input and a second input; a connection for connecting the output of said sensor to said first input in such a way that said comparator continuously monitors said output signal; and a connection for applying a reference voltage to said second input; said comparator being such as to change its output state at the point in time at which the amplitude of said output signal crosses said reference voltage level, wherein each pixel further comprises amplitude measurement circuitry for measuring the amplitude of the output signal from the sensor at the point in time at which the amplitude of the output signal crosses said reference voltage level, and a memory unit for storing a value representative of the amplitude of the output signal from the sensor, and wherein each pixel includes a further comparator whose output is connected to said memory unit, whose first input is connected to receive the output signal of said sensor and whose second input is connected to receive a ramp voltage so as to cause the further comparator to operate as a ramp ADC to enable the analogue value of the amplitude of the sensor output signal to be stored as a digital value in said memory unit. - View Dependent Claims (18, 19)
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Specification