Autofocus chip with reference level determination circuit
First Claim
1. A camera autofocus apparatus, comprising:
- a photodiode sensor having photodiodes and a full well diode, the full well diode providing a full well charge and the photodiodes providing image values;
reference level storage means for storing a reference voltage equivalent to the full well charge;
converter means for converting the image values to digital values based on the reference voltage; and
autofocus means for performing image correlation operations responsive to the digital values.
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Abstract
The present invention is an autofocus chip which produces reference levels or voltages from CCD charge sources rather from voltage sources chip. The CCD sensor of the chip has normal photodiodes and bright diodes. A high voltage reference is produced from the maximum charge or full well level of one of the bright diodes of the sensor, stored and used as the high reference of an A/D converter in the chip. The reference traverses the same path as the image values produced by the photodiodes. A low voltage reference for the A/D converter is produced by storing the reset level voltage of the bright diode or of each pixel. Correlated double sampling for each pixel is accomplished when the low reference level in the A/D converter is updated with the reset value of each pixel. The reset level also traverses the same path as the image signals. By setting the high reference level each time the chip is enabled and the low reference level for each pixel, the reference levels are adapted to the environmental changes experienced by the chip or to changes due to manufacturing tolerances. The bright diode level is used to determine the integration time for the sensor during an autofocus operation by comparing the charge in the bright diode with the photodiode having the largest charge.
31 Citations
9 Claims
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1. A camera autofocus apparatus, comprising:
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a photodiode sensor having photodiodes and a full well diode, the full well diode providing a full well charge and the photodiodes providing image values; reference level storage means for storing a reference voltage equivalent to the full well charge; converter means for converting the image values to digital values based on the reference voltage; and autofocus means for performing image correlation operations responsive to the digital values. - View Dependent Claims (2, 3, 4, 5)
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6. A camera autofocus apparatus, comprising:
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photodiode sensor having a full well diode and photodiodes; an amplifier connected to said sensor; an image signal buffer connected to said amplifier; a reference storage circuit connected to said amplifier; an analog-to-digital converter connected to said buffer and said storage circuit; and an autofocus processing circuit connected to said sensor, amplifier, buffer, circuit and converter. - View Dependent Claims (7)
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8. A method of autofocus, comprising:
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(a) determining reference levels for a conversion operation from a bright diode of a sensor and a reset voltage; (b) performing conversions using the reference levels; and (c) performing autofocus operations responsive to the conversions. - View Dependent Claims (9)
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Specification