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US 2005/0088331 A1Published application
Variable quantization ADC for image sensors
AssigneeMicron Technology, Inc.
InventorAlexander Krymski
Life of this patent
Estimating the term…
Abstract
An A/D converter suitable for use in a system in which the signal power of noise increases with the signal power of the signal, such as an imaging system, utilizes a variable quantization system for converting analog signals into digital signals. The variable quantization is controlled so that at low signal levels the quantization is similar or identical to conventional A/D converters, while the quantization level is increased at higher signal levels. Thus, higher resolution is provided at low signal levels while lower resolution is produced at high signal levels.
Claims43
An analog to digital (A/D) converter, comprising:
- a counter circuit for storing a digital word;
- a ramp generator for generating a sequence of reference voltages which vary in accordance with at least a first transfer function of said digital word and a second transfer function of said digital word;
- a comparator for comparing the magnitude of one of said reference voltages with a magnitude of an input signal;
- and
- a control circuit for determining the digital word corresponding to the input signal by repeatedly:
- comparing the magnitude of the input signal with the magnitude of a most recently generated reference voltage of said sequence,
- incrementing said counter, and
- causing said ramp generator to generate a new one of said sequence
- until the magnitude of the most recently generated reference voltage of said sequence exceeds the magnitude of said input signal.
6 more elements
A imaging system, comprising:
- a pixel array;
- a sample and hold circuit, coupled to said pixel array;
- a driver, coupled to said sample and hold circuit;
- an analog to digital (A/D) converter, coupled to said sample and hold circuit, said A/D converter comprising:
- a counter circuit for storing a digital word;
- a ramp generator for generating a sequence of reference voltages which vary in accordance with at least a first transfer function of said digital word and a second transfer function of said digital word;
- a comparator for comparing the magnitude of one of said reference voltages with a magnitude of an input signal;
- and
- a control circuit for determining the digital word corresponding to the input signal by repeatedly:
- comparing the magnitude of the input signal with the magnitude of a most recently generated reference voltage of said sequence,
- incrementing said counter, and
- causing said ramp generator to generate a new one of said sequence,
- until the magnitude of the most recently generated reference voltage of said sequence exceeds the magnitude of said input signal;
- a digital processing circuit, coupled said A/D converter;
- a storage circuit, coupled to said digital processing circuit;
- and
- a control circuit, coupled to said pixel array, sample and hold circuit, driver, A/D converter, digital processing circuit, and storage circuit.
14 more elements
A processor based system, comprising:
- a bus;
- a processor coupled to said bus;
- a imaging subsystem, coupled to said bus;
- wherein said imaging subsystem comprises:
- a pixel array;
- a sample and hold circuit, coupled to said pixel array;
- a driver, coupled to said sample and hold circuit;
- an analog to digital (A/D) converter, coupled to said sample and hold circuit, said A/D converter comprising:
- a counter circuit for storing a digital word;
- a ramp generator for generating a sequence of reference voltages which vary in accordance with at least a first transfer function of said digital word and a second transfer function of said digital word;
- a comparator for comparing the magnitude of one of said reference voltages with a magnitude of an input signal;
- and
- a first control circuit for determining the digital word corresponding to the input signal by repeatedly
- comparing the magnitude of the input signal with the magnitude of a most recently generated reference voltage of said sequence,
- incrementing said counter, and
- causing said ramp generator to generate a new one of said sequence, until the magnitude of the most recently generated reference voltage of said sequence exceeds the magnitude of said input signal;
- a digital processing circuit, coupled said A/D converter;
- a storage circuit, coupled to said digital processing circuit;
- and
- a second control circuit, coupled to said pixel array, sample and hold circuit, driver, A/D converter, digital processing circuit, and storage circuit.
17 more elements
A method for converting an analog signal to a digital word, comprising:
- measuring a magnitude of said analog signal;
- if said magnitude is not greater than a predetermined threshold, mapping said magnitude to a digital word in accordance with a first transfer function;
- and
- if said magnitude is at least equal to said predetermined threshold, mapping said magnitude to the digital word in accordance with a second transfer function.
1 more element
(canceled):
A method for operating an imaging system, comprising:
- receiving an analog pixel signal from a pixel;
- converting said analog pixel signal into a digital word, wherein said converting comprises:
- measuring a magnitude of said analog signal;
- if said magnitude is not greater than a predetermined threshold, mapping said magnitude to a digital word in accordance with a first transfer function;
- and
- if said magnitude is at least equal to said predetermined threshold, mapping said magnitude to the digital word in accordance with a second transfer function.
3 more elements
40-43. (canceled)
An imaging system comprising:
- a pixel array;
- an analog to digital (A/D) converter circuit that receives analog signals from the pixel array and converts the analog signals to digital signals with a variable level of quantization, said A/D converter circuit comprising,
- a linear A/D converter, for producing intermediate values from said analog signals, and
- a processing circuit that remaps value said intermediate values produced by said linear A/D converter using
- a mapping table.
2 more elements
(canceled):
46-47. (canceled):
Dependencies are inferred from the claim text.