Back to results
US 7,804,537 B2Granted
Combined linear-logarithmic image sensor
AssigneeSTMicrolectronics S.A.
InventorsGraeme Storm, Jonathan Ephriam David Hurwitz
Life of this patent
Estimating the term…
Abstract
An image sensor includes an array of pixels, with each pixel including a photodiode, and a first output circuit for deriving a linear output signal by applying a reset signal to the photodiode and reading a voltage on the photodiode after an integration time. A second output circuit derives a logarithmic output signal by reading a near instantaneous illumination-dependent voltage on the photodiode that is a logarithmic function of the illumination. In the logarithmic mode, the pixels are calibrated to remove fixed pattern noise. The pixels may be operated in linear and log modes sequentially, with the linear output being selected for low light signals and the log output being selected for high light signals.
Claims16
An image sensor comprising:
- an array of pixels, each pixel comprising
- a photodiode,
- a first output circuit for deriving a linear output signal by applying a reset signal to said photodiode and reading a voltage on said photodiode after an integration time, said first output circuit comprising
- a reset switch for applying the reset voltage to said photodiode, said reset switch comprising a reset transistor including a conducting terminal connected to said photodiode, and
- a readout switch for turning on the conducting terminal of said reset transistor after expiration of the integration time, said readout switch comprising a readout transistor including a conducting terminal connected to the conducting terminal of said reset transistor and to said photodiode, and including a control terminal,
- a second output circuit for deriving a logarithmic output signal by reading a near instantaneous illumination-dependent voltage on said photodiode that is a logarithmic function of the illumination, said second output circuit comprising
- an amplifier including an output and at least one input connected to the conducting terminal of said reset transistor, to the conducting terminal of said readout transistor and to said photodiode, and
- a log select switch for connecting said amplifier to said photodiode, said log select switch comprising a log select transistor including a pair of conducting terminals connected between the output of said amplifier and the control terminal of said readout transistor, and including a control terminal to receive a log select signal, and
- said first and second output circuits sequentially providing the linear and logarithmic output signals;
- and
- an output selection circuit coupled to said array of pixels for selecting between the linear output signal and the logarithmic output signal as an output signal.
8 more elements
An image sensor comprising:
- an array of pixels, each pixel comprising
- a photodiode,
- a first output circuit connected to said photodiode for generating an output signal to be a linear output signal, said first output circuit comprising
- a reset switch for applying a reset voltage to said photodiode, said reset switch comprising a reset transistor including a conducting terminal connected to said photodiode, and
- a readout switch for turning on the conducting terminal of said reset transistor, said readout switch comprising a readout transistor including a conducting terminal connected to the conducting terminal of said reset transistor and to said photodiode, and including a control terminal,
- a second output circuit connected to said photodiode for generating the output signal to be a logarithmic output signal by reading a near instantaneous illumination-dependent voltage on said photodiode that is a logarithmic function of the illumination, said second output circuit comprising
- an amplifier including an output and at least one input connected to the conducting terminal of said reset transistor, to the conducting terminal of said readout transistor and to said photodiode, and
- a log select switch for connecting said amplifier to said photodiode, said log select switch comprising a log select transistor including a pair of conducting terminals connected between the output of said amplifier and the control terminal of said readout transistor, and including a control terminal to receive a log select signal,
- said first and second output circuits sequentially providing the linear and logarithmic output signals;
- and
- an output selection circuit coupled to said array of pixels for selecting between the linear output signal and the logarithmic output signal as the output signal.
8 more elements
A method for operating an image sensor comprising an array of pixels, each pixel comprising a photodiode, the method comprising:
- deriving a linear output signal from each pixel using a first output circuit comprising a reset switch for applying a reset voltage to the photodiode, the reset switch comprising a reset transistor including a conducting terminal connected to the photodiode, and a readout switch for turning on the conducting terminal of the reset transistor after expiration of an integration time, the readout switch comprising a readout transistor including a conducting terminal connected to the conducting terminal of the reset transistor and to the photodiode, and including a control terminal;
- deriving a logarithmic output signal from each pixel using a second output circuit by reading a near instantaneous illumination-dependent voltage on the photodiode that is a logarithmic function of the illumination, the second output circuit comprising an amplifier including an output and at least one input connected to the conducting terminal of the reset transistor, to the conducting terminal of the readout transistor and to the photodiode, and a log select switch for connecting the amplifier to the photodiode, the log select switch comprising a log select transistor including a pair of conducting terminals connected between the output of the amplifier and the control terminal of the readout transistor, and including a control terminal to receive a log select signal;
- sequentially providing the linear and logarithmic output signals;
- and
- selecting between the linear output signal and the logarithmic output signal as an output signal.
2 more elements
Dependencies are inferred from the claim text.