Image sensors and driving method thereof

A driving method of an image sensor, comprising the steps of:

• applying a voltage from a variable power source to a photosensitive element of a plurality of photosensitive elements to charge electric charge the photosensitive element and holding the electric charge by turning on and off an analog switch connected to the photosensitive element;
• storing photoelectric charge generated in the photosensitive element during a storage period by applying light to said photosensitive element;
• outputting the charge of said photosensitive element to an amplifier connected to said photosensitive element;
• reading a voltage by said amplifier after the step of storing and outputting the photoelectric charge in the photosensitive element;
• holding the read signal in a signal detector;
• applying a voltage having an amplitude of at least a maximum voltage variation of the photosensitive element from the variable power source to the amplifier by turning on the analog switch again;
• comparing an output of the amplifier with the previously held signal in the signal detector;
• reading the signal output from the amplifier as a true signal at an equal point where the output of the amplifier is coincident with the previously held signal in the comparison;
• and
• determining the voltage of the variable power source before the turning off again of the analog switch as a charge voltage to be input to the photosensitive element.

A driving method of an image sensor, comprising the steps of:

• giving a predetermined voltage from a variable power source to an amplifier through an analog switch;
• holding an output of the amplifier against the voltage from the variable power source in a signal detector;
• giving a fixed voltage from the variable power source to a photosensitive element of a plurality of photosensitive elements to charge electric charge in the photosensitive element by turning on and off the analog switch;
• storing photoelectric charge in the photosensitive element during a storage period by applying light after the step of charging electric charge;
• reading the photoelectric charge stored in the photosensitive element by the amplifier;
• and
• comparing the read value with the previously held value to read the read value as a true signal.

An image sensor, comprising:

• a plurality of photosensitive elements each having a first terminal connected to a predetermined voltage;
• a plurality of analog switches each having a first terminal connected to the second terminal of the photosensitive elements, respectively;
• a plurality of amplifiers each having an input terminal connected to the second terminal of the photosensitive elements, respectively;
• a variable power source connected to a second terminal of the analog switches;
• and
• a signal detector, connected to an output terminal of the amplifiers, for holding a first signal output from the amplifiers and for comparing the first signal held with a second signal output from the amplifiers after the first signal,
• the image sensor storing photoelectric charge generated by the photosensitive elements during a storage period and reading the photoelectric charge as a variation of a voltage.