A/D converter and readout circuit

An A/D converter for an image sensor, comprising:

• a gain stage having an output and an input for receiving a signal from the image sensor, the gain stage performing multiple-times sampling of a first signal from a pixel of the image sensor and integration of sampled values in a first period and performing multiple-times sampling of a second signal from the pixel and integration of sampled values in a second period with reversed polarity relative to the integration of the first signal, the first signal containing a component associated with noise, the second signal containing a photo-induced signal component and the component associated with noise, and the gain stage including a first capacitor for the sampling, a second capacitor for the integration, and an operational amplifier circuit for performing sampling of a signal in the first capacitor and integration of the sampled signal by use of the second capacitor;
• an A/D converter circuit providing a digital signal, the digital signal having one of first and second values in accordance with a signal from the output of the gain stage;
• a circuit providing a signal, the signal representing the number of times the first value appears;
• a logic circuit generating a control signal in response to the digital signal;
• and
• a D/A converter circuit providing a predetermined voltage signal to the gain stage in the first period while providing a voltage signal to the gain stage in the second period, the voltage signal corresponding to the control signal.