1. Field of the Invention
The present invention relates to a solid-state image sensing apparatus having two-dimensionally arrayed pixels and, more particularly, to a solid-state image sensing apparatus having a plurality of output channels and a reading method thereof.
2. Description of the Related Art
Conventionally, in an image sensing apparatus using a solid-state image sensing element, the speed of image data reading from the solid-state image sensing element must be increased as the number of pixels increases. However, the driving frequency of a solid-state image sensing apparatus cannot be raised indiscriminately because it has an upper limit (e.g., 20 to 30 MHz) based on the semiconductor manufacturing process or design rule.
There are various known techniques dealing with this restriction, i.e., techniques for reading out image signals in parallel by increasing the number of signal output lines.
According to one of the techniques, pixel signals of the same color are added on an output line, and a sum signal of a plurality of pixels are output from a plurality of output terminals (Jpn. Pat. Appln. KOKAI Publication No. 8-182005).
In another technique, a column read is employed to read out pixels corresponding to color filters. When image data are read out while shifting the pixels of the second or fourth row by one column, outputs of the same color can always be obtained from four output terminals (Jpn. Pat. Appln. KOKAI Publication No. 9-4680).
There is still another technique using a parallel output structure. Signals of specific pixels arrayed in a matrix are output from one of two horizontal signal lines (Jpn. Pat. Appln. KOKAI Publication No. 2000-12819).
Alternatively, a plurality of output circuits are arranged in correspondence with divided regions of a pixel array so that a plurality of pixels are simultaneously read out as addresses (Jpn. Pat. Appln. KOKAI Publication No. 2000-32344).
Furthermore, various proposals have been made for an image sensor having a parallel output structure (U.S. Pat. No. 6,512,546 and “8M color imager with two output registers and four outputs”).
However, the prior art described above is not always optimized for various kinds of aspects including moving image sensing, automatic exposure (AE) control, automatic white balance (AWB) control and automatic focusing (AF) control.