Matsushita Electric Industrial Co., Ltd. developed a CMOS A/D converter for the digital lead channel LSI oriented to a next generation of storage that substantially exceed a conventional conversion speed of 500M samples/second. The digital lead channel LSI shown in Figure is a system LSI that extracts recorded digital and clock data from the reproducing (analog) signals on magnetic disk. The A/D converter oriented to the digital lead channel LSI is required to correspond to the wide band of analog input accompanying the high-speed operation and recording density of magnetic disk in order to implement high-speed data transfer. Thus, the A/D converter used for the conventional lead channel LSI used the parallel conversion system that is most advantageous to high-speed A/D conversion and micro fabricated the CMOS transistor building up a circuit to correspond to high-speed operation and wide band. However, with the micro fabrication of the CMOS transistor the process technique deteriorates and the effect of the offset due to dispersion in properties also causes the precision of A/D conversion to deteriorate. To deal with this situation, the offset correcting technique was used together to compensate for the offset. It is pointed out that the offset correcting technique is difficult to correspond to continuous data such as video or music data because its circuit size cannot be ignored and A/D conversion is generally interrupted during correcting operation.
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