前言
在數(shù)據(jù)采集系統(tǒng)中，模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" 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title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換" title="模數(shù)轉(zhuǎn)換">模數(shù)轉(zhuǎn)換器是其中至關(guān)重要的環(huán)節(jié)，模數(shù)轉(zhuǎn)換器的精度以及系統(tǒng)的成本直接影響到系統(tǒng)的實(shí)用性，因此，如何提高模數(shù)轉(zhuǎn)換器的精度和降低系統(tǒng)的成本是衡量系統(tǒng)是否具有實(shí)際應(yīng)用價值的標(biāo)準(zhǔn)。
一般來說，想提高模數(shù)轉(zhuǎn)換器的精度，勢必會引起成本的增加，這就要求我們按照具體的精度要求合理的設(shè)計(jì)模數(shù)轉(zhuǎn)換器，來達(dá)到具體的要求和降低系統(tǒng)的成本。在精度要求不是很高的場合，我們經(jīng)常利用嵌入微控制器片內(nèi)的A/D轉(zhuǎn)換器來實(shí)現(xiàn)模數(shù)轉(zhuǎn)換，以此來降低系統(tǒng)的成本，但由此又產(chǎn)生了另外的問題，嵌入式模數(shù)轉(zhuǎn)換器是否具有所要求的精度，若超出測量范圍如何與測量電路進(jìn)行接口，以及如何減小微控制器的電磁干擾提高嵌入式模數(shù)轉(zhuǎn)換器的精度問題。這都要求我們采取不同的措施來提高嵌入式模數(shù)轉(zhuǎn)換器的精度。
1 精度與分辨率
ADC的精度和分辨率是兩個不同的概念。精度是指轉(zhuǎn)換器實(shí)際值與理論值之間的偏差；分辨率是指轉(zhuǎn)換器所能分辨的模擬信號的最小變化值。ADC 分辨率的高低取決于位數(shù)的多少。一般來講，分辨率越高，精度也越高，但是影響轉(zhuǎn)換器精度的因素很多，分辨率高的ADC，并不一定具有較高的精度。精度是偏移誤差、增益誤差、積分線性誤差、微分線性誤差、溫度漂移等綜合因素引起的總誤差。因量化誤差是模擬輸入量在量化取整過程中引起的，因此，分辨率直接影響量化誤差的大小，量化誤差是一種原理性誤差，只與分辨率有關(guān)，與信號的幅度，采樣速率無關(guān)，它只能減小而無法完全消除，只能使其控制在一定的范圍之內(nèi)，一般在±1／2LSB范圍內(nèi)。
1.1 偏移誤差
偏移誤差是指實(shí)際模數(shù)轉(zhuǎn)換曲線中數(shù)字0的代碼中點(diǎn)與理想轉(zhuǎn)換曲線中數(shù)字0的代碼中點(diǎn)的最大差值電壓。這一差值電壓稱作偏移電壓，一般以滿量程電壓值的百分?jǐn)?shù)表示。在一定溫度下，多數(shù)轉(zhuǎn)換器可以通過對外部電路的調(diào)整，使偏移誤差減小到接近于零，但當(dāng)溫度變化時，偏移電壓又將出現(xiàn)，這主要是由于輸入失調(diào)電壓及溫漂造成的。一般來說，溫度變化較大時，要補(bǔ)償這一誤差是很困難的。
1.2 增益誤差
增益誤差是轉(zhuǎn)換器輸出全“1”時，實(shí)際模擬輸入電壓與理想模擬輸入電壓之差。它使傳輸特性曲線繞坐標(biāo)原點(diǎn)偏離理想特性曲線一定的角度，即增益誤差表示模數(shù)轉(zhuǎn)換特性曲線的實(shí)際斜率與理想斜率的偏差，它的數(shù)值一般用滿量程的百分比來表示。
ADC的理想傳輸函數(shù)的關(guān)系式是
（1）
式中Un是沒有量化時的標(biāo)準(zhǔn)模擬電壓，由于存在增益誤差，式（1）變?yōu)?br />
（2）
式中的K為增益誤差因子。當(dāng)K＝l時，沒有增益誤差。當(dāng)K＞1時，傳輸特性曲線的斜率變大，臺階變窄，在輸入模擬信號達(dá)到滿量程值之前，數(shù)字輸出就己全“l”狀態(tài)。當(dāng)K＜1時，傳輸特性曲線的斜率變小，臺階變寬，輸入模擬信號己超滿量程值時，數(shù)字輸出還未達(dá)到全“1”狀態(tài)輸出。
在一定溫度下，可通過外部電路的調(diào)整使K＝l，從而消除增益誤差。
1.3 線性誤差
線性誤差又稱積分線性誤差，是指在沒有偏移誤差和增益誤差的情況下，實(shí)際傳輸曲線與理想傳輸曲線之差。線性誤差一般不大于1／2LSB。因?yàn)榫€性誤差是由ADC特性隨輸入信號幅值變化而引起的，因此線性誤差是不能進(jìn)行補(bǔ)償?shù)模揖€性誤差的數(shù)值會隨溫度的升高而增加。
1.4 微分線性誤差
微分線性誤差是指實(shí)際代碼寬度與理想代碼寬度之間的最大偏差，以LSB為單位，微分線性誤差也常用無失碼分辨率表示。
由于時間和溫度的變化，電源可能會有一定的變化，有時可能是造成影響ADC精度的主要原因，因此在要求比較高的場合，必須保證電源的穩(wěn)定性，使其隨溫度和時間的變化量在所允許的范圍之內(nèi)，但在一般的場合，往往可以不考慮其對系統(tǒng)的影響。
2 嵌入式模數(shù)轉(zhuǎn)換器的結(jié)構(gòu)及影響轉(zhuǎn)換的原因和消除方法
所謂嵌入式模數(shù)轉(zhuǎn)換器是指將模擬多路開關(guān)、采樣保持、A/D轉(zhuǎn)換、微控制器集成在一個芯片上，經(jīng)常采用逐次比較型進(jìn)行A/D轉(zhuǎn)換，模擬輸入信號一般為非負(fù)單極性，且輸入信號的電壓范圍為0～AVREF，A/D轉(zhuǎn)換器具有獨(dú)立的模擬電源與參考電壓。
在實(shí)際應(yīng)用中，由于輸入信號的輸出電阻不同，如果輸出電阻過大，會引起實(shí)際測量的電壓分壓過小，因而引起測量值較實(shí)際值偏小；或者由于輸入信號為雙極性模擬信號，不能直接與嵌入式微控制器相連，必須采取特殊措施，使雙極性模擬信號轉(zhuǎn)換為可以直接測量的非負(fù)單極性信號；還有如果輸入信號幅值過大，以至于超過參考電壓，也必須引入將壓環(huán)節(jié)，使輸入電壓低于參考電壓，等等，下面對以上影響逐一進(jìn)行分析。
2.1 模擬輸入信號阻抗對采樣的影響
采樣過程是采樣電容充電，跟蹤輸入模擬信號電壓的過程，由于采樣電路存在模擬多路開關(guān)阻抗、采樣開關(guān)阻抗和輸入信號源阻抗，因此，其轉(zhuǎn)換時間受模擬多路開關(guān)阻抗、采樣開關(guān)阻抗與輸入信號源阻抗的影響，模擬多路開關(guān)與輸入信號源的阻抗越大則其轉(zhuǎn)換時間越長。
逐次比較型A/D的輸入端等效電路如下圖所示：
圖1 逐次比較型A/D的輸入端等效電路
其中，RIN為輸入模擬信號內(nèi)阻，VS為輸入模擬電壓信號，RSH為模擬多路開關(guān)與采樣開關(guān)的等效電阻，VSH為采樣電容的充電電壓，由等效電路可以看出，輸入模擬信號內(nèi)阻越大，則采樣電容充電時間越長，因此，對于采樣頻率要求越高的場合，要求模擬輸入信號內(nèi)阻必須越小，在應(yīng)用時必須首先估算在規(guī)定的采樣頻率下，對模擬輸入信號內(nèi)阻的要求。由電路理論可以求得RIN所允許的最大值（假設(shè)采樣時間為T）：
如果信號源內(nèi)阻達(dá)不到要求，則需使用一個輸出阻抗很小的緩沖器，例如可以使用電壓跟隨器，使信號源的輸出阻抗達(dá)到A/D轉(zhuǎn)換器所要求的輸入阻抗的范圍之內(nèi)。
2.2 模擬信號極性及幅值的變換
在數(shù)據(jù)采集系統(tǒng)中，采集的模擬信號并非都是非負(fù)單極性信號，經(jīng)常是雙極性信號，因此在使用嵌入式A/D轉(zhuǎn)換器的時候，需要對模擬輸入信號進(jìn)行極性轉(zhuǎn)換，我們可以采用運(yùn)算放大器組成的線性網(wǎng)絡(luò)來對其極性及幅值進(jìn)行轉(zhuǎn)換，但須注意的是在引入線性網(wǎng)絡(luò)的同時，又引入了一定量的非線性誤差，其線性網(wǎng)絡(luò)原理圖可用下圖表示：
圖2 線性網(wǎng)絡(luò)原理圖
只要改變電阻R1、R2、R3的大小以及它們的比例關(guān)系便可調(diào)整模擬輸入信號的大小使其符合測量要求。
下面介紹一種常用的芯片AT90S8535關(guān)于其A／D轉(zhuǎn)換器使用時應(yīng)該注意的情況。
AT90S8535是ATMEL公司生產(chǎn)的一款基于AVR RISC結(jié)構(gòu)的，低功耗的8位單片機(jī)，其內(nèi)部集成有模數(shù)轉(zhuǎn)換器，模數(shù)轉(zhuǎn)換器具有以下特點(diǎn)：
10位分辨率；
±2LSB精確度；
0.5LSB集成線性度；
65～260μs轉(zhuǎn)換時間；
8通道；
自由運(yùn)行模式和單次轉(zhuǎn)換模式；
ADC轉(zhuǎn)換結(jié)束中斷；
休眠模式噪聲消除。
AT90S8535具有10位分辨率的逐次逼近型A／D轉(zhuǎn)換器。ADC與一個8通道模擬多路器相連，這樣就允許A口作為ADC的輸入引腳。ADC包含一個采樣保持放大器，ADC框圖如下所示：
圖3ADC框圖
ADC可以工作于兩種模式——單次轉(zhuǎn)換和自由運(yùn)行。在單次轉(zhuǎn)換模式下，用戶必須啟動每一次轉(zhuǎn)換，而在自由運(yùn)行模式下，ADC會連續(xù)采樣并更新ADC數(shù)據(jù)寄存器。ADCSR的ADFR位用于選擇A／D轉(zhuǎn)換器的運(yùn)行模式。
由于模擬通道的轉(zhuǎn)換總是要延遲到轉(zhuǎn)換的結(jié)束，因此，自由運(yùn)行模式可以用來掃描多個通道，而不中斷轉(zhuǎn)換器。一般來說，ADC轉(zhuǎn)換結(jié)束中斷用于修改通道，但需考慮一下因素；結(jié)果一旦準(zhǔn)備好，中斷就被觸發(fā)，在自由運(yùn)行模式，中斷一被觸發(fā)，則下一次轉(zhuǎn)換馬上開始。如果中斷觸發(fā)過后，模擬通道改變，而下一次轉(zhuǎn)換已經(jīng)開始，則仍舊使用以前設(shè)置。
3.1 ADC噪聲消除技術(shù)
AT90S8535的內(nèi)外部數(shù)字電路會產(chǎn)生電磁干擾，從而影響模擬測量精度。如果要求測量精度較高，則應(yīng)采取如下技術(shù)以減少噪聲：
1) AT90S8535的模擬部分及其他的模擬器件在PCB板上要有獨(dú)立的地線層。模擬地與數(shù)字地單點(diǎn)相連；
2) 使模擬信號通路盡量短。使模擬走線在模擬地上通過，并盡量保持遠(yuǎn)離高速數(shù)字通路的走線；
3) AVCC要通過一個RC網(wǎng)絡(luò)連接到VCC；
4) 利用ADC的噪聲消除功能減小來自CPU的噪聲；
5) 如果A口的一些引腳作數(shù)字輸出口，則在ADC轉(zhuǎn)換過程中，這些口不要改變其狀態(tài)。
3.2 ADC噪聲消除功能的實(shí)現(xiàn)
ADC可以在CPU空閑模式下進(jìn)行轉(zhuǎn)換，這一特征使得可以抑制來自CPU的噪聲。為了實(shí)現(xiàn)這一特性，需采取一下措施：
A) 必須選擇單次轉(zhuǎn)換模式，ADC的轉(zhuǎn)換結(jié)束中斷必須使能；
ADEN=1;ADSC=0;ADFR=0;ADIE=1;
B) 進(jìn)入空閑模式。一旦CPU停止，則ADC將開始轉(zhuǎn)換；
C) 如果在ADC轉(zhuǎn)換結(jié)束之前沒有發(fā)生其它中斷，則ADC中斷將喚醒MCU并執(zhí)行ADC轉(zhuǎn)換結(jié)束中斷。
微控制器片內(nèi)A/D轉(zhuǎn)換器由于自身的結(jié)構(gòu)、性能特點(diǎn)，在許多應(yīng)用中會遇到與獨(dú)立A/D轉(zhuǎn)換器不同的問題，但大多數(shù)嵌入微控制器的A/D器都具有像AT90S8535相似的結(jié)構(gòu)和特點(diǎn)，采取的消噪技術(shù)和方法也大致相同，我們需根據(jù)具體情況具體分析需采取嵌入A/D還是獨(dú)立A/D，并根據(jù)具體需求采取必要的措施來提高A/D轉(zhuǎn)換器的精度。