| 摘要 |
<p>An A/D converter includes a D/A converter (2) which generates a reference voltage (ref) ; a comparator (1) which compares a sampled analog input voltage with the reference voltage; and a sequential comparator control circuit (3) which repeats comparison steps comprising inputting a digital value (D7...D0) into the D/A converter in accordance with the result of the determination by the comparator so as to obtain the result of the conversion. The sequential comparator control circuit inputs an initial digital value to the D/A converter so that a reference voltage larger than one half (1/2) of a maximum allowable value of the analog input is supplied to the comparator at the time the A/D conversion commences. The sequential comparator control circuit holds or changes the content of the digital value input to the D/A converter at each comparison step in accordance with the result of the comparison. The comparison step is commenced with any bit except the most significant bit. At this time, when the analog input voltage is determined to be larger than the reference voltage, the most significant bit(D7) of the initial digital value is fixed (not changed) until the A/D conversion is finished, regardless of the result of the determination by the comparator.</p> |
