| 摘要 |
PURPOSE:To measure exactly the minute variation portion of an input signal without requiring a high stable reference voltage by providing a high accuracy D/A converter converting a digitized input signal to an analog signal, and an arithmetic device. CONSTITUTION:An input signal is amplified by an input amplifier 3 and applied to an A/D converter 5. This A/D converter 5 samples a led-in signal in some period, converts it to a digital signal and outputs it to a high accuracy D/A converter 7 of the following stage. On the other hand, an operational amplifier 11 reads a signal of A+alpha in a sampling period T2 and simultaneously reads a signal A corresponding to a reference value from the high accuracy D/A converter 7. Subsequently, the subtraction of these two signals A+alpha-A is executed, only a minute variation portion alpha is fetched, and this alpha is amplified. In such a way, the minute variation portion of the input signal can be measured exactly without requiring a high stable reference voltage.
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