| 摘要 |
PURPOSE:To prevent a significant figure from being omitted, and to obtain a high resolution in a low input area without using an expensive high resolution A/D converting element, by amplifying an input voltage by a larger amplification factor as the input voltage of an A/D converter becomes small, and decreasing the input voltage to the A/D converting element. CONSTITUTION:An A/D converting element 1 of an A/D converting circuit inputs an input voltage V2 and outputs an A/D-converted output data D. Also, a variable amplifying circuit 2 amplifies an input voltage V1 by an amplification factor determined by an output of an amplification factor deciding circuit 3 by an amplifier which can vary the amplification factor, and outputs it to the element 1. By this circuit 3, an amplification factor K of the circuit 2 is determined in accordance with the input voltage V1, and the amplification factor K is inputted as an amplification factor code together with the data D to the element 1. In this state, as the input voltage V1 becomes small, it is amplified by a large amplification factor and the input voltage V2 to the element 1 is decreased, an omission of a significant figure is prevented, and the resolution in a low input area is improved, without using an element of an expensive high resolution for the element 1.
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