| 摘要 |
PURPOSE:To obtain a D/A converter capable of formation of IC by providing a reference voltage generating part consisting of two capacitors, an operational amplifier and plural analog switches and a voltage adding part. CONSTITUTION:A capacity ratio Ca/Cb is set at 1/2 between capacitors C3 and C5 of a reference voltage generating part, and the capacities Cc and Cd of capacitors C13 and C14 of a voltage adding part are set equal to each other. Switches SW1 and SW2 are closed and the reference voltage Vref of the C3 is applied. The SW2 is kept as it is with an SW6 closed. The electric charge of the C3 is transferred to the C5 through an operational amplifier 4. The output voltage VOP of the amplifier 4 goes to -Vref/2. Then only the SW9 is closed after closing SW7 and 8, and the electric charge of the C5 is discharged. Then the electric charge is transferred to the C5 after closing again the SW2 and 6. Thus the voltage VOP goes to -Vref/4. This action is repeated until the weighting is secured with VOP=-Vref/8. When both SW2 and 6 are closed, an SW11 or 16 is closed according to the digital output after an SW10 is closed. Thus an analog output is obtained from an operational amplifier 12.
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