| 摘要 |
PURPOSE: To allow both A/D and D/A converters to operate with plural power supply voltages or a reference voltage by allowing the both converters to have inside reference voltage generators, to sense the impressed power supply voltages, and to select one of the two inside reference voltages. CONSTITUTION: When a power source is supplied, a power supply reset circuit 42 of an automatic power supply voltage sensing circuit 40 generates a 3 V/5 V reset signal. A 3 V/5 V detecting circuit 44 operates a peak reference voltage generating circuit 46 and a common mode reference voltage generating circuit 48 with 3 V. That is, a voltage reference generates a 2.0 V on-chip peak reference voltage and a 1.3 V common mode reference voltage, and as a result, an analog output range from 0.3 V to 2.3 V is obtained. When a power supply voltage VA+ is a value which is high enough for supporting the operation of the peak reference voltage 4 V, a 3 V/5 V selection signal reconstitutes the voltage reference circuit in a 5 V mode. Then, when a 4.0 V peak reference voltage and a 2.3 V common mode reference voltage are generated, an analog output range from 0.3 V to 4.3 V can be obtained.
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