| 摘要 |
PROBLEM TO BE SOLVED: To protect a P-channel FET for constituting a source follower circuit against a deterioration. SOLUTION: The P-channel FET 12 is arranged so as to receive a supply of an analog input voltage Vin between a gate terminal and a drain terminal and to supply the voltage between a source terminal and the drain terminal as an analog output voltage (output terminal voltage) Vout. In a power-down mode in which the output terminal voltage Vout is fixed to a voltage of a low potential power source GND by a circuit of a rear stage, a control signal Vcnt asserted to an 'H' level is given. An input switch 21 is opened in response to this control signal and a pull-down switch 22 is closed, and hence the gate terminal is fixed to a voltage of the low potential power source GND. The gate terminal becomes the same potential as that of a back gate terminal, and can prevent characteristic deterioration of the P-channel FET 12. In this case, a constitution in which the back gate terminal is fixed to a high potential in response to the control signal or a constitution in which the gate terminal and the back gate terminal are short circuited may be performed.
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