Signal transmitting apparatus
An output terminal is connected to an application terminal of a power supply voltage via a pull-up resister and a backcurrent prevention diode. An output transistor is disposed between the output terminal and a ground. A capacitor is connected between the gate of the output transistor and the output terminal. A charge-discharge circuit charges or discharges the gate of the output transistor in accordance with an input signal, and thus turns on or off the output transistor, so as to generate an output signal corresponding to the input signal, at the output terminal. The charge-discharge circuit set a charge current and a discharge current of the gate of the output transistor as an adjustment target current, and changes the adjustment target current nonlinearly in accordance with the power supply voltage.
1 . A signal transmitting apparatus comprising:
an output terminal configured to be connected to an application terminal of a power supply voltage via a pull-up resister and a backcurrent prevention diode;
an output transistor disposed between the output terminal and a ground;
a capacitor connected between the gate of the output transistor and the output terminal; and
a charge-discharge circuit configured to charge or discharge the gate of the output transistor in accordance with an input signal, wherein
the charge or discharge of the gate of the output transistor causes the output transistor to be turned on or off, so that an output signal corresponding to the input signal is generated at the output terminal,
the backcurrent prevention diode has a forward direction from the application terminal of the power supply voltage to the output terminal, and
the charge-discharge circuit sets a charge current and a discharge current of the gate of the output transistor as an adjustment target current, and changes the adjustment target current nonlinearly in accordance with the power supply voltage.
2 . The signal transmitting apparatus according to claim 1 , wherein
compared with a case where the power supply voltage has a predetermined first voltage value, in a case where the power supply voltage has a predetermined second voltage value larger than the first voltage value, the charge-discharge circuit sets the adjustment target current to be larger and allows a nonlinear relationship between the power supply voltage and the adjustment target current.
3 . The signal transmitting apparatus according to claim 1 , wherein
the charge-discharge circuit maintains a value of the adjustment target current at a predetermined reference current value when the power supply voltage is a predetermined boundary voltage or less, while the charge-discharge circuit sets the value of the adjustment target current larger than the reference current value, and increases the same along with an increase in the power supply voltage, when the power supply voltage is higher than the boundary voltage.
4 . The signal transmitting apparatus according to claim 1 , wherein
the power supply voltage is within a voltage range from a predetermined minimum voltage to a predetermined maximum voltage,
the charge-discharge circuit changes the adjustment target current in accordance with the power supply voltage, so that a first value is larger than a second value,
the first value is a value obtained by dividing a slew rate of the output signal when the power supply voltage is equal to the minimum voltage by the minimum voltage, and
the second value is a value obtained by dividing the slew rate of the output signal when the power supply voltage is equal to the maximum voltage by the maximum voltage.
5 . The signal transmitting apparatus according to claim 1 , wherein
the charge-discharge circuit charges the gate of the output transistor so as to turn on the output transistor when the input signal has a first level, while the charge-discharge circuit discharges the gate of the output transistor so as to turn off the output transistor when the input signal has a second level, and
the charge-discharge circuit includes a charging circuit configured to supply the charge current to the gate of the output transistor during a period while the input signal has the first level, and a discharging circuit configured to draw the discharge current from the gate of the output transistor during a period while the input signal has the second level.
6 . The signal transmitting apparatus according to claim 1 , wherein
the drain of the output transistor is connected to the output terminal via another backcurrent prevention diode having a forward direction from the output terminal to the ground, or the drain of the output transistor is directly connected to the output terminal.