Abstract: According to an embodiment, a semiconductor device includes a radio-frequency amplifier circuit, a first switch, a second switch, and a third switch. The first switch is coupled between a first node and an input end of the radio-frequency amplifier circuit. The second switch is coupled between the first node and an output end of the radio-frequency amplifier circuit. The third switch is coupled between the first node and a reference potential node. A control end of the third switch is coupled to one of the first node and the reference potential node.

Abstract: A circuit is formed on an SOI. The bias generator is connected to the gates of first and second transistors. In the bias generator, a first variable current source is connected to the power supply circuit via a power supply node. A third transistor is connected between the first variable current source and a ground-voltage source. A gate thereof is connected to the gate of the first transistor. A first operational amplifier controls a gate voltage of the third transistor so that a voltage at a second node between the first variable current source and the third transistor becomes almost equal to a reference-voltage. A first characteristics changer is connected to the gate of the third transistor or a second node, to change at least one loop gain characteristics and phase characteristics of a loop from the first operational amplifier, through the third transistor, to the first variable current source.

Abstract: A circuit is formed on an SOI. The bias generator is connected to the gates of first and second transistors. In the bias generator, a first variable current source is connected to the power supply circuit via a power supply node. A third transistor is connected between the first variable current source and a ground-voltage source. A gate thereof is connected to the gate of the first transistor. A first operational amplifier controls a gate voltage of the third transistor so that a voltage at a second node between the first variable current source and the third transistor becomes almost equal to a reference-voltage. A first characteristics changer is connected to the gate of the third transistor or a second node, to change at least one loop gain characteristics and phase characteristics of a loop from the first operational amplifier, through the third transistor, to the first variable current source.

Abstract: A voltage switching circuit of an example includes a switching element that switches an electrical connection between a first terminal and a second terminal, a first control circuit that controls the switch element, a regulator circuit that generates a first internal voltage and supply the first control circuit with the first internal voltage, a voltage selection circuit that selects one of a first voltage from the first terminal and a second voltage from the second terminal and supply the regulator circuit with the selected one of the first voltage and the second voltage, a second control circuit that controls the voltage selection circuit, and a voltage generation circuit that generates a second internal voltage using at least one of the first voltage and the second voltage, the second internal voltage is supplied to the voltage selection circuit and the second control circuit.

Abstract: A power switch circuit includes an oscillation circuit that generates a clock signal based on a supplied first voltage. A boosting circuit receiving the clock signal and boosting the first voltage based on the clock signal to output a boosted first voltage as a second voltage is provided. A detection circuit that detects a difference in voltage levels between an input voltage and the first voltage and outputs a voltage selection signal based on the detected difference is provided. A voltage selection circuit that selects one of the first voltage and the second voltage based on the voltage selection signal and outputs the selected voltage is provided. A switching element switching according to a control voltage based on an enable signal and the selected voltage is also provided.

Abstract: A power switch circuit includes an oscillation circuit that generates a clock signal based on a supplied first voltage. A boosting circuit receiving the clock signal and boosting the first voltage based on the clock signal to output a boosted first voltage as a second voltage is provided. A detection circuit that detects a difference in voltage levels between an input voltage and the first voltage and outputs a voltage selection signal based on the detected difference is provided. A voltage selection circuit that selects one of the first voltage and the second voltage based on the voltage selection signal and outputs the selected voltage is provided. A switching element switching according to a control voltage based on an enable signal and the selected voltage is also provided.

Abstract: A voltage switching circuit of an example includes a switching element that switches an electrical connection between a first terminal and a second terminal, a first control circuit that controls the switch element, a regulator circuit that generates a first internal voltage and supply the first control circuit with the first internal voltage, a voltage selection circuit that selects one of a first voltage from the first terminal and a second voltage from the second terminal and supply the regulator circuit with the selected one of the first voltage and the second voltage, a second control circuit that controls the voltage selection circuit, and a voltage generation circuit that generates a second internal voltage using at least one of the first voltage and the second voltage, the second internal voltage is supplied to the voltage selection circuit and the second control circuit.

Abstract: In an embodiment, a voltage conversion circuit includes a first voltage conversion unit stepping up or stepping down an input DC voltage and a second voltage conversion unit stepping up or stepping down an input DC voltage. A switcher is configured to switch between using both the first and second conversion units or just one of the first and second conversion units. The switcher can optionally be controlled according to an input voltage level such that both the first and second voltage conversion units can be used for a voltage step-up or voltage step-down operation or just one of the first and second voltage conversion units can be used.

Abstract: According to one embodiment, an overcurrent protection circuit for controlling an output transistor connected between a power source and an output terminal is provided. The overcurrent protection circuit has an overcurrent limiting circuit, a current-voltage control circuit, and a first control circuit. The current-voltage control circuit configured to control a gate voltage of the output transistor so that an output current is proportional to an output voltage of the output terminal Tout. The first control circuit is configured to allow the current-voltage control circuit to control the output transistor so that the output current is proportional to the output voltage when the output voltage is equal to or lower than a predetermined threshold voltage. The first control circuit is configured to allow the current-voltage control circuit to stop controlling the output transistor when the output voltage exceeds the threshold voltage.

Abstract: In an embodiment, a voltage conversion circuit includes a first voltage conversion unit stepping up or stepping down an input DC voltage and a second voltage conversion unit stepping up or stepping down an input DC voltage. A switcher is configured to switch between using both the first and second conversion units or just one of the first and second conversion units. The switcher can optionally be controlled according to an input voltage level such that both the first and second voltage conversion units can be used for a voltage step-up or voltage step-down operation or just one of the first and second voltage conversion units can be used.

Abstract: According to one embodiment, an overcurrent protection circuit for controlling an output transistor connected between a power source and an output terminal is provided. The overcurrent protection circuit has an overcurrent limiting circuit, a current-voltage control circuit, and a first control circuit. The current-voltage control circuit configured to control a gate voltage of the output transistor so that an output current is proportional to an output voltage of the output terminal Tout. The first control circuit is configured to allow the current-voltage control circuit to control the output transistor so that the output current is proportional to the output voltage when the output voltage is equal to or lower than a predetermined threshold voltage. The first control circuit is configured to allow the current-voltage control circuit to stop controlling the output transistor when the output voltage exceeds the threshold voltage.