Level shifter, DC-DC converter, and level shift method

A DC-DC converter comprising:

• a first n-channel transistor and a second n-channel transistor which are cascode-coupled between a power supply and a ground;
• a coil whose one terminal is coupled between the first n-channel transistor and the second n-channel transistor;
• a capacitive element whose one terminal is coupled between the other terminal of the coil and an output terminal and whose other terminal is grounded;
• a booster circuit configured to generate a first voltage by boosting a power supply voltage;
• and
• a level shifter configured to change a potential level of a control signal that controls the first n-channel transistor, wherein the level shifter comprises:
• a first cascode portion, including a first transistor of a first conductivity type and a second transistor of a second conductivity type which are cascode-coupled to each other, configured to transmit a first input signal;
• a second cascode portion, including a third transistor of the first conductivity type and a fourth transistor of the second conductivity type which are cascode-coupled to each other, configured to transmit a second input signal which is in a complementary relation with the first input signal;
• a latch portion configured to output, as a control signal, a first output signal and a second output signal obtained by changing, based on the first voltage, potential levels of the first input signal and the second input signal;
• and
• a potential-difference suppression circuit, coupled in parallel to the first cascode portion, configured to control a potential difference between a drain and a source of each of the first transistor and the second transistor,
• wherein a drain of the first transistor is coupled to a drain of the second transistor at a first node, and the potential-difference suppression circuit includes a first protection element and a second protection element having one terminal coupled to one terminal of the first protection element at a second node which is coupled to the first node.

A level shift method comprising:

• receiving a first input signal, at a first cascode portion including a first transistor of a first conductivity type and a second transistor of a second conductivity type which are cascode-coupled to each other;
• receiving a second input signal which is in a complementary relation with the first input signal, at a second cascode portion including a third transistor of the first conductivity type and a fourth transistor of the second conductivity type which are cascode-coupled to each other;
• outputting a first output signal and a second output signal obtained by changing, based on a first voltage obtained by boosting a power supply voltage, potential levels of the first input signal and the second input signal;
• and
• controlling a potential difference between a drain and a source of each of the first transistor and the second transistor, by a potential-difference suppression circuit in which one terminal of a first protection element is coupled to a drain of the first transistor, the other terminal of the first protection element is coupled to a source of the first transistor, one terminal of a second protection element is coupled to a drain of the second transistor, the other terminal of the second protection element is coupled to a source of the second transistor, and the one terminal of the first protection element and the one terminal of the second protection element are coupled to each other, so that the potential difference does not exceed the power supply voltage.