Patent ID: 7023178

Claim:
A voltage measuring apparatus which measures voltage between a first node and a second node of a circuit having a plurality of voltage sources, comprising: a first switch group having a first type first MOSFET with a first type conductivity and a first type second MOSFET with the first type conductivity, a first main electrode of the first type first MOSFET being connected to the first node, voltage corresponding to voltage of the first main electrode being applied to its control electrode, the first type first MOSFET being turned ON and OFF in accordance with the voltage of the control electrode, a first main electrode of the first type second MOSFET being connected to the second node, voltage corresponding to voltage of the first main electrode being applied to its control electrode, and the first type second MOSFET being turned ON and OFF in accordance with voltage of the control electrode; a capacitor being connected between a second main electrode of the first type first MOSFET and a second main electrode of the first type second MOSFET; a second switch group having a second type first MOSFET with a second type conductivity that is opposite from the first type conductivity and a second type second MOSFET with the second type conductivity, the second main electrode of the second type first MOSFET being connected to the second main electrode of the first type first MOSFET, the second type first MOSFET being turned ON and OFF in accordance with a signal inputted to its control electrode, the second main electrode of the second type second MOSFET being connected to the second main electrode of the first type second MOSFET, the second type second MOSFET being turned ON and OFF in accordance with a signal inputted to its control electrode; a third switch group having a second type third MOSFET with the second type conductivity and a second type fourth MOSFET with the second type conductivity, a second main electrode of the second type third MOSFET being connected to a control electrode of the first type first MOSFET, the second type third MOSFET being turned ON and OFF in accordance with a signal inputted to a control electrode, a second main electrode of the second type fourth MOSFET being connected to a control electrode of the first type second MOSFET, the second type fourth MOSFET being turned ON and OFF in accordance with a signal inputted to a control electrode; and a controller turning ON the first switch group in accordance with ON operation of the third switch group and turning OFF the first switch group in accordance with OFF operation of the third switch group, wherein the first main electrode of the second type first MOSFET of the second switch group and the back gate electrode thereof are connected to each other.