REFERENCE VOLTAGE CIRCUIT
Provided is a reference voltage circuit with improved temperature characteristics. A current based on a current flowing through a first depletion transistor whose gate and source are connected to each other is caused to flow through a third depletion transistor having the same threshold, to thereby generate a voltage between a gate and a source of the third depletion transistor. A current based on a current flowing through a second depletion transistor whose gate and source are connected to each other is caused to flow through a fourth depletion transistor having the same threshold, to thereby generate a voltage between a gate and a source of the fourth depletion transistor. A reference voltage is generated based on a difference voltage of the two voltages, to thereby obtain a reference voltage having less voltage fluctuations with respect to a temperature change.
1 . A reference voltage circuit, comprising:
a first constant voltage circuit including a first depletion transistor; and
a second constant voltage circuit including a second depletion transistor having a threshold different from a threshold of the first depletion transistor,
wherein the reference voltage circuit generates a reference voltage based on a potential difference between an output voltage of the first constant voltage circuit and an output voltage of the second constant voltage circuit.
2 . A reference voltage circuit according to claim 1 ,
wherein the first constant voltage circuit includes a third depletion transistor having the same threshold as the threshold of the first depletion transistor, for supplying a current based on a current flowing through the first depletion transistor,
wherein the second constant voltage circuit includes a fourth depletion transistor having the same threshold as the threshold of the second depletion transistor, for supplying a current based on a current flowing through the second depletion transistor, and
wherein the output voltage of the first constant voltage circuit comprises a voltage generated between a gate and a source of the third depletion transistor, and the output voltage of the second constant voltage circuit comprises a voltage generated between a gate and a source of the fourth depletion transistor.
3 . A reference voltage circuit according to claim 2 ,
wherein the first constant voltage circuit includes:
the first depletion transistor including a gate and a source which are connected to each other, and a drain connected to a first power supply terminal;
a first MOS transistor including a gate and a drain which are connected to the gate and the source of the first depletion transistor, and a source connected to a second power supply terminal;
a second MOS transistor including a gate connected to the gate of the first MOS transistor and a source connected to the second power supply terminal; and
the third depletion transistor including a drain connected to the first power supply terminal and the source connected to a drain of the second MOS transistor and an output terminal of the first constant voltage circuit, and
wherein the second constant voltage circuit includes:
the second depletion transistor including a gate and a source which are connected to each other, and a drain connected to the first power supply terminal;
a third MOS transistor including a gate and a drain which are connected to the gate and the source of the second depletion transistor, and a source connected to the second power supply terminal;
a fourth MOS transistor including a gate connected to the gate of the third MOS transistor and a source connected to the second power supply terminal; and
the fourth depletion transistor including a drain connected to the first power supply terminal and the source connected to a drain of the fourth MOS transistor and an output terminal of the second constant voltage circuit.
4 . A reference voltage circuit according to claim 2 ,
wherein the first constant voltage circuit includes:
the first depletion transistor including a gate and a source which are connected to each other, and a drain connected to a first power supply terminal;
a first MOS transistor including a gate and a drain which are connected to the gate and the source of the first depletion transistor, and a source connected to a second power supply terminal;
a second MOS transistor including a gate connected to the gate of the first MOS transistor, a source connected to the second power supply terminal, and a drain connected to an output terminal of the first constant voltage circuit; and
the third depletion transistor including the gate connected to the second power supply terminal, a drain connected to the first power supply terminal, and the source connected to the drain of the second MOS transistor, and
wherein the second constant voltage circuit includes:
the second depletion transistor including a gate and a source which are connected to each other, and a drain connected to the first power supply terminal;
a third MOS transistor including a gate and a drain which are connected to the gate and the source of the second depletion transistor, and a source connected to the second power supply terminal;
a fourth MOS transistor including a gate connected to the gate of the third MOS transistor, a source connected to the second power supply terminal, and a drain connected to an output terminal of the second constant voltage circuit; and
the fourth depletion transistor including the gate connected to the second power supply terminal, a drain connected to the first power supply terminal, and the source connected to the drain of the fourth MOS transistor.
5 . A reference voltage circuit according to claim 2 ,
wherein the first constant voltage circuit includes:
the first depletion transistor including a gate and a source which are connected to an output terminal of the first constant voltage circuit, and a drain connected to a first power supply terminal; and
the third depletion transistor including the gate and a drain which are connected to the output terminal of the first constant voltage circuit, and the source connected to a second power supply terminal, the third depletion transistor operating in a non-saturation region, and
wherein the second constant voltage circuit includes:
the second depletion transistor including a gate and a source which are connected to an output terminal of the second constant voltage circuit, and a drain connected to the first power supply terminal; and
the fourth depletion transistor including the gate and a drain which are connected to the output terminal of the second constant voltage circuit, and the source connected to the second power supply terminal, the fourth depletion transistor operating in a non-saturation region.
6 . A reference voltage circuit according to claim 3 , further comprising differential amplifier means,
wherein the differential amplifier means comprises:
an operational amplifier including an inverting input terminal connected to the output terminal of the first constant voltage circuit and a non-inverting input terminal connected to the output terminal of the second constant voltage circuit;
an output circuit of the reference voltage circuit, which is provided to an output terminal of the operational amplifier; and
a feedback circuit which includes a first output terminal and a second output terminal and is provided to the output terminal of the operational amplifier,
wherein the first output terminal of the feedback circuit is connected to a gate terminal of the third depletion transistor, and
wherein the second output terminal of the feedback circuit is connected to a gate terminal of the fourth depletion transistor.
7 . A reference voltage circuit according to claim 4 , further comprising differential amplifier means,
wherein the differential amplifier means receives the output voltage of the first constant voltage circuit and the output voltage of the second constant voltage circuit as inputs, and generates the reference voltage based on the potential difference between the output voltage of the first constant voltage circuit and the output voltage of the second constant voltage circuit.
8 . A reference voltage circuit according to claim 5 , further comprising differential amplifier means,
wherein the differential amplifier means receives the output voltage of the first constant voltage circuit and the output voltage of the second constant voltage circuit as inputs, and generates the reference voltage based on the potential difference between the output voltage of the first constant voltage circuit and the output voltage of the second constant voltage circuit.