Constant current circuit and voltage reference circuit
View Patent ↗Provided is a constant current circuit in which an enhancement N-channel transistor can operate in a weak-inversion state even at high temperatures. A constant current circuit includes a current mirror circuit, a constant-current generation block circuit, and an off-leak circuit, wherein the off-leak circuit is constituted by a first enhancement N-channel transistor having a gate and a source connected to an earth terminal and a drain connected to an output of the constant current circuit. This suppresses an increase in a gate-to-source voltage of the enhancement N-channel transistor which generates a constant current, thereby maintaining its operation in a weak-inversion state.
1. A constant current circuit comprising:
a current mirror circuit;
a constant-current generation block circuit; and
an off-leak circuit constituted by a first enhancement N-channel transistor having a gate and a source connected to an earth terminal and a drain connected to an output of the constant current circuit, and synchronizing a surplus current flowing in the constant-current generation block circuit at high temperatures.
2. The constant current circuit according to claim 1 , wherein the constant-current generation block circuit includes:
a second enhancement N-channel transistor having a gate and a drain connected to each other and a source connected to the earth terminal; and
a third enhancement N-channel transistor having a gate connected to the gate of the second enhancement N-channel transistor while a first resistor is connected between a source of the third enhancement N-channel transistor and the earth terminal.
3. A voltage reference circuit comprising:
a constant current circuit according to claims 2 ;
a sixth enhancement N-channel transistor having a gate connected to an output terminal of the constant current circuit;
a second current mirror circuit having an input terminal connected to the sixth enhancement N-channel transistor; and
a third resistor and a diode connected to an output terminal of the second current mirror circuit.
4. The constant current circuit according to claim 1 , wherein a cascode transistor is connected between the constant-current generation block circuit and the current mirror circuit.
5. The constant current circuit according to claim 4 , wherein the off-leak circuit has a drain connected between the current mirror circuit and the cascode transistor.
6. A voltage reference circuit comprising:
a constant current circuit according to claims 5 ;
a sixth enhancement N-channel transistor having a gate connected to an output terminal of the constant current circuit;
a second current mirror circuit having an input terminal connected to the sixth enhancement N-channel transistor; and
a third resistor and a diode connected to an output terminal of the second current mirror circuit.
7. A voltage reference circuit comprising:
a constant current circuit according to claim 4 ;
a sixth enhancement N-channel transistor having a gate connected to an output terminal of the constant current circuit;
a second current mirror circuit having an input terminal connected to the sixth enhancement N-channel transistor; and
a third resistor and a diode connected to an output terminal of the second current mirror circuit.
8. The constant current circuit according to claim 1 , wherein the constant-current generation block circuit includes:
a fourth enhancement N-channel transistor having a gate and a drain between which a second resistor is connected and a source connected to the earth terminal; and
a fifth enhancement N-channel transistor having a gate connected to the drain of the fourth enhancement N-channel transistor and a source connected to the earth terminal.
9. A voltage reference circuit comprising:
a constant current circuit according to claims 8 ;
a sixth enhancement N-channel transistor having a gate connected to an output terminal of the constant current circuit;
a second current mirror circuit having an input terminal connected to the sixth enhancement N-channel transistor; and
a third resistor and a diode connected to an output terminal of the second current mirror circuit.
10. A voltage reference circuit comprising:
a constant current circuit according to claims 1 ;
a sixth enhancement N-channel transistor having a gate connected to an output terminal of the constant current circuit;
a second current mirror circuit having an input terminal connected to the sixth enhancement N-channel transistor; and
a third resistor and a diode connected to an output terminal of the second current mirror circuit.