Reference voltage circuit
View Patent ↗Provided is a reference voltage circuit capable of generating a temperature-independent reference voltage more stably. Each of N-type metal oxide semiconductor (NMOS) transistors ( 1 ) and ( 2 ) has a source and a back gate that are short-circuited, and hence threshold voltages (Vth 1 ) and (Vth 2 ) of the NMOS transistors ( 1 ) and ( 2 ) respectively depend only on process fluctuations in the NMOS transistors ( 1 ) and ( 2 ) and not on process fluctuations in other elements. As a result, a temperature-independent reference voltage (Vref) may be generated more stably.
1. A reference voltage circuit for generating a reference voltage, comprising:
a first power supply terminal;
a second power supply terminal;
a current supply circuit that has an input terminal to which a current is input, and a first output terminal and a second output terminal from each of which a current determined based on the current flowing through the input terminal is output;
a first resistor;
a first non-depletion mode metal oxide semiconductor (MOS) transistor of a first conductivity type,
the first MOS transistor having a gate connected to the first output terminal, a source and a back gate that are connected to the first power supply terminal, and a drain connected to the first output terminal via the first resistor,
the first MOS transistor operating in weak inversion;
a second non-depletion mode MOS transistor of the first conductivity type,
the second MOS transistor having a gate connected to a connection point between the first resistor and the first MOS transistor, a source and a back gate that are connected to the first power supply terminal, and a drain connected to the input terminal,
the second MOS transistor having an absolute value of a threshold voltage of the second MOS transistor smaller than an absolute value of a threshold voltage of the first MOS transistor,
the second MOS transistor operating in weak inversion,
wherein a value of the threshold voltage is independent of structural variations in the first resistor and wherein a difference in the threshold voltage of the first and second MOS transistors is independent of structural variations in the first resistor; and
a second resistor across which the reference voltage is generated,
the second resistor being provided between the second output terminal and the first power supply terminal.
2. A reference voltage circuit according to claim 1 , wherein the current supply circuit comprises:
a third MOS transistor of a second conductivity type,
the third MOS transistor having a gate and a drain that are connected to the input terminal, and a source and a back gate that are connected to the second power supply terminal;
a fourth MOS transistor of the second conductivity type,
the fourth MOS transistor having a gate connected to the input terminal, a source and a back gate that are connected to the second power supply terminal, and a drain connected to the first output terminal; and
a fifth MOS transistor of the second conductivity type,
the fifth MOS transistor having a gate connected to the input terminal, a source and a back gate that are connected to the second power supply terminal, and a drain connected to the second output terminal.
3. A reference voltage circuit according to claim 2 , wherein the current supply circuit further comprises a plurality of cascode circuits that are respectively provided between the drain of the third MOS transistor and the input terminal, between the drain of the fourth MOS transistor and the first output terminal, and between the drain of the fifth MOS transistor the second output terminal.
4. A reference voltage circuit according to claim 1 , wherein the current supply circuit comprises:
an amplifier that has an output terminal, a non-inverting input terminal connected to the input terminal of the current supply circuit, and an inverting input terminal connected to the first output terminal of the current supply circuit;
a third MOS transistor of a second conductivity type,
the third MOS transistor having a gate connected to the output terminal of the amplifier, a source and a back gate that are connected to the second power supply terminal, and a drain connected to the input terminal;
a fourth MOS transistor of the second conductivity type,
the fourth MOS transistor having a gate connected to the output terminal of the amplifier, a source and a back gate that are connected to the second power supply terminal, and a drain connected to the first output terminal; and
a fifth MOS transistor of the second conductivity type,
the fifth MOS transistor having a gate connected to the output terminal of the amplifier, a source and a back gate that are connected to the second power supply terminal, and a drain connected to the second output terminal.
5. A reference voltage circuit according to claim 1 ,
wherein the first MOS transistor and the second MOS transistor are formed on substrates having the same concentration, and
wherein only one of the first MOS transistor and the second MOS transistor is formed by being subjected to channel doping.
6. A reference voltage circuit according to claim 1 ,
wherein the first MOS transistor and the second MOS transistor are formed on substrates having the same concentration, and
wherein the first MOS transistor and the second MOS transistor are formed by being subjected to channel doping once, and only one of the first MOS transistor and the second MOS transistor is formed by being subsequently subjected to channel doping once more.
7. A reference voltage circuit according to claim 1 , wherein the first resistor and the second resistor are formed of the same kind of material.
8. A reference voltage circuit according to claim 7 , wherein the material comprises polycrystalline silicon.
9. A reference voltage circuit according to claim 1 , wherein each of the first resistor and the second resistor comprises a MOS transistor that operates in a linear region.
10. A reference voltage circuit according to claim 1 ,
wherein each of the first resistor and the second resistor comprises a plurality of connected resistors, and
wherein each connection between the plurality of resistors is arranged such that the each of the first and second resistors has a variable resistance.
11. A reference voltage circuit according to claim 1 ,
wherein each of the first resistor and the second resistor comprises a plurality of interconnected resistors and fuses, and
wherein selected connections between the plurality of resistors includes a disconnected fuse such that the each of the first and second resistors has a variable resistance.
12. A reference voltage circuit according to claim 1 , further comprising a start-up circuit for allowing, when a drain current of the second MOS transistor is lower than a predetermined current value, a start-up current to flow into the gate of the second MOS transistor.
13. A reference voltage circuit according to claim 1 , further comprising a cascode circuit between one of the first power supply terminal and the second power supply terminal, and a circuit comprising the current supply circuit, the first resistor, the first MOS transistor, the second MOS transistor, and the second resistor.
14. A reference voltage circuit for generating a reference voltage, comprising:
a first power supply terminal;
a second power supply terminal;
a current supply circuit that has an input terminal to which a current is input, and an output terminal from which a current determined based on the current flowing through the input terminal is output;
a first resistor;
a first non-depletion mode MOS transistor of a second conductivity type,
the first MOS transistor having a gate connected to the output terminal, a source and a back gate that are connected to the second power supply terminal, and a drain connected to the output terminal via the first resistor,
the first MOS transistor operating in weak inversion;
a second non-depletion mode MOS transistor of the second conductivity type,
the second MOS transistor having a gate connected to a connection point between the first resistor and the first MOS transistor, a source and a back gate that are connected to the second power supply terminal, and a drain connected to the input terminal,
the second MOS transistor having an absolute value of a threshold voltage of the second MOS transistor smaller than an absolute value of a threshold voltage of the first MOS transistor,
the second MOS transistor operating in weak inversion,
wherein a value of the threshold voltage is independent of structural variations in the first resistor and wherein a difference in the threshold voltage of the first and second MOS transistors is independent of structural variations in the first resistor;
a third MOS transistor of the second conductivity type,
the third MOS transistor having a gate connected to the output terminal, and a source and a back gate that are connected to the second power supply terminal; and
a second resistor across which the reference voltage is generated,
the second resistor being provided between a drain of the third MOS transistor and the first power supply terminal.