Constant current source circuit
A current source includes a first MOS transistor of a first channel type including a drain connected to an output terminal, and a source directly connected to a first power supply, a second MOS transistor of the first channel type including a drain connected to a gate, the gate of the second MOS transistor being connected to the gate of the first transistor, and a source directly connected to the first power supply, a third MOS transistor of a second channel type opposite the first channel type including a drain connected to the drain of the second MOS transistor, a fourth MOS transistor of the second channel type including a drain connected to the source of the third MOS transistor, a gate connected to a first bias voltage, and a source directly connected to second power supply voltage, and a control voltage generator that detects an output voltage on the output terminal and provides a shifted version of the output voltage to the gate of the third MOS transistor.
1. A current source comprising:
a first MOS transistor of a first channel type including:
a drain connected to an output terminal; and
a source directly connected to a first power supply voltage;
a second MOS transistor of the first channel type including:
a drain connected to a gate, the gate of the second MOS transistor being connected to the gate of the first MOS transistor; and
a source directly connected to the first power supply voltage;
a third MOS transistor of a second channel type opposite the first channel type including:
a drain connected to the drain of the second MOS transistor;
a fourth MOS transistor of the second channel type including:
a drain connected to the source of the third MOS transistor;
a gate connected to a first bias voltage; and
a source directly connected to a second power supply voltage; and
a control voltage generator that detects an output voltage on the output terminal and provides a shifted version of the output voltage to the gate of the third MOS transistor.
2. The current source as claimed in claim 1 , wherein the drain of the first MOS transistor is connected to the output terminal through a fifth MOS transistor of the first channel type including:
a drain connected to the output terminal;
a gate connected to a second bias voltage; and
a source directly connected to the drain of the first MOS transistor.
3. The current source as claimed in claim 1 , further comprising:
a fifth MOS transistor of the second channel type, including:
a drain connected to the drain of the third MOS transistor;
a gate connected to a second bias voltage; and
a source connected to the source of the third MOS transistor.
4. The current source as claimed in claim 1 , wherein the control voltage generator comprises:
a fifth MOS transistor of the second channel type including:
a gate connected to the first bias voltage; and
a source directly connected to the second power supply voltage;
a sixth MOS transistor of the first channel type including:
a drain connected to the drain of the fifth MOS transistor;
a gate connected to the output terminal; and
a source connected to the gate of the third MOS transistor; and
a seventh MOS transistor of the first channel type including:
a drain connected to the gate of the third MOS transistor;
a gate connected to the gate of the first MOS transistor; and
a source directly connected to the first power supply voltage.
5. The current source as claimed in claim 4 , wherein the source of the sixth MOS transistor is connected to the gate of the third MOS transistor through a first resistor.
6. The current source as claimed in claim 5 , wherein the drain of the seventh MOS transistor is connected to the gate of the third MOS transistor through a second resistor.
7. The current source as claimed in claim 1 , further comprising:
a fifth MOS transistor of the first channel type including:
a drain connected to the drain of the first MOS transistor;
a gate connected to a second bias voltage; and
a source directly connected to the first power supply voltage.
8. A current source comprising:
a first MOS transistor of a first channel type including:
a drain connected to an output terminal; and
a source directly connected to a first power supply voltage;
a second MOS transistor of the first channel type including:
a drain connected to a gate, the gate of the second MOS transistor being connected to the gate of the first MOS transistor; and
a source directly connected to the first power supply voltage;
a third MOS transistor of a second channel type opposite the first channel type including:
a drain connected to the drain of the second MOS transistor; and
a control voltage generator that detects an output voltage on the output terminal and provides a shifted version of the output voltage to the gate of the third MOS transistor,
wherein the drain of the first MOS transistor is connected to the output terminal through a fourth MOS transistor of the first channel type including:
a drain connected to the output terminal;
a gate connected to a bias voltage; and
a source directly connected to the drain of the first MOS transistor.
9. A current source comprising:
a first MOS transistor of a first channel type including:
a drain connected to an output terminal; and
a source directly connected to a first power supply voltage;
a second MOS transistor of the first channel type including:
a drain connected to a gate, the gate of the second MOS transistor being connected to the gate of the first MOS transistor; and
a source directly connected to the first power supply voltage;
a third MOS transistor of a second channel type opposite the first channel type including:
a drain connected to the drain of the second MOS transistor; and
a source directly connected to a second power supply voltage;
a fourth MOS transistor of the second channel type including:
a drain connected to the source of the third MOS transistor;
a gate connected to a first bias voltage; and
a source connected to the source of the third MOS transistor; and
a control voltage generator that detects an output voltage on the output terminal and provides a shifted version of the output voltage to the gate of the third MOS transistor.