Temperature-independent current source circuit

1. A current source comprising:

a first transistor having a first terminal for receiving a first current, and a grounded second terminal;

a second transistor having a first terminal for outputting a predetermined part of a second current, a second terminal grounded through a first resistor, and a control terminal coupled to a control terminal of the first transistor;

a third transistor having a first terminal coupled to the first terminal of the second transistor, for outputting a residual part of the second current, a second terminal coupled to the control terminal of the second transistor, and a control terminal coupled to the first terminal of the first transistor;

a second resistor coupled between the control terminals of the first and second transistors and the ground; and

a current mirror having an input terminal coupled to the first terminal of the second transistor and an output terminal coupled to the first terminal of the first transistor, for mirroring the second current to the first current.

2. The current source of claim 1 , wherein the first, second, and third transistors are bipolar transistors, and the first terminals are collectors, the second terminals are emitters, and the control terminals are bases.

3. The current source of claim 2 , wherein the first and second transistors and the first resistor are operable to generate a current that is substantially proportional to the temperature at the collector of the second transistor; and

the first and third transistors and the second resistor are operable to generate a current that is substantially inversely proportional to the temperature at the collector of the third transistor.

4. The current source of claim 3 , wherein:

the third transistor functions as a buffer for a circuit-part that supplies the current that is substantially proportional to the temperature; and

the third transistor functions to supply part of the current that is inversely proportional to the temperature for a circuit-part that supplies the current that is inversely proportional to the temperature.

5. The current source of claim 2 , wherein a size ratio of the first and second transistors and the first resistor and second resistor are chosen to generate a substantially temperature-independent current at the output terminal of the current mirror.

6. The current source of claim 1 , wherein an input current and an output current of the current mirror are substantially the same.

7. A current source comprising:

a first transistor having a first terminal for receiving a first current; and

a second transistor having a control terminal coupled to a control terminal of the first transistor, a first terminal for outputting a predetermined part of a second current, and a second terminal grounded through a first resistor, wherein

the first and second transistors and the first resistor are operable to generate a current that is substantially proportional to the temperature at the first terminal of the second transistor;

a third transistor having a control terminal coupled to the first terminal of the first transistor and a second terminal coupled to a control terminal of the first transistor, the third transistor functioning as a buffer the third transistor having a first terminal coupled to the first terminal of the second transistor, for outputting a residual part of the second current; and

a current mirror having an input terminal coupled to the first terminal of the second transistor and an output terminal coupled to the first terminal of the first transistor, for mirroring the second current to the first current;

wherein the first transistor and a second resistor, coupled between the control terminal of the first transistor and the ground, are operable to generate a current that is substantially inversely proportional to the temperature at the first terminal of the third transistor; and

wherein the first current and the second current are substantially independent of the temperature.