CURRENT SOURCE WITH ADJUSTABLE TEMPERATURE COEFFICIENT

Abstract

A current source with adjustable temperature coefficient is provided. The current source uses a first current generation unit and a second current generation unit to respectively produce a positive temperature coefficient current and a negative temperature coefficient current. A current addition unit is used to add the positive and negative temperature coefficient currents, and compose the positive and negative temperature coefficient currents according to a predetermined proportion. Finally, a reference current of adjustable temperature coefficient and value is output.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1A is a simplified circuit diagram of a conventional bandgap voltage reference circuit.

FIG. 1B is a circuit diagram of a conventional bandgap voltage reference circuit.

FIG. 2 is a circuit diagram of a current source with adjustable temperature coefficient according to a preferred embodiment of the present invention.

Claims

1. A current source with adjustable temperature coefficient, for generating an output current with a specific temperature coefficient, comprising: a first current generation unit, for generating a first current with a positive temperature coefficient;a second current generation unit, having a voltage replicator and a second resistor, for generating a second current with a negative temperature coefficient; anda current addition unit, coupled to the first and second current generation units, for composing the first and second currents according to a first predetermined proportion, so as to generate an output current with the specific temperature coefficient, wherein the temperature coefficient of the output current is determined by adjusting the first predetermined proportion.

2. The current source with adjustable temperature coefficient as claimed in claim 1, wherein the first current generation unit further generates a first internal voltage with a positive temperature coefficient, and the first current generation unit comprises: a first resistor, for determining the first current passing through the first resistor according to the first internal voltage.

3. The current source with adjustable temperature coefficient as claimed in claim 2, wherein the first current generation unit further comprises: a first current mirror, having a first end and a second end on a primary side and a first and a second end on a subordinate side, wherein the first ends on the primary and subordinate sides of the first current mirror are connected to a first system voltage;a second current mirror, having a first end and a second end on the primary side and a first end and a second end on the subordinate side, wherein the first end on the primary side of the second current mirror is connected to the second end on the subordinate side of the first current mirror, the first end on the subordinate side of the second current mirror is connected to the second end on the primary side of the first current mirror, the second end on the subordinate side of the second current mirror is electrically connected to the first end of the first resistor, and the second end on the primary side of the second current mirror generates a second internal voltage with a negative temperature coefficient;a first transistor, having an emitter electrically connected to the second end on the primary side of the second current mirror, and a base and a collector electrically connected to a second system voltage; anda second transistor, having an emitter electrically connected to the second end of the first resistor, and a base and a collector electrically connected to the second system voltage.

4. The current source with adjustable temperature coefficient as claimed in claim 3, wherein the voltage replicator has an input end electrically connected to the second end on the primary side of the second current mirror, for receiving the second internal voltage, and replicating the second internal voltage according to a second predetermined proportion and outputting it as a third internal voltage; and the second resistor is electrically connected to the voltage replicator, for determining the second current passing through the second resistor according to the third internal voltage output by the voltage replicator.

5. The current source with adjustable temperature coefficient as claimed in claim 4, wherein the voltage replicator comprises: an operational amplifier, having a first input end electrically connected to the second end on the primary side of the second current mirror, for receiving the second internal voltage; anda third transistor, having a gate electrically connected to an output end of the operational amplifier, a source electrically connected to a second input end of the operational amplifier and to the first end of the second resistor, wherein the source voltage of the third transistor is the third internal voltage; andthe second current generation unit further comprises: a fourth transistor, having a source electrically connected to the first system voltage, and a gate and a drain electrically connected to a drain of the third transistor.

6. The current source with adjustable temperature coefficient as claimed in claim 5, wherein the first current mirror comprises: a fifth transistor, having a source and a drain respectively being the first and second ends on the subordinate side of the first current mirror; anda sixth transistor, having a source and a drain respectively being the first and second ends on the primary side of the first current mirror, and a gate electrically connected to the gate of the fifth transistor and to the drain of the sixth transistor.

7. The current source with adjustable temperature coefficient as claimed in claim 6, wherein the current addition unit comprises: a seventh transistor, having a gate electrically connected to the gate of the fourth transistor, a source electrically connected to the first system voltage, and a drain outputting a third current; andan eighth transistor, having a gate electrically connected to the gate of the sixth transistor, a source electrically connected to the first system voltage, and a drain electrically connected to the drain of the seventh transistor, wherein the drain of the eighth transistor outputs a fourth current;wherein the sum of the third and fourth currents is the output current.

8. The current source with adjustable temperature coefficient as claimed in claim 1, wherein the current addition unit comprises: a first current generator, electrically connected to the first current generation unit, for outputting a third current according to the first current; anda second current generator, electrically connected to the second current generation unit, for outputting a fourth current according to the second current;wherein the first predetermined proportion is determined by adjusting the proportion between the first current and the third current, as well as the proportion between the second current and the fourth current; andthe current addition unit outputs the third and fourth currents in parallel as the output current.

9. A method of generating an output current with a specific temperature coefficient, comprising: making a current source pass through a first transistor and a second transistor, wherein the first transistor has a first base-emitter voltage and the second transistor has a second base-emitter voltage, and converting the difference between the first and second base-emitter voltages into a first current;applying the first base-emitter voltage via a voltage replicator to a first impedor so as to generate a second current;amplifying the first current by a first magnification as a third current;amplifying the second current by a second magnification as a fourth current; andadding the third and fourth currents to generate the output current with a specific temperature coefficient.

10. The method of generating an output current with a specific temperature coefficient as claimed in claim 9, wherein the first and second transistors have different junction areas.

11. The method of generating an output current with a specific temperature coefficient as claimed in claim 9, wherein the step of converting the difference between the first and second base-emitter voltages into the first current is bridging the first and second base-emitter voltages over a second impedor to generate the first current.

12. The method of generating an output current with a specific temperature coefficient as claimed in claim 9, wherein the first current is a positive temperature coefficient current, and the second current is a negative temperature coefficient current.

13. The method of generating an output current with a specific temperature coefficient as claimed in claim 9, wherein a specific temperature coefficient is obtained by adjusting the proportion between the first magnification and the second magnification.