Relaxation oscillator with improved temperature stability

1. An oscillator comprising:

a comparator;

a first current source coupled to a reference potential node;

a first resistive element coupled between the first current source and a voltage rail, a node between the first current source and the first resistive element being selectively coupled to a first input terminal of the comparator;

a second current source coupled between a second input terminal of the comparator and the voltage rail; and

a first capacitive element selectively coupled between the second input terminal of the comparator and the reference potential node.

2. The oscillator of claim 1 , further comprising a third current source coupled between the voltage rail and the first input terminal of the comparator.

3. The oscillator of claim 2 , further comprising:

a second capacitive element selectively coupled between the first input terminal of the comparator and the reference potential node; and

a second resistive element selectively coupled between the second input terminal of the comparator and the reference potential node.

4. The oscillator of claim 3 , wherein a capacitance of the first capacitive element is the same as the capacitance of the second capacitive element.

5. The oscillator of claim 3 , further comprising a first switch coupled in parallel with the second capacitive element.

6. The oscillator of claim 5 , further comprising a second switch coupled in parallel with the first capacitive element.

7. The oscillator of claim 6 , further comprising:

a third switch coupled between the first input terminal of the comparator and the second capacitive element;

a fourth switch coupled between the second input terminal of the comparator and the first capacitive element;

a fifth switch coupled between the first input terminal of the comparator and the node between the first resistive element and the first current source; and

a sixth switch coupled between the second input terminal of the comparator and the second resistive element.

8. The oscillator of claim 7 , wherein:

the comparator is configured to generate a signal by comparing voltages at the first input terminal and the second input terminal;

the first switch, the fourth switch, and the fifth switch are configured to be controlled based on the signal; and

the second switch, the third switch, and the sixth switch are configured to be controlled based on an inverse of the signal.

9. The oscillator of claim 7 , wherein:

the first switch, the fourth switch, and the fifth switch are configured to be closed during a first phase of the oscillator; and

the second switch, the third switch, and the sixth switch are configured to be closed during a second phase of the oscillator.

10. The oscillator of claim 3 , further comprising a fourth current source selectively coupled between the voltage rail and the node between the first current source and the first resistive element.

11. The oscillator of claim 10 , wherein the fourth current source is further selectively coupled between the voltage rail and the second resistive element.

12. The oscillator of claim 1 , further comprising a switch coupled in parallel with the first capacitive element.

13. The oscillator of claim 1 , wherein the first input terminal comprises a negative input terminal of the comparator and wherein the second input terminal comprises a positive input terminal of the comparator.

14. A method for generating an oscillating signal, comprising:

sinking a first current through a first resistive element coupled between a first node and a voltage rail during a first phase;

sourcing a second current to a first capacitive element coupled between a second node and a reference potential node during the first phase;

sourcing a third current to a second resistive element coupled between the second node and the reference potential node during a second phase;

sourcing a fourth current to a second capacitive element coupled between the first node and the reference potential node during the second phase; and

comparing voltages at the first node and the second node to generate the oscillating signal.

15. The method of claim 14 , further comprising:

sourcing a fifth current to the second resistive element during the first phase; and

sinking a sixth current through the first resistive element during the second phase.

16. The method of claim 14 , further comprising:

discharging the first capacitive element during the second phase; and

discharging the second capacitive element during the first phase.

17. The method of claim 14 , wherein a capacitance of the first capacitive element is the same as the capacitance of the second capacitive element.

18. An apparatus for generating an oscillating signal, comprising:

means for sinking a first current through a first resistive element coupled between a first node and a voltage rail during a first phase;

means for sourcing a second current to a first capacitive element coupled between a second node and a reference potential node during the first phase;

means for sourcing a third current to a second resistive element coupled between the second node and the reference potential node during a second phase;

means for sourcing a fourth current to a second capacitive element coupled between the first node and the reference potential node during the second phase; and

means for comparing voltages at the first node and the second node to generate the oscillating signal.

19. The apparatus of claim 18 , further comprising:

means for sourcing a fifth current to the second resistive element during the first phase; and

means for sinking a sixth current through the first resistive element during the second phase.

20. The apparatus of claim 18 , further comprising:

means for discharging the first capacitive element during the second phase; and

means for discharging the second capacitive element during the first phase.