METHODS AND CIRCUITS FOR TRIODE REGION DETECTION

• US 20090267652A1
• Filed: 04/28/2008
• Published: 10/29/2009
• Est. Priority Date: 04/28/2008
• Status: Active Grant

• Current Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Santo, Hendrik, S, Dilip, Vi, Kien
• Granted Patent: US 8,378,957 B2
• Time in Patent Office: Days
• US Class Current: 327/74
• CPC Class Codes: H03K 17/18 Modifications for indicating state of switch

Abstract

The present invention relates to circuits and methods for detecting transistor operation in the triode region including a circuit for a transistor in a constant current source. The circuit comprises a detector having a first input, a second input, and an output. The first input of the detector is coupled to the source of the transistor and the second input of the detector is coupled to the set point terminal of the constant current source. The circuit also comprises a flag coupled to the detector output. The detector has parameters selected so that, when the voltage at the source of the transistor satisfies a reference condition, the output of the detector sets the flag. The reference condition is established relative to the voltage at the set point terminal of the constant current source and relative to the triode transition voltage of the transistor at a selected drain-source current.

Claims

1. A circuit for detecting operation in the triode region of a transistor in a constant current source comprising:

a detector having a first input, a second input, and an output, wherein the first input of the detector is coupled to the source of the transistor and the second input of the detector is coupled to the set point terminal of the constant current source; and

a flag coupled to the output of the detector;

the detector having parameters selected so that, when the voltage at the source of the transistor satisfies a reference condition, the output of the detector sets the flag, wherein the reference condition is established relative to the voltage at the set point terminal of the constant current source and relative to the triode transition voltage of the transistor at a selected drain-source current.

2. The circuit of claim 1, wherein the output of the detector sets the flag when the voltage at the source of the transistor is less than the voltage at the set point terminal of the constant current source plus a constant.

3. The circuit of claim 1, wherein the output of the detector sets the flag when the voltage at the source of the transistor is less than the voltage at the set point terminal of the constant current source times a constant.

4. The circuit of claim 1, wherein the selected drain-source current is the present drain-source current of the transistor.

5. The circuit of claim 1, wherein the selected drain-source current is the maximum designed-for drain-source current of the transistor.

6. A liquid crystal display comprising the circuit of claim 1.

7. A circuit for detecting operation in the triode region of a transistor in a constant current source comprising:

a detector having a first input, a second input, and an output, wherein the first input of the detector is coupled to the gate of the transistor;

a program voltage source coupled to the second input of the detector; and

a flag coupled to the output of the detector;

the detector having parameters selected so that, when the voltage at the gate of the transistor satisfies a reference condition, the output of the detector sets the flag, wherein the reference condition is established relative to the voltage at the program voltage source and relative to the triode transition voltage of the transistor at a selected drain-source current.

8. The circuit of claim 7, wherein the output of the detector sets the flag when the voltage at the gate of the transistor deviates from the voltage at the program voltage source by more than a constant.

9. The circuit of claim 7, wherein the output of the detector sets the flag when the voltage at the gate of the transistor deviates form the voltage at the program voltage source by more than the voltage at the program voltage source times a constant.

10. The circuit of claim 7, wherein the selected drain-source current is the present drain-source current of the transistor.

11. The circuit of claim 7, wherein the selected drain-source current is the maximum designed-for drain-source current of the transistor.

12. A liquid crystal display comprising the circuit of claim 7.

13. A circuit for detecting operation in the triode region of a transistor in a constant current source comprising:

a detector having a first input, a second input, and an output, wherein the first input of the detector is coupled to the gate of the transistor;

a program voltage source coupled to the second input of the detector, wherein the voltage at the program voltage source is established relative to the triode transition voltage of the transistor at a selected drain-source current; and

a flag coupled to the output of the detector;

the detector having parameters selected so that, when the voltage at the gate of the transistor satisfies a reference condition, the output of the detector sets the flag, wherein the reference condition is established relative to the voltage at the program voltage source.

14. The circuit of claim 13, wherein the output of the detector sets the flag when the voltage at the gate of the transistor deviates from the voltage at the program voltage source more than a constant.

15. The circuit of claim 13, wherein the output of the detector sets the flag when the voltage at the gate of the transistor deviates from the voltage at the program voltage source by more than the voltage at the program voltage source times a constant.

16. The circuit of claim 13, wherein the selected drain-source current is the present drain-source current of the transistor.

17. The circuit of claim 13, wherein the selected drain-source current is the maximum designed-for drain-source current of the transistor.

18. A liquid crystal display comprising the circuit of claim 13.

19. A method for detecting operation in the triode region of a transistor in a constant current source comprising:

detecting the voltage at the source of the transistor;

detecting the voltage at the set point terminal of the constant current source;

establishing a reference condition relative to the voltage at the set point terminal of the constant current source and relative to the triode transition voltage of the transistor at a selected drain-source current;

determining if the voltage at the source of the transistor satisfies the reference condition; and

setting a flag if the reference condition is satisfied.

20. The method of claim 19, further comprising determining if the voltage at the source of the transistor deviates from the voltage at the set point terminal of the constant current source by more than a constant.

21. The method of claim 19, further comprising determining if the voltage at the source of the transistor deviates from the voltage at the set point terminal of the constant current source by more than the voltage at the set point terminal of the constant current source times a constant.

22. The method of claim 19, wherein the selected drain-source current is the present drain-source current of the transistor.

23. The method of claim 19, wherein the selected drain-source current is the maximum designed-for drain-source current of the transistor.

24. A method for detecting operation in the triode region of a transistor in a constant current source comprising:

detecting the voltage at the gate of the transistor;

detecting the voltage at a program voltage source;

establishing a reference condition relative to the voltage at the program voltage source and relative to the triode transition voltage of the transistor at a selected drain-source current;

determining if the voltage at the gate of the transistor satisfies the reference condition; and

setting a flag if the reference condition is satisfied.

25. The method of claim 24, further comprising determining if the voltage at the gate of the transistor deviates from the voltage at the program voltage source by more than a constant.

26. The method of claim 24, further comprising determining if the voltage at the source of the transistor deviates from the voltage at the program voltage source by more than the voltage at the program voltage source times a constant.

27. The method of claim 24, wherein the selected drain-source current is the present drain-source current of the transistor.

28. The method of claim 24, wherein the selected drain-source current is the maximum designed-for drain-source current of the transistor.

29. A method for detecting operation in the triode region of a transistor in a constant current source comprising:

detecting the voltage at the gate of the transistor;

establishing the voltage of a program voltage source relative to the triode transition voltage of the transistor at a selected drain-source current;

detecting the voltage at the program voltage source;

establishing a reference condition relative to the voltage at the program voltage source;

determining if the voltage at the gate of the transistor satisfies the reference condition; and

setting a flag if the reference condition is satisfied.

30. The method of claim 29, further comprising determining if the voltage at the gate of the transistor deviates from the voltage at the program voltage source by more than a constant.

31. The method of claim 29, further comprising determining if the voltage at the source of the transistor deviates from the voltage at the program voltage source by more than the voltage at the program voltage source times a constant.

32. The method of claim 29, wherein the selected drain-source current is the present drain-source current of the transistor.

33. The method of claim 29, wherein the selected drain-source current is the maximum designed-for drain-source current of the transistor.