Linear and multi-sinh transconductance circuits

• US 20010038312A1
• Filed: 12/05/2000
• Published: 11/08/2001
• Est. Priority Date: 08/31/1998
• Status: Active Grant

• Current Assignee: SMSC Analog Technology Center, Inc. (Microchip Technology Incorporated)
• Original Assignee: SMSC Analog Technology Center, Inc. (Microchip Technology Incorporated)
• Inventors: Smith, Douglas L., Zakowicz, Robert J.
• Granted Patent: US 6,489,848 B2
• Time in Patent Office: Days
• US Class Current: 330/261
• CPC Class Codes: H03F 1/3211 in differential amplifiers
• CPC Class Codes: H03F 2200/372 Noise reduction and elimination in amplifier
• CPC Class Codes: H03F 2203/45138 Two or more differential amplifiers in IC-block form are combined, e.g. measuring amplifiers
• CPC Class Codes: H03F 3/3076 with symmetrical driving of the end stage
• CPC Class Codes: H03F 3/3081 Duplicated single-ended push-pull arrangements, i.e. bridge circuits using FET's H03F3/3061

Abstract

The present invention teaches a variety of transconductance circuits formed having two or more class AB transconductor amplifiers coupled in parallel. The class AB transconductor amplifiers have non-linear voltage to current transfer functions and are each designed with an offset chosen such that the combination of the individual nonlinear transfer functions achieve a more linear transconductance circuit.

Claims

1. A transconductance circuit characterized by a voltage to current transfer function, the transconductance circuit comprising first and second class AB transconductance amplifiers coupled in parallel across differential input and output pairs, the first class AB transconductance amplifier having a positive offset and the second class AB transconductance amplifier having a negative offset, wherein the negative and positive offsets are selected to improve linearity of the voltage to current transfer function of the transconductance circuit.

2. A transconductance circuit as recited in

claim 1

, wherein a voltage to current transfer function of the first class AB transconductance amplifier is substantially a hyperbolic sine (sinh) function, and a voltage to current transfer function of the second class AB transconductance amplifier is substantially a sinh function.

3. A transconductance circuit as recited in

claim 1

wherein the negative offset and the positive offset are of substantially identical magnitude.

4. A transconductance circuit as recited in

claim 1

wherein the first class AB amplifier includes a pair of differentially coupled diamond followers and a common load resistance R_DGEN, each diamond follower having four transistors and two bias current sources, the transconductance of the first class AB amplifier being a function of transistor gain, the available bias current and the common load resistance R_DGEN.

5. A transconductance circuit as recited in

claim 4

wherein the positive offset is due to an imbalance between the sizes of the transistors of the first class AB transconductance amplifier.

6. A transconductance circuit as recited in

claim 4

wherein the positive offset is due to an imbalance between the bias current sources of the first class AB transconductance amplifier.

7. A transconductance circuit as recited in

claim 4

wherein the positive offset is due both in part to an imbalance between the sizes of the transistors of the first class AB transconductance amplifier in part to an imbalance between the bias current sources of the first class AB transconductance amplifier.

8. A transconductance circuit as recited in

claim 4

wherein the positive offset is due to the coupling of at least one resistor in series with an emitter or a base of a transistor located along the signal path.

9. A transconductance circuit as recited in

claim 8

wherein the at least one resistor is a component of the first class AB transconductance amplifier.

10. A transconductance circuit as recited in

claim 4

wherein the negative offset and the positive offset are of substantially identical magnitude.

11. A transconductance circuit as recited in

claim 4

wherein the negative offset and the positive offset are of different magnitude.

12. A transconductance circuit as recited in

claim 4

wherein the transistors are bipolar transistors.

13. A transconductance circuit as recited in

claim 4

wherein the transistors are field-effect transistors.

14. A transconductance circuit as recited in

claim 1

further including third and fourth class AB transconductance amplifiers connected in parallel with the first and second class AB transconductance amplifiers.

15. A transconductance circuit as recited in

claim 1

wherein the transconductance circuit is formed on a single integrated circuit.

16. A transconductance circuit as recited in

claim 1

wherein the first and second class AB transconductance amplifiers are of identical type.

17. A transconductance circuit as recited in

claim 1

further including at least one additional class AB transconductance amplifier coupled in parallel across differential input and output pairs, the at least one additional class AB transconductance amplifier having an offset selected to improve linearity of the voltage to current transfer function of the transconductance circuit.

18. A transconductance circuit as recited in

claim 17

wherein the offset of the at least one additional class AB transconductance amplifier is a zero offset.

19. A transconductance circuit as recited in

claim 1

wherein the first class AB amplifier includes four transistors Q1-Q4 and a current source Iq, the current source Iq providing bias current to the collector of transistor Q1 and the bases of transistors Q1 and Q2, the emitters of transistors Q1 and Q3 coupled, the emitters of transistors Q2 and Q4 coupled, and the bases of Q3 and Q4 coupled.

20. A transconductance circuit as recited in

claim 1

wherein the first class AB amplifier includes four transistors Q1-Q4 and a current source Iq, the current source Iq providing bias current to the collector of transistor Q3 and the bases of transistors Q3 and Q4, the emitters of transistors Q1 and Q3 coupled, the emitters of Q2 and Q4 coupled, and the bases of Q1 and Q2 coupled.

21. A transconductance circuit as recited in

claim 1

wherein the first class AB amplifier includes four transistors Q1-Q4 and first and second current sources Iq, the first current source providing bias current to the collector of transistor Q1 and the bases of transistors Q1 and Q2, the second current source Iq providing bias current to the collector of transistor Q3 and the bases of transistors Q3 and Q4, the emitters of transistors Q1 and Q3 coupled, and the emitters of Q2 and Q4 coupled.

22. A transconductance circuit as recited in

claim 1

wherein the first class AB amplifier includes six transistors Q1-Q6, first and second current sources, and a bias circuit, wherein the first current source provides bias current to the base of transistor Q5 and the collector of transistor Q1, the second current source provides bias current to the base of transistor Q6 and the collector of transistor Q3, bias current is provided to the bases of transistors Q1 -Q4 via transistors Q5 and Q6 and the bias circuit, the emitters of Q1 and Q3 are coupled, and the emitters of Q2 and Q4 are coupled.

23. A transconductance circuit characterized by a voltage to current transfer function, the transconductance circuit comprising:

a differential input pair;

a differential output pair;

a first class AB transconductance amplifier including a pair of differentially coupled diamond followers, each diamond follower having four transistors and two bias current sources, the transconductance of the first class AB amplifier being a function of transistor size and the available bias current, the first class AB transconductance amplifier having a positive offset; and

a second class AB transconductance amplifier including a pair of differentially coupled diamond followers, each diamond follower having four transistors and two bias current sources, the transconductance of the second class AB amplifier being a function of transistor size and the available bias current, the second class AB transconductance amplifier having a negative offset,

wherein the first and second class AB transconductance amplifiers are coupled in parallel across the differential input and output pairs, and the negative and positive offsets are selected to improve linearity of the voltage to current transfer function of the transconductance circuit.

24. A transconductance circuit as recited in

claim 23

, wherein a voltage to current transfer function of the first class AB transconductance amplifier is substantially a hyperbolic sin (sinh) function, and a voltage to current transfer function of the second class AB transconductance amplifier is substantially a sinh function.

25. A transconductance circuit as recited in

claim 23

wherein the negative offset and the positive offset are of substantially identical magnitude.

26. A transconductance circuit as recited in

claim 23

wherein the positive offset is due to an imbalance between the sizes of the transistors of the first class AB transconductance amplifier.

27. A transconductance circuit as recited in

claim 26

wherein the negative offset is due to an imbalance between the sizes of the transistors of the second class AB transconductance amplifier.

28. A transconductance circuit as recited in

claim 23

wherein the positive offset is due to an imbalance between the bias current sources of the first class AB transconductance amplifier.

29. A transconductance circuit as recited in

claim 28

wherein the negative offset is due to an imbalance between the bias current sources of the second class AB transconductance amplifier.

30. A transconductance circuit as recited in

claim 23

wherein the positive offset is due both in part to an imbalance between the gains of the transistors of the first class AB transconductance amplifier in part to an imbalance between the bias current sources of the first class AB transconductance amplifier.

31. A transconductance circuit as recited in

claim 23

further including additional circuitry coupled in parallel with the first and second class AB transconductance amplifiers, the additional circuitry suitable for providing the transconductance circuit electrical characteristics not provided by the first and second class AB transconductance amplifiers.

32. A transconductance circuit as recited in

claim 23

wherein the negative offset and the positive offset are of different magnitude.

33. A transconductance circuit as recited in

claim 23

wherein the transistors are bipolar transistors.

34. A transconductance circuit as recited in

claim 23

wherein the transistors are field-effect transistors.

35. A transconductance circuit as recited in

claim 23

, wherein the first class AB transconductance amplifier further includes a first common load resistance R_DGEN and the second class AB transconductance amplifier further includes a second common load resistance R_DGEN.

36. A transconductance circuit as recited in

claim 23

wherein the positive offset is due to the coupling of at least one resistor in series with an emitter or a base of a transistor located along the signal path.

37. A transconductance circuit as recited in

claim 36

wherein the at least one resistor is a component of the first class AB transconductance amplifier.

38. An operational amplifier comprising:

an input stage characterized by a voltage to current transfer function, the input stage including a plurality of class AB transconductance amplifiers coupled in parallel, each of the plurality of class AB transconductance amplifiers having an offset, the offsets of the plurality of class AB transconductance amplifiers selected to improve the linearity of the voltage to current transfer function of the input stage; and

a second stage coupled in series with the input stage.

39. An operational amplifier as recited in

claim 38

, wherein a first of the plurality of class AB transconductance amplifiers includes a pair of differentially coupled diamond followers and a first common load resistance R_DGEN, each diamond follower having four transistors and two bias current sources, the transconductance of the first class AB amplifier being a function of transistor gain, available bias current and the first common load resistance R_DGEN.

40. An operational amplifier as recited in

claim 39

wherein a voltage to current transfer function of the first class AB transconductance amplifier is substantially a hyperbolic sin (sinh) function, and a voltage to current transfer function of the second class AB transconductance amplifier is substantially a sinh function.

41. An operational amplifier as recited in

claim 39

wherein the offset of the first class AB transconductance amplifier is due to an imbalance between the sizes of the transistors of the first class AB transconductance amplifier.

42. An operational amplifier as recited in

claim 39

wherein the offset of the first class AB transconductance amplifier is due to an imbalance between the bias current sources of the first class AB transconductance amplifier.

43. A transconductance circuit as recited in

claim 42

wherein the positive offset is due to the coupling of at least one resistor in series with an emitter or a base of a transistor located along the signal path.

44. A transconductance circuit as recited in

claim 43

wherein the at least one resistor is a component of the first class AB transconductance amplifier.

45. An operational amplifier as recited in

claim 39

wherein the transistors are bipolar transistors.

46. An operational amplifier as recited in

claim 39

wherein the transistors are field-effect transistors.

47. An operational amplifier as recited in

claim 38

wherein the operational amplifier is formed in a dual in-line integrated circuit package.

48. An operational amplifier as recited in

claim 38

wherein the second stage is an output stage.

49. An operational amplifier as recited in

claim 38

wherein the second stage is a gain stage.

50. An operational amplifier as recited in

claim 38

wherein the second stage is one of a plurality of stage s subsequent to the input stage.

51. A multiple stage circuit comprising:

a transconductance stage suitable for converting a voltage signal into a current signal, the transconductance stage having at least two parallel coupled transconductance amplifiers, inputs of the at least two parallel coupled transconductance amplifiers being directly coupled, wherein outputs of the at least two parallel coupled transconductance amplifiers are not directly coupled; and

a plurality of stages subsequent to the transconductance stage, the plurality of stages subsequent to the transconductance stage including;

a second stage responsive to a current signal, wherein an input of the second stage is coupled to an output of a first of the at least two parallel coupled transconductance amplifiers; and

a third stage responsive to a current signal, wherein an input of the third stage is coupled to an output of a second of the at least two parallel coupled transconductance amplifiers.

52. A multiple stage circuit as recited in

claim 51

wherein the first transconductance amplifier has a positive offset and the second transconductance amplifier has a negative offset, the negative and positive offsets being selected to improve linearity of the multiple stage circuit.

53. A multiple stage circuit as recited in

claim 51

wherein the first transconductance amplifier is a first class AB amplifier having a positive offset and the second transconductor amplifier is a second class AB amplifier having a negative offset, the negative and positive offsets being selected to improve linearity of the multiple stage circuit.

54. A multiple stage circuit as recited in

claim 53

wherein the negative offset and the positive offset are of substantially identical magnitude.

55. A multiple stage circuit as recited in

claim 53

wherein the first class AB amplifier includes a pair of differentially coupled diamond followers and a common load resistance R_DGEN, each diamond follower having four transistors and two bias current sources, the transconductance of the first class AB amplifier being a function of transistor gain, the available bias current and the common load resistance R_DGEN.

56. A multiple stage circuit as recited in

claim 55

wherein the positive offset is due to an imbalance between the sizes of the transistors of the first class AB transconductance amplifier.

57. A multiple stage circuit as recited in

claim 55

wherein the positive offset is due to an imbalance between the bias current sources of the first class AB transconductance amplifier.

58. A multiple stage circuit as recited in

claim 55

wherein the positive offset is due both in part to an imbalance between the sizes of the transistors of the first class AB transconductance amplifier in part to an imbalance between the bias current sources of the first class AB transconductance amplifier.

59. A multiple stage circuit as recited in

claim 55

wherein the positive offset is due to the coupling of at least one resistor in series with an emitter or a base of a transistor located along the signal path.

60. A multiple stage circuit as recited in

claim 59

wherein the at least one resistor is a component of the first class AB transconductance amplifier.

61. A multiple stage circuit as recited in

claim 55

wherein the transconductance circuit further includes third and fourth parallel coupled class AB transconductance amplifiers also coupled in parallel with the first and second class AB transconductance amplifiers.