Highly linear variable gain amplifier

• US 20040027200A1
• Filed: 08/12/2002
• Published: 02/12/2004
• Est. Priority Date: 08/12/2002
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: Microtune (Texas), L.P. (Qualcomm, Inc.)
• Inventors: Ashby, Kirk B., Werther, Oliver I.
• Granted Patent: US 6,888,406 B2
• Time in Patent Office: Days
• US Class Current: 330/254
• CPC Class Codes: H03F 2203/45454 the CSC comprising biasing means controlled by the input signal
• CPC Class Codes: H03F 2203/45671 the LC comprising one or more diodes as level shifter
• CPC Class Codes: H03F 2203/45722 the LC comprising one or more source followers, as post buffer or driver stages, in cascade in the LC
• CPC Class Codes: H03F 3/45098 PI types H03F3/45125, H03F3/45152 take precedence
• CPC Class Codes: H03G 1/0023 in emitter-coupled or cascode amplifiers H03G1/0029 takes precedence

Abstract

Disclosed are systems and methods which provide very linear amplification of signals using a linearized transconductance circuit. A transconductance amplifier configuration is shown which provides highly linearized operation utilizing a Darlington pair feedback circuit. Also shown are gain control configurations in which current steering circuitry is adapted to operate in its most linear region.

Claims

1. A highly linear variable gain amplifier system comprising:

a fine gain selection circuit, wherein said fine gain selection circuit provides highly linear operation throughout a predetermined dynamic range; and

a coarse gain selection circuit, wherein said coarse gain selection circuit provides a coarse gain adjustment corresponding to said predetermined dynamic range.

2. The system of claim 1, wherein said fine gain selection circuit comprises a current steer circuit.

3. The system of claim 1, wherein said fine gain selection circuit comprises a plurality of current steer circuits, wherein each current steer circuit of said plurality of current steer circuits corresponds to a coarse gain stage of said coarse gain selection circuit.

4. The system of claim 1, wherein said coarse gain selection circuit comprises a plurality of selectable gain stages.

5. The system of claim 4, wherein each said gain stage of said plurality of selectable gain stages comprises a current mirror circuit.

6. The system of claim 4, wherein said coarse gain selection circuit provides binary coarse gain increments.

7. The system of claim 6, wherein said predetermined dynamic range is from 0 dB to 6 dB.

8. The system of claim 6, wherein said predetermined dynamic range is from 0 dB to 8 dB.

9. The system of claim 1, further comprising:

selection circuitry for selecting a desired level of gain provided by said coarse gain selection circuit.

10. The system of claim 9, wherein said selection circuitry comprises a current steer for selecting current of a gain stage of said coarse gain selection circuit for output.

11. The system of claim 10, wherein said fine gain selection circuit is disposed in said system between said selection circuit and said coarse gain selection circuit.

12. The system of claim 10, wherein said selection circuitry is disposed in said system between said fine gain selection circuit and said coarse gain selection circuit.

13. The system of claim 9, wherein said selection circuitry comprises a switch for disabling a gain stage of said coarse gain selection circuit.

14. The system of claim 1, further comprising:

a transconductance amplifier, wherein an output of said transconductance amplifier is provided to said coarse gain selection circuit and said fine gain selection circuit to thereby provide a variable gain amplifier configuration.

15. The system of claim 14, wherein said transconductance amplifier comprises a feedback loop providing feedback of signals between two sets of differential pair transistors, wherein said feedback loop comprises a Darlington pair of transistors.

16. A system for providing linear amplification of signals, said system comprising:

a transconductance amplifier; and

a variable gain circuit coupled to an output of said transconductance amplifier, wherein said variable gain circuit includes a fine gain control portion and a coarse gain control portion.

17. The system of claim 16, wherein said coarse gain control portion of said variable gain circuit comprises:

a plurality of current mirrors coupled to said output of said transconductance amplifier.

18. The system of claim 17, wherein said plurality of current mirrors are adapted to provide gain in predetermined increments.

19. The system of claim 18, wherein said predetermined increments correspond to a dynamic range of said fine gain control portion of said variable gain circuit.

20. The system of claim 18, wherein said predetermined increments are less than 8 dB.

21. The system of claim 18, wherein said predetermined increments are 6 dB.

22. The system of claim 17, wherein said fine gain control portion of said variable gain circuit comprises:

at least one current steer circuit.

23. The system of claim 22, wherein said fine gain control portion of said variable gain circuit comprises:

a plurality of current steer circuits.

24. The system of claim 16, wherein said transconductance amplifier includes a feedback circuit having a buffer transistor providing buffering of a base current of a feedback loop transistor.

25. The system of claim 16, wherein said variable gain circuit further includes a coarse gain selection portion.

26. The system of claim 25, wherein said coarse gain selection portion comprises a current steer circuit for switchably selecting an output of a gain stage of said coarse gain control portion.

27. The system of claim 25, wherein said coarse gain selection portion comprises a switch for enabling a gain stage of said coarse gain control portion.

28. The system of claim 16, wherein said transconductance amplifier and said variable gain circuit are disposed upon a same substrate to thereby provide an integrated circuit.

29. The system of claim 16, wherein said signals are cable television signals.

30. The system of claim 29, wherein said signals are provided said amplification by said system at a cable system head-end.

31. A system for providing linear amplification of signals, said system comprising:

a transconductance amplifier, wherein said transconductance amplifier includes a feedback circuit having a buffer transistor providing buffering with respect to a feedback loop transistor; and

a variable gain circuit coupled to an output of said transconductance amplifier, wherein said variable gain circuit includes a fine gain control portion and a coarse gain control portion.

32. The system of claim 31, wherein said buffer transistor provides buffering of a base current of said feedback loop transistor.

33. The system of claim 31, wherein said coarse gain control portion of said variable gain circuit comprises:

a plurality of current mirrors coupled to said output of said transconductance amplifier, wherein said plurality of current mirrors are adapted to provide gain in predetermined increments.

34. The system of claim 33, wherein said predetermined increments correspond to a dynamic range of said fine gain control portion of said variable gain circuit.

35. The system of claim 33, wherein said fine gain control portion of said variable gain circuit comprises:

at least one current steer circuit.

36. The system of claim 35, wherein said fine gain control portion of said variable gain circuit comprises:

a plurality of current steer circuits, wherein a current steer circuit of said plurality of current steer circuits is coupled to each current mirror of said plurality of current mirrors.

37. An amplifier providing linear amplification of signals, said amplifier comprising:

a transconductance amplifier including a feedback circuit having a buffer transistor providing buffering of a base current of a feedback loop transistor, wherein said buffer transistor is sized and biased for optimum speed of the device to minimize the delay with respect to the feedback loop.

38. The amplifier of claim 37, further comprising:

a variable gain circuit coupled to an output of said transconductance amplifier, wherein said variable gain circuit includes a fine gain control portion and a coarse gain control portion.

39. The amplifier of claim 38, wherein said coarse gain control portion of said variable gain circuit comprises a plurality of current mirrors coupled to said output of said transconductance amplifier, wherein said plurality of current mirrors are adapted to provide gain in predetermined increments correspond to a dynamic range of said fine gain control portion of said variable gain circuit.

40. The amplifier of claim 39, wherein said fine gain control portion of said variable gain circuit comprises:

a plurality of current steer circuits, wherein a current steer circuit of said plurality of current steer circuits is coupled to each current mirror of said plurality of current mirrors.

41. A method for providing highly linear variable gain amplification of a signal, said method comprising:

adapting a transconductance amplifier for linear operation;

providing coarse gain selection, wherein said coarse gain selection provides coarse gain adjustments corresponding to a predetermined increments; and

providing fine gain adjustment, wherein said fine gain adjustment provides highly linear operation throughout a predetermined dynamic range, wherein said predetermined dynamic range corresponds to said predetermined increments.

42. The method of claim 41, wherein said adapting said transconductance amplifier for linear operation comprises:

buffering a feedback transistor of said transconductance amplifier.

43. The method of claim 41, wherein said providing coarse gain selection comprises:

providing a plurality of current mirror circuits, ones of which providing different weighting with respect to said transconductance amplifier.

44. The method of claim 43, wherein said providing coarse gain selection comprises:

selecting a current for output using a current steer switch circuit coupled to a current mirror circuit of said plurality of current mirror circuits.

45. The method of claim 43, wherein said providing coarse gain selection comprises:

enabling a current mirror circuit of said plurality of current mirror circuits.