Automatic modulation system

• US 4,237,555 A
• Filed: 09/14/1979
• Issued: 12/02/1980
• Est. Priority Date: 09/14/1979
• Status: Expired due to Term

• Current Assignee: ITT Corporation (ITT, Inc.)
• Original Assignee: International Telephone and Telegraph Corporation
• Inventors: Dishal, Milton
• Primary Examiner(s): Bookbinder, Marc E.
• Application Number:
  US06/075,626
• Time in Patent Office: 445 Days
• Field of Search: 455/108, 455/116, 455/126, 455/129, 332/37 R, 332/37 D, 332/38
• US Class Current: 455/108
• CPC Class Codes: G01S 1/0428 Signal details
• CPC Class Codes: H03C 1/06 Modifications of modulator to reduce distortion, e.g. by feedback, and clearly applicable to more than one type of modulator
• CPC Class Codes: H03F 1/34 Negative-feedback-circuit arrangements with or without positive feedback H03F1/02 - H03F1/30, H03F1/38 - H03F1/50, H03F3/50 take precedence ; for rejection of common mode signals H03F3/45479
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H03G 3/3047 for intermittent signals, e.g. burst signals
• CPC Class Codes: H04B 2001/0433 with linearisation using feedback

Abstract

The feedback controlled modulation system comprises an extended range, gain controlled detector system disposed in a first feedback loop coupled between the output and input of an amplifier having a non-linear input-output characteristic; a gain controlled reference signal source coupled to the output of the detector system to provide a difference signal in the first feedback loop; and a gain controlling pulse generator coupled to the source and the detector system to simultaneously control the gain of the source and the gain of the detector system to control the shape of the difference signal so as to linearize the non-linear characteristic without loss of loop stability and without causing amplitude distortion in the first feedback loop. In addition, the modulation system includes an exciter which provides controllable amplitude, rectangular pulses; an amplitude modulator disposed in the first feedback loop coupled to the input of the amplifier and output of the exciter responsive to the rectangular pulses and an amplified version of the shaped difference signal; a second feedback loop coupled between the output and input of the exciter to provide an extremely flat top for each of the rectangular pulses; and a third feedback loop coupled to the first and second feedback loops responsive to a predetermined gated portion of the amplified version of the difference signal to produce a control signal for the second feedback loop to accurately control the amplitude of the flat top rectangular pulses so as to hold the amplitude of a baseline portion of the output signal of the modulator exactly at the threshold of the linearized characteristic.

Claims

1. A multistate feedback controlled modulation system for linearizing and stabilizing an amplifier having an input-output characteristic including a linear portion and at least a lower non-linear portion comprising:

an extended range, gain controlled detector system disposed in a first feedback loop coupled to the output and input of said amplifier;

a gain controlled reference signal source coupled to an output of said detector system to provide a difference signal in said first feedback loop;

a gain controlling pulse generator coupled to said source and said detector system to simultaneously control the gain of said source and the gain of said detector system to control the shape of said difference signal so as to linearize said lower non-linear portion of said characteristic without loss of loop stability and without causing amplitude distortion in said first feedback loop;

an exciter to provide controllable amplitude, rectangular pulses;

a first amplitude modulator disposed in said first feedback loop coupled to the input of said amplifier and the output of said exciter responsive to an amplified version of said difference signal and said rectangular pulses;

a second feedback loop coupled between an output and an input of said exciter to provide an extremely flat top for each of said rectangular pulses; and

a third feedback loop coupled to said first and second feedback loops responsive to a predetermined gated portion of said amplified version of said difference signal to produce a control signal for said second feedback loop to accurately control the amplitude of said flat top rectangular pulses so as to hold the amplitude of a baseline portion of the output signal of said modular exactly at the threshold of said linearized characteristic.

2. A system according to claim 1, wherein

said first feedback loop is a fast acting feedback loop.

3. A system according to claim 2, wherein

said third feedback loop is a very slow acting feedback loop.

4. A system according to claim 1, wherein

said amplifier is a Class C power amplifier.

5. A system according to claim 1, wherein

said source includes

a pulse forming network driven by pulses to provide said reference signal having a predetermined shape,

a preemphasis circuit coupled to the output of said pulse forming network, and

a gain controlled reference amplifier coupled to the output of said preemphasis circuit, and the output of said control pulse generator.

6. A system according to claim 5, wherein

said pulse forming network includes

a pulse current generator driven by said pulses,

a droop compensating circuit coupled to said current generator responsive to a compensating pulse,

a first filter network coupled to the output of said current generator,

a first linear amplifier coupled to the output of said first filter network,

a second filter network coupled to the output of said first linear amplifier,

a second linear amplifier coupled to the output of said second filter network, and

a third filter network coupled to the output of said second linear amplifier.

7. A system according to claim 6, wherein

said reference amplifier includes

at least one amplifier stage having its gain changed by said control pulse generator at a given number of said different amplitude levels of said reference signal.

8. A system according to claim 7, wherein

said given amplitude levels are minus 26 db, 32 db, 40 db and 46 db from the peak of said reference signal.

9. A system according to claim 7, wherein

said detector system includes

at least two gain controlled amplitude detectors.

10. A system according to claim 7, whrein

one of said two detectors is controlled by said controlling pulse generator to be operative during said linear portion of said characteristic and the other of said two detectors is controlled by said controlling pulse generator to be inoperative during said linear portion of said characteristic.

11. A system according to claim 10, wherein

said one of said two detectors is controlled by said controlling pulse generator to be inoperative during said lower non-linear portion of said characteristic and said other of said two detectors is controlled by said controlling pulse generator to be operative during said lower non-linear portion of said characteristic and to have its gain changed at given number of different amplitude levels.

12. A system according to claim 11, wherein

said given amplitude levels are minus 26 db, 32 db, 40 db and 46 db from the peak of said reference signal.

13. A system according to claim 11, wherein

said linear portion of said characteristic ends at and said lower non-linear portion of said characteristic starts at a predetermined level down from the peak of said reference signal, said one of said two detectors being switched to its inoperative state and said other of said two detectors being switched to its operative state at said predetermined level.

14. A system according to claim 11, wherein

said controlling pulse generator includes

a plurality of amplitude comparators equal in number to said given amplitude levels to produce a corresponding number of first gate pulses to control said reference amplifier and a corresponding number of second gate pulses to control said two detectors.

15. A system according to claim 14, wherein

said plurality of comparators number four, and each of said four comparators produce a different one of said first and second gate pulses.

16. A system according to claim 15, wherein

a first of said four comparators produces a first of said first and second gate pulses at a first predetermined level down from the peak of said reference signal, a second of said four comparators produces a second of said first and second gate pulses at a second predetermined level down from the peak of said reference signal which is lower than said first level, a third of said four comparators produces a third of said first and second gate pulses at a third predetermined level down from the peak of said reference signal which is lower than said second level and a fourth of said four comparators produces a fourth of said first and second gate pulses at a fourth predetermined level down from the peak of said reference signal which is lower than said third level.

17. A system according to claim 16, further including

a trailing edge gain switch coupled to each of said four comparators rendered operative at the peak of input pulses driving said controlling generator to provide a value for said first, second, third and fourth levels for the trailing edge of said input pulses which is different than the values for said first, second, third and fourth levels for the leading edge of said input pulses.

18. A system according to claim 14, further including

a trailing edge gain switch coupled to each of said plurality of comparators rendered operative at the peak of input pulses driving said controlling generator to provide a value for each of said given amplitude levels for the trailing edge of said input pulses which is different than the values for each of said given amplitude levels for the leading edge of said input pulses.

19. A system according to claim 14, wherein

said controlling pulse generator further includes

a first instantaneous recovery limiting amplifier coupled between said pulse forming network and certain ones of said plurality of comparators, and

a second instantaneous recovery limiting amplifier coupled between said first amplifier and the others of said plurality of comparators.

20. A system according to claim 19, wherein

said plurality of comparators number four with two of said four comparators being coupled to said first amplifier and the remaining two of said four comparators being coupled to said second amplifier.

21. A system according to claim 20, wherein

one of said two of said four comparators and one of said remaining two of said four comparators has a first comparison potential applied thereto to produce a first of said first and second gate pulses at the output of said one of said two of said four comparators at a first predetermined level down from the peak of said reference signal and a second of said first and second gate pulses at the output of said one of said remaining two of said four comparators at a second predetermined level down from the peak of said reference signal which is less than said first level, and

the other of said two of said four comparators and the other of said remaining two of said four comparators has a second comparison potential different than said first comparison potential applied thereto to produce a third of said first and second gate pulses at the output of said other of said two of said four comparators at a third predetermined level down from the peak of said reference signal which is different than and between said first and second levels and a fourth of said first and second gate pulses at the output of said other of said remaining two of said four comparators at a fourth predetermined level down from the peak of said reference signal which is less than said second level.

22. A system according to claim 21, further including

a trailing edge gain switch coupled to each of said four comparators rendered operative at the peak of input pulses driving said controlling generator to provide a value for said first and second comparison potentials for the trailing edge of said input pulses which is different than the values for said first and second comparison potentials for the leading edge of said input pulses.

23. A system according to claim 14, wherein

said one of said two detectors is coupled to the output of said amplifier by a first directional coupler coupled to the output of said amplifier, and

said other of said two detectors is coupled to the output of said amplifier by said first directional coupler, a second directional coupler coupled to said first directional coupler and an instantaneous recovery limiting RF amplifier coupled between said second directional coupler and the input of said other of said two detectors.

24. A system according to claim 23, wherein

said characteristic includes an upper non-linear portion, and

said first feedback loop includes

at least one amplifier stage coupled to said controlling pulse generator for control of the gain thereof to linearize said upper non-linear portion of said characteristic.

25. A system according to claim 1, wherein

said source includes

at least one amplifier stage having its gain changed by said controlling pulse generator at a given number of different amplitude levels of said reference signal.

26. A system according to claim 25, wherein

said given amplitude levels are minus 26 db, 32 db, 40 db and 46 db from the peak of said reference signal.

27. A system according to claim 25, wherein

said detector system includes

at least two gain controlled amplitude detectors.

28. A system according to claim 27, wherein

one of said two detectors is controlled by said controlling pulse generator to be operative during said linear portion of said characteristic and the other of said two detectors is controlled by said controlling pulse generator to be inoperative during said linear portion of said characteristic.

29. A system according to claim 28, wherein

said one of said two detectors is controlled by said controlling pulse generator to be inoperative during said lower non-linear portion of said characteristic and said other of said two detectors is controlled by said controlling pulse generator to be operative during said lower non-linear portion of said characteristic and to have its gain changed at said given number of different amplitude levels.

30. A system according to claim 29, wherein

said given amplitude levels are minus 26 db, 32 db, 40 db and 46 db from the peak of said reference signal.

31. A system according to claim 30, wherein

said linear portion of said characteristic ends at and said lower non-linear portion of said characteristic starts at a predetermined level down from the peak of said reference signal, said one of said two detectors being switched to its inoperative state and said other of said two detectors being switched to its operative state at said predetermined level.

32. A system according to claim 29, wherein

said controlling pulse generator includes

a plurality of amplitude comparators equal in number to said given amplitude levels to produce a corresponding number of first gate pulses to control said source and a corresponding number of second gate pulses to control said two detectors.

33. A system according to claim 32, wherein

said plurality of comparators number four, and each of said four comparators produce a different one of said first and second gate pulses.

34. A system according to claim 33, wherein

a first of said four comparators produces first of said first and second gate pulses at a first predetermined level from the peak of said reference signal, a second of said four comparators produces a second of said first and second gate pulses at a second predetermined level down from the peak of said reference signal which is lower than said first level, a third of said four comparators produces a third of said first and second gate pulses at a third predetermined level down from the peak of said reference signal which is less than said second level and a fourth of said four comparators produces a fourth of said first and second gate pulses at a fourth predetermined level down from the peak of said reference signal which is less than said third level.

35. A system according to claim 34, further including

a trailing edge gain switch coupled to each of said four comparators rendered operative at the peak of input pulses driving said controlling generator to provide a value for said first, second, third and fourth levels for the trailing edge of said input pulses which is different than the values for said first, second, third and fourth levels for the leading edge of said input pulses.

36. A system according to claim 32, further including

a trailing edge gain switch coupled to each of said plurality of comparators rendered operative at the peak of input pulses driving said controlling generator to provide a value for each of said given amplitude levels for the trailing edge of said input pulses which is different than the values for each of said given amplitude levels for the leading edge of said input pulses.

37. A system according to claim 32, wherein

said controlling pulse generator further includes

a first instantaneous recovery limiting amplifier coupled between said source and certain ones of said plurality of comparators, and

a second instantaneous recovery limiting amplifier coupled between said first amplifier and the others of said plurality of comparators.

38. A system according to claim 37, wherein

said plurality of comparators number four with two of said four comparators being coupled to said first amplifier and the remaining two of said four comparators being coupled to said second amplifier.

39. A system according to claim 38, wherein

one of said two of said four comparators and one of said remaining two of said four comparators has a first comparison potential applied thereto to produce a first of said first and second gate pulses at the output of said one of said two of said four comparators at a first predetermined level down from the peak of said reference signal and a second of said first and second gate pulses at the output of said one of said remaining two of said four comparators at a second predetermined level down from the peak of said reference signal which is less than said first level, and

the other of said two of said four comparators and the other of said remaining two of said four comparators has a second comparison potential different than said first comparison potential applied thereto to produce a third of said first and second gate pulses at the output of said other of said two of said four comparators at a third predetermined level down from the peak of said reference signal which is different than and between said first and second levels and a fourth of said first and second gate pulses at the output of said other of said remaining two of said four comparators at a fourth predetermined level down from the peak of said reference signal which is less than said second level.

40. A system according to claim 39, further including

a trailing edge gain switch coupled to each of said four comparators rendered operative at the peak of input pulses driving said controlling generator to provide a value for said first and second comparison potentials for the trailing edge of said input pulses which is different than the values for said first and second comparison potentials for the leading edge of said input pulses.

41. A system according to claim 32, wherein

said one of said two detectors is coupled to the output of said amplifier by a first directional coupler coupled to the output of said amplifier, and

said other of said two detectors is coupled to the output of said amplifier by said first directional coupler, a second directional coupler coupled to said first directional coupler and an instantaneous recovery limiting RF amplifier coupled between said second directional coupler and the input of said other of said two detectors.

42. A system according to claim 41, wherein

said characteristic includes an upper non-linear portion, and

said first feedback loop includes

at least one amplifier stage coupled to said controlling pulse generator for control of the gain thereof to linearize said upper non-linear portion of said characteristic.

43. A system according to claim 1, wherein

said detector system includes

at least two gain controlled amplitude detectors.

44. A system according to claim 43, wherein

one of said two detectors is controlled by said controlling pulse generator to be operative during said linear portion of said characteristic and the other of said two detectors is controlled by said controlling pulse generator to be inoperative during said linear portion of said characteristic.

45. A system according to claim 44, wherein

said one of said two detectors is controlled by said controlling pulse generator to be inoperative during said lower non-linear portion of said characteristic and said other of said two detectors is controlled by said controlling pulse generator to be operative during said lower non-linear portion of said characteristic and to have its gain changed at a given number of different amplitude levels.

46. A system according to claim 45, wherein

said linear portion of said characteristic ends at and said lower non-linear portion of said characteristic starts at a predetermined level down from the peak of said reference signal, said one of said two detectors being switched to its inoperative state and said other of said two detectors being switched to its operative state at said predetermined level.

47. A system according to claim 45, wherein

said controlling pulse generator includes

a plurality of amplitude comparators equal in number to said given amplitude levels to produce a corresponding number of first gate pulses to control said reference amplifier and a corresponding number of second gate pulses to control said two detectors.

48. A system according to claim 47, wherein

said plurality of comparators number four, and each of said four comparators produce a different one of said first and second gate pulses.

49. A system according to claim 48, wherein

a first of said four comparators produces a first of said first and second gate pulses at a first predetermined level down from the peak of said reference signal, a second of said four comparators produces a second of said first and second gate pulses at a second predetermined level down from the peak of said reference signal which is lower than said first level, a third of said four comparators produces a third of said first and second gate pulses at a third predetermined level down from the peak of said reference signal which is less than said second level and a fourth of said four comparators produces a fourth of said first and second gate pulses at a fourth predetermined level down from the peak of said reference signal which is less than said third level.

50. A system according to claim 47, wherein

said controlling pulse generator further includes

a first instantaneous recovery limiting amplifier coupled between said source and certain ones of said plurality of comparators, and

a second instantaneous recovery limiting amplifier coupled between said first amplifier and the others of said plurality of comparators.

51. A system according to claim 50, wherein

said plurality of comparators number four with two of said four comparators being coupled to said first amplifier and the remaining two of said four comparators being coupled to said second amplifier.

52. A system according to claim 51, wherein

one of said two of said four comparators and one of said remaining two of said four comparators has a first comparison potential applied thereto to produce a first of said first and second gate pulses at the output of said one of said two of said four comparators at a first predetermined level down from the peak of said reference signal and a second of said first and second gate pulses at the output of said one of said remaining two of said four comparators at a second predetermined level down from the peak of said reference signal which is less than said first level, and

the other of said two of said four comparators and the other of said remaining two of said four comparators has a second comparison potential different than said first comparison potential applied thereto to produce a third of said first and second gate pulses at the output of said other of said two of said four comparators at a third predetermined level down from the peak of said reference signal which is different than and between said first and second levels and a fourth of said first and second gate pulses at the output of said other of said remaining two of said four comparators at a fourth predetermined level down from the peak of said reference signal which is less than said second level.

53. A system according to claim 52, further including

a trailing edge gain switch coupled to each of said four comparators rendered operative at the peak of input pulses driving said controlling generator to provide a value for said first and second comparison potentials for the trailing edge of said input pulses which is different than the values for said first and second comparison potentials for the leading edge of said input pulses.

54. A system according to claim 47, wherein

said one of said two detectors is coupled to the output of said amplifier by a first directional coupler coupled to the output of said amplifier, and

said other of said two detectors is coupled to the output of said amplifier by said first directional coupler, a second directional coupler coupled to said first directional coupler and an instantaneous recovery limiting RF amplifier coupled between said second directional coupler and the input of said other of said two detectors.

55. A system according to claim 1, wherein

said controlling pulse generator includes

a plurality of amplitude comparators equal in number to a given number of different amplitude levels to produce a corresponding number of first gate pulses to control said source and a corresponding number of second gate pulses to control said detector system.

56. A system according to claim 55, wherein

said plurality of comparators number four, and each of said four comparators produce a different one of said first and second gate pulses.

57. A system according to claim 56, wherein

a first of said four comparators produces a first of said first and second gate pulses at a first predetermined level down from the peak of said reference signal, a second of said four comparators produces a second of said first and second gate pulses at a second predetermined level down from the peak of said reference signal which is less than said first level, a third of said four comparators produces a third of said first and second gate pulses at a third predetermined level down from the peak of said reference signal which is less than said second level and a fourth of said four comparators produces a fourth of said first and second gate pulses at a fourth predetermined level down from the peak of said reference signal which is less than said third level.

58. A system according to claim 55, wherein

said controlling pulse generator further includes

a first instantaneous recovery limiting amplifier coupled between said source and certain ones of said plurality of comparators, and

a second instantaneous recovery amplifier coupled between said first amplifier and the others of said plurality of comparators.

59. A system according to claim 58, wherein

said plurality of comparators number four with two of said four comparators being coupled to said first amplifier and the remaining two of said four comparators being coupled to said second amplifier.

60. A system according to claim 59, wherein

one of said two of said four comparators and one of said remaining two of said four comparators has a first comparison potential applied thereto to produce a first of said first and second gate pulses at the output of said one of said two of said four comparators at a first predetermined level down from the peak of said reference signal and a second of said first and second gate pulses at the output of said one of said remaining two of said four comparators at a second predetermined level down from the peak of said reference signal which is less than said first level, and

the other of said two of said four comparators and the other of said remaining two of said four comparators has a second comparison potential different than said first comparison potential applied thereto to produce a third of said first and second gate pulses at the output of said other of said two of said four comparators at a third predetermined level down from the peak of said reference signal which is different than and between said first and second levels and a fourth of said first and second gate pulses at the output of said other of said remaining two of said four comparators at a fourth predetermined level down from the peak of said reference signal which is less than said second level.

61. A system according to claim 60, further including

a trailing edge gain switch coupled to each of said four comparators rendered operative at the peak of input pulses driving said controlling generator to provide a value for said first and second comparason potentials for the trailing edge of said input pulses which is different than the values for said first and second comparison potentials for the leading edge of said input pulses.

62. A system according to claim 1, wherein

said second feedback loop includes

a directional coupler coupled to the output of said exciter,

an envelope detector coupled to said coupler,

a first difference circuit having an output, one input coupled to said envelope detector and another input coupled to an electronic pedestal level adjustor receiving timing pulses on one input thereof,

a difference amplifier coupled to said output of said difference circuit, and

a second amplitude modulator having one input coupled to said difference amplifier, another input coupled to a carrier signal source and an output coupled to the input of said exciter.

63. A system according to claim 62, wherein

said third feedback loop includes

gate having an input coupled to said first feedback loop at an input of said first modulator disposed therein rendered operative to pass only said predetermined gated portion,

an amplifier coupled to an output of said gate,

a peak detector coupled to an output of said amplifier, and

a second difference circuit having one input coupled to the output of said peak detector, another input coupled to a DC level reference source and an output for said control signal coupled to said level adjustor.

64. A system according to claim 1, wherein

said third feedback loop includes

a gate having an input coupled to said first feedback loop at an input of said first modulator disposed therein rendered operative to pass only said predetermined gated portion,

an amplifier coupled to an output of said gate,

a peak detector coupled to an output of said amplifier, and

a difference circuit having one input coupled to the output of said peak detector, another input coupled to a DC level reference source and an output for said control signal coupled to said second feedback loop.