AMPLIFIER SYSTEM

• US 3,688,250 A
• Filed: 09/04/1969
• Issued: 08/29/1972
• Est. Priority Date: 09/04/1969
• Status: Expired due to Term

• Current Assignee: Donald L. Howlett
• Original Assignee: Donald L. Howlett
• Inventors: Howlett, Donald L.
• Primary Examiner(s): Borchelt, Benjamin A.
• Assistant Examiner(s): Moskowitz, N.
• Application Number:
  US04/855,172
• Time in Patent Office: 1,090 Days
• Field of Search: 340/15.5GC,15.5DP 181/15OS 330/22,200 323/22
• US Class Current: 367/67
• CPC Class Codes: G01V 1/245 Amplitude control for seismic recording control of amplification in general H03G
• CPC Class Codes: H03F 3/72 Gated amplifiers, i.e. amplifiers which are rendered operative or inoperative by means of a control signal
• CPC Class Codes: H03G 3/3026 the gain being discontinuously variable, e.g. controlled by switching

Abstract

A wide dynamic range automatic high speed digital gain ranging amplifier system having a plurality of amplifier stages coupled in cascade circuit relationship, wherein improved bandwidth is provided by DC coupling between the successive cascaded stages and a filter in a feedback path from the output of the last cascaded stage to the input of the first cascaded stage together with selectively timed chopper switching means for alternately interrupting the input signal to the cascaded stages and the feedback path in substantially mutually out of phase relationship. The respective outputs of the amplifier stages are coupled through a common output circuit to a comparator circuit for comparison with a predetermined reference signal. Sequencing means are provided for momentarily closing switch means in timed sequence for sequentially coupling the respective outputs of the successive amplifier stages to the comparator circuit during successive, relatively brief sampling time intervals. Means are provided for selectively maintaining one of the switch means in its closed position for a holding time interval of longer duration than the sampling time interval when an output signal coupled through said switch means to the common output circuit during one of the sampling intervals bears a predetermined relationship of the reference signal. In a preferred embodiment of the amplifier system, the common output circuit is coupled to an analog-to-digital converter and thence to digital recording means for recording signals corresponding to both the instantaneous digital value of the signal at the common output circuit and the gain level to which the signal is amplified, as determined by the one of said switch means selectively maintained closed to pass the signal to the analog-to-digital converter.

Claims

1. A wide dynamic range automatic high speed gain ranging amplifier system comprising a plurality of DC amplifier stages each having a respective input circuit and a respective output circuit, said amplifier stages being DC coupled in cascade circuit relationship whereby the respective output circuit of each successive amplifier stage is DC coupled to the respective input circuit of the next-following amplifier stage of the cascade circuit, means defining a feedback path including an active filter having a gain of at least unity coupled between the output of the last of said successive cascaded amplifier stages and the input of the first of said stages, selectively timed switching means for alternately interrupting the input signal path to the input of the first of said cascaded stages and the feedback path including said active filter in substantially mutually out-of-phase relationship, a common output circuit, means defining a comparator circuit for comparing a signal coupled to an input circuit thereof with a predetermined reference signal, sampling means for momentarily coupling the respective outputs of said amplifier stages to said comparator circuit during respective sampling intervals occurring in time sequence, means responsive to said comparator circuit for selectively maintaining one of said amplifier stage output circuits coupled to said common output circuit for at least a predetermined minimum holding time interval when the output signal sampled at said one of said amplifier stage output circuits bears a predetermined relationship to said reference signal.

2. Apparatus as defined in claim 1 further comprising analog-to-digital converter means coupled to said common output for converting an analog signal appearing at said common output during said holding time to a digital signal of corresponding value, and means for indicating which one of said amplifier stage output circuits is coupled to said common output circuit in correlation with the value of said digital signal.

3. A wide dynamic range automatic high speed gain ranging amplifier system comprising a plurality of DC amplifier stages each having a respective input circuit and a respective output circuit, said amplifier stages being DC coupled in cascade circuit relationship whereby the respective output circuit of each successive amplifier stage is DC coupled to the respective input circuit of the next-following amplifier stage of the cascade circuit, means defining a feedback path including an active filter having a gain of at least unity coupled between the output of the last of said successive cascaded amplifier stages and the input of the first of said stages, selectively timed switching means for alternately interrupting the input signal path to the input of the first of said cascaded stages and the feedback path including said active filter in substantially mutually out-of-phase relationship, a common output circuit, means including a plurality of normally open switch means for selectively coupling the respective outputs of said amplifier stages to said common output circuit, means defining a comparator circuit coupled to said common output circuit for comparing a signal appearing at said common output circuit with a predetermIned reference signal, sequencing means for momentarily closing said switch means in time sequence for sequentially coupling the respective outputs of said amplifier stages to said comparator circuit and means responsive to said comparator circuit for selectively maintaining one of said switch means in its closed position when the output signal coupled through said one switch means to said common output circuit bears a predetermined relationship to said reference signal.

4. Apparatus as defined in claim 3 further comprising high speed amplifier and impedance matching means coupled in circuit between said normally open switching means and the means defining said common output circuit.

5. A wide dynamic range automatic high speed gain ranging amplifier system comprising a plurality of DC amplifier stages each having a respective input circuit and a respective output circuit, said amplifier stages being DC coupled in cascade circuit relationship whereby the respective output circuit of each successive amplifier stage is DC coupled to the respective input circuit of the next-following amplifier stage of the cascade circuit, means defining a feedback path including an active filter having a gain of at least unity coupled between the output of the last of said successive cascaded amplifier stages and the input of the first of said stages, selectively timed switching means for alternately interrupting the input signal path to the input of the first of said cascaded stages and the feedback path including said active filter in substantial mutually out-of-phase relationship, a common output circuit, means defining a comparator circuit for comparing a signal coupled to an input circuit thereof with a predetermined reference signal, sampling means for momentarily coupling the respective outputs of said amplifier stages to said comparator circuit in timed sequence, means responsive to said comparator circuit for selectively maintaining one of said amplifier stage output circuits coupled to said common system output circuit when the output signal sampled at said one of said amplifier stage output circuits bears a predetermined relationship to said reference signal.

6. A wide dynamic range automatic high speed gain ranging amplifier system comprising a plurality of DC amplifier stages each having a respective input circuit and a respective output circuit, said amplifier stages being DC coupled in cascade circuit relationship whereby the respective output circuit of each successive amplifier stage is DC coupled to the respective input circuit of the next-following amplifier stage of the cascade circuit, means defining a feedback path including an active filter having a gain of at least unity coupled between the output of the last of said successive cascaded amplifier stages and the input of the first of said stages, selectively timed switching means for alternately interrupting the input signal path to the input of the first of said cascaded stages and the feedback path including said active filter in substantially mutually out-of-phase relationship, a common output circuit, means defining a comparator circuit for comparing a signal coupled to an input circuit thereof with a predetermined reference signal, sampling means for momentarily coupling the respective outputs of said amplifier stages to said comparator circuit in timed sequence, means responsive to said comparator circuit for selectively maintaining one of said amplifier stage output circuits coupled to said common output circuit when the output signal sampled at said one of said amplifier stage output circuits bears a predetermined relationship to said reference signal, analog-to-digital converter means coupled to said common output for converting an analog signal appearing at said output to a digital signal of corresponding value, and means for indicating which one of said amplifier stage output circuits is coupled to said common output circuit in correlation with the value of said digital signal.

7. A seiSmic signal processing system comprising a plurality of signal channels, each of said channels comprising a wide dynamic range automatic high speed gain ranging amplifier system including a plurality of DC amplifier stages each having a respective input circuit and a respective output circuit, said amplifier stages being DC coupled in cascade circuit relationship whereby the respective output circuit of each successive amplifier stage of the channel is DC coupled to the respective input circuit of the next-following amplifier stage of the cascade circuit, means defining a feedback path including an active filter having a gain of at least unity coupled between the output of the last of said successive cascaded amplifier stages and the input of the first of said stages, selectively timed switching means for alternately interrupting the input signal path to the input of the first of said cascaded stages and the feedback path including said active filter in substantially mutually out-of-phase relationship, a common output circuit for said seismic system, means defining a comparator circuit for comparing a signal coupled to an input circuit thereof with a predetermined reference signal, sampling means for momentarily coupling the respective outputs of the cascaded amplifier stages of each of said channels to said common output circuit in timed sequence, means responsive to said comparator circuit for selectively maintaining one of said amplifier stage output circuits coupled to said common output circuit for at least a predetermined time interval when the output signal sampled at said one of said amplifier stage output circuits bears a predetermined relationship to said reference signal, analog-to-digital converter means coupled to said common output for converting an analog signal appearing at said common output to a first digital signal of corresponding value, said converter being characterized by the capability of converting to digital form an analog signal applied thereto for said predetermined time interval, means for providing a second digital signal indicating which one of said amplifier stage output circuits is coupled to said common output circuit at least during times when one of said amplifier stage outputs is maintained coupled to said common output circuit, and means for recording signal information corresponding to said first digital signal in correlation with signal information corresponding to said second digital signal.

8. Apparatus as defined in claim 7 wherein the means for momentarily coupling the respective outputs of said amplifier stages to said comparator circuits in timed sequence comprises a digital control and multiplexer network coupled to the means for selectively maintaining one of said amplifier stage output circuits coupled to said common output circuit.

9. Apparatus as defined in claim 7 wherein said sampling means for momentarily coupling said outputs of said amplifier stages to said amplifier circuits in timed sequence comprises a digital control network coupled to the means responsive to said comparator circuit for selectively maintaining one of said amplifier stage output circuits coupled to said common output circuit and a channel multiplexer for selectively coupling the respective outputs of said channels to the common output circuit in timed sequence.

10. A signal processing system comprising a wide dynamic range automatic high speed gain ranging amplifier system including a plurality of DC amplifier stages each having a respective input circuit and a respective output circuit, said amplifier stages being DC coupled in cascade circuit relationship whereby the respective output circuit of each successive amplifier stage of the cascade circuit is DC coupled to the respective input circuit of the next-following amplifier stage of the cascade circuit, means defining a feedback path including an active filter having a gain of at least unity coupled between the output of the last of said successive cascaded amplifier stages and the Input of the first of said stages, selectively timed switching means for alternately interrupting the input signal path to the input of the first of said cascaded stages and the feedback path including said active filter in substantially mutually out-of-phase relationship, a common output circuit, means defining a comparator circuit for comparing a signal coupled to an input circuit thereof with a predetermined reference signal, sampling means for momentarily coupling the respective outputs of the cascaded amplifier stages to said common output circuit in timed sequence, means responsive to said comparator circuit for selectively maintaining one of said amplifier stage output circuits coupled to said common output circuit for at least a predetermined time interval when the output signal sampled at said one of said amplifier stage output circuits bears a predetermined relationship to said reference signal, analog-to-digital converter means coupled to said common output for converting an analog signal appearing at said common output to a first digital signal of corresponding value, said converter being characterized by the capability of converting to digital form an analog signal applied thereto for said predetermined time interval, means for providing a second digital signal indicating which one of said amplifier stage output circuits is coupled to said common output circuit at least during times when one of said amplifier stage outputs is maintained coupled to said common output circuit, and means for recording signal information corresponding to said first digital signal in correlation with signal information corresponding to said second digital signal.

11. A wide dynamic range automatic high speed gain ranging amplifier system comprising an amplifier network including a plurality of DC amplifier stages each having a respective input circuit and a respective output circuit, said amplifier stages being DC coupled in cascade circuit relationship whereby the respective output circuit of each successive amplifier stage is DC coupled to the respective input circuit of the next-following amplifier stage of the cascade circuit, means defining a feedback path including an active filter having a gain of at least unity coupled between the output of the last of said successive cascaded amplifier stages and the input of the first of said stages, selectively timed switching means for alternately interrupting the input signal path to the input of the first of said cascaded stages and the feedback path including said active filter in substantially mutually out-of-phase relationship, a common output circuit for said network, means for establishing a plurality of progressively different predetermined amplifier gain ranges for said amplifier network, means for time-sequentially sampling a signal translated through said network to said common output under said progressively different gain ranges, said sampling means including means for switching progressively from one of said amplifier gain ranges to another of said ranges, means defining a comparator circuit having an input coupled to said common output for comparing a signal sampled at said common output circuit with a predetermined reference signal, means responsive to said comparator circuit for selectively maintaining one of said predetermined amplifier gain ranges for at least a predetermined minimum holding time interval when the output signal sampled at said common output bears a predetermined relationship to said reference signal.

12. Apparatus as defined in claim 11 wherein the means for establishing said plurality of progressively different predetermined amplifier gain ranges includes a plurality of switching means DC coupled in circuit with successive amplifier stages of said cascade circuit.

13. Apparatus as defined in claim 11 wherein said means for establishing said plurality of progressively different amplifier gain ranges comprises switching means for selectively deriving an output signal amplified by a progressivelY different number of said cascade amplifier stages.

14. Apparatus as defined in claim 10 wherein said first and second digital signals are in the form of a floating point digital word comprising a mantissa and an exponent in the form:

Q + or - x b k wherein Q represents the magnitude of the amplitude of the input signal to said signal processing system;

wherein b represents the gain of each one of the cascaded amplifier stages;

wherein x, the mantissa, represents the first digital signal which corresponds to the output amplitude of a particular one of the cascaded amplifier stages selected by the signal sampling means;

wherein k, the exponent, represents the second digital signal which corresponds to the number of said cascaded amplifier stages through which the particular input signal is translated in order to arrive at the selected cascade amplifier stage output determined by the sampling means.

15. Apparatus as defined in claim 14 wherein said cascaded amplifier stages have a common amplification base b such that the exponents of each such cascaded stage are algebraically additive to form the value of said exponent corresponding to said second digital signal.

16. Apparatus as defined in claim 1 wherein each of said plurality of cascaded amplifier stages have substantially the same DC gain and AC gain, which is significantly greater than unity.

17. Apparatus as defined in claim 16 wherein both the AC gain and DC gain of each of said cascaded amplifier stages is significantly greater than unity and wherein the overall DC gain of the network including said plurality of cascaded stages together with said feedback path is substantially the same as the AC gain thereof.

18. Apparatus as defined in claim 10 wherein each of said plurality of cascaded amplifier stages have substantially the same DC gain and AC gain, which is significantly greater than unity.

19. Apparatus as defined in claim 18 wherein the overall AC gain of the network including said plurality of cascaded stages and said feedback path is significantly greater than unity and the overall DC gain of said network is substantially the same as the AC gain thereof within a predetermined low frequency pass band down to DC.

20. Apparatus as defined in claim 11 wherein the active filter of said feedback path has a predetermined high frequency roll-off characteristic and the network comprising said plurality of cascaded amplifier stages together with said feedback path has an overall gain for both DC and AC which is significantly greater than unity.

21. Apparatus as defined in claim 20 wherein both the AC gain and the DC gain of each of said cascaded amplifier stages is significantly greater than unity and wherein the overall DC gain of the network including said plurality of cascaded stages together with said feedback is substantially the same as the AC gain thereof.

22. Apparatus as defined in claim 10 characterized by an operating cycle which is completed within the signal cycle of an amplifier system input signal of predetermined frequency, said operating cycle including the functioning of the means for momentarily coupling the respective outputs of the cascaded amplifier stages to said common output circuit and for selectively maintaining one of said amplifier stage output circuits coupled to said output for said predetermined time interval required for said analog-to-digital converter means to sample an analog signal for conversion to a first digital signal.

23. A wide dynamic range automatic high speed gain ranging amplifier system comprising an amplifier network including a plurality of DC amplifier stages each having a respective input circuit and a respective output circuit, said amplifier stages being DC coupled in cascade circuit relationship whereby the respective output circuit of each successive amplifier stage is DC coupled to the respective input circuit of the next-following aMplifier stage of the cascade circuit, means defining a feedback path including an active filter having a gain of at least unity coupled between the output of the last of said successive cascaded amplifier stages and the input of the first of said stages, selectively timed switching means for alternately interrupting the input signal path to the input of the first of said cascaded stages and the feedback path including said active filter in substantially mutually out-of-phase relationship, a common output circuit for said network, means for establishing a plurality of progressively different predetermined amplifier gain ranges for said amplifier network, means for time-sequentially switching progressively from one to another of said predetermined gain ranges during successive sampling intervals, a comparator circuit adapted to compare a signal applied to an input thereof with a predetermined reference, means including said comparator circuit for comparing with said reference signals translated by said amplifier network to said common output during said sampling intervals as said amplifier network is switched progressively through said predetermined gain ranges for at least a predetermined holding time interval when the output signal sampled at said common output bears said predetermined relationship to said reference.

24. A wide dynamic range automatic high speed gain ranging amplifier system comprising an amplifier network including a plurality of DC coupled amplifier stages having both AC and DC amplification factors significantly greater than unity, each stage having a respective input circuit and a respective output circuit, a common output circuit for said network, means including a feedback loop coupling an output of said network to the input thereof together with selectively timed switching means for periodically coupling said feedback loop to said amplifier network while concurrently interrupting the application of input signals to said network for providing a net DC gain for said network that is substantially the same as the AC gain thereof, means for establishing a plurality of progressively different predetermined amplifier gain ranges for said amplifier network, means for time-sequentially switching progressively from one to another of said predetermined gain ranges during successive sampling time intervals, means comprising a comparator for comparing signals translated to said common output during said sampling intervals with a predetermined reference, means responsive to said comparator for selecting one of said gain ranges when said sampled output bears a predetermined relationship to said reference signal and for holding said predetermined gain range for at least a predetermined holding time interval while the sampled signal at said common output during said holding time interval is translated to said common output as a first signal and means for deriving a second signal indicating which one of said predetermined gain ranges is selected for a given holding time interval.

25. Apparatus as defined in claim 24 wherein said first signal is in analog form and wherein said apparatus further comprises analog-to-digital converter means coupled to said common output for converting said analog first signal to a corresponding digital first signal and wherein said predetermined holding time interval is at least as long as the characteristic minimum time required for said converter to sample said analog signal for conversion to a corresponding digital signal.

26. A wide dynamic range automatic high speed gain ranging amplifier system comprising an amplifier network including a plurality of DC coupled amplifier stages having both A.C. and DC amplification factors significantly greater than unity, each stage having a respective input circuit and a respective output circuit, a common output circuit for said network, means including a feedback loop coupling an output of said network to the input thereof together with selectively timed switching means for perIodically coupling said feedback loop to said amplifier network while concurrently interrupting the application of input signals to said network for providing a net DC gain for said network that is substantially the same as the AC gain thereof, means for establishing a plurality of progressively different predetermined amplifier gain ranges for said amplifier network, means for time-sequentially switching progressively from one to another of said predetermined gain ranges during successive sampling time intervals, means responsive to signals translated to said common output during said sampling intervals for selecting one of said gain ranges when said sampled output bears a predetermined value and for holding the said selected one of predetermined gain ranges for at least a predetermined holding time interval while the sampled signal at said common output during said holding time interval is translated to said common output during said holding time interval as a first signal and means for deriving a second signal indicating which one of said predetermined gain ranges is selected for a given holding time interval.

27. Apparatus as defined in claim 26 wherein said first signal is in analog form and wherein said apparatus further comprises analog-to-digital converter means coupled to said common output for converting said analog first signal to a corresponding digital first signal and wherein said predetermined holding time interval is at least as long as the characteristic minimum time required for said converter to sample said analog signal for conversion to a corresponding digital signal.

28. Apparatus as defined in claim 27 further comprising means for recording both said digital first signal corresponding to said first analog signal and a second digital signal corresponding to said second signal in digital form as a floating point word comprising a mantissa and an exponent in the form:

Q + or - x b k wherein Q represents the magnitude of the input signal to said amplifier system;

wherein b represents the gain of the individual amplifier stages of said network through which the input signal is translated to the common output;

wherein x, the mantissa, represents the first digital signal which corresponds to said first analog signal;

wherein k, the exponent, represents the second digital signal corresponding to said second signal indicating the selected gain range of said network during said holding time interval.

29. Apparatus as defined in claim 26 characterized by an operating cycle for said means for selecting one of said gain ranges and for holding said selected gain range during said holding time interval which is completed within the signal cycle of an amplifier system input signal of predetermined frequency.

30. Apparatus as defined in claim 19 wherein both the AC gain and DC gain of each of said plurality of cascaded stages is a whole number greater than unity.

31. Apparatus as defined in claim 14 wherein k unity and wherein b a positive integer greater than unity.

32. Apparatus as defined in claim 14 wherein the AC amplification values of k unity and of b a positive whole number greater than unity for both AC and DC amplification and wherein the net DC amplification of the plurality of said cascaded amplifier stages together with said feedback path is substantially the same as the AC gain thereof.

33. Apparatus as defined in claim 32 wherein both the AC and DC amplification value of b 8.

34. Apparatus as defined in claim 4 wherein said high speed amplifier and impedance matching means comprises a circuit having an input impedance which is at least of the order of 107 times the '"'"''"'"''"'"''"'"'ON'"'"''"'"''"'"''"'"' resistance of the normally open switching means coupled to its input.

35. Apparatus as defined in claim 34 wherein said normally open switching means comprises a solid state analog switch having a relatively High '"'"''"'"''"'"''"'"'OFF'"'"''"'"''"'"''"'"' resistance which is at least of the order 1010 ohms and a relatively low '"'"''"'"''"'"''"'"'ON'"'"''"'"''"'"''"'"' resistance.

36. Apparatus as defined in claim 3 further comprising respective phase adjusting means coupled in at least all but the longest of the respective signal paths including each of said respective amplifier stage outputs and said common output circuit.

37. Apparatus as defined in claim 36 wherein said phase adjustment means comprises an isolation stage adapted to block switching transients between the respective switch means and the input of the next-following cascaded amplifier stage.

38. Apparatus as defined in claim 37 wherein said isolation stage further provides means for adjusting the DC level of the common output of respective switch elements in each of said paths.

39. Apparatus as defined in claim 11 wherein said means for time-sequentially sampling a signal translated through said network to said common output under progressively different gain ranges comprises means for changing the gain of said network to the common output without changing the gain of the individual stages of said network.

40. Apparatus as defined in claim 11 wherein the means for sampling a signal translated through said network to said common output functions to achieve such sampling during times that are mutually exclusive with respect to times when said means for switching progressively from one of said amplifier gain ranges to another is in the process of accomplishing such switching.

41. Apparatus as defined in claim 14 wherein k unity and wherein b a positive number.

42. A wide dynamic range automatic high speed gain ranging amplifier system comprising an amplifier network including a plurality of DC coupled DC amplifier stages each having a respective input circuit and a respective output circuit, means defining a feedback path including an active filter having a gain of at least unity coupled between an output of said network and the input of said network, selectively timed switching means for alternately interrupting the input signal path to the input of said amplifier network and the feedback path including said active filter in substantially mutually out-of-phase relationship, a common output circuit for said network, means for establishing a plurality of progressively different predetermined amplifier gain ranges comprising a plurality of different circuit paths providing said progressively different amplifier gain ranges, means for time-sequentially switching progressively from one to another of said circuit paths during successive sampling time intervals, means responsive to signals translated through said circuit paths during said sampling intervals for selecting one of said circuit paths when said sampled output bears a predetermined value and for holding the selected circuit path for at least a predetermined holding time interval while the sampled signal is translated through said selected path to said common output as a first signal and means for deriving a second signal indicating which one of said circuit paths is selected for a given holding time interval.

43. An amplifier system comprising a network including a plurality of DC amplifier stages each having a respective input circuit and a respective output circuit, said amplifier stages being DC coupled in cascade circuit relationship whereby the respective output circuit of each successive amplifier stage is coupled to the respective input circuit of the next-following amplifier stage of the cascade circuit, means for deriving output signals from successive stages of said cascade circuit, means comprising a negative feedback path coupling the output of the last of said amplifier stages to the input of the first stage of said cascade circuit, said feedback path comprising an active filter having at least unity gain and being characterized as a low pass filter and selectively timed switching means for periodically interrupting said feedback paTh while signals are applied to the input of the first of said cascade stages and for interrupting the application of signals to the input of said first cascade stage while said feedback path is not being thus interrupted.

44. Apparatus as defined in claim 43 wherein both the AC gain and the DC gain of each of said cascaded amplifier stages is greater than unity and substantially the same and wherein the overall DC gain of said plurality of cascaded stages together with said feedback path is substantially the same as the AC gain thereof.

45. Apparatus as defined in claim 43 wherein the active filter of said feedback path has a predetermined upper high frequency roll-off characteristic and the network comprising said plurality of cascaded amplifier stages together with said feedback path has both an overall DC gain and an overall AC gain which is significantly greater than unity.

46. Apparatus as defined in claim 1 wherein said selectively timed switching means is adapted and arranged to interrupt said input signal path and connect the input of the first of said cascaded stages to common ground during the times when said switching means interrupts the feedback path including said active filter.

47. Apparatus as defined in claim 6 wherein said selectively timed switching means is adapted and arranged to interrupt said input signal path and connect the input of the first of said cascaded stages to common ground during the times when said switching means interrupts the feedback path including said active filter.

48. Apparatus as defined in claim 7 wherein said selectively timed switching means is adapted and arranged to interrupt said input signal path and connect the input of the first of said cascaded stages to common ground during the times when said switching means interrupts the feedback path including said active filter.

49. Apparatus as defined in claim 11 wherein said selectively timed switching means is adapted and arranged to interrupt said input signal path and connect the input of the first of said cascaded stages to common ground during the times when said switching means interrupts the feedback path including said active filter.

50. Apparatus as defined in claim 23 wherein said selectively timed switching means is adapted and arranged to interrupt said input signal path and connect the input of the first of said cascaded stages to common ground during the times when said switching means interrupts the feedback path including said active filter.

51. Apparatus as defined in claim 26 wherein said selectively timed switching means is adapted and arranged to interrupt said input signal path and connect the input of the network including said stages to common ground during the times when said switching means interrupts the feedback path including said active filter.

52. Apparatus as defined in claim 42 wherein said selectively timed switching means is adapted and arranged to interrupt said amplifier network input signal path and connect the input of said amplifier network to common ground during the times when said switching means interrupts the feedback path including said active filter.

53. Apparatus as defined in claim 43 wherein said selectively timed switching means is adapted and arranged to interrupt said amplifier network input signal path and connect the input of said amplifier network to common ground during the times when said switching means interrupts the feedback path including said active filter.

54. Apparatus as defined in claim 47 wherein the selectively timed switching means is programmed to interrupt the said input signal path and connect said amplifier input to ground prior to re-connecting said feedback path to said active filter and wherein said switching means is further programmed to interrupt said feedback path prior to ungrounding said amplifier input and re-connecting the input signal path thereto.

55. Apparatus as defined in claim 48 wherein the selectively timed switching means is programmed to interruPt the said input signal path and connect said amplifier input to ground prior to re-connecting said feedback path to said active filter and wherein said switching means is further programmed to interrupt said feedback path prior to ungrounding said amplifier input and re-connecting the input signal path thereto.

56. Apparatus as defined in claim 49 wherein the selectively timed switching means is programmed to interrupt the said input signal path and connect said amplifier input to ground prior to re-connecting said feedback path to said active filter and wherein said switching means is further programmed to interrupt said feedback path prior to ungrounding said amplifier input and re-connecting the input signal path thereto.

57. Apparatus as defined in claim 50 wherein the selectively timed switching means is programmed to interrupt the said input signal path and connect said amplifier input to ground prior to re-connecting said feedback path to said active filter and wherein said switching means is further programmed to interrupt said feedback path prior to ungrounding said amplifier input and re-connecting the input signal path thereto.

58. Apparatus as defined in claim 51 wherein the selectively timed switching means is programmed to interrupt the said input signal path and connect said amplifier input to ground prior to re-connecting said feedback path to said active filter and wherein said switching means is further programmed to interrupt said feedback path prior to ungrounding said amplifier input and re-connecting the input signal path thereto.

59. Apparatus as defined in claim 52 wherein the selectively timed switching means is programmed to interrupt the said input signal path to said amplifier network and connect said amplifier network input to ground prior to re-connecting said feedback path to said active filter and wherein said switching means is further programmed to interrupt said feedback path prior to ungrounding said amplifier network input and re-connecting the input signal path thereto.

60. Apparatus as defined in claim 53 wherein the selectively timed switching means is programmed to interrupt the said input signal path to said amplifier network and connect said amplifier network input to ground prior to re-connecting said feedback path to said active filter and wherein said switching means is further programmed to interrupt said feedback path prior to ungrounding said amplifier network input and re-connecting the input signal path thereto.

61. Apparatus as defined in claim 1 wherein said feedback path including said active filter comprises signal storage means for deriving a correction signal from the last of said cascaded stages during times when said feedback path is connected in circuit while the input signal path to the first of said cascaded stages is interrupted and for inserting a drift correction signal at the input of the first of said cascaded stages during subsequent times when said feedback path is being interrupted and said input signal path to the input of said first of said cascaded stages is restored following such interruption.

62. Apparatus as defined in claim 11 wherein said feedback path including said active filter comprises signal storage means for deriving a correction signal from the last of said cascaded stages during times when said feedback path is connected in circuit while the input signal path to the first of said cascaded stages is interrupted and for inserting a drift correction signal at the input of the first of said cascaded stages during subsequent times when said feedback path is being interrupted and said input signal path to the input of said first of said cascaded stages is restored following such interruption.

63. Apparatus as defined in claim 26 wherein said feedback path including said active filter comprises signal storage means for deriving a correction signal from said output of said network during times when said feedback path is connected in circuit while said input signal path to said Network is interrupted and for inserting a drift correction signal at the input of said network during subsequent times when said feedback path is being interrupted and said input signal path to the input of said network is restored following such interruption.

64. Apparatus as defined in claim 42 wherein said feedback path including said active filter comprises signal storage means for deriving a correction signal from said output of said network during times when said feedback path is connected in circuit while said input signal path to said network is interrupted and for inserting a drift correction signal at the input of said network during subsequent times when said feedback path is being interrupted and said input signal path to the input of said network is restored following such interruption.

65. A seismic signal processing system as defined in claim 7, wherein each of said amplifier channels includes an active filter having a signal output coupled to the input circuit of the amplifier system of the respective channel.

66. An apparatus as defined in claim 10, wherein said signal processing system includes an active filter having a signal processing system includes an active filter having a signal output coupled to the input of said amplifier system.

67. An amplifier system as defined in claim 23, wherein said system includes an active filter having a signal output coupled to the input of said amplifier network.

68. Apparatus as defined in claim 23, wherein said means for establishing a plurality of progressively different predetermined amplifier gain ranges for said amplifier network comprises means for changing the gain of said network to the common output by progressively switching from one to another of said amplifier stages without changing the gain of the individual stages of said network.

69. Apparatus as defined in claim 24, wherein said means for establishing a plurality of progressively different predetermined amplifier gain ranges for said amplifier network comprises means for changing the gain of said network to the common output by progressively switching from one to another of said amplifier stages without changing the gain of the individual stages of said network.

70. Apparatus as defined in claim 26, wherein said means for establishing a plurality of progressively different predetermined amplifier gain ranges for said amplifier network comprises means for changing the gain of said network to the common output by progressively switching from one to another of said amplifier stages without changing the gain of the individual stages of said network.

71. Apparatus as defined in claim 29, wherein said means for establishing a plurality of progressively different predetermined amplifier gain ranges for said amplifier network comprises means for changing the gain of said network to the common output by progressively switching from one to another of said amplifier stages without changing the gain of the individual stages of said network.

72. Apparatus as defined in claim 1, characterized in that said holding time interval is significantly longer than said sampling interval.

73. Apparatus as defined in claim 11, characterized in that said holding time interval is significantly longer than the sampling time interval.

74. Apparatus as defined in claim 23, characterized in that said holding time interval is significantly longer than said sampling time interval.

75. Apparatus as defined in claim 24, characterized in that said holding time interval is significantly longer than said sampling time interval.

76. Apparatus as defined in claim 26, characterized in that said holding time interval is significantly longer than said sampling time interval.

77. Apparatus as defined in claim 42, characterized in that said holding time interval is significantly longer than said sampling time interval.

78. A wide dynamic range automatic high speed gain ranging amplifier system comprising an amplifier network including a pluraliTy of DC coupled amplifier stages each having a respective input circuit and a respective output circuit, said amplifier stages being coupled in cascade circuit relationship, whereby the respective output circuit of each successive amplifier stage is coupled to the respective input circuit of the next-following amplifier stage of the cascade circuit, a common output circuit for said network, means for establishing a plurality of progressively different predetermined amplifier gain ranges for said amplifier network, means operating recurrently during seccessive operating cycles of said amplifier system for time-sequentially switching during each of said operating cycles from one to another of said predetermined gain ranges during successive sampling intervals occurring in timed sequence, means for comparing a predetermined reference with signals translated by said amplifier network to said common output during said sampling intervals, means for converting an analog signal appearing at said common output to a corresponding digital signal, means for selecting one of said gain ranges when the output signal sampled at said common output bears a predetermined relationship to said reference, means for deriving a second signal indicating which one of said predetermined gain ranges has been selected during the times that said signal at said common output is converted to a corresponding digital signal, means comprising a negative feedback path coupling the output of the last of said amplifier stages to the input of the first stage of said cascade circuit, said feedback path comprising an active filter having at least unity gain and being characterized as a low pass filter, and selectively timed switching means for periodically interrupting said feedback path while signals are applied to the input of the first stage of said cascade circuit and for interrupting the application of signals to the input of said first cascade stage while said feedback path is not being thus interrupted.

79. A system as defined in claim 78, wherein said means for establishing a plurality of progressively different predetermined amplifier gain ranges for said amplifier network comprises means for sampling the respective outputs of successive ones of said amplifier stages during said successive sampling intervals.

80. A system as defined in claim 78, wherein said means for establishing a plurality of progressively difference predetermined amplifier gain ranges comprises means for selectively switching the outputs of respective amplifiers in said network to said common output.

81. A system as defined in claim 79, wherein said means for establishing a plurality of progressively different predetermined amplifier gain ranges comprises means for selecting different gain paths without changing the gain of the individual amplifier stages of said network.

82. A system as defined in claim 79, wherein the means for switching from one to another of said gain ranges during said successive sampling intervals comprises means for progressively switching during each operating cycle from a beginning gain range which is a range at one end of said plurality of ranges.

83. A wide dynamic range automatic high speed gain ranging amplifier system comprising an amplifier network including a plurality of DC coupled amplifier stages each having a respective input circuit and a respective output circuit, said amplifier stages being coupled in cascade circuit relationship, whereby the respective output circuit of each successive amplifier stage is coupled to the respective input circuit of the next-following amplifier stage of the cascade circuit, a common output circuit for said network, means for establishing a plurality of progressively different predetermined amplifier gain ranges for said amplifier network, means for switching from one to another of said predetermined gain ranges, means for comparing a predetermined reference with signals translated by said amplifier network to said common output during saiD sampling intervals, means for converting an analog signal appearing at said common output to a corresponding digital signal, means for selecting one of said gain ranges when the output signal sampled at said common output bears a predetermined relationship to said reference, means for deriving a second signal indicating which one of said predetermined gain ranges has been selected during the times that said signal at said common output is converted to a corresponding digital signal, means comprising a negative feedback path coupling the output of the last of said amplifier stages to the input of the first stage of said cascade circuit, said feedback path comprising a low pass filter, and selectively timed switching means for periodically interrupting said feedback path while signals are applied to the input of the first stage of said cascade circuit and for interrupting the application of signals to the input of said first cascade stage while said feedback path is not being thus interrupted.

84. Apparatus as defined in claim 83 wherein said means for switching from one to another of said predetermined gain ranges operates recurrently during successive operating cycles of said amplifier system for time sequentially switching from one to another of said predetermined gain ranges during successive sampling intervals occurring in timed sequence.

85. Apparatus as defined in claim 83 wherein said low pass filter is an active filter having at least unity gain.

86. A wide dynamic range automatic high speed gain ranging amplifier system comprising an amplifier network including a plurality of DC coupled amplifier stages each having a respective input circuit and a respective output circuit, said amplifier stages being coupled in cascade circuit relationship, whereby the respective output circuit of each successive amplifier stage is coupled to the respective input circuit of the next-following amplifier stage of the cascade circuit, a common output circuit for said network, means for establishing a plurality of progressively different predetermined amplifier gain ranges for said amplifier network, means responsive to the level of a signal applied to the input of said amplifier network for selecting one of said gain ranges for translation of said signal through said amplifier network to said common output circuit, means for converting an analog signal thus translated to said common output circuit to a corresponding digital signal, means for deriving a second signal indicating which one of said predetermined gain ranges has been selected for translation of said signal to said common output for such conversion thereof to a corresponding digital signal, means comprising a negative feedback path coupling the output of the last of said amplifier stages to the input of the first stage of said cascade circuit, said feedback path comprising a low pass filter, and selectively timed switching means for periodically interrupting said feedback path while signals are applied to the input of the first stage of said cascade circuit and for interrupting the application of signals to the input of said first cascade stage while said feedback path is not being thus interrupted.