Patent US3978401A successfully refreshed from Google Patents.
US3978401A
Expired / Lapsed
US
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Distortion measurement system
Assignee: Sound Technology Inc
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Filing: 1975-10-29
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Granted: 1976-08-31
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Expires: 1995-10-29
Abstract
Abstract A distortion measurement system for measuring distortion as low as .002% includes an ultra low distortion oscillator having a relatively fast response which is achieved by switching the time constant of the control loops of the oscillator during settling. The analyzer section included in the distortion system has a unique notch filter which provides low distortion. This is achieved by adding together two 90° all pass phase shifters. In addition, automatic tuning is provided by two feedback control loops; one is responsive to out-of-phase signals which controls the RC filter circuits of the phase shifters and the other responds to the in-phase signals which controls the output summing junction of the notch filter. Finally, a feedforward type of simultaneous tuning is accomplished by ganging the oscillator frequency adjustment with the analyzer.
Inventors
- 👤 Jack G. S. Lum
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 11:31
CPC Classifications
H; H03; H03L; H03L5/00; G; G01; G01R; G01R23/00; G01R23/16; G01R23/20
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
62 words
A distortion measurement system for measuring the distortion in a signal of a predetermined frequency comprising: an ultra low distortion oscillator having frequency selective elements; analyzer means including notch filter means having frequency selective elements and a constant response in the passband; and means for ganging said frequency selective elements of said oscillator and analyzer means during changes in said predetermined frequency.
Claim 2
Dependent Claim
62 words
A distortion measurement system for measuring the distortion in a signal of a predetermined frequency comprising: an ultra low distortion oscillator having frequency selective elements; analyzer means including notch filter means having frequency selective elements and a constant response in the passband; and means for ganging said frequency selective elements of said oscillator and analyzer means during changes in said predetermined frequency.
Claim 3
Dependent Claim
34 words
A system as in claim 1 where said analyzer means includes integration means said ganging means being coupled to said integration means to provide for a rapid adjustment when said predetermined frequency is changed.
Claim 4
Dependent Claim
22 words
A system as in claim 1 where said notch filter means includes two cascaded all pass phase shifter means of 90° each.
Claim 5
Dependent Claim
45 words
A system as in claim 3 where each of said phase shifter means includes frequency selective elements having respective time constants of A and B and a notch frequency proportional to 1/√AB whereby for frequency tuning said time constants need not closely track each other.
Claim 6
Dependent Claim
86 words
A distortion measurement system for measuring the distortion in a signal of a predetermined frequency comprising: an oscillator of the Wien bridge type including an amplifier having an output and input, positive feedback means forming two legs of the bridge and having frequency selective elements, negative feedback means forming the other two legs of the bridge; analyzer means including notch filter means having frequency selective elements; and means for ganging said frequency selective elements of said oscillator and analyzer means during changes in said predetermined frequency.
Claim 7
Dependent Claim
86 words
A distortion measurement system for measuring the distortion in a signal of a predetermined frequency comprising: an oscillator of the Wien bridge type including an amplifier having an output and input, positive feedback means forming two legs of the bridge and having frequency selective elements, negative feedback means forming the other two legs of the bridge; analyzer means including notch filter means having frequency selective elements; and means for ganging said frequency selective elements of said oscillator and analyzer means during changes in said predetermined frequency.
Claim 8
Dependent Claim
121 words
A distortion measurement system for measuring the distortion in a signal of a predetermined frequency comprising: an ultra low distortion oscillator having frequency selective elements; analyzer means including notch filter means having frequency selective elements and a constant response in the passband said notch filter means including means for automatically tuning said filter means to said predetermined frequency despite component variations comprising, a first feedback control loop responsive to out-of-phase signals for varying said frequency selective elements of said notch filter means, a second feedback control loop responsive to in-phase signals for controlling the summing of said input to said output and means for ganging said frequency selective elements of said oscillator and analyzer means during changes in said predetermined frequency.
Claim 9
Dependent Claim
121 words
A distortion measurement system for measuring the distortion in a signal of a predetermined frequency comprising: an ultra low distortion oscillator having frequency selective elements; analyzer means including notch filter means having frequency selective elements and a constant response in the passband said notch filter means including means for automatically tuning said filter means to said predetermined frequency despite component variations comprising, a first feedback control loop responsive to out-of-phase signals for varying said frequency selective elements of said notch filter means, a second feedback control loop responsive to in-phase signals for controlling the summing of said input to said output and means for ganging said frequency selective elements of said oscillator and analyzer means during changes in said predetermined frequency.
Claim 10
Dependent Claim
72 words
A system as in claim 6 where said first and second loop include integrating-amplifier means and including variable amplifier means coupling said output of said filter means to both of said loops and means for ganging said variable amplifier means with both of said integrating-amplifier means for varying the amplification of such integrating-amplifier means inversely to the gain of said variable amplifier means whereby automatic tuning is achieved for all distortion ranges.
Claim 11
Dependent Claim
41 words
A system as in claim 6 where said first loop includes integrating-amplifier means and a light source driven by said integrating-amplifier means for feeding back a signal to at least one of said frequency selective elements of said notch filter means.
Claim 12
Dependent Claim
51 words
A system as in claim 8 including a variable resistor in series with said light source and integrating-amplifier means and connected to said ganging means for providing a change in drive current to said light source when said predetermined frequency is changed whereby no adjustment of said integrator-amplifier means is necessary.
Claim 13
Dependent Claim
51 words
A system as in claim 8 including a variable amplifier in series with said light source and integrating-amplifier means and connected to said ganging means for providing a change in drive current to said light source when said predetermined frequency is changed whereby no adjustment of said integrator-amplifier means is necessary.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1979-08-31 | 1980-03-01 | 1980-08-31 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1983-08-31 | 1984-03-01 | 1984-08-31 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1987-08-31 | 1988-03-01 | 1988-08-31 | $7700.00 | Window Closed / Lapsed |