Patent US3757241A successfully refreshed from Google Patents.
US3757241A
Expired / Lapsed
US
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A c amplifier having d c bias stabilization
Assignee: Keithley Instruments LLC
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Filing: 1971-11-24
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Granted: 1973-09-04
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Expires: 1991-11-24
Abstract
Abstract An A.C. amplifier is disclosed having first and second A.C. amplifier sections each including a high input impedance stage followed by an output stage, with the output stages of the two amplifier sections being D.C. coupled to an output amplifier. A first stabilizing circuit serves to stabilize the D.C. bias of one of the amplifier sections and a second stabilizing circuit serves to stabilize the D.C. bias of the other amplifier''s section in dependence upon the D.C. level of the output amplifier. The D.C. bias stabilization circuitry permits use of input stages, such as field effect transistors, which are not matched in their D.C. characteristics while still maintaining low noise characteristics.
Inventors
- 👤 R Kime
- 👤 P Cath
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 19:49
CPC Classifications
H; H03; H03F; H03F1/00; H03F1/30; H03F1/303; H03F2200/00; H03F2200/372
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
235 words
A D.C. bias stabilized A.C. amplifier comprising first and second high input impedance A.C. amplifiers each including a high input impedance amplifier device having an input circuit for receiving an A.C. input signal to be amplified and an output circuit connected across a D.C. bias source and exhibiting the characteristic of being nonconductive when the D.C. level at said input circuit is below a given bias level and increasingly more conductive as said D.C. level increases above said given bias level, each said output circuit carrying a first D.C. level signal which varies in dependence upon the conductive level of said device; and, first and second comparing means for respectively comparing a different one of said first D.C. level signals wiTh a reference second D.C. level signal and each said comparing means providing a third D.C. level signal in dependence upon said respective comparisons; one of said A.C. amplifiers having first stabilizing means for applying a first stabilizing D.C. level signal to the said input circuit of its said device to effectively vary the said given bias level thereof in a direction tending to decrease any difference in signal levels between its said first and second D.C. signal levels; and second stabilizing circuit means for applying a second stabilizing D.C. level signal to the input circuit of said other amplifier device in dependence upon the D.C. levels of both of said third D.C. level signals.
Claim 2
Dependent Claim
235 words
A D.C. bias stabilized A.C. amplifier comprising first and second high input impedance A.C. amplifiers each including a high input impedance amplifier device having an input circuit for receiving an A.C. input signal to be amplified and an output circuit connected across a D.C. bias source and exhibiting the characteristic of being nonconductive when the D.C. level at said input circuit is below a given bias level and increasingly more conductive as said D.C. level increases above said given bias level, each said output circuit carrying a first D.C. level signal which varies in dependence upon the conductive level of said device; and, first and second comparing means for respectively comparing a different one of said first D.C. level signals wiTh a reference second D.C. level signal and each said comparing means providing a third D.C. level signal in dependence upon said respective comparisons; one of said A.C. amplifiers having first stabilizing means for applying a first stabilizing D.C. level signal to the said input circuit of its said device to effectively vary the said given bias level thereof in a direction tending to decrease any difference in signal levels between its said first and second D.C. signal levels; and second stabilizing circuit means for applying a second stabilizing D.C. level signal to the input circuit of said other amplifier device in dependence upon the D.C. levels of both of said third D.C. level signals.
Claim 3
Dependent Claim
35 words
An A.C. amplifier as set forth in claim 1 wherein each said comparing means includes A.C. amplifying means for amplifying the A.C. signal component carried by the output circuit of its associated said amplifier device.
Claim 4
Dependent Claim
32 words
An A.C. amplifier as set forth in claim 2 wherein each said comparing means includes a differential amplifier for providing a said third D.C. level signal carrying an amplified A.C. signal component.
Claim 5
Dependent Claim
44 words
An A.C. amplifier as set forth in claim 1 including common comparing means interposed between both of said comparing means and said second stabilizing circuit means for providing an output D.C. level signal dependent upon a comparison of both said third D.C. level signals.
Claim 6
Dependent Claim
73 words
An A.C. amplifier as set forth in claim 4 wherein said second stabilizing circuit means is connected between the output of said common comparing means and the input circuit of said amplifier device of said other A.C. amplifier for applying said second stabilizing D.C. level signal thereto to stabilize the D.C. bias level thereof so that the third D.C. level signal of said other A.C. amplifier approaches that of said one A.C. amplifier.
Claim 7
Dependent Claim
18 words
An A.C. amplifier as set forth in claim 5 wherein said common comparing means includes a differential amplifier.
Claim 8
Dependent Claim
34 words
An A.C. amplifier as set forth in claim 6 wherein the output circuits of said first and second A.C. amplifiers are connected to the inputs of said differential amplifiers with direct current passing circuits.
Claim 9
Dependent Claim
45 words
An A.C. amplifier as set forth in claim 1 including common summing amplifier means interposed between both of said comparing means and said second stabilizing circuit means for providing an output D.C. level signal dependent upon the summation of both said third D.C. level signals.
Claim 10
Dependent Claim
82 words
An A.C. amplifier as set forth in claim 8 wherein said second stabilizing circuit means is connected between the output of said summing amplifier means and the input circuit of said amplifier device of said other A.C. amplifier for applying said second stabilizing D.C. level signal thereto to stabilize the D.C. bias level thereof so that the third D.C. level signal of said other A.C. amplifier is of opposite polarity from and approaches the magnitude of that of said one A.C. amplifier.
Claim 11
Dependent Claim
35 words
An A.C. amplifier as set forth in claim 9 wherein the output circuits of said first and second A.C. amplifiers are connected to the input of said summing amplifier means with direct current passing circuits.
Claim 12
Dependent Claim
35 words
An A.C. amplifier as set forth in claim 10 including means for connecting said first and second A.C. amplifiers in parallel to thereby reduce voltage noise while defining a single ended input A.C. amplifier circuit.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-09-03 | 1977-03-05 | 1977-09-04 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-09-03 | 1981-03-05 | 1981-09-04 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-09-03 | 1985-03-05 | 1985-09-04 | $7700.00 | Window Closed / Lapsed |