Patent US3781693A successfully refreshed from Google Patents.
US3781693A
Expired / Lapsed
US
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Logarithmic amplification circuit
Assignee: Northrop Grumman Guidance and Electronics Co Inc
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Filing: 1972-03-29
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Granted: 1973-12-25
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Expires: 1992-03-29
Abstract
Abstract A circuit for generating an output signal that is a logarithmic function of an applied input signal. The circuit comprises an input signal source exhibiting the properties of an ideal constant current source, an amplifier coupled to said source, and a diode or other logarithmic element coupled across the source and between the source and the amplifier. The circuit is designed such that the amplifier will present a substantially infinite impedance to the diode and this property coupled with the substantially infinite impedance of the source will cause essentially all the input current to flow through the diode and be unaffected by any other components in the circuit. The voltage across the diode will thus be an accurate logarithmic function of the input current signal throughout a range up to six decades or more.
Inventors
- 👤 P Ford
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 21:43
CPC Classifications
G; G06; G06G; G06G7/00; G06G7/12; G06G7/24
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
175 words
A logarithmic generator for producing an output signal that is a logarithmic function of an applied input signal comprising: a. input means for producing an input current signal, said input means having a very high internal impedance approximating the properties of an ideal current source; b. an amplifier having input and output terminals and having a very high input impedance; c. means for coupling an input terminal of said amplifier to said input means; and d. impedance means coupled across said input means between said input means and said input terminal of said amplifier, said impedance means consisting essentially of non-linear impedance means having an impedance that is negligible as compared to the impedance of said input means and said amplifier such that substantially all of said input current will flow through said non-linear impedance means, the voltage generated across said non-linear impedance means will be a logarithmic function of the current flowing through it and the signal produced at the output terminal of said amplifier will be a logarithmic function of said input signal.
Claim 2
Dependent Claim
175 words
A logarithmic generator for producing an output signal that is a logarithmic function of an applied input signal comprising: a. input means for producing an input current signal, said input means having a very high internal impedance approximating the properties of an ideal current source; b. an amplifier having input and output terminals and having a very high input impedance; c. means for coupling an input terminal of said amplifier to said input means; and d. impedance means coupled across said input means between said input means and said input terminal of said amplifier, said impedance means consisting essentially of non-linear impedance means having an impedance that is negligible as compared to the impedance of said input means and said amplifier such that substantially all of said input current will flow through said non-linear impedance means, the voltage generated across said non-linear impedance means will be a logarithmic function of the current flowing through it and the signal produced at the output terminal of said amplifier will be a logarithmic function of said input signal.
Claim 3
Dependent Claim
15 words
A logarithmic generator as recited in claim 1 wherein said amplifier comprises a differential amplifier.
Claim 4
Dependent Claim
34 words
A logarithmic generator as recited in claim 2 and further including means for controlling the gain of said differential amplifier for controlling the functional relationship between said output logarithmic signal and said input signal.
Claim 5
Dependent Claim
27 words
A logarithmic generator as recited in claim 3 and further including means for adjusting the reference position of said differential amplifier with respect to said input signal.
Claim 6
Dependent Claim
18 words
A logarithmic generator as recited in claim 1 wherein said non-linear impedance means consists essentially of a diode.
Claim 7
Dependent Claim
50 words
A logarithmic generator as recited in claim 1 wherein said non-linear impedance means consists essentially of a pair of diodes coupled in parallel and oppositely poled such that current will flow through one or the other of said diodes dependent upon the direction of flow of said input current signal.
Claim 8
Dependent Claim
16 words
A logarithmic generator as recited in claim 1 wherein said input means comprises a PIN diode.
Claim 9
Dependent Claim
18 words
A logarithmic generator as recited in claim 1 wherein said input means comprises a photon coupled pair unit.
Claim 10
Dependent Claim
190 words
Apparatus for monitoring the condition of a function and for producing an output signal that is logarithmically related to said monitored function comprising: a. means for monitoring said function and for producing a current signal that is linearly related to said function, said monitoring means having a very high internal impedance approximating the properties of an ideal current source; b. amplifier means having input and output terminals and having a very high input impedance; c. means for coupling said monitoring means to the input terminal of said amplifier means; d. impedance means coupled across said monitoring means between said monitoring means and said input terminal of said amplifier means, said impedance means consisting essentially of non-linear impedance means having an impedance that is negligible compared to the impedances of said monitoring means and said amplifier means such that substantially all of said current will flow through said non-linear impedance means wherein the voltage generated across said non-linear impedance means is a logarithmic function oF the current flowing through it such that the signal produced at the output terminal of the amplifier means will be logarithmically related to said monitored function.
Claim 11
Dependent Claim
190 words
Apparatus for monitoring the condition of a function and for producing an output signal that is logarithmically related to said monitored function comprising: a. means for monitoring said function and for producing a current signal that is linearly related to said function, said monitoring means having a very high internal impedance approximating the properties of an ideal current source; b. amplifier means having input and output terminals and having a very high input impedance; c. means for coupling said monitoring means to the input terminal of said amplifier means; d. impedance means coupled across said monitoring means between said monitoring means and said input terminal of said amplifier means, said impedance means consisting essentially of non-linear impedance means having an impedance that is negligible compared to the impedances of said monitoring means and said amplifier means such that substantially all of said current will flow through said non-linear impedance means wherein the voltage generated across said non-linear impedance means is a logarithmic function oF the current flowing through it such that the signal produced at the output terminal of the amplifier means will be logarithmically related to said monitored function.
Claim 12
Dependent Claim
22 words
Apparatus as recited in claim 9 wherein said monitored function is light intensity and wherein said monitoring means comprises a PIN diode.
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) | 1976-12-24 | 1977-06-25 | 1977-12-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-12-24 | 1981-06-25 | 1981-12-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-12-24 | 1985-06-25 | 1985-12-25 | $7700.00 | Window Closed / Lapsed |