Patent US1793874A successfully refreshed from Google Patents.
US3710089A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Highly precise and stable logarithmic circuit
Assignee: Yokogawa Electric Corp
•
Filing: 1971-12-20
•
Granted: 1973-01-09
•
Expires: 1991-12-20
Abstract
Abstract A logarithmic circuit of a highly precise and stable type useful in absorption metering apparatus where the range of input signals is narrow. The circuit receives an input signal which has the form of a product of an input reference signal and an exponential signal. The circuit, by means of a feedback operational amplifier, provides a difference signal proportional to the difference between the input signal and the input reference signal. The difference signal thereby includes its own reference signal component corresponding proportionally to said input reference signal. By means of a resistive voltage divider circuit, the difference signal is split into first portion equal to a constant a times the difference signal and a second portion equal to (1 - a) times the difference signal, and a is selected to be approximately 1 square root 2. The first portion is added to the corresponding reference signal component to form a sum signal by which another signal, equal to the square of the corresponding reference signal component, is divided to produce a quotient signal. The second portion is added to the corresponding reference signal component to provide a second sum signal which is in turn subtracted in a subtracting circuit from the quotient signal. The resulting output signal is linearly related to the logarithm of the input signal to within approximately 0.1 percent.
Inventors
- 👤 S Ohata
- 👤 Y Takeuchi
- 👤 T Ishiguro
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 10:02
CPC Classifications
G; G06; G06G; G06G7/00; G06G7/12; G06G7/24; G01; G01R; G01R15/00; G01R15/005
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
172 words
A circuit for accurately deriving the logarithm of an input signal which has the form of a product of an input reference signal and an exponential signal, comprising means for providing a difference signal proportional to the difference between said input signal and said input reference signal, said difference signal thereby including its own reference signal component corresponding to said input reference signal; means for providing a first portion of said difference signal equal to a constant a times the difference signal and a second portion of said difference signal equal to (1 - a) times the difference signal, where the constant a is approximately 1/ square root 2; means for providing a quotient signal which is equal to the square of the corresponding reference signal divided by the sum of said first portion and said corresponding reference signal; and means for subtracting from said quotient signal the sum of said second portion and said corresponding reference signal to provide an output signal which linearly approximates the logarithm of said input signal.
Claim 2
Dependent Claim
172 words
A circuit for accurately deriving the logarithm of an input signal which has the form of a product of an input reference signal and an exponential signal, comprising means for providing a difference signal proportional to the difference between said input signal and said input reference signal, said difference signal thereby including its own reference signal component corresponding to said input reference signal; means for providing a first portion of said difference signal equal to a constant a times the difference signal and a second portion of said difference signal equal to (1 - a) times the difference signal, where the constant a is approximately 1/ square root 2; means for providing a quotient signal which is equal to the square of the corresponding reference signal divided by the sum of said first portion and said corresponding reference signal; and means for subtracting from said quotient signal the sum of said second portion and said corresponding reference signal to provide an output signal which linearly approximates the logarithm of said input signal.
Claim 3
Dependent Claim
69 words
A logarithmic circuit as claimed in claim 1 wherein said means for providing a difference signal comprises feedback amplifier means receiving at an input terminal thereof said input signal, means for supplying a signal equal to saId input reference signal to said input terminal, the feedback amplifier means being arranged to subtract the input reference signal from the input signal and to provide at its output said difference signal.
Claim 4
Dependent Claim
30 words
A logarithmic circuit as claimed in claim 1 wherein said means providing said first and second portions of said difference signal comprises resistive voltage divider means formed of series-connected resistors.
Claim 5
Dependent Claim
43 words
A logarithmic circuit as claimed in claim 3 wherein said resistive voltage divider means comprises three resistors in series valued to provide at one junction a ratio of a: 1 and at the other junction a ratio of (1 - a) : 1.
Claim 6
Dependent Claim
88 words
A logarithmic circuit as claimed in claim 1 wherein said means providing a Quotient signal comprises means for adding a signal equal to said corresponding reference signal to said first portion to produce said sum signal, and a divider circuit having as inputs thereto said sum signal and a pair of signals whose product is the square of the corresponding reference signal, said divider circuit being arranged to provide at an output a signal which is the quotient of the squared reference signal divided by the sum signal.
Claim 7
Dependent Claim
59 words
A logarithmic circuit as claimed in claim 1 wherein said subtracting means comprises means for adding a signal equal to said corresponding signal to said second portion to provide said sum signal, and subtraction circuit means having said sum signal at one input and said quotient signal at another input and having an output equal to the difference therebetween.
Claim 8
Dependent Claim
203 words
In a measurement apparatus comprising a detector supplying, over a narrow range, an input signal having the form of a product of an input reference signal and an exponential signal whose exponent is of interest, the improvement which comprises a circuit for accurately deriving over said narrow range the logarithm of said input signal, said circuit comprising: amplifier means for providing a difference signal proportional to the difference between said input signal and said input reference signal, said difference signal thereby including a reference signal component corresponding to said input reference signal; voltage divider means for providing a first portion of said difference signal equal to a constant a times the difference signal and a second portion equal to (1 - a) times the difference signal, where the constant a is approximately 1/ Square Root 2; division circuit means for providing a quotient signal which is equal to the square of the corresponding reference signal divided by the sum of said first portion and said corresponding reference signal; and subtraction circuit means for subtracting from said quotient signal the sum of said second portion and said corresponding reference signal to provide an output signal which linearly approximates the logarithm of said input signal.
Claim 9
Dependent Claim
203 words
In a measurement apparatus comprising a detector supplying, over a narrow range, an input signal having the form of a product of an input reference signal and an exponential signal whose exponent is of interest, the improvement which comprises a circuit for accurately deriving over said narrow range the logarithm of said input signal, said circuit comprising: amplifier means for providing a difference signal proportional to the difference between said input signal and said input reference signal, said difference signal thereby including a reference signal component corresponding to said input reference signal; voltage divider means for providing a first portion of said difference signal equal to a constant a times the difference signal and a second portion equal to (1 - a) times the difference signal, where the constant a is approximately 1/ Square Root 2; division circuit means for providing a quotient signal which is equal to the square of the corresponding reference signal divided by the sum of said first portion and said corresponding reference signal; and subtraction circuit means for subtracting from said quotient signal the sum of said second portion and said corresponding reference signal to provide an output signal which linearly approximates the logarithm of said input signal.
Claim 10
Dependent Claim
42 words
A measurement apparatus as claimed in claim 7 wherein said input signal is from an absorption measurement arrangement, and wherein said measurement apparatus further comprises means for subtracting a constant signal from said output signal, and means for dividing the resultant signal.
Claim 11
Independent Claim
168 words
A method for accurately deriving the logarithm of an input signal which has the form of a product of an input reference signal and an exponential signal comprising providing a difference signal proportional to the difference between said input signal and said input reference signal, said difference signal thereby including a reference signal component corresponding to said input reference signal; multiplying said difference signal by a constant a to provide a first portion thereof, the constant a being approximately 1/ Square Root 2; multiplying said difference signal by (1 - a) to provide a second portion thereof; adding said first portion to said corresponding reference signal to provide a first sum signal; dividing the square of the corresponding reference signal by said first sum signal to provide a quotient signal; adding said second portion to said corresponding reference signal to provide a second sum signal; subtracting said second sum signal from said quotient signal to provide an output signal which linearly approximates the logarithm of said input signal.
Claim 12
Independent Claim
168 words
A method for accurately deriving the logarithm of an input signal which has the form of a product of an input reference signal and an exponential signal comprising providing a difference signal proportional to the difference between said input signal and said input reference signal, said difference signal thereby including a reference signal component corresponding to said input reference signal; multiplying said difference signal by a constant a to provide a first portion thereof, the constant a being approximately 1/ Square Root 2; multiplying said difference signal by (1 - a) to provide a second portion thereof; adding said first portion to said corresponding reference signal to provide a first sum signal; dividing the square of the corresponding reference signal by said first sum signal to provide a quotient signal; adding said second portion to said corresponding reference signal to provide a second sum signal; subtracting said second sum signal from said quotient signal to provide an output signal which linearly approximates the logarithm of said input signal.
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) | 1976-01-09 | 1976-07-10 | 1977-01-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-01-09 | 1980-07-10 | 1981-01-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-01-09 | 1984-07-10 | 1985-01-09 | $7700.00 | Window Closed / Lapsed |